High-strength steel strands have been developed using higher strength steel wire rods with higher carbon and silicon contents than conventional steel wire rods. The tensile load of the developed steel strands was 15%∼20% higher than the conventional steel strands : 322kN for 15.2mm diameter strands and 684kN for 21.8mm diameter ones. The developed strands have a fracture elongation comparable to the conventional ones. An increase in carbon concentration and dislocation density resulted in smaller relaxation loss than the conventional strands. The strengthening did not have negative effects on anchoring efficiency of the strands and hydrogen embrittlement. Therefore, special operations are not required for practical use of the developed high strength steel strands. Their higher-strength is expected to reduce the materials used for prestressed concrete members, to decrease the weight of concrete members, and shorten the construction period.
This paper describes the effect of Ca/Si molar ratio of C-S-H on concrete durability. Concrete durability depends on the physical and chemical properties of concrete. The physical and chemical properties of concrete are affected by the kinds and amounts of hydration products. C-S-H is dominant hydration product. And, Ca/Si ratio of C-S-H depends on types of mineral admixtures, mixture proportion and curing period. Therefore, it is important for estimating of concrete durability to clarify the properties of C-S-H. In this study, physical properties, such as density and surface area, of C-S-H with various Ca/Si ratios were measured. And chemical properties, such as chloride binding capacity and releasing due to carbonation were also measured. From the experimental results, physical and chemical properties of C-S-H depend on Ca/Si ratio. Based on these results, the effect of Ca/Si ratio of C-S-H on concrete durability, such as chloride diffusion and chloride binding was examined. The durability of blended cement concrete can be explained qualitatively in consideration of Ca/Si ratio of C-S-H.
In order to assure high accuracy in estimation of water content of fresh concrete by the neutron moisture meter, the establishment of a suitable calibration curve is the most important. In this study, fine aggregate containing the required amount of water in a container with fixed capacity is measured with the scattering-type neutron moisture meter. And the calibration curve is obtained from the relationship between the measured neutron counting and the amount of water added to fine aggregate. The kind of fine aggregate hardly influences the neutron counting. The neutron counting becomes large with the increase of particle size of fine aggregate, even when added water amount is the same. However, use of fine aggregate not less than 2.50 in fineness modulus dose not noticeably affect the neutron counting. The method with calibration curve using fine aggregate can evaluate the water content of fresh concrete with a good accuracy.
In the case of vibratory compaction of fresh concrete, it is not easy to assess the effects of insert depth, compaction time, and spacing of the vibrator. So far, compaction behavior inside fresh concrete is not theoretically elucidated yet. A vibratory compaction test by using an internal vibrator was conducted in a laboratory, and the pore-water pressures were measured. Near the surface of fresh concrete, the decrease in the pore water pressure was observed due to over-vibration. A falling-head permeability test was conducted to determine a coefficient of permeability. Comparing with the slump values, a reasonable relation between a coefficient of permeability and a slump value was observed. Applying Biot's two-phase theory, the pore-water pressure and the effective stress were theoretically analyzed by the element method (BEM). It is found that the pore-water pressures numerically determined are in reasonable agreement with those of the experiment. Thus the validity of the BEM analysis is demonstrated. The effective stress was analyzed on the basis of Drucker-Prager's equivalent stress, and stress distribution due to the internal vibrator is clarified.
Authors have been studying for about ten years as for the effective utilization of sludge water produced in ready mixed concrete plants due to washing of a mixer, agitating truck dram etc. Nowadays, JIS A 5308 permits the usage under 3 percent as solids of sludge for the unit cement content of new concrete. Recently, it is strongly requested to re-use a further large quantity of sludge water, in order to achieve the zero-emission. It is expected to re-use sludge water for concrete from the fact that sludge water consists of cement, fine particles of aggregate and water. This study, in order to utilize the larger quantity of sludge water than that now allowed, is to verify the properties of lean mixture concrete containing sludge which was designed for having the identical slump and compressive strength to comparative concrete. From the results of this study, it became clear that as for the lean mixture concrete containing stabilized sludge within the range of 3-9%, there was no problem about slump, bleeding, compressive strength, drying shrinkage and carbonation depth.
The purpose of this study is to develop mechanical properties of concrete using sewage sludge molten slag as fine or coarse aggregate. As sewerage system spreads, sewage sludge that comes out from process of sewerage disposal is increasing. However remaining capacity of final disposal site is almost outer limit, and it is difficult to secure new disposal site. To build the recycling society is important to build sustainable development, and at present 70 percent sewage sludge is recycled. Sewage sludge slag is recycled as construction materials, fertilizer and fuel. The following were clarified by this research. Amount of elusion of heavy metals from sewage sludge molten slag were lower than environmental standards. Strength, durability factor of freezing thawing decreased as the slag substitution ratio increased used sewage sludge slag as coarse aggregate. However, they did not decreased as the slag substitution ratio increased used sewage sludge slag as fine aggregate.
In order to investigate the application of waste roof tiles to fine aggregate for concrete, two kinds of waste roof tiles having different quality are selected. One is waste roof tile which is manufactured in Shimane prefecture and has been used long in Tottori city. The other is waste roof tile which is manufactured in Awaji Island and has been used long in this place. In this paper, the tests including drying shrinkage and freeze-thaw test for fresh concrete and hardened concrete are conducted and the properties are compared and examined with those of concrete with normal sand. The test results show that the dosage of a retardar type of air-entraining high-range water reducing agent required to attain the given slump when the waste roof tiles are used as fine aggregate for concrete. The fundamental properties of concrete with waste roof tiles such as slump and air loss with time, bleeding, setting time, compressive strength and drying shrinkage are almost the same as those of concrete with normal sand. However, the freeze-thaw resistance of concrete with waste roof tiles drop away compared to that of concrete with normal sand.
Alkali-aggregate reaction (AAR) is one of serious problems of concrete. It is known that fly ash, blast furnace slag, and so on can control the expansion of concrete by AAR. Natural zeolite is known as material that control AAR expansion, too. This paper shows the effect of aluminum hydroxide on control the expansion of concrete by AAR. It is possible to control the expansion of concrete by AAR when aluminum hydroxide to binder ratio is 4.0%. Especially, when a little of fly ash is combined, the effect of aluminum hydroxide is big. But, when aluminum hydroxide is used with much fly ash, the effect of aluminum hydroxide is not clear. The effect of aluminum hydroxide appears when it dissolves in concrete. In this paper, three different type of aggregate were used in order to clarify the effect of aluminum hydroxide on the expansion of concrete by AAR. The effect of aluminum hydroxide on AAR is somewhat different in the type of aggregate. However, it will clarify that aluminum hydroxide is one of an effective admixture to control the expansion of concrete by AAR. By combining aluminum hydroxide with adequate quantity of fly ash, big effect to control the expansion of concrete by AAR can be expected.
In order to improve the durability of concrete structures under harsh chloride-laden environments the use of surface coating and cross sectional restoration methods has been increased. For these methods polymer cement mortar becomes of a primary repair material. Then interface phenomena between the polymer cement mortar and concrete as the substrate needs to be clarified with regard to chloride penetration. In this paper the results of electrical resistance tests and chloride migration tests have been provided. Interface resistance of repaired concretes has been studied by comparing electrical resistance obtained experimentally and by calculations using the ohm's law on a series circuit. It is found that the interface resistance is controlled by the type of polymer cement mortars, mix proportions of concrete and the ages. Increased interface resistance is verified by decreased flux in the chloride migration tests. For repaired concrete by cross sectional restoration, the interface resistance may be ignored where the resistance obtained by the experiment and calculation was equal.
This paper presents development and the result of evaluation of filling material used polybutadiene foam in a waterproof structure at girder end. The polybutadiene foam used for the waterproof structure is excellent in water resisting property, flexibility, concrete adhesion, weatherability, and durability. Moreover, it was confirmed that the forming object has a difference in water resisting property in the up-and-down portion of the object. Therefore, when the number of lamination of the foaming object was increased, it proved that water resisting property improves. By installing the waterproof structure of having such characteristic features in the expansion gap of the road bridge, it becomes possible to attain reduction of traffic restriction, and reduction of maintenance expense.
In order to develop an estimation method of local temperature in thermal barrier coating (TBC), we observe the change in the microstructure of a CoNiCrAlY bond coat (BC) tested under oxidation in air at high temperatures. An oxide layer grows at the boundary between the BC and top coat (TC) while an Al-decreased layer appears underneath it. The thickness of the Al-decreased layer increases in proportion to the square root of the test time, and the growth rate can be described by the Arrhenius equation. The relationship among the layer thickness, time and temperature is formulated by the experimental results. Then, the temperature at the BC in a gas turbine component can be estimated by measuring the layer thickness on the basis of the relation. As the thickness of Al-decreased layer cannot exceed the BC thickness, there is the application limit. Moreover, the TC/BC boundary possesses eminent asperity, it brings about the error in the temperature estimation. The application limit and the fluctuation are assessed. The average Al-content in the BC is also measured by mean of an electron probe microanalyzer. The Al-content decreases in proportion to the thickness of Al-decreased layer. A prediction method of the Al-content is proposed on the basis of the relation.
This paper presents the effects of environment on fatigue crack propagation (FCP) in two magnesium alloys, rolled AZ31 and extruded AZ61. FCP tests have been performed using electro-hydraulic fatigue testing machine operating at a frequency of 1Hz at a stress ratio, R, of 0.05 in distilled water and in dry air. The dew point of dry air was −60°C. The obtained results were compared with those already established in laboratory air, and the effects of humidity and water environment were discussed on the basis of fractographic analysis of fracture surfaces. The effect of cyclic frequency was also studied. Both alloys exhibited basically the same FCP behaviour regardless of environment. FCP rates were nearly the same in laboratory air and in distilled water, while approximately an order of magnitude slower in dry air than in those environments. After allowing for crack closure, the effect of environment still existed, where FCP rates were the fastest in laboratory air, then in distilled water, in dry air in decreasing order. Fractographic analysis revealed that fracture surfaces were extensively brittle in laboratory air, while entirely covered with corrosion products in distilled water. It was believed, therefore, that different FCP mechanisms operated in laboratory air and in distilled water, possibly hydrogen embrittlement and anodic dissolution, respectively. The frequency dependence of FCP rate was not recognized in dry air and less remarkable in laboratory air over a wide range of frequencies of 0.01Hz to 10Hz, while FCP rates became faster with decreasing frequency in distilled water.
Resin transfer molding (RTM) process is getting popular for fabrications of complicated commercial products made from GFRP at low cost. For the RTM process of complicated components, it is indispensable to do trial and error over and over to find an optimal fabrication process. The trial process is time consuming and that is one of the reasons of the high cost of composites. To overcome this problem, it is useful to monitor the degree of cure of the target GFRP products. In the present study, the luminance change method is adopted for cure monitoring for the polyester-based composite. Polyester resin is usually adopted as matrix resin of the low-cost GFRP products. The polyester resin usually changes its optical property during the curing process. This enables us to monitor the degree of cure by means of the measurements of luminance change of the transmitted light or the reflected light. In this study, we use the system measured with the reflected light. The sensing system employs a LED as a light source and a photodiode as a light power sensor. This low-cost cure-monitoring system is applied to monitoring of the degree of cure of GFRP. The degree of cure is measured by means of commercially available dielectric sensors, and results are compared with the results of luminance change. The effectiveness is confirmed experimentally here.
The coating of phosphate glass on titanium (Ti) substrate was attempted by the pulsed laser deposition (PLD) method technique. In this study, for two types of phosphate glass targets, PLD was carried out in pure O2 vapors (200mTorr) on Ti substrate. The phosphate glasses of G6P with amorphous phase and G6Pc containing with crystal phase were used for glass coatings on Ti substrate. The coatings deposited by PLD method were studied by X-ray diffraction (XRD) analysis and FT-IR evaluation. Their microstructures of coating prepared by PLD method were observed by scanning electron microscopy with energy dispersive x-ray (SEM-EDX). The characterizations with XRD and EDX showed that the coatings produced by PLD method were very similar to the phases and compositions of used targets. It was found that PLD process can lead to the successful syntheses of coating with the same composition and phase as the starting target and be useful for synthesizing high performance coatings on Ti.