Research Of Ordinary Clay For The Synthesis Of One-part Alkali-activated Cement

Based on the comprehensive analysis of the research situation of domestic and foreign alkali-activated cement, one-part alkali-activated N-A-S cement and alkali-activated N-C-A-S cement were prepared by silicon-aluminum clays with different chemical composition such as Ning Xiang kaolin, Ping Xiang kaolin, Lin Li bentonite and Xiang Tan red soil, which were calcined with caustic soda, soda ash, soda lime. The article discussed performance and influence factors of alkali-activated cement, and phase composition, morphology structure and function keys of raw materials, clinkers of alkali-activated cement and the hydrates were characterized by combining with the scanning electron microscopy, thermal analysis, powder X-ray diffraction, fourier transform infrared spectrometer and other analysis technology. Mechanisms of clinker burning and hydration were discussed at last. The following conclusion was summarized:Firstly, one-part alkali-activated N-A-S cement were prepared by Ning Xiang kaolin, Ping Xiang kaolin, Lin Li bentonite and Xiang Tan red soil activated with alkali, and process was preliminarily optimized. The best process conditions and performances show respectively as follow. Calcining temperature is750℃, the mass ratio of NaOH and NingXiang kaolin is0.2, holding time is3h, and the3d compressive strength of one-part alkali-activated N-A-S cement reach14.7MPa; Calcining temperature is950℃, the mass ratio of NaOH and PingXiang kaolin is0.25, and the3d compressive strength of one-part alkali-activated N-A-S cement reach62.98MPa; Calcining temperature is850℃, the mass ratio of Na2CO3and LinLi bentonite is0.33, and the3d compressive strength of one-part alkali-activated N-A-S cement reach42.11MPa; Calcining temperature is750℃, the mass ratio of NaOH and XiangTan red soil is0.20, and the3d compressive strength of one-part alkali-activated N-A-S cement reach22.0MPa; But the later strength of all one-part alkali-activated N-A-S cement declined and had whiskering phenomenon.Secondly, one-part alkali-activated N-C-A-S cement were prepared by Ning Xiang kaolin, Ping Xiang kaolin, Lin Li bentonite activated with soda lime. The research shows compressive strengths of the alkali-activated N-C-A-S cement are closely related to calcination system, mole ratio of (Ca+Mg)/Si and Na/Al, and best preparation conditions are the same, calcining temperature is1100℃,(Ca+Mg)/Si is2.2, Na/Al is1.67, and the corresponding3d compressive strengths of the alkali-activated N-C-A-S cement prepared by Ning Xiang kaolin, Ping Xiang kaolin, Lin Li bentonite reach respectively48.2MPa,31.33MPa and34.55MPa. The later compressive strength of cement grows slowly in general and appear without whiskering phenomenon. However, the strength of one-part alkali-activated N-C-A-S cement prepared by Xiang Tan red soil calcined with soda-lime is not big, which may be caused by low aluminium content in red soil.Thirdly, thermal analysis shows the thermal behaviors of silicon-aluminum clay were changed greatly with alkali added, and IR analysis shows that inert quartz impurity can react with alkali at relatively lower temperatures. Therefore, the method of alkali fusion can effectively inspire the inert silicon-aluminium clays to produce cementing reactivity. X-ray diffraction analysis shows that the thermal decomposition temperature of clay minerals with alkali are lower than that without alkali, and other inert minerals such as quartz reacted with alkali and reduced or even disappeared. Moreover, the new phase of nepheline simultaneously appeared in the clinker, and zeolites appeared in the corresponding hydrates in addition to Xiang Tan red soil (zeolite-like amorphous phase). Therefore, the generation of zeolites and zeolite-like amorphous phase are cementing mechanisms of one-part alkali-activated N-A-S cement.Fourthly, XRD analysis shows the raw mineral phases completely disappears after silicon-aluminum clays calcined with soda-lime, and the generating phases are relatively complex and depend on the calcination conditions. Clinkers usually generate a lot of amorphous phases, soluble alkali salt and C2S. Early strength of one-part alkali-activated N-C-A-S cement is provided by zeolites and zeolites-like amorphous phase, which are generated from reacting among soluble alkali salt, silicon-aluminum non-crystal phase. However, the stable growing strength of cement in later stage is provided by C-S-H gel hydrated from C2S when PH declines.