A typical cement-based exterior wall consists of a top coat, a base coat, an insulation layer, a steel frame and an interior layer. The top coat and the base coat are often made of mortar. Efflorescence at the surface of the top coat is a critical problem from the aesthetic point of view. The efflorescence can be caused by leaching of Ca(OH)2 from the top coat and the base coat. This paper aims to mitigate the efflorescence of the top coat by incorporating metakaolin.
Cement in the top coats is substituted with metakaolin at different substitution rates (i.e. 0 - 20% by mass of cement). Mechanical properties of the top coats are measured. The extent of the efflorescence of two-layer specimens (i.e., top coat + base coat) is quantified by image analysis. The content of Ca(OH)2 and the porosity of the top coats are determined for explaining the mechanism of mitigation of efflorescence by incorporating metakaolin. The results show
that the compressive strength and the flexural strength of the top coats are improved when the substitution rates of metakaolin are lower than 15%. The metakaolin results in lower porosity and lower content of Ca(OH)2 in the tops, due to the filler effect and the pozzolanic reaction of metakaolin. The substitution of metakaolin for cement can effectively mitigate the
efflorescence of the top coats, and the efficiency of metakaolin increases with the substitution rate (from 0 to 20%). The conclusion is that metakaolin is a promising material for mitigating efflorescence of cement-based exterior wall.@en