This paper discusses the chemical, physical and mineralogical properties of classified fly ashes by using of electrostatic precipitator and modified fly ashes by calcination at 500°C or plasma reactor. In addition, the influences of burning conditions and types of coals on the properties of fly ashes are investigated. It is proposed that the electrostatic precipitator can also be applied to the separator. The electrostatic precipitator in coal fired power plant has a number of hopper in the direction of flue gases. Blaine values of fly ashes collected at 1st, 2nd and 3rd hoppers are respectively about 3000 (ordinary), 5000 (fine) and 8000cm2/g (superfine), regardless of burning condition and types of coals. The glass contents of fly ashes become greater as their blaine values are raised. The adiabatic temperature rise of mortar containing fly ash is increased with the fineness of fly ash. The pozzolanic reactivity of fly ash at early stage and at later stage are respectively related to the fineness and the glass contents of fly ash. But, the early hydration of cement was retarded by addition of superfine fly ashes. The carbon content in fly ash influences on the paste fluidity. The carbon content in fly ash is decreased by calcination and plasma treatment and the fluidity of paste is improved by the removal of carbon, .
In order to use fly ash being discharged from the boilers of a coal fired in thermal power station effectively, the authors aimed at self-compacting concrete using high-volume fly ash. However, the qualities of fly ash vary in each of the power station. This study shows the effects that the replacing ratio, the qualities and the specific surface area have on the fluidity, the setting time and the carbonation depth about self-compacting concrete including fly ash. The results obtained are as follows: The fluidity is improved with the decrease of the specific surface area of fly ash. The setting time is increased with the increment of the specific surface area of fly ash. The carbonation depth of self-compacting concrete is very susceptible to the replacing ratio of fly ash. And the effect that the specific surface area of fly ash has on the carbonation depth of self-compacting concrete is small.
The expansion of concrete with calciumsulphoaluminate-type expansive additive containing excess free-lime was larger than that with the conventional calciumsulphoaluminate-type expansive additive or with the free-lime type expansive additive. When the conventional expansive additives were used in the blast furnace slag cement mortar, the effect is smaller than in portland cement, however, the effect of calciumsulphoaluminate-type expansive additive containing excess free-lime was same as that of ordinary portland cement. By controlling the particle size, calciumsulphoaluminate-type expansive additive containing excess free-lime resulted in considerably large strength development even under the same expansion level.
The purpose of this study is to investigate the influences of polymer composition and protective layer of redispersible polymer powders on the properties of polymer-modified mortar susing ordinary portland and ultra rapid hardening cements. Polymer-modified mortars are prepared with ordinary portland and ultra rapid hardening cements, and six types of redispersible polymer powders, and tested for workability, strength, drying shrinkage, porosity and X-ray diffraction quantitative analysis of cement hydrate. It is concluded from the test results that the properties of the polymer-modified mortars are influenced by the protective layer of the redispersible polymer powders. The effectiveness of the redispersible polymer powders depends on the cement used. The properties of the polymer-modified mortars are not related with pore size distribution.
In this study, two-dimensional shear deformational behavior of solid-liquid two-phase model material was grasped experimentally and analytically, and the influence of aggregate particle was discussed rheologically. As the results, the behavior of matrix around aggregate particles under shear deformation was observed, and this behavior can be simulated by two-dimensional viscoplastic finite element method (VFEM). According to the result of numerical analysis, the viscosity of suspension increases with increasing of dispersing degree of aggregate particle. Furthermore, in the experiment used the materials with many aggregate particles, the mechanism of increasing of rheological constants with the touch of aggregate particles was examined.
The authors have proposed a visco-elasto-plastic suspension element method using a non-continuum model to simulate dynamically the fracture behavior of concrete. In this paper, the constitutive law used in the analytical method is improved to express the deformation behavior of concrete under repetitive compressive loading. A constitutive law proposed contains viscous and elastic elements for shear after failure. Some analyses of concrete under repetitive compressive loading were carried out by using the method. As a result, the deformation behavior of concrete under repetitive compressive loading is clarified. Kaiser effect of acoustic emission is also confirmed by this numerical analyses.
Impact-echo technique is a method for nondestructive evaluation, detecting elastic waves due to a mechanical impact. Although the impact-echo is reported to be promising for quantitative estimation, an applicability to evaluation of post-tensioning tendon ducts is not confirmed yet. To this end, the basic theory of the impact-echo should be clarified. In this paper, a specimen containing an ungrouted duct is tested. Theoretically, frequency responses of the specimen depend on the size, orientation of the void, and P-wave velocity, while wave motions in concrete structures are characterized by material properties, incident waves, and size of members. Thus, the frequency response is studied from the relationship between the wave length and the depth of duct. Experimentally, impact tests are conducted by dropping steel balls and shooting aluminum bullets. The analysis is carried by the boundary element method (BEM). As a result, the detection of resonance frequency due to the presence of void is clarified, relating with impact frequencies and the depth of duct.
Electro-migration and diffusion of ion in electrolyte solution are theoretically described in the Nernst-Plank equation. Also, electro-migration and diffusion of ion can be related by using the Einstein's relation in dilute solution. In concrete, however, the relationship between electro migration and diffusion is still unclear. In a previous study it was shown that it is possible to assess the diffusion coefficients of chloride ion in ordinary portland cement mortar, by following the Nernst-Plank equation, Einstein's relation, Debye-Hückel theory and electro neutrality. In this paper, using the same method, the authors assessed the diffusion coefficients of chloride ion in mortar made of several binder.
This paper deals with the corrosion of steel bar in concrete with ground granulated blast furnace slag (ggbs). The steel corrosion in it were investigated with the aid of electrochemical measurement. The ability of ggbs concrete to protect steel from corrosion was superior to the one of the ordinary Portland cement concrete, although the chloride binding capacity of ggbs concrete is inferior to the one of ordinary Portland cement concrete. On the other hand, the carbonation rate of ggbs was faster and there was the risk of steel corrosion due to carbonation of ggbs concrete. And the steel corrosion in ggbs concrete exposed to both chloride and carbonation was produced earlier and more severe than the one in ordinary Portland cement concrete.
Influences of water/cement ratio, type and moisture content of artificial lightweight aggregate on deterioration of lightweight concrete due to freezing and thawing cycles were experimentally studied by measuring strain changes in specimens. As a result, at the early cycle lightweight concrete contracted more than thermal strain through the freezing stage and expanded during the phases of thawing. At the lowest temperature, the specimen using lightweight aggregate containing large amount of water content contracted more than the other specimen. When expansion instead of contraction occurred on freezing, the rate of residual strain per cycle increased and then quickly destroyed after several cycles. The increase in contraction strain suggests that not only the gel water but also moisture in lightweight aggregate has been transferred to mortar by freezing of water in the aggregate. When there is no spaces where the water can diffuse, high hydraulic pressure is occurring in the capillaries near at zero degree during freezing.
In order to clarify the effects of various factors on the ASR expansion in mortar treated by autoclave, an autoclave treatment was performed for mortar immersed in NaOH solution. As the factors, W/C ratio of mortar, the concentration of NaOH solution, the treatment pressure and the treatment period were selected. From the experimental results, it can be concluded as follows: (1) The expansion immediately after autoclave treatment increases as the treatment period becomes longer. (2) For the concentration of NaOH solution and the treatment pressure, the pessimum value which the expansion immediately after autoclave treatment becomes greatest exists. (3) For the mortar immersed in 1mol/L NaOH solution and treated at the treatment pressure of 0.05MPa and the treatment period of 48 hours, the ASR expansion immediately after autoclave treatment is equal to 42% of the expansion at the age of 6 months by mortar bar method according to JIS A 5308.
The reinforced concrete structures have been considered durable for a long time. But recently, it has been reported that they are deteriorated by reinforcement corrosion to be suffered from chloride attack. Desalination, which is an electrochemical treatment of chloride extraction from concrete, has been developed as an essential repair method. Steel bar embedded in concrete acts as a cathodic electrode through desalination process and sodium ions are gathered about the steel bar. In this study, expansion of concrete due to alkali silica reaction during and after desalination was examined in concrete having reactive aggregates.
Desalination is one of the electrochemical methods, aiming to remove chlorides from reinforced concrete structures. However, it is impossible to extract all of chlorides contained in concrete. For this reason, it is important to improve the chloride removal efficiency and to estimate the durability of structures after treatment. In this study, distribution of Cl- (total chlorides and water soluble chlorides) was examined after applying desalination. The effect of discontinuous treatment was also investigated. Secondly, change of half cell potential and polarization resistance with time were measured after desalination. The results showed that the steel protection effect due to applying desalination had been maintained for long time. However, in this study, it was difficult to improve chloride removal efficiency by means of intermittent treatment. So, measuring of half cell potential and polarization resistance is useful to monitor the steel condition after treatment.
This paper presents an estimating method for maximum responses of loads and displacements for repaired columns by degraded stiffness method. Proposed method is based on the correlated stiffness ratio between the column stiffness at the first yielding of longitudinal steels and that the estimated unloading stiffness of damaged last cycles. Degraded stiffness ratio 0.64 was obtained by the tests of R/C columns used in this paper. From comparisons between experimental results and analysis, it is shown that the proposed analytical method is applicable to estimating the load∼displacement relationships of repaired columns.
According to results of material testing for existing concrete bridges, we found not only degradation of concrete strength but also large scattering in strength within a same member. In this research, firstly, we modeled strength distribution using the finite Fourier transform procedure based on limited number of sampling core testing. And then, we modeled the degradation curve of concrete and make up a methodology for identification of deterioration parameters involved based on core testing results and estimation of initial status of concrete by introducing a nonlinear programming procedure. Furthermore, we conducted sensitivity analysis of strength distribution on shear strength of concrete member by using the elasto-plastic finite element method and proposed an estimation equation of shear strength of concrete member taking strength distribution into consideration.
In this paper using the available data on interior reinforced concrete beam-column joints tested by the authors, the evaluation method of bond behavior of beam bars before yielding passing through the joint has been proposed. Here the several influencing factors were analyzed and quantitatively evaluated. The following conclusions can be made: (1) The relationship between average bond stress in a joint region (oτav) and tensile strain of beam bars at the column face (oεst) was formulated for the single layered bar arrangement and for the outer bars of the double layered bar arrangement, in which the effect of the bar diameter to column depth ratio, concrete compressive strength, axial compressive stress levels of columns, and the ratio of top to bottom reinforcement areas were considered. (2) Applying the oτav-oεst equation, the relationship between average bond stress in a joint and tensile strain at the column face of the inner bars of the double layered bar arrangement (iτav-iεst) could also be evaluated by considering the deformation condition due to shear distortion and shear cracking widths of the joint panel. (3) The strain distribution of beam bars at the column face could be evaluated by considering the relationships of oτav-oεst and iτav-iεst.
The Si-Ti-C-O fiber bonded ceramic material was creep-tested under three-point bend loading at 1400°C, where deflection was measured at the loading point by means of the laser beam type extensometer. Furthermore, creep process was analyzed by using the convenient analytical method and F.E.M. The creep constitutive equation was successfully determined through an inverse analysis using F.E.M; parameters included in the equation were settled so that the calculated deflection-test time curve might coincide with the measured one. The calculation exhibited that compressive creep hardly occurred in this material. The convenient analytical method was useful for setting the initial values of the parameters in the FEM calculation. In addition, creep fracture patterns were revealed through SEM observations.
The present paper shows the effect of loading path on the fatigue degradation of plain woven glass fabric polymer matrix composites under tension/torsion biaxial loadings. The loading path significantly affected the fatigue characteristics at low cyclic fatigue. The effect of loading path on the fatigue strength and the modulus decay in shear with respect to the number of loading cycles was most significant when the normal stress was applied longer for each loading period. For such cases, the fatigue life became short and the shear modulus decreased much during an early stage of fatigue. The loading path also affected the internal damage accumulation. The matrix cracks were curved when the stresses were not applied proportionally. Peculiar phenomena were also observed in normal stress-normal strain curves both in tension and shear. A model was proposed to explain the phenomena. On the contrary, the effect of loading path on the fatigue characteristics was not distinguishable at high cyclic fatigue.
Troubles of electric components and electronic devices are mainly caused by failure of solder joining parts, which results from thermal cycle fatigue due to the mismatch of thermal expansion coefficients among constituents. Therefore, it is an urgent problem to clear the fatigue and creep properties of solder joint and solder itself. In order to clarify the strength and crack growth behaviors of solder joint in fatigue and creep, a series of fatigue and creep tests was carried out on Cu/60Sn40Pb/Cu joints under shear stress condition. Results of fatigue tests under different loading frequencies indicate that fatigue lives can be evaluated uniformly by taking cumulative loading time to failure as a key parameter. Observations of shear strain behavior during fatigue and creep process make it clear that fatigue lives and creep rapture lives are well predicted by the minimum shear strain rate. Furthermore, results of crack growth tests in fatigue and creep under Mode II shear stress condition reveal that the modified J integral well governs the crack growth rate.
The main objective of this study was to make clear the value of the tensile modulus of carbon fiber with diameter variation along longitudinal direction. For this purpose, the load-elongation curves obtained in the previous report were used, in which the tensile strength was only dealt with for single fibers with the gauge lengths ranging from 2 to 100mm. It was found that the mean of tensile modulus E3 was different for different gauge lengths when the fiber diameter was determined as the minimum diameter d3 among the three diameters measured at both ends and the middle of the gauge section. The main reason is in the fact that a large variation of the fiber diameter among the gauge length was only incompletely taken into account in the definition of d3. Consequently, the equivalent diameter deq and the equivalent stress σeq and strain εeq were defined in order to give the tensile modulus E regardless of the diameter and the gauge length. Combining the two dimensional distributions of d3 and deq for respective gauge lengths obtained by the numerical diameter data of 0.1mm intervals in the previous report, and the distribution of E3 as a function of d3 together with a simple transformation equation between E and E3 including d3 and deq, the distribution of the estimated tensile modulus E for each gauge length was calculated. It was shown that the mean values E of the estimated tensile modulus E for different gauge lengths agreed very well, and the value E=195.5GPa was obtained as the most probable value of the tensile modulus for PAN carbon fiber, by averaging the value E of respective gauge lengths.