In this study, a qualitative and quantitative estimation of bond characteristic under comprehensive stress state due to applying the lateral pressure with tensile stress in the direction of a stud axis, was carried out. As a result, it is noted that a bond characteristic was greatly influenced of a lateral pressure with tensile stress and then a bond characteristic depending on lateral pressure was constructed.
Recently it is found that many RC structures are deteriorated by chloride attack, especially under marine conditions. RC superstructures of open type wharves are located right above the sea level, so it is prone to the damage by chloride included in seawater splash. Therefore, in order to use those wharf structures for long time in good condition, it is rather important to grasp the actual deterioration condition and to carry out the suitable maintenance works based on the prediction of deterioration. In this study, field investigation on wharves damaged by chloride attack was carried out, and a model representing deterioration progress was developed based on the field investigation results.
Recently, high-early strength type expansive admixture was developed and commercialized. In several concrete manufacturing plants, the effect has already been recognized not only to reduce of steam curing energy, and moist curing period after demoulding, and to improve of rate of mould rotation, but also to prevent drying shrinkage crack of concrete. In this paper, the applicability for the centrifugal reinforced concrete pipe using high-early strength type expansive admixture was examined. At present, the use of expansive admixture has been popular, but prevention of the crack and improvement of the external crack strength are big problem when producing type-2 pipe with specific diameter. The confirmation of the applicability was carried out regarding to ∅ 600mm type-2 pipe, in which the external crack strength was especially severe. The circumferential crack was easy to be generated in the pipe, and in some case, there was some the external crack strength was low, when using high-early strength type expansive admixture. Therefore, the causes of generation of the crack and of low external crack strength were estimated and examined. It is reported that the external crack strength can be improved by releasing the restraint of the circumference direction mould during the period of the pre-curing of steam curing.
Recently, the early deterioration of concrete structures caused by sulfuric acid was found in sewerage system. In this study, mortar specimens were exposed to sulfuric acid. The influence of W/C, sulfuric acid concentration and air content on the deterioration process was investigated. Internal evaluated strength was also measured using the Needle penetration method. The experimental results revealed that in the case of high sulfuric acid concentration deterioration was evident by large amount of surface erosion. In the case of low concentration deterioration was mainly due to the penetration of acid into the mortar. The use of Air Entraining Agent was found to inhibit the deterioration process. It was found that the internal evaluated strength distribution depended on the W/C and concentration of sulfuric acid. The reduction in evaluated strength occurred even beyond the neutralization depth of mortar.
The Pozzolanic reaction ratio of fly ash in concrete specimen taken from the 34 years old dam is determined by several methods. Experiments on laboratory prepared concrete and paste experiments have been carried out for 3 years as reference data for the Dam specimen. The reaction rates of fly ash in the paste are determined with elapsed time. Ca/Si and Ca/Al moler ratios of hydration products of pozzolanic reaction in the paste and the concrete are determined by EPMA (area analysis). The change of these moler ratios with time are correlated with the pozzolanic reaction rate of fly ash. It is determined that 50% of the fly ash content in the Dam concrete has undergone pozzolanic reaction in 34 years. Furthermore it is found that the evaluation of reaction rate of fly ash in old concrete structures using EPMA is convenient and practical.
Electro-chemical measurements are carried out to test the electro-chemical characteristics of steel bars embedded in concrete. Among several kinds of electro-chemical measurements, a) Mix potential (Half-cell potential) measurement, b) Polarization resistance measurement, c) Polarization curve measurement, are relatively widely used. Therefore, in a sense, they can be evaluated as an “established technology”. However, these measurements of steel bars in concrete essentially contain some inherent errors included in their measuring system. The factors affecting these errors are 1) potential difference between steel bar and reference electrode, 2) electrical resistance between steel bar and counter electrode. This paper describes a fundamental experiment carried out by using a double cellular system originated by authors, to evaluate these errors quantitatively. Based on the test results, the effects of above factors on electro-chemical measurements are evaluated.
Authors report the test results of the 12 specimens of columns with side walls under repeated horizontal load with fixed axial force. Variables are the spacing of hoop, existence of eccentric connection of side walls to a column, existence of partial slits between the column and the side walls and difference of loading history. In this paper, we describe the failure mode influenced by the variables, strength deterioration ratio, torsional deformation by eccentric connection, axial load carrying capacity, damping performance, etc. And the test results were compared with the calculated values on strength and stiffness. Resultantly, difference of hoop ratio and existence of the structural slit made difference of failure modes from total failure as a whole to separated failure of a column and side walls. And it was made clear that deformation ability was improved by the partial slit. Although strength can be presumed under some deviation from the existing evaluation methods, failure mode can be hardly presumed.
The life cycle analysis of high quality recycled aggregate made from demolished concrete by heating and rubbing was carried out. In order to evaluate the applicability of the fine powder produced during the recycled aggregate production as a soil stabilizer, the uniaxial compressive strength of some soil was examined when the cement soil stabilizer and the classified fine powder are added to the soil. As a result, the life cycle CO2 is a negative value because the evaluated deduction of CO2 emission of cement soil stabilizer manufacturing by the powder is larger than that of the recycled aggregate production. This technology is proved to be very effective to reduce CO2.
In prestressed concrete bridges with corrugated steel webs, structural part connecting steel web to concrete slab which is stiff in a transversal direction compared to conventional I-shaped steel girder bridges receives relatively high transverse bending moment resulting in pullout force to dowel and weld throat. There has been few researches that investigated transverse behavior focusing on the pullout force. Therefore, static load test and fatigue test were conducted to investigate transverse behavior of the structure in which three types of connections were tested, stud dowel connections, angle dowel connections and embedded connections. The results show that angle dowel connections and embedded connections have enough static resistance and fatigue durability but stud dowel connections have insufficient static resistance and fatigue durability because some studs are ineffective to resist transverse bending moment.
While concrete properties are influenced by curing temperature history, their variation can be described by a unique function by introducing a concept of equivalent age if the activation energy is rationally determined. Cement paste, mortar and concrete are made with two types of cement, ordinary Portland cement and low-heat Portland cement. In this study, they are cured at a constant temperature of 20°C, 40°C or 60°C until the test age. Experiments on compressive strength, static modulus of elasticity, dynamic modulus of elasticity and fracture energy are executed. On the basis of these experimental results of hardened cement paste, mortar and concrete cured at different temperatures, the values of apparent activation energies are evaluated and the development of these properties is discussed as a function of equivalent age.