Interpretation of hydration process of concrete based on electrical resistivity measurement
by Lianzhen Xiao
Ph.D. Civil Engineering
xxii, 191 leaves : ill. ; 30 cm
The hydration process of concrete has been studied using a non-contact electrical resistivity measurement. The current work is concentrated on the measurement and interpretation of the electrical resistivity of the concrete incorporated with fly ash, Ground Granulated Blastfurnace Slag (GGBS) and superplasticizers, which are popularlly used in modern concrete structures....[ Read more ]
The hydration process of concrete has been studied using a non-contact electrical resistivity measurement. The current work is concentrated on the measurement and interpretation of the electrical resistivity of the concrete incorporated with fly ash, Ground Granulated Blastfurnace Slag (GGBS) and superplasticizers, which are popularlly used in modern concrete structures.
Cement hydration stages have been classified and the hydration mechanism has been interpreted based on the analysis of resistivity development curve and the investigations of microstructure. The proposed concrete conduction model shows that the degree of hydration dominates concrete resistivity. This study provides theoretical base for new understanding of concrete hydration. It also proposes some practical applications of the resistivity measurement in the activity evaluation of mineral admixtures, the selection of a superplasticizer and the determination of concrete setting time.
The effects of fly ash and GGBS as mineral admixtures on concrete hydration at early ages have been investigated. Similar delayed characteristics points on the resistivity responses at the early ages have been observed in both the fly ash samples and the GGBS samples, which is confirmed with the degree of hydration and compressive strength measurements. An equation for calculating the degree of hydration is derived from the analysis of the resistivity. To quantitatively analyze the activity of fly ash and GGBS in a cement-based hydration system, a resistivity index, that reflects the combination effect of a mineral admixture at an early age, is proposed.
As another focus of this thesis, a criterion has been proposed for selecting a suitable superplasticizer using electrical resistivity and flowdity measurements. Two parameters, Kr and Kt, are originally defined. The more suitable superplasticizer is the one which gives the mixture a higher Kr and a higher Kt at the saturation dosage.
Concrete setting time, a crucial parameter in construction practice, is usually determined using the traditional penetration resistance method. The method is time consuming and labor intensive. In this study, the quantitative relationship between the setting time of concrete measured with the traditional penetration resistance method and the time at which the electrical resistivity critical points occurred has been developed. With the equations, the electrical resistivty measurement can be used as an alternative method to determine the setting times of concrete.