Exploring the Effects of Pozzolans on Different types of Portland Cements in Sustainable Cement-Based Applications

Abstract

The sources of pozzolans could be natural, industrial and agricultural wastes that are recycled into concrete and mortar applications. There have also been many studies and recommendations guiding the use of blending these pozzolans from multiple sources with cement with the aim of producing more durable, greener and sustainable mortar/concrete. These investigations are mostly based on testing these pozzolans with a certain type of cement and making recommendations on the optimum percentage replacements. This type of study underscores that a pozzolan can behave differently with other types of Portland cements with varying distinct chemical compositions that associate the cement with its type. This could result to a particular pozzolan having different optimum percentage cement replacements with different types of cement and hence results in less durable concrete of which this study intends to address. The pozzolan used in this study is Pulverized Calcined Clay (PCC) and the types of cement is based on the British and American standards classification. The cement variants used in this study is broadly rapid hardening and low heat cement form the two (2) major cement brands in Nigeria. The X-Ray Fluorescence (XRF) analysis was performed on the cements and the PCC to determine their oxide compositions and classify the pozzolan, the Strength activity index (SAI) of the pozzolan was also determined. The optimum percentage replacements (replacement level with maximum strength) of the cements with the pozzolan was also determined. The results indicate that the optimum replacements for the low-heat cement was at 20% replacement with PCC and substantially higher for the rapid-hardening cement. This could be adduced to the difference in the chemical compositions as shown in the XRF analysis. It was concluded that the optimum replacement of different cement types with a pozzolan could vary, resulting to less durable concrete when a single optimum replacement is recommended across all cement types. It is therefore recommended that the optimum replacements of cements with pozzolans should be specific to a cement type and recommended that optimum replacement for other cement types with same pozzolan be determined and not generalized across all cements.