This paper aims to evaluate the structural performance of PC bridge girders damaged by chloride induced deterioration by using FE analysis code. In this analysis, the authors considered with corrosive mass loss and mechanical behavior for PC steel bars, which were obtained by investigation research of the target structure. The analysis has been conducted not only to eval uate the decreasing in structural performance, but also to verify infl uence on eccentrically-location of deteri orated girders. As a result, it is clarified that the structural perfor mance of the target bridge deck has gone down 24% after 32 years in service. Also the ductility tremendously decreased by excessive corrosion of PC steel bar, because the failure mode will change from concrete crashing to the PC bar rupturing. Fathermore, the structural performance will bring disadvantage by eccentri cally-location of deteriorated girders.
High-resolution-type X-ray CT is used to investigate the pore structure of air entrained mortars (AE mortar). Pore size distribution, pore spacing factors and air contents are calculated based on the results of three dimensional image analysis. The number of fine pores with 40 to 50μm in diameter is the largest with the largest pore size extending to 300μm. Pore spacing factors of AE mortar range from 113 to 137μm while they are 290 to 495μm for Non-AE mortars. Conventional method using a microscope apparatus shows less pores with the size equal to or larger than 100μm. Freezing and thawing resistance of fly ash mortar can be improved by the presence of air entrained voids.
Since most of the pre-cast reinforced concrete (RC) products have thin thickness, failure mechanisms of thin RC members is thought to be different from ordinary members, which have over 200 mm thickness. Therefore, evaluation method of flexural capacity for thin RC members is in great demand. In this study, fracture processes of thin RC beams, which have 40, 70 and 100 mm thickness are studied experimentally under the four point bendin g tests. In addition, numerical ev aluation method for flexural capacity of thin RC members is developed and discussed. In the numerical method, tension softening of concrete is considered for each hight such as 40, 50 and 70 mm by fracture energy tests of concrete. As a result, it is found that reinforcement bars in thin RC beam don't perform mechanically as a ordinary RC beams. As for tension softening, 1/3 model of tension softening is adapted for RC beams which have under 70 mm thickness, 1/4 model of tension softening is applied to RC beam which has 100 mm thickness. Consequently, it is realized that the numerical method for flexural capacity of thin RC beams has good performance by taking into account tension softening of concrete.
A new model was proposed to estimate effective diffusion coefficients of moisture under the internal vaporization condition. The proposed model assumed a two-layer model of dried and saturated region inside the porous sample. The model is formulized by utilizing the relative relationship of the results of isothermal thermo-gravimetric analysis obtained from the saturated porous sample and the free water in liquid condition. The present model was applied to the measurement results of hardened cement pastes with a variety of types of water cement ratio (W/C), resulting in effective diffusion coefficients being estimated ranging from 5.31*10-6 to 8.99*10-6 [m2/s] when W/C was 0.3 to 0.5.
Deterioration of Reinforced Concrete (RC) due to salt attack is known as one of serious problems. Thus, development of non-destructive evaluation (NDE) techniques is important to assess the corrosion process. Reinforcement in concrete normally does not corrode because of a passive film on the surface of reinforcement. When chloride concentration at reinfo rcement exceeds the threshold level, the passive film is destroyed. Thus maintenance is desirable at an early stage. In this study, to identify the onset of corrosion and the nucleation of corrosion-induced cracking in concrete due to expansion of corrosion products, continuous acoustic emission (AE) monitoring is applied. Accelerated corrosion and cyclic wet and dry tests are performed in a laboratory. The SiGMA (Simplified Green's functions for Moment tensor Analysis) proce dure is applied to AE waveforms to clarify source kinematics of micro-cracks locations, types and orientations. Results show that the onset of corrosion and the nu cleation of corrosion-induced cracking in concrete are successfully identified. Additionally, cross-sections inside the reinforcement are observed by a scanning electron microscope (SEM). From these results, a great promise for AE techniques to monitor salt damage at an early stage in RC structures is demonstrated.
Liquid water in micro pore behaves peculiarly by wall friction. This study is aimed to build a model which takes into account the mech anism of fluid in micro pores for predicting the permeability in concrete. Yield stress model used frequently in fluid dynamics was applied to the flow of liquid water in concrete, and then the effect of kinetic and static friction on liquid water behavior from wall was expressed. Furthermore, viscosity model for liquid water in micro pore was proposed based on the result of experiments and then incorporated into thees timation scheme for liquid water flow through micro pores in concrete. The validity of these models was verified by comparing calculated data with experimental data of permeation test of saturated concrete.
In order to study the application of high strength fiber reinforced mortar which has design compressive strength 120N/mm2 to prestressed concrete structures, the authors carried out material tests, bending tests and shear tests of prestressed concrete beam specimens. From the material tests, we obtained material properties for the design of prestressed concrete structures such as compressive strength, tensile strength, Young's modulus, coefficient of creep, dry shrinkage and so on. The results of the bending tests and the shear tests of prestressed concrete beam specimen shows that experimental flexural strength and shear strength of prestressed concrete beam using high strength fiber reinforced mortar exceeds strength calculated by traditional design method. It is confirmed that high strength fiber reinforced mortar can be applied to prestressed concrete structures.
Freezing and thawing resistance of concrete with an initial crack was investigated. The specimens were classified into plane concrete, fiber reinforced concrete, and reinforced concrete. In the tests of plane concrete with an initial crack, the crack grows seriously by the frozen expansion pressure of the water infiltrated into the crack, though the concrete material had high resistance to freezing and thawing. In the experimental results of fiber reinforced concrete, the long polypropylene fiber was useful to prevent the spalling of concrete cover, though the crack growth was not prevented. Moreover, in the experimental results of reinforced concrfete, it was shown that the crack growth was effectively prevented by steel reinforcing bar.
Recently years, the surface penetrant as protection material has been adopted as one of the preventive measures of chloride induced deterioration of concrete structures. In this study, the concretes with two kinds of surface penetrants (silane type and silicate type) were investigated through the long-term exposure test. The properties of chloride ion penetration, the apparent diffusion coefficient of chloride ions and so on were evaluated using the different mixture proportion of concrete. This report is composed from the results of 5 years exposure test. The test results were summarized as follows: (1) Resisting the chloride ion penetration of surface penetrant was continued enough during 5 years exposure test, (2) The benefit of surface penetrant was cleared promising for the low-strength concrete.
Electrical conductivities of hardened cement pastes with and without mineral admixtures were investigated in relation to characteristics of coarse capillary pore spatial structure, which was revealed by SEMBSE image analysis technique. The pore structure was quantitatively evaluated by some parameters derived from the spatial statistical functions. There exists a good correlation between the coarse capillary pore structures and the electrical conductivity. The coarse capillary porosity and its spatial correlation distances do not contradict the total capillary porosity and pore connectedness which is induced from the FKG inequality. It is suggested that connectedness of invisible fine pores is also an increasing function of the fine porosity. In spite of the incorporation of mineral admixtures, the electrical conductivity of the pastes with the admixtures could be expressed with the same liner regression lines as the plain cement pastes without the admixtures. Furthermore, the incorporation of fly ash and silica fume did not decrease the continuity of coarse capillary pores. Nevertheless, the electrical conductivity decreased in the cement pastes with those admixtures. This fact suggests that more disconnected networks of fine capillary pores were generated in the cement pastes containing the mineral admixtures even if the total porosity was the same as the plain system without them.
This study reports the applicability of mechanoluminescent (ML) sensor to crack detection of concrete under dark-field. ML sensor could emit a visible light when the crack formed in concrete under dark-field. There was a linear relationship between the time-integra ted value of ML intensity and the energy required for the crack formation and propagation, which wa s estimated by load-CMOD curve obtained from bending tests on concrete beams. Based on fracture mechanics of concrete, the mechanism of luminescent of ML sensor was examined.