Relationships between reaction products and carbonation performance of alkali-activated slag with similar pore structure

Abstract

The composition of reaction products is one of the most significant factors affecting the carbonation performance of alkali-activated slag (AAS). However, the relationships between the reaction products and the carbonation performance of AAS have not been established. To address this gap, AAS pastes with different composition and similar pore structure were prepared by adding Al(OH)3 or Mg(OH)2 to evaluate the effect of the composition on the carbonation performance of AAS. Further, in order to gain insight into the influential mechanism of the composition, the principal reaction products in AAS were also synthesized. All produced specimens were tested for carbonation performance, alongside morphological, thermal and chemical characterizations. The results show that among the examined reaction products, the hydrotalcite-like phase (MAH) displayed the strongest carbonation resistance, which was almost immune to the attack of aggressive CO2. By contrast, the calcium aluminate hydrate (CAH) and calcium (alumino) silicate hydrate (C-(A)-S-H) were much more susceptible to the CO2-rich environment. Further, adding Mg(OH)2 to AAS could promote the formation of MAH and in turn, alleviated the carbonation depth of AAS. Whereas, the content of CAH and the A/S (Al2O3/SiO2) ratio of C-(A)-S-H were raised with the increase of Al(OH)3, resulting in a poor carbonation resistance of AAS. Moreover, a multi-factor model with R2 of 0.95 was established to associate the carbonation depth of AAS with the A/S ratio of C-(A)-S-H, the proportion of MAH, and the proportion of CAH. According to the proposed model, the carbonation depth of AAS is believed the most sensitive to the A/S ratio of C-(A)-S-H.