Fundamental Research(1.Apr.2011-31.Mar.2016)

1. A Study on the Repair of Concrete River Structures Affected by Frost Damage

Concrete river structures affected by frost damage are generally maintained using patching repair and surface coating techniques. However, no methods have been established for frost damage inspection of concrete used in sluices and other structures or for frost damage assessment at the water's edge. And knowledge regarding the range of available repair methods in response to frost damage and the applicability/sustainability of repair materials have not been clarified. In addition, there is concern over future increases in the need for maintenance and renewal costs related to sluice concrete structures built as part of river improvement efforts that were often implemented during Japan's period of high economic growth.
The purpose of this study is to clarify appropriate repair methods and measures against frost damage based on the environmental conditions and degree of deterioration of sluice concrete. To achieve this, the causes of frost damage are verified through the examination of sluice deterioration caused by frost action in combination with environmental conditions, repair methods and other factors.

2.A Study on the Durability of Surface Coating as a Method to Resist Frost Damage in Saline Environments

The deterioration of concrete structures affected by frost action in saline environments causes serious problems, including significant reduction of durability compared with the situation created by simple frost damage. As measures against such deterioration, a variety of surface coating methods designed to control salt damage are currently applied. However, the durability and other properties of concrete in actual environments where both salt and frost damage are factors have not yet been fully clarified.
The purpose of this study is to establish appropriate design and construction methods for surface coating as a way of resisting frost damage in saline environments by examining the durability, design, construction and scope of application for different surface coating methods (buried formwork, urethane coating and sheet application) through surveys of actual structures, laboratory experiments and others.

3.A Study on External Environments with On-site Coating and the Durability of Steel-structure Coating

In on-site coating of steel structures, coating performance is significantly affected by external environment factors during application, such as airborne salt and cold weather. It is therefore desirable to clarify the effect of airborne salt action on coating performance, and to establish methods to eliminate such influence. There is also a need to promote the standardization of application periodicity and to improve application efficiency by clarifying the workability, durability and other properties of coating materials that can be applied in low-temperature environments, and by establishing appropriate application methods.
The purpose of this study is to clarify matters that require attention during the application of on-site coating in relation to external environments by identifying the influences of the surroundings (e.g., airborne salt and cold weather) at the time of application, as well as by evaluating airborne salt environments and the workability, durability and other properties of coating materials for cold regions through laboratory acceleration, exposure, on-site application and other tests.

4.A Study on Durability Evaluation for Concrete Exposed to Cold Snowy Environments for Long Periods

The extent of deterioration in concrete structures depends significantly on the quality of their materials, as well as on weather and other external conditions/usage environments. In particular, measures to improve long-term durability are urgently needed in cold snowy environments affected by the combined influence of severe frost and salt damage. In this context, technologies that allow the prediction/evaluation of concrete durability are needed, and accuracy improvement through on-site verification is essential to support such technologies. As actual verification takes a very long time, durability is predicted based on the results of acceleration tests or relatively short-term on-site tests. However, the details of predicted/evaluated long-term durability and actual durability in real-world environments have not been fully verified.
The purposes of this study are to verify the long-term durability of concrete in actual environments and improve the accuracy of prediction/evaluation methods by continuously collecting data on the physical properties and durability of concrete specimens exposed to cold snowy environments for long periods.

5.A Study on Evaluation of the Load-bearing Capacity of RC Beams Subjected to Combined Deterioration Caused by Fatigue and Frost Action

In cold snowy regions, RC girders and other components of road bridges are subject to deterioration caused by frost and other action in addition to vehicle-related fatigue, and their durability and other properties are seriously affected as a result. Since fatigue and frost damage affect concrete repeatedly over periods of many years and manifest in the forms of internal cracking and reinforcement fatigue, there is a risk of sudden reductions in their load-bearing capacity and other properties. Combined deterioration caused by interaction progresses more rapidly than simple deterioration because the prnetration of snowmelt or other water into concrete via cracks caused by fatigue accelerates frost damage, and the reduced strength caused by such damage in turn accelerates fatigue damage. However, the nature of changes in the load-bearing capacity of RC girders and other components of road bridges as a result of combined deterioration caused by fatigue and frost action has not yet been fully clarified, as very few studies have focused on such changes.
The purpose of this study is to investigate technologies for evaluating the static load-bearing capacity of RC girders subjected to combined deterioration caused by fatigue and frost action. To achieve this, freeze-thaw and fatigue loading tests are conducted in a laboratory to clarify the load-bearing capacity and other properties of RC girders affected by combined deterioration. The values found in the experiments are also compared with and analyzed in relation to those obtained from finite element method analysis using material properties depending on the degree of deterioration, as identified using nondestructive test methods (e.g., ultrasonic testing).

6.A Study on sluice gate durability and maintenance against concrete frost damage

In cold regions, the concrete of sluice gates is exposed to severe conditions, such as frost. Thus, there is the need to evaluate such gates for concrete deterioration. Furthermore, the control stands and gateposts undergo particularly severe frost deterioration, as their corners tend to experience particularly rapid changes in temperature, which makes those corners prone to frost damage. There is the risk of sluice gate open-and-close operability and safety becoming worse from frost deterioration.
   However, the way in which frost damage causes a gate to lose its functionality has not been determined, and inspection and assessment methods have not been developed.
This study aims to improve preventive maintenance by establishing methods for assessing durability against concrete frost damage at sluice gates.

7.A Study on inhibitor’s effect on reinforcing bars in cold snowy regions

Many of the reinforcing bars in concrete structures in cold, snowy regions experience localized corrosion from deicing agents. The corrosion can reduce a structure’s safety and durability, so proper preventive measures are required. Various technologies, such as inhibitors, admixtures of salt-absorbing agents and small sacrificial anodes, have been applied as countermeasures, but some key points at construction have not been clarified, such as assessment methods, durability and method selection.
This study aims to make concrete structures more durable by systematizing the selection of agents and determining key points in the management of construction and maintenance through the systematization of performance requirements, investigations of examples in the field and laboratory experiments.

8.A Study on the use of antifreezing admixtures to improve the efficiency of winter construction work

Concrete’s strength depends greatly on its curing temperature, so in cold regions, heaters are usually used to warm the air at the installation site. However, when an antifreezing additive is added to the concrete mixture, curing can be done even with air at low ambient temperatures, without the need for warming measures (e.g., heaters and an enclosure that traps the warm air). Nevertheless, civil engineering guidelines have not been updated to include the latest antifreezing admixtures; those guidelines are based on studies from two decades ago.
   In this study, we have been conducting lab experiments of low-temperature concreting that applies the latest antifreezing admixtures. Our experiments include conditions in which the application of antifreezing admixtures has not been recommended by conventional guidelines, such as for fabricating thin concrete members, for using various types of cement and so on. The test results have been compiled to propose the execution methods and types of materials to be used with the antifreezing admixtures.
The study aims to promote the use of antifreezing admixtures and to increase the efficiency of winter construction while reducing associated costs and CO2 emissions, with the ultimate goal of improved winter construction.

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