Analysis and prevention of efflorescence on brick masonry. I - Soluble salt extraction

This work aims to reconsider the soluble salt extraction on fire clay bricks in order to take into account the influence of the hydraulic binder on the appearance of efflorescence on masonry. This interaction is not covered by standards, particularly the EN 771-1 and 772-5, wherein the active salt extraction procedure only considers a short shaking duration (one hour) in distilled water. The results show that a prolonged shaking duration at a basic pH allows to discern a rapid dissolution step for K, Na and Mg, followed by a slow and regular dissolution of those cations, due to an alkaline attack of the silicate phase of the brick. Calcium and sulphate ions mainly issued from residual anhydrite show a two step dissolution mechanism, accelerated by a basic pH.