NaCl和Na2SO4对水泥水化机理的影响

Effects of sodium chloride and sodium sulfate on hydration process

为了深入研究氯盐、硫酸盐对水泥基材料的水化机理的影响,将NaCl和Na2SO4掺入水泥中,运用TAMair微量热仪、X射线衍射仪(XRD)和电感耦合等离子体发射光谱仪(ICP)探究水泥的水化动力学以及水化产物的转变.结果表明:从水化放热速率和累计放热量上分析,NaCl和Na2SO4都可以加速水泥水化,相同质量的NaCl加速水化效果高于Na2SO4.在水化过程中SO4^2-离子浓度快速下降,然而Cl-离子浓度在水化10h之后才出现下降的趋势.当SO4^2-和Cl-同时存在时,SO4^2-先于Cl-与铝酸三钙(C3A)反应,NaCl能够促进石膏溶解并且加速钙矾石生成;从XRD图谱可以发现,在掺入NaCl的水泥浆体内,水化早期不会产生Friedel盐,只有随着钙矾石转变成单硫型钙矾石(SO4-AFm),Cl-开始反应生成Friedel盐.根据动力学微分曲线评价了NaCl和Na2SO4对水化机理的影响,在水化过程中NaCl促进了结晶成核与晶体生长(NG),对相边界反应(I)过程有一定的削弱作用,而对扩散过程(D阶段)影响很小.

To investigate the influence of chloride salt and sulfate on the hydration mechanism of cement-based materials,NaCl and Na 2SO 4 were mixed into cement,and the TAM air microcalorimeter,X-ray diffractometer (XRD),and inductively coupled plasma spectroscopy(ICP) were used to investigate the hydration kinetics of cement and the transformation of hydration products.The results show that both NaCl and Na 2SO 4can accelerate cement hydration from the hydration heat release rate and the cumulative heat,and the accelerating effect of NaCl is better than that of Na 2SO 4.The concentration of SO4^2- decreases rapidly during the hydration process,but the Cl - concentration does not decrease until 10 h hydration.When Na 2SO 4 and NaCl coexist,SO4^2- reacts with C 3A prior to Cl -,and NaCl promotes gypsum dissolution and accelerates ettringite formation.From the XRD pattern,it can be found that in the cement slurry mixed with NaCl,Friedel salt is not produced in the early stage of hydration,and only with the conversion of ettringite into monosulfide ettringite (SO4-AFm),Cl - starts to react to form Friedel salt.In addition,the influence of NaCl and Na 2SO 4 on the hydration mechanism of cement was discussed according to the hydration kinetic curve.During the hydration process,NaCl promotes the NG process,and has a certain weakening effect on the I process,but has little effect on the D process.