Behavior of Belite cement blended with Calcium sulfoaluminate cement: an Ecocement

Abstract

Belite Portland Cements (BPC) and calcium sulfoaluminate cements (CSA) are considered as environmentally friendly cements due to their lower CO2 emissions. These ecocements (BPC and CSA) emit about 0.03 and 0.18 less tons of carbon dioxide from raw materials, respectively, than Portland Cement (PC). However, BPCs have a technological disadvantage, due to the slow kinetic of hydration of belite (their main phase), causing low mechanical strengths at early ages. On the other hand, CSA cements are more expensive due their high alumina content, but they develop high mechanical strengths since early ages. Those are the main reasons why it is essential to develop strategies that could reduce their cost with competitive mechanical strengths.

A CSA clinker (ye’elimite as main phase) and a BPC (belite as main phase), have been mixed with the objective of producing a cheaper ecocement, labelled B#, that releases less CO2 than PC and with competitive mechanical strengths. Cements with 83 wt%, 75 wt% and 65 wt% of BPC with CSA have been prepared. Moreover, anhydrite has been added as set regulator. Pastes with water/cement ratio of 0.4 have been prepared. The hydration of these pastes have been characterized by laboratory X-ray powder diffraction, using Rietveld methodology and thermogravimetric analysis, to obtain mineralogical phase assemblage as a function of time during a year, including amorphous content and free water. Mineralogical phase assemblage has been correlated to compressive strengths, porosity and dimensional stability of mortars.