The ratio of basalt to river sand needs to be determined comprehensively based on project requirements, concrete performance requirements, cost budget and other factors. Different ratios will have a significant impact on the working performance, mechanical properties and durability of concrete.

The following analysis is carried out from two aspects: the performance comparison of basalt machine-made sand and river sand, and the impact of the ratio on the project:

Performance comparison of basalt machine-made sand and river sand

Working performance: The machine-made sand of different parent rock types has little effect on the working performance of concrete, but the amount of stone powder has a significant effect on the working performance of concrete. Generally speaking, as the amount of stone powder replacing fly ash increases, the slump and expansion of concrete out of the machine gradually decrease, and both reach the minimum value when the amount of stone powder is 60kg/m³. This is because fly ash has a morphological effect due to its unique spherical particles, which can improve the fluidity of concrete and effectively improve the working performance of concrete. As stone powder gradually replaces fly ash, the morphological effect of fly ash gradually weakens, and the fluidity and working performance of concrete will deteriorate to a certain extent.

Mechanical properties: Taking limestone powder concrete and basalt powder concrete of three strength grades C30, C35 and C40 as examples, at the age of 28 days, the compressive strength of limestone powder concrete is greater than that of basalt powder concrete with the same proportion; at the age of 7 days, except for the cases where the stone powder content of C35 strength grade concrete is 0 and 60kg/m³, the compressive strength values of other strength grade concrete and stone powder dosage are higher for limestone powder. This is because the early activity index of limestone powder is higher than that of basalt powder, and the use of limestone powder can promote the early hydration reaction of cement, generate more calcium hydroxide and C-S-H gel, and the increase in calcium hydroxide content can promote the hydration process of fly ash. As the reaction continues, the density of concrete structure is improved and the compressive strength gradually increases.

Impact of the ratio of basalt to river sand on the project

If the proportion of basalt is high: the frost resistance of basalt machine-made sand concrete is similar to that of ordinary river sand concrete, and is slightly better than that of ordinary river sand concrete. The introduction of mineral admixtures has significantly improved the frost resistance of concrete. As the amount of basalt increases, the effect becomes more and more significant, and it is better than the same amount of fly ash. When basalt is added in combination with slag and fly ash, its frost resistance is further improved. In addition, when basalt is added in a small amount (15%), it can reduce the carbonation depth of concrete. As the amount increases, the carbonation depth is slightly greater than that of the control concrete. At the same amount, the carbonation resistance of basalt mixed with fly ash and slag is better than that of single mixing.

If the proportion of river sand is high: the particle grading and morphology of river sand may be more conducive to the working performance of concrete, but it may not be as good as basalt machine-made sand concrete in terms of mechanical properties and durability.