无电极电测法研究混凝土孔结构的形成规律及应用

The proposal is aimed at which the pore structure information of immature concrete can not be determined and the porosity of hardened concrete can not be properly determined. A non-electrode electrical resistivity setup with a high accuracy is used to dynamically monitor structure forming and porosity decreasing process of concrete. The experiments are proposed to be conducted for obtaining a quantitative relationship between electrical resistivities of concrete and cement paste by testing and analyzing the influence of factors, such as aggregate volume fraction, aggregate particle size and distribution. The influence of the pore solution inside concrete on concrete electrical resistivity is investigated by directly measuring, indirectly deriving or comparing with a certain concentration NaCl solution. The time-dependent parameter cementitious factor in Archie's law during hydration is then obtained. A three-phase model of cementitious matrix, aggregate and ITZ between aggregate and cementitious matrix is proposed to describe concrete conductivity mechanism and to obtain pore structure formation. The porosity of concrete with hydration time is then derived by the electrical resistivity development of concrete. The chloride diffusion mechanism is also studied in the non-electrode setup. A method is proposed to obtain the porosity and the chloride diffusion coefficient of hardened concrete at any age by measuring its electrical resistivity and the electrical resistivity of the conductive solution based on Archie's law and NEL equation, respectively. The proposed strategies may have advantage over the other methods and also eliminate the contact problems from the traditional methods caused by the electrodes setups.

针对无法确定新拌混凝土孔结构及测试混凝土孔隙率技术的不足，本项目拟采用无电极电测法动态监测新拌混凝土结构形成阶段的电阻率变化过程，确定混凝土导电模型中的参数并推算孔结构的细化演变规律。通过改变骨料掺量和粒径等，探讨混凝土电阻率与净浆电阻率之间的定量关系，寻求骨料掺量及界面对混凝土导电模型参数的影响规律；分别用直接法、推算法和比较法揭示混凝土中液相电阻率与混凝土电阻率之间的定量关系，并确定混凝土导电模型中胶凝因子的依时变化方程，由此获得混凝土电阻率发展与混凝土孔结构形成规律的定量关系。通过测试硬化混凝土切片及切片中导电液相的电阻率，探索无电极电测法中，氯离子在混凝土中的扩散机制，根据混凝土的导电模型确定任意龄期硬化混凝土的孔隙率，并基于NEL方程，提出由电阻率推算氯离子扩散系数的方法。无电极电测法在监测混凝土孔结构形成规律上弥补了通用方法的不足，在确定混凝土渗透性上消除了电极法带来的误差。

在国家自然科学基金主任专项基金（51348001）的资助下，该课题按计划完成了研究任务。. 1）研究成果在SCI收录的学术期刊Magazine of Concrete Research上发表题为” Alternating current method to determine chloride diffusion coefficient of hardened paste and concrete”的论文1篇(67(1):27–32, 2015),论文请见链接：http://www.icevirtuallibrary.com/content/article/10.1680/macr.14.00130；. 2）针对新拌水泥基材的水化动力学参数与硬化阶段性能的相关性研究成果，完成论文“The hydration kinetics parameters and water-cement ratio effect from hardening paste, mortar and concrete based on electrical resistivity measurement”，并递交到期刊Cement and Concrete Research；. 3）探讨了不同水化温度和水泥-粉煤灰复合胶凝体系的电阻率变化规律，完成并递交论文“水泥-粉煤灰在变温条件下的早期水化性能”到武汉理工大学学报；. 4）申请了一项国家发明专利“无电极电测法测定混凝土氯离子渗透系数的方法”（2014.6递交）。. 完成了不同龄期的硬化水泥浆和混凝土切片的电阻率测试、氯离子渗透系数确定方法及计算。 研究了无电极电测系统中氯离子在混凝土中的扩散原理，基于Nernst-Einstein方程，确定NEL方程中氯离子迁移数等参数，通过混凝土切片的电阻率计算硬化混凝土氯离子的扩散系数，归纳出混凝土氯离子的扩散系数与水化龄期、混凝土氯离子渗透系数和净浆渗透系数之间的定量关系。在不同的水化龄期，氯离子渗透系数与时间对数的倒数之间存在一个双线关系，3天前的斜率大于3天后的。提出了一个参数KD来描述氯离子在水泥净浆或混凝土中离子迁移的连通性。该研究为评估混凝土耐久性提供实验和理论依据。