Combined effect of rice husk ash and cementitious capillary crystalline waterproofing materials on the performance of mortar

The cement industry is known to leave an enormous environmental footprint. Rice husk ash (RHA), due to its high silicon content, is commonly used as a supplementary cementitious material. However, excessive use of RHA may adversely affect the performance of mortar. Cementitious capillary crystalline waterproofing (CCCW) materials can produce crystals to fill cracks and pores in mortar through the permeation and crystallization of its internal active chemical substances. Therefore, the potential for the combined use of RHA and CCCW is investigated. The results of experiments demonstrate that the mechanical properties and impermeability of the specimens are further improved by the synergistic effect of the two materials. Compared to the control group, the compressive strength and flexural strength peak values of the specimens increased by 22.83 % and 25 %, respectively. The addition of CCCW mitigated the detrimental impact of RHA on the impermeability of the specimens. The microscopic tests indicated that the pozzolanic reaction and filling effect of RHA reduced the porosity of the specimens, enhancing their compactness. Additionally, the permeation and crystallization action of CCCW further contributed to this densification. In the joint utilization of both materials, the incorporation of CCCW serves to counteract the adverse effects of excessive RHA on the self-healing capacity of cracks within the specimens. Concurrently, the high specific surface area properties of RHA facilitate the permeation and crystallization processes of CCCW.