A study has been undertaken to determine the shear behavior of reinforced concrete beams subjected to high temperatures at one side. A total of nine specimens was tested. The parameters of the tests were (1) heating temperature (65, 90 175°C) and (2) heating period (1, 3, 6 or 12 months). Different combinations of these parameters were employed, and the shear strength deterioration rate was evaluated. The test results were confirmed by a non-linear finite element analysis. The relationship between the concrete compressive strength, which varied from heating face to upper portion, and the shear strength in specimens was discussed. To propose the shear design of the massive members like the Nuclear Power Plant Building, the massive concrete core test were confirmed. It is practicable that the relationship between the core compressive strength and the temperature in the core tests is used on the shear design.
This study comprehensively examines thee ffect of concrete surface coating material on the prevention of frost damage, conducting freezing and thawing tests of the Japan Society of Civil Engineers; new freezing and thawing test methods incorporating high-temperature drying conditions; and various tests on the performance of coating film. First, relatively excellent surface-coating materials for preventing frost damage were selected by tests with mortar specimens and coating film tests. Second, with these surface-coating materials, the effects of water cement ratio, curing methods and defects in concrete on the performance of coated concrete under freezing and thawing were investigated. From the test results, it was shown that coating material of flexible thick-film epoxy resin is the most effective in preventing frost damage; defects in concrete greatly affect flexural strength of concrete under freezing and thawing; and newly-proposed freezing and thawing tests can accelerate the deterioration of surface-coated concrete and the swelling of coating film itself.
Flexural shear tests were conducted in order to clarify the mechanical behavior of steel girders having corrugated web and composite prestressed concrete girders with corrugated steel web. In this study, a new type of shear connection at the interface of the corrugated steel web and the lower concrete flange in the composite prestressed concrete girders was proposed and also an application of composite prestressed concrete girders having corrugated steel web to the precast segmental construction was proposed. The experimental results indicated that the girders with corrugated steel web showed favorable shear resistance, and the pure shear stresses were seen in the corrugated steel web so that the prestressing forces were not transmitted to the corrugated steel web. A practical formula for estimating the buckling strength of corrugated steel web, in which intermediate buckling mode was included, was derived and good coincidence was shown between the calculated values obtained by this formula and the experimental ones.
Until now, crack property of concrete structure due to AAR have been estimated by means of number of cracks, crack width measured by a traverse method or an area method. However, the shape and the progress of crack, and the distribution are vaguely expressed and can't be quantified. This study applied a fractal analysis method to quantify the crack properties of concrete due to AAR. Condition of analysis, fractal characteristic value and appearance of crack were discussed. The damage degree due to AAR was quantitatively estimated. Both results of the analysis and the investigation on concrete structures were compared. The point of time of repairing the concrete structure was examined.
Many equations to predict drying shrinkage of concrete have been suggested. However, it is not completely clear about the quantitative relation between drying shrinkage strain obtained by equations and the value of drying shrinkage for member. In this paper, we deal with a simple method to predict drying shrinkage strain for member, which drying shrinkage strain is to be obtained by using the experimental data in the past or the result of length change test specified by JIS, with consideration for influence of construction times, thickness of member and reinforcing bar arrangement. The following became clear after the investigation on the influence of thickness of member and reinforcing bar arrangement on drying shrinkage of the wall structure which have been constructed in winter. The restraining actions of reinforcing bar on drying shrinkage can be evaluated by using empirical equation. The restraining actions of reinforcing bar increase as the amount of it increases and the tendency becomes gradual as the thickness of member becomes thick.
For the purpose of removing chloride ions from concrete, electric control of migration of ions in concrete was considered. However, the mechanisms of migration of ions and the effects of the electric control method are still unclear. So, in this paper, the effects and applicability of electric control method, i. e. desalination, were experimentally investigated. The method was evaluated by considering (1) the influence of carbonation, (2) the difference in intrinsic chloride ion contents in the specimen, and (3) the difference between intrinsic and extraneous chloride ions. Through these investigations, the effects of desalination were made clear.
The effectiveness of Ca (NO2) 2 and NaNO2 as a corrosion inhibitor has been confirmed. However, it may be important from the viewpoint of corrosion of reinforcement in the concrete contaminated with Cl- ion to reveal the behavior of NO2- ion in relation to Cl- ion concentration in pore solutions in concrete. In this study, the analyses of pore solution in NaCl containing-mortars with and without inhibitor were carried out to elucidate effects of the inhibitors on the chloride binding capacity of mortars. NO2- ion concentrations in the pore solution in NaCl-containing mortars treated with 1% Ca (NO2) 2 by mass of cement were lower than in the corresponding mortars with NaNO2. The addition of NaNO2 a little raised OH- ion concentration, but OH- ion concentration was reduced in the mortars containing Ca (NO2) 2. However, Cl-/NO2- ratio in the pore solutions in mortars containing Ca (NO2) 2 were lower than in mortars containing NaNO2 because of the dissipation of greater amounts of Cl- ions from the pore solutions in the former than in the latter.
The shear strength of beam-column members is becoming able to be estimated accurately by theoretical methods through many previous studies. For concrete piles however, no satisfactory method to predict the shear strength of the piles has been established. In this paper, the failure mechanism of the PHC piles with large diameter is considered firstly by means of the finite element analysis. Secondary, the estimation formula for predicting the ultimate strength of the piles is proposed based on the upper bound theorem of the limit analysis from the previous consideration.
The thermographic survey using thermal imager is considered to be a method for detecting the surface temperature differences between the delaminated area and the sound area of finishing materials on building walls. So, there exist some analytical studies using heat balance simulation on this method. However the numerical result obtained by a heat balance simulation can not always represent the easiness of judgement. In this study, by making simulated thermal image using finite element method with smoothing technique, the limitations of the method are discussed from a visual standpoint
Thermal imager is widely known as a device to measure the surface temperature of objects However, since the surface temperature of mortar or tile measured by this device is influenced by sun and other surrounding objects, it is difficult to know the accurate surface temperature distribution of finishing materials without being affected by such noises. In this study, by carrying out four series of experiments, the characteristics of thermal imager when measuring the surface temperature of finishing materials on building walls were discussed
A comprehensive study on scaling resistance of concrete exposed to deicing chemicals was examined. In Japan, the spreading amount of deicing salts has been increasing in recent years and the research is backward. The temperature conditions specified in ASTM C 672 were tentatively controlled automatically, and the scaling resistance was evaluated by not only visual rating but also measurement of the mass of scaled-off particles on many types of concrete specimens, in the variety of testing surface such as top, side and bottom surfaces, air content, water cement ratio, curing condition, deicing salts and in the application of a permeable sheet enable to make dense the surface layer of concrete. Besides, the assessment of scaling damage of concrete was attempted non-destructively from a side view of both strength and permeability
Mortars with and without damage by alkali-aggregate reaction were stored under atmosphere rich in CO2, and the change of the characteristics during the storage was measured for elucidating the effect of alkali-aggregate reaction on the carbonation of concrete. It was found that microcracks arising from the alkaline-aggregate reaction act as channels for the diffusion of CO2 and accelerate the carbonation of mortars. The resultant CaCO3 fills the cracks and pores, so that the characteristics of the mortars are improved at the expense of the alkalinity of the mortars. Neutralization of mortars was found to precede, seemingly, the carbonation under the atmosphere rich in CO2
This paper deals with the effects of ambient temperature, catalyst and accelerator contents on the working life of lightweight polyester mortars. At 10, 20 and 30°C, the lightweight polyester mortars using four lightweight aggregates are prepared with various catalyst and accelerator contents, and tested for working life. As a result, the working life can be controlled by varying the catalyst and accelerator contents at the respective ambient temperatures. Empirical formulas for predicting their working life are successfully proposed.
The Hyogoken-Nanbu Earthquake induced severe damages in many urban highway bridge systems. These are mainly caused by brittle failure modes in reinforced concrete bridge piers. The collapses of reinforced concrete bridge piers are the result of underestimating load demands, insufficient ductility, and insufficient shear resistance. In this study, the effects of these factors on the reliability of reinforced concrete bridge piers are investigated. In the analysis, the reliabilities associated with different limit states including ultimate state, yielding of reinforcing steel, and cracking of concrete are examined. For seismic loads, a practical reliabilitybased evaluation methodology for bridge piers is presented. The approach is demonstrated on a typical Japanese reinforced concrete bridge piers. The reliability under seismic loads is evaluated considering the effects of ductility.
The temperature dependence on the strength development was investigated for the mixing design and the quality control of concrete containing antifreezing admixtures. The strength development of antifreezing concrete could be described by gompertz curve using maturity function as well as that of ordinary concrete. Antifreezing admixtures accelerated the strength development and increased the long term strength. Therefore, the correction value for concrete strength in terms of outdoor air temperature designated in JASS 5 would be decreased. However, on freezing condition, the strength development was delayed even when using antifreezing admixtures. The datum temperature of maturity function was not necessarily lowered by using antifreezing admixtures. It was currently recommended admirable to be -10°C used for practical use. The temperature tracing curing was useful for the quality control and the decrease of the term of works.
It is quite a while since permeable forms were developed and put to practical use, aiming at improving the durability of concrete by means of preventing airs and honeycombs from forming on these concrete surface. Permeable forms are designed to drain excess water contained in the concrete immediately after their placement. Removal of excess water not only decrease the water-cement ratio of the surface concrete, but increases the density of the concrete, and eventually enhances its durability. However, few studies focus on the characteristics of pore structure, namely, the relationship between changes in the volume and distribution of capillary pore and the durability of concrete by the use of permeable forms. In this study, investigations were made paying attention to changes in pore structure on past data obtained from tests conducted on permeable forms. The data include pore size distribution, cement volume distribution, depth of accelerated neutralization, salt infiltration and surface strength. The investigations led to the following findings : 1) Use of permeable forms decrease the percentage of pore volume, especially that ranging between50 nm and 2μm. 2) In the case of pore size ranging between 50 nm and 2μm, correlations can be seen between the decrease in pore volume and such properties as neutralization, salt infiltration and surface strength.
Cracks and deformation occurred in grout-filled coupling sleeves of electric resistance welded steel tubes under monotonic tensile loading and tensile-compression cyclic loading are revealed by injecting epoxy resin into the cracks. Variables adopted in this study were types of loading, development length and shapes of circumferential ribs of reinforcing bars, strength of grout and some mechanical devices to improve bond characteristics. Following test results are obtained. (1) Cracks like cones at end zones of the sleeves, spaces behind circumferential ribs of reinforcing bars, horizontal cracks occurred at the tops of circumferential ribs, slip displacements at the ends of reinforcing bars and thinning of sectional areas of reinforcing bars in yielding zone are observed. (2) Kinds of cracks and states of deformation observed in the splices under cycle loading are almost similar to those under monotonic tensile loading. (3) Bond failure modes with or without yielding of reinforcing bars are seemed to be resulted from connection of horizontal cracks at the top of circumferential ribs. (4) Some mechanical devices improved strength and deformation capacity of the splices.
In order to certify the effect of the strengthening with carbon fiber sheets on the improvement of ductility of the reinforced concrete piers and to investigate the seismic properties after strengthening, static and pseudo-dynamic tests using reinforced concrete column specimens were carried out. From the experimental results, it was verified that the ductility of the piers can be improved by strengthening with carbon fiber sheets, and adequate volume and the necessary area of the carbon fiber sheets for the strengthening were obtained. Also, it was shown that the rupture of the carbon fiber sheets of the horizontal direction was occurred first at the corner of the column. From the results of pseudo-dynamic tests, it was confirmed that the piers strengthened by carbon fiber sheets could maintain well under the earthquake which had the maximum acceleration of 400 gal.
Testing methods for saturated surface-dry condition of the cohesive soil and sand mixture which is necessary for determine the amount of water based on the concept of effective water content in the manufacture of soil cement concrete are presented. The authors have proposed four methods in the previous papers1), 2) capable of determining the apparent saturated surface-dry condition of soil by means of the drying acceleration, silica gel, relative permittivity and pF method. In this paper, it is confirmed that the saturated surface-dry condition of mixtures of 6 types of cohesive soil, a river sand and a recycled fine aggregate with variable grain composition and moisture content can also be determined by both drying acceleration method and pF method. A relation between water absorption of the mixture and mixing ratio of cohesive soil and sand has been derived in a simple formula.
sturated surface-dry condition of aggregates can be estimated by the Japan Industrial Standard for the manufacturing of mortar and concrete. However in soil-cement concrete using cohesive soil in addition to sand and cement, the control of moisture content of soil is very difficult thereby no attention has focused on the saturated surface-dry condition of soil. The authors have defined the concept of apparent saturated surface-dry condition of soil in the previous papers and proposed four evaluation methods1), 2). In this paper, experimental results of strength and density of concrete with cohesive soil-sand-cement system using a new concept of effective water of soils are presented, and a mixture design principle for the soil-cement concrete using cohesive soil and sand is described.
This paper deals with the effects of the mix proportions and curing conditions on the flexural strengths of MDF cements before and after water immersion are discussed to find out the effective processing techniques for improving their water resistance. As a result, the hydrolysis of a water-solu-ble polymer and the accelerated hydration of ordinary portland cement during autoclave cure are most effective to improve the water resistance of MDF cements. The optimum autoclave curing condition for improving the water resistance is a heating under a pressure of 0.98 MPa at a temperature of 180°C for 7 hours.
The mechanical properties of steel fiber reinforced concrete subjected to tension and shear are investigated experimentally and their mathematical models are presented. High-strength concrete is used for specimen. The angle between a fiber and the crack surface is considered as a main parameter. The tensile behavior is influenced by the fiber angle. The maximum load is reduced when the fiber is not perpendicular to the crack surface. For shear loading, the maximum load is also reduced when the fiber direction is opposite to the shearing direction. These experimental results are expressed by using the multi-linear nonlinear model and the parallel structural model simultaneously and the validity of the modeling is confirmed through simulation.
This paper deals with the manufacturing systems of architectural precast concrete retaining wall textured. The one is the wall mounted with waste cut-ashlar on the face. The ashlar is set on the face of the concrete before setting. The other is the wall coated with sand. The sand is mechanically dropped on the face of concrete before setting. This technique can economically make the face of the concrete wavy as well as coated with sand. Since the pattern of both wall systems does not look regular norrandom but does appropriately fluctuate, it looks soft, warm and natural.
In constructing a particularly deep slurry wall down to a depth of 120 m by the tremie method, the tremie became blocked with concrete during the casting of one of the elements. This demonstrated a need for clarification of the mechanism of tremie clogging, knowledge of which would enable us to improve methods for the trouble-free construction of deep slurry walls. Of particular relevance is deciding on suitable materials and how to mix them, as well as managing concrete quality control and control of the tremie casting process. We have therefore tested concrete for various characteristics, separated it into components for analysis, measured pressures within the tremie, and carried out pressurization and dehydration tests on concrete to determine the. cause of tremie blocking. Based on our measurements, we have reached important conclusions regarding the selection of high-strength, high-fluidity concrete materials and their mixing, as well as regarding other measures to prevent tremie blocking. In this paper, we identify the mechanism of concrete clogging in a tremie and propose measures to prevent it.