Multiscale Performance Characterization of Concrete Formed by Controlled Permeability Formwork Liner

Abstract

It is well known that the permeation and retention of water with a controlled permeability formwork (CPF) liner directly contribute to discharging superfluous water and minimizing bubble content when fresh concrete is poured and cured. These phenomena considerably improve the properties of concrete. To comprehensively evaluate this technology, an extensive experimental program on evaluating the discharged water, moisture content, water-binder ratio variation during the casting process, and surface quality of specimens formed with the CPF liner and control formwork was conducted. Two types of CPF liners with different parameters in the vertical and horizontal permeability coefficients, weight, nominal thickness, and air permeability coefficient were considered. In addition, multiscale experimental characterization of concrete samples, including chloride ion permeability, abrasion resistance, ultrasonic test, scanning electron microscope, and mercury intrusion porosimetry, was performed. It demonstrated that the compactness, antipermeability, and rebound strength of specimens were increased effectively if the key parameters (e.g., permeability coefficients, weight, and thickness) of the CPF liner were properly chosen. Moreover, the fractal dimension of material porosity, which correlates to the cumulative volume of intruded mercury for the specimens, was computed, and it was capable of quantifying concrete surface densification and revealing the quality-improvement mechanism of concrete formed with the CPF liner.