首都大学東京　都市環境学部　都市基盤環境学科　コンクリート研究室

Recently, mortar - filling method has been adopted for the strengthening of existing structures using jacket plate around the structure. It is most important to fill up adequately the space between structure and jacket plate with mortar or cement past. There is a fear of insufficient filling for narrow space. It is required to make clear the components of materials in consideration of the space and the area for filling. In this study, the rheology of mortar or cement past is discussed based on the space for filling and the particle size of fine aggregate in order to clarify the factors affecting the fluidity of mortar and propose the mixture proportion.

Workability is defined as the property related to consistency and segregation resistance,. It has been evaluated according to slump test. There are several types of concrete of same slump but having different workability because of some mixture proportions and many materials. So, it is not adequate to consider that all of concrete, which satisfy the required slump, is available to construction. In this study, a several types of mixture proportions with same slump were conducted and the procedure of evaluation of workability was investigated using tamping test in consideration of shape - changing property. As a result, relation between TNU (Tamping Number per Unit area) and the volume ratio of fine particles in concrete might relatively represent workability of fresh concrete.

Most of small pre-cast concrete products are usually cured in steaming chamber. Therefore, the microstructure of the concrete is different from the concrete cured under the standard condition, (i.e., cured in 20 degrees C water for 28-day). Consequently, the carbonation rate is also different from the standard concrete. The hydrating reaction of the cementitious materials in the concrete could not continue, since the products are often stored at outdoor yard after the steam curing. In this study, the pore structures of the concretes in different curing conditions are investigated in order to estimate the durability of the precast concrete products. The curing conditions are the steam curing, sealing, and the standard curing.

a) Evaluation of Bonding Strength between Existing Concrete and Repairing Material

Since the number of existing concrete structures increases, repairing of these structures is in great demand. In addition, a tight bonding between existing concrete and repairing material is necessary for a successful repairing of concrete structure. As for shear bonding strength between base concrete and repairing material, it is difficult to evaluate accuracy shear bonding strength. In this study, some shear bonding strength tests are carried out to quantify relation between shear bond strength and degree of surface roughness in existing concrete. Failure mechanisms are investigated by employing acoustic emission method under the shear bond strength tests.

b) Investigation of Shear Bonding Behavior on Interface between Base Concrete and Repairing Material containing of Sprayed Mortar and CFRP Grid

There is an increasing demand on restore or strengthen method for existing concrete structures. As for the repairing technique, retrofitting method by using sprayed polymer mortar and Carbon Fiber Reinforced Plastic (CFRP) grids have been adopted because CFRP have such good characteristics as high tensile strength and high corrosion resistance. In this study, 4-point bending and pull-out test was carried out in a laboratory in order to investigate the shear bonding behavior between base concrete and polymer-modified mortar including CFRP grids. The shear bonding behavior is estimated based on results of the acoustic emission monitoring.

The splitting tensile strength test has been widely used to obtain tensile strength in concrete. However, it is known that the splitting tensile strength varies with specimen size, higher strength is obtained as decrease specimen size. This phenomenon is called size effect. In this study, splitting tensile strength tests are conducted for different sizes specimens to investigate relation between tensile strength and specimen size. In addition, failure processes are experimentally investigated by applying acoustic emission method. As a result, failure process is different depending on specimen size, similar strength could be obtained by introducing a correction factor to calculation equation of splitting tensile strength.

In advanced water treatment system, which consists of ozone contact and biological activated carbon adsorption basin, concrete were deteriorated by some factors based on chemical attack. However, deterioration mechanisms of concrete in the advanced water treatment system have been not clarified yet, it is in great demand for clarification of deterioration mechanisms. In this study, accelerated deteriorate tests are conducted in a laboratory to clarify deterioration mechanisms of concrete in ozone contact basin and biological activated carbonation adsorption basin. In addition, mortar specimens are soaked in some organic acid solutions. As a result, concrete does not deteriorate by water containing ozone.

a) Applicability of Extremely Dry Concrete made with Eco-Cement to Pavement

An incinerated city waste is main raw material of the Eco-cement. We should use the cement for long-term use of the landfilling area for the ash and for the conservation of natural resources, since the landfilling area for the ash cannot be prepared around the large city especially in our country. The eco-cement has a tendency to include relatively high amount of alkali metals and chloride ion compared with ordinary portland cement by the higher content of them in the main raw material. Therefore, the unit eco-cement content is should be controlled from the prevention of ASR. Also, the plain concrete, with no steel reinforcement, is suitable for the use of the cement if possible. The extremely dry concrete is the most suitable for the cement because it contains lower cement paste volume and lower unit cement content. The mechanical properties and the durability to frost action of the extremely dry concrete is investigated in this study.

b) Temperature Controlling of Sidewalk Pavement during Summer

It is serious problem for highly developed city that it is very high temperature in the daytime and the temperature is kept at night during summer. One of the reasons of the phenomenon is the higher pavement area by asphalt concrete or cement concrete. In order to improve the temperature properties at the city area, it may be essential to reduce of energy input to the pavement material and to release rapidly the stored energy to environment at night. We investigate the surface area of the pavement block on temperature behavior, since the sidewalk pavement directly influences to human being.

The thermal history is often given for concrete for quick demolding especially in precast concrete production. It is significant that structure of cement-based material before the thermal action can resist stress caused by the thermal history. The standard thermal histories recommended in specifications are not always reasonable because the formation of early age structure is different by type of cementitious material and water binder ratio. In this study, we investigate the influence of cementitious material type and water binder ratio on the structure of mortar after thermal action. The early age structures are changed by the different curing conditions before thermal action. Then we investigate compressive strength, elastic modulus and pore structure of hardened mortar after thermal history.

Existing concrete structures are deteriorated by aging, chemical attack and earthquakes. In the maintenance of these structures, it is important to estimate soundness of these structures, because optimum repairing method and strengthening method are selected based on results of estimation of soundness on these structures. Especially, nondestructive evaluation method for existing concrete structures is in great demand. In this study, elastic wave tomography method and acoustic emission method are applied to detect damaged area in concrete structure. As a result, it is found that elastic wave tomography method is applicable technique for detection of damaged area in concrete members. In addition, reliability of result of the elastic wave tomography is confirmed by employing AE monitoring.