Feasibility of lightweight aggregate concrete for structural and non-structural works in Tanzania

Extensive exploitation of granite aggregates in areas where there are natural lightweight aggregates from volcanic actions have caused serious geological and land degradation in Tanzania. Many Engineers have resorted to using normal weight aggregates in construction because of the feeling that lightweight aggregates (LWA) are too weak for that purpose and for lack of understanding of the design procedures for lightweight aggregate concrete (LWAC). Structures constructed by 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 from LWA. In Tanzania there are major deposits of LWA in Mbeya, Kilimanjaro and Arusha Regions which remain unexploited. Research was done to investigate the feasibility of using scoria and pumice aggregates in structural concrete. Scoria and pumice aggregates were obtained from Kilimanjaro and Mbeya Regions respectively. A mix design was carried out for both aggregates and it was found out that, it was possible to produce grade 25 concrete with scoria but the concrete made of pumice from Mbeya failed to reach the target strength of grade 20 concrete because the aggregates were too weak. The strength reached was less than 17 MPa, which is the minimum strength for structural LWAC. It was concluded that the use of scoria aggregates for structural concrete was feasible and that the pumice could be used for non-structural LWAC. Further research is needed to find alternative deposits of pumice with better strengths as the strength vary from place to place. Structural and Construction Engineers should be encouraged to use LWA especially in the areas where these deposits are present in order to reduce the cost of transport of normal weight aggregates from longer distances and also to protect the environment.