基于电阻率和ζ-电位法的低热硅酸盐水泥早期水化特性

Early Hydration Characteristics of Low-heat Portland Cement Based on Resistivity andζ-potential Method

为研究低热硅酸盐水泥早期水化特性,采用电阻率测试仪和电声法ζ-电位分析仪分别对低热水泥和普通硅酸盐水泥水化的电阻率和ζ-电位进行测试。结果表明:电阻率和ζ-电位曲线在表征水泥浆体阶段的水化过程上具有较好的一致性。在水化20 min内,低热水泥浆体的ζ-电位与Ca^(2+)浓度成正比,ζ-电位的急剧上升与{Ca 6[Al(OH)_(6)]_(2)·24H_(2)O}^(6+)浓度有关;水化20 min后,浆体中开始形成AFt和CSH,ζ-电位的变化受SO_(4)^(2-)与{Ca 6[Al(OH)6]_(2)·24H 2O}^(6+)、Ca^(2+)与HSiO_(3)-反应速率控制。与普通水泥相比,低热水泥在水化20 min内Ca^(2+)溶出速率更快,浆体中AFt形成时间更早;其诱导期持续时间短,主要受Ca(OH)_(2)晶体成核生长速率及渗透压作用控制;在减速期,低热水泥水化的电阻率时间对数曲线的斜率K m值略小,说明低热水泥石在加速期水化速率加快,水化产物填充孔隙,这导致在减速期孔隙间距缩短速率加快,结构密实速率略慢。

In this study,the electrical resistivity tester and electro-acousticζ-potential analyzer were used to test the resistivity andζ-potential of low-heat Portland cement pastes and ordinary Portland cement pastes,respectively,so as to explore the early hydration characteristics of low-heat Portland cement.The results demonstrate that the resistivity andζ-potential curves have good consistency in characterizing the hydration process of the cement pastes;within 20 min of hydration,theζ-potential of the low-heat Portland cement pastes is directly proportional to the Ca^(2+)concentrations;the sharply rise ofζ-potential is related to{Ca_(6)[Al(OH)_(6)]_(2)·24H_(2)O}^(6+)concentrations;after 20 min of hydration,ettringite(AFt)and calcium silicate hydrates(CSH)begin to form in the low-heat Portland cement pastes.Besides,the change ofζ-potential is influenced by not only the reaction rate of SO_(4)^(2-)and{Ca_(6)[Al(OH)_(6)]_(2)·24H_(2)O}^(6+)but also the reaction rate of Ca^(2+)and HSiO_(3)-.Compared with ordinary Portland cement,the low-heat Portland cement has a faster Ca^(2+)dissolution rate within 20 min of hydration,and the time of AFt formation is earlier in the low-heat Portland cement pastes;however,the induction period,which is mainly affected by the nucleation and growth rate of Ca(OH)2 crystals and osmotic pressure control,is shorter.During the deceleration period,the curve’s slope K m of resistivity correlating with the logarithmic of time for low-heat Portland cement pastes is slightly smaller,indicating that the hydration rate of the low-heat Portland cement stone increases during the acceleration period,and hydrates filled the pores,which resulted in that the rate of shortening is faster for the pore spacing,and the rate of structural compaction is slightly slower during the deceleration period.