Research Content -2013
- Influence Factor and Evaluation Method for Performance of Filling of Grouting Materials
- A Study on Workability of Fresh Concrete by Tamping Method
- Effect of Reinforcing Bar Array on Compactibility of Fresh Concrete
- Influence on Durability of Pre-cast Concrete Products under Curing Conditions
- Investigation of Shear Bonding Behavior on Interface between Base Concrete
and Repairing Material containing of Sprayed Mortar and CFRP Grid
- Estimation of Deterioration Factors and Mechanisms of Concrete at Advanced
Water Treatment System
- 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
- Size Effect on Concrete Fracture Energy Test
- 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
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
2. A Study on Workability of Fresh 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. 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.
3. 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.
4. 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.
5. 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.
6. 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. 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.
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 influence of macro surface geometry of the
pavement blocks on the direction of the reflection of inputted infrared.
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. Size Effect on Concrete Fracture Energy Test
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.
10. 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. 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.