The Effect of Pulverised Natural Pozzolana as a Partial Replacement for Portland Cement (CEM I) on Concrete Compressive Strength and Workability

Johannesburg , South Africa *tshepo@mkandtc.co.za The negative environmental impact (carbon emissions) of cement production and the rising cost of cement warrant investigating the inclusion of other naturally occurring materials as a partial replacement for cement in concrete. This study investigated the use of pulverised natural pozzolana as a partial replacement in the production of concrete. The effect of natural pozzolana on concrete properties was compared with that of fly ash, an artificial pozzolana. Concrete cubes were cast with mixes prepared by using pulverised natural pozzolana and fly ash to replace 0%, 5%, 10%, 20%, 30% and 50% of Portland Cement (CEM I), by mass, in the concrete mixes. The workabilities of the fresh concrete mixes were evaluated using the slump test, while compressive strengths of concrete cubes were determined at 1, 3, 7, 14, 28, 56, and 90 days. No trend was observed in the workabilities of the samples containing fly ash (relative to the control sample). The workabilities of the concretes with the natural pozzolana were slightly higher than those with fly ash, reaching an increase of 21 % (compared to the control sample) at 20 % replacement. In the compressive strength tests for both natural pozzolana and fly ash, increasing curing time (1 to 90 days) generally increased strength at each replacement percentage. Hence, natural pozzolana can be used to partially replace CEM I in producing concrete with different strengths for housing development, thereby contributing positively to sustainable development. What project managers need to know about geotechnical investigations in the case of housing developments