Strength of concrete confined by spiral reinforcement is hardly estimated because the mix proportion, properties of aggregates and so on significantly affect the strength. However, in structural designing according to the J.S.C.E standard specification, the strength is estimated from results of test carried on only conventional concrete. In recent years, high-strength concrete with extremely low water-cement ratio and self-compacting concrete with larger mortar content have been developed and practiced. Furthermore, many types of aggregates e.g. recycled aggregate and lightweight aggregate have been used for concrete. In this study, the effects of aggregate properties and concrete strength under uni-axial load on concrete strength under tri-axial load were investigated. It is clarified that in case of recycled aggregate concrete and lightweight aggregate concrete, ultimate strength of spiral reinforced concrete column estimated according to the J.S.C.E standard specification will be much higher than actual strength, and the specification will estimate the strength with too much margin for high-strength concrete and self-compacting concrete, although the specification will be proper only for conventional concrete.
A study was made of a method for increasing the durability of concrete structures by reinforcing concrete with short fibers to prevent the falling of covering concrete due to corrosion and expansion of reinforcing bars. Fiber-reinforced concrete is required to (1) prevent concrete from falling, (2) have little influence on concrete composition and construction and (3) be economical. Steel fibers, which are generally used, and four types of organic fibers were examined. As a result of the study, it was found that the number of fibers added to concrete had a greater influence on the prevention of concrete falling than the strength of the fiber and that adding more than 300, 000 fibers per cubic meter could prevent covering concrete from falling.
The purpose of this study is to estimate the properties of concrete in consideration of distribution of coarse aggregate quality. The properties of several particles of coarse aggregates and the properties of small specimens, which contain one coarse aggregate each, were measured. In addition, the estimation method of compressive strength and freezing and thawing resistance of concrete was constructed using Rigid-Bodies-Spring Model. The propriety of the estimation method was confirmed qualitatively.
The purpose of this study is to investigate the applicability of Chinese sand and fine powders of industrial waste as fine aggregate. At first, three types of fine aggregate were prepared mixing crushed sand, river sand and two types of Chinese sand. It was investigated that the type of fine aggregate influenced the properties of concrete. Secondly, fine particles under 0.15mm were mixed with Chinese sand, because Chinese sand has a little quantity of fine particle under 0.15mm. Type of fine particle were crushed stone fine powder, ferro-nickel slag fine powder and glass fine powder. The effects of type of fine particle on the properties of concrete were examined. Test results showed that the concrete with Chinese sands was poor viscosity and much bleeding, and these properties were improved with crushed stone fine powder.
It is urgent task for road administrators to establish a recycling system of the wastes in construction sites and rest areas on expressways. In this paper, it is reported the development of recycled concrete aggregate made from a part of the wastes and the test results of the performance of the concrete noise barrier that includes the recycled aggregate. As the results, the recycled concrete noise barrier has about the same level performance in terms of the effect of intercepting noise and the load-carrying capacity compared with that of the conventional concrete noise barrier. In addition, the cost of the recycled concrete noise barrier is 15% less than that of the conventional one.
Self-comapacting high performance concrete is becoming more and more accepted for structural applications. The performance requirement may include ease of placement and compaction without segregation. Self-compacting high performance concrete is used for prefabricated constructions companies for improving quality variance of concrete and the environment of workers. However, it is well known that it is difficult to control the quality of the self-compacting high performance concrete with additional powders. Quality of the concrete is affected strongly by the quality of powder or water content of gravel. There is a slight variation of limestone powder quality used for producing the self-compacting high performance concrete continuously. The purpose of this study is to investigate the effects of fineness of limestone powders and particle-size distribution on the performance of self-compacting high performance concrete for stabilizing the production of the concrete.
Crushed stone powder is produced when crushed stone are produced. And recycled concrete powder is produced with producing of recycled aggregate. Those powders are hardly reused. High fluidity concrete needs appropriate amounts of power for preventing concrete segregation. So, the purpose of this study is to investigate the applicability of the crushed stone powder and the recycled concrete powder to high fluidity concrete and the influence of powder quality. At first, evaluation index for concrete segregation was examined for evaluating effects of the powder to flesh concrete. At the result, the ratio between coarse aggregate weight in lower concrete of cylindrical vessel and one in upper after tamping by steel rod more accurately expressed the segregation in contracting. Then, it was found that plastic viscosity of mortar and volumetric percentage of coarse aggregate in concrete mainly influence the index. Next, it was investigated the influence of the 15 powders on properties of high fluidity mortar. The mortar segregation is expressed by plastic viscosity of the mortar because of the previous result. At the result, the surface of the crushed stone powder and the recycled concrete powder is rougher than other powder. Thus, the mortar flow with those powders is decreasing with increasing the plastic viscosity when quantity of the using powder is increasing.
In Japan, approximately 7.6 million tons of coal ash is produced from thermal electric power plants in fiscal 1999. To protect the environment and make effective use of resources, methods should be established for effective and large quantity use of coal ash. In this study, mix proportion theory of concrete containing large quantity of coal ash was discussed. As a result, the formula that was presented for the concrete containing coal ash with constant portland cement content was shown to be applicable to the concrete containing coal ash with constant powder content. Next, the new method and its formula for the concrete that always performed the same compressive strength to the portland cement only concrete with the appropriate combination of the cement and coal ash content were shown.
Authors have been studying for several years as for the effective utilization of sludge water containing cement and fine particles of aggregate. Nowadays, JIS A5308 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. Especially, the influence of portland blast-furnace slag cement and air-entraining and high range water-reducing admixture (SP) 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 a good quality concrete could be obtained regardless of the kind of cement and admixture, even though the sludge mass of 9% of cement content and the sludge age of 3 days, provided that setting retarder was used adequately.
The delaminating and peeling concrete accidents for the tunnels or the bridges are the social problem in Japan. It is desirable to develop the concrete structures with high durability and high serviceability. The polypropylene fiber is believed to be one among the synthetic fiber to prevent the spalling of concrete fragment. As polypropylene fiber is elastic and flexible, it does not pierce the hands or the feet of the workers. It is easy to treat. The wide use of the polypropylene fiber is expected. However, the melting point of the polypropylene fiber is very low. It's about 160-170°C. The resistance to the fire accident of concrete with polypropylene fiber is very important for the safety of the public. In this study, the effect of temperature on the concrete strength and vapor explosion was examined. The air space by the vapored polypropylene fiber sets free vapor pressure of moisture in concrete. It is shown that the low melting point of the polypropylene fiber is not disadvantage at the fire accident on concrete structures.
Gypsum is widely used for the manufacture of various building materials because of its advantages such as rapid setting, good thermal insulating property and fire resistance, but their use is limited to interior finishings because of its poor water resistance. This paper deals with an improvement in the water resistance of gypsum composites by polymer modification and partial replacement of gypsum with ground granulated blast-furnace slag, silica fume and ordinary Portland cement. Polymer-modified gypsum-based composites are prepared with various polymer-binder (a mixture of gypsum and mineral admixtures) ratios, and tested for water absorption, flexural and compressive strengths before and after water immersion. In addition, the long-term water resistance of the polymer-modified gypsum-based composites with a superplasticizer are investigated by 3-y water immersion. As a result, SBR modified gypsum-based composites with optimum mix proportions are developed from the viewpoint of water resistance and strength development. The high water resistance of the gypsum-based composites is achieved by polymer modification, superplasticizer addition, and partial replacement of gypsum with the mineral admixtures.
A shot peening process is generally utilized as one of the surface treatment processes to improve the fatigue life and the fatigue strength of cyclically loaded components. This improvement is achieved by inducing compressive residual stresses and work hardening effects in areas close to the surface. But the influence of the shot peening process on fatigue strength is not clarified enough. It's significant technologically and industrially to clarify the influence factor of shot peening on the fatigue strength. Former study of author confirmed that main effect on the fatigue strength of the SUS304 steel hitted by controlled steel ball is the hardening of austenite structure itself due to the shot peening. In this study, the SUS329J1 steel having both austenite and ferrite phases was also investigated from the viewpoint of the work hardening of both structures. An effect of the residual stress on fatigue limit is not observed at all. As a result, we found that the work hardening of the SUS329J1 steel by shot peening was attributed to both the strain-induced martensitic transformation and the hardening of austenite and ferrite phase themselves. Especially, the ferrite phase influences the Vickers hardness distribution of shot-peened material, and the hardness increment of the austenite phase is larger than other phase and mainly due to the fine structure.
Rubber diaphragms are widely used as elements in the mechanisms of keyboard switches. Generally, in evaluating operational feeling of keyboard switches, it is important to analyze their loading and unloading behavior to establish their force-displacement curve. Loading and unloading behavior of a rubber diaphragm exhibits high nonlinearity due to geometric and material effects. In this study, the finite element method is used to analyze the behavior and the analytical results are found to be in full agreement with experimental results. In addition, it is defined that a change of the value of a property parameter against a unit change of the value of a design parameter is a sensitivity coefficient. A Newton-Raphson method using these sensitivity coefficients is applied to modify property parameters towards pre-defined target property parameters. By several results of numerical experiments, it is expected that this design system, which has each property and its design parameter vectors and its sensitivity coefficients matrix in the database, directly gives the designer proper values of design parameters and considerably reduce design times
Although woven fabric composite materials have high performance, it is very difficult to reveal their mechanical behaviours due to the geometric complexity by theoretical analysis. Especially under damage development, several kinds of failure mode such as matrix cracking, fiber breaking and transverse cracking in fiber bundle affect the mechanical behaviour strongly. In order to analyze the mechanical behaviour, three-dimensional finite element analytical procedure based on damage mechanics has been developed. In this paper, the developed procedure is applied to plain woven fabric composites, and the mechanical behaviour under damage development by on-axis tensile load has been analyzed. On the other hand, on-axis tensile test has been performed in SEM and the damage development at the edge cross-section of specimen has been observed. As a result, it can be confirmed that the calculational and the experimental results have a good agreement. Then, the mechanical behaviour depends on the edge effect of free side surface. Therefore the effect of free edge has been evaluated quantitatively by numerical analysis from comparison with mechanical behaviour under periodic boundary condition without free side surface. From the above results, it is recognized that the proposed procedure is very useful for the material design of woven fabric composite materials.
In this study, the influences of the grain sizes on the magnesium alloy are investigated to evaluate the friction and wear properties under a dry condition by using a pin-on-disk test machine. Four kinds of ZK60 magnesium alloys with different grain sizes from 6mm to 100mm were used as test specimens and SUJ2 was used for counter materials. It was shown that the wear rate on the small grain size's specimen was increased by the larger plastic deformation near to the worn surface. And, it was also made clear that the coefficient of friction increased due to the influence of adhesive wear in the case of small grain sizes. On the other hand, in the case of large grain size's specimen, the wear-resistance properties increased as compared with the small grain size's specimen because the wear type was an abrasive wear without a plastic deformation. It is appeared that the average coefficient of friction on ZK60 magnesium alloy was about 0.3 in this test condition.
Under atmospheric pressure, homogenous nonequilibrium low temperature plasma was generated by an rf (13.56MHz) excitation of He gas. By using this cold plasma, ZnO films were deposited on glass substrates exposed to air at a room temperature Bis-Dipivaloylmethanato Zinc ((C11H19O2)2) was supplied into the plasma with carrier He gas. Thickness and electrical resistivity of the films were then measured. Dependence of rf power and anode-cathode gap on thickness and the electrical resistivity was investigated. In addition, microstructure of the films was studied by FE-SEM observation.
Tensile properties of heat-treated hemp and bamboo fibers were examined. The average tensile strengths of hemp and bamboo fibers without heat treatment are 863MPa and 516MPa, respectively. After heat treatment at 200°C for 7.2ks, both fibers show a 60 percent decrease in tensile strength. The tensile strength of hemp fiber is almost unchanged below 160°C, however it decreases drastically above this temperature. The bamboo fiber also has the same temperature dependence, but its degradation temperature decreases to 140°C. Young's moduli for both fibers are almost constant and independent of the heat treatment condition.