Pozzolan city, Compressive Strength And Ingress Of Selected Aggressive Ions In Kibwezi Bricks Based Cement

ABSTRACT

The quality of cement as a binding material in building and construction depends on many factors. Among the most important is its resistivity to the aggressive environment and its strength. The most aggressive ions to reinforced concrete are Cland SO4 2- . This study investigated the diffusivity of these ions into mortar made from a mixture of ground calcined clay bricks from Kibwezi region (GB) vis-a-vis ordinary Portland cement (OPC) and Commercial Portland Pozzolana cement (PPC). The test media were 3.5 percent Cland 1.75 percent SO4 2- solutions. Commercial OPC and PPC were also separately investigated. Cement samples were subjected to chemical analysis and pozzolanicity tests. GB was blended with OPC at replacement levels of 25, 35, 45 and 50 percent to make OPCGB. Similar blends were also made with PPC but at lower replacement levels of 15, 20 and 25 to make PPCGB. Water to cement ratios of 0.4, 0.5 and 0.6 were used to make cement mortars. Three blocks were prepared for each category of cement. The mortar blocks were subjected to compressive strength analysis and accelerated Cland SO4 2- ingress for 36 hours at 12 V. The ion profiling was done on the mortars and Diffusion Coefficients of the aggressive ions were approximated from Fick‟s second law of diffusion. The GB used met the Kenya Standard KS 02 1260 (1994). The results showed decrease in compressive strength with increase in replacement of OPC and PPC on 3rd and 7th day and with increase in w/c. The test cement showed a low compressive strength at early days of curing (3rd and 7th day) compared to 28th day in all the pozzolana cements. There was increase in compressive strength for OPCGB with increasing replacement levels from 25 to 35 percent. OPC showed the highest ingress at all w/c. The results suggested that there was a drop in the ingress of aggressive ions with increase in replacement up to 35 percent for OPC. A 15 percent replacement showed a better compressive strength development compared to 20 and 25 percent replacement for PPC. Pozzolanic cements showed lower apparent diffusion coefficients (Dapp) compared to OPC. PPC, OPCGB-35 and PPCGB-15 exhibited similar performance in terms of strength development, aggressive ions ingress, and Dapp. The test cements, PPCGB-15 and OPCGB-35 can thus be used in similar environments as commercial PPC.