A novel approach to improve carbonation resistance of Calcium Sulfoaluminate cement by assimilating fine cement-sand mix

Abstract

Calcium Sulfoaluminate (CSA) cement is regarded as a plausible alternative to Ordinary Portland Cement (OPC) to reduce environmental burdens caused by the production of the latter; however, susceptibility to carbonation of the former restricts its utilization in the construction sector. This study proposes and evaluates a novel solution to address the carbonation issue of CSA by partial replacement with a fine CSA (<2.4 μm) cement-sand (1:3) mix. For this purpose, the modified CSA (MCSA) samples were prepared by substituting fine CSA cement-sand paste in conventional CSA mortar by 0 to 30 wt% and then submitted to accelerated carbonation. The performance of different MCSA mixes, OPC, and conventional CSA was compared after carbonation from the mechanical, mineralogical, and microstructural perspectives. The investigation reveals that the MCSA having 20 wt% fine CSA cement-sand mix could be regarded as optimum MCSA (OMCSA) in terms of carbonation degree, mechanical and microstructural characteristics after carbonation. The OMCSA shows a decrease of 8% and 23% in carbonation degrees and an increase of 12% and 25% in compressive strength upon carbonation as compared to OPC and CSA. Mercury intrusion porosimetric analyses (MIP) show that the porosity of OMCSA is reduced upon carbonation compared to conventional CSA. In addition, mineralogical analyses reveal that OMCSA contains the highest amount of ettringite and less carbonated contents upon carbonation than other subjected samples. OMCSA results in negligible loss of ettringite due to fewer pores as carbon dioxide is unable to penetrate the system, making it resistant to carbonation. Thus, the current solution reduces the carbonation impacts of CSA cement and is a step forward to make it more durable and practical.