Effects of surface and subsurface mixing water of Nairobi, Machakos and Kajiado counties on cement mortar performance
Munyao, Onesmus Mulwa
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Mixing water is very vital for development of concrete and /or mortar. It can also be a source of aggressive ions in the cured concrete/ mortar. This study investigated the effect of mixing water on performance of cement mortar made from selected Ordinary Portland cement (OPC) and Portland pozzolana cement (PPC). Test cements were sampled from three local cement manufacturing plants while mixing water was randomly sampled from different construction sites in Kajiado, Machakos and Nairobi counties. Distilled and municipal treated tap water were used as controls. Water samples were analysed for pH and concentrations of alkali, chloride and sulphate ions. Cement mortar was made using the sampled water vis a vis tap and distilled water and cured in accordance with KS EAS 148-3: 2000. Compressive strength was determined at 2nd, 7th, 28th and 90th day of curing. Setting time, pozzolanicity and soundness tests of resultant cement mortar as well as chemical composition of cement were also investigated. Data obtained was subjected to statistical analysis using one way ANOVA. Test results showed that all test cements met the Kenya Standard requirements when mixed with tap and distilled water. It was observed that water samples with high chloride content exhibited a higher compressive strength gain whereas test water with high sulphate concentrations exhibited a high percentage decline in compressive strength in all test cements compared to distilled/tap water. The water samples with high sulphate content exhibited prolonged setting times whereas high chloride water samples exhibited shorter setting times in all test cements compared to distilled/tap water. Results showed that the pH of the water samples did not have any significant effect on the compressive strength development. Soundness and Pozzolanicity tests met the minimum KS EAS 148-5:2000 requirements in all test cements. The results indicated that mixing water used in majority of construction sites contain high levels of chloride and sulphate ions which could lead to failure of concrete and/or mortar and hence building and construction.