基于碟片法的溶蚀作用下水泥净浆微观结构演变研究

溶蚀作用下水泥基材料的微结构变化导致混凝土材料服役性能退化。为了克服传统试验因试样厚度影响而产生的脱钙不均匀现象,以NH4NO3溶液对约1mm的碟片状水泥净浆试件进行加速脱钙,通过控制质量损失来控制溶蚀程度。然后把质量损失作为衡量溶蚀程度的参数,结合压汞法(MIP)、环境扫描电子显微镜(ESEM)及能谱分析(EDS),研究不同溶蚀程度下水泥净浆的微观形貌、化学组成和孔隙结构变化规律。试验结果表明:试件钙硅比(Ca/Si)与质量损失大致呈两段线性关系。在第一阶段,水泥浆体试件Ca/Si逐渐降低,氢氧化钙(CH)分解,质量损失10%试件中CH已被严重溶蚀;水化硅酸钙(C-S-H)凝胶的Ca/Si随着溶蚀程度增加而降低,证明C-S-H凝胶第一阶段已开始分解。在第二阶段,主要表现为C-S-H凝胶继续分解。试验还发现,溶蚀后水泥净浆试件内部孔径小于50nm的孔略微增加,50~200nm的孔含量有部分减少;孔径大于200nm的多害孔大量增加。

Microstructure Evolution of Cement Paste Under Calcium Leaching Based on the Disc Method

The service performance of cement-based material will degrade,due to the microstructure changes under the action of leaching.In order to overcome the influence of decalcified specimen thickness,an accelerate leac-hing on disc-like cement paste specimens of about 1 mm thick by ammonium nitrate solution was performed in this study.The degree of calcium leaching was controlled by controlling the mass loss.Then the change of micro-morpho-logy,chemical composition and pore structure of decalcified specimen under different degrees were analyzed by mercu-ry intrusion porosimetry (MIP),environmental scanning electron microscope (ESEM),and energy dispersive spec-trometer(EDS).The results showed that the molar ratio of Ca to Si (Ca/Si)and weight loss presented linear relation-ship with two stages.In the first stage,the Ca/Si of cement pastes decreased gradually,calcium hydroxide (CH)dis-solved,especially,the CH was seriously dissolved in content with mass loss of 10%,and the hydrated calcium sili-cates (C-S-H)dissolved slightly.In the second stage,the C-S-H gel dissolved continually.In addition,pore structure of decalcified specimen had changed dramatically.The amount of pores with diameter less than 50 nm increased slight-ly,pores with diameter between 50-200 nm decreased and the amount of harmful pores with diameter larger than 200 nm increased greatly.