This paper describes the influence of pore structure on carbonation of concrete with belite-based cement and ground granulated blast-furnace slag at low water/binder ratio. The model of microstructure of concrete by using the mercury intrusion porosimtory results was attempted based on the concept that microstructure consists of two defferent pores with two defferent size; ink-bottle pore and non-ink-bottle pore that does not has ink-bottle pore. As a result, it is evident that when the water/binder ratio is low, there is a good correlation between the carbonation verociry and the cumulative volume of non-inkbottle pore with the radius of 70nm or more. Besides, it is indicated that the carbonation of concrete using blast-furnace slag is strongly influenced by both the ink-bottle pore and the non-ink-bottle pore with the radius of 70nm or less because the calcium carbonate produced by the cabonarion process fills up the open of pore.
Although a large number of researches has been carried out into the relation between total void content of porous concrete and properties of materials, or mix proportion, those conclusions are based on experiments. Little is known about a theoretical solution to void content. In this study, we contrived a theoretical model of void content in porous concrete aimed at the filling condition, that model was based on properties of mortar covered coarse aggregate in porous concrete. And then, we examined an theoretical equation of total void content leaded to the model. The result of our experiment clearly shows that void content calculated from the equation used properties of materials and mix proportion accommodated to measured void content. Moreover, we thought to need to incorporate air content in the model. We suggested a definition of porous concrete leaded to new concept of concrete used to relation between mortar-void of coarse aggregate ratio and paste-void of fine aggregate ratio. From the theoretical model, we proposed the mix design method of porous concrete that could calculate unit content of materials from target void content.
Bonded concrete overlay is considered as an advantageous method from an economical point of view, when rehabilitating structurally sound concrete pavements. However, it is difficult to secure the bonding between overlay layer and existing concrete slab. Two treating techniques for existing slab surface were studied to obtain the sufficient bonding strength between them, by both strength tests and long term observation of the experimental constructions. Finite element analyses were conducted to clarify the reasons of observed distress and determine the required bonding strength. Finally, the optimum procedures to treat the existing concrete slab were proposed.
Nowadays the half cell potential method or the polarization resistance method is mainly used as a non-destructive testing method to presume corrosion state of reinforcing bars in concrete. In these methods, however, some destruction works are needed such as to expose edges of reinforcing bars from concrete. Considering these situations, fundamental studies were executed to presume the positions and the corrosion state of reinforcing bars in concrete structures using the direct current resistivity method and the induced polarization method, in which no destruction works are needed. In order to achieve high accuracy and site applicability a portable electric measurement device was newly developed for reinforced concrete structures. In the experiment, the influence given to the apparent resistivity and the apparent chargeability whose differences between the corrosion state and the corrosion causes of reinforcing bars, etc. are the electrical nature of the reinforced concrete structure was examined. In addition, several kinds of inversion analysis were carried out using the three dimensional electric field program, which was already reported, and the validity of the experimental results were confirmed.
Every layer of pavement is constructed by rolling compaction. Because of the compaction in the same direction, mechanistic characteristics of vertical from horizontal directions are expected different. It has been experimentally confirmed there exist anisotropic characteristics in granular materials and the characteristics have been measured in a laboratory. Though the analytical solution for a cross anisotropic semi-infinite body is available, a solution for multilayered system has not been obtained. The solution is derived in this paper by directly applying Hankel transformation to the Navier's equations. By comparing responses of isotropic system, the characteristics of the system are demonstrated. The effect of interface slip is also examined in this paper.
Mechanisms of shear failure in a reinforce concrete (RC) beam were investigated, applying AE techniques. An RC beam with a small ratio (1.97) of the shear-span to the effective depth was studied under 4-point bending. To identify the mechanisms of AE sources, SiGMA procedure was applied. Cracking mechanisms in the RC beam were investigated by SiGMA analysis and AE parameter analysis. As a result, an accumulation process of microcracks in the shear span is visually clarified prior to the nucleation of the final shear compression failure plane. Concerning the crack classification, the difference between AE parameter analysis and SiGMA analysis is discussed for AE applications to monitoring.
During Hyogoken Nanbu Earthquake, significant damages were observed in the underground structures which were constructed mainly by cut and cover method. After the earthquake, seismic design of underground structures was reviewed and revised, and limit state design method was introduced instead of allowable stress design method. The authors intend to utilize precast segment method for construction of cut and cover tunnels for purpose of labor-saving and quality enhancement. However, fundamental data on the relationship between deformation characteristics of post-tensioning joint and damage of the structures, which are essential for the verification of various limit states, are quite limited. In this study, effects of the distribution and bond characteristics of prestressing steels as well as the existence of joint mortar on the load-deformation relationship of model specimens with post-tensioning joint were investigated.
In this study, in order to develop a rational and economical shotcrete method for repairing and reinforcing of existing concrete structures, a new mixing method with polyvinyl alcohol (PVA) short-fibre and micro hollow granular into shotcrete used for slope protection works was proposed and its applicability for practical use was investigated by conducting freeze thaw test and material strength test. From this study, it is confirmed that: (1) mixing PVA short-fiber and micro hollow granular into normal shotcrete, freeze thaw stability and tensile ductility of the shotcrete can be better improved; and (2) the proposed method can be applied for practical use for reinforcing the existing concrete structures.
Correlation between reinforcing steel in concrete and concrete cracking was experimentally investigated in order to examine deterioration process of concrete structure due to chloride induced deterioration. Cover depth and horizontal interval of reinforcing steel, modes of concrete cracking and threshold amounts of corrosion for crack onset, were considered for factors of the experiment. Concrete specimens for the experiment were measured by accelerated testing with chloride ion. From the results of experiment, the correlations with cover depth, horizontal interval and mode of concrete cracking were quantitatively evaluated, and secondly, a larger amount of corrosion than that of typically using was proposed under the accelerated experiment.
As the results of investigating the RC irrigation canals in Hokkaido, It is clear that air content and spacing factor of concrete affect an actualization of frost damage at 40 years after the construction. It is based on this tendency, a model to evaluate the influence of air content and spacing factor of concrete to time dependent behavior of relative dynamic modules of elasticity is developed. By using this model, it is possible to suggest air content and spacing factor of concrete demanded as opposed to service time and performance based design of RC structures.
In this study, a quantitative examination was carried out to determine how crack surface roughness affects the injection velocity (injection areal velocity) during crack repair by injection. The authors propose a modification to the formula for determining the injection areal velocity proposed in past research. This paper describes the results of an examination focusing on the prediction of injection time and injection volume in order to improve the planning and management of injection methods. The results confirmed that it is possible to predict approximately the injection time and the injection volume by considering the crack surface roughness on the formula for injection velocity. Furthermore, the result shows that there will be other factors affecting the injection velocity besides the crack width, the injection pressure, the material viscosity and the crack surface roughness, and shows the need to constrain the applicability of the proposed formula.
A new Nondestructive evaluation for internal defects in reinforced concrete is developed by employing thermography and heat charge due to electromagnetic inductance. A target of research is to identify defects existed in concrete cover Nondestructively. Because reinforcing steel-bar should be heated by electromagnetic induction, the effect of induction coil on uniform heating of rebar is first clarified. Based on findings, model specimens with artificial defects are tested. Thus, applicability and limitation of the proposed technique are demonstrated.
A new construction material called “steel slag hydrated matrix”, hereafter this term will be abbreviated as SSHM, produced from steel making slag, ground blast furnace slag powder without using portland cement and natural gravel was developed. However, its application has been limited to non-steel reinforcement material when used in structures under marine environment. In this research, the possibility to apply SSHM for steel reinforced structures has been investigated. The results showed that the resistance to chloride ion penetration, oxygen permeability, resistance of steel bar to corrosion in SSHM were equal to or even better than that of steel reinforced concrete material under marine environment. Moreover, the possibility to apply SSHM for steel reinforced material was confirmed in terms of durability.
When the melting slug of the waste is used for the fine aggregate for the concrete, workability and strength and durability decrease. Because the shape of melting slug is distorted, and the particle like the needle is contained, so that securing necessary workability of concrete is difficult in fresh concrete, and the problem of the decrease in strength and the decrease in the freezing and thawing resistance is caused in the stiffening concrete. Therefore, it uses it mixing it with other aggregates when melting slug is used as a fine aggregate for concrete. And the replacement rate of melting slug is assumed mixing about 30%. In this research, it is clarified that base degree 0.6-0.8 makes the rate of spherical particle, the maximum since the quality and the manufacturing condition of melting powder that makes the sewage sludge incineration ash and the coal ash a raw material are examined. The manufactured melting powder was clarified and it was clarified for the fine aggregate to able to substitute the whole quantity by substituting 3-20% of melting slug the melt ruining fresh properties and no strength and no durability.
An objective of this experimental study is to clarify the depression mechanism of fly ash on leaching alteration in hardened cementitious material. There are two major effects that derived from fly ash, firstly, compacting capillary pore among hydration phase with progression of pozzolanic reaction, secondly, lessen the crystal size and dispersing the location of CH crystal. Progression rate of CH alteration front depends on chain dissolution of CH crystal, so the depression on progressing rate of CH alteration front would be derived from the effects of fly ash as mentioned above. The influences of difference in amount of mixing water and sand on progression rate of CH alteration front in mortar would also be depressed by mixing fly ash.
The design method of RC members strengthened by U-shaped CFRP sheets has not yet been established. The aim of this study is to build a simplified evaluation method on the effects of shear strengthening of RC beam by U-shaped sheets. In this method, the failure process of RC member followed by complete debonding of sheet is modeled by evaluating the average strain of respective sheet located in the shear span. The uni-axial tensile test modeling RC member with U-shaped sheet is performed for investigating the adequacy of this method. Finally, the experimental results for the RC beams with U-shaped sheets reveal that this method can evaluate the effects of shear strengthening by the sheet with satisfactory accuracy.
Basic characteristics of the vibration of a running wheel chair on tile pavement and effects of width of joint and joint spacing of tile pavement were revealed by using of the vibration acceleration of seat of the wheel chair. Vibration level of the wheel chair was calculated by considering the frequency-weighted acceleration values, and the wheel chair vibration and the comfort of a seated person were evaluated according to ISO2631(1978). Furthermore, an estimate method of vibration level of the running wheel chair on arbitrary tile pavement was suggested, and the relation between the comfort of a seated person on the wheel chair and the dimension of tile pavement were figured out.
An application examination of semi-self compacting concrete for steel-concrete sandwich members were carried out from the field of fresh concrete properties. Mix proportions of this concrete were set up slump flow of 400-600mm, high compactivility, and little bleeding and effect of vibration were evaluated by reology characteristics. Evaluation of applicability were carried out by subsidence characteristic after filling to variation of various factors, improvement effect of compactivility by slight vibration, and evaluation of compactivility and effect of vibration by compacting experiments using one dimensional test chamber imitated steel-concrete sandwich members. It was confirmed that this concrete can be applied to steel-concrete sandwich members by good workability without no unfilled part between steel and core concrete.
This paper presents a practical use of half-cell potential measurements for the rational maintenance of concrete structures under severe environmental conditions of the chloride attack. The measurement values of half-cell potential varies due to measuring conditions, such as temperature, relative humidity and rainfall, as well as macrocell corrosion. Their fluctuations are highly likely to lead to the misinterpretation. However, the current research on an existing PC bridge indicates that the negative potential area on the equipotential contour map is an efficient indicator to locate the high chloride content points and the localized corrosion sites in spite of those fluctuations.
The permeable pavement was attracted as a method of a city environmental improvement. It was introduced to subsidence occurred by pumping ground water. Application on a heavy traffic road is also considered now in connection with a recent law about control runoff in urban area. However, problems which should be solved, such as the durability, remain to apply permeable pavements on the heavy traffic road. This paper is discussed about the durability of a permeable pavement etc. from the results of the follow-up survey over about 13 years of the national highway by which test construction of the permeable pavement was carried out in Japan on the heavy traffic road in 1993.
This study investigates the relationship between transferred shear force and relative displacement of the shear connector in steel-concrete sandwich beam. The models, which can consider the effects of the height, thickness and shape of the shear connector, concrete strength, and thickness of the base steel plate where the shear connectors were attached, were proposed. The predicted relationship between transferred shear force and relative displacement as well as the curvature distribution along the vertical part of the shear connector are found to agree with the experimental results. Finite element analysis with the proposed model indicates its applicability as a constitutive model for shear connector.