The strength testing methods for the quality control of shotcrete being used as a main tunnel support of the NATM are all performed at present with destructive testing methods by obtaining specimens. In actual construction work, however, more rational and simpler testing method than the pull-out testing method for testing young-age strength of shotcrete has been sought for. The authors estimated in this paper that the PARO tester used in printing factories for testing the hardness of paperrolls might be suitable to measure the range of young-age strength of shotcrete and that it would suit the purpose more effectively because it would not create much difference by the different impact directions. It was on these grounds that the authors verified the possibility of using the PARO tester for the purpose by carrying out some indoor tests. In addition, other tests were carried out to compare it with the testing method using Schmidt Hammers, which was formerly tried in the past, and to see if the difference in measurement values will occur due to the different impact directions of the PARO tester used on the hexagonal specimens. As the results of the subject tests, it has been confirmed that the proposed new testing method has good applicability for the estimation of concrete strength in range of 20-100 kgf/cm2, and therefore, has good possibility of being used for the eatimation of young age strength of shotcrete.
In the galvanic cathodic protection of atomospherically exposed reinforced concrete structures, the backfill has been used between concrete surface and zinc anode sheets. The backfill has electrical conductivity and water reserving capacity, so that it can maintains electrical contact and suppress anodic polarization. This system has been successfully used in several structures in warm region of Japan. However, there is few data in cold region. A series of tests has been conducted including freeze and thaw test, exposure test of RC and PC beams, and application test for brige beam at seaside in Hokkaido. The current decreased markedly in cold season, but enough polarization was obtained owing to the increase of cathodic polarization resistance. These test results revealed that this system works effectively in cold environment.
In recent years, as subject for large concrete structures, there has been a growing demand for mass concrete that offers both low-heat and high-strength in low-temperature environments. However, these performance demands are generally contradictionary. In order to develop the concrete technology satisfying these performance demands, basic properties of concrete were examined by using a new superplasticizer with the cementitious materials comprising moderate heat Portland cement, blast-furnace slag, silica fume, and gypsum. The result of the studies indicated that it is possible to produce high-performance concrete with low heat and high strength in low temperature environments, by means of properly combining the new superplasticizer and those materials with low water-binder ratio
The hydration of cements with various mineral composition and their microstructure formation in mortar were investigated. And the strength development of low W/C mortar was discussed form these factors. Analyses on the hydration degree of cement, composition of hydrate and pore structure of hardened mortar suggest followings ; The belite rich cement forms more C-S-H and less Ca (OH) 2 than the other cements. It is considered that the C-S-H hardly fills the large pores remained in early age, though the large Ca (OH) 2 fills them efficiently. It is also considered that the relatively small pores in later age are filled by the small increase of C-S-H. Therefore, the belite rich cement develops the relatively uniform hydrated layer composed mainly of C-S-H. It is the reasons why the belite rich cement shows the remarkable strength development in later age.
In order to analyze the distribution of temperature within concrete structures, it is understood that the characteristics of hydration heat and the boundary condition affect the accuracy of the analytical results. Especially, if the analysis is launched from the distribution of temperature around the concrete surface. Special attention is necessary to focus on the assumption of boundary condition due to the fact that the accuracy of analytical results is critically affected by the boundary conditions. Generally, the coefficient of heat conduction of the framework is utilized in the assumption of boundary conditions to carry out the analysis. However, because of the coefficient of heat conduction of framework varies with the properties of framework, surface condition and the environmental temperature, it is very difficult to measure and predict the distribution of temperature on the framework precisely. As a result, the author attempted to propose a new method to calculate the distribution of temperature of concrete by using infrared image analysis. Compared to the previous researches, this method offered more comprehensive consideration on the boundary condition from the surface of concrete to environmental atmosphere. In addition, it was also concluded that a three dimension FEM program for analyzing temperature distribution suggested by the authors was effective.
The objects of this paper are to expansion of proposed reducing rate due to opening effect for estimating the shear strength of shear wall with opening periphery above 0.4. The proposed reducing rate ru is expressed as follows, ru=√ΣAe/hl (1) In order to examine the validity of proposed reducing rate ru, the experiments were carried out by specimens having opening periphery above 0.4. The shear strength calculated by using Eq. (1) was compared with authors' and other researchers' experimental results. It was recognized that the results are very much in agreement with experimental results. And the relationships are not found with break mode. Eq. (1) is applied to the shear walls with opening until the opening periphery ratio 0.6.
In this paper, the equation describing concrete strength as a function of pore structure is proposed. The equation shows as follows : Fc=KD-a exp (-b P), where P : porosity of hardened cement paste in concrete (Effective Total Pore Volume), D : Medium pore size, K, a and b : constant. To verify the varidity of proposed equation, the following was investigated, (1) experimental conditions of compressive strength and pore structure of concrete, (2) effect of materials, age, curing condition on the relation between compressive strength and porosity, (3) relation between compressive strength, porosity and pore size by using artifical pores. As the results, the estimated strength using this particular equation showed a excellent correlation with the measured strength.
The tensile behaviour of cement composites reinforced with two different kinds of continuous fibre is experimentally investigated, and a mathematical model is proposed to explain this tensile behaviour. The proposed mathematical model, which is derived from frictional bond stress transfer between fibres and the matrix, gives reasonable agreement with the experimental results. This theoretical model demonstrates the followings : (i) The stress strain curves in the multiple cracking region consists of two regions depending on the stress transfer length of the two different fibres. (ii) The gradient of the stress-strain curve in the postcracking region can be represented as the sum of EfVf for each reinforcing fibres. (iii) When one fibre breaks upon reaching the ultimate strain in the post-cracking region, the stress supported by the fibre is redistributed to the remaining fibres. If these fibres can handle the extra force resulting from the stress redistribution, the composite will deform further and support the load. It is shown that the characteristics of the fibres and the volume fraction need to be properly combined in order to obtain high strength and high ductility. The proposed model will be useful in the design of the high-performance cement composites.
In general, it is expected that concrete structures using FRP rod as reinforcement could have high durability regardless of severity of service environment. However, for more reliable application is performed, there are some aspects that mast be resolved about long term behavior of FRP rod under high alkaline environment like as in concrete. In this study, 7 different kinds of FRP rod, which include 3 types of CFRP, 2 types of AFRP, a single type of GFRP and VFRP, are examined for durability in the high alkaline solution simulating the pore water of concrete under different prestress conditions and different exposing periods. Through this examination, it is concluded that there is a fair possibility of deterioration to occur by alkali attack not only on GFRP rod but also on the other kinds of FRP rod, such as CFRP and AFRP rods. Additionally, from the observation results by using SEM and EP-MA, main reasons of the deterioration on each FRP rod can be clarified.
This paper shows that the tension softening can be simulated by mean of finite element method with the proposed equivalent smeared crack model and random material strength. Various FEM numerical simulations demonstrate the influence of fracture energy, the scatter of concrete tensile strength, effect of boundary conditions of members on tension softening behaivor of concrete. The size effect of concrete tensile strength is given by mean of parametric numerical simulations.
A convenient method to determine the parameters of bi-linear tension softening model for concrete by using a standard fracture energy test and some standard material tests have been studied. For the purpose of describing the shape of bi-linear tension softening diagram, four parameters are introduced ; 1) softening initiation stress (Ft), 2) the first softening slope in the bi-liner model (T1), 3) the second softening slope (T2) and 4) fracture energy calculated by the bi-linear model (G'F). Once the empirical relationship between the model parameters and experimental parameters is established, the model parameters can be calculated from the equations. With introducing new experimental parameters, brittleness index (BRI) and initial fracture work (gβ), the required equations are established by using our own test data. A verification using the results of three-point bending test by other researchers was made to confirm the capability of the present method.
Cracking induced by a thermal stress must be taken into consideration when the mass concrete or high strength concrete with a higher cement content is placed'especially in winter time. The antifreezing agent, which is applied to the winter concreting, can control the freezing point of concrete and accelerate the hydration at a curing temperature even below normal freezing point whereas temperature rise due to hydration can not be restrained. We have developed a new antifreezing agent with higher range water-educing capability than that available at present, and have examined the improvement of the temperature rise associated with the reduce of cement content. Experiments have been carried out for the water-educing capability, freezing temperature, setting time, heat of hydration and compressive strength of concrete using the high-range water-educing and antifreezing agent. The applicability of this new admixture to different types of cement was also studied.
The relations between autogeneous shrinkage and hydration of cement pastes prepared with low heat cements and ordinary portland cement were studied. Two types of turning point which was not recognized in the chemical shrinkage curve was recognized in the autogeneous shrinkage curve. Time to first turning point was related to setting time of cement used. Second turning point was observed when gypsum was consumed. Low heat cement pastes expanded from first turning point to second turning point. This expansion was attributed to the formation of ettringite. It was suggested that shrinkage after second turning point was initiated with the morphological change of ettringite crystal.
Pseudo-dynamic and shaking table tests were carried out in order to investigate the effect of the strain velocity and viscous damping on seismic response tests. By developing the loading apparatus for small scale specimens, the pseudo-dynamic and the shaking table tests were conducted reasonably and reliably. From the experimental results, it was verified that the hysteresis loops of the specimens were varied by the strain velocity occurred in the reinforcement and the mortar. The difference of the experimental results between the two were scrutinized and the adequate damping ratio for the pseudo-dynamic tests was proposed.
Previous dealt with the visual assessment of the architectural concrete walls with the size of 900 mm square on the various conditions. However it is not sure that these results can be applicable to real walls of general buildings. The object of this paper is to make clear the size effect of the result by considering the assessment by concrete specimens with the size of 900 mm square, the assessment of composite photographs and the assessment of walls with real size of real buildings. The results obtained are as follows. : 1) The assessment of the concrete specimens is able to apply the assessment of the architectural walls. 2) The architectural concrete walls felt more impressive than the concrete specimens about warmth, abundance, roughness and simpleness. 3) The architectural concrete walls which felt light are felt comfortable.
This paper deals with the evaluation method of the apparent saturated-surface dry state of soil necessary for the precise control of strength on the basis of water-cement ratio. The newly proposed methods by the authors are the drying acceleration method, the silica gels sprinkling method, the relative dielectric constant method and the pF method. A detailed description of the drying acceleration method was presented in the previous paper, and the test samples, four types of sand, ten types of soil and a kaolin, were used as in the previous study. The major findings on this study are as follows. (1) The moisture content of the apparent.saturated-surface dry state of soil obtained from the singular point which can be found each moisture content-index relation of either the drying acceleration method, the silica gels sprinkling method and the relative dielectric constant method showed fairly. good agreement with each other, and the moisture content fall into that of pF.5.1-5.3 of pF-moisture content relation curves. (2) The moisture content of the apparent saturated-surface dry state of soil evaluated by four different methods coincide with each other without regards to the type of soil where by the silica gels. sprinkling method, the relative dielectric constant method and the pF method can be used for assessing the apparent.saturated-surface dry state of soil in addition to the drying acceleration method. (3) The silica gels sprinkling method can be used as a rapid test whereas the drying acceleration method should be the standard method. The relative dielectric constant method and the pF method require some special apparatus.
Deterioration of concrete due to frost damage manifests itself in the form of scaling or micro cracks that occur limitedly in the surface of the concrete, or micro cracks spread across the entire concrete. The former has become dominant as a result of proper use of AE agents. This indicates that the depth of frost damage is a key element in evaluating the decrease in the durability of concrete structures. In this study, The depth of frost damage was evaluated through ultrasonic velocity testing and pore size distribution measurements, using a test specimen in which frost damage are simulated. Furthermore, the effectiveness of the method was verified by applying to concrete structures.
Low-heat Portland cement was investigated to develop low-heat high strength concrete intended for use in low-temperature environments. Pulverized blastfurnace slag, limestone powder and silica fume were examined to improve strength at early age at low temperature. The low-temperature properties of the low-heat Portland cement were improved by using highly pulverized blastfurnace slag and increasing the calcium sulfate content. These results are due to the formation of C-S-H and ettringite at low temperature.