Evaluation of clay pozzolanas as partial replacement of cement for shelter construction

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The issue of housing in Ghana has become a national problem due to overpopulation and high cost of building materials, especially cement. Whereas the materials for the production of cement are imported, there exist alternative and durable local materials for the production of both ordinary and composite or blended cement. Pozzolana cement is one of such blended cements. The study focused on the evaluation of pozzolanic properties of clay samples from four (4) deposits at Asokwa (near Obuasi), Nkonsia (7km from Wenchi), Mankesim and Hwereso (25km from Kumasi) for the production of pozzolana cement in Ghana. The clays were calcined at 600°C - 1000°C, milled and passed through 75μm standard sieves. The burnt clays were then used to replace 20% - 40% of cement and moulded into mortar cubes. Also, pozzolana lime mortars at three different mix ratios were moulded. On calcination, Asokwa and Mankesim clays became highly pozzolanic at 800°C, Hwereso and Nkonsia clays were at 900°C and 600°C respectively. The 28-day compressive strength at 20-40% replacement of cement by mass showed that Nkonsiaa clay pozzolanas can replace cement up to 40%, Asokwa and Mankesim clays up to 30% and Hwereso at 25%. 1:2:6 lime pozzolana sand mortar cubes gave appreciable 28-day dry compressive strength. The water absorption of the pozzolana cement was not different from the ordinary cement but they set faster than ordinary portland cement. All the clays were highly siliceous, containing more than 60% silica. Minerologically, all the clay samples are kaolinite with some amount of quartz. Of the four clays, Mankesim and Asokwa pozzolana cement products were mildly affected by sulphate attack whilst Nkonsia and Hwereso products were seriously damaged, showing the least resistance. Their compressive strengths were greatly reduced after one year in sulphate solutions. It is shown that using 25% of the total cement used in Ghana from pozzolana cement would save the country at least $6.7m (about 15.1 billion cedis) in foreign exchange per annum, generate employment for the youth and provide revenue to both the central government and local authorities. The pozzolana cement from Asokwa, Mankesim and Nkonsia clays can be used for general construction, including concrete works, up to 30% replacement of cement and up to 40% replacement for masonry works and production of sandcrete blocks. For Hwereso clay pozzolana cement, it can only be used for masonry works and sandcrete blocks with up to 25% replacement of cement.
A thesis submitted to the Board of Postgraduate Studies, Kwame Nkrumah University of Science and Technology, Kumasi, in partial fulfilment of the requirement for the award of the Degree of Master of Philosophy in Chemical Engineering, 1998