Assessment of Pozzolanic Reactivity for Calcined Spent Bleaching Earth Ash (SBEA) using Strength Activity Index (SAI), Frattini Test and X-Ray Diffraction (XRD)

Abstract

This research briefly investigates and compares three different and distinct methods of assessing the pozzolanic reactivity of a cementitious replacement material, Spent Bleaching Earth Ash (SBEA). SBEA is waste by-product of the edible oils refining industry and has some pozzolanic properties that could possibly be enhanced through calcination. Many methods have been developed to assess the reactivity of pozzolans and three of the most common ones were employed in this research; namely the Strength Activity Index (SAI), Frattini Test and X-Ray Diffraction (XRD) methods. These three methods were chosen as they measured reactivity based on fundamentally different methods; the SAI method relies on the mechanical strength of mortar cubes, XRD based it on the morphology of the material whilst the Frattini test looks into consumption of artificially-introduced calcium hydroxide by the pozzolan. This investigation allows correlation to be drawn between the three methods and at the same time, the effectiveness of calcination on SBEA can also be evaluated. The calcined SBEA was obtained through a 700°C heating process in the furnace at the for 4 hours. Both the SAI and Frattini tests were in good agreement and showed that the calcined SBEA consistently under-performed compared to uncalcined SBEA at both testing ages. This was, however, disputed by the XRD result which showed that SBEA benefitted from the calcination process as it lost over 7 % in crystallinity, hence making it more reactive. This outcome tells us that the selection of testing methods for pozzolanic reactivity must be done carefully and ideally several methods be used concurrently in order to correlate the results.