How is aggregate specified?

Classification refers to the determination of the particle size distribution for the aggregate. Leveling limits and maximum aggregate size are specified because these properties affect the amount of aggregate used, as well as cement and water requirements, workability, pumpability, and concrete durability. The size of fine aggregates is defined as 4.75 mm or less. That is, aggregates that can be passed through a number 4 sieve, with a mesh size of 4.75 mm.

Fine aggregates include things like sand, silt, and clay. Crushed stone and crushed gravel can also be included in this category. The density of the aggregates is necessary in the dosing of the mixture to establish weight-volume ratios. Specific gravity is easily calculated by determining densities by water displacement.

All aggregates contain some porosity and the specific gravity value depends on whether these pores are included in the measurement. There are two terms used to distinguish this measurement: absolute specific gravity and apparent specific gravity. Absolute specific gravity (ASG) refers to solid material excluding pores, and apparent specific gravity (BSG), sometimes called apparent specific gravity, includes pore volume. In order to dose the mixture, it is important to know the space occupied by the aggregate particles, including the pores within the particles.

The BSG of an aggregate is not directly related to its particular performance, although the BSG specification is often made to meet minimum density requirements. Both gravel and crushed stone are generally acceptable for manufacturing quality concrete (Photo), although gravel is generally preferred for exposed aggregate. All aggregates contain some moisture depending on the porosity of the particles and the moisture status of the storage area. The permitted percentage of harmful substances for fine and coarse-grained aggregates are listed in Tables 1 and 3 of ASTM C 33, respectively.

Although aggregate is considered inert filler, it is a necessary component that defines the thermal and elastic properties of concrete and dimensional stability. Aggregate particles in this test are classified as flaky when their smallest dimension is less than 0.6 of their nominal size. If there is a deficiency in a locally available fine aggregate, concrete may benefit from the addition of air entrainment, additional cement, or a supplemental cementitious material (SCM) to address these deficiencies. Therefore, when selecting an aggregate source, knowledge of the mineral properties of quarry rock can provide an excellent clue as to the suitability of the resulting aggregate.

The fundamental relationship between the water-cement ratio and strength begins with the correction of the contribution or absorption of moisture by the aggregates. Most stacked coarse-grained aggregates are in the AD state with an uptake of less than one percent, but most fine aggregates are often in the wet state with a surface moisture of up to five percent. For example, a freshly ground aggregate may contain more dust and, therefore, be less receptive to bonding with an asphalt binder. Photo 7 - The size distribution of fine to coarse-grained aggregates plays an important role in the workability and performance of concrete.

Aggregate is a collective term for mineral materials such as sand, gravel, and crushed stone that are used with a binding medium (such as water, bitumen, portland cement, lime, etc.) Although relatively unimportant for loose aggregates, the chemical properties of aggregates are important in a pavement material. Aggregates are extracted from natural sand or sand and gravel pits, hard rock quarries, dredging submerged deposits, or mining underground sediment. The alkali content and type of aggregate in the system are likely to be unknown and therefore, if mixed with unsuitable materials, a risk of alkali-silica reaction is possible. OD monitors the moisture content of coarse-grained and fine aggregates on a regular basis to promote consistency and uniformity from batch to batch.


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