A study of cement Type II hydration partially substituted by Brazilian spent cracking catalyst fines

Abstract

In fluidized catalytic cracking refinery units, two kinds of wastes are generated: the equilibrium catalyst, which is withdrawn continuously from the catalyst regenerator, and the catalyst fines (Epcat), which are dragged by the gas stream leaving the regenerator, being separated by cyclones or electrostatic precipitators. This work aims to study the early cement hydration stages of Type II Portland cement, when substituted partially by Epcat. For this purpose, pastes were prepared with water/(cementitious material) ratio (W/C) of 0.5 and substitution degrees up to 30 mass% of cement per Epcat, which were analyzed during the first 24 h of hydration by non-conventional differential thermal analysis. The results show that the higher is the substitution degree of cement by Epcat, the higher is the formation of ettringite and the higher is the acceleration effect of tricalcium silicate hydration reactions. The deconvolution of the NCDTA curves obtained for the early cement hydration stages indicates that, in the early hydration stages, ettringite and tobermorite have an inverse relationship formation as a function of the degree of substitution, which shows a linearly growing ettringite content, as tobermorite content decreases. The released accumulated energy, calculated from NCDTA curve data, shows that Epcat has pozzolanic activity, which increases with the degree of substitution, also shown from the respective curve deconvolution data.