ABSTRACT
Hot weather, which is characterized by high ambient temperature and low relative humidity causes rapid setting of cement paste and difficulties during concreting. Admixtures that retard rapid setting of cement paste and modify workability of concrete are necessary to prevent fresh concrete from the adverse effects of hot weather. However, in Nigeria the retarding admixtures are imported and also expensive. Sugar a locally sourced admixture is another substitute that has been established to be a retarder, but its effects varies with the chemical composition of cement. This research therefore assessed the effects of sugar as retarder on properties of concretes made with selected brands of Portland cement produced in Nigeria. The concrete specimens were prepared by using 0%, 0.06% and 0.1% additions of sugar by weight of cement. A nominal mix of 1:2:4 with water cement ratio of 0.5 was used for the research. Setting time tests were performed at two different temperatures; at normal laboratory temperature of 27oC and simulated hot ambient temperature of 43oC (similar to that of Sokoto, Birnin Kebbi, Maiduguri, etc.). A total of 540 concrete cubes of size 100mm�“ 100mm �“ 100mm were produced, out of this number 360 cubes were used for compressive and split tensile strengths tests at 3, 7, 28 and 56 days curing periods. The remaining 180 cubes were also used for abrasion and water absorption test at 28 and 56 days curing periods. The results showed that the initial setting times of the control pastes made with cements A, B, C, D and E at 43oC reduced by 45.94%, 40%, 38%, 24.73% and 51.85% respectively when compared with the control pastes at normal laboratory temperature of 27oC. The reduction effects were completely eliminated by the addition of 0.1% and 0.06% of sugar in all the brands of cement at 43oC. Thus, significant increase in initial setting times were recorded. Similar trends were observed for the final setting time in all the brands of cement. The results further revealed that the 0.06% addition of sugar had the best results in strengths tests of the specimens made with cements A, B and D therefore 0.06% proved to be optimum dosage. On the other hand, 0.1% addition of sugar had the best results in strengths test of the specimens made with cement C which implies 0.1% as optimum dosage. However, cement E showed a decrease in strengths at every percentage additions of sugar at all the curing periods. The research concluded that the use of sugar as a retarding admixture in concretes made with the brands of cement enhanced the properties of concretes when an optimum dosage was used. It is recommended that, sugar can be used as retarder when concreting in hot dry weather regions in Nigeria, but should not be used as a retarding admixture in cement E brand.