Effect of calcium and sodium-activated bentonites as waterproofing additives in polymer-modified cement mortars

Abstract

Abstract Cement mortar is typically formulated by blending fine aggregate and water, yielding a matrix characterized by heterogeneity and porosity. However, these inherent characteristics can exacerbate structural leakage, allowing water infiltration in buildings. Bentonite is a promising waterproofing additive for various mortar types, owing to its remarkable water swelling properties and recognized attributes of being non-toxic and cost-effective. Hence, this study examined calcium or sodium-activated bentonites as cost-effective waterproofing additives in polymer-modified cement mortars. A commercial mortar with varying amounts (0-2wt.%) of these bentonites was prepared. The research focused on characterizing the additives and assessing mortar performance regarding fluidity, water absorption, mechanical strength, resistance to water penetration under negative and positive pressure, and microstructural features. Results showed sodium bentonite had a smaller particle size, higher reactivity, and swelled three times more than calcium bentonite. These additives altered the fresh mortars rheological properties due to flocculation. Incorporating 2 wt.% of sodium bentonite into the mortar did not significantly change the water absorption or crushing strength of samples cured at room temperature for 28 days. However, it led to an 18.6% reduction in water penetration under positive pressure and prevented liquid percolation to the upper surface of the samples during tests under negative pressure.

Keywords

• Mortar
• Bentonite
• Waterproofing
• Swelling
• Hydration