Understanding the role of nano-C-S-H-polycarboxylate composites on compressive strength and frost resistance of Portland-sulfoaluminate cement blended concretes

The use of sulfoaluminate cement (SAC) to improve the early performance of Portland cement (PC)-based materials is well known. However, studies on the properties of PC-SAC blended concretes with nano-C-S-H-polycarboxylate composites (CSH) as accelerator are scarce. In this study, the properties and microstructures of PC-SAC composites containing CSH were investigated. The compressive strength and frost resistance of mortar and concrete were tested. The improvement mechanism of PC-SAC with CSH was evaluated using multiple micro-testing methods. The results showed that adding CSH remarkably improved the early compressive strength of PC-SAC blended concretes within the curing age of 3 d. Moreover, the incorporation of CSH significantly increased the frost resistance of concretes. Specifically, adding 0.6 wt% CSH caused a reduction in the relative dynamic elastic modulus of concretes by 12.68%, 24.85%, and 9.24% after 50, 100, and 150 freeze–thaw cycles, respectively. Furthermore, CSH seeding accelerated PC-SAC hydration to generate more products and optimized the pore structure with a smaller pore size to improve the properties of cement composites. Using CSH to modify PC-SAC concretes contributes to the rapid demolding of precast concrete components and improves the service life of assembled concrete buildings in cold regions.