This paper describes the validity of a new parameter for the content and grading of fine aggregate used in the quantitative rheological formula of fresh mortar when the mortar is assumed as a Bingham body. The rheological constants of fresh mortar, i.e. the yield value and the plastic viscosity were measured at 20±2°C with a parallel-plate plastometer using the mortar specimens of 30cm in diameter and about 3cm in height. All the measurements of these rheological constants were carried out by the same procedure within six minutes after mixing. The consistency of each mortar mix ranged from 110 to 250 in terms of JIS flow value. The rheological constants of fresh mortar using coarser fine aggregate were found to be smaller than those of mortar using finer one at the same mix proportion. By assuming that the particle of fine aggregate is a sphere, the effective volume fraction was obtained from the fine aggregate volume fraction of mortar and the thin paste (10μm) adhered over the surface of the particles. A good correlation was obtained between the fine aggregate effective volume fraction and the yield value or the plastic viscosity. So this parameter is considered suitable for the evaluation of the effects of grading and content of fine aggregate on the rheological constants of fresh mortar.
It is well known that the creep of concrete is influenced by the ambient relative humidity. But there is no sufficient information about the effects of moisture content in concrete specimens at the loading age on the creep behaviour and other mechanical properties. This experimental program was carried out to investigate the effects of moisture content on the strength and creep of concrete under uniaxial and triaxial (i.e. hydrostatic pressure) compressive stress at 30°C. And the dependence of moisture content on the visco-elasticity of concrete was discussed rheologically. The compression creep tests were performed under the following conditions; the moisture contents were 100% (wet), 68, 44, 14, 0 (dry) and -4% (over dry), and the creep stresses applied to the sealed concrete specimens were 100, 200 and 300 (kgf/cm2). The test results showed that the compressive strength, Fc and the elastic strain, εc of concrete decreased with increasing moisture content, φ. It was considered that the strength reduction may be due to the change of surface energy, γ in the hydrated cement gel, and the larger elastic strain at lower moisture content level was brought in as the result of growing of void and crack in concrete during drying procedure. On the other hand, the moisture dependency of creep strain, εc was greatly different from the case of elastic strain: the magnitude of creep strain increased rapidly with increasing moisture from 0% to 40%, and then became nearly constant in the range of 40% over. From these facts, it was considered that the refraction point at 40% moisture in the (φ-εc) curve was brought by the repulsiveforce disjoining pressure which acts among many gel particles.
Ordinary cement concrete and mortar have such weakness as significant drying shrinkage, low strength and inferior extensibility, and thus they easily cause shrinkage cracks. It has already been known well that the steel fiber reinforcement of the concrete and mortar is very effective to the reduction of their drying shrinkage. Recently, surfactant-type shrinkage-reducing agents for the concrete and mortar have been developed in Japan. However, the composite effects of steel fiber reinforcement and shrinkage-reducing agent modification on the concrete and mortar have not yet been reported. The purpose of this study is to make clear the drying shrinkage reduction of steel fiber reinforced mortar containing a shrinkage-reducing agent. Steel fiber reinforced mortars with a shrinkage-reducing agent are prepared with variations of shrinkage-reducing agent and steel fiber contents, and tested for drying shrinkage and strength. The conclusions obtained from the test results are summarized as follows: (1) The drying shrinkage of the mortars is greatly reduced with increasing shrinkage-reducing agent and steel fiber contents, and becomes approximately one-half of that of ordinary mortar (without the steel fibers and shrinkage-reducing agent), (2) The drying shrinkage can be predicted as a function of the shrinkage-reducing agent and steel fiber contents and water-cement ratio, and (3) The addition of the shrinkage-reducing agent to the mortars does not deteriorate their strength.
The ductility improvement of confined concrete and steel fiber reinforced concrete is mainly due to the lateral confining effect of lateral bars and steel fiber, respectively, caused by the Poisson's effect of concrete after failure; and this effect can be related to the behavior of plain concrete under multiaxial stress states. Thus, it is quite important to obtain the complete stress-strain relation from the reliable experimental data on the post-failure behavior of concrete under low hydro-pressure, when the ductility improvement of such composite concretes is analytically discussed. In the present study, the effects of various parameters on the plastic deformation behavior of axially loaded plain concrete subjected to low lateral confining stress were examined. The parameters used included the shape of specimen, water-cement ratio, magnitude and loading path of lateral stress, and ratio of two lateral stresses. Furthermore, the effects of the end confinement by steel ring, end friction, and steel fiber reinforcement on the plastic deformation behavior of concrete were discussed.
The Japan Society of Civil Engineers has recommended the allowable chloride content of fine aggregate in RC and pretensioned PC member to be 0.1% and 0.03% by weight, respectively. In Kyushu about 90% of the fine aggregates used for concrete works are sea sand. However, the relationship between the salt content of concrete and corrosion of reinforcing bar and PC wire has not been clearly known and the basic concept for the recommended salt content is not firmly established yet. Under these circumstances, the authors have made experimental studies on rusting of reinforcing bar and PC wire in concretes. Although the experiments are still being conducted, the results up to date are as follows. (1) The measured values of salt contant in the specimens placed on land were found to be reduced to about one half of the designed amount, but in other cases in sea and on coast reached up to 1-2% near the surface. It is thought that the phenomenon for the latter cases was caused by infiltration of chloride ions. (2) Though the PC wires were covered with rich mix concrete, their rusting was remarkable as compared with that of reinforcing bars. In the case when the salt content of concrete was 0.2-2.0%, the pitting due to rust began influencing upon the ultimate tensile strength of PC wires. (3) When the salt content of concrete was 0.5-1.0%, the percentage of rusting weight of steel became remarkable. Every effort should be made to keep the salt content as low as possible when placing concrete.
The employment of confined concrete with circular reinforcement in the compression zone of concrete flexural members improves the ductility of those members so significantly. Therefore, the mechanical properties of the confined concrete should be revealed in order to establish a ductility design method for designing advanced asseismic concrete structures. The objects of this study, in which different experimental variables were adopted from those used in other researches, were to investigate the strength and deformation characteristics of concrete confined by lateral circular reinforcement and to establish the equations for evaluating the compressive strength (Fcf), corresponding strain (ε0, cf) and average gradient of falling branch in the region from ε0, cf to 2ε0, cf of the confined concrete (Ecf). The variables considered were the magnitude of average confining stress (psσsy), the ratio of pitch of circular reinforcement to the diameter of specimen (S/D) and concrete strength (F0). The main results obtained are as follows. (1) The equations for estimating the values of the above-mentioned characteristics were established by clarifying the effects of S/D, psσsy, and F0 on those characteristics. (2) In order to obtain yielding of circular reinforcement, the value of S/D should be less than about 0.7 irrespective of the values of psσsy and F0. (3) The examination of feasibility of those induced equations, based on the experimental data about the scale effect of confined concrete as well as those presented by other researchers, shows that the proposed equations can be used to estimate the values of Fcf, ε0, cf and Ecf very successfully.
The necessity of systematization has been widely discussed for maintanance, diagnosis, repair and rehabilitation of existing bridges. This study was intended to give objective and quantitative basis for the rating and the evaluation of serviceability of cracked reinforced concrete slabs. The factors used to judge the serviceability of slabs were selected and rated quantitatively, and the applicability of the reciprocal averaging method and the fuzzy analysis were tested as the synthetic rating method. The results obtained are summarized as follows: (1) The current rating method based on “crack density” was not able to evaluate the extent of crack penetration into the slab, and the crack density did not correspond to the load carrying capacity of the slab when it exceeded a certain degree. (2) The reciprocal averaging method as one of the synthetic rating methods was found to be effectively used by taking more than 3 evaluating factors. It was possible to evaluate quantitivly the relative serviceability by selecting the upper and the lower limits. (3) The fuzzy analysis may possibly be used to do rating accurately without trying extra measurments and to estimate the type of damage in reinforced concrete slabs.
Viscoelastic constants of PMMA under dynamic load have been determined in the past with several methods based on the theories of longitudinal vibration, lateral vibration and longitudinal wave propagation. In this paper, the values of these constants used in the 3-elements linear viscoelastic solid model were employed to make the numerical prediction of impact response of PMMA. The theoretical results were obtained by using the one-dimensional longitudinal viscoelastic wave propagation theory and Bernoulli-Euler theory for viscoelastic beam. The impact load history was calculated numerically by using the nonlinear integral equation derived from the Hertz theory of contact. The time histories of strains and deflection were obtained from the numerical values of impact load. The strains on a rod and a beam were measured with strain gauges, and the deflection of a beam was obtained from the output of an optical follower measured in a short period after lateral impact of a rod on a beam. The theoretical predictions were in good agreement with the experimental results. It was shown that the time history of strain on a rod was more sensitive to viscoelastic constants than that on a beam or the deflection history of a beam, and the short time response of deflection of a beam after impact was scarcely affected by viscoelastic constants. This should be a useful knowledge when the method for determining viscoelastic constants is evaluated.
The effect of particle concentration on the sand erosion damage of polystyrene was investigated by using the sand-blasting type test method. Glass-beads with diameter of 120 and 150μm were used as impacting particles. The impact velocity was varied from 15m/s to 100m/s, the particle concentration defined as the weight of particles contained in a blasting air was from 0.2g/l to 30g/l, and the impact angle was from 30 deg to 90 deg. The erosion rate decreased gradually until a certain value of particle concentration was reached, and then decreased abruptly with an increase of particle concentration. Corresponding to this behavior, two different erosion damage mechanisms were observed. At relatively low impact velocity and/or particle concentration, so called the ring-pattern damage was observed and the damaged pattern changed to imperfect shape with an increase of particle concentration. This was due to the interference of impacting and rebounding particles. Consequently, the erosion rate decreased as the result of lowering of average impact velocity. In the other damage mechanism, so-called heat-deformation damage, which was observed at relatively high impact velocity and/or particle concentration, large deformation of material occurred remarkably. This was due to softening of material by heat generated by particle impact, and the weight loss, therefore, decreased. The damage transition from the ring-pattern to the heat-deformation depended on impact velocity and particle concentration, e.g. it occurred at lower particle concentration when impact velocity was relatively high and vice versa. These behaviors were also discussed from the viewpoint of kinetic energy of impacting particles.
FRP, one of the most general composite materials, is being used commercially more and more as a structural material. However, there have been only a few reports dealing with the degradation of inner structure of FRP due to fatigue. The present paper deals with this problem of degradation in FRP during the fatigue process. The FRP used in this study were GRP, CRP, and hybrid composites (which are composed of the former two). Firstly, the strength of GRP and its constituents was measured and the results were compared. Secondly, the residual strength of GRP and the change in strength of glass fiber strands in the matrix during fatigue, as well as the fatigue life of GRP, were investigated. The fatigue process of GRP was related to the degradation of the constituents in the matrix from the results mentioned above. After carrying out the similar experiments and discussion on CRP, the fatigue process of hybrid composites was discussed by comparing those of other two materials.
The present paper deals with the preparation mechanical properties of three kinds of whisker reinforced aluminum matrix composites (Si3N4/Al, SiC/Al and K2O·6TiO2/Al). The squeeze casting method was employed for the preparation, and the bending and tensile strengths, the elastic modulus and the identation hardness of the composites were investigated. The results obtained are summarized as follows: (1) The composites were producible within the range of 10 to 45% volume fraction of whisker. (2) The bending and tensile strengths of the composites increased with an increase in the volume fraction of whisker, and the maximum bending strength was 860MPa at the volume fraction of 45% SiC whisker and the maximum tensile strength was 435MPa at the volume fraction of 43% SiC whisker. (3) The elastic modulus of the composites increased with an increase in the volume fraction of whisker, and agreed appoximately with the prediction based on the rule of mixture. (4) The indentation hardness of the composites increased with an increase in the volume fraction of whisker. (5) The Si3N4 and SiC whisker reinforced aluminum matrix composites fractured, accompanying the failure of whisker. On the other hand, the K2O·6TiO2 whisker reinforced aluminum matrix composites fractured by separating at the whisker-matrix interface.
Embrittlement of Al-Ga alloys, containing upto 25wt% Ga, was investigated by the tensile tests at various temperatures, optical microscope and SEM observation methods. The results obtained are as follows. (1) At the range of temperature from -40°C to 100°C, the fracture stress of pure Al and Al-5wt% Ga alloy decreased slowly with increasing temperature, but that of alloys containing more than 10wt% Ga, even in solid solution, rapidly decreased at the range of temperature from 0°C to 30°C. (2) The elongation of pure Al and Al-5wt% Ga alloy increased with increasing temperature, but that of Al-10wt% Ga alloy dropped suddenly over the range of temperature from 0°C to 30°C, and the elongation of Al-17wt% Ga alloy was little at the range of all over the testing temperature. (3) The fracture of pure Al and Al-5wt% Ga alloy was of plastic type, but that of Al-10wt% Ga alloy was an intergranular cracking. (4) The elongation of Al-10wt% Ga alloy increased with increasing temperature above 100°C. From the above results, it is clear that the embrittlement trough exists in the solid solution Al-Ga alloy.
The constant tensile speed and constant load tests were carried out in liquid zinc on the precracked specimens of Ni-Cr-Mo steel (SNCM 439) and Cr-Mo-W-V tool steel (SKD 6) quenched and tempered, and the embrittling behavior of both steels were compared with that in low strength steel (SS 41). The maximum load Pmax obtained from load P vs. deflection Δx2 curve was much smaller in liquid zinc than in air or salt bath both in SNCM 439 and SKD 6 steels. In SNCM 439 steel with medium strength, the maximum load in liquid zinc Pmax(zinc) decreased with a decrease in tensile speed x1 and with an increase in testing temperature T, and the crack propagation was stable before and after Pmax(zinc) as did in low strength SS 41 steel. In SKD 6 steel with highest strength, on the other hand, Pmax(zinc) was only slightly dependent on x1 and T, and the unstable crack propagation ocurred at Pmax(zinc). The crack propagation in liquid zinc occurred along preaustenite grain boundary in both SNCM 439 and SKD 6 steels. The embrittlement coefficient, the ratio of maximum load in liquid zinc to that in salt bath or air, φ=Pmax(zinc)/Pmax(salt), was smaller in the steel with higher strength. Under the constant load test, the crack growth initiation time in liquid zinc ti increased with a decrease in stress intensity factor K, and ti was shorter in high strength SKD 6 steel than in low strength SS 41 steel under the same K.
It has been ascertained that the slip-initiation in iron-foil under fatigue is almost dominated by the linear cumulative damage rule ∑ni/Ni=1 irrespective of temperature rise or fall when the ambient temperature varies stepwise. In this paper, in order to establish the rule dominating the slip-initiation under the condition of continuous temperature change, the validity of an integral form of the rule, ∫(1/N)dn=1, was examined by the tests in which the temperature was varied linearly in the low temperature range. The following conclusions were drawn from the results obtained. The linear cumulative damage rule ∫(1/N)dn=1 almost holds for the slip-initiation under the condition that the temperature varies linearly at low temperatures irrespective of temperature rise or fall. Therefore, it is considered that the rule is applicable to the slip-initiation under any temperature variation in such a temperature range that strain aging does not occur in iron-foil.
The tensile fatigue behavior of adhesive bonded joint of FRP was investigated under low cycle repeated stress, and the effect of the type of overlay plate in the adhesive bonded part and the effect of water environment on fatigue strength were examined. The specimen used was ortho phthalic acid unsaturated polyester reinforced with glass mat or roving cloth. The mother plate and overlay plate of the specimen were made of the same material. The fatigue testing machine was developed originally by the authors and it was driven by compressed air. The stress cycle was 100cycles/min. constant and the testing temperature was 40°C constant. The following results were obtained from the experiments: (1) The fatigue strength was almost the same for all type joints, when the shearing strength of the adhesive surface area was adopted as the stress amplitude. (2) The strength of adhesive bonded joint was ranked between 1/4 and 1/10 levels of that of the plain specimen. (3) The fatigue strength of adhesive bonded joint was much influenced by water and it was decreased considerably. (4) The formula useful to estimate the fiatgue life was proposed as Eq. (1).
This paper describes a method of predicting low-cycle fatigue life in long-term hold-time tests at elevated temperatures. In order to develop a proper life prediction method under creep-fatigue conditions, especially for the case of long hold-time, the correlation between the static creep rupture data and the low-cycle fatigue data in hold-time tests was examined. The specimens used were an unnotched and three round notched ones of austenitic stainless steels of SUS 304 and SUS 316 having elastic stress concentration factors of 2.6, 4.2 and 6.0. Zero-to-tension low-cycle fatigue tests were carried out by four modified creep machines at 873K using trapezoidal stress waves with 10, 30, 60, and 1440min hold-time. Static creep tests were also carried out on those specimens. Two fracture regions were found to exist in the failure cycles-test frequency plot: one is the cycle-time dependent fracture region where the elastic stress cocnentration reduces the low-cycle fatigue life and the other is the pure time dependent fracture region where it does not. A new prediction method of fatigue life of the unnotched and the notched specimens in low-cycle tests with various hold times from the static creep rupture time and low-cycle fatigue life data obtained in no hold-time and comparatively short hold-time tests was proposed.
The charge carrier trapped centers responsible for the thermoluminescence in irradiated NaCl:Cu+ and NaCl:Ca2+, Cu+ single crystals have been detected by ESR. Cu2+ ions accompanying positive ion vacancies at their next nearest neighbor sites disappeared by heating the NaCl:Cu+ crystals at about 70°C, which corresponds to the temperature where the first glow peak appears. This indicates that the peak is due to the recombination of thermally released electrons and Cu2+ ions. The higher temperature glow peaks showed different emission spectra from that of the first peak, indicating that the mechanisms are different. The Cl2- molecular ions stabilized by the I-V (impurity-vacancy) dipoles and the D1-like centers were observed in NaCl:Ca2+, Cu+ crystals, which work as the hole trapped species in thermoluminescence.
The solution within the crevice of SUS 304 stainless steel during the nucleation and growth of crevice corrosion in a chloride solution were analyzed chemically. An accelerated crevice corrosion test method using activated carbon was applied to develop crevice corrosion. The experimental results obtained are following: (1) The current passed during the crevice corrosion test had two-stage linear relationship with the concentration of metal ions in the crevice. Selective dissolution of Cr took place. (2) The Concentration of chloride ions had two stage linear relationship with the metal ion concentration dissolved into the crevice. (3) pH of the solution in the crevice depended on the current passed in the crevice corrosion test. (4) The ultra-violet absorption spectra of the solution in the crevice had a few peaks different from those of a solution prepared by mixing chlorides of Fe, Cr and Ni. (5) The polarization curve in the pre-electrolyzed solution did not exhibit the passive region presumably due to the formation a complex of hydroxy-chloride in the crevice.