Early Age Properties of Zeolite Cementitious Materials
The cement industry is recognized as being responsible for a large amount of CO2 emission during the production of portland cement. In order to minimize CO2 emissions by limiting the use of cement, natural pozzolans may be a sustainable solution for making concrete. One such natural pozzolan is alumina-silicate based clinoptilolite type of natural zeolite. It has three dimensional crystalline frame structures with extremely small pores having alkali and alkaline earth cations. In the present research, application of natural zeolite as a supplementary cementitious material for producing durable concrete has been investigated. In this respect, clinoptilolite zeolite with very high purity (97%) replaced portland cement at 0, 5, 10, 15, and 20% by mass. Setting time, workability, as well as heat of hydration of paste via isothermal calorimetry was conducted to assess the effects on early age properties. Research results revealed that replacement of zeolite increase the demand for water in the fresh mixture, although this situation can be overcome by adding low amount of high range water reducing admixture without any segregation. Research results also shown that zeolite accelerates the setting time due to the nucleation effect of C-S-H precipitation. Additionally, replacement of portland cement with zeolite can produce lower heat of hydration in the cementitious paste due to adsorption of water by its grain along with slow dissolution process of the fresh mixture. However, from practical point view, incorporation of 15% natural zeolite was found as an appropriate option for improving the early age properties.