Evaluation of the Pozzolanic Activity of Natural Zeolite Tuffs

摘要

The pozzolanic activity of a large number (24) of natural zeolite tuffs was investigated. The selected zeolite tuffs originated from over the world and the most important previously studied deposits have been included into the experiment. The selection of zeolite tuffs also aimed to cover the range of commonly occurring zeolites, available in sufficient quantities to allow application as supplementary cementitious material. To identify the main pozzolanic properties governing the pozzolanic reaction, the starting materials were selected over broad ranges of chemical and mineralogical compositions. In addition, the zeolite crystallinity (mean crystallite size) was chosen to vary considerably, allowing to evaluate the effect of the material intrinsic physical properties on the pozzolanic activity. Finally, a number (20) of common natural and synthetic (alumino)silicate materials were also subjected to experimentation to widen the range of parameter variability and evaluate the activity of mineral phases commonly encountered in zeolitised tuffs. The granulometry of all starting materials was reduced to similar sizes by wet grinding. To reduce the complexity of the blended cement system, the pozzolanic reaction in pozzolan-portlandite mixtures was investigated. Pastes of (alumino)silicate starting material, portlandite and H2O in a 1:1:2 weight ratio were mixed and stored in an air-free environment at 40°C. The amounts of portlandite consumed at 3, 7, 14, 28, 56, 90, and 180 days were determined by thermogravimetric analysis. The experiment repeatability was evaluated by sample duplication. Based on the kinetic analysis of the results, the dependence of the pozzolan activity on the pozzolan chemical and mineralogical composition, and on physical properties such as sample granulometry and main component crystallinity was assessed. In addition, the zeolite exchangeable cation content was selectively varied by cation exchange to investigate its control on the pozzolan activity. The results obtained serve to facilitate the identification and evaluation of natural (alumino)silicate pozzolan deposits of interest such as natural zeolite tuffs with respect to their pozzolanic activity and reaction product assemblage.