Pilot study results of the strength behaviour of aggregate-lime-natural pozzolan mixes

Abstract

Paper presented at the 23rd Annual Southern African Transport Conference 12 - 15 July 2004 "Getting recognition for the importance of transport", CSIR International Convention Centre, Pretoria, South Africa. Rapid depletion of natural road construction material reserves and strict environmental laws has lead to the use of marginal materials in recent years. In Tanzania the use of natural pozzolans is becoming a technically viable option. The paper determines the influence of moulding moisture content on the strength behaviour of aggregate-lime-natural pozzolan mixes in fresh and hardened states. The paper will determine the influence of the moulding moisture content on California bearing ratio (CBR) and the tensile and compressive strengths of laboratory-cured specimens. In this study, two different mixes were prepared, one each from the individual pozzolans and one control sand-cement mix. The two pozzolans were obtained from separate sources in Tanzania, and were activated using hydrated lime. The fresh strength behaviour was evaluated by CBR test; UCS and Double Punch Tensile tests (DPTT) were done to evaluate the hardened state strength. Unconfined compressive strength and DPTT tests were done after 28, 90 and 180 days of curing under ambient conditions in the laboratory. Two moisture contents were used; optimum and 20 percent above optimum for all mix combinations. A trial mix was prepared using Mbeya pozzolan mix, moulded at 20 percent below optimum to determine the strength behaviour. It was found that the natural pozzolan mixes provide engineering properties comparable with that of cement stabilised materials and are therefore a viable solution. Double punch tensile test method was also found to be a simpler and viable method for the tensile strength determination of lightly cement stabilised materials.