Short and long-term behaviour of R.C. beams made with CSA binder

A worldwide increase of the use of Calcium Sulfoaluminate cement (CSA) is observed in the recent years, especially for application for which fast development of mechanical properties and volume stability are required. Moreover, the lower CO2 emission deriving by the CSA manufacturing process than Portland cement (OPC), allows to classify such type of cement as “green binder”. Limited information are still to date available in the scientific literature regarding the short and long-term behaviour of reinforced concrete elements made using pure CSA cement or blended with Portland. The aim of this work is to improve the knowledge about the use of CSA concrete for structural and non-structural application, providing information about the flexural behaviour of reinforced concrete structural beams made replacing different portions of CSA cement with OPC. Mechanical characterization at different ages of the concrete mixtures was performed as well as the monitoring of the volume change properties. Moreover, study of the influence of the environmental condition and service load on the flexural behaviour of the beams was performed. Concretes made with pure CSA or CSA blended with OPC have generally highlighted better mechanical properties than the reference mix made with OPC cements, including a reduction of the drying shrinkage deformations as the amount of CSA cement increases. However, despite the higher compressive strength obtained for the pure CSA and blended concrete mixtures, a comparable elastic modulus with that measured for the reference mixture was observed. The bending tests performed on the beam samples evidenced as the addition of CSA cement seems not influential for crack pattern in terms of crack width, while a better response was observed in case of pure CSA concrete. Moreover, a higher ductile behaviour was obtained for the beam made with a CSA cement amount equal to 30% of the total cement content, reasonably due to the relaxation concrete phenomena, as also confirmed by the long-term results regarding the same type of beams. In fact, such beam has highlighted the highest mid-span deflection at long-term compared with the other monitored beams. However, comparing the experimental results was observe an improvement of the flexural behaviour increasing the CSA amount. In particular the beam made replacing 50% of OPC with CSA binder that has highlighted the lowest percentage increase over time in terms of crack width and mid-span deflection.