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Research Content -2014

  1. Influence Factor and Evaluation Method for Performance of Filling of Grouting Materials
  2. Effect of Reinforcing Bar Array on Compactibility of Fresh Concrete
  3. Influence on Durability of Pre-cast Concrete Products under Curing Conditions
  4. Investigation of Shear Bonding Behavior on Interface between Base Concrete and Repairing Material containing of Sprayed Mortar and CFRP Grid
  5. Estimation of Deterioration Factors and Mechanisms of Concrete at Advanced Water Treatment System
  6. Reduction of Environmental Impact by Construction of Concrete Structures
  7. Influence of Formation of Structure of Hydrates in Early Age on Structure of Hardened Mortar under Thermal History Condition
  8. Size Effect on Concrete Fracture Energy Test
  9. Damage Estimation of Buckle Plate Slab under Wheel Load Running Test by Elastic Wave Tomography and Acoustic Emission



1. Influence Factor and Evaluation Method for Performance of Filling of Grouting Materials

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. It is known that the filling performance can be estimated by flow in grouting material. A grouting material which has larger than 250 mm flow can fill for narrow space. In this study, influence factors for filling in grouting materials which were uniformed at 250 mm flow, were investigated by several tests. As a result, it is suggested that the boundary of filling for narrow space is determined by plastic viscosity.

2. Effect of Reinforcing Bar Array on Compactibility of Fresh 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.

3. Influence on Durability of Pre-cast Concrete Products under Curing Conditions

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.

4. 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, 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.

5. Estimation of Deterioration Factors and Mechanisms of Concrete at Advanced Water Treatment System

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 and abrasion by activated carbon. 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. As a result, it is estimated that concrete in biological activated carbon adsorption basin has been deteriorated by carbonic acid which comes from breathing of microorganism in activated carbon. Then, abrasion test for mortar specimens by fine aggregate in water were conducted in a laboratory to investigate resistance properties for abrasion.

6. Reduction of Environmental Impact by Construction of Concrete Structures

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. We investigate packing properties caused by replacement of Eco-cement by finer blast furnace slag powders and mechanical properties of mortar mixtures using the mixed powders.

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 rock type of aggregate on thermal properties of pavement block for sideway.

7. Influence of Formation of Structure of Hydrates in Early Age on Structure of Hardened Mortar under Thermal History Condition


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.

8. Size Effect on Concrete Fracture Energy Test

Fracture energy test conducted by three-point bending of notched concrete beam. It is well known that the fracture energy varies with specimen size and geometry. The fracture energy can be obtained that total energy of the works of the applied load and specimen weight is divided by ligament area. In this case, ligament area is calculated by width and height from notch tip of specimen. However, even if specimens have same ligament area, shape and area of fracture plane are individually different, therefore same fracture energy cannot be obtained from the specimens which made by same concrete mixture. So, true area of fracture plane and the ligament area are different. In this study, the relation between fracture energy and area of fracture plane is investigated based on several types of specimens. As a result, it is suggested that area of fracture plane plays an important role for fracture energy of concrete.

9. Damage Estimation of Buckle Plate Slab under Wheel Load Running Test by Elastic Wave Tomography and Acoustic Emission


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. Acoustic emission (AE) and elastic wave methods were applied fatigue test to investigate damage process and to estimate soundness of the slab. As a result, damage degree of concrete in BP slab could be estimated by elastic wave method..

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2013/12/3
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