Effect of fly ash on compressive strength degradation due to calcium leaching procedure

The purpose of this paper is to deal with the influence of fly ash on compressive strength of degraded cement pastes due to calcium leaching. The accelerated experiment has been performed by using a 6 mol/l ammonium chloride solution because natural leaching is a slow process. In order to obtain the mechanical response of different cement pastes, specimens of different water/cement ratios and fly ash contents were prepared. At specified leaching durations, a compression test was performed on the sound and leached specimens. The compression tests show that the loss of compressive strength has a significant linear correlation with the leached ratio of all specimens. This indicates that the decrease in strength is mainly governed by the dissolution of calcium hydroxide. The residual compressive strength loss was related to the mix proportion. The loss of compressive strength increases with water/cement ratios in general. In addition, the addition of fly ash increases the residual compressive strength of totally leached pastes, because more calcium hydroxide is consumed owing to secondary hydration.