Interpretation of hydration process of cement-based materials using resistivity measurement

The object of this thesis presented is to interpret the hydration process of cement based material using electrical resistivity measurement (ERM). A non-contacting electrical resistivity apparatus is introduced. The characteristics of the resistivity development curve is described in detail. The critical points on the curves can be used to identify the hydration into dissolution period, induction period, acceleration period, deceleration period and diffusion-controlled period. The physical meaning of typical curve is also interpreted. The research has showed that ERM can provide useful information relative with both ion concentration in pore solution and porosity changes in hydrating cement-based materials. The pore solution provides information about the chemistry of cement hydration and the porosity change provides the basis for applying ERM for microstruture change. In this research, the simple two-component parallel model is proposed to evaluate the hydration process and the modified equation is Archie's law. The porosity formation curve is proposed from the 2-point method.; The influences of w/c, fly ash, superplasticizer on the setting and hardening and on the changes in electrical resistivity were determined. The results show that typical curve of electrical resistivity are shifted backwards when w/c was increased or fly ash and superplasticizer were used. A strong correlation was established between the results of the electrical resistivity measurements and the results of penetration measurements with the Vicat-test. The Electrical resistivity measurement presented in this thesis provides a non-destructive and objective way to determine and assess both the setting time and some mechanical properties of the cement, during the entire setting process. The results of electrical resistivity agree with other methods, such as heat evolution with time, setting time and compression strength.