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Aggregate
Properties of Materials- Chapter 5
| Question | Answer |
|---|---|
| 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
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