Effect of Partial Replacement of Cement with NBRRI Pozzolan on the Mechanical Properties of Concrete

The cost of cement has been on a steady increase in Nigeria making it difficult for mass housing developments. The possibility of this price hike abating is not envisaged under the current socio-economic situation in the country. One of the ways to reduce dependence on cement in construction of houses is the partial replacement of cement with pozzolanic material which are readily available with little or no cost such as the one developed by Nigeria Building and Road Research Institute (NBRRI). This study inspected the mechanical attributes of concrete made with fractional replacement of cement with NBRRI pozzolan. Concrete mix, 1:1.5:3 was designed for all specimens with w/c of 0.45. NBRRI pozzolan (0%, 3%, 6%, 9%, 12% and 15%) by weight of cement were used for concrete production. The mechanical properties were measured at 7, 14, 21 and 28 days. It was obtained from the results that workability of concrete reduces from 62.5 to 50.5 mm as the percentage of NBRRI pozzolan increases from 0 – 15% respectively. The 28-day compressive, split tensile and flexural strengths of concrete at 12% replacement of cement by NBRRI pozzolan (30.92, 3.11 and 5.48 N/mm2) were found to be comparable to control (34.93, 3.2 and 5.12 N/mm2). It is concluded that 12% replacement of cement by NBRRI pozzolan in concrete (at 28-day curing) will reduce the amount of cement, decrease the cost of concrete production and give desired strength.