Recently, ultra high-early strength cement has come to be widely used in the field of concrete. Tests were conducted to clarify the effects of admixtures on the ultra high-early strength cement, selecting some kinds of admixtures with different composition, with reference in particular to the following items: (1) The kinds and dosages of water-reducing agents that have effect on them (2) The effect of air entrainment and compressive strength on them (3) The effect of curing temperature, unit cement content and strength on them (4) The effect of the time of setting of concrete on them As a result, it has been found that proper use of an optimum kind of admixtures can also improve the properties of concrete with ultra high-early strength cement as in the case with normal or high-early strength cement.
During the process of manufacturing fresh concrete, excess air of more than 3% gets sometimes entrapped during the mixing operation without AE agent. This phenomenon is supposed to due to the surfaces of the fine aggregates of sand and admixtures made hydrophobic by their contamination. The following examinations have been conducted of 27 kinds of sand collected throughout our country. (1) Extraction of sand by ethanol/benzene (vol. ratio 1:2) (2) Examination of oily layers of the extracted sand in respect of their water repellency (3) Examination of fine sand in respect of its water/kerosine interfare, respectively as it has been extracted and as it is to be extracted. As the result it has turned out that water repellent and hydrophobic sand tends to cause excess air to be entrapped. Kerosine test is proposed to be an effective method to examine hydrophobicity of sand surfaces.
“The JSMS Tentative Specification for the Chemical Admixtures for Structural Concrete” was drafted in 1968 by the Committee on the Chemical Admixtures for Concrete, Japan Society of Materials Science, and has since been put into practice. It was in conformity with this Tentative Specification that tests were carried out of thirty-five kinds of water-reducing agents generally on the market throughout Japan including both of accelerating sort and of retarding one. Double objects were intended in these tests, to examine the efficacy of these agents on one hand, and on the other to collect technical data for deliberation of possible requirement in future for revision of the“Tentative Specification”currently in practice.
The author reports hereunder on the compressive strength of concrete with particular reference on size and volume fraction of coarse aggregate. The aggregates used were glass marble, river gravel, crushed stone and expanded shale. Concrete with expanded shale has distinctive aspects in failure mechanism. It is shown, however, that in all cases the larger is the aggregate size and the more aggregate is contained in the concrete, the lower is concrete strength, and that the strength of single-sized aggregate concrete is expressed as a plane in a space co-ordinates with the strength and aggregate size and volume fraction of coarse aggregate as its axis. The author extends the rule to the ordinary concrete and presents an interpretation that concrete has its own strength composition according to the volumetric distribution of size of coarse aggregate.
The purpose of this experimental study is to investigate the strength of concrete having the cubic aggregates of cement mortar under uniaxial compression. The cement mortar aggregate with and without thin coating of paraffin were provided respectively, to examine the effect of bond between aggregate and mortar matrix on the compressive strength of concrete. The cylindrical concrete specimens of φ10×20cm were made by mixing the above mentioned aggregate and the cement mortar, and were tested at the age of 28 days of concrete. The test results are summarised as follows; (1) The bond strength between the aggregate without paraffin coating and the mortar matrix was about 13-14kg/cm2. (2) The bond strength between the paraffin coated aggregate and the mortar matrix was almost zero. (3) The compressive strength of concrete decreased with increase of the volume fraction of aggregate in concrete, regardless of the surface condition of aggregate. (4) The compressive strength of concretes hardly increased in spite of increase of the compressive strength of aggregate, expect the concrete having lower volume fraction of aggregate than 0.2. (5) The compressive strength of concrete having the aggregate with paraffin coating was only about 20-25 percent of the strength of concrete having the uncoated aggregate, under higher volume fraction of aggregate in concrete than 0.45.
The abbreviation CPC may stand either for concrete-polymer composite, for concrete-plastics composite, or for concrete-polymer combination, like WPC which may stand either for wood-polymer composite, or for wood-plastics combination, as the present author chooses to use for convenience. CPC is a composite material developed for the purpose of improving the properties of concrete and mortar and is generally prepared from vinyl-type monomers impregnated in concrete or mortar used as base materials, by their polymerization either by heat or by radiation. In the experiment reported in this paper CPC has been prepared by heat polymerization of methyl methacrylate monomer (With addition of benzoyl peroxide as catalyst) impregnated in dried mortar, and its various properties, such as its strength, waterproof virtue, heat resistance, chemical resistance, are tested and discussed. In this case, the polymer loading (Percent) of CPC for testing is 13±0.5% by weight of the untreated mortar. The conclusion obtained from these experiments is summarized as follows (1) CPC has a structure that many voids in mortar used are filled by polymethyl methacrylate, and the polymer is incorporated into the mortar perfectly, so that its properties for example strength, water proofing property, chemical resistance, etc. are excellent compared with those of mortar as the base material. (2) The heat resistance and resistance to boiling water at 100°C, of CPC, are good, regardless of containing the polymer as a constituent.
Concrete is subject to cracks because of its high hardening-and-drying-shrinkage, and also of its low tensile strength and extensibility. It is owing to that defect in concrete that the roof-deck cannot be perfectly free from cracks. Various plans have so far been devised and carried into effect to cope with these drawbacks in concrete of generating cracks and propagating them, so as to secure for the roof-deck complete waterproof virtue. Most of these waterproof contrivances consist of covering the roof-deck with layers of films which we may call roofing membranes. Of the roofing membranes then it is required as of paramount importance in the roofing system that they will on no account rupture, whatever may be the width of the cracks that occur in the concrete of the roof-deck. Special attention must, therefore, be paid to adjustment of such physical properties of the roofing membranes as its tensile strength, its maximum elongation, its modulus of elasticity and its resilience, of its thickness and of its adhesive strength to the roof-deck. In this paper the resistance of the roofing membranes to the cracks in the concrete of the roof-deck is theoretically and experimentally discussed. As the result the condition that effectively protects the roofing membranes from rupture in spite of the cracks in the concrete of the roof-deck is proposed as follows: τs≤4d/lRs where τs: Shear-adhesive strength of the roofing membrane material to the concrete of the roof-deck in kg/cm2 d: The thickness of the roofing membrane in cm Rs: The limit of resilience of the roofing membrane in kg/cm2 l: The crack width in the concrete of the roof-deck in cm. This equation has also been applied to polymer roofing membranes which were made up of synthetic polymeric roofing sheets and polyurethane fluid-applied roofings, and their resistance to cracks in the concrete of the roof-deck has been tested.
Though earlier investigations regarding stress distribution in the compression zone of concrete members in flexure have dealt with the problems in the limited range of extreme fiber strain from zero to the ultimate flexural strain of about 0.003, it is essential in studying the post-crushing behavior of reinforced concrete beams to know the properties of concrete stress block under the excessive flexural strain beyond the ultimate value. The eccentrical compression test, similar to Hognestad's method, were carried out on normal-weight and light-weight aggregate concrete, in which emphasis was laid on obtaining the descending branch of resultant force in the compression zone versus extreme fiber strain diagram. Variables in this experimental investigation were type of aggregate for concrete and strength of concrete. The test results show that the coefficients k1k3 and k2, related to magnitude and position of resultant force, can be obtained continuously with the increase of extreme fiber strain beyond the ultimate value if the loading condition is adequate to control the sudden release of strain energy. The complete stress-strain curves derived from the eccentrical compression tests are presented and compared with the stress-strain curves obtained from the control cylinder tests. The influences of the shape of compression zone on the properties of stress block are also discussed. The results are quantitatively applicable to analysing the behavior of reinforced concrete flexural members near failure.
In the process of prestressing concrete (Abbrev. PC) construction, grouting is a very cumbersome and costly job. But non-grouted PC members sometimes cause such troubles as the stress corrosion of the prestressing tendon. Viscous asphalt is an efficient anticorrosive agent for the prestressing tendon, and it prevents by virtue of its grease effect the tendons and sheath from being bonded together. The first section of the present study describes the test results of friction coefficients of asphalted PC bars sheathed in wrapping paper. We may conclude, from the test result, that the asphalted PC bars show smaller values of friction coefficient than conventional ones in steel sheath. The second section gives an account of the test made of the unbonded PC beams with various depths. No appreciable difference in flexural behaviors of unbonded PC beams was found between those with the asphalted PC bars and those with bare bars in the steel sheath. It was found that the larger the flatness of the section of the unbonded PC beams at failure was the greater the working tensile force in the bars was. The third section gives an account of the test made of the effect of bars location in the section of unbonded beams. It was found that the unbonded PC beams with large eccentricities for resultant prestressing force and with concentrated location of the bars gained higher utilization of PC bar strength at failure. In the fourth section, the flexural properties of the assembled precast unbonded PC beams were investigated. It was found that monolithic beams of lightweight concrete with large eccentricity of resultant prestressing force and with concentrated location of the bars gained higher utilization of PC bar strength.
As the low cost fillers commonly used with the thermosetting resins there are typical fillers such as talcum, clay, silica and glass. It is generally expected that these filleres will perform such functions, when used to fill the thermosetting resins, as to increase viscosity, pot life, opacity, hardness, thermal conductivity, and at the same time to decrease compound cost, maximum exotherm, shrinkage, etc. On consideration of improvement of electrical properties, especially arc resistance by blending the fillers with thermosetting resin, except the above fillers, it is known that various fillers such as CaCO3, TiO2, Mica and Asbestos are suitable. To meet these demands however, our knowledge of fillers is generally poor, and further study of them indetails is required. Epoxy resin was adapted as the sample and Epikote 828 was used. As the curing agent, amin type one was used and was mixed with the basic quantities to the 100 parts of Epikote. Furthermore, as the fillers, halogen, oxide, carbonate, sulphate and silicate mineral was used. Then the measurement of arc resistance was carried out according to the standard method of ASTM D 495-61, the test at the high voltage low current arc. The following results have been obtained from these experiments. Such fillers as Fluorite, Diaspore, Dolomite, Enstatite, Pyrophyllite, Chlorite, Supentine and Eucryptite are superior in the elevation of arc resistance, and superior to Talcum in such properties as higher loading, lower cost, facilitating casting, long pot life, lower exotherm etc.
The behaviors of typical metals during plastic deformations such as rolling, plastic tension etc. and also during fatigue process have been investigated by utilizing the X-ray microbeam technique. On the other hand, the improvement of microbeam technique has also been attempted. In this study, the total misorientation and micro lattice strain caused by plastic tention were investigated by the X-ray microbeam method in a way different from the reported study. The diffraction patterns were photographed in a normal incidence as well as in oblique incidences, the angle between the specimem normal and the incident beam ψ0 being varied in three steps of 10, 20, 30°. For the sake of comparison, the normal strain ε in the direction of incident beam was kept constant by increasing the axial normal strain for larger values of ψ0. The applied normal strain ε was varied in three steps in succession of 4, 8 and 12% for all incidences. The materials used for the purpose were 0.17% carbon steel and 99.5% aluminium, and for each of these materials three or four typical diffraction arcs were traced at three steps of loading. In a simillar way of keeping the normal strain ε constant, calculations were carried out so as to retain the shear strain γ along the reflecting plane constant (4, 8 and 12%). From the experimental results, the total misorientations and micro lattice strains for these cases were obtained. The experimental and calculated results obtained may be summarized as follows. (1) In case the normal strain ε is kept constant, the total misorientation increases in the larger incident angle ψ0 both with carbon steel and aluminium, while the micro lattice strain remains almost constant with aluminium, contrary to its tendency of increase with carbon steel. (2) In the case of maintaining the shear strain γ constant, there is but little change in the total misorientation with both the materials, but their micro lattice strain decreases slightly in the larger ψ0. (3) The increment of total misorientation Δβ is mainly influenced by the increment of shear strain Δγ with both the materials. On the other hand, the increment of micro lattice strain Δ(Δd/d) is primarily effected by the increment of shear strain Δγ or the increment of normal strain Δε with carbon steel and aluminium, respectively.
In this paper the report is made of the measurement performed of the stress relaxation of plasticized PVC sheet under biaxial large deformation by means of a biaxial tensile tester. It is assumed that the material is an isotropic, homogeneous and incompressible, and the strain energy function W may be described in the following equation. W=W(I1, I2) The function W can be represented as the function of time t with respect to the stress relaxation. That is W=W(I1, I2, t). The partial derivatives of the strain energy are given in the following equation as the function of invariants of deformation tensor and time from the theory of continuous media. ∂W/∂I1(I1, I2, t)=1/2H(λ12-λ22)[λ13f1(t)/λ12-λ1-2λ2-2-λ23f2(t)/λ22-λ1-2λ2-2] ∂W/∂I2(I1, I2, t)=1/2H(λ22-λ12)[λ1f1(t)/λ12-λ1-2λ2-2-λ2f2(t)/λ22-λ1-2λ2-2](1) The force fi in formula (1) has been measured by the stress relaxation experiment as a function of time t, and ∂W/∂Ii can be obtained by substituting fi(t) in formula (1). It is observed that the relation between log(∂W/∂Ii) and log t is approximately expressed as a stright line having slope k. According to the slope of the line ∂W/∂Ii(t) is approximately represented in the following equation as a function of time. ∂W/∂Ii(I1, I2, t)=At-ki where i=1, 2, A=A (I1, I2, t=t0). The value of k is not constant for all deformation measured and also for different temperature. Some contour maps representing the surfaces of ∂W/∂I1 and ∂W/∂I2 as function of I1 and I2 are obtained for this materials at some fixed time t. It follows that the shape of contour map has not been influenced by the time, but it has been remarkably influenced by the temperature.