Evaluation of pozzolanic activity of volcanic tuffs from Tibet, China

This paper presents a study of the characteristics and pozzolanic activity of three volcanic tuffs to assess the quality and availability of the tuffs for use as supplementary cementitious materials in cement-based composites. The main parameters of the tuffs (chemical composition, proportion of vitreous phase, mineral species and rock structure) were assessed by chemical composition analysis and x-ray diffraction. The pozzolanic activity component (PAC) of tuff, calculated from chemical composition and amorphous phase content, is proposed as an intrinsic index of pozzolanic activity without consideration of particle size and was used to evaluate the tuffs. The pozzolanic reaction degree (PRD) of the tuff/cement pastes was determined by hydrochloric acid dissolution. The pozzolanic activity strength index (PASI) was evaluated as the ratio of the compressive strength of the blended tuff/cement mortar to that of a control cement mortar. The results showed that the tuffs possess great potential for pozzolanic activity in terms of PAC, PRD and PASI because they have high contents of silicon dioxide and aluminium oxide and plentiful amorphous phases. A correlation between PAC and pozzolanic activity index was revealed and a consistent relationship between PRD and PASI was also found.