Effects of Magnesium Sulfate and Sodium Sulfide on Fresh and Hardened Cement Mortar

Abstract

In this study, the effects of magnesium sulfate and sodium sulfide on fresh and hardened cement mortar were examined. Water/cement ratios of 0.63 and 0.72 were used to produce two 410 kg/m3 dosed mortars. Various concentrations of sulfate salt solutions were prepared and used as mixing water. Solutions of magnesium sulfate and sodium sulfide and reference mortars were prepared with 1 l of mixing and drinking water, respectively. The mortars were produced in 26 (2 x 13) different mixtures. Eight samples were produced from each mixture for tests including shrinkage tests. Vibratory table experiments were used to determine the workable life of the mortars. The experiments were conducted by using a Vicat apparatus to determine the effects of the tested chemical substances on the setting duration. Six samples, which were prepared from each mixture, were held in water at a temperature of 20 ± 2°C until the test was started. The samples were aged for 7 d, 28 d, and 90 d, and two specimens from each aged sample were tested under bending and compression tests. The shrinkage tests involved measuring size changes of the two samples for duration of 90 d by holding the samples in a controlled environment at 21°C and 55%–65% humidity. Analysis was performed on the effects of sulfate salts on fresh and hardened concrete mixes. It was concluded from the results that magnesium sulfate had the most detrimental effect on the concrete mixes. In contrast, sodium sulfide increased the compressive strength of the concrete mix.