Mechanical performance of sulfo-based rapid hardening concrete systems focusing on blends with Portland cement

Calcium sulfoaluminate cement (CSA) represents an eco-friendly alternative to Portland cement (PC) thanks to its low CO2 emission during production. Its main phase is the ye’elimite (C4A3‾S) which reacts with water forming ettringite. This reaction is characterized by the rapidity and the initial high heat production; indeed, CSA is known as a rapid hardening cement. Moreover, the huge ettringite formation during hydration is the main responsible of its performance, like the high early age strength and the low shrinkage evolution. Thanks to its properties, CSA cement was widely used in China during 70’s. However, the lack of bauxite deposits and the consecutive increasing cost of its raw material led to a loss of interest for such systems. Nowadays this interest is regenerated due to the environmental issue. Thus, new solutions are investigated in order to limit the carbon footprint of cement industry, decreasing, at the same time, the economic impact of CSA cement production. A possible solution is represented by blend systems with Portland cement. Such materials combine the PC low cost with the CSA low CO2 emission in systems which maintain the rapid hardening behavior and the long term performance evolution. The main issue for this new material is the lack of knowledge on its behavior, properties and performance in both early and later age, especially for structural applications. This research program has the aim to study a blend system in concrete scale at a CSA/PC ratio of 50/50 comparing its mechanical performance with a CSA and a PC concrete, equal in the 28th day strength class. Eventually, a comparison is done between the collected results for the three investigated systems with the well-known PC constitutive laws reported in the main technical documents. Aspects investigated directly during the campaign are compared with the same aspects calculated by the reported formulations. This comparison defines a first evaluation on the applicability of these already-known formulations in the structural design with CSA based concretes.