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.
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