For investigating correlations among external and internal cracking of concrete as well as the stirrup damage caused by ASR deterioration, several specimens arranged by main reinforcement and stirrup are exposed under outdoor environment. The detailed observation and evaluation are performed for specimens with severe deterioration degree. As a result, it is noted that cracking in external concrete is perpendicular to surface and stagnate at the depth of stirrup; while, the internal cracking has the trend to generate with various direction and short length due to the constraint from stirrup. Further, it is considered that the stirrup confinement is effective when suffering deterioration without stirrup rupture; however, under the circumstance where stirrup rupture occurs, external cracking has the possibility to extend through the deeper position around the rupture location of stirrup, accompanied by acutely increasing width and differences in level on the surface.
Distribution of air voids in concrete was regarded as 2D spatial point processes. Characteristics of their distribution were evaluated by several spatial statistics functions. Furthermore, a characteristic distance between air voids was defined in the nearest neighbor distance function. Correspondence between the characteristic distance and the conventional spacing factor was investigated. Clustered distribution of air voids due to the presence of aggregate particles were properly estimated by the spatial statistics functions. However, as far as the cement paste matrix was concerned, it was possible to assume that air voids were distributed randomly except a range of short distances. Thus, spatial structure of air-void systems, in particular the characteristic distance between air voids could be simply simulated as a random point process. Furthermore, the characteristic distance of real air-void distribution was almost the same as the conventional spacing factor. Compared to the conventional spacing factor that is obtained by following the ASTM C457 procedure, the characteristic distance is quite easy to obtain. Furthermore, taking account of the fact that the characteristic distances measured for real distribution in concretes are plotted within the 95% confidence interval of binominal random point process, air-void systems in concrete can be assumed as 2D Poisson point process. Thus, a simple equation to obtain the spacing factor from a point process was proposed. The spacing factor was correctly estimated by the equation. Therefore, the characteristic distance of air voids defined in this study can be used as a new distance parameter between air voids, alternatively it may be used as a parameter to estimate the traditional spacing factor.
In order to investigate the effects of drying shrinkage of concrete on shear strength of reinforced concrete (RC) beam without shear reinforcement, the loading test of the RC beams was carried out. Major factors were water-to-binder ratio of 50% and 35%, effective depth of 250,500 and 1000mm as well as the amount of concrete shrinkage. Test results showed that the drying shrinkage of concrete decreased the shear strength of RC beams as well as enhanced significantly the size effect on shear strength of RC beams. Heightening of concrete strength also enhanced the size effect on shear strength of RC beams. Based on the results, a mechanism of the combined effects of drying shrinkage, effective depth and concrete strength on the shear strength of RC beams was proposed. Furthermore, the conventional equation which incorporated an equivalent tension reinforcement ratio considering shrinkage effects showed fairly good agreement with the experimentally obtained shear strength including its size effect.
Shear resistant mechanism was evaluated by using the detailed stress distribution obtained from analysis of RC beam failed in shear. First, the validity of the local stress distributions of concrete and stirrups obtained from 3-D RBSM was confirmed by comparing the test results of RC beams failed in shear. Next, the applicability of decoupling shear resistant mechanism of beam and arch actions using the stress distributions obtained from analysis was presented. In addition, it was clarified that based on the analytical results, shear resistant mechanism at shear strength of the analyzed RC beams was composed by arch mechanism and truss mechanism in beam action independent on web reinforcement ratio. As a result, the necessity for redesigning the shear strength equation based on the shear resistant mechanism was proposed.
The purpose of this research is to quantify the amount and the diameters of connective pore structure and to study the effects on the mass transfer properties. Specifically, the diameters of “ink-bottled pore structure” were specified with a combination of the data from a mercury intrusion porosimeter and water vapor adsorption. As a result, ink-bottled pore diameters in hardened cement paste were 10nm-20nm. Also, the amounts of ink-bottled pore structures were decreased by the use of admixtures, and the mass transfers were inhibited. It was estimated that these results were related to the nano/meso-C-S-H structures.
Surface defects of reinforced concrete structures are often evaluated only by appearance, so the effect surface defects have on the mass transfer resistance of the surface layer of concrete has not been fully explored. In this study, sand streaks and surface bubbles were intentionally caused by varying specimen shape for mortar as a basic study, and their effects on chloride permeability were studied experimentally. As a result, bleeding water could be related to the generation of sand streaks and surface bubbles, and, when sand streaks and surface bubbles occurred, chloride ion penetration was found to be deeper than in the reference specimen. On the other hand, even when sand streaks and surface bubbles did not occur, depending on the specimen shape, in some cases there were locations where bleeding water tended to accumulate. Due to the accumulation of bleeding water, the surface quality of the mortar was reduced, and there was a possibility that the chloride ion permeability increases.
Increasing demand on the reduction of CO2 emission in the construction industry has required development of new concrete without ordinary Portland cement. Such concrete, e.g., geopolymer, has draw-back in terms of carbonation resistance when applied to reinforced concrete structures. To account for this improvement, the authors focused on clinker-free concrete involving dehydrated sludge powder (DSP) produced from waste ready-mixed concrete, which is returned from construction site to concrete manufacturer without used for construction work. In this study, durability of proposed clinker-free concrete with a binder combining DSP with other industrial by-products was studied in terms of carbonation resistance and cracking resistance. As a result, it was confirmed that, at an appropriate water-binder ranges and using DSP with less than about 8,000 cm2/g of specific surface area by 60-80% of binder, the proposed concrete showed equivalent or higher carbonation resistance than that of normal concrete, and when applied to PCa members, showed sufficient cracking resistance under restraint rebars, while free shrinkage strain was 100 to 200 μ larger than that of normal concrete.
This study aims to clarify the shear reinforcement effect for RC beams by post shear reinforcing methods with plate and head anchored shear reinforcing bars (PHB). Three specific test series with total of seven RC slender beams were carried out under the four point bending test to investigate the influence of spacing, diameter and embedded length of PHB without the normal construction methods. All specimens had a rectangular cross section with a/d ratio of 3.2. The results showed that the shear capacity of RC beams was affected by the spacing of PHB, whether they are crossed by shear cracks or not. However the effect was smaller than that by using effective coefficient βaw. This effect was reduced by enhancing the spacing of PHB, however the reduction ratio can be improved with a larger shear reinforcement ratio. Furthermore, the shear reinforcement effect can be promoted by shorter embedment length. Finally, this paper proposed the equations to predict the shear capacity of RC beams with PHB by considering the spacing and the number of PHB. The shear capacity calculated from the proposed equation showed a reasonable accuracy to estimate the experimental shear capacity.
Yakabi Bridge was the first highly durable PC road bridge in Japan constructed for minimum maintenance (corrosion protection by multiple means), through the use of concrete containing ground granulated blast furnace slag #6000, prestressing steel strand with individually coated wires, epoxy resin coated reinforcing bar, plastic duct for the ducts, waterproof construction on the bridge surface, aluminum parapet rail for the parapets, and rubber bearing for the bearings. This paper summarizes the results of the research activities carried out through academic-industrial-government cooperation into the construction of a PC structure with high durability against salt damage over a period of 16 years that included a program of follow-up tests on the actual bridge and additional tests on exposed test specimens in order to verify the effect of these measures against salt damage. The analysis verified that construction method of high durability PC road bridge using these materials was very effective as a measure against salt attack.