The size of coarse-grated aggregates is the primary factor in determining the strength of concrete. In general, you'll want smaller coarse-grated aggregates for stronger concrete, with 20mm aggregates meeting the threshold for strong concrete and 40mm aggregates for normal strength concrete. The shape and texture of the aggregate affect the properties of fresh concrete more than hardened concrete. Concrete is more workable when a smooth, rounded aggregate is used instead of a rough or elongated angular aggregate.
Most natural sands and gravel in riverbeds or seashores are smooth and rounded and make excellent aggregates. Crushed stone produces much more angular and elongated aggregates, which have a higher surface-to-volume ratio, better bonding characteristics, but require more cement paste to produce a workable mix. When determining the strength of normal concrete, most concrete aggregates are several times stronger than the other components of concrete and are therefore not a factor in the strength of normal strength concrete. Aggregate is commonly considered inert filler, accounting for 60 to 80 percent of the volume and 70 to 85 percent of the weight of concrete.
The density of the aggregates is necessary in the dosing of the mixture to establish weight-volume ratios. 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. All aggregates contain some moisture depending on the porosity of the particles and the moisture state of the storage area. As the aggregate size decreases, the mixture requires more water to suspend the particles and create a viable solution.
The stone is mined, crushed and ground to produce a variety of aggregate sizes that conform to “coarse-grained” and “fine” specifications. This surface moisture in the fine aggregate creates a thick film on the surface of the particles, separating them and increasing the apparent volume. The size, shape, and properties of the aggregate directly influence the workability, strength, durability, and absorption rate of your ready-mix concrete. Once processed, aggregates are handled and stored to minimize segregation and degradation and prevent contamination.
An experienced concrete professional can use your project evaluation to identify the best shape and size of concrete aggregate for each phase of construction. 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. A smooth surface can improve workability, but a rougher surface generates a stronger bond between the paste and the aggregate creating greater strength. The selection of good quality coarse-grated aggregates is essential for the production of concrete that meets the desired strength and durability requirements.
The main natural resource is volcanic material, while synthetic aggregates are produced by heat or heat treatment of materials with expansive properties. The classification or size distribution of the aggregate is an important characteristic because it determines the paste requirement for workable concrete.
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