Effect of alkali dosage and silicate modulus on the deterioration of alkali-activated concrete properties subjected to sodium chloride attack and freeze thaw cycles

The deterioration mechanism of alkali-activated slag-fly ash-steel slag concrete (AAC) under sodium chloride attack and freeze-thaw (SF-T) cycles was investigated through a multi-scale methodology. Results showed that appropriate water glass modulus and higher Na2O dosage increased the compressive strength and salt-frost resistance of AAC. The mass loss in AAC was concentrated in the first 100 SF-T cycles, but PCC increases linearly with the SF-T cycles. The salt-frost resistance of PCC was similar to that of AAC samples Na2O dosage of 5 %. Higher Na2O dosage reduces the amount of unreacted precursor, thus reducing the porosity and improving the pore structure of concrete. However, increasing Na2O dosage has not limited the crack development, and the crack width in AAC was greater than in PCC after SF-T cycles. The porosity and average pore size of the concrete increased after SF-T cycles. Friedel's salt was only present in PCC, and NaCl crystals were observed in AAC. •Unlike PCC, the mass loss of AAC is concentrated in the first 100 SF-T cycles.•Increasing Na2O dosage enhance strength and salt-frost resistance in AAC.•The crack width of PCC after SF-T cycles is finer than that of AAC.•Friedel' s salt is only present in PCC, but NaCl crystals are observed in AAC.