R&D Program
Priority Project Research Research on the maintenance and reconstruction of the infrastructure subject to frost damage and combined effect of deterioration

1. Studies on Methods for Maintaining Structures against Frost Damage and Combined Deterioration Specific to Certain Types of Structures

For concrete structures that have been harmed by frost damage and combined deterioration and that show kinds of damage that are unique to them, methods for inspection, diagnosis and evaluation that address deterioration characteristics and countermeasures will be developed, focusing on bridge slabs and river structures.

<Bridge slabs>
It has become apparent that, in addition to suffering from fatigue, existing RC slabs experience deterioration and damage from freezing and other causes. Moreover, cracks in layers have been observed. These are types of deterioration and damage that differ from those with a single cause, such as salt damage or alkali-silica reaction (ASR). Appropriate measures are required from the viewpoints of maintaining traveling safety and preventing harm to third parties.
However, the relation between the deterioration and damage of RC slabs and the deterioration and damage of pavement has not been determined, and repair and reinforcement methods that address the deterioration characteristics have yet to be established.
The RC slabs of road bridges that will suffer from the combined deterioration of frost damage and fatigue are the subject of this study. The ultimate goals of the study are @ to develop performance evaluation methods based on the characteristics of deterioration and damage and A to develop rational repair / reinforcement techniques that address the degree and extent of deterioration and damage. Toward achieving these goals, the following will be studied through laboratory tests using test specimens and through field research on actual structures: 1. determining the factors that contribute to deterioration and analyzing their relative importance, 2. clarifying the processes of deterioration and damage, 3. testing the performance of deteriorated RC slabs, including their performance in terms of load resistance performance and fatigue life, and 4. examining methods for evaluating load resistance performance using numerical analysis techniques such as FEM analysis.

<River structures>
Under severe environments of cold and snow, the concrete of river structures has suffered from ongoing frost damage. Also, for many of the structures that were built during Japan's period of rapid growth, deterioration from abrasion caused by flowing water and river ice has been progressing in combination with the frost damage.
However, no methods have been established for diagnosing the severity of deterioration and the extent of damage for each site. Moreover, the situation of deterioration and the repair and maintenance history have not been organized or analyzed. Standards for maintenance and repair techniques have yet to be formulated.
This study focuses on the deterioration of river structures caused by frost damage and abrasion. The study aims to develop techniques for accurate inspection, diagnosis and repair in response to deterioration combined with frost damage and to develop a method for applying those techniques in the field. This will be conducted through problem analysis of the following: methods for inspecting and diagnosing deterioration, a review of improvement measures, problem analysis on previous repair sections and the development of a structural improvement method.

2.Studies on common techniques for improving the durability of concrete against frost damage and combined deterioration

Field sites require the efficient implementation of measures that meet the required performance according to roles concrete structures are to play or to environmental requirements. However, it is difficult to objectively evaluate deterioration and to choose a construction method, since such techniques for concrete structures in cold, snowy regions have not been systematized.
Therefore, this study aims to establish techniques: efficient inspection, diagnosis and evaluation methods for frost damage and combined deterioration; highly reliable repair and reinforcement methods; and methods for renewal and new construction that achieve high durability. At the same time, the study plans to systematize measures and to develop common techniques for improving the durability of various concrete structures.

<A method for predicting deterioration in order to determine repair/ renewal time>
For the efficient repair and renewal of concrete structures, it is essential to predict the progress of deterioration. A prediction formula for frost and salt combined deterioration is the fruit of previous studies. In applying the formula to each site, there has been the problem of how to set the parameters such that they properly reflect the exposure environment.
This study aims to develop a formula that can be used to predict combined deterioration for concrete structures of various kinds.

<Construction labor savings in winter through the use of cold-resistant hardening accelerators>
The construction of bridges and river structures during the drought period in winter requires temporary enclosures against snow and cold, and heat curing. Using a cold-resistant hardening accelerator enables construction in winter time with easy sheet curing; consequently, efficient construction and cost reductions are expected.
Previous studies investigated the effects of using cold-resistant hardening accelerators on the prevention of initial frost damage to concrete and examined the applicability of Portland blast-furnace slag cement to concrete which uses a cold-resistant hardening accelerator. In addition to these, this study examines the applicability of cold-resistant hardening accelerators to members whose profile is thinner and to members with a small volume, with the aim of suggesting points to keep in mind regarding material choice and construction methods when using cold-resistant hardening accelerators in the repair of concrete structures.

<Improving durability and saving labor by applying a surface penetrant during winter construction>
The use of a surface penetrant is expected to improve durability by reducing the penetration of water and salt. However, there have been problems, since the penetrant cannot be applied for construction in winter or scaffolding needs to be set up for penetrant application in non-winter seasons.
This study will evaluate applicability and quality (depth of penetration, durability against combined deterioration, etc.) of surface penetrants in low-temperature environments in winter and will compile points to note for the purpose of suggesting a construction method that considers quality.

<Establishing a high-durability design method for members subject to the combined deterioration of frost damage and salt damage>
There are various options for improving the freeze-thaw resistance of construction members against the combined deterioration of frost damage and salt damage, including increasing the air content per volume, reducing the water: cement ratio, and selecting high-quality cement. However, a method for determining the freeze-thaw resistance of members has not been established, leaving administrators at sites to set specifications on their own.
This study aims to clarify how the air content per volume, the bubble distribution and the cement mix proportion affect durability against frost damage and salt damage. It also aims to understand the difference between examination methods with the purpose of suggesting performance requirements, reasonable evaluation guidelines and test methods, and standard specifications.

Focused studies
3.Techniques to determine the range of deterioration to be removed from concrete structure

One of remedial measures for concrete structures is a patching repair method, by which degraded area is removed and restored with the application of new concrete or repairing materials. However, existing studies have pointed out that further deterioration occurs due to frost damage unless the degraded area is removed and repaired completely. Currently, repair designs are based on results from limited areas of examination. As a consequence, it is often the case that a structure given a patching repair method undergoes recurring deterioration because the degraded area partially remains.

4.Study on concrete crack control in a cold environment

Cracks accelerate the combined deterioration that occurs from frost damage, salt damage and alkali-silica reaction. Measures to control cracks are effective in extending the lifespans of concrete structures. Self-healing ability, which refers to cracking control achieved by changing the mix proportion or using additives, has been gaining attention. It has become necessary to examine the applicability of such measures to sites in cold regions. However, JIS standards have not been prepared for shrinkage-reducing agents that are expected to control cracking. Also, the effects of such agents on shrinkage reduction and freeze-thaw resistance have not been determined.
To control the crack-related deterioration of concrete structures and to extend their life spans, this study examines evaluations on the self-healing ability of concrete structures with various mineral admixtures and measures to control cracks by using shrinkage-reducing agents for the purpose of suggesting techniques to control shrinkage cracking in cold regions.

Basic studies
5.Establishing a non-destructive method for controlling the penetration depth of silane surface penetrants

Silane surface penetrants have been increasingly used to control frost damage and salt damage to concrete structures. However the depth of penetration into members is rarely controlled directly during construction. Therefore, efficient control methods to determine the state of penetration in members in non-destructive or minimally destructive ways are required.
Silane surface penetrants do not penetrate members only vertically; they also penetrate concentrically in directions horizontal to the surface. This study focuses on this characteristic of silane surface penetrants and aims to suggest an easy non-destructive method for roughly controlling the penetration depth of silane surface penetrants during construction.

6.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.

7.Study on the durability evaluation of construction materials that have undergone prolonged exposure to a cold, snowy environment

The Materials Research Team has been continually examining the deterioration of construction materials at exposure test sites and trial construction sites across Japan. Comparative examinations of deterioration at sites, the predicted values derived from an existing prediction formula, and laboratory test results will enable suggestions of effective construction methods in response to improved prediction accuracy and the deterioration process.
This study aims to understand the situation of deterioration for construction materials in cold, snowy environments through the continuous examination of exposure test bodies and existing structures for the purpose of examining methods for prediction evaluations and repairs.

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