Abstract
1. Background The materials of structural buildings are mostly metal and concrete. The processes of metal smelting and concrete sintering consume a lot of energy and produce massive carbon dioxide emission. If the service life of structural buildings can be extended, the carbon dioxide emission will be relatively reduced. By the way, if materials with longer durability are used, the construction and dismantling frequency will be curtailed in a certain period, thus help waste reduction. Therefore, the environmental impact of constructional development can be lessened, the public resistance to constructional development will mitigate, and the quality of living environment will be enhanced. For extending the service life of public facilities, Executive Yuan proposes that “when a facility is reaching its service life or its service efficiency abates, a complete and accurate evaluation mechanism is required to decide whether it shall be dismantled and rebuilt or it shall be invested to extend its service life and enhance its efficiency. The priority of facilities shall be determined according to their importance and necessity. Life extension proposal shall be planed and executed. Therefore, the Government’s investment can be optimally allotted and applied.” They point out the importance of construction material durability research. However, it will be difficult to execute the evaluation mechanism above, if the relative atmosphere exposure test result database is not built. 2. Research Method and Procedure In Taiwan, the atmosphere exposure test result data is relatively less, and also, the test periods are mostly only one or two years due to funding shortage; they are not enough to show the durability performance of construction materials. For atmosphere exposure test, Material Test Center and Tainan Test Center can do long term exposure tests and represent the local characteristics of urban area, rural area, Northern Taiwan and Southern Taiwan. Besides, Taiwan is ocean-surrounded, chlorine ion can generate large damage to structural buildings in coastal region. Thus, coastal region is also included in this study. 3. Important Discovery (1) The test result shows that, in different environment, coastal area generates the highest corrosion velocity, industrial area is the second, and windy urban area and rural area are the last. Although, salt is the greater corrosion factor than sulfur dioxide, Taiwanese test literatures indicate that almost all the corrosion products contain sulfur, no matter where the test environment is. It is inferred that the industrial areas are mostly locate in West coast in Taiwan, where sulfur dioxide and chlorine ion concentrations are both high, producing double degradation effect to reinforced concrete buildings. (2) The test result shows that wet/dry cycling would accelerate concrete degradation caused by carbon dioxide. Therefore, due to wave and rising and ebbing tide, the degradation of harbor structure buildings in tidal flat shall be more cautious than normal coastal structures. 4. Major Recommendations (1) The relationship between time and depth of chlorine ion invading concrete shall be stated, in order to help calculating and evaluating when chlorine ion penetrates concrete and reaches steel bar surface. (2) In practical situation, corrosion happens most often at joint area, such as welding and bolts. However, most literature did not perform relating tests. It is recommended to include the relating tests in subsequent studies and to compare with the test results on normal ordinary plate specimen. (3) The data collected in long-term atmosphere exposure test can be compared with accelerated degradation tests, to find out the relation between atmosphere exposure degradation and accelerated degradation.