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Aggregate

Properties of Materials- Chapter 5

QuestionAnswer
Aggregate Combination of distinct parts gathered into mass or whole. Or simply, a mass of crushed stone, gravel, sand etc
Natural sources for aggregates gravel pit, river run deposits, rock quarries
Manufactured aggregates slag waste, expanded shale and clay to produce light weight aggregates
Igneous rocks Hardened and crystallized molten volcanic material (Ex: basalt, granite)
Sedimentary rocks Deposits formed in layers and cemented together with natural cemented process to form layers of rocks
Metamorphic rocks Either igneous or sedimentary rocks exposed to heat and pressure reforming the grain structure (Ex: quartzite, marble)
Aggregates acceptance depends on: - Their physical and chemical properties. - Cost and Availability: Using local available material produces cost effective measure.
Aggregates Uses - Base material (buildings, pavements) - Mixed with cementing agent (asphaltic concrete "AC" mixtures, Portland cement concrete "PCC" mixtures)
Aggregate Properties Depend on the properties of individual particles and the characteristics of the combined material. More precisely:  Physical properties  Chemical properties  Mechanical properties
Aggregate Shapes Angular, rounded, flaky, elongated
Aggregate surface texture Smooth texture and rough texture
Rough texture Key element in determining the performance of aggregates as a whole in the structure
Soundness/Durability The ability of aggregate to withstand weathering (important in severe weather climates)
Toughness, Hardness and Abrasion Resistance The ability of aggregates to resist the damaging effects of loads
Absorption Percentage of water absorbed by aggregates. a.k.a. moisture content in the SSD condition
Conditions of aggregate moisture content - Dry - Saturated surface dry - Moist
Bulk Specific Gravity Weight of Aggregate/Volume of container
Strength and Modulus Response of whole aggregate to stress
Gradation Particle size distribution of aggregate
Large aggregates Pros: desirable for economic considerations Cons: - Harsher to mix - Dimension of const. members - Clearance between rebars - layer thickness
Maximum Aggregate Size Smallest sieve size through which 100% of the aggregate samples particles pass (one sieve larger than nominal maximum)
Nominal Maximum Aggregate Size Largest sieve that retains any of the aggregate particles, but generally not more than 10% OR One sieve larger than the first sieve to retain more than 10% of the material using all the specified sieves
Maximum Density Gradation The density of an aggregate mix is a function of the size distribution of the aggregates.
Fineness Modulus Measure of fine aggregate gradation for use in PCC mixes. 1/100 of the sum of the cumulative percentage weights.
Deleterious substance Any material that adversely affects the quality of PCC or AC made with the aggregate. (Ex: clay lumps, soft particles, coatings)
Stripping Moisture-induced damage where separation of the asphalt film from the aggregate through the action of water, reduces the durability of the asphalt concrete and results in pavement failure.
Affinity of Asphalt Does the aggregate love water (hydrophilic) or hate water (hydrophobic)?
Stripping factors Porosity, absorption, existence of coatings and other deleterious substances
Aggregate Sampling and Testing Sampling Gradation Specific Gravity for fine and coarse Aggregate Absorption Bulk unit weight
Two main uses of aggregates in civil engineering - As an underlying material for foundations and pavements - As ingredients in portland cement and asphalt concretes
Coarse Aggregates Aggregate particles that are retained on a 4.75 sieve
Fine Aggregates Aggregate particles that pass through a 4.75 sieve
Reasons why aggregates are used for underlying materials, or base courses - Adds stability to a structure - Provides drainage layer - Protects structure from frost damage
How much does aggregates make up in PCC? 60% to 75% of volume 79% to 85% of weight
How much does aggregate make up in AC? 75% to 85% of volume 92% to 96% of weight
Angular and rough-textured aggregates Higher stability but worse workability. Improves bonding and increases interparticle friction. Desirable in AC and base courses
Flaky and elongated aggregates Undesirable for asphalt concrete because they are difficult to compact during construction and are easy to break.
What generates stresses in aggregates that can fracture the stones? Water freezing in the voids
Why is absorption important in PCC? Because the moisture captured in the aggregate voids is not available to react with the cement or to improve workability of the plastic concrete
Why is absorption important in Asphalt? Absorbed asphalt is not available to act as a binder
Why are large aggregates more economically advantageous? Less surface area and therefore require less binder but they are harsher and have less workability
ASTM defines coarse aggregates as particles retained on what size sieve? And fine aggregates are the particles that pass this same sieve. 4.75 mm (No. 4)
What type of gradation is desired for many construction applications? Dense, because of it's high stability. Aggregates occupy most of the volume of the material, thus less binder is needed which reduces cost.
Type of gradation where the majority of aggregates pass one sieve and is retained on the next smaller sieve One-sized distribution. Used as chip seals of pavements.
Type of gradation where aggregates are missing one or more sizes of material. Gap-graded distribution.
Type of gradation where aggregates are missing small aggregate sizes that would block the voids between larger aggregate. Open-graded distribution.
What can be used to control alkali-silica reactivity? Fly ash, ground granulated blast furnace slag, silica fume, natural pozzolans, limestone
Created by: smh02