ABSTRACT
The rate of strength development of concrete depends mainly on cement type, water-cement ratio, and sometimes the use of admixtures or super plasticizer (SP). SPs are indispensable in modern concretes, providing high workable concrete at low water to cement ratios, and resulting in the production of high strength, durable and sustainable concrete. However, the issues of cement-SPs incompatibility, when wrong combination is used, have been identified by some researchers. This research therefore aimed at assessing the influence of Rheobuild-600 on concretes made with different brands of Portland cements manufactured in Nigeria. Optimum dosage of SP for the research was established by weight of cement A. Building Research Establishment (BRE), method of concrete mix design was used to design a grade 30 concrete that was used in the research. 30% of the quantity of mixing water was deducted from the design water content in order to determine the effect of SP on workability. Concrete samples were prepared using five brands of cements. A set of 320 100mm x 100mm x 100mm concrete cube specimens were cured by complete immersion in water. Another set of 320 cubes were exposed to 1% concentration of MgSO4 solution. The samples were then, tested for compressive and tensile strengths at the ends of 3, 7, 28 and 56 days of curing. Furthermore, the quantity of cement saving was determined when the dosage of SP was increased from 0.2 to 1.5%. The research established that the workability of the concrete mixes were found to fall between medium and high workability when 1% SP was used. Compressive strength increased for the super-plasticized concrete over the non-super-plasticized concrete which were found to be 40.31%, 37.65%, 51.62%, 52.08%, and 65.32% for cements A, B, C, D, and E respectively. Also, the quantity of cement saving was found to be up to 25.05% when 1% Rheobuild-600 is used. It was concluded that the cement brands investigated vi were all compatible with Rheobuild-600 in terms of higher performance on strength, workability, and durability of concrete. Cement E was found to be the most compatible brand because of the higher strength obtained. The research recommends that though the five brands of cements studied were found to be compatible with Rheobuild-600, the optimum dosage of the Rheobuild-600 should be determined for any selected cement before used.