Ready mixed concrete plants near the cement factory often use cement of high temperature, because fresh cement is directly provided from the cement factory. According to a previous investigation, concrete with high temperature cement indicates significant slump-loss. The purpose of this study is to propose an effective mixture to reduce slump-loss of the concrete. The experimental study firstly investigates flowabilities of paste using alternative materials of cement, i.e. fly-ash and limestone powder. In addition, this paper reports slump tests of concrete using the powder materials. The experimental investigation indicates that concrete with 20% replacement of fly-ash can effectively reduce slump-loss.
The purpose of this study is to investigate the effect of post-curing condition on hydration behavior of slag blended cement pastes. Pastes of ordinary portland cement (OPC) and blended cement, containing 40% ground granulated blast furnace slag (GGBFS), were cured at 60°C for 24 hours and subsequently stored in limewater at 20°C. The development of the microstructure in the cement paste was studied by mercury intrusion porosimetry (MIP). The amount of calcium hydroxide, carbonates and combined water was measured by Thermogravimetric/Differential Thermal Analyzer (TG/DTA), and hydration products were analyzed and quantified by using X-ray diffraction (XRD)/ Rietveld method. The reaction ratio of BFS was estimated by selective dissolution method. The strength development after 3 days of BFS blended cement pastes was higher than OPC pastes when pastes cured in limewater at 20°C following the initial high temperature curing period. The reaction rates of C2S and BFS increased for the pastes subjected an initial high temperature curing followed by water curing at 20°C as post-curing. C3S and C3A were almost completely consumed at 28days irrespective of curing conditions. Theoretical volume changes of hydration products calculated from XRD/Rietveld corresponded with the development of compressive strength and MIP. Vaterite, a calcium carbonate polymorph, was observed in BFS blended cement pastes that were exposed to the atmosphere as post-curing condition. This phenomenon corresponds to a decrease in Ca/Si molar ratio which is likely the product of the C-S-H paste giving up a Ca ion. It was concluded that physicochemical properties of BFS blended cement pastes change significantly following the initial curing conditions.
Super high strength concrete with compressive strength of 150 to 200N/mm2 using hybrid fiber reinforcement of organic and steel fiber was developed. Properties of fluidity of fresh concrete and effect of curing condition on strength development were studied. Viscosity of fresh concrete was significantly reduced by newly developed Maleate polycarboxylate-based superplasticizer. Strength development of high strength concrete was enhanced by high temperature steam curing. Hybrid fiber reinforcement was effective to improve toughness and fire resistance of super high strength concrete. The higher the aspect ratio and tensile strength of steel fiber, the higher the toughness of concrete became. Hybrid fiber reinforcement enables to reduce spalling and to maintain fire resistance for 3 hours in super high strength concrete columns.
This study was carried out to examine the application of sewage sludge molten slag as coarse aggregate for concrete and the influence of the quality of molten slag on the mechanical properties of concrete. As a result, it was clarified that the mechanical properties of concrete by using molten slag coarse aggregate depended on the quality of molten slag. The concrete by using molten slag coarse aggregate which was good strength had performance equivalent to normal aggregate concrete. In the quality standard of molten slag for concrete, it is necessary to provide not only the density and water absorption but also the standard related to the strength of aggregate.
In recent years when the quality of many concrete structures is progressively deteriorating due to carbonation, chloride damage, etc., various repair methods are being applied to prolong the life of public structures. Among these methods, the concrete surface coating method, where a material is applied over the surface to prevent substances from invading and deteriorating the concrete, has a long history, more than a quarter of a century. Many new protection techniques based on this method are being proposed even today. On the other hand, the adhesive ability of the concrete surface coating method has been one of the most important evaluation items for measuring the durability of coatings, and the measurement of adhesive strength in the single vertical axial direction has been mainly used for this evaluation. However, this test method has difficulties meeting our original purpose of comparing the adhesion performance between samples, because the test tends to often produce the same result: substrate destruction. Taking the above circumstances into account, another evaluation method that images the peeling-off of the coating films, i.e., the peel-off resistance measurement, was introduced. This method enabled us to observe clear differences between samples where the concrete substrates had been damaged by the adhesion strength measurement. In addition, some of the concrete surface coating methods showed a phenomenon that appeared at the peeled-off or damaged part of samples and varied in quality over time. From a series of concrete surface coating tests using both evaluation methods, we drew the conclusion that we could make clear the adhesion of coating films in a more practical and accurate way.
To estimate the volume fraction of martensite induced in austenitic stainless steel during tensile deformation, the resistivity of a specimen was measured at a temperature of 77, 187 or 293K. Since the distribution of the martensite in the specimen was observed in the specimen having the small slenderness ratio. Accordingly, the specimen having the large slenderness ratio was used to estimate the martensite volume by the resistivity. The negative resistivity region was observed on the resistivity- plastic strain curve regardless of the specimen temperature. It was suggested that the negative resistivity was caused by the formation of ε martensite that is a precursor of the martensite and the process of the resistivity was controlled by the formations of the ε martensite and the microscopic plastic deformation induced by the martensite. The linear relation between the resistivity and the volume fraction of the martensite was confirmed by the experiment and a simple model. It was clarified that the resistivity could be used as an index of estimating the deformation-induced martensite in austenitic stainless steel.
In order to obtain information about relationships between fatigue strength of a SUS316NG austenitic stainless steel and hardening behavior due to dynamic strain aging during fatigue tests, rotating bending fatigue tests were carried out at 300°C for notched specimens for stress concentration factors being less than 2.0 and for burnished hourglass type specimens. As for the notched specimens, fatigue fracture occurred before the specimens hardened enough during fatigue tests and the fatigue strengths did not reach the expected values from fatigue strengths of notched specimens for stress concentration factor being greater than 2.0. As for the burnished specimens, the specimen surfaces hardened enough previously to fatigue test but the fatigue strength also did not reach the expected value. Internal fracture occurred for burnished specimens and fish-eye patterns were observed on the fracture surfaces.
Tin (Sn) thin films with various thicknesses were electrodeposited on Cu substrate with and without Ni undercoat. The change of the internal stress in Sn films was measured by the X-ray diffraction method. For the case of 2.2μm thick film without Ni undercoat, the initial internal stress was tensile and then gradually changed into compression. After 15h, the compressive stress became below -25MPa and remained constant afterward. Filament-type whiskers were grown on the surface after the stress changed into compression. For Sn films thicker than 4.3μm, the initial stress was compression and only nodule-type whiskers were grown on the surface. For the case of 2.2μm thick film with Ni undercoat, the stress was maintained in tension and no whisker was observed. For the cases of thicker films with and without Ni undercoat, the stress was compression around -30MPa just after deposition, and did not change with time. Nodule and mount-type whiskers were formed on the surface, but no filament-type whisker was observed. The compressive stress introduced by bending in 2.2μm thick film with Ni undercoat resulted in the formation of mount-type whisker. The postbake process induced the tensile stress in 2.2μm thick film and eliminated the formation of whiskers.
Zirconia/SiC composite ceramics have a high crack-healing ability at low temperature. We investigated the effects of SiC composite, environment on the crack-healing behavior. We also investigated the fatigue strength of heat-treated specimens. The main conclusions are as follows : (1) For crack-healing of ZrO2 ceramics it is necessary both a composite SiC and an oxidation environment. (2) When ZrO2/SiC ceramics are heat-treated in air, a phase-transformation by SiC composite caused not only the crack- healing but improvement of the fracture toughness and bending strength.
Although a lot of interface crack problems were previously treated, few solutions are available under arbitrary material combinations. This paper deals with an edge interface crack in bonded finite and semi-infinite plates under tension. Then, the effects of material combination on the stress intensity factors are discussed. A useful method to calculate the stress intensity factor of interface crack is presented with focusing on the stresses at the crack tip calculated by the finite element method. The stress intensity factors are indicated in charts under arbitrary material combinations. For small edge interface crack, it is found that the dimensionless stress intensity factors FI and FII are not always finite depending on Dundurs' parameters α and β. In the present study, the variations of the dimensionless stress intensity factors FI and FII are clarified under arbitrary material combination with varying the relative crack length a/W. It is found that when a/W ≤ 0.4 the value of FI increases with increasing α and when a/W ≥ 0.4 the value of FI decreases with increasing α.
In this study, residual and internal stresses of PAN-based carbon fiber in CFRP were measured by confocal Raman microspectroscopy with sub-micro scale spatial resolution. For single carbon fiber, the relationships between the change of Raman bad shift and applied stress were obtained by single fiber tensile test. The relationship for Raman band peak at 2691cm-1 indicated high linearity and high stress resolution. Residual stresses of carbon fiber in CFRP were determined by using the relationship for 2691cm-1 Raman line. Residual stresses of several carbon fibers in 4∼7μm depth from the specimen surface were measured. Then, residual stresses were compressive and the mean stress was about -625MPa. The mapping measurement of residual stress of carbon fiber in CFRP was conducted. The fibers on the specimen surface had low compressive stress, and fibers in matrix had high compressive stress. Last, the mapping measurement of residual and internal stresses near the crack tip in CFRP under mode I loading was conducted. Change of stress field around the crack tip was observed from differences between residual and internal stress distributions. Therefore, the availability of confocal Raman microspectroscopy to stress evaluations of CFRP was confirmed.
The global warming is one of the most important problems for many countries. It is necessary to use fly ash instead of cement to decrease CO2 emission. This study shows influence of curing conditions in early-age on the pore structure of concrete with fly ash. The microstructure of dried concrete can be divided into 2 parts, if the volume of macro pore having larger than 50nm diameter and mode pore diameter are considered. One is porous microstructure because of drying. The other is the microstructure of concrete in which the hydration continues even after finishing moist curing. When the concrete blended fly ash in 15% of binder is cured in moisture for 7days, fly ash reacts effectively and the depth of parts influenced by drying is the same as that of concrete used only cement. If the mixture includes fly ash in 30% of binder and it is cured in moisture for 3 or 7 days, the microstructure is more porous than the other mixture. When the concrete is cured in moisture for 28 days, all microstructures have almost the same pore structures. Carbonation of dried concrete is also focused on in this study. Then, it evaluates the contribution of fly ash as a binder to carbonation rate with k-value. As fly ash fraction increases, carbonation depth becomes larger. However, when fly ash fraction is 15% and the concrete is cured in moisture for 7 days, the carbonation depth is almost the same as that of concrete used only cement. If fly ash is used in this condition, k-value shows 0.4 and k'-value, which is in the case of considering inhomogeneous of structure, shows the almost 1.0. The fly ash could be used as a general material if the fraction is 15% and the period of the moist-curing is 7days.