Reducing Cost By Using River Sand

It is entirely feasible to replace silica sand, which is expensive, with natural (river) sand. River sand costs about 1/15 of the cost of silica sand, reducing the cost of the UHPC matrix significantly. Our research has shown that completely replacing silica sand with river sand can result in a viable UHPC. As shown in the figures below, the reason is that the matrix still achieves good packing density (the gradation matches the ideal packing curve). After 48 hours of heat treatment after demolding, the 7-day compressive strength of our specimens was 158.6 MPa (23.0 ksi).

Figure above: Gradations of UHPC mix with natural sand instead of silica sand.

Figure above: Spread from mix with natural sand meets specifications

Higher packing density, and therefore superior properties, can be achieved by replacing a portion of the silica sand with river sand. The results of our experiments show that superior performance can be achieved if just 10% of the total sand content (the rest being natural sand) is fine silica sand where the compressive strength and tensile strength of UHPC are 169.7 MPa (24.6 ksi) and 11.3 MPa (1.6 ksi), respectively.