The bending properties of synthetic fiber reinforced concrete were evaluated from the standpoints of bending strength and bending toughness coefficient based on the results of bending tests. In addition, bond properties between fibers and matrix were evaluated with regards bond strength and bond toughness coefficient as results of fiber bond tests. Polyvinyl alcohol (PVA) fiber had strong chemical bonds with matrices, resulting in high bending strength of fiber reinforced concrete. The chemical bond, however, was lost in large deflection zone during load applying stage, and the pullout load reduced greatly. Consequently, both the bond toughness coefficient of fibers and bending toughness coefficient of fiber reinforced concrete were also decreased. Though the bond strength of polyethylene & polypropylene monofilament (PE&PP) fiber was lower compared to PVA fiber, PE&PP fiber showed higher bond toughness coefficient. It was reasoned that the surface area per unit volume of PE&PP fiber was actually larger. As a result, the bending toughness coefficient of PE&PP fiber reinforced concrete was also higher. It was clearly shown that the bond properties of fibers strongly influence on the bend properties of fiber reinforced concrete.
This study examined the uptake of CO2 in the demolished and crushed concrete by conducting an exposure experiment using crushed mortar and crushed concrete. The results of the experiment show that CO2 uptake increases significantly when the particle size is small and when repeatedly wetted and dried. The uptake of CO2 in concrete rubble obtained from intermediate processing factories was also examined. The amount of CO2 uptake in one ton of concrete rubble was estimated to be 11 kg. Using this value, the life cycle CO2 (LCCO2) of reinforced concrete was calculated and shown to be about 5.5% less than the uptake of CO2 compared with a case that did not consider it.
A moist-curing mat with a high water holding capacity was developed exclusively for moist curing on a horizontal plane. A moist-curing mat was laid over a specimen installed outdoors under a condition close to that for a real structure for comparison with a specimen on which water was sprayed and with another that was not cured. Studies were made to check the enhancement of surface wetness and strength, changes in surface pore structure and enhancement of durability. As a result, it was found that laying the newly developed moist-curing mats could provide higher relative humidity near the surface, better rebound hammer test results, reduced pore volume and smaller pore size at a depth of 0 to 10 mm, greater resistance to freezing and thawing, and reduced depths of carbonation and chloride penetration than spraying water on concrete or not curing concrete.
Seismic risk assessment was conducted in order to quantitatively evaluate damage and loss of a structure due to seismic actions. First of all, The analytical procedures of the proposed risk assessment system, which consists of five phases is shown. Among five Phases, calculation of vulnerability and damage function by means of EFM-method (Phase IV) and the seismic risk assessment (Phase V) are carefully studied. Then, simulations of the risk assessment for two types of reinforced concrete railway viaducts were carried out. The numerical results provided the fragility curves, the damage functions, the expected damage loss, and seismic risk curves which were quite acceptable in the light of engineering experiences. It should be noted that these calculated results reflect the differences in strength demand, directions of structures.
This paper describes the results of the survey on actual condition of 27 ASR-affected bridges in Toyama Prefecture ,where it has been carried out twice in 1990 and 2006 in order to verify the effectiveness of repair and strengthening method applied to them. Especially, by examining the mineralogical feature and alkali-silica reactivity of river sands and gravels used in concrete, the progress of deterioration of concrete with time due to ASR was investigated based on the regional classification of river systems in Toyama Prefecture. Furthermore, the practical ASR mitigation and maintenance procedure in this district was proposed by taking characteristics of reactive aggregates into considerations.
In Japan, several different test methods, correspondingly applying either the test method regulated in foreign countries or the originally proposed method, have been used to evaluate scaling resistance of concrete according to a researcher's convenience. In this study, the influences in testing conditions exerting the occurrence of scaling were examined using ASTM C672 method and RILEM CDF method. Between both test methods, there existed the differences of the mass of scaled-off particles and the coefficient of variations. Also, the ways how to apply the chloride solution in test, resulted in the change of the amount of scaling. It was confirmed, from the viewpoint of scaling rate, the total mass of scaled-off particles due to change of the water cement ratio and the test method were found to be almost governed by the amount of scaling developed at the early cycle of the freeze-thaw test.