Abstract
Alternative current impedance spectroscopy (ACIS) is a promising non-destructive testing method to monitor long-term change and assess the durability of concrete. This study investigates the influences of Ethylene Diamine Tetraacetic Acid (EDTA) on the hydration of hardening cement by ACIS. It is found that EDTA retards the early-age hydration of cement but can facilitate the later age reaction. Pastes with EDTA show comparable or higher compressive strength than Control at 28 d, especially when the dosage is higher than 0.4%. Microstructural characterization results reveal the working mechanism of EDTA originating from its complexing effect on free ions. The resistivity evolution of the pastes detected by ACIS can well reflect the effects of EDTA on the cement hydration in different ages. Proportional relations are identified between the resistivity and other hydration parameters, such as reaction degree, chemical shrinkage, compressive strength. The results of this study indicate a wider prospect of ACIS in monitoring the microstructure evolution and macro-properties of cementitious materials.
Highlights
Ordinary Portland cement has been widely used for more than a century [1,2]
Pastes with Ethylene Diamine Tetraacetic Acid (EDTA) show comparable or higher compressive strength than Control at 28 d, especially when the dosage is higher than 0.4%
Based on the microstructure characterization and new indications generated from alternative current (AC) impedance analysis, we can see that the evolution of AC resistivity of paste with time can precisely reflect the hydration processes of cement paste with and without EDTA, especially at the very early age
Summary
Ordinary Portland cement (hereafter-termed cement) has been widely used for more than a century [1,2]. How ever, the hardened properties of cement paste and concrete are substantially determined by the hydration process and microstructure evolution during hardening or setting [3,4]. Enormous research attention has been attracted to the hardening process of cement. Various methods have been utilized to characterize the hydration process of hardening cement, such as calo rimetry, chemical shrinkage, ultrasonic velocity measurement, scanning electron microscope, etc. Electrical methods to measure the resistance, impedance and other electrical parameters are proved feasible and convenient to monitor the hydration process of cement [9,10,11]. By applying current on the materials, the structure evolution of cement can be monitored by resistivity or impedance non-destructively
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