Aggregates for Concrete - Portland Cement Association

Aggregates for Concrete - Portland Cement Association

Aggregates for Concrete Design and Control of Concrete Mixtures Chapter 6 Overview Geology Classification

Characteristics of Aggregates Potentially Harmful Materials Alkali-Aggregate Reactivity Beneficiation Handling and Storage

Aggregates for Concrete Aggregate Geology Aggregate Classification Normal-weight,

lightweight, heavyweight Natural aggregate Manufactured aggregate Recycled-concrete

aggregate Marine-dredged aggregate Natural Aggregate Gravel and sand

Mixture of several minerals Pits, rivers, lakes, seabeds Quality depends on parent bedrock

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

Recycled-Concrete Aggregate Recycled-Concrete Aggregate

Marine-Dredged Aggregate Tidal estuaries, seashore Two concerns: seashells and salt Avoid uncrushed shells

Avoid using high chloride aggregates in reinforced concrete Aggrega te Characte

r-istics Grading Grading

Grading Limits Fine-Aggregate Grading Coarse-Aggregate Grading

CoarseAggregate Grading Maximum Size vs. Nominal Maximum Size

Maximum size 100% passing Nominal maximum size typically 85% to 95% passing Nominal Maximum Size

Combined Aggregate Grading Combined Aggregate Grading

Combined Aggregate Grading 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

Fineness Modulus Particle Shape and Surface Texture

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 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. Absorption and Surface

Moisture Bulking Resistance to Freezing and Thawing

D-Cracking 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 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) Shrinkage

Resistance to Acid Acids generally attack calcareous aggregates Calcareous aggregates neutralize acid Siliceous aggregates are attacked by sodium hydroxide

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)

Potentially Harmful Materials Potentially Harmful Materials

Alkali-Aggregate Reactivity Alkali-Silica Reaction 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) Aggregate Beneficiation Improving quality through processing

Heavy media separation

Jigging Rising-current classification

Crushing Handling and Storing Aggregates

Handling and Storing Aggregates Summary Geology

Classification Characteristics of Aggregates Potentially Harmful Materials Alkali-Aggregate Reactivity Beneficiation Handling and Storage

Questio ns ?

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