This paper consists of two experiments to investigate bond behavior for repair and strengthening ofconcrete members, one concrete with fiber sheet in uni-axial tensile test, the other bond fiber sheet to RC member test with notch which limited location of shear crack. Uni-axial tensile test was carried out to change three parameters which were kind of fiber sheet (aramid fiber and carbon fiber), compressive strength of concrete and bond length of fiber sheet. RC member test was carried out to change one parameter which was kind of fiber sheet. The results of this experiments are that bond strength equation between concrete and fiber sheet to include compressive strength and bond length of sheet in uni-axial tensile test and effective bond area in RC members test were obtained. Therefore it was almost possible to estimate bond strength of RC members with fiber sheet due to bond strength equation and effective bond area.
In PC box girder bridge used corrugated steel girder at web, corrugated steel girder is fabricated in site as a rule. In this case, it is considered the welded joint, the bolt joint as the joint technique of corrugated steel girder. In this study, supposing unwelded joint under consideration of quality control in site and workability and considering scenery of structure, strength evaluation and drop off the number of bolts in the joint portion was investigated. As a result, it was cleared that the bolt joint has more strength evaluation than backling strength of corrugated steel girder and it can be dropped off the half number of bolts.
This study has aimed at clarifying the sequence and saturation of multiple cracking evolution in Random Short Fiber Reinforced Cementitious Composites with Pseudo Strain Hardening Behavior (PSH-RSFR-CCs). For this purpose, uniaxial tensile tests were conducted with Polyethylene fiber composites. Unsaturated multiple crack evolution was observed as well as saturated evolution in these tests depending on fiber volume fraction and testing age. Plausible mechanisms were suggested to characterize these two crack evolution types. Furthermore, two micromechanics based performance indices were proposed as measures of crack saturation.
The moment tensor of acoustic emission (AE) is physically derived from a crack-motion vector. Thus, a relation between crack orientation determined from the moment tensor and the stress intensity factors in the linear elastic fracture mechanics (LEFM) is investigated. In bending tests of notched beams, the normalized stress intensity factors KI and KII are determined from the moment tensors of AE events. A criterion applied to crack classification of AE source is confirmed to be reasonable from the relation between the stress intensity factors and the shear ratio. Variations of KI and KII under crack extension are obtained. It is found that results are comparable to analytical results by BEM analysis.
In this paper, a mechanical model for the macroscopic shear failure of both reinforced concrete membrane elements and reinforced concrete/fiber concrete deep beams in terms of entire load-displacement characteristics is developed. The analysis employs a smeared crack band model under remote shear force in a simple manner. The proposed formulation identifies a development of multiple diagonal cracks along the macroscopic shear failure plane. The model is in good agreement with a membrane elements shear test and a deep beam shear test. The procedures developed in this study would be useful in predicting the deformation behavior of reinforced concrete structures which is becoming increasingly important.
This paper investigates how significantly the error in prescribed parameters affects identified results supposing that thermal properties in a massive concrete are identified. Error sensitivity equation which represents sensitivity of the identified results with respect to error in prescribed parameter is derived in order to make analytical evaluation of the error effect. By using the sensitivity equation, we pointed out importance of selecting proper record length used for this identification, as change in the record length produces change in the identified results. Furthermore, we examined which prescribed parameter values need to be assigned accurately in order to make accurate estimates. Monte Carlo simulation is employed to verify the results obtained from the sensitivity equation.
Stress-strain characteristics of concrete confined by carbon fiber sheet were investigated through uniaxial compression test. Experimental variables adopted in this study were amount, elastic modulus, tensile strain capacity of carbon fiber sheet, concrete strength and sectional shape of specimens. Main test results obtained are as follows. (1) Two types of stress-strain curves of confined concrete with carbon fiber sheet are observed. One is ordinary curve having peak point and the other is curve showing only monotonous increment of stress without peak point. (2) A new model for the stress-strain curve which can express the two types of curves is proposed, and equations to estimate characteristics required for expression of the curves are derived. (3) Comparisons between experimental results and calculated ones show that the model estimate the test results with good enough agreement.
For saving of capping labor in compressive strength tests of concrete, unbonded capping systems using rubber pads and steel retaining caps have been standardized by ASTM C 1231 and AS 1012.9. These standards, however, do not sufficiently specify requirements for the testing apparatus and control of rubber pad. In consideration of such circumstances, the authors conducted detailed experiments on steel retaining caps and rubber pads in order to define proper dimension of them and to specify the quality of rubber pads. Based on these experiments, this paper proposes a new rubber pad control method and describes a reasonable unbonded capping system using the proposed method.
The false setting of cement caused by the aeration was studied from the analysis of the cement characters, its hydraulic reactivity, its hydration reaction, the paste rheological properties and the relationship among them. The aeration of cement was simulated by the treatment of cement exposing under an environment of temperature, 20°C and relative humidity, 80%. With a longer treatment, cement showed larger amounts of ignition loss. Hydration products with particle sizes under 0.3 μ m were formed on cement particles and the amount was increased with the increase of treatment time. Although the treatment did not change the Blaine specific surface area, it changed the BET specific surface area as much as 1.4 times higher during seven days of treatment. The treatment significantly decreased the hydration reactivity of interstitial phases of cements. The treatment longer than certain period of time brought a false setting in cements, which was not occurred in fresh cement paste. When aerated cements was mixed with water, sulfate ion was supplied to liquid phase from alkaline sulfates or calcium sulfate hemihydrate. However, the sulfate ion was not consumed by the ettringite formation reaction because of the low reactivity of interstitial phases. As the results of poor consumption of sulfate ion, gypsum crystals deposited from liquid phase to form large automorphic plate crystals and finally cement paste was thought to show the false setting, i.e. plaster set.
Interfacial affinity and interaction between fillers and polymer matrix were investigated for improving the properties of MMA polymer concrete. The investigations were performed by both dynamic-mechanical approach and analysis of filler-polymer-solvents interactions by using Teas's triangular chart. Morishita's index and acid-base balance parameter were also analyzed to study the dispersion state and the surface characteristics of fillers. The results demonstrated that alumina having acidic surface provided strong adhesion and interaction for the MMA polymer matrix. By contrast, the fillers involvingCaO and SiO2 as main chemical components had basic surface leading to repulsion against to the polymer matrix.
Recently, organic admixtures including fluidizing agent and high-range water-reducing agent are indispensable for high-performance concrete and high strength concrete. However, the influence of organic admixture (superplasticizer) on the process of chloride ion penetration into hardened concrete is not still fully understood. So, the authors experimented on the influence of two kinds of superplasticizer. We found out the influence of naphthalenesulfonic acid-based and polycalboxylic acidbased admixture on the process of chloride ion penetration into hardened mortar by using original rapid chloride permeability tester. From the result of the above, it is construed that the difference of the major constituent of the superplasticizer will exercise no influence on the penetration of the chloride ion into hardened mortar. However it is explained that the penetration of the chloride ion become smaller in order of the mortar to which polycalboxylic acid-based admixture is added, plain mortar, and mortar to which naphthalenesulfonic acid-based admixture is added. It is also explained that much of the chloride ion is fixed in order of naphthalenesulfonic acid-based admixture, plain, polycalboxylic acid-based admixture, by using EPMA and XRD.