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 relation between flow and plastic viscosity is discussed to clarify the fluidity of mortar which has good performance for filling narrow space. In addition, the relation between the index of segregation of mortar and the particle size of fine aggregate is investigated segregation resistance of mortar.

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. In addition, some fresh concrete samples including ferro-nickel slag (FNS) fine aggregate and FNS coarse aggregate were also conducted tamping test to investigate fluidity and segregation resistance of concrete.

Compaction by using vibration is important to obtain high quality concrete. Faulty construction usually occurs when compaction of fresh concrete is not appropriate. However, it is difficult to control compaction by using vibration because compaction time and insert interval time of vibration depend on judge of workers. Also, working environment affects compactibility of fresh concrete. In this study, compactibility of fresh concrete is investigated to understand effect of reinforcing bar array.

Most of small pre-cast concrete products are usually cured in steaming chamber, and curing of them are not needed at construction site. So, the advantage of pre-cast concrete is able to shorten the work period. Therefore, it is expected promotion of utilization of pre-cast concrete products. On the other hand, removing of large scale pre-cast concrete products is not easy, and there is little information on durability of them. In addition, continuity of the hydration reaction of them is expected from rainfall after construction. Here, molds of concrete structures are normally removed at early age of concrete, and then the microstructure of the surface of concrete is different from inside. Study on relation between the microstructure of concrete and water supply is not enough. Therefore, mechanical properties and durability are investigated focusing on the relation between the microstructure of surface of concrete and water supply.

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, 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. Assuming the fracture energy of interface between existing concrete and repairing material, the shear bonding behavior is analytically estimated.

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, visual inspections at all water treatment plants were conducted out to obtain much information on deterioration of concrete. In addition, water quality survey was also carried out at water treatment plants. Core samples taken from ozone contact basin and biological activated carbon adsorption basin, were tested on several chemical analysis.

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 influence of macro surface geometry of the pavement blocks on the direction of the reflection of inputted infrared.

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..

Nucleation of the fracture process zone is a key issue for determining of the fracture energy. The fracture process zone is known to be created in front of an existing crack in concrete. It is well known that the fracture energy varies with specimen size and geometry. In addition, development and size of the fracture process zone play an important role in fracture energy in concrete. Therefore, it is important to investigate development process of the fracture process zone and generation mechanisms of micro-cracks in the zone. In this study, three-point bending tests are conducted in notched concrete beams which have different notch depths and different maximum sizes of aggregate. The generation mechanisms of micro-cracks in the fracture process zone are discussed based on results of AE measurement. SiGMA (simplified Green’s functions for moment tensor analysis) procedure is applied to identify AE sources because the technique is applicable to classify micro-crack into three modes of tensile, mixed-mode and shear cracks. In addition, the relation between the fracture energy and the width of the fracture process zone is discussed.

Tokyo Metropolitan Government has drawn up a long-term bridge strategy for long time use of existing bridges. Especially, Kiyosu bridge and Eitai bridge in Tokyo have been designated as a nationally important cultural property, maintenance of these bridges is in great demand. Buckle plate (BP) slab have been adopted for these bridges. BP slab consists of steel plate and concrete, its characteristic is that steel plate and concrete are not connected structurally. The adopting of BP slab is rare in highway bridges in Japan. Since there is little information about fatigue durability on BP slab, fracture mechanisms and fatigue durability on BP slab have not been clarified yet. In addition, it is important to draw up a maintenance strategy of BP slab. In this study, wheel load running test was conducted to real-size BP slab specimen to investigate fatigue durability and fracture mechanisms. The specimen was subjected to 1.29 million loading cycles before applying Acoustic Emission (AE) monitoring and elastic wave method. Results of AE source location in wheel load running test is in good agreement with peeling area between concrete and steel plate. In addition, damage degree of concrete in BP slab could be estimated by elastic wave tomography.