This paper reports the calculation me thod for flexural cracking capac ity of precast plain concrete and reinforced concrete products. The specification published by the Japan Society of Civil Engineers suggests that the flexural cracking strength of concrete member depends on the depth of beam and is governed by the ratio of the depth to characteristic length derived from fracture energy. But the equation for flexural cracking strength is not able to apply to most of precast co ncrete products because of its small dimension. For establishing performance based design for precast concrete products, fracture energy tests of concrete with thin section and loading tests for actual products were carried out. And the relationship between flexural cracking strength and tensile strength that covered every section was proposed in this paper.
Global warming is one of the most important problems in the world. It is necessary for many countries to reduce emission of carbon dioxide for sustainable society. It can reduce the emission from manufacturing cement to use fly ash as alternative binder to cement generally. This study shows influence of curing temperature changes to performance of fly ash as a binder. Curing temperature variations are 4 conditions in this experiment; Condition-A is 20℃ or 30℃. Condition-B is 10℃ in early-age and 20℃ or 30℃ after curing at 10℃. Condition-C is that curing temperature is a graded rise from 10℃ to 30℃. Condition-D is curing in water outside. It investigates compressive strength of mortar, k-value and amount of calcium hydroxide at each condition. It also evaluates strength and k-value with maturity(temperature-time factor), which is cumulative temperature. Fly ash fraction in this experiment is 15% in mass of binder. Maturity can evaluate strength of mortar even if datum temperature is - 10℃ as usual. On the other hand, k-value can not be evaluated with maturity in this case. However, if datum temperature is suitable for the reaction of fly ash, for example, it is from 13 to 19℃ in this experiment, k-value also can be evaluated by maturity. Datum temperature is 17℃ in this experiment and it can change depending on quality of fly ash used. It is found that, even if it is cured in low temperature and fly ash cannot react well in early age, fly ash can react and contribute to strength of mortar as a cementitious material in higher temperature environment. Therefore fly ash could be used more generally depending on curing condition and fly ash fraction.
This paper presents the fundamental properties of Ultra High Performance-Strain Hardening Cementitious Composites (UHP-SHCC), which were depeloped for repair applications. In particular, mechanical properties such as tensile response, shrinkage and bond strength were investigated experimentally. Protective performance of the material such as air permeability, water permeability and penetration of chloride ion was also confirmed comparing to that of ordinary concrete. This paper also introduces the usage of the material in repair of concrete st ructures. Laboratory tests concerining the deterioration induced by corrosion were conducted. The UHP-SHCC that coverd the RC beam resisted not only crack opening along the rebar due to corrosion but also crack opening due to loading tests.
The forced vibration test of RC slab by using a portable shaker was proposed. The first resonance frequency was given by the vibration test in thickness direction at each measured point. In the vibration tests of the RC beam specimens with a innner void, resonance frequency was clearly decreased in the void part. Also, it was shown that the resonance frequency of the crack part decreased in the vibration test of RC slab sampled from practical road bridge. Moreover, in the experimental result of the measurements on a highway bridge in service, it was shown that the proposed metod was useful for non-destructive testing of RC slab under traffic loading.
This paper reports the requirements for deleterious expansion due to delayed ettringite formation (DEF) based on field experience. In recent years, the delete rious expansion of concrete have been reported. The concrete have been characterized by expansion and cracking after several years of service in environments exposed in wet conditions. In many cases, the concrete consists of white cement, limestone and copper slag and it has been manufactured at elevated temperatures for early shipment. From detailed analysis, it was made clear that the cause of deleterious expansion was DEF. The gaps which are featured in DEF-damaged concrete were observed around limest one aggregate. There was a possibility that use of limestone aggregate affects DEF-related expansion while the condition of steam curing was the most effective factor for DEF-related expansion. Based on experimental data, the mechanism of DEF-related expansion and the methodology of diagnosing DEF-deterior ated concrete structures were discussed in this paper.
ASR diagnosis and evaluation of load carrying capacity have been performed on the pre-tensioned PC beam which was cut out of a national high way bridge. The bridge was replaced lately after 25years service due to ASR deterioration. Comprehensive investigations such as crack measurement, material strength test, petrographic investigation, beam bending test have been performed on the deteriorated beam. Cracks have been observed on all sides and the appearance has been classified as severe deterioration grade. Petrographic investigation concluded that the reacted mineral was mainly reactive cristobalite contained in andesite of fine aggregates and EPMA investigation found that the reaction seemed to be the final stage. The late expansive ASR has been superimposed by cryptocrystalline quartz in coarse aggregates and it is still in progress. Deteriorated concrete cores with no visual crack have reduced only 10% of compressive strength compared with design strength, but significant loss has been observed on the elastic modulus. The static bending load test on the deteriorated test beam showed 95% of design load capacity indicating that the visual deterioration on surfaces has affected slight damages at this moment. But loss of bending rigidity has been appeared on the deteriorated beam .after bending cracks have started. This comprehensive study including the petrographic diagnosis and the appraisal on mechanical performance of the deteriorated beam conclude that there is a possibility of ASR deterioration in progress and further loss of mechanical performance though the beam had some margin for loading capacity at this moment.
This research is to obtain the basic data for evaluate quantitatively the water contents of the hardened cement paste. The experiments were performed by using hardened cement paste with varying water content and different water-cement ratio, in order to investigate the relationship between neutron intensity and water contents. As a result, we could evaluate the water content and distribution qualitatively by computed tomography. In addition, the mass attenuation coefficients obtained showed the possibility of estimating the water content of the hardened cement paste.
In this study, to evaluate flexural strength and shear strength with def ective anchorages due to corrosion of reinforcemen t, the bending test of the RC beams r eceived damage in the anchorage region due to corrosion was carried out. As a result, it is se ems that the residual shear strength of RC beams with defective anchorages depends on shear span ratio in addition to the anchorage performance. Furthermore, the authors propose an evaluation model for an shear strength of RC beams with defective anchorages on the basis of these experimental results and analy tical result. The value of residual shear strength calculated using this model corresponds to the test results in the past.
In this study, the influence of the heating process on fracture mechanics parameters of concrete has been investigated experimentally. As the first step for the heating test, the influence of material contents in concrete on fracture mechanics parameter was investigated at room temperature. Then heating tests that changed the maximum temperature and the cooling method were carried out. Consequently, a strong correlation between the fracture mechanics parameter and the sand percentage was indicated. After the heating, the strength of concrete decreased. The water-cooling after heating damaged the surface of specimen and influenced on the maximum load of P-CMOD curve and the tension softening curve.
The aim of this paper is to propose the method for evaluating the shear carried by steel fibers of reinforced concrete with steel fibers (RSF) beams. Ten RSF beams with various steel fiber volume fraction, stirrup ratio and specimen size were tested by a four-point bending test. The crack surface displacement was examined by the image analysis. Length of the diagonal crack was measured. The tension softening curves were used to calculate the stress transferred across the diagonal crack. The contribution of steel fibers on the shear resistance of RSF beams has been investigated based on the fracture mechanics. The shear carried by steel fibers calculated from the proposed method showed good agreement with experimental values.
The current standard specifications of JSCE fo r the diagonal compressive capacity of RC beams only consider the effect of the compressive strength of conc rete and are not applicable to high strength concrete. This research aims to investigate the effect of vari ous parameters on the diagonal compressive capacity and propose a predictive equation. Twenty five I-beams were tested by three-point bending. The verification of the effects of concrete strength, stirrup ratio and spacing, shear span to effective depth ratio, flange width to web width ratio and effective depth was performed. The diagonal compressive capacity had a linear relationship to stirrup spacing regardless of its diameter. The effect of spacing became more significant with higher concrete strength. Thus, the effect of concrete strength and stirrup spacing was interrelated. On the other hand, there were slight effects of the other parameters on the diagonal compressive capacity. Finally, a simple empirical equation for predicting the diagonal compressive capacity of RC beams was proposed. The proposed equation had an adequate simplicity and can provide an accurate estimation of the diagonal compressive capacity than the existing equations.
This study presents an investigation of the shear be havior of segmental concrete beams with draped external tendons. Deviator force and transfer mechanism of prestressing force from an anchorage that affect the shear failure mechanism have been examined base d on the results of experimental procedure and FEM with different location of deviator and inclined angle of draped tendons. The modified model proposed by authors has been extended for segmental concrete beam s with draped external tendons with considering the effect of deviator force and transfer mechanism of prestressing force from the anchorage. The results from the extended modified model for draped external tendons had a good agreement with experimental results.