Time-dependent-change of flowability of fresh concrete is very important for developping concrete practice design method. In this study, as the first step of establishing a method for predicting the change, time-depending-change test of highly flowable mortar was carried out. The main factors of this experiment were dosage of superprasticizer and temperature of mortar. The test showed that rheological constants becomes larger with time for less dosage of superprasticizer and higher temperature of mortar. A prediction model of time-dependent-change of viscosity for highly flowable mortar was investigated referencing Hattori-Izumi theory. The stability ratio of the theory was estimated using the experimental results The ratio varies with dosage of superplasticizer and temperature of mortar. It is concluded that the prediction model can be developed when the variation of the stability ratio is fully understood.
Authors have been studying for several years as for the effective utilization of sludge water produced in ready mixed concrete plant containing cement and fine particles of aggregate. Nowadays, JIS A 5308 permits the usage under 3 percent as solids of sludge for the unit content of cement of new concrete. This study, in order to utilize the larger quantity of sludge water than that now allowed in the mixing plants, is to obtain the basical data on the properties of fresh concrete and of hardened concrete. In this study, the influence of composition of sludge and double adding of setting retarder has been discussed experimentally on the view points of slump, bleeding, compressive strength and drying shrinkage. From the results of this study, it was clarified that in the range of cement: fine sand is from 1:1 to 8:1, the composition of sludge has no large influence on the properties of new concrete. And the double adding of setting retarder has no good effect on the improvement of properties of sludge.
The purpose of this study is making the performance of the recycled aggregate using the aggregate test result of the recycled aggregate into an indicator. And the last purpose of this study is modifying to the recycled aggregate concrete with which are satisfied of the performance demanded with the indicator of the recycled aggregate. It tries to predict estimate Carbonation and Drying shrinkage of the concrete which mixed recycled aggregate using the indicator of recycled aggregate from the result of an experiment in the first half of this paper. The method for modifying to the mix design of the recycled aggregate concrete which has the strength demanded using the prediction equation obtained from the result of the compression test of the concrete in the second half is shown.
Recycled aggregates, may give an important contribution towards decreasing the negative consequences that production and dumping of constructions and demolition waste nowadays impose on the environment. This paper describes an experimental investigation on the properties of fresh and hard of recycled concrete mixing normal aggregates with recycled ones. The results of the investigation are as follows: The recycled concrete owns almost same characteristics of consistency and entrained air as normal concrete. The mixture of recycled aggregates negatively affects the performance of fresh concrete. Meanwhile, the decrease of strength and elastic modulus in the hardened concrete is slightly small due to the increase of replacement of recycled coarse aggregates. Also in the using of large amount of recycled aggregate, it causes the deduction of durability, and the increase of drying shrinkage and carbonation.
The wedge splitting test method developed by Tschegg was applied to investigate the fracture mechanical properties of concrete. The load-displacement curves of concrete, mortar and steel fiber reinforced mortar under the mode I fracture conditions were measured by different notched specimens and wedge splitting procedures. From the load-displacement curves, fracture parameters such as the specific fracture energy and notch-tensile strength were analyzed. The influences of the specimen size and ligament length on the fracture parameters were investigated from the analytical results. The observed differences in the fracture parameters between wedge splitting tests and three-point bending tests were also analyzed and discussed.
A gas pressure difference of 0.2N/mm2 was maintained between the cross sections of concrete with simultaneous increase of loading in the split tensile strength test configuration. A single crack that formed in the longitudinal direction parallel to the loading increased the gas permeability of the concrete. It was found that gas permeability was gradually increased at a crack opening of about 0.02mm and then rapidly increased until the crack opening reached 0.08mm. The degree of water saturation of concrete had significant effect on the formation of the crack and hence failure of the concrete under investigation. Oven dried concrete exhibited gradual increase of the gas permeability while water saturated concrete showed rapid increase of the gas permeability at the crack opening of 0.02mm. In this way the gas permeability of concrete subjected to the split tensile strength test was controlled by the failure mechanism.
It is generally considered that the admixing of fly ash improves various properties of concrete including durability. However, the admixing of fly ash also reduces the resistance against carbonation of concrete due to consuming Ca(OH)2 by pozzolan reaction. Then, it is important to evaluate the corrosion behavior of reinforcing steel embedded in concrete using fly ash. In this study, the influence of fly ash admixed into concrete as the substitute for cement or fine aggregate on corrosion behavior of reinforcement due to both chloride attack and carbonation, was evaluated by means of electrochemical techniques. The results showed that when fly ash was admixed as the substitute forr fine aggregate, restrained permeation of CO2 or Cl- into concrete resulted in small corrosion loss of steel. However, when fly ash was admixed as the substitute for cement, corrosion loss of reinforcing steel was not restrained under the severe corrosion condition in this study.
Six kinds of coarse aggregates were used in order to evaluate the reactivity of alkali-silica reaction of aggregates by using JIS A 1145, 1146 and ASTM C 1260 methods. The evaluation obtained by the chemical or mortar bar of methods specified in JIS did not agree with that by the accelerated mortar bar method specified in ASTM. The expansion of mortar bar due to ASTM C 1260 was dependent on the type of aggregate. It was also observed that the expansions of mortar bar under the accelerated condition (in NaOH solution of 1mol/l at 80°C) were influenced by the size of specimen, added alkali content and alkali content intruded into specimen from the solution in test container during test period.
Recently, it has been reported that corrosion in reinforced concrete members can be attributed due to defects in construction such as joint. And concrete near the joint is easily penetrated by carbon dioxide and thus the steel bar becomes corrosive. However, there are only few researches that investigate the corrosion rate of the steel bars at the joint in carbonated concrete members. Therefore the following investigations are carried out in this study. First, to investigate the corrosion rate of the steel bar near the joint in carbonated concrete members in laboratory. Second, to investigate which control method, electrodeposition method or surface-sealing method, is effective to reduce the corrosion rate on the steel bar near the joint in carbonated concrete members in laboratory. And lastly, to verify the results of the first two objectives in existing reinforced concrete member induced by carbonation. In summary, it was shown that the corrosion rate on the steel bar generally becomes high at or under the joint. And it was confirmed that electrodeposition method was more effective as control method for the reduction of the corrosion rate on the steel bar near the joint in carbonated concrete member than surface-sealing method.
In Japan, the polymer-modified cement mortar (PCM) with the corrosion inhibitor has often been used as repair materials for deteriorated reinforced concrete structures due to the chloride-induced steel corrosion. In this study, the reinforced concrete specimens with two levels of chloride content were prepared and exposed to wet and dry cycles in the chamber for a long period to clarify the macro-cell corrosion of steel bar in the concrete. The effectiveness of the type and dosage of corrosion inhibitor, LiNO2 or Ca(NO2)2, in PCM and the degree of chipping around steel bars in repair work in preventing the steel corrosion in concrete were comparatively investigated by means of electro-chemical measurements such as linear polarization resistance and AC impedance methods. From the experimental results, it was found that PCM with both corrosion inhibitors of LiNO2 and Ca(NO2)2 had almost the same effect in preventing the steel corrosion when their NO2- molecular ratio to Cl- was constant, and that the chipping and patching work beyond steel bars was more effective in restoring the passive state of steel bars. Furthermore, both the linear polarization resistance and the AC impedance methods were very useful as a nondestructive inspection method for estimating the corrosion behavior of steel bars in repaired and unrepaired concrete with PCM.
Recently, polymer-modified mortars have been used for repairing damaged concrete structures, but their adhesive strength to concrete substrates has been variable and the effects of treatments of concrete substrates have not carefully been considered. In this study, the effects of treatments of concrete substrates on the adhesive strength of polymer-modified mortars to the concrete substrates were investigated for two types of concrete substrates with different water permeations, four types of polymer-modified mortars with polymer-cement ratios of 0 and 5%, and a repair mortar. The treated concrete substrates were in the absolutely dry condition, water-saturated and surface-dried condition and primer-coated condition. The polymer-modified mortars were placed on the concrete substrates, and cured at 20°C and 40% (RH). The adhesive strength was measured at 7 and 28 days after placing. As a result, the adhesive strength of the polymer-modified mortars to the concrete substrates with high water permeation was affected by the treatments. The adhesive strength of the polymer-modified mortars to the primer-coated concrete substrates was higher than that to the concrete substrates treated with other methods.
Surface coating for concrete has been used for damage from salt injury or neutralization. We have studied adhesive evaluation technique on coating for concrete structure because some parts of coating were peeled off at the early stage of coating. We have also examined adhesive characteristics of coating in order to find out negative factors in painting execution. In this paper, we report the results of the evaluation and the examination, and also discuss a test method of coating for concrete structure, aiming at the future specifications.
From the viewpoint of deterioration mechanism of concrete structures, water is one of the most important factors. If water vapour permeability is required to control water content of concrete structures, silane surface treatment is typical hydrophobic surface treatment which restricts water penetration into concrete, but allows water vapour to move out. In this study, the influence of molecular structure of solvent-free silanes with various application rate and water content of concrete on the hydrophobic performance was investigated. As results, the influence of molecular weight of solvent-free silane and water content of concrete was cleared. Hydrophobicity of concrete is influenced by impregnation preformance which depends on molecular structure of Silane. In the repair of existing concrete structures, silane with large alkyl size which has much better good impregnation performance are expected to have best performance.
The purpose of this study is to investigate the application of high fluid mortar for patching materials. Patching works are used for popular methods to repair or strengthen the concrete structures. In the case of bigger volume is required in replacing the concrete member, patching with framework or spraying is applied as recasting method. This paper describes the possibility of high fluid mortar, which can be used for patching materials under severe conditions. This high fluid mortar has been developed for non-shrinkage grouting materials. The main improvement in this investigation is to add polyester based shrinkage reducer and mix the polyolefin based plastic fibers complexly.
The most of piezoelectric ceramics have strong anisotropy caused by perovskite crystal structure. The ferroelectric properties of polycrystals are dominated by microscopic crystal orientations. In our previous study, a crystallographic homogenization method has been proposed to evaluate macroscopic ferroelectric properties with consideration of microscopic inhomogeneous structures. In this study, ferroelectric properties have been investigated for two kinds of piezoelectric ceramics, BaTiO3 and PbTiO3. Especially, the influence of microscopic crystal orientations on macroscopic ferroelectric properties was numerically studied. It was concluded that PbTiO3 polycrystal shows inferior piezoelectric constant but BaTiO3 can have superior one compared with single crystal by controlling crystal orientations. This phenomenon could be explained by crystal orientation dependence of ferroelectric properties of single crystal.
Multiple wave scattering in unidirectional fiber-reinforced composite materials is studied computationally for elastic shear waves polarized parallel to the fibers. In this paper, a collocation method is proposed to numerically solve the system of multiple scattering equations expressed in terms of the eigenfunction expansion coefficients of the wave field. The computation is shown to be facilitated by assuming certain periodicity of the fiber arrangement, and taking only a few low-order terms of the expansion valid for the wavelength much larger than the fiber radius. Using the proposed method, multiple scattering of the shear wave in unidirectional SiC/Ti-alloy composite is analyzed, and the macroscopic as well as the microscopic wave fields in the composite are demonstrated. Furthermore, the phase velocity of the composite is identified from the analysis, which dependence on the frequency and the fiber volume fraction is discussed in detail in comparison to the results due to some previous multiple scattering theories.
Subject to an inclined load, we obtain the energy release rate for interface cracks in an isotropic elastic material with various modulus ratios. The energy release rate is calculated by the path independent E-integral using the finite element method with a singular element. In the finite element analysis, we impose avoiding the overlap of the extended crack, which may occur in the large angle kinking. Under the maximum energy release rate criterion, we examine the extension behavior of the interface cracks.
A simple method for measuring Young's modulus of a coating layer is proposed based on a free bending vibration, and an experimental approach, by which a first-mode natural frequency of a flexuaral vibration produced by an impact of hammer is measured, is tried to estimate Young's modulus of the coating layer. The natural frequency equation with variable of the specimen geometries and Young's modulus is obtained by Timoshenko beam theory, and then Young's modulus of the coating layer is estimated by minimizing the objective function defined from the natural frequency equation. The proposed measuring method is applied to PMMA coating and thermal barrier coating. It is shown to be able to estimate the Young's modulus of both of coatings by the proposed method with good accuracy.