High reactivity pozzolan: a critical evaluation of Pozzolanic Activity Index (PAI) with lime using X-Ray Diffraction

Mineral pozzolanic admixtures are present in many of cementitious materials used in the production of structural concrete. The selection of the pozzolan requires prior characterization of its reactive potential, which can be obtained directly by using the modified Chapelle test, or indirectly, by performing a compressive strength test of the mortar with Portland cement or hydrated lime. The objective of this study is to quantify the pozzolanic activity index with lime of rice husk ash, silica fume and metakaolin, as well as the use of fillers such as limestone and quartz dust as inert reference material. The X-ray diffraction (XRD) of pastes identical to those used in standard mortars allows us to analyse portlandite consumption, an essential indicative of pozzolanic activity. The combined analysis of IAP with lime and X-ray diffraction (XRD) is aimed at verifying the rate of consumption of calcium hydroxide in the mixtures recommended by standard procedures, creating an opportunity to critically analyse their suitability. The results indicate that the NBR 5751 procedure is not appropriate to compare the reactive potential of super pozzolan, since the investigation showed that the amount of lime in the mixture was completely consumed, preventing a comparative evaluation of the compressive strength results based on standardized testing.

Mineral admixtures; Pozzolanic activity; Compressive strength.