Influence of stone powder content of machine-made sand on mortar

2021-06-29

In the machine-made sand, the part less than 0.075mm is called stone powder. The content of machine-made sand and gravel powder is stipulated in the transportation industry regulations. The powder content of the machine-made sand used along a certain expressway in northeastern Yunnan, Yunnan, has basically exceeded the allowable value of the specification. Many engineering faces have no sand available or the problem of long-distance transportation of river sand, and the cost has increased a lot.

Opinions are inconsistent with regard to the influence of stone powder content on the workability of machine-made sand concrete. Some scholars believe that compared with river sand concrete, stone powder increases the water demand of concrete and causes the workability of concrete to become worse; another part believes that the impact of stone powder on the workability of machine-made sand concrete has a degree of problem, that is, the most serious problem. The content of excellent stone powder exceeds this level, and stone powder has an adverse effect on the workability of concrete.

Wu Mingwei and others studied the effect of stone powder less than 0.08 ram in machine-made sand on the performance of concrete mixtures. They believe that stone powder is an inert admixture with small particles, which supplements the lack of fine particles in concrete and increases the solid surface area for water. The volume ratio reduces bleeding and segregation, and the stone powder can form a soft paste with cement and water, which increases the volume of concrete and improves the workability of concrete.

In response to this problem, the paper adopts machine-made sand with different stone powder content to study the influence of its angular outflow time, mortar fluidity, mortar flexural strength, and mortar compressive strength to investigate the best value of stone powder content.

Test conclusions: (1) When the content of machine-made sand and stone powder is less than 4%, it is easy to segregate and bleeding, and the workability is poor, and the smaller the content of stone powder, the easier the bleeding. (2) When the content of machine-made sand and gravel powder is between 4% and 8%, there is no obvious increase or decrease trend in the angular outflow time of the fine aggregate, the fluidity of the mortar, the flexural strength and the compressive strength of the mortar. (3) When the content of machine-made sand and stone powder is between 8% and 18%, when the fluidity is the same, the water demand of the mortar will increase with the increase of the stone powder content; the mechanical properties change significantly.