Construction joints have to be executed very carefully. Generally, fresh concrete is placed after operation of green cut or chipping of old concrete. Cement mortar or epoxy resin is placed just before fresh concrete is placed. In this paper, characteristics of polymer-modified mortar as a joint material are investigated as a stand point of flexural and shearing behaviors of RC beam having a vertical or horizontal construction joint under various conditions. Experimental parametars are such as an open-time which is a time between placement of polymer-modified mortar on joint and placement of fresh concrete, a thickness of polymer-modified mortar, ages of concrete, kinds of joint materials and so on.

View full abstract

RC structures certainly have construction joints because of their structural and executional reasons. Construction joint works are done at reinforcement or extension of reinforced concrete structures such as heap up of sea wall, lane width expansion of RC bridge and so on. Generally, cement paste, cement mortar or epoxy resin is used as a joint material. Polymer-modified mortars are promising materials as joint materials. In this paper, chracteristics for strength of construction joint are investigated concerning to flexural strength of concrete beams which have a vertical or horizontal joint.

View full abstract

To explain the mechanisms of the deterioration of fiber-reinforced concrete caused by freezing and thawing, observation has been made with such experimentals as: (1) Metrology of dynamic modulus of elasticity. (2) Rigidity flexural strength tests. (3) Measurements of pore structure distribution. (4) SEM observation. As a result of the attempt, the following has been made clear.
With the concrete reinforced with glass, aramid and PVA fiber, freezing and thawing are liable to give rise to cracks in the matrix concrete, resulting in inferiority in rigidity. Despite the above, none of drastic lowering of flexural strength is to be seen, which might be derived from the reason that fibers play a role of bridging the cracks. On the other hand, generation of cracks in the matrix owing to freezing and thawing seldom occur with the steel-fiber reinforced concrete. Furthermore lowering in bending strength or rigidity is hardly caused.

View full abstract

The objective of this research is to evaluate quantitatively the effect of sand property on the value of flow which represents deformability of mortar. On the basis of the correlation between relative flow area of paste and free water-powder ratio by volume, modeling of relative flow area of mortar was explained. From the result obtained, it became clear that the effect of sand property on the value of mortar flow can be evaluated quantitatively by the water retaining factor for sand (βs, water retained by sand) and the flowing factor for sand (Es, water-sand ratio by volume increase unit relative flow area of mortar).

View full abstract

The sectional area of urban-type elevated RC bridge piers is generally made small because of restricted conditions around the piers. For this reason, main reinforcements are usually multi-layers. In order to evaluate their influence quantatively, reversed cyclic loading tests were conducted on a large-size model (1/3 scale) that adopted the reinforcement arrangement of actual piers and a small-size model (1/10 scale). Accroding to the experimental results, a large size model showed no serious decline in ductility, of which ductility factor was nearly equal to that of a small model. However, reinforcement pull-out of a large size model was three times larger than that of a small model due to multi-layered reinforcement arrangements, which implies that reinforcement pull-out may give a considerable effect on the behavior of actual bridges. Next, on the basis of the relationship between the moment-rotation angle derived from reinforcement pull-out analysis of reversed cyclic loading tests, RC non-linear analysis was conducted, taking the reinforcement pull-out as a rotational spring. From the test results, it was found that actual load-displacement behavior is well simulated.

View full abstract

It has been reported that suitable quantity of the viscosity agent welan gum, a kind of natural water soluble polysaccharide, is very effective for stabilizing the rheological property of highly fludized concrete. In this paper, we have just studied basic properties of welan gum experimentally and effect of welan gum on fresh concrete such as self-consolidating property. As a result, we understand that viscosity of welan gum's water solution. is not affected by calcium-concentration and pH, except for a little bit high viscosity in alkaline solution. And we learned that it stabilizes the rheological property and mobility in small space of highly fluidized concrete to apply suitable quantity of welan gum for concrete, in addition, the product provides long term stability and improves self-consolidating property in wide range of slump-flow. We made clear partially how the product provides these effects.

View full abstract

The temperature rise due to cement hydration differs from locations of the mass concrete structure. The development of mechanical properties is dependent on the temperature rise condition. In this study, properties of concrete subjected to the adiabatic temperature rise condition were investigated experimentally. The supper low heat cement is also used as well as normal cements. The evaluating procedure for the time dependent development of mechanical properties is also presented as the test results.

View full abstract

In this paper, a method to estimate the crack height in concrete structures by ultrasonic testing is investigated. This method is based on the relation between the crack height and the maximum echo amplitude obtained from the received wave. In the beginning, a regressive equation for estimating the crack height is developed from the experiments for specimens with slits. Next, the reflection of incident wave at the bottom surface of structures is investigated on the influences on the echo amplitude of received wave. From these results, it is confirmed that the proposed method is applicable to actual cracks in concrete structures.

View full abstract

This study introduces an advanced simulation model of radar response on embedded layer in concrete. The applicability of the simulation is verified by comparing the test results with calculated results. In this model, the electromagnetic wave was assumed to have two different propagation modes at the interface (normal incidence and oblique incidence) depending on the subsurface objects. A new approach has also been proposed to analyze the attenuation in each interface which has different electromagnetic properties and the horizontal resolution of target object (reinforcement bar).
Since analytical results by proposed model coincide well with the test results, it is concluded that this simulation technique can be used to analyze radar response on subsurface objects in concrete.

View full abstract

Shear strength of concrete beams reinforced with FRP rods was studied through experiment and analysis. The effect of longitudinal tensile reinforcement on the diagonal tension failure strength was calculated using the lattice model. The evaluation method for shear carrying capacity was proposed based on the examination of contribution of concrete and shear reinforcement, respectively. The shear carrying capacity was determined from the ratios of concrete contribution at the failure to the contribution at the diagonal cracking and shear reinforcement contribution from the truss analogy to the actual contribution predicted by the lattice model. Finally, the applicability of proposed equation was examined by experimental data and it was found to be reasonable.

View full abstract

The difference between the normal-shear formulation and volumetric-deviatoric-shear formulation on which microplane models by Hasegawa and Prat, respectively, are based is examined by numerical analysis for a wide range of stress conditions. The normal-shear formulation can predict reasonably well the constitutive relations under biaxial stress and low confinement stress conditions but can not describe well the strength increase and brittle-ductile transition under high triaxial stress conditions. Prediction accuracy of the volumetric-deviatoric-shear formulation is poor not only in biaxial stress and confinement stress conditions but also in uniaxial tension softening.

View full abstract

The previously developed microplane concrete model is improved to expand its applicability and reformulated as the enhanced microplane concrete model serving as a more general constitutive law. One of the main improvements is to take into account the resolved lateral stress in normal compression response on a microplane as well as the resolved lateral strain. Another main improvement is to adopt a model for the transition from brittle to ductile fracture for the shear response on a microplane at increasing resolved normal compression stress. These improvements endow the model with the capability to describe complicated interaction between microplanes through the macroscopic stress tensor. Similar effects are taken into account in the microplane hysteresis rule using the concepts of back-stress and objective-stress.

View full abstract

It is verified that the enhanced microplane concrete model can predict well the experimentally obtained constitutive relations for concrete reported in the literature, covering various stress conditions. Extracting the invariants of the stress and strain tensors from the analytical responses obtained by the present model, one can reproduce the experimental relations in terms of the invariants. The present model can also predict the stiffnesses for reversible nonlinear elastic response during unloading and reloading, which are obtained by applying small loading pulses. Analysis of concrete confined by a steel tube confirms that the present model can describe the passive confinement effect well. Examination of the microplane responses in each analysis explains the load-carrying mechanisms in concrete in terms of the responses on the microplanes.

View full abstract

The preventive effects of mineral admixtures and concrete surface coatings against chloride attack is reported. Concretes of high, low and medium water to binder ratio, with and without mineral admixtures, or with and without a protected surface coatings were designed. Reinforced concrete slab specimens were subjected up to 70 cycles of wetting and drying by ponding 4.0% sodium chloride solution and drying in atmospheric air. And, a literature survey was conducted. As a result, it can be said that the service life of concrete structures incorpolating mineral admixtures or protected with surface coating materials becomes significantly longer than that of the structures made of plain concretes when exposed to chloride environments.

View full abstract

The deveropment of a concrete which consolidate under its own weight could lead to substantial improvement in the quality of concrete structures. In order to realize such self-consolidating concrete, high range water reducing agent (HRWR) and fine powdered materials were used. Furthermore a special viscosity agent was used to stabilized flowability of the concrete. In this paper, the results of experiments on fresh concrete properties were provided. Influences of factors such as water-to-powder ratio, dosage of HRWR, volume fraction of coarse aggregate etc. were investigated regarding the flowability and filling capacity of the concrete. From the results obtained herein, mix-proportioning guide line for the self-consolidating concrete could be established.

View full abstract

This paper presents various aspects of the kinematic nonlinear interaction of coupled RC/soil system under static and dynamic loads. Conducted are parametric studies for two types of underground structures subjected to high shear deformation transferred through the nonlinear surrounding soil. In this analysis influences of several factors, such as material nonlinearity of RC and soil, stiffness of structure and reinforcement ratio, are investigated. Failure modes, residual deformations and induced force to the RC from soil are examined for rationalized guidelines serving future improvement of the underground structural design.

View full abstract

Most of the indices developed for evaluating pavement surface conditions are formulated based on an assumption that they can be uniquely evaluated from the severity of physical distresses. However, each distress takes place by assorted causes and commonly appear in diverse patterns.
Fuzzy sets theory was applied in this study to develop a new pavement surface evaluation method. It was found that no explicit critical points exist which give the criteria for repairs. Each rating on necessity for repairs varies gradually according to the change in surface condition scores calculated by the new formula developed by fuzzy quantification theory.

View full abstract

The behavior of concrete and reinforced concrete structures is significantly affected by their sizes. The size effect on flexure and shear strengths of concrete beams has been already confirmed experimentally. This paper presents some results of the size effect on flexure and shear failures for different concrete and reinforced concrete beam sizes subjected to concentrated and uniformly distributed loads. The analysis was carried out by a computer simulation using the program ANACS (Advanced Nonlinear Analysis of Concrete Structures). Using the arc-length method the post peak behavior can be predicted well even for snap back instability.

View full abstract

An enhanced computational model for the prediction of reinforcing bar behavior under the generic condition of axial pullout and transverse displacement is presented. Based on the compatibility relationship between the transverse displacement and the curvature induced in the embedded bar, the localized phenomenon of the bar close to the interface is formulated, and its formulation makes it possible to express the reduced pullout stiffness of embedded bars encountered under combined axial pullout and transverse dowel action.

View full abstract