Date: February 12, 2015
The choice of fine aggregate, whether it is manufactured or natural sand, can greatly impact the fresh concrete properties of a mixture such as the workability, pumpability, and finishability.
Natural sand has an ideal shape for use as fine aggregate in concrete. The natural sand particles are well-rounded and are usually nearly spherical. Spherical particles decrease the percentage of voids within the concrete mixture so no additional paste is required to fill these voids. Well-shaped natural sands are ideal for workability of mixtures. Natural sand does not require more water to enhance the workability of the mixture so the amount of bleed water in the concrete will not be increased.
Manufactured sand or manufactured fine aggregate (MFA) is produced by reducing larger pieces of aggregate into sand-sized aggregate particles. Manufactured sands tend to be used in mixtures in areas where natural sand is not available or not cost effective to be hauled to the needed location. MFA tends to be more angular and flaky due to the crushing process. Highly angular particles tend to increase the paste content of concrete because additional lubrication is required for particles with sharp corners.
Overall, the spherical shape of natural sand is ideal in a concrete mixture to provide the best material to pump, handle on the job and finish the surface.