In-situ measurement of nominal compressive elastic modulus of interfacial transition zone in concrete by SEM-DIC coupled method

Abstract

Due to the small dimensions of interfacial transition zone (ITZ) in concrete, the measurement of ITZ is subjected to difficulties of deformation measuring at macro-scale and loading at micro-scale. This work presents a coupled strategy between the scanning electron microscope (SEM) technology and the digital image correlation (DIC) method to experimentally study the mechanical properties and thickness of ITZ. Such the SEM-DIC coupled method not only requires a relatively uncomplicated preparation of samples, but also overcomes the difficulty of measuring the nominal compressive elastic modulus (ENC) of ITZ. A cuboid sample composed of aggregates and mortar is designed to make it convenient to conduct in-situ compressive tests by the SEM-DIC coupled method. The ENC of ITZ is obtained by analyzing the stress measured by an in-situ loading device and the strain acquired by DIC method. Results reveal that the ENC of ITZ can be well measured by the proposed method and the values are obviously less than that of aggregates and mortar. Also, the distribution of ENC is described with a quadratic polynomial function. With this coupled method, the effects of aggregate type and water-cement ratio (w/c) on the mechanical properties and thickness of ITZ are further explored. It is indicated that ITZ areas with limestone aggregates and high water-cement ratio deform with more tendency than those with granite aggregates and low water-cement ratio.