2.4. Test Methods

According to the requirements of GB/T17671-1999 [27], the compressive strength of CMM mortar was detected using the Mechanical Strength Tester HYE-300-10 (Beijing Seyu LuTong Instrument Mile Co., Ltd., Beijing, China). The performance results of mortar/paste mix at different hydration ages were the average values of three mortars/pastes. The dispersion of a data set is reflected by standard deviation. The dispersion coefficients corresponding to the properties of mortar/paste are calculated via standard deviation formula. CMM mortar and paste are cured using a cement autoclaved machine YZF-2S (Tianjin ShouKe Experimental Machine Co., Ltd., Tianjin, China). The main autoclaved test parameters were as follows: pressure is 2.0 MPa; temperature was 215.7 °C; the heating rate was 3~4 °C/min [28]. The expansion rate of CMM paste was measured via high precision length measuring instrument based on GB/T 750-1992 [28]. In addition, the mass fraction of f-CaO in CFB fly ash and CMM was detected according to the China standard YB/T 4328-2012 [29].

The exothermic rate and cumulative hydration heat of CMM paste were examined using the isothermal instrument at 20 °C for 72 h. The mineral composition of CMM was examined through X-Ray Powder Diffraction (XRD) of Japan Science and Technology Instrument Co., Ltd. (Kyoto, Japan) The SEM-EDX of CMM was tested using a Gemini 300 thermal Field emission scanning electron microscope and Oxford X-MAX Energy Dispersive X-ray Detector (Hitachi Corporation, Ibaraki, Japan). The ²⁹Si MAS spectra of CMM were detected through the JMM-EC600R MAS NMR spectrometer. The distributions of Ca, Al, Si, O, As, Cr, Zn and Cu in the CMM0.5–12 h were examined by the Electro-Probe Microanalyzer (EPMA- JXA-8530F Plus, Kyoto City, Japan) to obtain the qualitative and quantitative results for the above elements. According to GB 5086.1-1997 standard [30], the solid (sample) /liquid (deionized water) ratio was 1:10. Then, the solid and liquid were introduced into the rotating mixer with 30 r/min and 18 h. The leaching results of heavy metals (As, Cr, Zn, and Cu) in CMM and CFB fly ash were determined using high precision Thermofil ICP-MS (RQ type) equipment. Finally, the results of heavy metal leaching were compared with WHO International standards for safe drinking water.