Optimising the setting behaviour of accelerated cement paste containing poly(AANa-co-DMAA)

During recent decades, alkali-free accelerators have appeared on the market as setting accelerator additives for shotcrete. In this work, copolymers poly(AANa-co-DMAA) with a variation of their charge densities (monomeric molar ratios) were synthesised by aqueous solution polymerisation and characterised by Fourier transform infrared spectroscopy. Then the copolymers were used to optimise the setting behaviour of cement paste in the presence of alkali-free accelerator. The setting times of cement pastes with a combination of alkali-free accelerators and copolymers were tested. Isothermal calorimetry, X-ray diffraction, thermal gravimetric analysis and total organic carbon were also performed to obtain the comprehensive optimisation effects of poly(AANa-co-DMAA). The results clearly show that the capacity of the alkali-free accelerator for shortening the setting time of cement paste was enhanced significantly by introducing poly(AANa-co-DMAA). More AA units in the copolymers have better adsorption capacity, leading to a faster dissolution rate of tricalcium aluminate and the formation of massive ettringite crystals, thus finally the setting time of the cement paste with a combination of alkali-free accelerators and copolymers was shortened markedly compared with that containing alkali-free accelerators alone. The good synergy effect of the copolymers and alkali-free accelerator indicates great potential for practical applications.