When it comes to the strength of normal concrete, most concrete aggregates are several times stronger than the other components. Aggregates are also essential for the strength, thermal and elastic properties, dimensional stability and volume stability of concrete. Cement is more likely to be affected by shrinkage, so the inclusion of aggregates in the mixture can control this and prevent cracking. The shape of the aggregate influences strength, but has a more immediate impact on the workability of plastic concrete.
Rough, angular particles pack more tightly, have more surface area, and have greater inter-particle friction than smooth, rounded particles, reducing workability. Angular particles also require a little more cement paste to coat them than rounded particles. Therefore, mixtures containing them will require a slightly higher cement content. The size of coarse-grated aggregates is the main factor in determining the strength of concrete.
In general, smaller coarse-grated aggregates are better for stronger concrete, with 20mm aggregates meeting the threshold for strong concrete and 40mm aggregates for normal strength concrete. Since fine aggregates are used to fill the voids of coarse-grained aggregates, the smaller the coarse-grained aggregates, the finer the fine aggregates should be. The gradation of aggregates, whether in a concrete with mortar or in a traditional concrete mix, implies a balance between strength and workability and is always a delicate balance. The absorption and surface moisture of aggregates are simple but critically important aspects of producing concrete that consistently achieves the specified or desired strength.
Aggregate in precast concrete is a structural filler, but its role is more important than what that simple statement implies. Concretes with voids rank between good and poorly leveled in terms of performance and economy. The purpose of aggregate dosing and sizing is to maximize the volume of aggregate in concrete (and, therefore, minimize the volume of the cement paste) while preserving strength, workability and aesthetics. The shape of your aggregates is important for the workability of the concrete, the quantity you want to place and the strength of the concrete you want to make. Mortar concrete is commonly used in precast concrete countertop mixes, as surface finish is very important.
This is a summary of the most important factors to consider when selecting and dosing concrete aggregate. To produce good quality, durable concrete containing a portion of recycled concrete aggregate, test concrete mixes and close control of the properties of old recycled concrete are often required, with mix adjustments made as needed. The size distribution of fine to coarse-grained aggregates plays an important role in the workability and performance of concrete. Recycled concrete will have higher absorption and lower specific gravity than conventional aggregates. In conclusion, if you are looking for medium strength concrete, get 40mm aggregates; however if you are looking for high strength, 20mm is best. To ensure good quality durable concrete containing recycled aggregate it is important to test mixes and closely control properties.