Reusing Waste Concrete Recycled Powder in Mortar: Paste Substitution versus Cement Substitution

Abstract

Waste concrete recycled powder (WCRP) occupies up to 30% of crushed old concrete and is hard to be reutilized due to its high porosity and low cementitious reactivity. Traditionally, the WCRP is reused as cement substitution in mortar/concrete production, but this substitution method has certain disadvantages. In this research, a novel substitution method, called the paste substitution method, was applied by replacing part of the cement paste with WCRP; a total of 28 trial mortar mixes containing WCRP added as either paste substitution or cement substitution were made for evaluation and analysis. By comparing the test results, it could be found that the incorporation of WCRP using the paste substitution method can remarkably enhance the compressive strength by at most 38.3%, densify the microstructure, and meanwhile greatly reduce the cement consumption by at most 26.7%. The cementing efficiency factor of WCRP in compressive strength was calculated for the first time, and its value is 0.289. Regression analysis showed that there exists good correlation between the compressive strength and effective water/cementitious materials (W/CM) ratio.