硅酸盐白水泥石面层加速碳化程度与微观结构

Accelerating Carbonation Degree and Microstructure of Surface Layer of Hardened White Portland Cement

为研究加速碳化对白色硅酸盐水泥石强度、碳化程度和微观结构的影响,采用热重分析(TG)定量表征水泥石中的Ca(OH)(CH)及CaCO含量,通过扫描电镜-能谱分析(SEM-EDS)和压汞仪(MIP)测试水泥石的微观结构.结果表明:与同龄期的自然养护试样相比,碳化养护3、14、28 d时水泥石抗压强度分别提高10.7%、7.3%和5.8%,抗折强度分别提高17.9%、16.1%和14.3%;碳化14 d时的试样继续干湿循环养护7 d仍可明显提高CH含量,碳化28 d后的碳化程度趋于稳定;碳化试样的孔隙率略高且平均孔径更低,其50~200 nm的较大孔数量明显减少,而小于20 nm的微孔数量相对更多;常压下加速碳化反应直接发生在水泥水化产物CH晶体的表面,在CH晶体棱角处的碳化程度最高,碳化产物与之共生.

In order to explore the effect of accelerated carbonation on the mechanical properties,carbonation degree and microstructure of hardened white Portland cement,the contents of Ca(OH)(CH)and CaCOwere quantitatively characterized by thermogravimetric analysis(TG),the microstructure was analyzed by electron scanning electron microscope energy spectrum(SEM-EDS)and the mercury intrusion porosimetry(MIP).Compared with natural curing samples of the same age,the results show that carbonation curing can significantly enhance the compressive strength of cement paste at all ages.Carbonation for 3,14,28 d can increase the compressive strength by 10.7%,7.3%and 5.8%respectively,and the flexural strength by 17.9%,16.1%and 14.3%respectively.The content of CH can still be significantly increased for the sample carbonized for 14 d after continuous dry wet cyclic curing for7 d,and the carbonization degree tended to be stable after 28 d of carbonization.The porosity of carbonized samples is slightly higher than that of natural curing samples,and the average pore diameter is lower.The number of larger pores of 50-200 nm is greatly reduced,while the number of micro pores less than 20 nm is relatively more;the accelerated carbonation reaction under atmospheric pressure occurs directly on the surface of CH crystal produced in cement hydration.The carbonation degree is the highest at the edges and corners of the CH crystal,and the carbonation product coexists with it.