Optimum Level of Partial Replacement of Cement with Ground Rice Husk Ash (GRHA) in Concrete

For Rice Husk Ash (RHA) to be effective as a pozzolana, the fraction of Silica in amorphous state which exhibits high reactivity should be maximized by controlled burning. Due to practical difficulties, RHA produced in power plants and brick kilns in most parts of Sri Lanka does not contain significant fractions of amorphous Silica and thus have not shown high replacement potential of Cement in mortar or concrete. Thus, this study focussed on grinding RHA with high crystalline Silica content with the intention of producing higher reactive particle surface area to be used for partially replacing Cement in concrete. Main objective of the study was to find optimum partial replacement fraction of Cement by Ground Rice Husk Ash (GRHA) in concrete in terms of compressive strength.

For the study, RHA samples from brick kilns around Anuradhapura, where higher burning temperatures are used, were collected and ground in a ball mill for a fixed duration for the transformation into GRHA with a similar fineness as Cement. Prescribed concrete mix proportions were used with Cement replaced by GRHA. Standard concrete cubes were tested for compressive strength and other related tests, such as tensile strength, permeability and heat of hydration, were conducted to check for deviations. These studies revealed that a 35% replacement of Cement by GRHA is the optimum value to satisfy relevant parameters of the prescribed concrete mix.