Influence of crusher type in the shape of fine crushed aggregate grains

Quarries have invested in equipment to increase production and improve the quality of their products, such as vertical shaft impact crushers (VSI). This type of crusher works with autogenous comminution of the material to improve the shape of the coarse aggregates. However, there are few studies about the influence of crushers in the shape of fine aggregate grains. In this context, gneiss and granite fine crushed aggregates, produced in cone crushers and VSI were studied. Parameters such as coefficient of volumetric shape, aspect ratio, and circularity were used to compare these aggregates with the river sand. The results showed that there is a difference between the shape of the sand river and the fine crushed aggregates. Among the crushed aggregates, those from the VSI showed improvements in grain shape, compared to aggregates from cone crushers. However, this improvement decreases with the reduction of grain size. Mortars produced with the studied aggregates were also evaluated. It was verified their influence on the consistency, the air content and compressive strength at 28 days. For the study in the mortar, the crushed aggregates were separated in fractions by sieving and composed to obtain the same granulometric distribution for all the aggregates. The mortars made with the crushing aggregates from the VSI showed higher fluidity, lower air content and higher compressive strength when compared to the crushed aggregates produced in the cone crusher.