1. Introduction
An accurate estimation of the Young’s modulus is important for proper structural design of concrete members, and ensuring their serviceability, such as controlling deflections and crack widths. In particular, the time-dependent development of the tensile Young’s modulus at early ages is needed for estimation of the tensile stresses that are generated due to restrained thermal and hygral shrinkage. These tensile stresses may lead to premature cracking of concrete members. Currently, the tensile modulus is assumed to be equal in value to the compressive modulus and is estimated using empirical correlations based on the compressive strength of concrete [1, 2]. The Architectural Institute of Japan (AIJ) [3] points out that employing the tensile modulus is more appropriate for estimation of the risk of early-age cracking; however, the specification indicates that the compressive modulus may be used instead of the tensile modulus because investigations dealing with the tensile modulus are currently insufficient. Since the tensile behavior of concrete is more significantly affected by the presence of flaws (e.g., microcracks or large capillary pores common in early-age concrete), it is important to develop tools to predict or measure the tensile properties more accurately.