Improving the frost-resistance performance of supersulfated cement by reducing the crystalline-to-gel ratio through the addition of nano-SiO2

The poor frost resistance of supersulfated cement (SSC) is of great concerns for its application. This research assessed the frost resistance performance of SSC with 1 wt.% and 3 wt.% cement clinker activator (C1 and C3) and explored the effects of nano-SiO2 (NS) (1 wt.% and 3 wt.%, N1 and N3) on the frost resistance of SSC through macro- and micro-evaluation on loss of the compressive strength/the mass/the relative dynamic elastic modulus and XRD/MIP/SEM. Results showed that the frost resistance of C1 sample was superior than those of C3 sample. The addition of NS enhanced the frost resistance of SSC: the maximum mass loss was reduced by about 92.8% and the maximum relative dynamic elastic modulus loss was decreased by about 34.6%. This could be ascribed to the change of the porous microstructure: the portion of micro-pores smaller than 20 nm increased and the microstructure was densified. Moreover, Moreover, NS changes the long needle-like crystalline phase (AFt) shape to a short rod -like shape, the latter of which was more tightly wrapped by the gel phase, leading to a more compact microstructure, and the detachment of AFt from gel matrix (would be introduced by the difference of their contraction/expansion rate under F -T cycles) could result in the poor performance of SSC, while this could be relieved by the reduction of the AFt-to-gel ratio as seen from the NS-added SSC sample.