Sulphate and Chloride Ingress and The Effect in Selected Cements Mortar Prisms Immersed in Sea Water and Leather Industry Effluent
Ngari, Reginah Wangui
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The effect of ingress of Cl and SO4 on compressive strength development and the ions diffusivity in selected Ordinary Portland Cement (OPC) was investigated. The aggressive media used included sea water (SW) and waste water from leather industry (WLI). Three brands of commonly used cements of OPC in Kenya were used. Mortar prisms were prepared for each brand of cement at different water to cement ratio; (w/c) of 0.5, 0.6, 0.65 and 0.7 and allowed to cure for 28 days in a highly humid environment. The aggressive ions ingress in the mortar prisms was accelerated using a potential difference of 12V ± 0.1V DC power source. Analysis of diffusivity and diffusion coefficient of Cl - and SO42- was finally done. Compressive strength analysis was done before (at the 2 nd, 7th, 14th and 28th day) and after exposure to the aggressive ions. The diffusivity of chlorides was more pronounced than that of sulphates. Diffusivity was observed to be higher at higher w/c for all cement categories. The apparent diffusion coefficients (D app) of chlorides were found to be higher than those of sulphates. Dapp values for chlorides were found to be in the range of 1.730 x 10-10 m2/s to 4.683 x 10-10m2/s and for sulphates within 1.0610 x 10-11 m2/s to 6.2240 x 10-11 m2/s. The Dapp values were approximated from solutions to Fick’s 2nd law using the error function. Cement A at all w/c showed lower D app values than both cements B and C. Compressive strength increased with curing age with the highest observed at 28 days. Cement A was generally found to have the highest compressive strength for all w/c ratios. The compressive strength was observed to increase after the mortar prisms were - 2- exposed to SW as opposed to the ones exposed to WLI. The percent gain in compressive strength was found to increase with increase in w/c with the highest observed to be about 38 % at 0.7. The percent loss in compressive strength also increased with w/c with the greatest observed to be about 17 %. Generally, it was also observed that compressive strength gain / loss increased with increase in w/c.