Research was conducted in Tanzania to investigate the properties of a concrete made by a replacement of 0%, 6%, 12% and 18% with RHA in Portland limestone Cement. What was investigated was the influence of the ash on the workability, strength development and water permeability of the concrete. The water/binder ratio was kept constant. The results obtained indicated that workability of the concrete decreases with an increase in ash content and suggests that there is an optimum replacement content which give maximum concrete strength. Beyond this optimum ash content, the strength of the concrete decreases. It was also found out that the permeability of the concrete decreased with an increase in RHA content and this confirmed earlier findings by some researchers that the introduction of RHA in concrete makes the concrete more durable. Other benefits of using RHA in concrete are increased resistance to chemical attack, reduced effects of alkali-silica reactivity, reduced shrinkage rates, increased insulation properties of concrete, reduced amount of plasticizers, and reduced potential for efflorescence. The other obvious advantage of using RHA apart from reduced environmental pollution is the reduction of carbon emission which is associated with the production of Portland cement. Any partial replacement with RHA in Portland cement implies reduced carbon emission which is the cause of global warming and which the world is fighting against.