The dephosphorized slag obtained from steel making process is a promising material for use as admixture in portland cement concrete. The synthesized belite (β-2Ca0·SiO2) admixture was developed by burning the dephosphorized slag at 1100°C. This synthesis contains a large amount of β-C2S, synthesized by nothing free-CaO components in the deshosphorized slag. The optimum mixing ratio and amounts of SiO2, CaO and the optimum burning temperature were determined. Though strength of mortar replaced OPC by 10-30mass% of the synthesized belite admixture was low at shorter ages, but it was expected to increases the strength at later ages. The adiabatic temperature rise was showed lower than OPC mortar. These properties was contributed by the existence of β-C2S in the synthesized belite admixture.
In the case where concrete is placed at places requiring high durability, the LCA method has made clear that placing durable high-strength concrete is more effective in reduction of environmental burden than placing ordinary concrete a few times. It has also been found that preparing of high-strength concrete by mixing an ettringite-formed high-strength additive makes it possible to decrease the unit weight of cement requited to attain a designed strength, thus further contributing to reducing environmental burden. Owing to its decreased unit weight of cement, the high-strength concrete produces less amounts of fines when crushed and, therefore, can probably be recycled in full as aggregate.
Reuse of waste fresh concretes can contribute the resource saving and control of industrial wastes emission. Addition of a suger set-retarding agent and a superplasticizer to the waste fresh concrete and subsequent wet-screening resulted in the Eco mortar, for which an applicability to the preceding mortar for concrete pumping constructions was studied. It was shown through the experiments of setting, fluidity and compressive strength that the appropriate amount of the chemical admixture to meet the requirements can be determined as a function of ambient temperature and the Eco mortar can be used in the next day or later. Full-scale concrete pumping experiment using the Eco mortar as a preceding mortar was conducted in a ready-mixed concrete plant and a pumping efficiency equivalent to the 1 : 3 mortar was obtained.
The deformational behavior of steel fiber reinforced concrete is important because it affects the crack width which influences the durability of the structure. In this study the deformational behavior of steel fiber reinforced concrete subjected to uniaxial tension and shear was investigated experimentally. In the experiment the effects of the volumetric fiber content, the fiber geometry and the fiber embedment length were investigated. Highstrentgh concrete was used in the specimen. From the experimental results models for the deformational behavior of steel fiber reinforced concrete under uniaxial tension and shear were obtained.
In expressways high bridge piers exist in mountainous areas. Some of such high piers are higher than 50m, and were designed to have hollow cross sections to minimize self-weight. The longitudinal reinforcement was curtailed at several levels according to the previous seismic codes. Since seismic retrofit of high bridge piers has been conducted in few cases and has many restrictions, planning and desigh of seismic retrofit involves a number of technical decisions. From the experimental results, authors proposed design method for seismic retrofit of high piers with carbon fiber sheets and a retrofitting work of hollow circular piers with an average of 53 m were performed according to the study.
In order to reduce the labor needed in the arrangement of shear reinforcement, a new method of simple mechanical splice for shear reinforcement was developed. And also in order to examine the effect of this splice on mechanichal performance of RC member, (a) tensile test for reinforcements using developed splice, (b) uniaxial compression test for RC columns, (c) flexural-shear test for RC beams, and (d) reversed cyclic loading test for RC columns, were carried out. In these tests for RC columns and beams, the comparisons between specimens with shear reinforcement using conventional anchorage and using developed splice were made. Test results indicate that shear reinforcement using developed splice as well as using conventional anchorage have the effectiveness of preventing the buckling of the longitudinal bars, confinement associated with shear reinforcement, and shearing performance.
Carbon fibers are one of the most effective materials for seismic strengthening. However fire endurance of strengthening with carbon fiber reinforced plastics (CFRP) should be taken into account because of its combustibility. This paper describes the several tests in accordance with methods of Japanese Industrial Standard; tensile strength tests of CFRP exposed with elevated temperature, residual tensile strength tests of CFRP exposed with elevated temperature, quasi-noncombustibility tests of CFRP and fire resistance tests of wall, column, column with wing walls and T-shaped beam specimens strengthened with CFRP. As the results of the tests, tensile strength of CFRP at 40 °C decreased to approximately 40-50 % of normal tensile strength. Residual tensile strength of CFRP had heated up to 200 °C were two-thirds of normal tensile strength. CFRP covered with a plaster board had quasinoncombustibility. For fire resistance, reinforced concrete members strengthened with CFRP maintained their functions during 2 hours. Reinforced concrete walls or slabs with CFRP penetrations maintained their functions during 2 hours.
This paper investigated the volume changes of high strength mortars cured in water. The effects of characteristic microstructure on the volume stability were considered in relation to the formation of microcracks. The results indicated that mortars without silica fume exhibited continuous swelling for long ages and the ones with silica fume shrank for a certain period after immersed in water, but started to swell at long ages. Cracking at long ages was confirmed for mortars with and without silica fume. However, there were distinct differences in the characteristics of crack pattern, such as the situation for cracking and their effects on the strength development between both. It was suggested that a mechanism other than autogenous shrinkage was involved in the volume changes that occurred in mortar with an extremely low water/binder ratio. Generation of internal expansive pressure due to the late cement hydration should be taken into account in the mechanism that cause microcracks in mortars at long ages.
In the construction of steel-concrete composite structures, the use of self-compacting concrete is effective because the compacting with vibrator is generally impossible. In this case, it is necessary to avoid the formation of excessive gaps between steel and concrete due to the initial subsidence and shrinkage of concrete. This paper describes the influences of the kinds of cements and admixtures on initial subsidence and gaps formed under the diaphragms. Furthermore, the effectiveness of pressing place method to reduce the amount of gap is discussed. As a result, it is found that subsidence behavior and the amount of gap under the diaphragm differ considerably depending on the kinds of self-compacting concrete. In addition, it is found that the pressing place method is useful to reduce the amount of subsidence and gap formed under the diaphragm.
Steel fiber reinforced concrete is a material the tensile properties of which are improved by the bridging effect of fibers. It is still necessary to make clear its mechanical properties under variousloading in order to apply steel fiber reinforced concrete to general concrete structures. In this study the pullout properties of three kinds of steel fibers under repeated loading are investigated experimentally. Based on the experimental results a model to express the pullout properties is developed using a multi-linear model.
This study aims to obtain useful basic data for design performance of prestressed concrete (PC) structures and creating macro-models of prestressed concrete beams. It deals with the investigation of effects which various factors such as connection type (compressed type, unit type), PC tendon type (round or deformed), lateral reinforcing steel quantity, etc. would have on various characteristics such as rotational angle distribution of plastic hinging region, PC tendon strain distribution, lateral reinforcing steel strain distribution, crack pattern, plastic hinge length, etc. It further reports on load baring and deformation mechanism for PC beams with different connecting system and PC tendon type.
Carbonation of mortar was examined when limestone powder was substituted for cement, water and sand.In addition, the influence of factors such as total porosity, air content and unit cement content oncarbonation of mortar were considered. The total porosity of mortar defined in this paper as porosity which includes the influence of air content is an important consideration of carbonation. The amount of carbon dioxide which penetrates mortar is determined by its total porosity. The carbonation coefficient decreases linearly with a decrease in total porosity, due to the linear decrease of carbon dioxide penetrating the mortar. The penetration rate of carbon dioxide is controlled by the unit cement content. As a result, the carbonation coefficient is inversely proportional to the unit cement content of mortar.
This paper reports about experimental results carried out in order to obtain data about yield rigidity of concrete member reinforced with strands which have higher tensile strength and lower bond strength with concrete than usual deformed bars. The following things was made clear, 1) bond failure occurs easily as shear span ratio become smaller, 2) yield rigidity become smaller as shear span ratio become smaller, 3) bond between strands and concrete of specimens whose shear span ratio are more than 3.5 works effectively. And in case of specimens whose shear span ratio are 4.5, yield rigidity is almost equal to calculated value by the way of calculating it which distance from neutral axis and strain in a cross section are in proportion, and calculating method of yield rigidity of concrete member reinforced with strands is supposed.
There are several voids in the ground behind lining concrete of aged tunnels. This induces the structural instability. It is necessary that these voids are filled with a backfilling grouting material to improve the stability of the tunnels. Conventional grouting materials have some problems, e.g. its high cost, and the difficulty in injection into targeted portions. We have developed a new grouting material to solve these problems. This grouting material consists of cement, bentonite, high water absorbent polymer, set accelerating agent and water. This paper reports on the design concept of this material, fundamental properties, the results of field experiments, and the applications to actual aged tunnels.
An idea for concrete recycling is proposed for the 21st century. When demolished concrete is crushed after heating, aggregate is obtained with satisfied qualities for concrete without destruction of the shape. For produced powder, the chemical composition is presumed. The possibility of recycling cement with reducing of limestone is shown. If thus concrete recycling included cement and aggregate is done, resources and carbon dioxide discharge are reduced. Before long, the external diseconomies like these will be reflected the cost of product. Concrete recycling included cement should be intended for reducing external diseconomies for environment.