open access

https://doi.org/10.14943/doctoral.k9940

https://hdl.handle.net/2115/57097

A Study on Durability Design Method for Control of Scaling due to Combined Action by Freeze-Thaw and Chloride

日本語

2011-03-24

Hokkaido University

200 p.

Concrete structures play an important role in supporting the lives and safety of those who use them. To extend the service life of such structures, it is necessary to develop a rational maintenance and management plan that considers life cycle cost reduction. Accordingly, it is important to be able to predict concrete deterioration in an appropriate way. While freeze-thaw are typical deterioration factors in cold regions, areas where antifreeze is used as well as coastal areas are also affected by chloride. It is known that the combined effects of freeze-thaw and chloride act to accelerate the progress of scaling (i.e., scale-like peeling on the surface of concrete). Scaling may lead to a deterioration in the appearance of structures, and the early corrosion of steel materials due to reduced covering. However, since the form of scaling-related deterioration differ from those caused by ordinary frost damage in which cracking progresses, it is difficult to apply the results of past studies on frost damage prediction and evaluation to design without modification. Against this background, at the first period of this study, laboratory experiments and surveys on deterioration in actual structures were conducted in this study in accordance with ASTM C 672. The model of scaling progress and the concept of a design method to resist scaling were summarized. The laboratory tests confirmed that the influences of the water-cement ratio and the type of cement used were significant. It was found that scaling progression can be predicted and evaluated using variables found by non-dimensionalizing the water-cement ratio and freeze-thaw cycle through division by the average of the values obtained from the experiments. And, it was found that the risk of scaling acceleration depended strongly on the balance between the young’s modulus of concrete and the freeze pressure incline by unfreezing water in concrete surface layer. It was closely related to the pore saturation state and the coefficient of permeability. In the deterioration survey on actual structures, it was demonstrated that the variables (cycles) representing the freeze-thaw history used in the laboratory test can be applied to the prediction of scaling progression at the crowns of breakwaters by replacing them with the number of in-service years. Within the scope of this study, it was found that the damage after 300 cycles in accordance with ASTM C 672 (using artificial seawater) was equivalent to the damage that would be sustained over a period of 20 to 33 years in an actual environment for a design water-cement ratio of 53 to 60%. The concept of design to control scaling progression was comprehensively summarized. At the second, as for countermeasure, it paid attention to surface penetrants (silane-type). The surface penetrants (silane-type) are expected to help control the deterioration of concrete caused by combined action due to freeze-thaw and chloride. Although the method offers high economic efficiency and workability and cases of its implementation are increasing, no durability verification method and deterioration prediction method after construction have yet been established. A field test and exposure test were conducted on the wheel-guard concrete of a road bridge and seaside testing ground in Hokkaido to evaluate the persistence of the effect of these materials. As a result, persistence of the scaling control effect was confirmed in the case of application to a replacement member. In addition, the effect on the reduction of the life cycle cost was evaluated based on the findings of the study.

2011-03-24

甲第9940号

博士(工学)

工学研究院

博士論文

Version of Record