Study on the calculation of the paste thickness on coated coarse aggregate based on stereology

Abstract

Coarse aggregates in concrete are wrapped by cement mortar. On the one hand, coarse aggregates are bonded by cement mortar; on the other hand, cement mortar is the medium of transferring force when the concrete is stressed. So the workabilityandstrengthofconcrete are influenced by paste thickness on coated coarse aggregate (PTCCA). But PTCCA is not easy to be measured and more discrete. Asasolution, the concepts of average paste thickness on coated coarse aggregate (APTCCA) and effective paste thickness on coated coarse aggregate (EPTCCA) were proposed. The discrete element software PFC3D was used to simulate the standard concrete cubes with different volume content and gradation of coarse aggregate. According to volume content and gradation of coarse aggregate, the equations for predicting the APTCCA and EPTCCA were proposed. The equation for predicting coarse aggregate area in two-dimensional (2D) section according to coarse aggregate volume content was proposed. The correction factor of irregular aggregate was discussed. The recycled brick coarse aggregate concrete cubes were designed to verify the equations established in this paper. The test results showed that: The prediction equation of coarse aggregate area in 2D section was established by volume fraction and diameter of coarse aggregate, the correlation coefficient between the predicted values and the true values was 0.9892. The prediction equation of EPTCCA was established by volume fraction and diameter of coarse aggregate, the correlation coefficient between the predicted values and the true values was 0.9867. The prediction equation of APTCCA was established by coarse aggregate volume fraction, the correlation coefficient between the predicted values and the true values was 0.9788. The average roundness of recycled brick coarse aggregate (RBCA) was 0.42 and the variance was 0.0176. The confidence intervals of roundness of RBCA was [0.41,0.43] with 95% reliability. The average equivalent roundness of RBCA was 0.83 and the variance was 0.003. The confidence intervals of equivalent roundness of RBCA was [0.81,0.84] with 95% reliability.