In the process of application of high-early strength type expansive admixture to chemically prestressed concrete pipes, the technology of improving the external loading crack strength has been developed. This technology is based on the mould restraint controlled method by mounting springs on the clamping bolts for the circumference direction mould. The expansive energy of expansive concrete in steam curing process can be utilized for introducing chemical prestress effectivelly by releasing the restraint of mould due to actuation of springs. In this paper, the mould restraint controlled method for the circumference direction mould are reported.
Recently, shrinkage cracking in high-strength concrete caused by autogenous shrinkage and drying shrinkage becomes a major problem. Most of past researches on shrinkage behavior have been conducted under limited conditions of temperature and humidity, and especially the research under different temperatures is very scarce. In this research, three different temperatures and relative humidity were chosen, and the shrinkage behaviors for high-strength concrete and normal-strength concrete under these conditions were measured. Additionally, the mass change and dynamic modulus of elasticity at different ages were measured from these specimens. The research revealed that the shrinkage behavior of concrete greatly depends on the ambient temperature and relative humidity. Further it was recognized that the shrinkage behavior is closely related to degree of hydration, behavior of water evaporation from cement paste, and micro-cracking caused by rapid drying.
The New PLS (New Pre-lining Support) Method is one of pre-lining Method, in which the perimeter of the tunnel face is excavated with a chain cutter, and immediately reinforced with a concrete shell. This method is applied under the severe condition of urban area. It is considered that improving the deformation properties, ex. the thoughness, of concrete is important to apply this method under severer condition. In this paper, it is described that the property of the steel fiber reinforced shell-concrete using New PLS Method, and the result of the execution test.
Nondestructive evaluation (NDE) for corrosion of reinforcement in concrete is in critical demand for maintenance of concrete structures. Although such electrochemical methods as based on half-cell potential, polarization resistance, and concrete resistivity are available, estimation of corrosion in concrete is marginally successful. Consequently, a compensation technique of the half-cell potential is developed by simplifying the boundary element method and taking into account the concrete resistivity as IBEM. In combination of this compensation with the polarization resistance, a practical NDE is proposed. After confirming an applicability of the procedure in laboratory tests, problems of in situ observation are examined.
This study was carried out to examine on the possibility of the reuse of used tires in the concrete field, from the standpoint of recycling of industrial waste. The physical properties of the mortar and the porous mortar using the rubber-chops processed from used tires as fine aggregate were examined for practical use. As a result, the compressive strength of concrete using rubber-chops was decreased. But assuming the reuse as floor slabs, the sound transmission ability in high frequency range was lowered and found out to be applicable for the concrete slab. Moreover, it could also be applicable for sound absorption material, as the sound absorption performance of porous mortar mixed with rubber-chops was shown good enough, in the range of 300Hz or more.