Recently, fly ash, which is a byproduct from burning pulverized coal in coal-fired power plants, has been used to improve a durability of concrete structures in Okinawa Prefecture. Especially, the superstructure and substructure of Irabu bridge, which has been in service since January 2015, was constructed by using fly ash concrete in order to achieve the durable more than 100 years. This paper showed results of durability investigations on fly ash concrete (FAC) which a part of fine aggregate was replaced by non-JIS fly ash exposed to the coastline in northern Okinawa Main Island for about 11 years. It was found from the results that FAC reduces the chloride permeability of concrete, natural current method and polarization resistance method can diagnose the corrosion levels of reinforcing bar in FAC and normal concrete (BC) specimens using the same criteria, and progress of carbonation does not affect to corrosion of reinforcing bar in FAC and BC specimens under a coastal area with high humidity. Also, from petrological diagnosis on a concrete core taken from BC specimen, it was revealed that ASR is not the main cause of the cracks observed on the surface of specimens.
The purpose of this study was to clarify the mechanism of transformation of cement minerals and the property of ions diffusivity in hardened cement paste on the basis of the results of the diffusion cell tests. The aqueous solutions enclosed in the cells were sulfuric acid, hydrochloric acid, sodium sulfate and sodium chloride. As a result, this study provided an explanation about the mechanism of the dissolution of portlandite and other cement minerals caused by pH decrease due to the action of proton and the penetration of anions. Furthermore, based on the explanation, this study considered the mechanism of the expansion failure caused by ettringite formation in case that monocarboaluminate is a main cement minerals in AFm phase. In addition, this study provided the evidence that the effect of Co-existence of cations on the diffusivity of anions should be taken in to account when considering the expansion failure of hardened cement paste due to chloride ions diffusivity and sulfate ion penetration.
Since Hyogo-Ken Nanbu earthquake in 1995, seismic retrofit of existing expressway RC piers has been carried out. In the seismic retrofit methods with continuous fiber, method of wrapping continuous fiber sheets on a pier has been mainly used. However, because this method requires hardening of continuous fiber sheets with resin, there is concern for curing quality and workability of resin. Therefore, we have developed a new seismic retrofitting method which can be easily applied without resin. It is a method of winding a continuous fiber rope on existing RC piers without using resin. We have carried out cyclic loading tests of columns retrofitted with this method, and confirmed that ductility is much improved. And we clarified that the ductility is affected by shear-to-flexural capacity ratio, pier width, spacing of winded continuous fiber rope, and material of continuous fiber rope.
Since Hyogo-Ken Nanbu earthquake in 1995, seismic retrofit of existing expressway RC piers has been carried out. In general, RC jacket method, steel jacket method and continuous fiber sheets jacket method have been applied to the seismic retrofit of RC piers. We have developed a new seismic reinforcing method using a continuous fiber rope, which is expected as a simple and economical method. This paper describes the proposed empirical formula of ductility capacity derived from the results of conducted experiment of RC columns on which the seismic retrofitting method with a continuous fiber rope is applied.
This paper describes an effect of artificial crack length on fatigue load carrying mechanism of cracked reinforced concrete (RC) beams without stirrups. To make clear the mechanism, cyclic loading experiments and finite element (FE) analyses were conducted by using the specimens which had different length of artificial cracks. The experimental results indicated that the load carrying mechanism was governed by tied arch effect due to horizontal cracks which was propagated from artificial crack tips regardless of loading conditions. In case of the beams whose static strength was enhanced due to tied arch effect, the number of cycles at failure was the same as the sound beam under the cyclic load of 40% upper limit load ratio. It was demonstrated that the reason was localization of relative damage accumulation area caused by linearization of the load path. The analytical results showed that the linearization occurred by stress concentration at the position of crack tips which existed inside of B-region. It was made clear that when the crack tips existed inside of D-region, horizontal cracks were easy to be propagated with increase in the number of loading cycles.
This research aims to clarify the shear resistance mechanism of RC T-beams. The static bending tests were conducted for RC T-beams with the various shear span ratio and shear reinforcement ratio. The experimental shear capacities of all T-beams exceeded that of calculation by ignoring the flange width. The enhancement of the shear capacity due to the compression flange was larger in the smaller shear span ratio. In addition, T-beams with the different shear span ratio showed the different cracking behavior related to the continuity of the cracks at the web and the flange. Furthermore, this study proposes the evaluation method of the shear resistance in the arch action with the strains of the tensile bars at the support. Comparing with the rectangular beams, the T-beams with the same shear reinforcement ratio showed the larger shear resistance in the arch action at the peak load. The beam action was easy to disappear with the wider stirrup spacing.