Effect of the stearic acid modified metakaolin on sulfate resistance of mortar based on the experimental study and capillary theory analysis

In this study, a stearic acid modified metakaolin (MMK) was developed to improve the sulfate resistance of cement-based materials, which could effectively avoid the adverse effects of traditional hydrophobic modifier on the mechanical properties of cement mortar itself. Firstly, the effects of the stearic acid content and grinding time on the water contact angle of the MMK were studied, and the results showed that the MMK had the maximum water contact angle when the stearic acid content was 5% and the grinding time was 20 min. On this basis, abundant systematic tests were conducted to study the effects of the MMK mass fraction on water contact angle and water absorption of the mortar. Subsequently, the sulfate resistance of the mortar with MMK was examined under partial immersion, including the apparent morphology, linear expansion rate, relative dynamic elastic modulus, compressive strength and microstructure. Finally, a mathematic model considering water absorption and evaporation was developed, and the effects of the MMK on the corrosion height, capillary absorption and water evaporation of the specimen under partial immersion in sulfate solution were analyzed. The model analysis showed that the MMK could reduce the capillary water absorption height of the specimen under partial immersion in sulfate solution, and the mechanism of sulfate resistance for the mortar with the MMK was to reduce the amount of corrosive ions by reducing the capillary coefficient.

Automated summary

A stearic acid modified metakaolin (MMK) was developed to improve the sulfate resistance of cement-based materials, and it effectively avoided the adverse effects of traditional hydrophobic modifier on the mechanical properties of cement mortar itself. The optimal water contact angle of MMK was achieved with 5% stearic acid content and 20 min grinding time. The MMK reduced the capillary water absorption height of the specimens, thus enhancing the sulfate resistance of the mortar.