Studies on the possible use of local sand, Mbeya pozzolana and calcium sulphate hemihydrate in the cement industry

The possibility of using local sand for testing ordinary portland cement was investigated. Graded sand from three sources and British Standard sand were used in the preparation of mortar cubes for compressive strength tests. The results show that graded sand from Mpiji and Tabata can be used as standard sand in the cement industry. The suitability of Mbeya pozzolana as a partial substitute for ordinary portland cement, the effect of industrial calcium sulphate hemihydrate additions and partial substitutions on the compressive strength of pozzolanic cement mortar were studied. It was found that the pozzolana in question has a pozzolanic activity of 10.4 N/mm2. Ten to thirty percent pozzolana by weight can be partially substituted for ordinary Portland cement for use in high concrete works and up to fourty percent can be affected for low concrete works. Calcium sulphate hemihydrate additions and partial substitutions were found to lower the compressive strengths at early stages but at later ages the compressive strength was equal to or even greater than those of plain 'pozzolanic cements. However, additions greater than 9.1 percent to pozzolanic cement with 30% pozzolana (PZC30) had the effect of lowering the strength at all curing ages in question. Furthermore, pozzolanic cement with 109 pozzola (PZC10) can be substituted with ten percent hemihydrate without detrimental effect on the ultimate strength