Electrochemical Accelerating Leaching Behavior of Plastic Concrete for Cut-Off Walls

Abstract

Plastic concrete is a ductile material with a low elastic modulus (1000–3000 MPa), good flexibility, a and strong ability to adapt to the surrounding soil deformation. Hydraulic concrete mainly serves in a watery environment, so the leaching behavior of plastic concrete is crucial and cannot be neglected. Meanwhile, improving the crack resistance and effect of anti-seepage is also a primary task for cut-off walls. In this paper, in order to investigate the mechanical performance and leaching behavior of plastic concrete, a uniaxial compressive strength test was performed on plastic concrete specimens of a specific age (28 days) and different percentages of replacement cement by single bentonite (40%, 50%, and 60%) and bentonite (30%) together with clay (10%, 20%, and 30%), and the compressive strength, elastic modulus, pH value of the leaching solution, ultrasonic transmit time, electrical resistivity, and calcium ion dissolution concentration of plastic concrete have been evaluated. Moreover, the quantitative relationship between pH value and calcium ion concentration change was built through the electrochemical accelerating leaching method. According to the results, adding 40–60% soil materials can entirely meet the compressive strength (2–7 MPa), elastic modulus (below 3000 MPa), and relative permeability coefficient (below 1 × 10−7 cm/s) of plastic concrete used for cut-off walls while the compressive strength and elastic modulus of plastic concrete with 30% replacement cement by bentonite would be higher than 7 MPa and 3000 MPa, respectively. The leaching resistance of plastic concrete can be improved by more than 30% by adding bentonite coupled with clay, and three representative zones were observed through SEM and energy spectrum analysis, and Ca/Si molar ratio decreased by 30% after leaching.