Matric suction of fine sand and its effect on the shape stability of 3D printed cement mortar

Abstract

Shape stability is one of the most important requirements for 3D concrete printing, and small particles in aggregates are known to be helpful in enhancing the shape stability. However, a fundamental approach to relate the shape stability and the particle size of aggregates needs further investigation. This study explores the role of capillary attraction among the aggregates, which is called matric suction, in developing shape stability. Incorporation of fine silica sand controls the configuration and the average size of fine aggregates, and pressure plate method catches the increases in the matric suction of the fine aggregates. Applying the generalized Hooke's law with the concept of the effective stress explains that the matric suction acts as confining stress and induces eigenstrain, contributing to the resistance against the compression. The results of this study help to deeper understand the critical effect of adopting small-sized aggregates on the shape stability in the mix design of 3D printing concrete. The consideration of matric suction will serve as a quantitative basis for the mix design.