摘要
基于水泥水化进程,考虑水泥水化进程中孔隙率和孔隙溶液离子浓度的动态演变规律,建立水胶比、水泥组分与硬化水泥浆体电导率间的关系,提出一种硬化水泥浆体电导率的动态计算模型.结果表明:所提模型可以计算不同龄期及水胶比硬化水泥浆体的电导率,整体计算误差在10%以内,尤其28 d硬化水泥浆体电导率的计算误差小于5%;随着水化龄期的增长,硬化水泥浆体孔隙溶液离子浓度先增大后稳定,且孔隙率不断降低,二者耦合作用使硬化水泥浆体的电导率随龄期增大不断降低;随着水胶比的增大,孔隙溶液的离子浓度和电导率均降低,但由于孔隙率的增大,使得硬化水泥浆体电导率增大.
水泥基材料的电导率受孔隙率、孔隙溶液饱和度、孔隙溶液电导率等多因素的影
本文基于水泥水化进程,利用水化动力学、质量守恒定律和电解质溶液导电理论,建立硬化水泥浆体电导率的动态计算模型.该模型能反应水泥水化过程中孔隙溶液离子浓度、孔隙溶液电导率、孔隙率以及硬化水泥浆体电导率的动态变化,同时也能指导水泥基材料电学性能调控设计,为水泥材料的电测技术提供理论基础.
水泥水化过程中会发生可溶性盐溶解和硅酸盐水化2种反应,均会导致水中出现大量游离的导电离子,如N
复合材料电导率理论认为硬化水泥浆体的电导率是由固相、液相、气相电导率组成,其计算
式中:n为硬化水泥浆体的组成相数;、、分别为第i相的电导率、孔隙率、连通性系数;下标s、p、g分别表示固相、液相、气相.
Rajabipou
硬化水泥浆体的电导率由其孔隙溶液的电导率和孔隙率决定,而孔隙溶液的电导率和孔隙率都与水泥水化息息相
式中:为离子的价态;为离子浓度,mol/L;为离子等效电导率,S·
由式(2)可知,孔隙溶液电导率与离子种类和浓度相关.水泥水化反应过程中产生的离子会受到水泥化学组分、水化程度、水胶比(mw/mB)的影响.史才军
由电荷守恒可知O
(4) |
综上,可得水化后期硬化水泥浆体的电导率为:
(5) |
式中:(
忽略溶质对溶液体积的影响,孔隙溶液的孔隙率与水胶比、水化程度相
采用Tomosawa模型模拟水泥的水化进程,假定水泥颗粒呈球形,水泥水化过程可分为诱导期阶段、相界面反应过程和扩散反应过程.纯水泥的水化动力学方程用式(6)表
式中:α为水泥水化度;t为水泥水化龄期,h;Sw为水泥与水接触的有效表面积,g/c
硬化水泥浆体中N
式中:b为“结合因子”, N
假设所有水溶性碱都是以硫酸盐的形式存
(9) |
式中:m(Na2O)、m(K2O)分别为水泥中Na2O、K2O的质量,g.
由式(
为检验硬化水泥浆体电导率动态计算模型的可行性,本文对上述步骤进行逐一验证,验证结果及分析见下文.
水泥的密度为3.16 g/c

图1 硬化水泥浆体水化程度的试验结果与计算结果
Fig.1 Test and calculated results of hydration degree of hardened cement pastes
普通硅酸盐水泥的化学组成(质量分数)见

图2 不同水胶比下硬化水泥浆体孔隙溶液的离子浓度
Fig.2 Ion concentration of pore solution of hardened cement paste under different mw/mB
不同水胶比下硬化水泥浆体孔隙溶液的电导率()见

图3 不同水胶比下硬化水泥浆体孔隙溶液的电导率
Fig.3 Electric conductivity of pore solution of hardenedcement paste under different mw/mB
硬化水泥浆体的孔隙率、电导率及其计算误差见
由
为进一步验证模型的准确性,对文献[
(1)基于水泥水化进程,明确了硬化水泥浆体电导率与水胶比、水泥组分、水化程度的关系,建立了硬化水泥浆体电导率动态计算模型,该模型整体计算误差在10%以内,其中对龄期为28 d的硬化水泥浆体电导率的计算误差小于5%.
(2)该模型能定量表征硬化水泥浆体孔隙溶液离子浓度、孔隙溶液电导率、孔隙率以及硬化水泥浆体电导率随水化龄期的动态变化.随着水化龄期的增长,硬化水泥浆体孔隙溶液离子浓度增大,孔隙溶液电导率也增大,孔隙率和硬化水泥浆体电导率减小.
(3)该模型能定量表征水胶比对硬化水泥浆体电导率的影响.随着水胶比增大,硬化水泥浆体孔隙溶液离子浓度降低、电导率降低,同时液相填充的孔隙率增大,导电传输介质水增加,有利于导电离子的传输,硬化水泥浆体电导率增大.
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