This research was carried out to develop a simple method to judge the compaction degree of roller compacted dam concrete. For this purpose, the extremely stiff consistency and lean mix concrete was placed into prisms and large scaled specimens, and compacted by surface vibrator. The compaction process was observed through a transparent side panel of the specimen mould and the cement paste pressure was measured simultaneously by pressure gauge embeded in the bottom part. On the other hand, compressive strength was measured at the age of 28 days. Cement paste moved downward at early compaction stage, subsequently the moving direction changed to upward and spaces between aggregate particles were filled up thoroughly by cement paste. The pressure in cement paste increased only a little at early compaction stage, subsequently increased rapidly and attained to the maximum value at a certain compaction level, and then turned to decrease. The periods taking to reach to the maximum pressure were nearly equal to those corresponding to the maximum compressive strength. Therefore, the adequate compaction degree could be judged by measuring the cement paste pressure from embeded pressure gauge during compaction process. It was observed that this method could be also applicable to the concrete with maximum size of 80mm coarse aggregate. Still more, the gauge attached to the end of steel pipe was embeded in the large scaled specimen, and after compaction effort the pipe could be pulled out easily and be reused.
This paper deals with the elastic anaylsis of prestressed concrete beam members on the assumption that after deformed they retain the original planarity of their concrete section while the bond-slip of the tendon steel is allowed for. In an initial effort differential equations governing their bending and prestressing are derived based on the potential energy principles; then the finite element formulation of the problem is implemented; and associated numerical examples are subsequently solved whereby to examine the effects of the bond-slip between the reinforcement and the concrete after the tensioning, and of the friction between the tendon and the duct at the transfer of prestress.
This study is to investigate the effect of lateral confinement such as stirrups and hoops on both the elasto-platic behaviors and the ultimate limit capacities in reinforced concrete beams under high-speed loadings. From the experimental results for RC beam specimens having various binding ratios, the relation between ultimate limit capacities and binding ratios was obtained quantitatively, and the conventional procedure for flexural analysis is developed by introducing both the effect of confinement and the strain-rate effect. To improve the ultimate limit capacities against high-speed loadings, reinforcing steel bars were simply added in parallel with the axial reinforcements so as to improve the efficiency of the lateral confinement. This way of reinforcing can be of effective.
Many investigation and studies have made in the past regarding carbonation of concrete, but hardly any explanation has been made concerning the basic mechanism by which carbonation occurs. The present study explains the mechanism of carbonation based on the chemistry of pore solution which has been spotlighted re-cently as a promising means of elucidating the deterioration mechanism of concrete, along with which it is pointed out that the chemical factor governing the rate of carbonation is the pH of pore solution.
Experimental studies were carried out to clarify the mechanism of the flexural behavior of reinforced concrete beams with low reinforcement. Experimental results showed that the strain of tensile reinforcement at the crack portion reached the strain hardening point immediately while the reinforcement at the other portion was under the yielding stress. The load-deflection curves were shown to fluctuate after the yielding of the beam due to the local strain hardening and the bond failure near the crack portion. An analytical model to evaluate these phenomena was obtained.
Migration of CO2, gas and diffusion of moisture are the most dominant factors for the carbonation of concrete. Although many previous studies reported about the influence of mix proportion and type of cement on carbonation of concrete, the carbonation speed is influenced also by curing condition and age of the specimens. Moreover, Some studies reported that the carbonation speed became slower and slower as the testing duration was longer. In this paper, mortar specimens with various types of mix proportion were tested by an accelerated carbonation tests to study the influence of the Mix proportion. The test data was analyzed from the view point of the micro structure measured by mercury porosimeter.
Although higher water cement ratio makes concrete workable, the durability is strongly reduced. Recently there are some ideas to use holed Molds in order to take off the surplus water from the surface after casting the concrete. In this paper, the mechanism of water dissipation and changing the micro structure were studied. Effectiveness of holed Molds to increase the resistance to the carbonation of concrete was also proved by experimental tests.
Carbonation of concrete is one of the most important factors for durabilityc of concrete structures. Although there are some formulae to predict the carbonation speed, quite few experimental studies have been reported concerning the influence of environmental moisture and temperature on the carbonation speed, so far. In this paper, a parametric study was performed to investigate the influence of environmental moisture and temperature on the carbonation speed of mortar. While accelerated carbonation tests were carried out, water cement ratio, relative humidity and temperature were changed. In the moisture condition of 40-50 % RH, the carbonation was mostly accelerated. The higher the temperature, the faster the speed of carbonation became. Temperature increased proportionally in the tested range from 15°C to 37.5°C. Finally carbonation speed of concrete was estimated all over Japan on the basis of the mean values of climate data (relative humidity and temperature) in each region reported by Japan Meteorological Agency.
This paper describes the test results about the properties of Low Heat Supper Flowable Nonsegregating Under-water Concrete by using ternary cement contains cement, G. B. F. S snd Flyash. Test results are summerized as follows; 1) Performance of the concrte, like flowability, setting, strength, adiabatic temperature rising are influenced by property and proportion of cementitious materials and agent. 2) Flowability was closely related to the cellulose deviature absorption phenomenon on cementitious materials and fine aggregate. We prporsed new mixing method of Nonsegregating Underwater concrete which could improve the flowability and stability of concrete.
At the Bijyogi Interchange of the Expressway Itabashi-Toda Line, the “Makurabari” is installed atop diaphragm walls foundation that are combined with side walls of underpress and used to support a reinforced concrete pier. Static loading tests were performed with regard to the structures for the dual purpose of checking the items stated below and gathering data for planning. 1) Capacity regarding seismic horizontal force. 2) Effectiveness of the “Makurabari” for stress distribution. 3) Reinforcement methods used for the joints of the pier, the “Makurabari” and the walls. The results of the tests clarified the following points. 1) The strength and the ductility are adequate. 2) Based on elastic analysis, the effective width used in the design is safe. 3) One part of the reinforcement of the pier is anchored in the “Makurabari” and the walls. 4) The methods of bar arrangement (longitudinal bar and stirrup) with regard to the torsion of the “Makurabari”.
In this paper, a macro model and its analytical method are proposed for analizing the maximum strength of multistory framed shear walls. The features of the proposed model are following : the shear resistance and bending moment distribution of columns and the slip shear strength of wall panel are considered. The analytical method is based on the lower bound theorem in the limit analysis. By using this model thirty specimens selected by the JCI committee, which failed in shear failure or in flexural failure mode, were analized. From the analytical results it is shown that the model is more adequate than the others' models in accuracy of analysis and range of application.
In order to establish a method of mesuring the flow properties of high-strength concrete, experiments have been conducted reffering to the Two-Point Method suggested by G. H. Tattersall. As a result, the following have been proven; 1) The tested apparatus is applicable to use on high-strength concerete with a widerange of consistency by means of using Tattersall's rotating impeller. 2) The value of relative plastic viscosityobtained by the Two-Point Method can be used for the viscosity equation of high-density suspension. 3) Relativeyield value have a close correlation to coarse aggregate volume concentration. Therefore, the plastic viscosityand yield values of concrete can be estimated based on those of mortar and concrete mixture.
The purpose of this study is to develop super flowing concrete (SF concrete) which can be placed uniformly and compacted densely without any mechanical vibrator. This SF concrete is produced by using superplasticizer to provide high fluidity and cellulose viscous agent to increase resistance against material segregation. This paper reports the relationship between consistency of SF concrete and admixing ratio of superplasticizer and cellulose viscous agent, but also the characteristics of specimens that are placed SF concrete having different consistency. The series of tests clarifies that SF concrete offers uniform and dense concrete structure without any vibration.
A total pore structural analysis was made for Autoclaved Lightweight Concrete (ALC), and the resulting bimodal pore distribution model was adopted to examine the moisture characteristics of ALC. To combine the isothermal adsorprion data with mercury porosimetry data, basic thermodynamic model was developed, and an automated and high resolution experimental techniques were also presented. Two critical moisture content involved in the water absorption and thermal conductivity of moist specimen were discussed in terms of the bimodal pore distribution model.
This study reviews the Rapid Test Methods for measuring the Unit Water Content in fresh concrete. These are the Rapid Drying Method and Radioisotope (RI) Method. Several examinations on the performance of the two methods are carried out.The required efficiency for the instruments employed in the methods is that sample weight should be more than 4kg and measuring time be within 20 minutes. Results show that using these methods combined with the Automatic Recorded Batching Weight makes the concrete quality control more efficient and more powerful.
A method was proposed for predicting the lives of reinforced concrete structures which were determined by corrosion of einforcing steel due to chloride. The present method was based on the expressionderived from the various experiments. In order to study the applicability of this prediction methodto real structures, a reinforced concrete structure in ocean environment was investigated which wasconstructed 30 years ago.Concerning cracking of concrete and corrosion of reinforcing steel, the predicted results almost agreed wite the results, of the field investigation. Consequently, proposed method showed validity on life prediction of reinforced concrete structures deteriorated due to chloride.