Sulphate resistance of silane coupling agent reinforced metakaolin geopolymer composites

Sulphate resistance is an important index for evaluating geopolymer durability. This study investigates the beneficial effects of silane coupling agent (SCA) addition on the sulphate corrosion resistance of metakaolin-based geopolymer composites via strength tests and various characterisation techniques such as XRD, FTIR, SEM-EDS, and Si-29 NMR. The results show that the compressive and tensile strengths and corrosion resistance coefficient of the geopolymer first increased, then decreased with increasing SCA dosages. The geopolymer incorporated with the optimum dosage of 0.1 wt% SCA exhibits the highest strengths, fluidity, and sulphate resistance coefficient. SCA addition effectively compacts the pore structure, thus making it difficult for SO42- to invade the matrix. The SEM-EDS diagram reveals that before and after sulphate attack, the Na content of the pure geopolymer decreased from 7.37 wt% to 3.84 wt%, and the mass ratio decreased by 47%. However, the Na content of the geopolymer composite modified with SCA decreased from 5.64 wt% to 4.85 wt%, and the mass ratio only decreased by 14%, indicating that the addition of SCA reduced the Na precipitation rate of the geopolymer in the sulphate environment. The Si-29 NMR spectrum also reveals that the addition of SCA inhibits the resonance peak shift from Q(4) to Q(3) after 56 d of sulphate attack, which indicates improvement in the stability of the three-dimensional network structure in the geopolymer.

Automated summary

This study investigates the beneficial effects of silane coupling agent (SCA) addition on the sulphate corrosion resistance of metakaolin-based geopolymer composites. The results show that the addition of SCA improves the strength, fluidity, and sulphate resistance of the geopolymer by compacting the pore structure and inhibiting the invasion of SO42-.