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. 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 having larger than 250 mm flow can fill for narrow space. But, there is a fear of insufficient filling for narrow space due to the segregation and blocking of aggregate. In this study, the influence factors for filling in grouting materials uniformed at 250 mm flow and the segregation of mortar were investigated by several tests. As a result, it is suggested that the boundary of filling for narrow space is determined by plastic viscosity.

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, three types of concrete having the slump of 80 mm considering s/a were conducted. Concrete was cast in inside of fabricated reinforcing bars, the behavior of flowability to the space between fabricated reinforcing bars and formwork. Also, the compactibility of fresh concrete is investigated to understand effect of reinforcing bar array in consideration of distribution of acceleration.

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. 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. Recently, Blast furnace slug and Fly ash are used for a part of binder such as Portland cement for the pre-cast concrete. These mineral admixtures are affected by the condition of steam curing. In this study, the microstructures of pre-cast concrete with mineral admixture are investigated considering the steam curing condition.

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. And, the properties of the node of CFRP for the tensile load and the bond behavior of CFRP in the longitudinal direction are investigated in consideration of the type and space of CFRP.

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. In this study, visual inspections at all water treatment plants were conducted 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 chemical and physical actions. The chemical actions consist of two factors, 1) elution of the cementitious material by fresh water, 2) chemical attack by carbonic acid which comes from breathing of microorganism in activated carbon. Focusing on the chemical actions, accelerated deterioration tests of mortar specimens were conducted in a laboratory. Then, the prediction curves on concrete deterioration due to chemical actions were estimated based on laboratory tests.

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 freezing and thawing durability, especially on scaling under deicing agent condition, of extremely dry concrete made with eco-cement and replaced with blast-furnace slag powder. As a result, the replacement is very effective to reduce scaling under deicing agent condition.

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 surface geometry on retro reflection properties of pavement block for sideway.

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 temperature rising rate on the mechanical properties of hardened mortar after thermal history.

Fracture energy test conducts 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. However, even if specimens were made by same fresh concrete, same fracture energy cannot be obtained from different sizes of the specimens. In this study, fracture energy test was conducted to specimens with different heights of notch to evaluate the work of the applied load during the test. In addition, acoustic emission (AE) method was applied to the test to monitor fracture process zone. As a result, amount of the work of the applied load changed only at after the maximum load. Therefore, it is suggested that the work of the applied load at maximum load affects to the size effect of the concrete on fracture energy test.

Numerous RC deck slabs have been subjected to a variety of environmental conditions such as traffic loads, temperature and humidity. Especially, fatigue durability on RC deck slab decreases as time passage. In order to maintain and/or repair these aged RC deck slabs with a limited budget, deteriorated RC deck slabs have been reinforced by steel plate bonding method. This method was applied to a large number of aged RC deck slabs in bridges. Recently, delamination between concrete and steel plate detected in reinforced RC deck slabs. In this study, wheel load running test was conducted to RC deck slab specimen. The specimen was made by complied with old guideline in Japan. The experimental procedure consists of 3 steps, 1) non-reinforced RC deck slab was damaged by wheel load running test until crack density became 15 m/m2, 2) steel plate bonding method was applied to damaged RC deck slab, 3) reinforced RC deck slab was tested under wheel load running test. In the experiment, AE method was applied to the specimen in order to estimate failure process. In addition, impact elastic wave method was also conducted to detect delamination between concrete and steel plate. As a result, the delamination could be quantitatively estimated by centroid frequency in impact elastic wave method.

Prestressed Concrete (PC) has been widely used to log span concrete bridges. PC member consists of concrete and tendon ducts including tendon and cementitious grout. In case that tendon duct is not fully filled by cementitious grout, corrosion of the tendon occurs and then crack generates in PC member. The corrosion of tendon induces readily loss of cross-section area in tendon and leads to breaking of the member. It is important to detect improper grouting condition in tendon duct by using nondestructive evaluation techniques (NDT) in order to prevent collapse of PC member. Impact-echo method and elastic wave velocity tomography (EVT) method are widely studied for detecting un-grouted tendon duct. In this study, a fundamental study was carried out to evaluate un-grouted tendon duct in PC model specimens by using impact elastic wave method in a laboratory. 4 type specimens were prepared by changing the filling ratio of the cementitious grout in tendon duct. Prior to experiment in a laboratory, numerical experiment of the EVT was conducted for all cases. As a result, it is found that the EVT is not suitable method for small cross-section area in specimen, because resolution capability of equipment for detection of elastic wave is not enough to evaluate grouting condition. On the other hand, it is realized that the amplitude of the first motion in elastic wave is good index to evaluate grouting condition in the specimens.