Asphalt in old mixtures has a low penetration and a high penetration-index. Consistency of asphalt added a recycled agent can be predicted by a simple law of mixing, and it has a considerable relation to its chemical composition. Recycled mixtures can be compacted as easily as general mixtures. Resistance of recycled mixtures to deformation in the wheel tracking test is higher than new mixtures, and water-resistance is better too. Resistance of recycled mixtures to cracking is nearly equal to that of new mixtures. The influence of mixture stiffness on the performance of pavement is related to the pavement structure. If the quality of recycled mixture is variable, the conversion factor in the pavement structural design must be reduced.

抄録全体を表示

In case of pire structures, reinforcing steel bars are cut off by the way, then those are resulted to be anchored in tencile zone of members. Some pier structures are damaged by earthquake near those section.
Presented in this paper are
(1) Results of a series of experiments by using modified specimens on failure mechanism of those members.
(2) Some rational proposal for structural design method concerning to earthquake.
(3) On the basis of the results obtained;
Resisting moment capacity of anchored zone will be raised till equivalent level as base of piers, which guarantee 1.5 times against calculated moment.

抄録全体を表示

A study was made to explain the inconsistent and/or unexpected frost resistance of superplasticized concrete observed in the previous work. It was found that the observed difference in the durability was closely related to the spacing factor of air bubbles in hardened concrete. The addition of superplasticizers generally increased the spacing factor and this effect was enhanced when the slump increase by the admixtures was large. A suggestion was made to entrain about 0.5% more air than in usual concrete to ensure sufficient durability of superplasticized concrete. Air entrained at the time of superplasticizing was found not to be effective in improving the frost resistance. Superplasticizing ability of commercial admixtures was also discussed briefly.

抄録全体を表示

This paper experimentally clarifies how the ductility of overreinforced concrete beams is improved by transversely confining reinforcements. The results of flexural failure tests of 30 specimens indicate that the confining reinforcement with a close spacing and an enough amount gives a remarkable ductility to the beam, and that to confine compression zone of the beam only is more effective rather than to do its gross cross section. In addition, a stress-strain curve of the confined concrete proposed by the other investigators is modified herein, and it is shown that the modified curve enables to predict the flexural behavior of such a beam up to ultimate state with sufficient accuracy.

抄録全体を表示

This research work was intended to clarify the effects of steel fiber by way of shear reinforcement and furthermore to formulate equation of shear strength for design, considering the case of applying it to reinforced concrete structual member. Several testes of beam specimens were carried out so as to obtain fundamental informations regarding ultimate shear strength and shear failure mode. Based on test results, mechanism of shear resistance has been considered from macroscopic viewpoint, comparing with a case of normal reinforced concrete beam without web reinforcement. In consequence, experimental equation of shear strength, evaluating effects of steel fiber on shear reinforcement in terms of volume contents of steel fiber, has been proposed by modifying already formulated equation of shear strength of reinforced concrete beams without web reinforcement.

抄録全体を表示

The contents of the study were first to clarify the strength characteristics of the special super high early strength cement at different temperature, secondly, to clarify what effect freezing exerts on the increase of strenght when the concrete is subjected to freezing at the initial period of hardening, and thirdly, to clarify the resistivity when the concrete at the initial period of hardening or after sufficiently hardened is subjected to the repeated rapid freezing and thawing. It was clarified by this study (1) that the concrete using special super high early strength cement showed the very high manifestation of strength even at low temperature and short age, (2) that when the concrete was subjected to freezing at the initial period of hardening, the lowest compressive strength just before freezing, with which the increase of strength was able to be expected by continuing freezing, was about 50kg/cm² similarly to ordinary concrete.

抄録全体を表示

The use of steel fibre-reinforced concrete (SFRC) immune to rutting and distortion would provide excellent, smooth and durable overlays on the existing asphalt pavements. This paper aims to find a way of mechanical analysis of the SFRC overlay system and to set up a design method of the SFRC overlay slab thickness.
According to model and full scale loading test, it clearly appears that the SFRC overlay system has a great deal of resistance against actual traffic loads and can be presumed as a multilayered composit pavement which regard the existing asphalt pavement as a part of SFRC slab, and it is further shown that the “yield-line theory” can be applied basically to the design method of slab thickness.

抄録全体を表示

The properties of bond between reinforcing steel and concrete in a reinforced concrete structure are extremely complex, and an effective method of accurately testing bond strength has not yet been found. In this study are proposed a splitting and an eccentric pull-out test methods with a the principal aim to simulate the properties of bond failures of deformed bars. The former expresses the bond failure from splitting of concrete due to wedge actions of lugs of deformed bar, whil the latter expresses the bond failure due to shear of concrete between lugs of tension bars reinforced by lateral bars with short space, and detailed studies were made regarding shape and size of specimens, and procedures of testing in order that bonding performances can be satisfactorily tested.

抄録全体を表示

This paper discusses various factors affecting the temperature rise characteristics of massive concrete structures during construction on the basis of analyses of numerical values and actual measurements. Pertinent factors are concrete adiabatic temperature rise, thermal properties of concrete, placing temperature, ambient temperature, thickness of member, coefficient of heat transfer, and curing. The following became clear after the investigation on various factors affecting the temperature rise. The effect of concrete temperature rise appears clearly. If we show characteristics of it by an empirical equiation Q(t)=Q_∞(1-e^-rt), the effect of Q_∞ and r on temperature rise is independent. Further, in the paper I wish to propose a simple method which permits us to arrive at a solution of sufficient accuracy by means of results obtained through the investigation on various factors affecting the temperature rise.

抄録全体を表示

The major failure mode of reinforced concrete slabs subjected to a concentrated load on the small loading area is governed by punching shear. After the first study of Talbot in 1913, many research works have been carried out to investigate the mechanism and to derive a punching shear load equation. In Japan, the empirical equation analyzed statistically by Kakuta et al. has been used to be the most appropriate one to explain test results. However, it seems to be unappropriate to explain the punching shear load of one-way slabs using a rectangular loading pad. The authors have derived an equation applicable to one-way slabs also, which is composed of the ultimate shear strength in compression zone along the perimeter of the loaded area and the splitting strength of bottom covers induced by the dowel force of reinforcement.

抄録全体を表示

It is important that we fully understand physical properties of concrete in thermal stress analysis of mass concrete. The purpose of this paper is to investigate such properties of mass concrete. I used two kinds of aggregates and several sorts of mix proportions of concrete in this investigation, and obtained compressive strength, tensile strength, modulus of elasticity, Poisson's ratio, flexural strength and coefficient of thermal expansion.
Also I compared splitting strength with tensile strength obtained by pure tension test. In order to understand quantitatively and qualitatively these properties of mass concrete, I related them to maturity and curing ages. I moreover refer to the method of estimation of these properties from compressive strength obtained by the specimens in water curing at 20°C.

抄録全体を表示

The effects of material properties (concrete and steel), cross-sectional properties (reinforcement ratios and dimensions) and axial loads on the cross-sectional dissipating energy up to yield-ending point of RC beams are theoretically investigated. The dissipating energy of RC beams increases with an increase in both toughness (area under stress-strain curve) of concrete and compression reinforcement ratio. When pσ_sy (tension reinforcement ratio; yield strength of steel) is relativelly small, pσ_sy has little effects on the dissipating energy of RC beams. Equations for calculating upper and lower limits of tension reinforcement ratio for ductile failure of RC beams are presented by using toughness of concrete. Dissipating energy W_it, and plastic rotation capacity φ_ρ (=W_it/M_u) are proposed as toughness parameters of RC beams.

抄録全体を表示

The present paper describes the test results of flexurally restrained RC beams subjected to temperature gradients, considering the conditions prevailing in the cylindrical wall and the bottom slab of the RC LNG tanks. Experimentally obtained results concerning flexural rigidities, cracking behaviors, etc. are discussed comparing with those under room temperature.
The theoretical approach previously proposed by the authors is expanded to the cases in which RC members are flexurally restrained under temperature crossfall. The comparison of the theoretical results with those obtained from the experiments confirmed the validity of the proposed method, provided the temperature dependent material properties are to be taken into consideration.

抄録全体を表示

In the past, scale effect on the shear strength of reinforced concrete beams has been studied by some researchers, and it is found that the nominal shear strength V_c/bd, of beams without shear reinforcement decreases as the effective depth of the member increases. However, the effective depth in the previous studies was limited only to 110cm. In order to investigate the scale effect for larger-size reinforced concrete members, this study was undertaken on members with six different depths ranging from 10 to 300cm, all with constant b/d ratio, under uniformly distributed loads. The result reveals that the scale effect exists even for members deeper than 100cm and the nominal shear strength is inversely proportional to the fourth root of the effective depth.

抄録全体を表示

For calculating the deformation of reinforced concrete members under working load, it is important to estimate the tensile resistance of concrete after cracking. The authors has previously demonstrated the method for generally applying the Branson's approach to reinforced concrete members subjected to combined bending and axial force. However, it has been impossible to calculate strain by using the method.
In this paper, based on the extension of the Branson's approach, method for calculating mean steel strain in reinforced concrete members is studied, and it is found that an expression of the same type as the transition of centroidal axis location can be used also for the transition of neutral axis location in the effective section. By comparing test results with calculated results, it is concluded that the method is satisfactory.

抄録全体を表示

This paper describes the adhesion strength of the tunnel joints with the quick hardening resin mortar developed for a new small diameter automatic tunneling method. The authors examined the bending strength of small model tunnels and specimens sampled from a real tunnel constructed by the new tunneling method. The results obtained are summarized as follws:
(1) The bending test of the model tunnel shows that the adhesion strength of the tunnel joints with scarfed shape is almost equal to or more than the resin mortar strength.
(2) The fracture mechanism of the tunnel joints is divided into three types, and the bending strength distribution of the joints is also dinided into three regions because of the fracture mechanism.
(3) The adhesion strength of the tunnel joints are mainly affected by hardener ratio of the resin mortar.

抄録全体を表示