| Summary: | Considering the recent eco-friendly and efficient utilization of three kinds of solid waste, including calcium silicate slag (CSS), fly ash (FA), and blast-furnace slag (BFS), alkali-activated cementitious composite materials using these three waste products were prepared with varying content of sodium silicate solution. The hydration mechanisms of the cementitious materials were analyzed by X-ray diffraction, Fourier-transform infrared spectroscopy, scanning electron microscopy, and energy dispersive spectroscopy. The results show that the composite is a binary cementitious system composed of C(N)-A-S-H and C-S-H. Si and Al minerals in FA and BFS are depolymerized to form the Q<sup>0</sup> structure of SiO<sub>4</sub> and AlO<sub>4</sub>. Meanwhile, β-dicalcium silicate in CSS hydrates to form C-S-H and Ca(OH)<sub>2</sub>. Part of Ca(OH)<sub>2</sub> reacts with the Q<sup>0</sup> structure of AlO<sub>4</sub> and SiO<sub>4</sub> to produce lawsonite and wairakite with a low polymerization degree of the Si-O and Al-O bonds. With the participation of Na<sup>+</sup>, part of Ca(OH)<sub>2</sub> reacts with the Q<sup>0</sup> structure of AlO<sub>4</sub> and the Q<sup>3</sup> structure of SiO<sub>4</sub>, which comes from the sodium silicate solution. When the sodium silicate content is 9.2%, the macro properties of the composites effectively reach saturation. The compressive strength for composites with 9.2% sodium silicate was 23.7 and 35.9 MPa after curing for 7 and 28 days, respectively.
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