The role of Al2O3, MgO and CaO in promoting Cl- uptake by hydrotalcite-like phases in alkali-activated binders with MSWI FA
Caihong Xue, Wei Zhang, Qingxin Zhao
Abstract
Incorporating municipal solid waste incineration fly ash (MSWI FA) in alkali-activated materials (AAMs) production provides an economic and sustainable solution for the disposal of hazardous MSWI FA, which had succeeded in achieving desirable strength and solidification of toxic species, but the leaching of chloride originated from the MSWI FA is still an open problem that hinders the application of these AAMs. Therefore, Al 2 O 3 , MgO and CaO were used for the first time to regulate the in-situ chloride binding of AAMs with MSWI FA, where the chloride content is much higher than that in previous studies. The effect of curing temperature, chemical compositions of raw materials and carbonation on the role of three oxides in promoting chloride binding was systematically investigated. The chloride binding was quantified by IC and the reaction products were characterized by XRD , FTIR, TGA as well as SEM-EDS. The results revealed that both 10 % Al 2 O 3 and 10 % CaO improved the compressive strength but opposite effect was found with the addition of 10 % MgO. CaO was verified to be the most effective to promote chloride binding, while the mixes with MgO and Al 2 O 3 yielded the most Ht and gels, respectively. Carbonation increased the Ht content but decreased the bound chloride. The inconsistent variation in the Ht content and bound chloride indicated the necessity to consider the role of gels in chloride binding, not only the gel content but also the chemical composition. Nevertheless, the results confirmed the importance of CaO in promoting chloride binding, which is of great significance for the mix design of AAMs with MSWI FA. The obtained results hope to provide technic support for a better treatment of MSWI FA.