In Japan, the qualities of Portland blast-furnace slag cement have been rapidly improved by the“Separate Grinding Method”recommended by Dr. Touru Mori. The present author's study up to this time show that there exists a slight difference in quality between concretes using ordinary Portland cement and Portland blast-furnace slag cement under the condition of the approximately same water-cement ratio and slump, and that the former can be advantageously used for the conventional structures or those which have the massive section or may be affected by sea water. However, it should be noted that the high content of iron-blast-furnace slag in concrete retards the development of early strength, and thus it requires longer initial curing and mold retaining periods by one or two days than the ordinary Portland cement, while it provides higher resistances against heat, acid and sulfates in sea water and hot spring water.
The mix proportion, production and curing, of concrete placed in cold weather such as the average ambient temperature under 4°C and the 4weeks accumulative temperature below M. 370 D.D. (3.2°C), are specified in the code of JSCE and AIJ, respectively. Especially the temperature and duration of the initial curing, in order to prevent the early damage due to frosting, is carefully specified in these codes.1)2) Consequently the thermal insulation to keep concrete warm and (or) the heated curing during the cold weather concreting are the customary practice although the expense for such special treatments become a considerable level in the total cost. This report describes the results of performance tests on ANF-28, a special AE water reducing agent which is newly developed by Nisso Master Builders. ANF-28 concrete can resist to early freezing without heated curing down to -10°C and gives satisfactory strength without any deterioration of performance of concrete. Furthermore, this report includes two field test results at cold weather sites (forecasting temperatures, 5 to -10°C and 0 to -20°C).
In the field of civil engineering, the use of superplasticizer is expected to be applied practically to improve workability of low slump concrete. It is supposed that low slump concrete get smaller effect of superplasticizer or larger tendency of segregation because of its larger size of aggregate, smaller s/a or smaller unit cement content. But studies on the use of superplasticizer to low slump concrete are not enough, and especially reports about superplasticized concrete using aggregate of more than 40mm size is scarce. From such viewpoints, this study was aimed to clarify the influence of unit cement content on the effect of superplasticizer by examining the properties of superplasticized concrete in which slump of base concrete was 4 or 8cm and cement content was varied. The essential conclusions obtained are as follows. (1) The effect of superplasticizer on consistency of concrete changed with unit cement content (or unit fine powder content) of base concrete, and the consistency increased with increasing cement content. (2) There existed the minimum content of superplasticizer required to obtain its effect according to unit cement content, and it remarkably changed at about 260kg/m3 of unit cement content (or 390kg/m3 of fine powder content). (3) There existed the maximum possible gain in slump obtained from the addition of superplasticizer, which changed with unit cement content of base concrete. Segregation was produced if slump higher than the maximum value was attemped without increasing fine powder content of concrete. (4) The properties of superplasticized concrete of low slump except the above mentioned were almost the same as that of high slump.
In this report, one type of air entraining agent, two types of air entraining and water reducing agents and one type of superplasticizer were used as admixtures. The concretes with these admixtures were called A, B, C and D concrete, respectively. In order to compare the segregation properties of these concretes and a plain one P, the bleeding ratio and variation of unit weight of constituent materials in the vertical direction of prismatic test pieces due to compaction by an internal vibrator were measured. The conclusions were as follows; (1) The vibrating compaction time required for the concretes with admixtures was shorter than that of plain concrete on the condition of a given slump and water cement ratio, that is, P, A, B, D1 and C concrete in the order of its magnitude, and the time for D2 concrete with the same slump and lower water cement ratio was the shortest. (2) The degree of air loss due to vibrating compaction was C, B and A in the order of its magnitude. The larger the magnitude of air loss, the smaller the degree of segregation. (3) The bleeding ratios of A, B, C and D1 concretes were nearly equal, and that of P concrete was larger than those up to 90 seconds of vibrating time, but decreased to the same value with prolonged vibrating time. The bleeding ratio of D2 was equal to zero regardless of change of vibrating time. (4) The ratio of the subtraction of absolute volume of coarse aggregate in No. 1 layer from that in No. 4 layer concrete to that in the specified mix, (g4-g1)/g0, may be regarded as the segregation characteristic factor. The change of this factor due to vibrating compaction was closely related to the variation of mechanical properties.
Fiber reinforced concrete contains a large amount of short fibers randomly dispersed into cement concrete and this composite material is superior to normal plain concrete with respect to its flexural strength, impact resistance and ductility. But the consistency of concrete is extremely decreased by adding fibers so that in some cases it becomes difficult to place and mold by the ordinary method. These phenomena are observed irrespective of kinds of fibers used. In this paper, the effects of compaction methods on the strength of fiber reinforced concretes having poor consistency and containing a fairly large amount of fibers were investigated·Conventional steel fibers and alkali-resistant glass fibers were used. Test specimens (10×10×60cm) of plain and fiber reinforced concretes were compacted by external vibration with temporary or continuous compressive loading, and were tested in flexure. The mechanism of compaction effects was discussed. The test results indicate that the compaction with compressive loading increases the flexural strength of both types of fiber reinforced concretes as well as the extensibility of glass fiber reinforced concrete although the improvement is made within a certain limit of compaction loading.
This paper describes the analytical results of the physical properties of cement paste and mortar aged at 20±2°C up to 3 hours or 24 hours. The ultrasonic method was applied to investigate the longitudinal and the transverse pulse propagation properties. The dynamic modulus of elasticity, the dynamic modulus of viscosity and the relaxation time of cement paste and mortar were calculated from the pulse velocity, the frequency and the attenuation constant, respectively, and they were found to be frequency dependent in this time period. The dynamic modulus of elasticity of cement paste changed from 107 to 109dyn/cm2 depending upon the water cement ratio and the elapsed time, and the dynamic modulus of viscosity from 10 to 105dyn·sec/cm2, until the age of 3 hours. The dynamic shear modulus and the dynamic bulk modulus were calculated by the longitudinal and the transverse pulse velocities and the density of specimens. It is found that the visco-elastic analysis is a meaning method to predict the development of these properties for the cement paste and mortar.
The expansion characteristics of expansive concrete are greatly dependent upon the restraint condition of concrete itself. In this study, the restrained expansive strains of main (longitudinal) and lateral reinforcing steels embeded in expansive concrete as well as the relations between them were investigated experimentally and theoretically. Authors reported previously the method of calculating the restrained strains of expansive concrete having only longitudinal reinforcement, that is, under uniaxial restraint. But under biaxial restraint, the chemical prestressing in one direction due to the restraining steel reduces the expansion in another direction. By considering the poisson's effects, the next equation was proposed. εRX=εRx0-Kx×εRY+ν×εcey where, εRX, εRY; restrained expansive strains under biaxial restraint in the direction of X and Y, respectively, εRx0; restrained expansive strains under uniaxial restraint, ν; poisson's ratio (=0.2), εcey; elastic strain caused by chemical prestressing, Kx; expansion reducing coefficient. The results obtained from experiments and theoretical analysis are summarized as follows. (1) The restraint expansive strain of main (longitudinal) reinforcement are not strongly affected by the lateral reinforcement. (2) Chemical prestressing in the direction of main reinforcement reduces the expansion in the direction of lateral reinforcement and the expansion reducing coefficient K may be expressed as a function of lateral reinforcement ratio.
The failure characteristics such as strength and toughness of various types of concretes including steel fiber reinforced concrete and light weight concrete, were investigated in order to contribute to the establishment of evaluating methods of the characteristics. The following results were obtained. The shear strength measured from the direct a double shear tests was proportional to the tensile strength. The absorbed energy ratio Wcq/Wcp in compression was found to be a useful parameter to indicate the failure behaviour of concrete, that is, how suddenly concrete loses its load carrying capacity after the maximum loads reached. Wcp indicates the absorbed energy of a specimen up to the point of maximum load Pmax, and Wcq the one up to the failure point, where the load descends to 1/3 of Pmax. The ratio Wcq/Wcp was well related to the brittleness index, which is the ratio of compressive strength σc to tensile strength σt. The effect of steel fiber reinforcement on the improvement of concrete toughness was greater in flexure than in compression.
It is well known that the strength and modulus of elasticity of the porous materials vary with surface tension when they are wetted by different kinds of liquids, and the moisture content in the materials has an important effect on their mechanical properties. The test program was carried out to investigate the effect of the surface energy of impregnating liquids on the strength, elastic modulus and swelling of the following materials; river sand mortar, aerated cement mortar, calcium silicate board, hardened gypsum (α-type), Japanese cypress and glass plate. In this test, four kinds of liquids which have different surface energies were used as follows; 72.8erg/cm2 (water), 64.4, 42.9 (blended liquid) and 22.5 (methanol). The effects of moisture content on the flexural, compressive and tensile strengths were examined at the following moisture content: 100%, 80, 60, 40, 20 and 0% (absolute dry). The test results show that the strengths of all the testing materials except the frosted glass plate decrease with increasing surface energy of impregnating liquids. Each material has its own particular surface energy dependence of strength. The swelling of length in the cementitious materials and gypsum specimens increases with increasing surface energy of liquid. It is considered that the cause of the strength reduction of material is lowering of interfacial energy (γSL).
In order to investigate the fatigue life of concrete under varying repeated load, several stress fatigue tests were performed. In these tests, concrete cylinder specimens were subjected to the repeated load in which load levels were selected as to be between a constant minimum stress level and five different maximum stress level Sj (72∼82 percent of the ultimate static strength at each interval of 2.5%). The triangular-, normal-, uniform-, and exponential-distributions were used as the shape of the stress block for the varying repeated load. The order of the applied maximum stress level was selected at random. From the experimental results, it can be concluded as follows. (1). At each test condition, the sun of cycles ratio follows a logarithmic normal distribution. (2). Miner's rule may possibly be applied to predict the fatigue life under varying repeated load in which the magnitude of stress is changed quite very frequently.
The amount of waste concrete from demolished old buildings and pavements has increased in the last 10 years. This has brought about the disposal waste concrete problem in urban areas. Such waste concrete is hard to deal with properly and thus, it is important to recycle it as an aggregate for concrete from the view points of shortage of aggregate from river, energy and resouces saving as well as environmental preservation. The objective of this paper was to investigate the compressive, tensile and flexural strengths, drying shrinkage and durability against freezing and thawing cycles of the recycling concretes with the aggregates obtained by crushing old concrete buildings and concrete pavements. The main results obtained in this study are summarized as follows. (1) The physical properties of the aggregate produced from a concrete pavement are more favorable as an aggregate for concrete than those from a demolished concrete building. (2) The compressive, tensile and flexural strengths of the recycling concrete from a concrete pavement are greater than those of the recycling concrete from a concrete building. (3) The drying shrinkage of the recycling concrete is greater than the natural aggregate concrete. The recycling concrete made with the aggregate from a concrete building shows a greater shrinkage than that made with the aggregate from a concrete pavement. (4) The resistance of the recycling concrete from a concrete pavement against freezing and thawing cycles is better than that of the recycling concrete from a concrete building. The resistance of the recycling concrete made with a concrete pavement is increased by adding an AE admixture, being somewhat inferior to that of the natural aggregate concrete.
Recently polymethyl methacrylate concrete (PMMA-REC) has become widely used for the patching work and precast concrete production because of its good workability and high early strength. It is significant to determine the working life of PMMA-REC on the condition comparable to the ambient temperature in the application field. The purpose of this study was to examine the working lives of PMMA-REC and its binder under various temperature conditions. PMMA-REC was prepared with variation of initiator and promoter contents, and the effects of initiator and promoter contents on the working lives of PMMA-REC and its binder were tested under various temperature conditions. In conclusion, the working life of PMMA-REC is possible to be controlled with variation of initiator and promoter contents, and the nomographs for determining the promoter content at each initiator content under various temperature conditions are proposed.
There are various test methods to evaluate delayed failure susceptibility of prestressing steels depending upon loading ways, environments and shape of specimen. In order to find out the most suitable method, three kinds of delayed failure tests have been carried out on induction quenched and tempered SiCr prestressing steel bar and cold drawn prestressing steel wire, under the following conditions. Loading: constant load, constant strain and slow strain rate. Environment: 20% NH4SCN (50°C) and saturated Ca(OH)2(20°C). Shape of specimen: smooth or single edge cracked round bar. The following results were obtained. 1. The same tendency was observed between the test results with 20% NH4 SCM solution on the smooth specimen (FIP test) and those on the single edge cracked specimen. 2. The evaluation of delayed failure susceptibility obtained by SSRT on the smooth specimen was different from those obtained by FIP test and by the test on the single edge cracked specimen. This difference is considered due to the difference in applied stress between SSRT and constant load test. 3. FIP test was found to be practical one to evaluate the susceptibility of delayed failure of prestressing steels when judged from its availability and symplicity for carrying out tests.