05
Aggregate Classification Normal-weight, lightweight, heavyweight
Natural aggregate
Manufactured aggregate
Recycled-concrete aggregate
Marine-dredged aggregate<br>
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Natural Aggregate Gravel and sand
Mixture of several minerals
Pits, rivers, lakes, seabeds
Quality depends on parent bedrock<br>
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Manufactured Aggregate Crushed rock or air-cooled slag
Fine and coarse aggregate
Rough, angular texture
Cubical or elongated shape
More uniform in size
Less likely to be contaminated<br>
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Recycled-Concrete Aggregate<br>
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Recycled-Concrete Aggregate<br>
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Marine-Dredged Aggregate Tidal estuaries, seashore
Two concerns: seashells and salt
Avoid uncrushed shells
Avoid using high chloride aggregates in reinforced concrete<br>
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Aggregate Character-istics<br>
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Fine-Aggregate Grading<br>
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Coarse-Aggregate Grading<br>
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Coarse-Aggregate Grading<br>
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Maximum Size vs. Nominal Maximum Size Maximum size – 100% passing
Nominal maximum size – typically 85% to 95% passing<br>
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Nominal Maximum Size<br>
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Combined Aggregate Grading<br>
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Combined Aggregate Grading<br>
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Combined Aggregate Grading<br>
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Gap-Graded Aggregates Certain particle sizes omitted, typically one coarse aggregate size
Excess coarse aggregate – honeycomb, segregate
Excess fine aggregate – high water demand, shrinkage
Properly proportioned mixtures are readily consolidated with vibration<br>
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Particle Shape and Surface Texture<br>
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Bulk Density and Voids Bulk density – mass of aggregate in unit volume
Includes voids
30% - 45% voids in coarse aggregates
40% - 50% voids in fine aggregates
Angularity increases voids<br>
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Density and Relative Density Density = Relative density x density of water
Typically between 2400 and 2900 kg/m3 (150 and 181 lb/ft3)
Relative density typically between 2.4 and 2.9.<br>
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Absorption and Surface Moisture<br>
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Resistance to Freezing and Thawing<br>
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Abrasion and Skid Resistance Abrasion resistance used as quality index
Los Angeles abrasion test is most common
No correlation between aggregate abrasion and concrete abrasion
Siliceous content > 25% for good skid resistance<br>
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Strength Rarely tested
Tensile strength – 2 MPa to 15 MPa (300 psi to 2300 psi)
Compressive strength – 65 MPa to 270 MPa (10,000 psi to 40,000 psi)<br>
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Resistance to Acid Acids generally attack calcareous aggregates
Calcareous aggregates neutralize acid
Siliceous aggregates are attacked by sodium hydroxide<br>
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Fire Resistance and Thermal Properties Dependent on mineral constituents
Lightweight aggregates outperform normal-weight aggregates
Calcareous aggregates outperform siliceous aggregates
Coefficient of thermal expansion – 0.55 x 10-6 per °C to 5 x 10-6 per °C (1 x 10-6 per °F to 9 x 10-6 per °F)<br>
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Potentially Harmful Materials<br>
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Potentially Harmful Materials<br>
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Alkali-Aggregate Reactivity<br>
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Alkali-Silica Reaction<br>
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Alkali-Carbonate Reaction Rare due to general unsuitability of reactive aggregates
Tested through:
Petrographic examination (ASTM C295)
Rock cylinder method (ASTM C586)
Concrete prism test (ASTM C1105)<br>
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Aggregate Beneficiation Improving quality through processing
Heavy media separation
Jigging
Rising-current classification
Crushing<br>
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Handling and Storing Aggregates<br>
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Handling and Storing Aggregates<br>
45
Summary Geology
Classification
Characteristics of Aggregates
Potentially Harmful Materials
Alkali-Aggregate Reactivity
Beneficiation
Handling and Storage<br>
