Electrochemical techniques such as desalination and realkalization have been developed as the repair methods for reinforced concrete structures deteriorated by chloride attack or carbonation of concrete. Recently, these techniques have been applied to many actual structures. On the other hand, it has been suggested that there is some risk to accelerate the ASR expansion of concrete if the applying structures contain the reactive aggregate. In this study, the degree of ASR expansion accelerated by applying electrochemical repair method was investigated experimentally and at the same time, the suppression effect of ASR expansion due to the electrochemical treatment using the electrolyte containing lithium ions was also examined. The result of this study was that remarkable acceleration of ASR expansion due to applying electrochemical treatment was not observed and the ASR expansion of the specimens applied electrochemical treatment using lithium rich electrolyte tended to be smaller than the expansion of non-treated specimens.
The purpose of this paper is to develop an evaluation method for assessing the alkali-silica reactivity of concrete with a combination of the river sand and gravel used in the Hokuriku district. The 27 aggregate samples were collected from the stockpile of selected 8 ready-mixed concrete plants over the main river area in this district. The mineralogical features of the river sand and gravel, and their alkali-silica reactivity were tested by both the chemical method and the mortar bar method according to the specification by JIS A 1145-2001 and JIS A 1146-2001. Furthermore, a lot of cores were drilled from the concrete specimens, which were subjected to the accelerated curing condition of the immersion into 1N NaOH solution at 80°C or the saturated NaCl solution at 50°C in order to evaluate the alkali-silica reactivity of the concrete itself. By measuring the expansion behaviors of the cores in the accelerated curing condition, the rapid test method for the evaluation of the alkali-silica reactivity of the concrete itself was developed.
This study proposes a unique technique for improving qualities of concrete with recycled concrete coarse aggregate; a decompression and rapid release (DC-RR). In this paper, experimental studies with full scale specimens are described on the effectiveness of the DC-RR procedure on the performances of concrete structures with recycled concrete coarse aggregate, such as core strengths of columns, defections of slabs and crack widths of walls. It was found that, by applying the DC-RR procedure, the performances of full scale concrete specimens with recycled coarse aggregate were much improved and evaluated as almost equal to those with natural coarse aggregate.
Three kinds of decomposed granites are selected based on the content of materials finer than 75μm sieve and ignition loss among decomposed granites produced in Tottori prefecture. The selected decomposed granites are sifted with 10mm sieve and used as fine aggregate for concrete. In this paper, the properties of fresh and hardened concrete with decomposed granite and the application of decomposed granite to fine aggregate for concrete are investigated. The test results show that the dosage of a retarder type of air-entraining high-range water reducing agent (HWRA) required to attain the same slump value increases as the material finer than 0.15mm sieve included in the decomposed granite increases and its water retaining factor becomes larger. An increase in dosage of HWRA leads to an extension in setting time. Consequently, the setting time of the concrete with decomposed granite becomes long compared to that of concrete with normal sand. However, the fundamental properties of concrete with decomposed granite such as slump and air loss with time, bleeding, compressive strength, drying shrinkage and freeze-thaw resistance are almost the same as those of concrete with normal sand.
It is important to understand the curing methods of the high fluidity concrete and various properties in winter from the point of the plan as the construction. Therefore, we examined the high fluidity concrete that used admixtures such as binding agents, segregation reducing agent by using the large model test specimen. As results, the heat curing is effective means to obtain prescribed strength at the early age in the winter concrete construction. However, attention is required for the curing period and the state of moist at the heat curing. The freezing and thawing resistance decreases according to an initial the curing methods occasionally. The finding obtained by the experiment can be reflected in the construction plan.
Authors have been studying for several 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 content of cement 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. Sludge water consists of cement, fine particles of aggregate and water. All materials are one of the constituents of concrete. This study, in order to utilize the larger quantity of sludge water than that now allowed, is to verify the properties of concretes containing sludge which were designed for the identical slump and compressive strength to comparative concrete. From the results of this study, it became clear that as for the sludge concrete containing sludge within the range of 3-15%, there was no problem about the properties of fresh and hardened concrete, that is, slump, bleeding, compressive strength, drying shrinkage, carbonation depth and freezing and showing resistance, etc. In other words, within the range of 15% of sludge solid content, the concrete containing sludge water with setting retarder could obtain good performance as same as comparative concrete. It was also confirmed that the bulk volume of coarse aggregate was available for the design method of concrete mixture.
Nitrite-type hydrocalumite (calumite) is a corrosion-inhibiting admixture which can adsorb the chloride ions (Cl-) causing the corrosion of reinforcing bars and liberate the nitrite ions (NO-2) inhibiting the corrosion in reinforced concrete. Polymer-modified mortars with the calumite and a styrene-butadiene rubber (SBR) latex as a polymeric admixture are prepared with various polymer-binder ratios and calumite contents, and tested for flexural and compressive strengths, adhesion, water absorption, drying shrinkage, accelerated carbonation, and corrosion inhibition. As a result, regardless of the polymer-binder ratio, the replacement of the ordinary portland cement with the calumite causes a marked improvement in the corrosion-inhibiting property of the polymer-modified mortars but decreases in their strengths and adhesion, and increases in their water absorption, drying shrinkage and carbonation depth. However, such inferior properties are considerably improved with an increase in the polymer-binder ratio irrespective of the calumite content. It is concluded that the polymer-modified mortars with the calumite can successfully be used as patch materials for the repair work for deteriorated reinforced concrete structures.
Various types of polymer-modified mortar have recently been used to repair deteriorated concrete structures. The type of the polymer dispersion or redispersible polymer powder is considered to determine the physical properties of hardened polymer cement mortar. In this study, a prototype of polymer-modified mortar was made using such cement admixtures as polymer dispersion and redispersible polymer powder. Then, the physical properties of the polymer-modified mortar were measured to examine the effects of polymer dispersion and redispersible polymer powder on the physical properties of hardened polymer-modified mortar. It was found that the physical properties of polymer-modified mortar with a water-cement ratio of 0.4, a sand-cement ratio of 2.0, a polymer-cement ratio of 0.05, a flow value of mortar of 180±10 and a mass of unit volume of 2.1±0.1 varied according the types of polymer dispersion and redispersible polymer powder. A substantial variances were found in drying shrinkage and resistance to neutralization. It was suggested that the depth of neutralization were affected by the pore volume for pore diameters of 100μm and over in polymer-modified mortar.
The objective of this study was to investigate the effect of thermal cycles, encountered by an Super Sonic Transport (SST) in service, on the cumulative frequency of microcracks and the degradation of compressive strength in carbon fiber/polyimide resin composite materials. One thermal cycle was designated as a sequence from room temperature (RT) to -54°C, and then to +177°C, finally back to RT. Transverse microcracks initiated on the sectional free edge surface of the laminates were observed and counted by using an optical microscope. Approximate 10000 thermal cycles were given for five kinds of carbon fiber/polyimide composite material: IM7/PIRA, IM600/PIXA-M, IM600/PIXA-MT3, IM7/K3B, IM7/R1-16, as well as a Ti/Gr (polyimide CFRP) fiber metal laminate. For IM7/R1-16 thermal cycling tests were conducted up to 40000 cycles. Transverse microcracks were observed not only on the sectional free edge surface but also on the inside cross section of specimens cut after thermal cycling tests for IM7/R1-16. Static open-hole-compressive (OHC) strength was measured at RT before and after thermal cycling tests on the five kinds of material except for IM7/PETI-5. Static nonhole-compressive (NHC) strength was measured at RT on IM600/PIXA-M and IM600/PIXA-MT3. In addition, in order to know the estimates of thermal stress generated by the thermal cycles, the thermal stresses were calculated by the classical lamination theory (CLT) using basic lamina data given in a reference.
Although there are many studies on the microstructure of various metals with ultra-fine grain formed by ECAP (equal channel angular pressing), a few studies have investigated the fatigue characteristics of ECAPed metals. In the present study, 99.99% pure, oxygen-free copper was used. Before the ECAP process, the material was normalized at 500°C for 1 hour. A Bc route with 90° rotation after each ECAP cycle was utilized. To obtain the ultra-fine grain with 300nm grain size, a total of 4 passes of ECA pressing with Bc route were performed. Rotating bending fatigue tests of smooth specimens were carried out. Successive observations on the surface damage due to both the direct and the replica observation were carried out to clarify the fatigue mechanism of ECAPed copper. An optical microscope and a scanning electron microscope were used for the observation of the change in surface morphology. A transmission electron microscope was used for observation of microstructure. Putting the experimental results from the observation of each microscope together, fatigue damage of copper with ultra-fine grain was discussed.
In order to investigate effects of BN content and load variation on the fatigue crack growth behavior of Si3N4-BN composite ceramics (SNB), fatigue crack growth tests under constant amplitude loading and repeated two-step load sequences were carried out using compact type (CT) specimens. Crack length and macroscopic crack closure were measured using the unloading elastic compliance method. The maximum stress intensity factor for the same fatigue crack growth rate decreases with the increase of the BN content. This decrease with the increase of the BN content is resulted from the decline of the fracture toughness. Fatigue crack growth rate strongly depends on the maximum stress intensity factor, and is also influenced by the load amplitude. As for the load amplitude dependency of the crack growth rate, SNB40 is the most remarkable in comparison with SNB20 and SNB30. Regardless of the BN content, fatigue crack growth rate under repeated two-step loading was found to be accelerated in comparison with that under constant amplitude loading. The acceleration was due to the breaking of interlocking under high level loading. The acceleration of the crack growth rate of SNB40 is the most remarkable because the crack growth rate of SNB40 is strongly dependent on the load amplitude. The fatigue crack growth acceleration behavior under repeated two-step loading could not be explained by the equivalent stress intensity factor range ΔKeq in consideration of both of Kmax and ΔK. However, the equivalent effective stress intensity factor range ΔKeff, eq in consideration of both of Kmax and ΔKeff could account for the acceleration behavior qualitatively but not quantitatively.
The combination of centrifugal load and vibratory load acts on a component of turbo machinery, for example, a moving blade in a turbine. When the machine is used in frequent start-up and shut-down operation, the mixed mode fatigue evaluation should be done for such a component. The mixed mode loading is composed of the low cycle fatigue (LCF) due to the repetition of start-up and shut-down process and the high cycle fatigue (HCF) due to vibration. In a mixed mode loading, a short crack is generated by the LCF and it grows to some extent in LCF manner. At a certain crack depth, the condition for HCF crack propagation is satisfied and the transition from LCF to HCF crack propagation occurs. After the transition, the crack propagates rapidly in HCF crack propagation mode. The evaluation of the transition point has been usually done using the fracture mechanics on the basis of (ΔKeff)tn, ∞, which is the effective threshold stress intensity factor range of a long crack at an extremely high stress ratio condition. However, it has been shown that the (ΔKeff)th becomes lower than (ΔKeff)th, ∞ in short crack region of hard material, which suggests that the transition into HCF crack propagation occurs at a shorter crack depth than that predicted on the basis of (ΔKeff)th, ∞. The test results showed that the transition occurred at about 1/2-1/3 of the predicted life. The consideration of short crack effect on the (ΔKeff)th is important, especially in the case of mixed mode loading of turbo machinery.
It is well known that fatigue strength of spot weld of high strength steel sheet is not improved, compared with that of low strength steel sheet. In order to predict and improve the fatigue strength of spot weld, it is necessary to clarify the factors which determine fatigue strength. However, the governing factors and the effect of steel grade have been obscure. Therefore, a valid prediction method of fatigue strength of spot weld is desired. In this study, firstly, small specimens with total length of less than 3mm are taken from each region (base metal, HAZ and nugget) in spot weld of low strength steel sheet (mild steel) and high strength steel sheet (590MPa-grade steel). And then, tensile and high cycle fatigue properties are individually evaluated by newly-developed testing technique. Secondly, finite element analyses of spot-welded joints under cyclic loading are carried out and fatigue limit of the joints are predicted by using the above-mentioned local material strength properties. Predicted result of mild steel is higher than that of 590MPa-grade steel, which coincides with experimental results. Furthermore, it is clarified that fatigue strength of HAZ, which is the crack initiation site of joint, is almost equal in both steels and this may be one of the reasons why the fatigue strength of the joint of 590MPa-grade steel does not exceed mild steel.
A new form of dismantiable adhesive technology has been developed. This is a revolutionary development in the construction industry, which makes it possible for the bonded building materials to be separated by the simple appication of heating over 100°C. This article describes the design of dismantlable adhesives (elastomer type and emulsion type) and the evaluation of uses for building materials. For the elastomer type dismantlable adhesive, the weight fraction of thermally expansive particles from 5 to 15% is suitable for both bond strength and dismantlement of joints. For the emulsion type, that from 5 to 20% is suitable for these characteristics. The bond strength of joints could not decrease after durable test at 60°C, 95%RH for 30 days. Then the joints were spparated easily by heating at from 150 to 180°C. In this technology, manufacturing process in equal to the case using conventional adhesives and the time of heating for dismantlement is quite short. So it is efficient for not only performance (adhesion and dismantlement), but also manufacturing and cost.
Fracture mechanics based considerations were made for investigating the ring-crack formation of ceramic plates contacted with a ceramic sphere under a combined normal and tangential indentation load. The intrnsic tensile strength of the ceramic plate did not dictate the onset of ring-crack formation. The size of pre-existing defects (being less than one micron) that may result in the ring-crack initiation were somwhat smaller than the grain size of the ceramic plate. On the other hand, the stress gradient induced beneath the contact was significantly dependent on the contact angle of normal/tangential combined load; when the contact angle is increased, the mean dimension of defects which lead to ring-crack initiation becomes large, whereas the location of the induced crack is progressively away of the contact circle. The stress gradient induced beneath the contact was taken into account for calculating the stress intensity factor of the pre-existing surface defect. The fracture toughness value thus estimated for the ceramic plates satisfactorily predicted the onset of ring-crack formation of all the ceramic plates examined.