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Evaluation and Management of Concrete Structures Affected by Alkali-Silica Reaction ­ A Review

B. Fournier, M.A. Bérubé, M.D.A. Thomas, N. Smaoui and K.J. Folliard

Abstract: Unexpected or premature concrete deterioration due to alkali-aggregate reactivity is a widespread problem worldwide. Routine site inspections performed on a regular basis may permit identification of the problem; however, AAR in concrete cannot generally be diagnosed without detailed site investigations. Such investigations would include determination of the distribution and severity of the various defects affecting the concrete structure and in-situ testing, as well as laboratory testing of samples collected from the affected concrete structures. For critical structures such as large dams and fair to large size highway bridges, detailed investigations including a more extensive sampling program might be necessary to quantify the current condition of the concrete, to assess structural integrity, and to evaluate the potential for future deterioration (prognosis). Such investigations can involve a detailed sampling program for further testing in the laboratory and in-situ monitoring of the progress of expansion/deterioration. The results of the above processes of investigation will then be analyzed to propose appropriate management actions to be taken for each of the particular applications. The most common management actions for concrete structures affected by ASR can generally be grouped into activities to 1) control moisture access to the concrete by improving drainage systems or applying physical barriers or a variety of waterproof coatings, 2) slow down the process of ASR through chemical treatments such as the use of lithium-based compounds, 3) restrain expansion forces using physical containment, post-tensioning, encapsulation, and 4) try to control the deleterious effect of AAR expansion by releasing stresses using slot-cutting. The effectiveness of the above methods has shown to vary widely from one application to another; however, it is generally recognized that most of the above remedial measures are temporary solutions that may help to save some time and money until the deleterious process of AAR expansion has stopped.

Keywords: Alkali-aggregate reaction, alkali-silica reaction, petrography, performance of concrete, condition survey, remedial measures, repair of concrete.

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ACI member Dr. Benoit Fournier is Manager of the Concrete Technology Program of CANMET-MTL (Ottawa, Canada). His main research interests are in the area of concrete durability and the evaluation and use of supplementary cementing materials in concrete. He is member of ACI Committee 221 on aggregates. ACI member Dr. Marc-André Bérubé is an associate professor at the Department of Geology and Geological Engineering of Laval University (Québec City, Canada). His research interests mainly concern various aspects related to AAR in concrete, in particular aggregate testing, preventive measures, and management of affected structures. Michael Thomas is a professor of civil engineering at the University of New Brunswick in Canada. He has been active in the field of cement and concrete research for 20 years previously working at the University of Toronto and Ontario Hydro in Canada, and the Building Research Establishment in the U.K. He is a previous winner of ACI's Wason Medal and the ACI Construction Practice Award and is a member of numerous ACI committees Dr. Nizar Smaoui is a project manager at the Materials Division of the Service d'Expertise en Matériaux (Québec City, Canada). He obtained his Ph.D. from Laval University (Québec City, Canada) on the structural evaluation of ASR-affected structures. Dr. Kevin Folliard is a Fellow of the ACI and an Assistant Professor in the Department of Civil Engineering at the University of Texas in Austin. He received the ACI Young Member Award for Professional Achievement in 2002.

1.0

INTRODUCTION

The properties of aggregates greatly affect the strength, durability and structural performance of concrete. In concrete, aggregates are subjected to a highly basic and alkaline environment where some mineral phases, generally stable in normal environmental conditions, can produce significant deterioration as a result of deleterious chemical reactions commonly called alkaliaggregate reactions (AAR). Alkali-silica reaction (ASR) is the most commonly recognized form of AAR worldwide; it has been identified in concretes made with rocks showing a variety of compositions and textures. ASR refers to chemical reactions between alkali hydroxides (Na+, K+ - OH-) in the concrete pore fluid and certain siliceous phases present in the aggregate materials. The reaction results in the formation of a secondary calcium-rich alkali-silica gel which has a strong affinity with water. As the gel absorbs water, internal swelling pressure develops causing volume change and fracturing of the reacting aggregate particles, cracking of the surrounding cement paste and subsequent deterioration of the concrete, which in turn can result in a significant reduction in the service life of affected concrete structures. The extent of ASR-induced concrete deterioration and the rate at which it occurs generally depends on several factors, including: 1) the inherent reactivity (nature and level of reactivity) of the aggregate material, 2) the pH of the concrete pore fluid which is related to the total alkali content of the concrete mixture, 3) the availability of moisture, 4) the temperature and thermal gradients, and 5) configuration and structural restraint provided to the concrete structure or element.

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This paper deals with the evaluation and management of concrete structures affected by ASR; it includes approaches for detecting ASR in existing structures, a review of the tools to evaluate the current condition (current expansion and extent of deterioration) and the potential for future expansion (prognosis), as well as the methods of ASR mitigation in affected concrete structures (Fournier and Bérubé 2000, CSA 2000).

2.0

GLOBAL MANAGEMENT PROGRAM

Figure 1 presents a global approach for the evaluation and management of concrete structures potentially affected by ASR. Premature/unexpected deterioration in concrete structures is often detected during routine site inspections that are generally performed on a regular basis to monitor the overall condition of concrete structures. At that stage, every mechanism that may have contributed to the deterioration observed should be considered as a possible source. The visual condition survey is generally accompanied by sampling of a selected number of concrete structures and laboratory testing of the cores collected from them. In many cases, the extent of the damage affecting the concrete structures and/or the results of the laboratory investigations will not warrant any short-term major intervention, and the progress of the concrete deterioration will be monitored through periodic inspections. In the case of critical structures (e.g. large dams and moderate to large size highway bridges) or when the extent of deterioration is determined to be significant, detailed investigations may be necessary. A very important part of the investigation at this stage concerns assessment of the current condition, e.g. degree of expansion/damage reached to date, and of the trend for future deterioration of the concrete. This may require additional sampling for a detailed testing program in the laboratory and in-situ investigations to quantify the current condition (severity rating) of the concrete, to evaluate the potential for future expansion (prognosis) and, if necessary, to assess structural integrity. Table 1 lists the various field and laboratory investigations generally performed in the investigation of ASR in concrete structures. The results of the above investigations will then be analyzed, and decisions will be made regarding the implementation of extensive monitoring programs, selection of repairs and/or mitigation requirements will be taken.

3.0

DOCUMENTARY EVIDENCE

One of the first phases in the evaluation program for the diagnosis of ASR is to review available documents relating to the design, construction, survey and maintenance of the structure(s) under study. Information that may assist in the appraisal of the structure includes: · The type and location of the structure and, hence, its likely exposure conditions due to its nature of operation and geography. · The age of the structure, and details and dates of any modifications or repairs. ASR may take from 3 years to more than 25 years to develop significantly in concrete structures depending on the nature of the aggregates used, the moisture and temperature conditions, and the concrete alkali content. · Plans, drawings (e.g., reinforcement detailing) and specifications. · Details on the concrete mixtures used, particularly mix proportions, the source(s) of cement and aggregates, and details of any analyses or tests carried out on concrete materials. The

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potential availability of samples of these materials should also be investigated; some agencies store samples of cements and aggregates used in major projects. Previous inspection/testing reports, especially dates when deterioration was first observed. Information from other structures in the area that may have been constructed with similar materials, especially if these structures are exhibiting signs of deterioration typical of ASR.

Details regarding the concrete materials, especially the composition and proportion of the cement and the type of aggregate used, are most useful when assessing the likelihood of ASR at this stage. It is recognized that information of this nature is often unavailable or lacks specific detail in the case of many structures; however, it is important to collect whatever data are available.

4.0

FIELD INSPECTION AND SAMPLING OF CONCRETE STRUCTURES FOR THE DIAGNOSIS OF ALKALI-SILICA REACTION Field Inspection

4.1

Generally, visual site inspection is carried out to 1) assess the nature and the extent of distresses and deterioration, 2) assess the exposure conditions to which the structures (or parts of those) are subjected and 3) select sampling sites. Survey forms and procedures for the condition surveys of concrete structures have been developed and are currently being used by several organizations including FHWA (Van Dam et al. 2002), Ontario Structure Inspection Management System (Reel and Conte 1988). Common visual symptoms of ASR have been described in numerous documents since Stanton identified and reported the first case of ASR in concrete structures in the late 1930s (Stanton 1940). Recent publications on the topic include: Hobbs 1988, Stark 1991, BCA 1992, Farni and Kosmatka 1997, ACI 1998, LCPC 1999, CSA 2000, Fournier and Bérubé 2000, Van Dam et al. 2002, and Folliard et al. 2003. Symptoms of ASR affecting concrete structures generally consist of (1) expansion causing deformation, relative movement and displacement, (2) cracking, (3) surface discoloration, (4) gel exudations and, occasionally, (5) pop-outs; however, the presence of one or many of these features is not necessarily an indication that AAR is the main factor responsible for the damage or distress observed. 4.1.1 Environmental conditions

ASR typically develops or sustains in concrete elements with internal relative humidity >8085%. Expansion and cracking due to ASR is generally most severe in concrete elements or parts of structures subjected to an external, or constantly renewable, supply of moisture. Surfaces of concrete elements affected by ASR and exposed to sun, wetting and drying cycles, and frost action usually show more extensive cracking and deterioration. 4.1.2 Movements, displacements and deformations

The extent of ASR often varies throughout the volume of the concrete or within the various components of the affected structure. The overall, uneven or differential concrete swelling due to AAR may cause distresses such as relative movement, misalingment, distorsion, excessive

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deflection, or separation of adjacent concrete members or structural units, closure of joints causing extrusion of jointing and sealing materials, and ultimately spalling of concrete at expansion or construction joints (Fig. 2A to 2E). Concrete deformation and movement may also be caused by other mechanisms such as loading, thermal or moisture movements, differential shrinkage, gravity and foundation effects, hydraulic pressure, creep, impact, and vibrations (BCA 1992). 4.1.3 Nature and extent of cracking

Cracking is likely to develop in concrete elements wherever the tensile strain from the combined effects of internal expansive or shrinkage mechanisms, structural loads and reinforcement restraint exceeds the tensile strength of the concrete (ISE 1992). Improper mixture proportioning, poor workmanship or inadequate curing may also cause concrete to crack. The pattern of cracking due to AAR is influenced by the shape or geometry of the concrete element, the environmental conditions, the presence and arrangement of reinforcement, and the load or stress fields applied to the concrete. Cracking is usually most severe in areas of structures where the concrete has a constantly renewable supply of moisture, such as close to the waterline in piers, from the ground behind retaining walls, beneath pavements slabs, or by wick action in piers or columns. Concrete elements undergoing AAR and experiencing cyclic exposure to sun, rain and wind, or portions of concrete piles in tidal zones often show severe surface cracking resulting from induced tension cracking in the "less expansive" surface layer under the expansive thrust of the inner concrete core (Stark and Depuy 1987, ACI 1998). "Map- or pattern" cracking is often associated with, but not exclusive to, ASR (Fig. 3A to 3D); it is often observed in ASR-affected concrete components free of major stress or restraint. Drying shrinkage, freezing/thawing cycles and sulfate attack can also result in a pattern of cracks showing a random orientation. In reinforced concrete members, or under stress and loading conditions, the ASR cracking pattern will generally reflect the arrangement of the underlying steel or the direction of the major stress fields (Fig. 3E and 3F). In pavement and slabs on grade, ASR cracking usually develops perpendicular to transverse joints and parallel to free edges along the roadside (Fig. 4A), and against the asphalt pavements where is less restraint; these cracks often progress to a map pattern. Longitudinal cracking is often observed in reinforced concrete decks, columns and beams affected by ASR (Fig. 3F, 4B and 4C). Concrete components affected by AAR may show more than one pattern of cracking at a time; common associations are predominant longitudinal cracks interconnected by a finer, randomly oriented, cracking pattern (Fig. 4D). Surface macrocracking due to ASR rarely penetrates more than 25 to 50 mm of the exposed surface (in rare cases reaching depths >100 mm) where they convert into microcracks. The width of surface macrocracks generally varies from 0.1 mm to 10 mm in extreme cases. 4.1.4 Surface Discoloration

Cracks caused by ASR are often bordered by a broad brownish zone, giving the appearance of permanent dampness (Fig. 3A to 3C). Sections of concrete members that are badly damaged may develop a patchy surface discoloration, however this is not necessarily an indication of AAR.

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4.1.5

Pop-outs

The expansion of individual unsound or frost-susceptible aggregate particles (such as laminated, schistose and argillaceous, clayey or porous particles or certain varieties of chert, ironstones) at or near the concrete surface due to frost-action is likely to be the main factor for the development of pop-outs in northern countries (Fig. 4E). Alkali-silica reactive aggregates undergoing expansion near the concrete surface may induce the detachment of a conical portion of the surface leaving the reactive aggregate in the bottom. Pop-outs can also be caused by a poor bond between the cement paste and dusty coarse aggregate particles, the expansion of frost-susceptible clayey/argillaceous or low-density porous cherty aggregates at or near the concrete surface. 4.1.6 Surface Deposits (gel exudation vs efflorescence)

Although surface gel exudation is a common and characteristic feature of ASR, the presence of surface deposits is not necessarily indicative of ASR as other mechanisms (such as frost action or the transmission of water through cracked concrete components) can also cause efflorescense (without the present of ASR gel) (Fig. 4F). It is good investigative practice during a site survey to record the extent and location of surface deposits along with their colour, texture, dampness, and hardness. A chemical and/or Xray analysis of a small sample of the surface deposit is also helpful to determine if ASR gel is present. 4.1.7 Interpretation of the findings from the field inspection

It is not always possible to determine from field observations whether ASR is the only/main factor responsible for the observed distresses since some of the visual signs of deterioration generally associated with ASR may have been caused by other processes such as internal sulphate attack, or plastic or drying shrinkage (Oberholster 1984, Stark and Depuy 1987, Hobbs 1988). CSA (2000) classifies the occurrence of the features obtained from field surveys of concrete structures as indications of low, medium and high probability of ASR (Table 2). 4.2 Sampling program

The selection of the structures to be sampled, and the extent of the sampling program (in terms of the numbers of components investigated and samples to be collected), will depend on several factors. These factors include the nature and extent of the distresses observed, the "criticality" and the complexity of the structure (e.g. nature and types of components, physical access to the components), the objectives of the investigation program and the extent of the laboratory testing program to be performed (e.g. type and number of laboratory tests), as well as on economical factors. In many cases, the routine inspection program of a targeted investigation on a selected group of structures, includes sampling limited to a few cores collected for a preliminary assessment by petrographic examination in the laboratory to determine the likely cause of concrete deterioration. When ASR is suspected from the visual condition survey, the cores are typically collected from components showing typical signs of AAR (see section 4.1) or the type of

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deterioration affecting the structure investigated. It may also be advisable to collect cores from both deteriorated and non-deteriorated components of the structure(s). According to the results obtained through petrographic examination and other laboratory diagnostic methods, a more extensive sampling program may be necessary to establish the extent of the problem and select further management actions. In order to evaluate the respective influence of the exposure conditions on the deterioration observed, core specimens must be collected from different areas or components of the structure that are more or less severely deteriorated or exposed to environmental elements. Samples, typically 100 mm diameter cores are to be taken from the various locations selected (although large aggregate or closely spaced reinforcement may necessitate cutting larger or smaller cores, respectively),. Cores should be as long as possible in order to provide a profile of the concrete from the surface to the interior of the element. If the original documentation or subsequent reports show that different concrete mixtures were used in different parts of the structure, then each mix type should also be represented as part of the sampling program, especially if the components involved show various types or degrees of deterioration. A detailed record of all sampling operations should be made on site. The use of a sampling form or "Site Core Record" accompanied by pictures showing the characteristics of the components sampled is most appropriate. The samples collected should be marked carefully, photographed and, immediately after coring, wrapped in a plastic film and sealed in a plastic bag to prevent them from drying out. The samples are then brought to the laboratory for further testing. If the surfaces of the cores are dry, they should be dampened and replaced in a plastic bag for an additional 24 h before examination. Detailed procedures for the sampling of concrete structures for the diagnosis of ASR are further described in BCA 1992 and CSA 2000.

5.0

LABORATORY INVESTIGATIONS

The main objectives of the laboratory investigations are described in Table 1 and summarized as follows: · Diagnosis ­ to confirm the presence of ASR and determine whether the apparent damage to the structure can reasonably be attributed to ASR. · Prognosis ­ to predict the potential for further deterioration due to ASR. 5.1 Petrographic Examination

Petrographic examination of concrete specimens is a very powerful and critical technique in the evaluation of the condition of concrete, and especially in the diagnosis of the cause of its deterioration (Ray 1983, Jensen et al. 1989, Hobbs 1988, BCA 1992, Walker 1992, St-John et al. 1998, ASTM C 856-02). Table 3 summarizes the various features that can be obtained from petrographic examination of concrete for ASR. The cores are first examined and photographed in an `as-received' condition. The "macroscopic" description is performed with naked-eye, a magnifying lense (7-10x) and even a stereobinocular microscope (magnification of up to 40-50x) if available. Certain features may be

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highlighted by rewetting the core surfaces and making observations as the core dries. Following the macroscopic description of the cores, various types of specimens may be prepared from the drilled cores. These mainly consist of polished sections or slices, broken surfaces, and thin sections. The examination of each of these will generally give useful complementary information (Table 3). The examination of polished surfaces with the naked eye and lowpowered (stereo-binocular) microscopy is an efficient method for studying large areas of concrete and determining the presence, distribution and extent of certain macroscopical features. The examination of thin sections can provide further critical information to positively identify diagnostic features of ASR (e.g., sites of expansive reactions) and to confirm the existence of features identified on polished surfaces. To maximize information generation through petrographic examination, polished surfaces and thin sections of concrete can be prepared from samples taken at various depths (including the surface) within the structure. When the core is taken from an area showing surface distress, the section for microscopic examination is taken from a region of the core exhibiting damage. At depths below the original concrete surface, visible signs of deterioration may not be obvious, and suitable areas for examination may have to be chosen on the evidence of damp patches, reaction rims around aggregates or the presence of gel on the surface of the core. 5.1.1 Typical petrographic symptoms of ASR

Typical petrographic features of ASR, as observed on polished concrete sections, broken surfaces, and thin sections have been described in numerous publications, including Bérubé & Fournier 1986, Hobbs 1988, Stark 1991, BCA 1992, Walker 1992, St. John et al. 1998, CSA 2000, Fournier and Bérubé 2000, Folliard et al. 2003); they are summarized hereafter. Microcracking Microcracking due to ASR is generated through forces applied by the expanding aggregate particles and/or swelling of alkali-silica gel within and around the boundaries of reacting aggregate particles. The extent of ASR-related microcracking in a deteriorated concrete specimen depends on many factors such as the amount of reaction/expansion undergone by the concrete (which in turn depends on the inherent reactivity of the aggregate, the moisture conditions, the alkali content of the mix, etc.) and the total restraint to which the concrete element is subjected. BCA (1992) and St. John et al. (1998) compare typical cracking patterns in concrete specimens affected by various deleterious mechanisms. A significant proportion of aggregate particles in concrete typically show pre-existing cracks that were generated through blasting and crushing in the quarrying operations (Fig. 5A). However, the proportion of cracked aggregate particles significantly increases with progressing AAR (Bérubé et al 1988, Samoui et al. 2004a). In the early stages of the reaction, microcracks due to ASR are generally limited to the aggregate particles and the cement paste-aggregate interface (Fig. 5B). In more severe cases, i.e. with the progress of expansion, microcracks will extend from the aggregate particles to the cement paste, sometimes covering considerable distances through the paste where they are often filled with secondary reaction products (Fig. 5C and 5D). In badly cracked concrete specimens, cracks, even filled with gel, may run through non-reactive aggregate particles. Consequently, great care should be taken to correctly identify the sites (or the aggregate particles) that have generated the

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expansive forces. The reactive aggregate particles might show numerous signs of "chemical instability" such as reaction rims, partial "gelification", internal microcracks containing secondary reaction products, etc. The examination of UV-impregnated polished (St. John et al. 1998) slabs or thin sections are commonly used methods for the examination of microcracks in concrete (Fig. 5F). The presence of extensive microcracking in a concrete specimen taken from a suspect structure does not necessarily indicate that expansion occurred within the structural member; significant expansion of concrete cores has been observed after they were extracted from a structure (Hobbs 1988). Reaction product "gel" The ASR generates secondary reaction products containing silica, alkalis and calcium as typical constituents. A so-called "alkali-silica gel" showing variable aspects will be found lining or filling voids and fractured surfaces of the cement paste and the aggregate particles (Fig. 6A to 6F). These deposits will cover more or less important surfaces depending on many factors, such as the extent of the reaction-expansion processes that have occurred, the availability of water, etc. The above reaction products, which can be observed under the petrographic microscope, the stereo-binocular and the scanning electron microscope, are characteristic features of ASR. However, the abundance of gel deposits is not necessarily indicative of the magnitude of any resultant expansion and cracking (BCA 1992). Large amounts of gel in a concrete specimen do not necessarily indicate that large expansion or extensive cracking have occurred in the structure. On the other hand, cracking due to ASR has been observed in many concrete structures while very little gel was found in concrete specimens taken from the affected components. The confirmation of the presence and the nature of reaction products is not always easy. Great care should be taken when preparing polished or thin sections from affected concrete specimens to avoid "leaching" of the alkali-silica gels. This could be achieved using a nonaqueous lubricant to avoid dissolution of the water-soluble compounds (BCA 1992). Staining techniques have been proposed to facilitate identification of the reaction product gel in concrete affected by ASR (Natesaiyer et al. 1991, Stark 1991, Guthrie and Carey 1997). A technique developed at Cornell University (Natesaiyer et al. 1991) consists in applying a uranyl acetate solution on polished or fresh broken surfaces of concrete specimens to be examined followed by a visual observation of the section under a UV light (Fig.7A); the technique has even been used on field structures (Stark 1991, AASHTO 1993, ASTM C 856-02). By applying the uranyl acetate solution to a surface containing the gel, the uranyl ion substitutes for alkali in the gel, thereby imparting a characteristic yellowish-green glow when viewed in the dark using short wavelength ultraviolet light. ASR gel fluoresces much brighter than cement paste due to the greater concentration of alkali and, subsequently, uranyl ion in the gel. This technique should be used with great care following appropriate health and safety procedures because of the potentially hazardous nature of the product. Technically speaking, the results of the test should be interpreted with great care. Some aggregates fluoresce naturally; also, although the technique may help locate the presence of gel in the concrete, it will not differentiate between a harmless presence of gel and that which is detrimental (the source of the observed distresses). The test is consequently recommended as ancillary to more definitive petrographic examinations and physical tests for determining concrete expansion.

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Reaction rims Dark reaction rims are observed at the internal periphery of a number of alkali-silica reactive aggregates in deteriorated concrete specimens. These are particularly evident on polished sections or slabs of affected concrete cores (Fig. 7B and 7C). However, these rims must not be mixed up with pre-existing (e.g., before the introduction of the aggregate particle in the concrete) "weathering" rims that are often found in the outer (but also internal) portion of weathered gravel particles. When concrete cores are fractured for examining "fresh" broken surfaces, cracks that have formed within the aggregate particles and the cement paste, due to the ASR processes, will form zones of weakness where the core will preferentially break. The fractured surfaces thus created (which in many cases correspond to "ASR cracking surfaces") often show a dark rim surrounding internal deposits of whitish color (Fig. 7D). Such a feature does not correspond to a reaction rim per se; it actually corresponds to a typical arrangement of reaction products deposited on the cracking surface, i.e. 1) a dark rim covering the immediate internal periphery of the particle, and 2) white deposits going through the central portion of the particle showing a powdery aspect. Examination under the scanning electron microscope (SEM) confirms the dark rim to be a layer of calcium-rich alkali-silica gel (Fig. 7E), while the whitish deposits are formed by a rosette-like crystalline product (Fig. 7F). Those are typical products of ASR. Loss of the cement paste-aggregate bond The interfacial region between the cement paste and the aggregate particles certainly represents, because of its nature and the arrangement of hydrates that form herein, a preferential zone of weakness where cracks will initiate and run. Loss of the cement paste-aggregate bond has been reported as a petrographic consequence but is not necessarily indicative of AAR. 5.1.2 Quantitative petrographic examination of core samples

Grattan-Bellew (1992) and Dunbar and Grattan-Bellew (1995) described a method to evaluate the condition of concrete by counting the number of typical petrographic features of ASR on polished concrete sections (16x magnification). The Damage Rating Index represents the normalized value (to 100 mm2) of the presence of these features after the count of their abundance over the surface examined has been multiplied by weighing factors representing their relative importance in the overall deterioration process (Table 4) (Shrimer 2000). Rivard et al. (2000) used the method to estimate the amount of expansion reached by concrete specimens cored from a large concrete dam affected by ASR; the authors also found that the relative importance of the different petrographic features of ASR, in terms of how they correlate with the measured expansion due to ASR, can vary significantly from one aggregate to another (Rivard et al. 2002). At Laval University, the DRI method was recently used to quantify the condition of laboratory-made concrete specimens incorporating various aggregate types and subjected to accelerated test conditions in the laboratory (38oC and R.H. > 95%) (Smaoui et al. 2004a). The same method was used to determine the condition of concrete cores sampled from blocks exposed at the CANMET-MTL outdoor exposure site in Ottawa, Canada and incorporating similar aggregates (Smaoui et al. 2004b). All of the above specimens were examined at known expansion levels due to ASR. They used the quite good correlations thus obtained to estimate the amount of expansion reached by concrete cores extracted from structures affected by ASR incorporating siliceous limestone aggregates (Bérubé et al. 2004a). The authors concluded that,

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unfortunately, the DRI method could not differentiate between concretes affected most and least visually and mechanically by ASR. High DRI values and consequently exaggerated estimated expansion to date were obtained for all concretes investigated (Bérubé et al. 2004a). Salomon et al. (1994) and Rivard et al. (2000) used an image-analysis technique based on the examination of UV-impregnated polished concrete sections to quantify the cracking pattern in AAR-affected concrete. The latter found that parameters of the microcracking system in the concrete (e.g. cracking density) could be related to the expansion level reached by the concrete specimens, and that such a technique could be used to estimate the amount of expansion reached to date by a concrete structure affected by ASR. 5.1.3 Conclusion on petrographic examination

Petrographic examination of polished and thin sections is the most powerful tool in establishing the occurrence of ASR and whether the extent of the reaction is sufficient to cause the level of concrete deterioration observed on site. If signs of damaging reaction commensurate with visually observed symptoms of ASR on the structure under investigation cannot be found by petrographic examination of an appropriate number of representative core specimens, it would appear that ASR is not the main cause of damage and other mechanisms should be sought. The petrographic examination must be conducted by a qualified petrographer experienced in the examination of concrete affected by ASR. CSA A864 classifies the occurrence of features obtained from petrographic examination to give an overall assessment of the probability of ASR (Table 5). 5.2 Comparing observations from field condition surveys and petrographic examination

Furthermore, CSA 2000 analyzes the findings from both the site and petrographic examination to determine the likely contribution of ASR to the overall observed deterioration (Table 6). 5.3 Mechanical testing of core specimens

Numerous studies have shown that losses in the engineering properties of unrestrained concrete affected by ASR do not occur at the same rate and in direct proportion to the amount of expansion undergone by the ASR-affected concrete (Smaoui et al. 2004c). 5.3.1 Compressive and Tensile Strengths

Several authors have shown that tensile strength is a much better indicator of the progression of ASR than compressive strength (Blight et al. 1981, Swamy and Al-Asali 1986, Clayton 1989, ISE 1992, Siemes and Visser 2000, Smaoui et al. 2004c) which is generally affected only at much higher expansion levels (Table 7; Fig. 8 and 9). Direct tensile strength (traction tests) is also more sensitive to ASR than splitting tensile (Brazilian) strength (Clayton 1989, ISE 1992, Siemes and Visser 2000, Smaoui et al. 2004c). The use of the tensile-to-compressive strength ratio was suggested as a good indication of internal damage due to AAR (Nixon and Bollinghaus 1985). The tensile-to-compressive strength ratio of sound concrete typically varies from 0.07 to

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0.11. In investigations dealing with AAR, it was suggested that a ratio <0.06 was indicative of internal deterioration due to ASR. Since the ultimate compressive strength of concrete supplied in the field is generally greater than the designed 28-day strength, a reduction in compressive strength due to AAR is unlikely to be critical in current practice, and failure through loss in compressive strength is also unlikely (ISE 92, Swamy 1995). 5.3.2 Flexural Strength and Modulus of Elasticity

A number of tests have shown that losses in elastic modulus and flexural strength could lead to substantial reductions in flexural rigidity and structural stiffness of affected members. Hobbs (1986) and Smaoui et al. (2004c) noted that the modulus of elasticity is more affected than the compressive and indirect tensile strengths, both of which having been quite similarly affected by ASR. The rate of reduction in modulus of elasticity can vary according to the type of reactive aggregate (Table 7) (Smaoui et al. 2004c); important reduction in the modulus of elasticity can occur even at a low level of AAR expansion ­ actually even when compressive strength of the affected concrete is still increasing (Pleau et al. 1989) (Fig. 8 and 9). According to Clark (1990), there would be no significant reduction in modulus of elasticity for expansions <0.05%. Losses in modulus of elasticity and flexural strength between 20 and 60% were reported for expansions ranging from 0.1 to 0.3% (ISE 1992), and could even reach 80% for the former at very high expansion levels (Fig. 9). For the two reactive aggregates tested in their study, Smaoui et al. (2004c) found relatively similar reductions in the modulus of elasticity measured in compression and in traction (Table 7). Swamy and Al-Asali (1986, 1988) observed that the dynamic modulus of elasticity is affected at an early age, even before reaching the 0.1% expansion level. 5.3.3 Stiffness Damage Index

Wood et al. (1989) reported a significant alteration of stress-strain curves for concrete specimens affected by ASR. Chrisp et al. (1989, 1993) thus proposed the Stiffness Damage Test (SDT) that consists in measuring the strain of concrete cores or cylinders subjected to 5 cycles of compression stress between 0 and 5.5 MPa. The authors found that concrete affected by ASR typically showed significantly higher strains at the peak stress, and were consequently more ductile than unaffected concrete. Smaoui et al. (2004a), using a modified version of the SDT (using a peak load of 10 MPa instead of 5.5; compressive stress rate of 0.1 N/mm2/s) (Fig. 10), found that when using the energy dissipated during the first loading cycle (area of the first hysteresis) and the plastic deformation accumulated over the course of the five loading/unloading cycles, a reasonable estimate of the amount of expansion reached by laboratory concrete specimens could be obtained (Fig. 11). The authors applied this method to estimate the amount of expansion reached by cores collected from bridge structures affected at various degrees by ASR in the Quebec City area (Bérubé et al. 2004a). The results obtained (i.e., estimated expansion values to date) were corresponded with the extent of the visual and mechanical damages affecting the various concrete members investigated. The authors suggested that the method be used as part of an inspection program for the management of ASR-affected structures (Bérubé et al. 2004b).

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5.4

Expansion tests on concrete cores

The most commonly used method involves the testing of concrete cores maintained at 38°C and 95% R.H. After an initial "conditioning" period during which the concrete core will reach a volumetric equilibrium with respect to its new condition (i.e. unrestrained, high temperature and humidity additional expansion of preexisting ASR gel due to unrestrained and very humid test conditions), expansion is measured and tentatively related to a potential for further expansion due to ASR. However, difficulties are often encountered in the interpretation of the test results (Bérubé et al. 2002c, 2004c), mainly because : (1) unknown true correlation between "free expansion" of cores and the actual expansion in reinforced concrete members; (2) uncertain correlation of ASR expansion with respect to temperature, which is normally lower in the field (e.g., 7°C yearly average in the Montréal area, Canada), and (3) extreme humidity in the expansion tests, and (4) the possibility that the tested concrete may be abnormally cracked and porous with respect to the overall field concrete member under study. A further complication arises from the leaching of alkalis from relatively small specimens stored at 100% relative humidity; this can lead to an underestimation of the residual potential for ASR. Immersion tests on cores in 1N NaOH solution at 38°C are generally considered to indicate the absolute degree of reactivity of the aggregates present in the concrete under study (Bérubé et al. 2002c). 5.5 Determination of the alkali content of concrete

A simple technique involving the hot-water extraction of alkalis can be used to help assess the potential for future distress of concrete (Rogers and Hooton 1989, Bérubé et al. 2002d). Over time, significant alkalis can be released from aggregates and contribute to an increase in the concrete alkali content (Bérubé et al. 2002e). Since the alkali content can be subject to considerable variation within a single concrete element, or between different concrete components of the same structure, separate determinations should be made on a number of samples taken from different components at different depths, and representing concrete showing varying severity of deterioration and subjected to different exposure conditions (rain, sun, buried or underwater portions of the structures, etc.).

6.0

IN-SITU TESTING AND MONITORING

Although the severity or the extent of the damage affecting concrete structures may not require any short-term major intervention, it may be appropriate to carry out periodic inspections to monitor the evolution of the deterioration. Large structures such as hydraulic dams are often instrumented from the time of construction to monitor any relative movements that may affect their serviceability. Data generated from expansion, deformation and displacement measurements on the instrumented structure(s) are analyzed to determine the rate of expansion and the potential for future expansion. These data could then be used in the selection and implementation of further repair actions on the structure.

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6.1

Deformation measurements

In-situ deformation measurements can be performed by installing demec gauges and/or metallic references/devices at the surface of the concrete members showing visual distresse indicative of possible ASR; periodic length-change measurements are then taken using extensometers of various shapes and ranges, invar wires/rods or optical systems (leveling) (Fig. 12 and 13). Fiberoptic and vibrating wire systems can also be used, with deformation measurements being performed and the data transmitted automatically to central servers for further treatment. On a larger scale, instruments such as inclinometers and inverted pendulums can be installed in strategic parts of the structure to evaluate the relative movement, deflections, clearances at joints, etc. (e.g. Thompson et al. 1995, Danay et al. 1993, Gaudreault 2000). Evidence of stress build-up in reinforcing steel and the surrounding concrete resulting from restrained ASR expansion can be obtained from the measurements of stress in reinforcing bars (Fig. 16E and 16F) and the overcoring technique (Danay et al. 1993). 6.2 Measurement of surface cracking

As mentioned above, a very important part of the investigation to select mitigation actions for structures affected by ASR concerns the assessment of the current condition (i.e., the level of expansion/damage reached to date) of the concrete. The measurements of the width of surface cracks crossed by a set of straight lines drawn at selected locations on the surface of ASRaffected members bas been proposed to estimate the amount of expansion reached to date by field concrete (ISE 1992, LCPC 1997). Actually, the development and the extent of surface cracking on concrete structures or members exposed to the elements is a function of many factors. In the case of concrete members undergoing internal expansion due to ASR and subjected to wetting and drying cycles (cyclic exposure to sun, rain, wind, or portions of concrete piles in tidal zones, etc.), the concrete often shows surface cracking because of induced tension cracking in the "less expansive" surface layer (because of variable humidity conditions and leaching of alkalis) under the expansive thrust of the inner concrete core (with more constant humidity and pH conditions). The extent of surface cracking on those elements is then somewhat related to the overall amount of expansion reached by the affected concrete member. Smaoui et al. (2004b) conducted surface cracking measurements (crack widths along straight lines) on a number of concrete blocks and slabs undergoing ASR expansion testing at CANMET-MTL's outdoor exposure site in Ottawa, Canada. The authors found that, although surface cracking globally tends to increase with expansion, and that such a measurement could give average estimated expansion values relatively close to the expansion measured on the specimens (for parts of the specimens exposed to the most severe conditions), the results were still highly variable, and the estimated expansion values are generally lower than the measured expansions (Fig. 14). Periodic crack mapping allows monitoring of the evolution of superficial cracking which accompanies the early signs of distress. A method proposed by the Laboratoire des Ponts et Chaussées in France consists of quantifying surface cracking by recording and summing the crack widths measured along a set of lines drawn on the surface of the concrete element investigated (LCPC 1997) (Fig. 15). The so-called "Indice de fissuration (cracking index)" is then calculated giving the average measurement of the crack opening (in mm) per metre.

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Measurements are carried out periodically to monitor the evolution of cracking, and the results are used in a management system to determine the frequency of monitoring and further actions to be taken. Crack mapping can be accompanied by small-scale periodic deformation measurements using glass plates or metallic references located on both sides (or bridging) of surface cracks (Fig. 12 and 13). Structures that exhibit crack widths in excess of those tolerable may at some point be subjected to more detailed investigations (LCPC 2003), which may include a structural analysis to determine their integrity. 6.3 Temperature and humidity measurements

It is commonly accepted that AAR develops or sustains in concrete elements with internal relative humidity >80-85% (relative to 23oC). The relative humidity in a concrete structure can be measured over time with depth or laterally in various concrete elements using various techniques such as wooden stick, portable or permanent probes (Stark and Depuy 1987, Stark 1990, Siemes and Gulikers 2000, Jensen 2000, Bérubé et al. 2004b) (Fig. 16A and 16B). Probes usually generate temperature readings that can be used to make any corrections required for temperature variations. 6.4 Non-destructive Testing

Periodic pulse velocity measurements can be made on specific components or parts of the affected structure (at the surface or in the bottom of drilling holes), and might permit assessment of the evolution and the extent of internal cracking or deterioration. Impact echo measurements have been used to monitor the performance of concrete pavements affected by ASR after topical treatments with a lithium nitrate solution (Johnston et al. 2000, Stokes et al. 2003). 6.5 Full-scale Loading

When the visual survey and the in-situ measurements indicate a severe level of deterioration, it might be necessary to evaluate whether the stability of the structure is in danger. Finite-element modelling based on the results obtained from in-situ and laboratory testing might give valuable results. Full-scale loading tests in the field will ultimately permit assessment of the real structural loss in performance (or serviceability) of the affected structure (Blight and Alexander 1987, Blight et al. 1981, Imai et al. 1987) (Fig. 16C and 16D). The criteria for load tests are usually based on some limiting deflection criteria and recovery of the deflection with time (CSA 2000). Full-scale loading tests have shown that structures affected by ASR suffered only limited reductions in elastic rigidity despite significant external signs of deterioration (Swamy 1989, Ono 1989, Blight et al. 1981).

7.0

COLLECTIVE ASSESSMENT OF LABORATORY AND FIELD FINDINGS

The Laboratoire des Ponts et Chaussees in France has developed a system for the evaluation of structures affected by internal expansion processes. A condition survey is first carried out on the

15

bridges to identify those with damage that may significantly affect a critical (structural) element of the bridge or that may cause a risk for the security of users (Priority I). For such structures, appropriate equipment to monitor the rate of expansion is immediately installed (e.g. demec gauges, invar-rods extensometers, infra-red distancemeter (Fig. 13E and 13F). Samples cored from the structures are also examined in the laboratory to evaluate the internal condition of the concrete. For other structures that show "non-critical" signs of deterioration but may warrant monitoring, a program consisting of expansion and surface crack measurements is implemented (LCPC 2003). Periodic measurements of surface cracking and length changes are carried out to monitor significant changes in the rate of deterioration and plan further actions. Bérubé et al. (2002c) proposed an approach based on a combination of laboratory and in-situ testing procedures to estimate the potential for future expansion and deterioration of ASRaffected concrete using the following parameters (Fig. 17): (1) inherent concrete expansion and residual absolute reactivity of the aggregate (expansion tests on cores), (2) residual "active" alkalis in the concrete (water-soluble alkali content), (3) the humidity condition in the affected element, (4) the temperature and (5) the stress conditions (reinforcement detailing). The individual risk indices corresponding to each of the above features are combined to determine the overall Potential for Further Expansion in service (PFE). The Institution of Structural Engineers (ISE 1992) described a management system for concrete structures affected by ASR based on the following factors considered to affect the structural significance of ASR in a particular element: (1) expansion characteristics of the concrete, (2) consequences of failure, (3) site environment, (4) stress levels, (5) reinforcement detailing, and (6) the residual strength of the concrete (Table 8). One of the basic parameters used in the system is the total amount of expansion to be expected for the investigated structure. The so-called Expansion Index includes five levels from which expansion is estimated and they are determined from: (1) the amount of "free" expansion that has already occurred up to the time of investigation, and (2) the amount of expansion that is expected to occur in the future. The former may be estimated by measuring crack widths at the surface of the affected concrete components, while the potential for future expansion can be estimated from free expansion tests on cores taken from the structure, with corrections being applied to account for the behaviour of concrete under restraint. Threshold values of total expansion have been proposed according to the potential effects of expansion on the structural behaviour of concrete affected by ASR. The nature of reinforcement has an important effect on the structural performance of concrete affected by AAR. The Structural Severity Ratings thus determined, are in turn used to determine required actions (Table 9). Following a major research project conducted in collaboration with Laval University, Ministry of Transportation of Québec, ICON-CANMET, and IREQ-Hydro Québec, a metholodogy has been proposed for the evaluation and management of ASR-affected highway structures in Québec (Bérubé et al. 2004b, 2004d). In this methodology, the most important criterion retained is the number of years before the steel reinforcements risk exceeding their elasticity limit, which is considered to take place when the concrete has reached 0.2% expansion, provided that the steel/concrete bond remains satisfactory. This delay is calculated from: (1) the expansion attained to date by the concrete, and (2) the current expansion rate. The first parameter is estimated from (1a) the surface cracking or better, (1b) from the Stiffness Damage Test (SDT)

16

described above (Section 5.3.3). The second parameter is estimated from (2a) the surface cracking and the age of the structure or better, (2b) from expansion tests on cores combined with a number of considerations related to the temperature, humidity, and stress conditions prevailing in the field (above metholodogy proposed by Bérubé et al. 2002c), or the best, (2c) from in-situ expansion monitoring. The importance and the frequency of the monitoring (survey, coring, testing, in-situ monitoring of surface cracking and expansion, etc.) depends on the time to potential plastification of the steel reinforcements, according to three categories: >15 years, 5 to 15 years, and <5 years (>10 years, 3 to 10 years, and <3 years in the case of non critical members). The evaluation and management strategy includes a number of more or less extensive investigation steps and a more or less frequent follow-up afterwards.

8.0

MANAGEMENT ACTIONS ON STRUCTURES AFFECTED BY ASR

The management of concrete structures affected by ASR involves overall interpretation of the results of both field and laboratory investigations. This is essential to develop long-term monitoring programs, and to determine the nature and the extent of the repair program required. As mentioned before, the main factors controlling the development of extensive damage in a structural or massive concrete element due to ASR are: (1) the proportion and inherent reactivity of the siliceous phases in the aggregates, (2) the pH of the concrete pore solution which in turn is related to the internal and external souces of alkalies, (3) the availability of moisture, (4) the temperature and thermal gradients and (5) the configuration and structural restraint provided to the concrete structure or element. In general, management action against ASR often consists of one or more of the following: · No further action necessary; · Continue regular monitoring and inspections (in-situ and periodical laboratory investigations); · Perform minor or periodic (small scale or maintenance) repairs to minimize moisture ingress and deterioration; · Perform significant restoration including chemical (e.g. injection of CO2, treatment with lithium) and physical (stress relief, strengthening, post-tensioning) interventions to reduce or restrain the expansion process due to ASR; or · Replace the damaged structure. 8.1 Improvement of drainage

Considering the critical influence of moisture on the development of extensive ASR expansion in concrete, it is commonly recommended to critically review the drainage systems serving the affected members. Modifications could be implemented to allow water to drain away from the structure rather than onto or through parts of it (Hobbs 1988). The application of a waterproof membrane or asphaltic layer on the upstream face of concrete dams or water retaining structures may provide protection against ingress of water in the concrete.

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8.2

Crack injection

Filling macrocracks or construction joints with cement grout or epoxy resin is generally done to restore structural continuity or to limit water penetration; it is also commonly performed before applying a waterproof sealing or water repellent agent. In a number of cases, the effectiveness of this approach was limited since cracks reappeared a few months after treatment (Bérubé and Fournier 1987, Ishizuka et al. 1989). Injection of modern flexible grouts may prove to be more effective than rigid epoxy resins to prevent leakage through joints or cracks in a concrete member where AAR expansion is still active. 8.3 Application of coatings

Care should be taken since this type of approach, even if it will change the aesthetics of the structure, is unlikely to strengthen or add stability to the existing structure and will not necessarily assure the control of future expansion due to AAR (CSA 2000). The effectiveness of this approach relies on the capacity of the proposed system to reduce the availability of moisture to the affected concrete element; consequently, it is generally applicable to small structural cross sections, but is unlikely to be efficient for massive concrete elements. Ventilated cladding might minimize moisture ingress and permits the drying of concrete, unlike coatings which can trap moisture (Wood and Angus 1995). The effectiveness of surface treatments against AAR is influenced by the actual effectiveness of the specific product to control moisture exchange between the concrete and the atmosphere; coatings that permit the escape of water vapor are preferable to allow progressive drying of the concrete. There seems to be a consensus regarding which type of product offers the best performance; these products are made from acrylics or similar polymers combined with cements with or without silane (Durand 1993). Some silanes and siloxanes have shown beneficial effect in controlling moisture content in concrete and the extent of deleterious expansion due to AAR (Bérubé et al. 2002a and 2002b) (Fig. 18A and 18B). Grabe and Oberholster (2000) reported that a silane treatment on ASR-affected concrete railway sleepers has been effective in slowing down deterioration due to ASR, thus increasing the service life of the sleepers (Fig. 18C and 18D). Putterill and Oberholster (1985) have found that some surface film coatings, such as polyurethane coatings and water repellent agents, e.g. water-based silicates, did not effectively prevent long-term water penetration. Badly cracked concrete piers supporting the Hanshin Expressway in Japan were repaired at an age of 7 years by first filling the cracks with an epoxy resin injected under pressure and then either coating with an epoxy resin or impregnating with silane followed by a cosmetic coating of a polymer cement paste (Hobbs 1988). Ono (1989) also reported limited effectiveness of crack injection followed by surface coatings on concrete structures in Japan. This approach did not prove to be effective in controlling the expansion of the piers since, after four years of further exposure, some crack widening had been observed (Fig. 19A to 19C). The use of a flexible protective moisture-proof membrane may help to manage small volumetric changes of the repaired concrete component. The method of treatment will depend on the extent of cracking. Hairline cracks can generally be effectively coated whereby the coating can bridge the narrow cracks; however, wider cracks will require sealing with epoxy before coating (ACI 1998). Surface coatings will generally not be a solution for mass

18

concrete or concrete elements constantly in contact with a source of moisture (e.g. buried parts of concrete structures). Durand (2000) reported the results of monitoring ASR-affected concrete foundations of electric steel towers that had been subjected to various types of repairs, including epoxy injection, coating, strengthening and encapsulation. The data showed that the foundations to which a bituminous coating had been applied for the buried portions and the exposed parts coated with a flexible polymer membrane continued to expand at a significant rate after the repair work (Fig. 19D and 19E). Impermeable surface coatings may represent an interesting approach to prevent further deterioration of concrete (e.g. due to frost action) when expansion due to AAR is terminated. In the case of non-structural distress, repair may include removal and replacement of only severely damaged concrete and application of a protective moisture-proof coating or relatively impermeable concrete layer. For structurally adequate pavements affected by AAR, maintenance and rehabilitation measures may include: (1) undersealing where voids exist beneath the slab, (2) joint and crack repair, (3) joint and crack sealing, (4) improvement of drainage, and (5) improvement of load transfer (ACI 1998). Extensive work performed in South Africa has shown that the most cost-effective solution for the rehabilitation of road pavements cracked by AAR was the use of different types of pavement overlays (Van der Walt et al. 1981). 8.4 8.4.1 Chemical treatment Reducing internal pH

Because the extent of ASR is related to the pH of the concrete pore fluid, attempts have been made to reduce the pH level by injecting CO2 into the concrete (Cavalcanti and Silveira 1989). Implementation of this process was not found to be practical or economical for most concrete structures, and it can lead to carbonation, reduced passivity of the reinforcement and can lead to steel corrosion. 8.4.2 Lithium to Treat Existing Structures

Lithium salts either spread on the surface of ASR affected concrete pavements or introduced into the concrete by vacuum impregnation, or during the electrochemical chloride removal process, have been used (Stokes 1995, Stokes et al. 2003). A review of treated structures in the United States is provided by Folliard et al. (2003). Although early treatments used lithium hydroxide (LiOH) solution, lithium nitrate (LiNO3) solution is now the preferred choice as it is pH neutral, easier to handle, and has better penetration rates. Topical Treatment Topical application has been the most common method of applying lithium to ASR-affected concrete (primarily pavements and bridge decks) in recent years (Fig. 20A). It is not clear from past topical applications of lithium whether or not topical treatment of lithium leads to sufficient penetration to reduce ASR-induced damage. The potential for lithium ingress is significantly influenced by the extent of deterioration of the concrete at the time of treatment. Cracking will clearly facilitate ingress of the solution, but, if the deterioration of the concrete has proceeded to far, it may too late to treat the affected concrete.

19

When considering the topical application of lithium, the application rate becomes quite important. There are two main factors to consider: (i) if the application rate is too high, the solution may run off the surface to be treated resulting in wastage (and possibly increasing environmental concerns) and (ii) under certain conditions, solution ponded on the surface may evaporate precipitating LiNO3 salt on the treated surface, which may lead to reduced surface friction of trafficked surfaces. Experience has indicated that the optimum application rate in most cases is 0.16-0.40 L of 30-% LiNO3 solution per m2 of concrete surface (4 to 10 gal per 1000 ft2). A number of other controls may be necessary, and the following guidelines are reproduced from a recent specification to serve as an application (Folliard et al., 2003): · Prior to treatment, the surface shall be cleaned (e.g. using a road sweeper). · At the time of treatment, the road surface shall be free of loose sand, debris and similar materials, but need not be dry. · Treatment shall not be applied during periods of rain or if rain is expected within 6 h. · The treatment shall be applied in a minimum of two applications. · Each application shall not exceed 0.20 L/m2. · Individual applications shall be applied at least 30 min apart. · The application rate shall be adjusted to provide uniform surface coverage such that the material does not run off the surface. · If a white residue covers over 5% of the applied surface area due to evaporation, water shall be applied to the surface. Although there have been a number of structures treated topically with lithium solution, there have been few attempts to determine either the depth of penetration or the efficacy of the treatment. One exception to this is the treatment of State Route 1 in Delaware (Stokes et al 2003). Approximately 6.4 km of 8-year-old, ASR-affected concrete pavement was treated with six applications of 30%-LiNO3 at a rate of 0.24 L/m2 over a period of three years (two treatments per annum). Control sections were left untreated at either end of the project. Four years after the first application, one of the control sections was showing severe deterioration in the form of excessive cracking and spalling at the longitudinal and transverse joints. Figure 20B shows photographs of the control and treated sections at this age, and it is evident that the treated sections exhibit less deterioration. One year later, this control section was rehabilitated by grinding the surface layers and placing an asphalt overlay. At the time of writing, the other control section is beginning to show advanced deterioration while the treated section continues to perform satisfactorily. Cores were taken four years after the first application and were tested in the laboratory to determine the depth of lithium penetration. The concentration profiles shown in Fig 21A and 21B indicate that the depth of penetration is a function of the extent of cracking. In the more heavily cracked areas (crack widths in the region of 1 mm at the surface), the lithium had penetrated to a depth of at least 50 mm. Although a treated depth of 50 mm may not seem too significant in pavement with a total thickness of 330 mm, the surface of concrete pavements frequently show more advanced deterioration due to ASR as it is less restrained, and experiences more exposure to moisture, salt and cycles of freezing and thawing, and traffic loads at the surface. Thus, a remediation strategy that is confined to the surface 50 mm of concrete may still slow down the overall rate of deterioration of the structure.

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Electrochemical Methods Although the precise requirements of the system will vary from structure to structure, the basic components of the system are the same, these being: · Survey to determine the location, continuity and cover depth to the rebar. Location and depth are determined using a pachometer, and continuity by measuring electrical resistivity between rebar connections (should be less than 1 ohm). Electrical connections must also be made between the rebar and the power supply. The number of connections should be no less than one per 50 m2. · Repair of any cracks, spalls and delaminations. · Installation of electrolyte media on concrete surface. Sprayed cellulose fibers are typically used on vertical surfaces (e.g. columns), whereas synthetic felt mats are more suitable for horizontal surfaces (e.g. bridge decks). The fibers or mats will be presoaked with the electrolyte. · Installation of anode. Either a steel or titanium mesh can be used as the anode, and this is usually installed between two layers of the electrolyte media. Electrical connections are made to each anode mat and the power supplies. · Cover installation with plastic sheeting to prevent evaporation. · Install electrolyte circulation system. To maintain the concrete surface (and cellulose fibers or felt mats) in a saturated condition, the electrolyte must be continuously circulated through the system. For columns, this is achieved by collecting the electrolyte that drains out of the bottom of the system and pumping it back up to the top. For horizontal surfaces, this may require the drilling of holes into the lowest points of the surface and allowing the electrolyte to drain through the deck where it is collected and pumped back to the top surface. · For large footings with relatively small proportions of steel reinforcement, consideration will be given to drilling vertical holes in the concrete to act as wells for the electrolyte. An anode will be installed in each hole and will be connected to the power supply. · If it is required that the bridge deck remain in service during treatment, steel plates can be placed over the installation. · The power supply is then switched on and adjusted to give a current density of 1 A/m2. (AC/DC rectifiers with a 40-V output are usually capable of treating 100 m2 of concrete surface area, depending on the electrical resistivity of the concrete). · The current and voltage are monitored throughout treatment. · Cores will be taken at weekly intervals to determine the lithium (and chloride) concentration profile · It is envisaged that an 8-week treatment will be required Various lithium compounds have been used to date including lithium nitrate, lithium hydroxide and lithium borate. Limited testing of bridge decks treated electrochemically have indicated that a significant quantity of lithium is absorbed from the electrolyte during treatment and that depths of penetration of at least 30 mm are possible (greater depths were not tested). Whitmore and Abbott (2000) described the treatment of five concrete pier footings of a bridge in New Jersey (USA) using an electrochemical system. The treatment involved installation of titanium mesh on the top surface of each footing, and the addition of several anode "reservoirs" and auxiliary cathodes (Fig. 21C) to accelerate migration of the lithium solution. The system ran for four weeks, with an average consumption of 1.6 US gallon of lithium solution per yd3 of concrete (Vector Corrosion Technologies 2001) (Fig. 21D). 21

Vacuum Impregnation Originally developed in Europe in the early 1970s, the vacuum injection/impregnation processes have been utilized in North America since the mid 80s for the in-situ restoration of concrete, stone and masonry structures. The process is commonly used to restore structural integrity associated with cracking and generally involves the following steps: · The object or member to be treated is first enclosed. · A low-pressure zone is then created by applying a vacuum source to the enclosure. Partial vacuum is achieved by adhering vacuum and introducing porting devices onto the fracture or surface to be repaired. · A suitable repair material/product is introduced into the enclosed system. The negative pressure created by vacuum withdraws moisture from the concrete matrix and the fracture surfaces, along with deleterious gases and/or materials; the concrete-drying process can actually be monitored using in-line hydrometers installed in the special vacuum tubing (Boyd et al. 2001). Under negative pressure, appropriately selected repair products and materials can penetrate into the deteriorated system thus filling cracks, interconnected cracks, voids and even microcracks. It has been reported that the vacuum processes can actually actually fill cracks as fine as 5 µ using low-viscosity resins (Boyd et al. 2001). Also, in deteriorated systems, vacuum processes will hold the broken/loose pieces together during the permeation process, thus eliminating the internal damage caused by the effects of induced high pressures using pressure injection. While there is science involved, there is also a considerable amount of art involved in achieving optimum results with the vacuum processes. Better results would be expected for treatments performed under more temperate conditions. Vacuum injection/impregnation has already been used for repairing ASR affected members. For example, in Southern California, TECVAC reported the treatment of alkali-silica damaged high line tower pier footings to a depth of ~4.5 m with minimal excavation (<2 m); core drilling the member revealed interconnected lateral cracking at a depth of ~1.25 m. The Pennsylvania State DOT recently treated a structure under the "Evaluation of Lithium Vacuum Impregnation on a Structure" (ELVIS) (October 2003, in Johnstown, PA). The treatment was performed on the abutment wall, sidewalk, the parapet and the deck (Marcy Lucas, PENNDOT, personal communication 2003). 8.5 Strengthening

Over the past few decades, a large number of investigations have been carried out to study the effect of ASR on reinforced concrete members (e.g. Putterill and Oberholster 1985, Kobayashi 1989, Swamy 1990, Swamy and Al Asali (1987, 1989), Abe et al. 1989, Inoue et al. 1989, Clayton et al. 1990, Hobbs 1990, ISE 1992, Swamy 1995, Jones and Clark 1996, Monette et al. 2000, Smaoui et al. 2004c). A number of those studies have shown that physical restraint or containement (e.g., encapsulation of the affected member by a surrounding non-reactive concrete, applied stress or reinforcement) can significantly reduce deleterious expansion due to ASR in the direction of restraint. Post tensioning in one or two dimensions, or by encasement in conventional reinforced concrete, is currently used as a mean to restore the integrity of the structure; however, it should

22

generally be restricted to relatively small masses of structural concrete because of the huge forces that may result from the expansive process due to AAR (Rotter 1995, CSA 2000). Posttensioned tendons or cables are considered to be an effective solution for thin arch dams (Singhal and Nuss 1991) or structural members of bridge/highway structures (Fig. 22A to 22D); however, they may be less attractive for large concrete structures because of the necessity of periodic distressing (Rotter 1995). Strengthening by introducing reinforcement with straps, steel plates and tensioning through bolts was also found to be effective in providing containment for selected AAR affected concrete members (Wood and Angus 1995) (Fig. 22E and 22F). Methods to restrain expansion and movement in mass concrete foundations such as tower bases have also included rock anchors and/or encapsulation (Bérubé et al. 1989, Durand 2000) (Fig. 23, 24A to 24C). Chipping of the badly cracked surface concrete layer to somewhat sound concrete is generally done to assure a proper bond with the repair material or concrete. Care should be taken in designing the encapsulating element because, if sufficient reinforcement is not provided to control stresses due to AAR expansion, the only beneficial effect of encapsulation may be to limit the ingress of moisture (CSA 2000). Strapping or encapsulation of AAR-affected reinforced concrete columns by or with composite materials may be an interesting solution providing sufficient structural strengthening is assured (Carse 1996) (Fig. 24A to 24C). 8.6 Slot cutting

This approach was applied to a number of AAR-affected gravity dams in order to relieve stress build-up due to AAR. This may provide only a temporary solution for concrete structures in which the expansion process due to AAR is not terminated; re-cutting may then be necessary thus increasing the cost of the rehabilitation program. A 4-year cycle program of slot cutting for the intake structure at Mactaquac Dam, New Brunswick, was proposed because of the continuing growth rate. It is important to note, however, that slot-cutting will modify the distribution of internal stresses in the concrete structure and reduce the internal restraint of concrete expansion (Gocevski and Pietruszczak 2000); consequently, the expansion rate is likely to increase after the cutting and before the relief gap is closed (CSA 2000). Additional reinforcement may be necessary to assure stability of concrete elements during and after slot-cutting. At Mactaquac Dam, the installation of large capacity (330 t) 19 strand tendon anchors was necessary to enhance stability of the structure once slots were cut (Thompson 1990, Thompson et al. 1995) (Fig. 25A and 25B). In addition, adequate sealing of the relief cuts is required to prevent the ingress of moisture. 8.7 Replacement

Even if replacement of the AAR-affected concrete member may represent the safest remedial measure, it is rarely economically acceptable. In most cases, only selected parts of the structures will be replaced, while modifications to the mostly deteriorated or affected parts of the structure can be undertaken to meet acceptable load conditions.

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9.0

CONCLUSION

Alkali-aggregate reaction has always been, and will continue to be, a concern for the construction industry because there is presently no way to completely cure the problem before it stops by itself, which can take decades to happen after extensive damage has developed. Extensive and expensive investigation, monitoring, and repair programs are sometimes required, despite their frequent ineffectiveness. Many organizations, because of their responsibilities to the public, are often faced with the necessity of adopting expensive repair programs only for esthetic purposes on structures affected by AAR but that are not structurally in danger. The relative importance of the problem depends on the type and the role of the structure affected. It is more serious for large structures such as hydraulic dams and some highway structures and buildings where relative movements, deformations, and cracking cannot be tolerated because of the risk of loss of structural integrity and potential danger to public safety.

10.

REFERENCES

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Table 1: Investigations Tools for the Diagnosis and Prognosis of ASR in Concrete Structures (adapted from BCA 1992).

Test / investigation Documentary evidence on concrete structures investigated Site investigation (condition survey) Section 3.0 Main Objective Collect and review available documents relating to the design, construction, survey and maintenance of the structure(s) · Assess the nature and the extent of distresses and deterioration · Assess the exposure conditions to which the structures are subjected to · Select sampling sites · Describe general condition of the concrete cores · Identify macroscopic features of ASR · Identify reactive rock types and their distribution · Identify presence and distribution of reaction products · Identify sites of expansive reaction · Identify pattern of internal cracking · Quantify the extent of damage due to ASR (e.g. cracking, gel) and possibly progression with time · Assess general condition of concrete Diagnosis XXX Prognosis X

4.0

XXX

X

Petrographic examination (Table 3) · Macroscopic description · Microscopic examination using polished slabs, thin sections (impregnated or not), broken pieces of concrete (possible uranyl acetate treatment) · Quantitative petrographic analysis on polished slabs Mechanical testing · Compression and splitting tensile testing · Direct tensile strength · Flexural Strength and Modulus of Elasticity · Stiffness Damage Test

5.1 5.1 XXX X

5.1

XXX

X

5.1.2

XX

X

5.3.1 5.3.1 5.3.2

XX XX XX X X (if repeated with time) X (if repeated with time)

5.3.3

· Assess possible ASR method is more sensitive to ASR · Assess possible ASR Modulus is more sensitive to ASR · Assess structural properties of members · Internal damage due to ASR · Expansion level reached to date · Evolution of the reaction/expansion · Confirmation of deleterious expansion · Potential for future expansion · Assist in the identifcation of reactive aggregates and determination of the absolute reactivity of aggregates · Potential for future expansion · Determine the alkali content within the concrete to assess potential sources of alkalis and possible concentration · Determine the possible contribution of sodium chloride to the alkali content of the concrete

XX

Expansion test on concrete cores · Cores at 38oC, R.H. > 95% · Cores in 1N NaOH at 38oC

5.4 5.4

XX X

XXX X

Determination of the alkali content of concrete Determination of the chloride content of concrete

5.5

XX

X

--

X

X

X: Results could be useful if test can be done; XX: do when possible; XXX: Important test

32

Table 2: Classification System for Field Inspection (from CSA A864-00)

Feature Expansion and/or displacement of elements Cracking and crack pattern Low None Probability of ASR Medium High Some Structure shows symptoms of increase in concrete volume leading to concrete spalling, displacement and misalignment of elements Extensive map cracking or cracking Some cracking ­ pattern aligned with major reinforcement typical of ASR (i.e. map cracking or cracks aligned with major reinforcement or stress) Slight surface discoloration Line or cracks having dark associated with some cracks discoloration with an adjacent zone of light colored concrete White exudations around Colorless, jelly-like exudations some cracks readily identifiable as ASR gel associated with some cracks Outdoor exposure but Parts of components frequently sheltered from wetting exposed to moisture ­ e.g. rain, groundwater or water due to natural function of the structure (e.g. hydraulic dam or bridge)

None

Surface discoloration Exudations

None

None

Environment

Dry and sheltered

33

Table 3: Features Obtained from Petrography and Methods of Examinations

Features · Presence of damp patches, discoloration or staining at the surface of the cores, gel exudations at the surface and/or around the periphery of the core · Aggregates particle shape and distribution (e.g. preferential orientation of particles) versus the direction of coring Megascopic examination · Cracking type and location/orientation (i.e. surface macrocracking, (using a 10x lense) around and/or through aggregate particles), width, depth, crack orientation in the cement paste and versus the aggregate particle shape · Presence of secondary products in voids/pores, cracks, around aggregate particles or exuding from the core · Reaction rims around aggregate particles · Description of the fine and coarse aggregates (petrographic nature, texture, grain size, shape, distribution, proportion, etc.) · Characterization of the micro-cracking pattern, including intensity, size Microscopic examination on range of crack sizes, apparent association with particular aggregate polished sections (using a type, cracking in or around aggregate particles, extension in the cement stereo-binocular microscope) paste); cracks filled or not with ASR products, etc. · Reaction and/or alteration rims · Reaction products (location and distribution, etc.) · Estimate of the relative proportion of the concrete constituents · Characterization of the air-void parameters · Cement paste-aggregate bond, etc. · Petrographic nature of coarse and fine aggregates, presence of secondary products in air voids (e.g. calcium hydroxide, ettringite, alkali-silica gel, calcium carbonate, gypsum, etc.) · Sites of expansive reaction - occurrences of features that provide evidence of reaction and emanation of expansive forces, i.e. reactive Microscopic examination of aggregate particles showing cracking internally or at the thin sections cement/aggregate interface with cracks propagating into the (petrographic microscope) surrounding matrix and cracks filled or partially filled with gel. · Basic characteristics of the concrete might be assessed by experienced petrographers, such as: water to cement ratio, degree of cement hydration, paste porosity, cement clinker composition, presence of filler or supplementary cementing materials such as fly ashes and slags, presence of contaminants... Examination of broken · Presence, distribution and abundance of reaction products on fractured concrete pieces (fracture surfaces (paste and aggregates), in voids of the cement paste, aggregatesurfaces) cement paste bond, etc. (using a stereo-binocular · Presence of other reaction products (e.g. ettringite, etc.) and/or SEM) Methods of Examination

34

Table 4 : Weighing Factors for the Damage Rating Index

Petrographic feature Coarse aggregate with cracks Coarse aggregate with cracks and gel Coarse aggregate debonded Reaction rims around aggregate Cement paste with cracks Cement paste with cracks and gel Air voids lined or filled with gel Weighing factor x 0.25 x 2.0 x 3.0 x 0.5 x 2.0 x 4.0 x 0.50

Table 5: Classification System for Petrographic Examination (from CSA A864-00)

Probability of ASR Low Medium Nature and Extent of Features No gel present, no sites of expansive reaction, presence of other indicative features rarely found Presence of some or all features generally consistent with ASR: · Cracking/microcracking (associated with known reactive particles) · Potentially reactive aggregates · Internal fracturing of known reactive aggregate particles · Darkening of cement paste around reactive aggregate particles, cracks or voids ("gelification") · Reaction rims around the internal periphery of reactive particles · Damp patches on core surfaces · Evidence of site of expansion reaction, i.e. locations within the concrete where evidence or reaction and emanation of swelling pressure can be positively identified, and/or · Presence of gel in cracks and voids associated with reactive particles and readily visible to the unaided eye or under low magnification

High

35

Table 6: Diagnosis from Site and Laboratory Observations (from CSA A864-00)

Evidence of ASR Site Laboratory Low Low Interpretation If neither site nor laboratory investigations produce significant evidence of ASR, the reaction can be positively eliminated as a possible cause of damage and alternative mechanisms must be sought. The presence of considerable displacement, movement or cracking of the structure is not sufficient to suggest ASR if neither the type of damage observed on site nor the results of laboratory examinations are consistent with ASR. If the evidence from site indicates a low probability of ASR but a high incidence of reaction observed in the laboratory, it is not possible to establish a causal link between the deterioration on site and ASR. The most likely explanation for this result is that ASR has occurred but the operation of other mechanisms has prevented typical manifestations of ASR in the structure. Other possible mechanisms must be sought and eliminated before ASR is implicated as the main or sole cause of damage. If the evidence from site indicates a high probability of ASR but no evidence of reaction was observed in the laboratory examination, three possibilities exist: · The sampling program excluded locations where significant reaction had occurred, · The features observed on site, although consistent with ASR, are a result of another mechanism, or · The reaction is not sufficiently advanced to reach a conclusion. A judgment must be made whether to carry out further sampling, seek the presence of alternative mechanisms, or both. If the evidence from both site and laboratory investigations indicates a medium probability of ASR, then it may be concluded that ASR has occurred and may be a contributory cause of damage; however, it is likely that other mechanisms exist and have contributed to the overall deterioration of the structure. If the evidence from site and laboratory investigations both imply a medium to high probability of ASR, it may be concluded that ASR is at least a significant contributory cause of the damage to the structure. In the absence of any other mechanism, it may be reasonable to assume that ASR is the principal or sole cause of damage.

Low

High

High

Low

Medium

Medium

High

High

36

Table 7: Summary of Mechanical Test Results Performed on Laboratory Specimens Incorporating Reactive Aggregates (Smaoui et al. 2004c).

Aggregate Extremely reactive sand (Texas) Siliceous Limestone (highly-reactive) (Canada) Expansion (%) 0.002 0.039 0.114 0.210 0.328 0.392 0.007 0.038 0.095 0.128 0.166 0.002 0.008 0.014 0.017 0.025 Compression Strength Modulus 1 % loss % loss 1 0.0 0.0 1.9 34.0 5.7 34.8 15.6 45.3 21.7 49.8 29.5 53.3 0.0 0.0 11.6 8.8 13.6 21.7 16.9 24.2 18.8 42.5 0.0 0.0 - 0.2 - 3.8 - 4.2 - 14.0 - 8.6 - 12.5 - 16.2 3.0 Splitting-tensile Strength % loss 1 0.0 8.8 27.3 32.8 34.8 36.3 0.0 8.9 14.4 17.3 18.1 0.0 2.8 0.8 - 8.8 - 2.8 Traction Tensile Strength Modulus 1 % loss % loss 1 0.0 0.0 25.6 32.0 31.5 42.9 48.0 45.4 52.2 46.2 63.8 52.0 0.0 0.0 35.3 9.5 47.6 15.8 49.9 24.2 52.9 32.4 0.0 0.0 8.1 - 3.0 5.9 2.3 0.3 - 2.0 6.7 0.3

Limestone (non-reactive) (Canada) 1

Reduction with respect to the 28-day results for the same concrete, except for the mixtures incorporating the highly-reactive Texas sand where it is compared to the 28-day properties of concrete made with a non-reactive coarse limestone aggregate and a non-reactive fine aggregate.

37

Table 8 : Proposed Management Approach for ASR Affected Structures (ISE 1992)

Expansion Index of ASR ** Reinforcement I II III IV V Detailing Consequence of failure *** Class ** x Y x Y x Y x Y x Y 1 n n n n n n n n n n Dry (always 2 n n n n n n n n n D < 75% R.H.) 3 n n n n n n n D D C Intermediate 1 n n n D D C D C D C (always < 2 n n D C D C C C C B 85% R.H.) 3 n D D B C B B A B A Wet (buried 1 D D D C D C C B C B parts, rain, 2 D D C B C B B B B A condensation) 3 D C C A B A A A A A Note: n: negligible; A: very severe; B: severe; C: moderate; D: mild * Reinforcement detailing 1: Three-dimensional cage of very well anchored reinforcement 2: Three-dimensional cage of conventionally anchored reinforcement 3: One- or two-dimensional cage of reinforcement, or a three-dimensional one that is inadequately anchored ** Expansion Index of ASR I: Expansion up to 0.06%: only marginal effect on strength for structures properly designed with good reinforcement (Classes 1 or 2) II: Expansions from 0.06 to 0.10%: compressive strength marginally affected; tensile strength may be reduced; structures with Class 2 and 3 reinforcement systems must be assessed with care III: Expansions from 0.10 to 0.15%: mild ­steel reinforcement may yield; detailed appraisal necessary IV: Expansions from 0.15 to 0.25%: high-yield steel may yield; detailed appraisal is needed. V: Expansions > 0.25%: severe damage; structure subjected to special study. *** Consequence of failure: x: The consequence of structural failure is either not serious or is localized Y: Risk exists for life or limb or a significant risk of serious damage to property. Site Environment

Table 9: Management action on ASR-affected structures (ISE 1992)

Management procedure Improve drainage, protect surfaces from water run off and ponding Overall crack survey including estimate of expansion to date, frequency (years) Coring for stiffness and expansion tests for current and future expansion Coring for stiffness and strength tests to evaluate specific failure mode Detailed inspection and monitoring of cracks and overall movements; frequency (months) Evaluate benefits of load reduction, strengthening to improve detail class or replacement of critical elements Inspection for spalling risk from secondary corrosion and frost damage; frequency (years) A (very severe) XX XX (1y) XX XX XX (1m) XX XX (1y) Structural Severity Rating B C (severe) (moderate) XX XX XX (1y) XX XX XX (2m) XX XX (1y) XX (3y) XX X XX (4m) X XX (3y) D (mild) XX XX (6y) XX O XX (12m) O XX (6y)

XX : desirable;

X : May be required;

O : seldom required

38

Routine Inspection program

Site inspection Visual sympto ms of ASR Sampling Documentation Lab investigations (petrography)

DIAGNOSIS Damage due to ASR ?

No

Investigate for other deleterious mechanis m(s)

Yes or maybe No Need further investigations ? Yes

Detailed investigation program

Extensi ve sampling program Laboratory investigations · Petrographic examination · Mechanical testing · Expansion testing (Prognosis) · Water soluble alkalis In-situ testing · Detailed field inspection (d istribution/extent of damage) · Expansion and movement · Surface cracking · Structural evaluation

Collecti ve assessment of lab and fiel d investigations Is further expansion likely ? Yes

Management approach

Monitoring · "Small-scale" measurements · "Large-scale" measurements Mi tigati on and repair · Treat ments (lithiu m, sealers) · Confinement and strengthening · Stress relief

Fig. 1 : Global flow chart for the evaluation and management of concrete structures for ASR

39

A

B

C

D

E

Fig. 2:

(A). Relative movement of a concrete pier caused by the expansive forces generated by the adjacent retaining wall affected by ASR (on the left). (B). AAR expansion of concrete causing extrusion of sealing material and spalling at the edge of sections of a five-year-old concrete pavement affected by ASR. (C). Relative movement and associated spalling between a pier block showing ASR cracking and an adjacent deck slab causing spalling of concrete and extrusion of sealing material along the joint. (D). Cracking and spalling of concrete due to ASR in a 20-year-old median highway barrier; freeze-thaw action has greatly influenced the extent of deterioration. (E). Radial expansion in a curved section of a concrete sidewalk affected by AAR. Asphaltic material has been placed to fill the gap between the sidewalk and the curb.

40

A

B

C

D

E

F

Fig. 3: (A). Map-cracking due to ASR and de-icing salt scaling affecting a median highway barrier. (B). Mapcracking due to ASR affecting the parapet wall of a 25-year-old highway bridge; cracks show typical staining giving the appearance of permanent dampness. (C). Map-cracking in the wing wall of a 30-year-old railway bridge affected by ASR. (D). Severe cracking on a large hydraulic dam affected by ASR. (E). Longitudinal cracking on the edge of the deck and in the column of a 20-year-old highway bridge affected by ASR. The presence of reinforcement and related stress fields has influenced the pattern of cracking. (F). Fine longitudinal cracking in a reinforced concrete column of a 20-year-old highway bridge affected by ASR.

41

A

B

C

D

E

F

Fig. 4: (A). Longitudinal cracking on the deck soffit of a 20-year-old highway bridge affected by ASR. (B). Longitudinal cracks interconnected by random cracks in a 20-year-old concrete pavement affected by ASR. (C). Longitudinal cracking in a precast, reinforced concrete beam affected by ASR. The edge beams, ie, those exposed to the action of wetting and drying, typically show a more advanced stage of ASR deterioration than the interior beams. (D). Longitudinal cracks interconnected by random cracks in a 25-year-old quay affected by ASR. (E). Pop-out created by the expansion of a frost-susceptible porous coarse aggregate particle. (F). Efflorescence and exudations of alkali-silica gel at the surface of a concrete foundation adjacent to a 25-year-old highway bridge affected by ASR.

42

A

B

C

D

E

F

Fig. 5: (A to D): Sections of concrete cut and polished from concrete prisms subjected to the Concrete Prism Test and incorporating a highly-reactive limestone coarse aggregate. (A). Few particles with pre-existing microcracks (expansion 0.002%). (B&C). The proportion of cracked aggregate particle increases with increasing expansion (B: 0.065%; C: 0.149%). (D). Extensive cracking both in the aggregate particles and the cement paste; also, void filled with alkali-silica gel (Expansion > 0.25%). (E). Polished concrete section incorporating a reactive volcanic aggregate and showing reaction rims and extensive cracking in the reactive aggregate particles. (F): Polished section of concrete impregnated with a fluorescent dye to help identify the presence and distribution of cracks and voids in the concrete.

43

A

B

C

D

E

F

Fig. 6: (A&B). Fractured surfaces of concrete cores showing deposits of alkali-silica gel on the cracked surfaces of the aggregate particles and in voids of the cement paste. (C). Photograph taken under the stereobinocular microscope showing desiccated gel lining a crack in the cement paste of a concrete core affected by ASR. (D). Thin section of concrete showing ASR-induced cracks filled with alkali-silica gel within reactive greywacke aggregate particles. (E). SEM micrograph showing deposits of alkali-silica gel on the surface of a broken concrete core affected by ASR. (F). SEM micrograph showing alkali-silica gel lining voids of the cement paste in a concrete sample affected by ASR.

44

A

B

C

D

E

F

Fig. 7: (A). Surface of a broken concrete core after treatment with uranyl acetate solution under UV illumination; the alkali-silica gel, which offers a greenish-yellow staining colour, surrounds reacted particles of siliceous sandstone. (B & C). Polished sections of concrete cores showing dark reaction rims around reacted aggregate particles. (D). Stereobinocular micrograph showing typical deposition of reaction products on the fractured surface through the alkali-silica reactive particles. (E). SEM micrograph showing the layer of gel forming the dark rim on Fig. (D). (F). SEM micrograph of the crystalline products showing a rosette-like microtexture corresponding to the white deposits inside the aggregate particle of Fig. (D).

45

Fig. 8: Residual mechanical properties as percentage of values obtained at the same age from unaffected concrete; the expansions of the companion test prisms are also given (Pleau et al. 1989)

Fig. 9: Lower bound of residual mechanical properties as percentage of values of unaffected concrete at 28 days (ISE 1992)

46

Test cylinder at an expansion level of 0.392%

12

1.2 Dissipated energy (joules x 10-3/m3) 1.0 0.8 0.6 0.4 0.2 0.0 0.000

Québec R2 = 0.98 Potsdam R2 = 1

New Mexico R2 = 0.99

10

8

Stress (Mpa)

Texas R2 = 0.92

6

4

2

0 0 100 200 300 400 500 600 700 800

Limeridge R2 = 0.83

0.080 0.160 0.240 0.320 0.400 Expansion (%)

Strains (micrometers/m)

Fig. 10: Stress-strain curves obtained during the Stiffness Damage Test for a test cylinder incorporating a reactive fine aggregate from Texas (expansion of 0.392% at the time of testing).

Fig. 11: Linear relationships obtained between the energy dissipated during the first cycle of the Stiffness Damage Test and the expansion of the test cylinders made with various types of reactive aggregates.

A

B

Fig. 12: Devices used for the in-situ monitoring of deformation/movement associated with cracks. (A). Device used at the Mactaquac Dam in New Brunswick (Canada) (Thompson et al. 1995). (B). System used at the St. Lambert Lock structure in Montreal (Canada) (Gaudreault 2000).

47

A

B

C

D

E

F

Fig. 13 : (A). Device (sensor) used for the in-situ monitoring of movement associated with cracks (from Baillemont te al. 2000). (B to D). In-situ measurements of expansion in concrete columns affected by ASR. (E). Set-up or the instrumentation for the in-situ monitoring of cracks and expansion on a highway structure affected by ASR. (F). Equipment ("infrared distancemetre") used to monitor in-situ expansion in the highway structure illustrated in (E) (LCPC 1999).

48

0.48

Estimated expansion (%)

0.4 0.32 0.24 0.16 0.08 0 0 0.1

y = 0,65x + 0,035 2 R = 0,63

0.2

0.3

0.4

0.5

Measured expansion (%)

Fig. 14: Relationship between the expansion estimated from the surface cracking (longitudinal measurements) and the longitudinal expansion measured on the top of 51 concrete blocks exposed outdoors. The experimental variation is large; the estimated expansion is on average 65% of the measured expansion (slope of regression line).

A

10 9 8 7 6 5 4 3 2 1

14 13 12 11 10 9 8 7 6 5 4 3 2 1 1

4 9 14

-0.7 0.05 0.1 0.4 ------

C

14

Major cracks

1 10

5 10

1.9 -0.05 -0.3 2.4 0.3 2.2

O

Interval OA OB OC 1 6 11

0.1, 0.1 1.2 0.05 --1.4 -0.5 0.05 --

B

Crack opening (mm) Avg. / Avg. / Global crack m Average (CI) 0.8 0.11 0.8 4.8 0.8 3.39 4.0

2 7 12

0.8 -0.05 0.3 -0.3 -0.2 1.5 --

3 8 13

---0.2 0.3, 0.5 ---0.1, 0.2 --

Base length (m) 1 1 1.4

# cracks 6 7 7

Total cumulative 4.8 0.8 5.6

AB

1.4

8

5.05

0.63

3.6

Fig. 15: Example of measurement of the "Indice de fissuration" (cracking index) (LCPC 1997)

49

A

B

C

D

E

F

Fig. 16: (A). In-situ measurement of relative humidity, using a portable probe, in a concrete column affected by ASR. (B). Set-up for the in-situ monitoring of temperature, humidity and expansion (vibrating wire) in a bridge deck affected by ASR (Siemes and Gulikers 2000). (C). Arrangement of trucks during a full-scale loading test performed on a motorway portal structure affected by ASR in South Africa (Blight et al. 1983). (D). During the full-scale loading test illustrated in (C), displacement was measured at several points of the beam by means of gauges bedded on the lower deck of the portal. (E). Photograph of the western haunch of the structure showing the damage due to ASR. The hole in the middle of the member was cut to expose reinforcement for strain gauging (Blight and Ballim 2000). (F). Strain gauges mounted on the second reinforcing bar from the right. (Pictures C to F: courtesy of G.E. Blight, University of Witwatersrand, Johannesburg, South Africa)

50

C oring and s am pl e pre parat ion

Residual expansion in the laboratory (Coeff. EXP, 0-16)

Expansion test on cores in air at 100% and 38°C (1-2 years, avg. %/year) Expansion test on cores in 1N NaOH at 38°C or, preferably, Extraction of aggregates from cores and concrete test CSA A23.2-14A or ASTM C 1293 (% after 1 year) Hot water extraction of alkalies on pulverized concrete (kg/m3 Na2Oe) Ambiant external or, preferably, internal humidity (annual avg. % RH) Ambiant external or, preferably, internal temperature (annual avg. °C) Reinforcement (% steel) and/or other restraints (MPa) Maximum A or B

Absolute degree of reactivity of aggregates (Coeff. ABR, 0-4)

Water-soluble (active) alkali content (Coeff. ALK, 0-4)

Humidity effect (Coeff. HUM, 0-1)

Humidity effect (Coeff. HUM, 0-1)

Temperature effect (Coeff. TEM, 0.4-1)

Temperature effect (Coeff. TEM, 0.4-1)

Effect of reinforcement and other restraints (Coeff. STR, 0.1-1) A (1-16)

Effect of reinforcement and other restraints (Coeff. STR, 0.1-1) B (1-16)

Potential rate of expansion due to ASR (Coefficient PFE, from 1-16) and expected % per year)

Fig. 17:

Laboratory assessment of the potential rate of ASR expansion of concrete members in service either already affected by ASR or not (Bérubé et al. 2002c)

51

A

Control Sealed

B

C

D

Fig. 18: (A). Application of sealers on highway median barriers affected by ASR (Bérubé et al. 2002a). (B). Unsealed/control (section on the left) and sealed (section on the right) of a highway median barrier treated with silane. The photograph has been taken three years after the treatment; the treatment had a dramatic beneficial impact not only on the cosmetic appearance of the affected concrete member, but also contributed in reducing internal humidity content and expansion of the concrete (Bérubé et al. 2002a). (C). Condition of concrete sleepers affected by ASR in the Sishen-Saldanha railway line in South Africa. (D). As part of the management programme, a number of cracked concrete sleepers in the Sishen-Saldanha railway line were treated with silane. Further monitoring of the elements showed that the treatment of affected sleepers with silane has been effective in reducing the rate of deterioration due to ASR (Grabe and Oberholster 2000). (Pictures C and D: courtesy of R.E. Oberholster, PPC Technical Services, Cleveland, South Africa)

52

A

B

Vertical cracking

C

D

E

Fig. 19: (A & B). Reinforced concrete pier of the Hanshin expressway in Kobe (Japan) affected by ASR. As part of the repair programme for the damaged piers, treatments with various types of coating was applied. In the case of the piers illustrated in (B), vertical cracks reappeared a few years after the treatment. (C). Beams were also repaired by using either polyurethane resins or epoxy resins. Cracks also reappeared shortly after the treatment (Ono 1989). (D & E). Massive electric tower foundations affected by ASR. As part of the repair programme for the above members, some of the foundations were treated by applying a bituminous coating on the buried surfaces (D) and a flexible water-resistance polymer membrane on exposed concrete surfaces (E).

53

A

B

Not treated Treated (6)

Fig. 20: (A). Topical application of lithium-based solutions at the surface of a pavement section affected by ASR. (B). During the period between 1998 and 2001, a section of concrete pavement in Delaware (USA) has been treated with topical applications of a lithium-based solution in order to slow the progression of ASR-induced damage. Typical ASR-related distresses observed in the pavement are severe cracking and spalling at joint. This figure illustrates the condition of the un-treated (control) and treated sections (after six topical treatments), thus confirming the beneficial effect of the treatment (Stokes et al. 2003),. (Pictures A & B: courtesy of D.B. Stokes, FMC Corporation ­ Lithium Division, Charlotte, USA)

54

800

A

Lithium (ppm)

200

B

600

Lithium (ppm)

400

Cracking: Heavy Moderate Light

150

100

200

50

0 0 10 20 30 40 50

Depth (mm)

0 0 10 20 30 40 50

Depth (mm)

C

Lithium (solution) ANODE (grade 1 titanium)

Wood Dam

D

+

RECTIFIER DC power supply

Spacer

3' max.

Rebar Lithium filled Anode reservoir Pile Cap 3' max.

Fig. 21: (A & B). Depth of penetration of lithium after the topical treatment of concrete pavement sections affected by ASR in Delaware. (C&D). Repair of pier footings of a highway structure suffering from severe cracking and spalling due to ASR using an electrochemical system for lithium impregnation (Whitmore and Abbott 2000). (Picture D: courtesy of D. Whitmore, Vector Construction Group, Winnipeg, Canada)

55

A

B

C

D

E

F

Fig. 22: (A to D). General view of a highway structure affected by ASR in South Africa. Cracking due to ASR was observed in the pile caps supporting reinforced concrete columns. The cracked concrete was first removed (B). Additional steel reinforcement was added around the pile cap (C)., while external strengthening was provided by means of prestressed cables (D). (E). General view of Montrose bridge (Scotland) (F). Close view of strengthening remedial work to the tower top. The work consisted in introducing reinforcement by straps, plates and tensioned bolts to provide full containment for the top chord and tower top area (Wood and Angus 1995). (Pictures A to D: courtesy of R.E. Oberholster, PPC Technical Services, Cleveland, South Africa) (Pictures E and F: courtesy of J.G.M. Wood, Structural Studies & Design Ltd., Chiddingfold, UK)

56

A

B

C

D

E

F

Fig. 23: (A to F). Rapair of a group of electricity tower concrete foundation affected by ASR in Quebec City (Canada). Map-cracking and gel exudation affecting a 29-year-old concrete foundation. The foundations had suffered from significant swelling and consequent due to ASR. The repair programme selected consisted in splitting the foundations in two blocks (B), followed by the encapsulation with reinforcing steel and silica-fume concrete (C to F) (Bérubé et al. 1989, Durand 2000).

57

A

B

C

D

E

F

Fig. 24: (A to C): Concrete anchor block for electricity towers affected by ASR (see Fig. 23). The repair approach for this ASR-affected concrete element was to apply a bituminous coating on the buried surfaces and a flexible water-resistance polymer membrane on exposed concrete surfaces, as well as to provide external strengthening through the use of steel frames, rods and plates (Bérubé et al. 1989, Durand 2000). (D). View of a bridge structure affected by ASR in Australia. Vertical cracking has been observed in the prestressed octagonal piles supporting the structure about 13 years after commissioning. The repair strategy consisted in monitoring progress of ASR expansion and then repair the piles in which ASR had nearly exhausted itself. Photograph D illustrates glass-fibre composite repair to 500 above high water level and concrete encasement to bed level. (E). View of coffer dam and split aluminium formwork. (F). As an alternate method to the glass-fibre composite, wrapping was also carried out with two layers of carbon fibre composite materials. (Pictures D to F: courtesy of A. Carse, Queensland Transport, Brisbane, Australia)

58

A

B

C

Diamond coated wire

D

Fig. 25: Alkali-aggregate reaction has been extensively affecting the structures at the Mactaquac Generating Station (Fredericton, Canada). Since the early 1970's. a comprehensive remedial measures and long-term AAR management program has been developed and implemented. As part of the program, diamond wire saw cuts have been used to de-stress and control the expansion in the water retaining structures since 1988 (Thompson et al. 1995). (A to D). In order to assure stability in the intake structure resulting from slot cutting, multistrand post tensioned tendons were installed from the downstream face of the intake structure (B) (see concrete anchor blocks on the downstream face on Fig. A and C) to the lower drainage gallery. (D). Close view of the set-up for the slot-cutting with diamondcoated wire. (Thompson 1990, Thompson et al.1995).

59

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