Recently, the deterioration of concrete due to alkali-aggregate reaction or salt attack has become a serious matter. In order to improve the durability of concrete, it has been recommended that blast furnace slag be incorporated into concrete. On the other hand, it can be expected that the use of superplasticizer is effective to improve the workability of this type of concrete. This study was conducted for the purpose of establishing appropriate mix designs for superplasticized concrete incorporating blast furnace slag, as well as gainning an understanding of properties of fresh and hardened concretes. A superplasticizer and two types of high range water reducing agent (AE type) were used in this study. The slag contents were 0, 50 and 70%, respectively. The effects of these factors were measured by slump test, rheological test, segregation test, strength test, etc. The results showed that the flowability of cement paste increased with an increase in slag content, at a constant dosage of admixture. This effect of slag was influenced by the type and addition method of admixture. Also, the slump loss of superplasticized concrete increased with an increase in slag.
In the construction of reinforced concrete structures, the construction joint work of early-age concrete is often required. Conventional techniques for adhesion improvement in the construction joint work are wire-brushing, green-cut, retarder spraying and epoxy resin-based adhesive spraying. However, it is difficult to apply the conventional techniques to the early-age concrete within 72 hours after placing because of the poor strength development of the concrete. The author has developed an improved technique using polymer emulsion treatment for the construction joint work of the early-age concrete. The purpose of this study is to make clear the effects of polymer type, jointing time and jointing method on the adhesion of the construction joints to which the polymer emulsion treatment technique is applied. Concrete was placed into molds, and the surfaces of early-age concrete were treated by polymer emulsion spraying with or without subsequent polymer cement paste spraying. Then, jointing concrete was mixed and placed on the treated concrete surfaces at various jointing times for preparing construction joint. The adhesion in tension of the construction joints was determined at curing periods of 28 days and 6 months for the jointing concrete. In conclusion, the treatment of the early-age concrete surfaces by polyacrylic ester emulsion spraying within 36 hours after placing provides high adhesion in tension of the construction joints, as compared to the treatments using styrene butadiene rubber latex and ethylene-vinyl acetate emulsion. Spraying of the polymer cement pastes on the construction joints treated by the polymer emulsion spraying causes an improvement of the adhesion in tension of the joints. Accordingly, it is considered that the polymer emulsion treatment is most useful for the construction joint work of the early-age concrete.
Relation of fracture process zone to tension softening behavior of concrete has been studied using fracture energy tests for various concrete, focusing on change in properties of the internal structure of concrete. Six series of test for the following materials were performed; high strength concretes, normal concretes, concretes with different maximal particle size, concretes in seven different ages, fiber reinforced mortars, and frozen mortars. The parameters of bi-linear tension softening model for the materials were determined based on a data fit technique to discuss the relation between the tension softening properties and the factors which affect the internal structures of concrete. The results indicate that the behavior in the beginning of descending branch of the tension softening diagram corresponds to micro crack localization and extension and that successive behavior in the tail of tension softening is attributed to the bridging mechanism at the interface between the matrix and aggregates.
Condensed silica fume (CSF) is an ultra-fine and high reactive pozzolan. Some properties of fresh and hardened concretes can be significantly improved by the use of CSF. CSF has been used in concrete to make a high-strength and durable concrete. This study aims at revealing the influence of CSF on the chloride permeability of concrete and the chloride corrosion of steel bars embedded in concrete. From the experimental results, it was confirmed that the use of small amounts of CSF could effectively reduce the chloride permeability of concrete and improve the protective function of concrete against the chloride corrosion of steel bars. With respect to the strength development of concrete and the protection against the chloride corrosion of steel bars in concrete, the most favorable replacement ratio of cement by silica fume was approximately 10%.
The structures for water supply facilities are relatively old, and sometimes they have been used for about 100 years since their construction. Nevertheless, most of them are still in a good usage state as a whole, although there are some deteriorating local places. The characteristics of water supply facilities are following; (1) free residual chlorine always acts, (2) chlorine content is relatively high in a water reservoir because the specific value of chlorine is controlled at a faucet, (3) a hydraulic pressure always acts, and (4) water always flows on the structure. Therefore, the residual free chlorine, hydraulic pressure and water stream among others are considered as the main deterioration factors. In this study, these deterioration factors are discussed from the present state survey and some experiments. Consequently, it became clear that these factors have an important influence on the deterioration. Although the deterioration is reported as a process of neutralization, it is accompanied with strength reduction. Therefore, the deterioration phenomenon in this study is different from carbonation. That is, it is caused by dissolution into water of silica and calcium in the concrete and increase of pore volume.
The mechanical properties of resin concrete are greatly influenced by the circumferential temperature, since the concrete is made by using polymer as a binder of aggregate instead of portland cement. Therefore, the range of circumferential temperature suitable for this type of structural material should be clarified. In this study, the experimental investigation on creep characteristics of unsaturated polyester resin concrete used in practice was carried out, with consideration for the change of mechanical properties due to temperature. The main results obtained are as follows. (1) The compressive strength of resin concrete cured for 28 days at 20°C was over 800kgf/cm2, and increased 15% more after 1 year. The same value of increment was obtained after 1 day curing at 80°C. (2) When the polymerization degree was high enough, the value of final creep coefficient of resin concrete at the circumferential temperature of 20°C became about 0.5. It was considerably smaller than that of cement concrete. (3) The allowable circumferential temperature of resin concrete for practical use as a structural material was found to be under 50°C. (4) It is possible to estimate the final creep strain of resin concrete by extending the curve of the relationship between the measured creep and loading time straightly on the logarithmic coordinates.
The usefulness of polystyrene aggregate concrete made of polystyrene beads and cement mortar, to absorb energy and to reduce contact loads during hard impact at low velocities has been investigated with a drop hammer impact rig. The influences of the mix proportions of polystyrene concrete, velocity of impactor (a solid shaped 31.6kg cylindrical mass) onto polystyrene concrete blocks and the thickness of polystyrene concrete specimens which were rigidly supported on a concrete base, on the contact force at impact, were investigated experimentally. The tests results show that polystyrene concrete has excellent energy-absorbing properties for reducing the contact loads while prolonging the duration of impact. So, an overlying layer of this material could provide protection to a structure by dissipating a large amount of energy, thereby decreasing the impact force transmitted to the structure.
As a diagnostic application of the acoustic emission (AE) waveform analysis, crack inspection based on the moment tensor analysis is proposed. Because moment tensor components contain information on crack kinematics, the decomposition of eigenvalues of the moment tensor is possible and the contributions of shear motion and tensile motion to crack nucleation can be determined from the ratio of eigenvalues. Thus, cracks are classified into the type of dominant motion. After the crack types are determined, crack orientations can be decided from the directions of eigenvectors. The procedure developed was applied to a pull-out test of anchor bolt and a cylindrical tension test. The results confirm the applicability of the procedure to inspecting internal cracks by the quantitative AE waveform analysis based on the moment tensor inversion.
The object of this paper is to clarify the quantification of the tactile effect of building materials from the physical one. Sensation and perception were interpreted on the basis of psychology and physiology. The concept of psychophysio-dynamics was proposed connecting psychophysics with psychodynamics. It was found that the tactile effect of building materials can be pridicted from the physical values of warmth, hardness and roughness. The applicability was verified.
Recently, polymer-modified mortars and rust-inhibitors have widely been used as repair materials for reinforced concrete structures. The purpose of this study is to make clear the corrosion-inhibiting property of the polymer-modified mortars with the rust-inhibitors and the effectiveness of the treatment of bonded concrete surfaces around reinforcing bars (rebars) with the rust-inhibitors in repairing works for such concrete structures. Polymer-modified mortars using three types of cement modifiers with variation of rust-inhibitor content are prepared, and two types of specimens 40×40×160mm embedded with rebars of φ10×130mm are molded as follows: (1) Type A Specimen: A rebar is completely embedded in a polymer-modified mortar in the specimen. (2) Type B Specimen: Each half portion of a rebar is filled with a cement mortar and a polymer-modified mortar in the specimen. Sometimes, the bonded surface of the cement mortar is treated with a rust-inhibitor. The specimens are cured, and subjected to accelerated corrosion. After that, the corroded areas of the rebars are measured to evaluate the corrosion-inhibiting property of the polymer-modified mortars and rust-inhibitor. The conclusions obtained from the test results are summarized as follows; (1) The corrosion-inhibiting property of the polymer-modified mortars is improved with the addition of the rust-inhibitor. (2) In Type B specimens using the base mortar without the rust-inhibitor, the addition of the rustinhibitor causes a maked decrease in the corrosion rate of the rebars in the repair mortar and an increase in that of the rebars in the base mortar. (3) In Type B specimens using the base mortar with the rust-inhibitor, the use of the repair mortars with the rust-inhibitor causes a rust inhibition of the rebars in the base mortar. (4) In Type B specimens with the bonded mortar surfaces treated with the rust-inhibitor, the corrosion rate of the portions of the rebars close to the treated mortar surfaces decreases and that of the end portions of the rebars increases markedly.
In order to improve the ductility of reinforced concrete (RC) members, it is very effective to confine the concrete laterally in the compression zone of section by spirals or hoops. As for the mechanical properties of confined concrete, many researchers have conducted experimental and theoretical studies, and proposed different stress-strain relationships for confined concrete. In the large deformation zone after the maximum load, however, buckling of longitudinal reinforcement may occur in RC members even if they have an adequate amount of lateral confinement, and this leads to a significant reduction in the load carrying capacity. Therefore, it is important to investigate the effects of various factors on the buckling of longitudinal reinforcement in order to make clear the load carrying behaviors of RC members after the maximum load. In this study, the effects of (i) spacing of lateral confinement (s), (ii) diameter of longitudinal bar (d), (iii) cover for lateral confinement (c) and (iv) the number of intervals having the length of s (n) on the longitudinal strain at buckling of reinforcing bars were investigated by carrying out the uni-axial loading test on RC square column specimens. Test results showed that the strain at buckling of longitudinal reinforcement became larger with a decrease in s, c or n and with an increase in d. The effect of s became more significant when the d-value became larger within the s-values selected in this study. On the other hand, the effect of d was more remarkable when the s-value became smaller.
Application of confined concrete to the compression zone of reinforced concrete columns is very useful to improve flexural ductility of the columns. However, equations to estimate confining reinforcement necessary for flexural ductility required are not established sufficiently. In this paper, the amount of confining reinforcement to give flexural ductility requirement to the columns are investigated. The main results obtained are as follows. 1) The equation (4) to calculate the required confining reinforcement ratio (ptr) was derived from the analytical investigation and examination on the previous experimental data as for the effects of various factors on ptr. The factors employed in the investiation were the rotation angle required in plastic hinges, the axial force ratio, the material properties such as concrete strength and the ratio of core area to the whole area of column sections. 2) Examination of eq. (4) indicates that (a) the ultimate rotation in plastic hinges (θu) calculated by eq. (4) is more conservative than the ultimate rotation angle of members (Ru) obtained by test columns. (b) Ru of columns failed in shear is smaller than θu, estimated by eq. (4), and (c) NZS code tends to recommend rather large confining reinforcement under low axial force ratio and rather small one under high axial force ratios.
Accurate and easy calculation of the ultimate flexural strength (Mu) of reinforced concrete (RC) columns is necessary to design the columns under flexural moment, axial force and shear force. In this paper, the following results are obtained from investigation on the ultimate flexural strength Mu. (1) Stress block coefficients κ1κ3 and κ2 at the maximum value of κ1κ3 were indicated to be useful for calculating Mu in RC columns. These two coefficients denote the ratio of the average stress of stress-strain curve up to an arbitrary strain to the compressive strength and the ratio of the strain at the location of center of gravity of the corresponding area to the arbitrary strain, respectively. (2) Equations to estimate the coefficients κ1κ3 and κ2 for calculating Mu were derived from the examination of the two coefficients, based on the stress-strain relations proposed previously for plain concrete and confined concrete. (3) Equations to calculate Mu, in which confined concrete in the compression zone and intermediate longitudinal reinforcement of the column sections are considered, were derived under the assumption of the use of the coefficients κ1κ3 and κ2, as well as the yielding of each longitudinal reinforcement in tension or compression. The evaluation of the previous experimental results of the ultimate flexural strength Mu by these equations gave about 10 percent smaller values on an average than the experimental ones, irrespective of axial load magnitude.
Recently, the roller compacted concrete is being used increasingly as a material for concrete dam and concrete pavement. The construction method for these structures requires no slump concrete, because the concrete is transported by damp trucks and compacted by vibrating rollers. It is essencially important to design an adequate mix proportion in concrete and to compact sufficiently at the field for the roller compacted concrete. The usage of portland blast furnace slag cement has increased for the concrete construction in Japan, because the cement contributes the energy saving and improvement of concrete durability. In this paper, the mixing tests for the roller compacted concrete using the portland blast furnace slag cement were carried out to determine the optimum mix proportion through testing of various properties of hardened concrete, such as flexural strength, length change, resistances for freezing and thawing cycles, and fatigue strength. Consequently, the use of the portland blast furnace slag cement was found to be quite effective as the cementicious material for the roller compacted concrete, excepting the case that the early-age strength is required. Furthermore the properties of the hardened roller compacted concrete were found to be much influenced by the compaction degree of concrete.
Blowing cement particles into voids in sandy soil by air pressure was made to improve the watertightness. The ranges of sand particle size used in this study were 0-5mm, 2.5-5mm and 5-10mm. The blowing experimented on 0-5mm sand was more effective than those done on other sands from viewpoint of watertightness improvement in spite of the fact that the set layer thickness of 0-5mm sand was less than those of the others. This method had noticeable effects with increasing air pressure and density of sand. The amount of cement supply and blowing cycles were another important factors to bring the method in success, and it was recognized that the optimum combination of the factors was in existence. The watertightness of sand treated by cement only and cured for 7 days was almost the same as that of the one treated by cement admixed with set accelerating admixture and cured for 1 day.