Isamu Yoshitake

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.

Pipe Heating System with Underground Water Tank for Snow Thawing and Ice Prevention on Roads and Bridge Decks

In order to prevent traffic accidents on snow-covered bridge decks, the writers developed a new pipe heating system that uses only groundwater stored in a large underground tank. The underground tank provides geothermal energy, i.e., groundwater of constant temperature, through heating pipes embedded in concrete pavements with no electric heater or fuel boiler. The pipe heating system was constructed at approximately 50% of the cost of comparable systems. In addition, there is a reduction of 10% in operating costs compared with the previous system. The present paper outlines its design and construction and provides fundamental data for the developed system. The piped heating system has kept the road conditions safe during the winter season by always removing the snow and ice from the heated road and bridge sections earlier than the surrounding roads. According to long-term temperature measurements, this system has prevented the road temperature from decreasing below 0°C, even through nighttime and morning periods. This report presents the system as an economical and effective solution for snow thawing and ice prevention.

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.

Moving-Wheel Fatigue for Bridge Decks Strengthened with CFRP Strips Subject to Negative Bending

This paper presents the negative bending of reinforced concrete slabs strengthened with near-surface mounted (NSM) carbon fiber-reinforced polymer (CFRP) strips. Six slab specimens, three of which are strengthened with CFRP strips, are tested in static and fatigue loads. A wheel-running fatigue test machine is used to simulate vehicular loads on a bridge deck. The effectiveness of CFRP strengthening for bridge decks in cantilever and pseudonegative bending is examined based on moment-carrying capacity and cyclic behavior under the wheel-running fatigue loads, including crack patterns and damage accumulation. The moment-carrying capacity (static) of the cantilever slab strengthened with the NSM CFRP strips is improved by 68.4% when compared to that of an unstrengthened slab. The damage accumulation rate of the strengthened cantilever slab owing to the fatigue load is significantly lower than that of the unstrengthened slab. The damage accumulation of the strengthened slab gradually increases and is irrever...

Composite Deck Having Transverse Stiffeners Bonded with a Cementitious Adhesive Subjected to Moving-Wheel Fatigue

This paper presents the behavior of a new composite deck system for twin-girder bridges subjected to moving-wheel fatigue load. The one-half scale system consists of a RC slab with transverse rib stiffeners welded to steel deck plates, which can eliminate the need for posttensioning frequently required for twin-girder bridges. A carbon-fiber-blended cementitious adhesive is used to improve the bond between the concrete slab and the steel deck. The response of the deck system shows a rapid increase in deflection within early fatigue cycles, followed by gradual development when the cycle and loads increase. Energy dissipation of the slab and the level of elastic recovery are discussed. A damage index based on the two-term Weibull function is employed to quantify the degree of fatigue damage. The Weibull damage model reasonably agrees with the simple Palmgren-Miner rule from a practical point of view and supports the adequacy of the proposed system in fatigue configurations. A postfatigue test is conducted to examine the residual capacity of the deck system with emphasis on bond performance of the cementitious adhesive. Bond failure between the concrete and steel deck is not observed, thereby corroborating the effectiveness of such an adhesive on improving the composite behavior of the system.

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.

Simplified Test of Cracking Strength of Concrete Element Subjected to Pure Shear

Most investigations dealing with research on shear focus on concrete members such as reinforced concrete (RC) and prestressed concrete (PC) beams, columns, and slabs. It is difficult for such investigations, which include effects of reinforcing materials and so on, to evaluate shear cracking load in detail. Cracking caused by shear, however, may be a significant consideration for durability evaluation of concrete structures. Pure shear strength is an important property for estimation of cracking because shear failure is caused by fracture of the element. A simple test setup that employs only a universal testing machine has been found to be suitable for obtaining the pure shear cracking strength of concrete without reinforcement. The purpose of the study is to reevaluate the pure shear cracking strength property of plain concrete elements through testing. Based on laboratory testing, it is reconfirmed that reinforcement has little influence on the pure shear cracking strength. However, the shear cracking s...

Recyclability of Concrete Pavement Incorporating High Volume of Fly Ash

Recyclable concrete pavement was made from fly ash and crushed limestone sand and gravel as aggregates so that the concrete pavement could be recycled to raw materials for cement production. With the aim to use as much fly ash as possible for the sustainable development of society, while achieving adequate strength development, pavement concrete having a cement-replacement ratio of 40% by mass was experimentally investigated, focusing on the strength development at an early age. Limestone powder was added to improve the early strength; flexural strength at two days reached 3.5 MPa, the minimum strength for traffic service in Japan. The matured fly ash concrete made with a cement content of 200 kg/m3 achieved a flexural strength almost equal to that of the control concrete without fly ash. Additionally, Portland cement made from the tested fly ash concrete was tested to confirm recyclability, with the cement quality meeting the Japanese classification of ordinary Portland cement. Limestone-based recyclable fly ash concrete pavement is, thus, a preferred material in terms of sustainability.

Proposal of design formulae for equivalent elasticity of masonry structures made with bricks of low modulus:English

Bricks of low elastic modulus are occasionally used in some developing countries, such as Indonesia and India. Most of the previous research efforts focused on masonry structures built with bricks of considerably high elastic modulus. The objective of this study is to quantify the equivalent elastic modulus of lower-stiffness masonry structures, when the mortar has a higher modulus of elasticity than the bricks, by employing finite element (FE) simulations and adopting the homogenization technique. The reported numerical simulations adopted the two-dimensional representative volume elements (RVEs) using quadrilateral elements with four nodes. The equivalent elastic moduli of composite elements with various bricks and mortar were quantified. The numerically estimated equivalent elastic moduli from the FE simulations were verified using previously established test data. Hence, a new simplified formula for the calculation of the equivalent modulus of elasticity of such masonry structures is proposed in the present study.