Yoichi Mimura

A prediction method of Tensile young's modulus of concrete at early age

Knowledge of the tensile Youngs modulus of concrete at early ages is important for estimating the risk of cracking due to restrained shrinkage and thermal contraction. However, most often, the tensile modulus is considered equal to the compressive modulus and is estimated empirically based on the measurements of compressive strength. To evaluate the validity of this approach, the tensile Youngs moduli of 6 concrete and mortar mixtures are measured using a direct tension test. The results show that the tensile moduli are approximately 1.0–1.3-times larger than the compressive moduli within the materials first week of age. To enable a direct estimation of the tensile modulus of concrete, a simple three-phase composite model is developed based on random distributions of coarse aggregate, mortar, and air void phases. The model predictions show good agreement with experimental measurements of tensile modulus at early age.

Uniaxial Tension Test of Slender Reinforced Early Age Concrete Members

The present study aims to obtain the tensile properties of early age concrete based on a uniaxial tension test employing RC slender members. First, the paper shows that concrete strain is equal to the strain of rebar at the mid-span of the RC member. The tensile Young’s modulus and the strain capacity of early age concrete are estimated using strain measurements. The experiment indicated that the tensile Young’s modulus at an early age is higher than the compressive modulus. This observation was similar to one found in a previous investigation which used a direct tension test of early age concrete. Moreover, the paper describes how an empirical equation for mature concrete can be applied to the relation between uniaxial tensile strength and splitting tensile strength even in early age concrete. Based on a uniaxial tension test, the paper proposes an empirical equation for the relationship between standard bond stresses and relative slip.

Development of a New Composite Slab System Using a Carbon Fiber–Blended Cementitious Adhesive

AbstractThis paper presents an experimental study to develop a new composite slab system consisting of a concrete deck with reinforcing bars, steel plates welded with rib connectors, and a carbon fiber–blended cementitious adhesive. The adhesive has unique characteristics such as rust resistance and being waterproof and can be sprayed onto a steel substrate. The foci of the present research are bond performance of the adhesive, which is an interfacial medium between the concrete and steel plates, bond-slip response of the interface, and structure-level investigations. Test parameters include the presence of an adhesive layer, the age of the concrete-steel interface linked with the adhesive, and the configuration of rib connectors. Adequate curing time for the concrete-steel interface with the adhesive is found to take at least 7 days to achieve reasonable composite action. The adhesive layer significantly improves the performance of the interface, including bond slip and load-carrying capacities. The shap...

Composite Strips with Various Anchor Systems for Retrofitting Concrete Beams

This paper presents the performance of anchor systems for reinforced concrete beams retrofitted with carbon fiber reinforced polymer (CFRP) strips. Nine simply-supported beams are tested with various anchor systems such as steel hooks, steel plates with anchor bolts, CFRP anchor plates, and near-surface mounted (NSM) CFRP strip. The effects of these anchors on the behavior of the retrofitted beams are discussed, including load-carrying capacity, failure modes, and ductility characteristics. Test results indicate that end-anchorage is an important parameter when a CFRP-retrofit design is conducted. Mechanical bolts and NSM CRFP anchors are recommended.