Improving the water permeability of mortar by using a hydrochar additive derived from coconut coir fiber

Mortar has been widely applied as a coating for various purposes on building infrastructures, including basements, water tanks, retaining walls, dams and building exteriors, where resistance to moisture and water is highly required. Various chemicals have been added to mortar to reduce its water permeability. However, they raise environmental problems, therefore, environmentally friendly additives are indispensable. The purpose of this study was to enhance the water resistance, compressive strength, and crack recovery ability of mortar with the addition of hydrochar from biomass. Hydrochar was prepared from the hydrothermal carbonization of coconut coir fiber at 150°C for 4 hours. The hydrochar was added to the mortar at different particle sizes and ratios to cement. Mortars were made by mixing cement, sand, water, superplasticizer, and hydrochar; and they were tested after 28 days. The results showed that the addition of 1 wt% hydrochar with a particle size of 150-250 µm reduced the water permeability of mortar, as evidenced by a 36.45% decrease in secondary water absorption and a 14.94% reduction in percentage of void. In addition, the compressive strength increased by 10.29% compared to the control mixture. Hydrochar can absorb water bubbles in the mortar mixture; however, excessive hydrochar causes the mortar to be more porous. The addition of hydrochar in mortar demonstrated superior crack recovery abilities because it functions as a connection medium to accelerate the recovery.