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There has been serious land degradation in Tanzania due to extensive exploitation of granite aggregates even in areas where there is plenty of natural lightweight aggregates. Many Engineers have resorted to using normal weight aggregates in construction not only due to the feeling that lightweight aggregates (LWA) are too weak for structural purposes but mainly due to lack of knowledge of the design procedures for lightweight aggregate concrete (LWAC). Structures made of normal weight aggregates have higher dead loads which demand reduced span lengths, deeper structural members, more reinforcement and increased foundation area when compared to those made of LWAC. In Tanzania there are major deposits of LWA in areas of previous volcanic eruptions namely Kilimanjaro, Mbeya and Arusha and these remain largely un-exploited. Research was done to investigate the feasibility of using scoria and pumice aggregates in structural lightweight concrete. The aggregates were obtained from Kilimanjaro and Mbeya respectively. A mix design for grade 20 concrete was performed for both aggregates. It was found out that it was possible to use the scoria aggregates for structural concrete but not the pumice without mineral additives or chemical admixtures. Using pumice aggregates without any additives, the strengths obtained were less than 17 MPa which is the minimum strength acceptable for structural LWAC. It was concluded that the use of scoria aggregates for structural LWAC was feasible and that the pumice aggregates could be used for non-structural LWAC. Further research is required to find alternative deposits of pumice with better strengths for use in structural LWAC as the strengths of these aggregates vary from place to place and even within the same locality. Structural and Construction Engineers in Tanzania are now in a position to design and use LWAC as the design procedures have now been elaborated. The use of light weight aggregates especially in areas where these deposits are present will reduce the current costs of transport of normal weight aggregates from long distances and this will also protect the environment. |
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