Research Content -2012
- Influence Factor and Evaluation Method for Performance of Filling of Grouting
- A Study on Workability of Flesh Concrete by Tamping Method
- Influence on Durability of Pre-cast Concrete Products under Curing Conditions
- A Study on Repairing and Strengthening Methods for Existing Concrete Structure
- Influence on Splitting Tensile Strength in different Sizes of Concrete
- Development of Mortar Consisted Cementitious Material for Advanced Water
- Reduction of Environmental Impact by Construction of Concrete Structures
- Influence of Formation of Structure of Hydrates in Early Age on Structure
of Hardened Mortar under Thermal History Condition
- Evaluation of damaged Area in Existing Concrete Structure by Elastic Wave Tomography method and AE Monitoring
1. Influence Factor and Evaluation Method for Performance of Filling of
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.
2. A Study on Workability of Flesh Concrete by Tamping Method
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.
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. 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.
4. A Study on Repairing and Strengthening Methods for Existing Concrete
a) Evaluation of Bonding Strength between Existing Concrete and Repairing Material
5. Influence on Splitting Tensile Strength in different Sizes of Concrete
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.
6. Development of Mortar Consisted Cementitious Material for Advanced Water
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.
7. 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. 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.
8. 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.
9. Evaluation of damaged Area in Existing Concrete Structure by Elastic Wave Tomography method and AE Monitoring
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.