The use of special admixtures as a convenient mean of attaining the high strength of concrete products has been highlighted last few years. In this study, the effect of a polycyclic sulfonate, a powerful water-reducing agent, on the strength of concrete was determined and the result was compared with that of polynaphthalene sulfonate, the formaldehyde condensation product of naphthalene sulfonate. It was found that these compounds possess the following desirable properties as the admixtures for the high strength concrete ; (a) a powerful water-reducing action, (b) no air-entraining property and (c) non-retardant property. The products made with an appropriate dosage of these compounds in 500-700 kg/m3 cement mix by the routine method showed the strength over 1 000 kg/cm2.
This paper describes “The Recommendation for Design and Installation Practices of Large Diameter Spun Prestressed Concrete Piles”, proposed recently by the Concrete Committee of JSCE. One of the specific features prescribed in the recommendation is that the bearing capacity of PC piles should be decided depending upon the installation procedure to be used. In designing the pile size, a consideration should be given to the safety for seismic loads at the ultimate state. The N-Mu interaction curves for various PC piles of 0.3 to 1.2m diameter are also presented in the appendix.
This paper presents the experimental results of the relaxation behavior of three types of prestressed wires under various testing conditions including variations of the initial stress, temperature, stressing time prestretching. Also presented are brief discussions on the mechanism of stress relaxation of the steel and the application of the metallurgical theory to the relaxation behavior of the prestressed wire under actual conditions. The mechanism responsible for the decrease of stress relaxation loss in the prestressed wire the reduction of the number of mobile dislocations by either the realignment of dislocation due to cell formation or the strain aging due to free carbon and nitrogen atoms. In practice, the low stressing rate and long prestretching time give smaller relaxation loss than the other conditions because the number of mobile dislocations decreases. When the strain fluctuates, the apparent relaxation loss is smaller than the pure relaxation loss under a constant strain. It is, therefore, necessary to take into consideration the decrease of the mobile dislocations during the stress relaxation under a constant strain before the strain start to fluctuate.
Failure of concrete has been discussed mainly in the stress system. However, the failure strain system is also important for structural analysis. This paper delineates the failure strain system of plain concrete under biaxial stress, by obtaining the critical tensile strain, namely the maximum principal strain at failure, and by examining the author's results of axial force-internal pressure tests. The conclusions obtained are as follows : (1) The critical tensile strain of plain concrete can be expressed by the following simple linear equation with octahedral normal stress at failure. εcr=aσoct+b Where 'a' and 'b' are the constants obtainable from the strengths and the critical tensile strains in uniaxial compression and tension tests. (2) The octahedral failure stress of plain concrete under the state of tension-compression can also be approximated by a simple linear equation. However, the octahedral failure stress under the state of biaxial tension deviates from this equation. (3) The results of axial force-internal pressure tests can be explained well by the critical tensile strain theory. (4) The critical tensile strain theory is applicable for the strength of plain concrete under the state of biaxial tension as well as under the state of compression-tension.
The present paper is concerned with the characteristics of fracture criteria of concrete in multiaxial stress states, their representation and a proposal for design under such conditions. The concepts of fracture surface in the processes of fracture initiation, subsequent fracture and final fracture were introduced first, and then the typical ways of representing each of these fracture surfaces were discussed by taking the generalized Griffith's criterion as an example. Secondly, the experimental results of concretes together with cement paste and mortar under multiaxial stresses were obtained and compared. It was observed that all the results resemble each other when they are represented in terms of the stresses normalized by using the uniaxial compressive strength. Finally, based on these results, the design criteria were proposed.
In recent years many artificial lightweight aggregates have been introduced and marketed widely as structural concrete aggregates. The water absorption property of lightweight aggregates exerts influence on the fundamental properties of fresh and hardened concretes. Since the absorption property of the aggregates shows wide variations, 15 kinds of aggregates, including 11 artificial lightweight aggregates, one expanded slag, 2 pumices and one river gravel, were selected as the specimens for several water absorption tests under various conditions such as in normal water, boiling water, pressurized water and vacuum in order to find the common nature and interrelation among them. The rapid absorption tests such as boiling or pressurized test were not applied to the fine aggregates because of their high absorbability. The main results obtained are as follows : (1) The water saturation coefficient is about 70% by volume for fine artificial lightweight aggregates after one-day immersion in water, but it is generally lower for the coarse aggregates except for the natural aggregates. (2) The water absorption of the heat-treated aggregates is very high and it is proportional to the heat-treatment temperature. (3) From the water absorption after 30 minutes boiling, the long-term absorbability and pumpability of the lightweight aggregates can be estimated rapidly and easily. (4) The absorption in boiling water is proportional to that under pressurized condition for lightweight aggregates. This correlation is particularly notable for the oven-dried aggregates. (5) The absorption from the crosscut section of artificial aggregates is proportional to those under boiling and pressurized conditions as well as to the aggregate particle size of non-pelletized artificial aggregates. Such absorption characteristics enables us to estimate the permeability of these internal structures.
Though various studies on the shrinkage of concrete have been made by many researchers, most of them have not dealt with its mechanism. In order to explain the shrinkage mechanism of concrete, the shrinkage test and water loss test were performed in this study on three different concretes (a crushed stone concrete and two lightweight aggregate concretes). From the test results, the relationship between shrinkage strain and water loss as well as the effect of ambient humidity on shrinkage and water loss were discussed. The results of this study can be summarized as follows : (1) The water loss of concrete by drying increases with increasing water content in concrete and with decreasing relative humidity in the atmosphere. (2) When the ambient humidity is low, it is suggested that the mechanism of water loss may be divided into two processes. (3) The shrinkage strain decreases with increasing ambient humidity. (4) It is suggested that the shrinkage mechanism of concrete may be divided into two processes. In the first process, the water loss from the aggregate or capillary pore is so dominant that the shrinkage accompanied with the water loss increases slowly. In the second process, the water loss from the gel pore becomes significant and subsequently the shrinkage increases rapidly. (5) The shrinkage of concrete is roughly proportional to the water loss. However, the proportional constant varies depending upon the kind of concrete.
In the previous researches and developments of polymer-impregnated concretes (abbreviated as PIC), relatively expensive methyl methacrylate monomer was used for impregnation and the concretes (base materials) impregnated with such monomer were covered by polyethylene film, aluminium foil, etc., during the polymerization process in order to prevent the evaporation of monomer. It is the object of this study to eliminate these disadvantages in the previous studies and prepare low-priced polymer-impregnated concretes reasonably. In the experiments reported here, styrene monomer having about 1/3 of the cost of methyl methacrylate monomer was selected for impregnation and the basic conditions for manufacturing polystyrene-impregnated concretes were examined by using the heat-polymerization-in-hot-water method, which enables impregnated monomer to polymerize, but prevents the evaporation of monomer from the base material by hydrostatic pressure. In this case, the polystyrene-impregnated mortar or concrete was specially prepared by the heat-polymerization-in-hot-water method after impregnating a dried mortar or concrete with styrene monomer (with addition of trime-thyrolpropane trimethacrylate (TMPTMA) as a crosslinking agent and benzoyl peroxide as a catalyst), and the basic conditions of its process, that is, the composition of impregnating monomer, the temperature of hot water, the immersion time and the polymer-impregnating thickness (or polymer-penetrating depth), were examined. The conclusions obtained from these experiments are summarized as follows : (1) The composition of suitable impregnating monomer is : styrene 90, TMPTMA (crosslinking agent) 10, 50 % DOP solution of benzoyl peroxide (catalyst) 4-6 (by weight). (2) The heat-polymerization-in-hot-water can be attained by immersing the mortar or concrete impregnated with the monomer in hot water at temperature of 70°C to 90°C for 2 hours or more. (3) The polymer-impregnating thickness can be controlled by varying the evacuation time as well as the soaking time (in the monomer) of the base materials.
The present study utilizes the finite element method for analyzing the mechanical behavior of singly-reinforced concrete prismatic members with various covering depths. The concrete and the steel bar were represented by the finite elements, and the closely spaced bond linkages similar to those employed by Nilson were used to joint adjacent nodal points of the concrete element and steel element. The nonlinear material properties, nonlinear bond-slip relations, and the influences of progressive cracking and bond failure were taken into consideration in the analysis. The results are summarized as follows : (1) The covering depth influences the distribution of stress in steel. (2) For the reinforced concrete member with a length of 20 cm and a covering depth of 4 cm, a primary transverse crack occurs at the center of the member, and then the secondary cracks initiate midway between the primary crack and the ends of the member. However the secondary cracks initiated near the bar do not spread to the outer side even though the load increases. The bond failure occurs at the primary cracking position and at the ends of the member as soon as the secondary cracks appear. (3) The minimum space of transverse cracks is about (D+2t), where D is the diameter of the steel bar and t is the covering depth. (4) The difference between the crack width at the concrete surface and that at the bar surface increases with increasing the covering depth, but the difference does not exceed 30 per cent of the crack width at the concrete surface.
The reinforcement of “a notched-anchorage”, which is an intermediate anchorage with a suitable pocket for accomodating the anchor plate and the prestressing jack, should be designed to resist particularly the following tensile forces : (a) the tensile force (Z') in the bursting zone and (b) the tensile force (Z) around the corner of the notch. In this paper, the effects of several influencing factors on the magnitude of the tensile forces are investigated in detail by using the finite element method. From this investigation, the following conclusions are obtained : (1) The tension Z' increases with decreasing the angle θ of inclination of the prestressing force (P1) with respect to the axis of the member. But its magnitude is comparatively small, and Z'/P1 is about 0.05 in case of θ=0°. (2) The direction of the maximum tensile stress at the corner of the notch inclines by about 40° to the plane on which the prestressing force is applied. (3) The total tensile force Z depends mainly on the angle θ, and the maximum value of Z/P1 is about 0.20 in case of θ=0°. In addition, it is pointed out that the corner zone of the notch can be designed by full prestressing, and a new design method is presented here.
Recently a demand for adopting a noiseless and vibrationless construction method in the field work is growing more and more in Japan. PW-method (or the pile wall construction method) presented in this paper is an unique noiseless and vibrationless construction technique of continuous retaining wall in the field by using precast prestressed concrete piles having special cross-section. Since 1967, when this method was first applied to shore protection works at the Neyagawa River by the Bureau of Construction of Osaka Prefecture, it becomes popular year by year. This paper introduces the outline of “Draft of design code of self-supporting prestressed concrete sheet piles” prepared by the Research Group on “Pre-fabrication of bank-revetment works” in the Society of Materials Science, Japan. Various advantages of PW-method over the retaining wall construction method with temporary horizontal sufforts as well as further improvements needed for PW-method are also discussed. In addition, a convenient method of determining the embedded length of piles is proposed on the basis of the theoretical and experimental results.