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Aggregates for Concrete

Aggregate

( 60 - 80 % by volume )

FUNCTIONS OF AGGREGATE IN CONCRETE · Economy (aggregate as space filler) · Strength · Reduction in shrinkage and expansion

DESIRABLE CHARACTERISTICS OF AGGREGATES · · · · Hard, strong & durable Free of organic impurities Low alkali reactivity with cement Proper gradation (for good workability and packing of voids)

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Cracking of concrete from use of alkali-reactive aggregate

Aggregate of Same size

Same size

Different sizes combined

The level of liquid in the graduates, representing voids

Classifications of Aggregate

· By Size

­ Coarse aggregate - particles retained on No.4 sieve (4.75mm or 3/16 in.) ­ Fine aggregate - particles passing No. 4 sieve.

· By Source

­ Natural mineral aggregate - sand, gravel , crushed stone. ­ Artificial or synthetic aggregate - blast-furnace slag, expanded clay, expanded shale.

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Classifications of Aggregate (continued)

· By Types of Rock

­ Igneous rock - formed on cooling of the magma.

· Intrusive igneous - formed by slow cooling beneath earth's surface. Characteristics: completely crystalline minerals, coarser grain. Examples: granite, trap rock. · Extrusive igneous - formed by more rapid cooling at or near earth's surface. Characteristics: finer grain, minerals with smaller crystals or glassy structures. Examples: basalt, perlite.

Classifications of Aggregate (continued)

· Classification of igneous rock based on SiO2 content

­ Acid - more than 65% SiO2 ­ Intermediate - 55 to 65% SiO2 ­ Basic - less than 55% SiO2

­ Sedimentary Rock - formed from disintegration of other rocks and deposited as sediments

· Examples: limestone, sandstone, shale

­ Metamorphic Rock - Igneous or sedimentary rocks that have changed its structure due to heat and pressure. Usually harder and denser.

· Examples: marble, slate.

Prediction of Behavior of Aggregates in Service

· From past performance record - The best basis for prediction of performance. · From mineral composition. For example: the minerals amorphous opal, chalcedony & tridymite are known to cause alkali-silica reaction. · From results of tests - This method is most commonly used.

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L.A. Abrasion Test

· Test for hardness or resistance to abrasion

ASTM C 131 - For aggregates smaller than 37.5 mm (1.5 in.)

Los Angeles Abrasion Machine

ASTM C 535 - For aggregates larger than 19.0 mm (3/4 in.)

L.A. Abrasion Machine

L.A. Abrasion Machine

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L.A. Abrasion Test Procedures

1. Run sieve analysis on test sample to determine weight retained on #12 sieve (1.7 mm or 0.067 in.). Place test sample in L.A. testing machine (rotating drum with metal balls inside) C131 - 5,000 g sample, 6 to 12 metal balls (depending on aggregate size) C535 - 10,000 g sample, 12 metal balls 2. The L.A. machine is rotated at a speed of 30 to 33-rpm for 500 revs.

L.A. Abrasion Test Procedures (Continued)

3. Run sieve analysis on test sample after the test. 4. L.A. loss is computed as: Change in Wt retained on #12 sieve Original Wt retained on #12 sieve X100%

FDOT Specs: L.A. Loss should be less than 45%

L.A. Abrasion Test Result Example

Weight of sample retained on #12 before test = 5,000 g Weight of sample retained on #12 after test = 3,254 g Result reported: L.A. Loss = (5000 - 3254)/5000 X 100% = 34.92%

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Aggregate Soundness Test ASTM Method C88 Purpose: To measure resistance of an aggregate to weathering through cycles of soaking in sodium or magnesium sulfate and oven drying.

Aggregate Soundness Test Procedures

1. Separate aggregate into different sizes by sieving. From each size fraction, weigh out a sample of specific amount o be tested. 2. Immerse each test sample in sodium sulfate or magnesium sulfate for 16 to 18 hours. (Sodium sulfate is more severe) 3. Dry test sample to constant weight in an oven at 110 C. 4. Repeat procedure (steps 2 & 3) for 5 or 10 cycles.

Aggregate Soundness Test Procedures (continued)

5. Determine % weight loss of each sample after test by sieving it through a specified sieve. 6. Calculate and report: % Soundness Loss = Weighted average of % weight loss after test

FDOT SPECS: Soundness loss < 12% (Sodium sulfate, 5 cycles)

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SOUNDNESS TEST RESULT EXAMPLE

_____________________________________________________________ Grading of Original Weighted SIZE Sample (%) % Wt. Loss % Loss _____________________________________________________________ 2 1/2 - 1 1/2 in. 20.0 4.8 0.96 1 1/2 - 3/4 in. 3/4 - 3/8 in. 45.0 23.0 8.0 9.6 3.60 2.20

3/8 in. - #4 12.0 11.2 1.34 _______________________________________________________________ Total 100.0 8.1 _______________________________________________________________ Soundness Loss = 8.1%

Test For Potential Alkali Reactivity ( Mortar Bar Method ) (ASTM C227)

Procedure:

­ Make bars of mortar 1 in x 1 in x 12 in ( 1 part cement to 2.25 parts of graded aggregate ). ­ Measure the length of the bars after 24 hours in the molds, and store the bars at a constant temperature of 100 °F in sealed moist containers. ­ Measure length changes at 1, 2, 3, 6, 9 and 12 months. ­ If expansion is greater than 0.05% at 3 months or 0.10% in 6 months, the aggregate is considered to be alkali reactive.

Measuring length change of mortar bar with a length comparator

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Organic Impurities Test ( For Sand ) ASTM C40

· Determines the presence of injurious organic compounds in natural sands · Procedure:

1. Mix the sand with a 3 % solution of Sodium Hydroxide and allow it to stand for 24 hours. 2. Compare the color of the liquid to a solution of Potassium Dichromate in Sulfuric Acid (light yellowish color). 3. If the color of the liquid is darker, organic impurities might be present, and further tests (such as ASTM C87) should be made before the sand can be approved for use.

Organic Impurity Test

Standard Color Pass Fail

Effect of Organic Impurities in Fine Aggegrate on Strength of Mortar (ASTM C87)

· Procedure

­ Make 3 (2-inch) cube specimens of mortar with washed aggregate, and 3 specimens with unwashed aggregate with specified consistency and proportions. ­ Run compressive strength test at 7 days. ­ Calculate and report:

(average strength of mortar with unwashed agg.) X 100% (average strength of mortar with washed agg.)

· The strength ratio should be greater than 95% (according to ASTM C33 Specifications).

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Materials Finer than No. 200 Sieve (ASTM C117)

· It is desirable to have low percentage of material passing No. 200 sieve. Typical maximum allowable: 1% for coarse aggregate. 3 - 5% for fine aggregate · Determine % passing No. 200 sieve by wet sieving and drying. · Two methods:

­ Method A - uses only water ­ Method B - uses water and a wetting agent

Materials Finer than No. 200 Sieve Test

Lightweight Particles in Aggregate (ASTM C 123)

· This method determines the percentage of lightweight particles in aggregates. · Basic Procedure:

­ A heavy liquid with a specific gravity of 2.0 (typically a solution of zinc chloride) is used to separate coal and lignite. A heavy liquid with a spec. gravity of 2.4 (typically a solution of zinc bromide) is used to separate chert and shale. ­ The separated lightweight particles are washed, dried and weighed. Results are reported in %.

· Typical maximum allowed: 0.5 - 1% for Coal and Lignite 3 - 8% for Chert and shale

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Clay Lumps and Friable Particles in Agg. (ASTM C142)

· Basic Procedure:

­ Soak aggregate in water for 24 hours. ­ Roll and squeeze aggregate particles between thumb and forefinger to attempt to break them into smaller sizes. ­ Use wet sieving and oven drying to determine the weight of the particles broken down. ­ Report results in % by weight

· Typical allowable limits: 3% for fine aggregate. 2 - 10% for coarse aggregate.

Sieve Analysis

· To determine gradation (size distribution) of aggregates. · Standard Sieves:

6", , 3", 1.5", 3/4", 3/8", #4, #8, #16, #30, #50, #100, #200

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The next standard sieve is half the size of the preceding standard sieve.

Sieves and Sieve Shaker for Coarse Aggregate

Sieves and Sieve Shaker for Fine Aggregate

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Gradation Chart with Sieve Size Raised to 0.45 Power

Sieve Opening (mm)

0.04 0.07 0.15 0.3 0.6 1.2 2.5 10 20

100

With Intermediate Aggregate 80

Percent Passing

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Without Intermediate Aggregate 40 Theoretical Optimum Density Line

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0.45 Power Chart

Sieve Opening (Inches) Raised to the 0.45 Power

Fineness Modulus of Sand

· A number to quantify the fineness of an aggregate. · The sum of the cumulative percentages retained on the standard sieves 6", 3", 1.5", 3/4", 3/8", #4, #8, #16, #30, #50 and #100 sieves, divided by 100. · Fineness modulus is usually used only for fine aggregate.

Calculation of Fineness Modulus Example:

Sieve 3/8" #4 #8 #12 #16 #30 #50 #100 #200 Cum. %Pass Cum. %Retained 100 0 98 2 85 15 F.M. = 273/100 78 = 2.73 72 28 42 58 23 77 7 93 2 Total = 273

1-1/2

#325 #200 #100 #50

0

#16

#30

3/8

3/4

#8

#4

40

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Gradation Limits for Fine Aggregate (ASTM C33 Spec.)

Cum. %Pass Cum. %Retained 100 0 95-100 0-5 80-100 0 - 20 50-85 15 - 50 25-60 40 - 75 10-30 70 - 90 2-10 90 - 98 Total: 215 - 338 · Possible range of F.M.: 2.15-3.38 · However, ASTM C33 limits allowable F.M. to be 2.3 - 3.1. Sieve 3/8" #4 #8 #16 #30 #50 #100

Gradation Requirements for Coarse Agg. (ASTM C33)

Sieve 2" 1.5" 1" 3/4" 1/2" 3/8" #4 #8 #16 Cum. % Passing No.4 No.56 No. 57 100 90-100 100 100 20-55 90-100 95-100 0-15 40-85 10-40 25-60 0-5 0-15 0-5 0-10 0-5 No. 67 No.8

100 90-100 25-55 0-10 0-5 -

100 85-100 10-30 0-10 0-5

Terminology on Aggregate Gradation

· Maximum Size - The smallest sieve that 100% of the aggregate must pass. · Nominal Maximum size - The smallest sieve which the major portion of the aggregate must pass. It may retain 5% to 15% of the aggregate, depending on the size number of the aggregate. (Definition in Superpave: One size larger than the first sieve to retain more than 10%) Well-Graded or Dense-Graded - Well distributed in various sizes, resulting in low air voids and high density when compacted.

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Terminology on Aggregate Gradation

· Uniform Gradation - mostly one size. · Gap-graded - missing a few sizes. · Both uniform and gap-graded aggregates are Open-graded ( high air voids and low density ).

Maximum Density Gradation Fuller's Maximum Density Curve: %P = (d / D)0.5 X 100%

where: %P = % Passing the sieve d = Size of the sieve D = Maximum aggregate size

FHWA Maximum Density Curve: %P = (d / D)0.45 X 100%

Densities of Aggregate

permeable voids solid impermeable voids

True Density = Mass of Aggregate Vol. of solids

Bulk Density = Mass of Aggregate Vol of (solids + voids) Apparent Density = Mass of Aggregate______ V. of (solids + imperm. voids)

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Measurement of Dry Bulk Specific Gravity For an impermeable solid (Wt. in Air) - (Wt. in Water) = Wt. of Water of Same Volume (or Wt. of water displaced) Specific Gravity = Wt. in Air_______ (Wt i Ai Wt i W t )

Specific Gravity =

Density _ Density of water

=

Weight of sample / Volume _ Density of water Weight of sample _ Volume x Density of water Weight of sample _ Weight of water displaced

=

=

For a Permeable Aggregate

(Saturated-Surface-Dry Wt in Air) - (Wt. In Water) = Wt of water of volume of (solid + voids)

Dry Bulk Spec. Gravity = Dry Wt. In Air________ (SSD Wt. In air) - (Wt. in water)

permeable voids volume of agg.

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Measurement of Absorption and Moisture Content

% Absorption = SSD Wt. - Oven-Dry Wt. X 100% Oven-Dry Wt % Natural Moisture = Natural Wt. - Oven-Dry Wt. X 100% Oven-Dry Wt SSD Bulk Specific Gravity = SSD Wt. in Air________ (SSD Wt. In air) - (Wt. in water)

Determination of Specific Gravity of Fine Aggregate

A Bulk Dry Sp. Gr. = B+S-C

A = Mass of oven-dry sample in air, g B = Mass of Pycnometer filled with water to calibration mark, g C = Mass of Pycnometer with sample and water to calibration mark, g S = Mass of saturated surface dry sample, g B + S ­ C = Mass of water displaced

CALCULATIONS (Cont.)

Bulk SSD Sp. Gr. =

S B+S-C

B = Mass of Pycnometer filled with water to calibration mark, g C = Mass of Pycnometer with sample and water to calibration mark, g S = Mass of saturated surface dry sample, g

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Measurement of Bulk Unit Weight

Bulk Volume

Bulk Unit Weight = Wt. of Agg.___ Bulk Vol. of Agg.

Unit Weight Test on Coarse Aggregate

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Storing and Handling of Aggregate

Avoid Segregation (1) Do not store in high coneshape pile.

Storing and Handling of Aggregate

(2) Do not let aggregate run down slope.

Storing and Handling of Aggregate

(3) Avoid a blowing wind.

wind

fine agg.

coarse agg.

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Use of smaller but more piles

Flat pile of larger area but lower height

Effects of Particle Shape and Surface Texture of Aggregate on Concrete

· Rough textured and angular aggregates give better bonding between the aggregate and the cement paste and thus higher strength for the same water cement ratio. · However, rough and angular aggregates requires more water to produce the same workability in a fresh concrete. · The two effects offset one another. With satisfactory gradation, both crushed and noncrushed aggregates (of the same rock type) generally give about the same strength for the same cement content. · It is undesirable to have flat and elongated particles.

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FDOT Specifications for Coarse Aggregate for Concrete

Coal & lignite Clay lumps & friable particles

Clay lumps Friable particles At source At point of use 2.0% max 2.0% max 1.75% max 3.75% max

1.0% max 3.0% max

Materials passing No. 200 sieve

Chert (spec. grav. less than 2.4) Free shell Cinders & clinkers Organic matter

3.0% max 1.0% max 0.5% max 0.03% max

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FDOT Specifications for Coarse Aggregate for Concrete

L.A. Abraison Loss Soundness Loss (Sodium sulfate, 5 cycles) Flat or elongated pieces

45% max 12% max 10% max

(A flat or elongated particle is one having a ratio between the maximum and minimum dimensions exceeding 5 to 1)

Gradation

Must meet gradation requirements for the specified stone size

FDOT Specifications for Fine Aggregate for Concrete

Shale Coal and lignite Clay lumps Cinders and clinkers Organic impurity test 1.0% max 1.0% max 1.0% max 0.5% max Pass

(If Fail, run Test for the Effect of Organic Impurities on Strength of mortar. Strength ratio at 7 and 28 days shall not be less than 95%)

Materials passing No. 200 sieve 4% max Gradation requirement - Slightly different from ASTM C33. Slightly finer materials are allowed.

Lightweight Aggregates

· Bulk unit weight of less than 70 pcf. (Normal natural aggregate has a unit weight of 95 to 105 pcf.) · Examples: pumice (natural agg.), expanded clays, expanded shale, expanded perlite, expanded slag. · Used to produce structural lightweight concrete or nonstructural insulating concrete.

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Heavyweight Aggregates

· Bulk unit weight of over 130 pcf. · Used to produce heavyweight concretes for use as nuclear radiation shields. · Examples: iron ore, titanium ore, steel punchings.

Blast-Furnace Slag

· waste product from the blast-furnace process for manufacturing of steel and iron. · Bulk unit weight of 70 to 85 pcf. · Used in making precast concrete products, such as masonry blocks, where high strength is not required. · Sulfur content in slag may cause durability problem in concrete. FDOT spec. limits sulfur content to a maximum of 1.5%

Recycled Concrete as Aggregate

· Old concrete crushed to proper gradation can be used as aggregate. · The strength and durability of the concrete produced are limited by those of the old concrete. · Generally has a higher absorption, a lower specific gravity, and a lower strength than a normal natural aggregate. · FDOT spec. allows a maximum L.A. Abrasion Loss of 50% for recycled concrete aggregates.

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Crushing Concrete Slabs ­ Making Recycled Aggregate

Recycled Aggregate -- Crushed PC Concrete

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