Two natural zeolites with different characteristics were calcined at various temperatures in order to improve the benefits provided by their use in blended cements as cement replacement material. Natural zeolites were firstly characterized for their crystallinity by X-ray diffraction analysis, specific surface area by nitrogen absorption, and pozzolanic activity by electrical conductivity method, before and after the calcination. In order to assess the performance of calcined natural zeolite as cement replacement material, blended Portland cement pastes and mortars with raw and calcined zeolites were tested for their water requirement, free lime content, pore size distribution and compressive strength. The experimental results indicated that calcined zeolites are more desirable with lower water requirement and higher strength performance as cement replacement material than the raw zeolites. Blended cement with calcined natural zeolite showed higher compressive strength performance, when compared to that with the raw zeolite due to decreased porosity and refined pore structure of the hardened cementitious system. (C) 2014 Elsevier Ltd. All rights reserved.