水泥-粉煤灰-矿粉-偏高岭土四元胶凝材料氯离子固化机理研究

Chloride Binding Mechanism in Cement-Fly Ash-Slag-Metakaolin Quaternary Cementitious Materials

本文在水泥、粉煤灰和矿粉组成的三元胶凝材料基础上掺入第四元矿物掺合料偏高岭土,利用X射线衍射(XRD)和热重分析(TGA/DTG)定性分析了四元胶凝材料水化产物与氯离子固化能力的关系,并在此基础上利用TGA/DTG和Rietveld外标法定量分析不同形态氯离子固化量。研究表明,掺入偏高岭土能够增加体系早期水化反应速率,促进粉煤灰和矿粉早龄期水化,增加了四元胶凝材料水化AFm相(单硫型水化硫铝酸钙)和C-S-H凝胶含量。同时也增加了体系中铝钙摩尔比,使得单硫型硫铝酸钙(Ms)在碳酸盐存在的条件下更加倾向于转化为半碳型碳铝酸钙(Hc)。氯离子等温吸附结果表明,AFm相含量与氯离子固化能力呈正相关。Rietveld外标法结果表明,掺入偏高岭土后四元体系的氯离子化学固化能力提高,物理吸附能力降低,与三元体系相比,氯离子化学固化量提高了94.16%,物理吸附量降低了7.62%,TGA/DTG定量结果表明Rietveld定量分析具有可行性。

Based on the ternary cementitious materials composed of cement,fly ash and slag,the mineral admixture metakaolin was added to prepare quaternary cementitious materials.The relationship between hydration products of quaternary cementitious materials and chloride binding capacity was qualitatively analyzed by X-ray diffraction(XRD)and thermogravimetric analysis(TGA/DTG).The content of chloride by chemical binding and physical adsorption was quantitatively analyzed by TGA/DTG and Rietveld’s external standard method.The results show that the addition of metakaolin increases the hydration rate of cement in early stage,and promotes the hydration of fly ash and slag powder,which makes the quaternary cementitious material hydrated to produce more AFm(4CaO·Al_(2)O_(3)·CaSO_(4)·13~19H_(2)O)and C-S-H gel.At the same time,the quaternary hydration system also increases the molar ratio of aluminum to calcium,which makes the monosulfoaluminate more inclined to the conversion of monocarboaluminate in the presence of carbonate.The results of isothermal adsorption of chloride ions show that the content of AFm phase is positively correlated with the binding capacity of chloride ions.The results of Rietveld’s external standard method show that with the addition of metakaolin,the chemical chloride binding capacity of quaternary system is increased,but the physical adsorption capacity of quaternary system is reduced.Compared with the ternary system,the chemical chloride binding capacity increases by 94.16%,and the physical adsorption capacity decreases by 7.62%.TGA/DTG quantitative results show that Rietveld’s method is feasible.