The objective of this paper is to investigate the effects of fine aggregate grading and granule volume in concrete on the behavior of fresh super workable-concrete with viscosity agent, for the full-sandwich structure. The granule volume was adjusted by blast furnace slag powder as fine aggregate. The behavior of fresh concrete was studied by slump-flow test evaluating defomablity and by V-type funnel test evaluating flowability through small openings, which is one of the most important properties of self-compactable concrete. It is experimentally verified that these properties are not remarkably changed by fine aggregate of different kinds or granule volume, but the self-compactability of concrete is improved by using of blast furnace slag powder as granule.
The fluidity of highly-flowing concrete is influenced by the fluidity of composed mortar. This paper discusses the rheological-estimation of the fluidity of highly-flowing mortars. It is considered that the characteristic of fine aggregate is the most influential factor for fluidity of mortar. The viscosity equation proposed by Mori and Ototake for the condensed suspension liquids was examined first for its application to highly-flowing mortar. Mortars with different volume concentrations of fine aggregate suspended in highly-flowing paste were tested. The results of the rheological tests a Brookfield type viscometer indicated good applicability of the equation. Provided that the fluidity of mortar behaves as a Bingham fluid, it can be estimated by the plastic viscosity and yield value. The tests were also made on two types of highly-flowing mortar used for highly-flowing concrete with 60-70cm of slumping flow value. The effect of fine aggregate varied with water content, sand content and sand grading. The test results showed that the character of sand remarkably affects the fluidity of highly-flowing mortar.
The diversity of concreting methods in recent years has led to a demand for long retardation of concrete setting. Conventional research has achieved retardation for up to about 3 days by the addition of a set retarder, but few studies have dealt with concrete that is placeable after a much longer period. This paper reports the effects of the set retarder dosage and temperature on the slump, period of set retardation, time limits for superplasiticizing and compressive strength of concrete. The usability of concrete with long-retarded setting is disscussed as well.
Self-compactable high performance concrete, which can be poured in casting forms without any compaction, is of importance to many engineers because of the reliability of economic and efficient construction of concrete structures by utilizing very little manpower for placing of void free concrete. By the mix design method proposed in this paper, it is possible to choose the required average strength, water content and sand/aggregate ratio to suit special and particular conditions of concrete structures under various environmental conditions.
The strength and the durability of concrete are affected by interfacial zone (also called transition zone) which is porous and made around aggregate. In this paper, this interfacial zone of cement pastes which contain limestone powder (LP) or granulated blast furnace slag (BS) is evaluated with Vickers hardness test and fluorescence microscope to clarify its structure and character. The addition of LP makes the interfacial zone become thinner to some extent as LP reduces bleeding rate because of its large specific surface area. So the thickness of the interfacial zone of cement paste with LP is related more closely to the water-powder ratio than the water-cement ratio. The specific surface area of LP, however, affects the character of the interfacial zone only a little. On the other hand, the specific surface area of BS affects well the character of the interfacial zone. The interfacial zone of specimens with BS of large specific surface area becomes tighter and thinner than the one with BS of small specific surface area, though the interfacial zone of all specimens with BS is tighter than the one without BS.
This research was carried out to study the basic properties of concrete making good use of the properties of lapilli as coarse aggregate. The following results were obtained. (1) The level of specific gravity under an oven dried condition and the percentage of solid volume of this lapilli were L and A in the classification of lightweight aggregate. The 24hr absorption was 70.45% and the percentage of floating particles in the lightweight coarse aggregate was 11.5%. The 10min absorption was about 80% of 24hr absorption. (2) The concrete weight of unit volume was almost the same as that of the grade 2 lightweight concrete, and the maximum compressive and flexural strengths were 105 and 23.8kgf/cm2 at the age of 28 days, repectively. (3) The 24hr absorption and drying weight loss percentage of the lapilli concrete were much greater than those of the gravel aggregate concrete. The drying shrinkage was almost half that of the gravel aggregate concrete before the age of 14 days and then approached that of the gravel aggregate concrete. The thermal conductivity was 60% that of the gravel aggregate concrete. (4) The washed finish by use of 20% super retarder solution was effective to expose color of lapilli on the concrete surface. The reduction of flexural strength by the finish was only about 5%. The impact absorption and elastic repulsion on the concrete surface could be improved to the level of an elastic asphalt mixture, which can reduce a burden to a body due to exercise. (5) The concrete blocks with exposed lapilli on the surface were used experimentally for pedestrian pavements. The depth of the surface abrasion was about 0.8mm and the color tone was good enough after 10 months of use.
Resin concrete (REC) is a concrete in which aggregates are bonded with synthetic resin instead of cement hydrates in ordinary cement concrete. For the structual use of the resin concrete, the thermal and temperature-dependent mechanical properties of RECs were experimentally examined. RECs with various resin contents were prepared by using two kinds of unsaturated polyester resins and two kinds of epoxy resins with different heat distortion temperatures (HDT) and glass transition temperatures (Tg), and tested for thermal properties such as specific heat, thermal conductivity and coefficient of thermal expansion, and temperature-dependent mechanical properties such as dynamic Young's modulus, logarithmic decrement, creep coefficient and compressive and flexural strengths. Thermal properties of RECs were very similar to those of ordinary cement concrete. Deformation and strength properties of RECs were temperature-dependent, and showed distinct inflection points in temperature in the respective properties where temperature-dependence became dominant. The inflection points were related to the HDT of the resins used rather than Tg, and were not affected by the resin content. The points can be defined as “heat distortion temperatures of RECs”. The maximum ambient temperature must be limited to these points or lower for the structural use of RECs. Consequently, the high HDT of the resins is preferable for structural RECs.
The after-set type prestressing tendon is newly developed for post-tensioning of concrete. Without grouting, this tendon has the same structural properties as the grouted tendon. This paper presents the properties of after-set type prestressing tendon and the flexural behavior of concrete beams using the new tendon. After-set type prestressing tendon is composed of prestressing steel coated with a cold setting epoxy resin in a corrugated polyethylene sheath. The hardening time of the resin can be controlled by the amount of curing catalyst that hardens after stressing and then bonding with concrete occurs through the sheath. The concrete specimens embedding the tendon and the beams reinforced with the tendon were prepared. The pull-out test, fire resistance test and flexural test of the beams were carried out. In conclusion, the bond strength of after-set type prestressing tendon is equal or superior to that of the prestressing steel with cement grout. The concrete cover of after-set type prestressing tendon needs about 55mm, 65mm and 75mm for 30 minutes, 1 and 2 hours of fire resistance periods respectively. The concrete beams using the after-set type tendon show the flexural behavior similar to the concrete beams using the prestressing steel with cement grout.
In this paper, the dynamic properties of the distributed and unbonded prestress system was analyzed by giving the following prestress. One end of the bar-type element was fixed and the unit-tensile-prestress was given from the other end. Then another element was attached to the first one's end and the unit-tensile-prestress to the complex was given from its end. This process was repeated until it became the prescribed size. The system was analyzed and the equations of the prestress distribution was formulated. The result of the analysis shows that the prestress accumulates and the direct tightening load decreases when the constant distributed and unbonded prestress is given. Also the experiments were carried out to verify the equations.
In this paper, by using the available data on interior beam-column subassemblages tested by the authors, the estimation method of story deformation angles at beam-yielding and maximum-load, and ultimate story-drift has been proposed. And the estimated values are compared with the measured values. The following statements can be made from this study: (1) The story deformation angles at beam-yielding and at maximum-load are estimated approximately by the addition of deformation in beams, columns and joint panel of subassemblages. These deformations in structural members of subassemblages are estimated by the equations previously developed by the authors. (2) The ultimate story deformation angles are estimated approximately by the estimation equation proposed in this study, considering the shear stress level in the joint panel and the amount of transverse reinforcement of joint.
This paper presents the results of tests made to study the effects of accumulative damage, column height, and longitudinal steel ratio on the vibrating properties of R/C columns. The random waves acceleration recorded by actual earthquakes in Japan-Nihonkaichubu-were induced on the specimens. Two kinds of dynamic tests were carried out. The column specimens which have three kinds of height and two kinds of longitudinal steel ratio were tested. From the test results2), the changes in vibrating properties were examined and compared with the last test results. It was found that the effect of accumulative damage on the damping factor was larger than that on the natural frequency and the dynamic damage in the natural frequency was mainly affected by steel yielding. Furthermore, the effects of column height on the natural frequency and damping factor agreed well with the expectation, and the effect of longitudinal steel ratio was not so significant.
Some kinds of reinforced concrete structures in the natural environmental condition suffered from damages due to combined causes, i.e. chloride corrosion, carbonation, alkali-aggregate reaction (AAR), and so on. In this study, it is tried to clarify the effects of these combined deteriorating causes on the steel bar corrosion and durability of concrete structures. The first objective of this study is to investigate the effects of water cement ratio, AAR and chloride content on carbonation in concrete. The second one is to make clear the microstructure of concrete affected by combined causes. The pore volume and pore size distribution of mortar were determined by a mercury penetration method. The test results are summerized as follows; (1) The carbonation rate in concrete is not affected by the chloride content. This phenomenon is proved from the results obtained by the pore distribution measurement. (2) The carbonation rate and microstructure of concrete are affected largely by water cement ratio. (3) The chloride corrsion of reinforcing steel is accelerated by the degree of carbonation.
Acoustic emission (AE) is a phenomenon caused by the propagation of elastic wave generated from micro cracks as sources. A procedure named as SiGMA (simplified Green's function for moment tensor analysis) to identify the crack kinematics from AE waveforms has been developed recently. By this procedure, the crack location, crack orientation and crack type can be determined. To apply the SiGMA procedure for AE source inversion in two-dimensional (2D) models, the SiGMA-2D procedure is proposed in this paper. The in-plane uniaxial compression tests of poly-methyl-metacrylate plates having an internal through-thickness slit are carried out for the experimental verification of SiGMA-2D solutions. These results confirm the applicability of the SiGMA-2D procedure for elucidating the crack mechanism. Crack identification by using SiGMA-2D is also performed in the mixed-mode fracturing of concrete and mortar plates, and the fracture process is investigated.