New Understanding of Cement Hydration Mechanism through Electrical Resistivity Measurement and Microstructure Investigations

The new understanding for the hydration mechanism of cement has been achieved based on the noncontact electrical resistivity measurement. The cement hydration process is divided into dissolution, dynamic balance, setting, hardening, and hardening deceleration stages according to the characteristic points on the electrical resistivity development curve rho(t)-t and the differential curve d rho(t)/dt-t. The microstructure analysis corresponding to each hydration stage is conducted with scanning electron microscope, x-ray diffraction, differential thermal analysis, and Fourier transform infrared spectroscopy techniques. This study provides the theoretical foundation for understanding the relationship between setting behavior, hardening properties, and resistivity development

Property characterization of self compact concrete at early age

The process of hydration and solidification of self compact concrete (SCC) has a significant influence on the long term strength and durability of SCC. There is little information regarding the early hydration for SCC. The electrical property characterization of SCC provides a direct and practical method for monitoring and investigating the hydration process of young SCC. In conventional method of electrical resistivity measurement for cement-based materials, there is a problem in contact between specimen, and electrodes. This study adopts electrodeless measurement technique to investigate the electrical resistivity of SCC at early stage. The method eliminates the contact problem and polarization effect. The results obtained by this method have much better accuracy. The test results provided the electric parameters for SCC with different chemical admixture incorporations. The variations and characteristics for SCC with different chemical admixture incorporations. The variations and characteristics of the measured electrical parameters were used to characterize the phuysical and chemical properties of young SCC. These parameters were used to study and analyse the hardening process of young SCC

Electrical Measurement to Assess Hydration Process and the Porosity Formation

The change of electrical resistivity with time at early ages was used to investigate the hydration process and the porosity development. Porosity reduction process of cement-based materials hydration was developed by a proposed method. The porosity reduction is fast at the setting period. The results find that the pore discontinuity occurs faster at lower water/cement ratios than at higher water/cement ratios which is similar to the results of the Percolation method

Hyperbolic method to analyze the electrical resistivity curve of Portland cements with superplasticizer

Electrical measurement was employed to investigate the early hydration characteristics of cement pastes with different dosages of superplasticizer in the same W/C ratio. The hyperbolic method was applied to analyze the electrical resistivity development. The peak point (P-h) on the hyperbolic curve could be easily read. The time (t(h)) to reach the point Ph had strong relations with the setting time. th was delayed with the increment of the dosage of superplasticizer. The time th was used to plot the relationship between the initial setting time and final setting time. The hyperbolic equation was established to predict the ultimate resistivity. The retardation effect of the superplasticizer was confirmed in the same W/C ratio by setting time and isothermal heat evolution

CHARACTERIZATION OF FRESH SCC PROPERTIES WITH ELECTRICAL RESISTIVITY

The process of hydration and solidification of self compact concrete (SCC) has a significant influence on the long term properties. Characterization of fresh SCC's properties is an essential work for quality control and improvement of SCC. The study focuses on the characterization of fresh SCC properties with electrical resistivity measurements. The study adopts a non-contact resistivity measurement method that can provide accurate and reliable information of fresh SCC. The influence of various mineral, chemical admixtures and theological modifying agents on fresh SCC's properties can be identified by resistivity measurement. Other characterization methods such flow ability and segregation resistance of SCC can be related to electrical resistivity measurement. The characteristics points from electrical resistivity curves are correlated to the conventional and important parameters in construction practice