Abstract

The sealant that fills the joints of an exterior walls of building is subjected to weather loads, such as sunlight, ambient temperature, and rain, as well as a movement of the joints. As a result, the sealant gradually deteriorates under the combined deterioration factors of weathering and movement. Meanwhile, the results of a 15-year outdoor dynamic exposure test conducted in Japan using the methodology of ISO 11617 showed that the progress of damage varies greatly depending on the type of sealant and the stress relaxation rate. However, the mechanism of damage progression is unclear. In the present study, we focused on the load when the sealant moves and developed a load-measuring apparatus as the first step in clarifying the relationship between the progress of damage and the load. The load was measured at −20, 23, and 40 °C for test specimens with different stress relaxation rates, and it was confirmed that the developed load-measuring apparatus was able to measure the load correctly. Furthermore, it was shown that it is difficult for the stress of the sealant with a high stress relaxation rate to relax over time at low temperature but easy at high temperature, and the load increases when switching from the compressed state to the extended state.

Abstract

Reinforced concrete structures are commonly used in civil engineering. However, the number of deteriorations in these structures is increasing, especially problems related to steel corrosion. Also, according studies, corrosion is responsible for about 3.5 % of annual GDP with recovery costs in world. Thus, this study analyzed the corrosion of steel bars at 70-year-old, which are in corrosion process by natural aging. Tests were performed to analyze the bars microstructure, using SEM and EDS, as well as analysis of the current mechanical characteristics, with tensile test. Through SEM, it was possible to measure the layer of the corrosion products formed at the samples edge, and to observe the fragility of this region, with the presence of several microcracks. EDS test contributed to verify the oxygen difference from the nucleus until to the specimen edge. It was possible to notice that in the edge, presence of oxygen is much greater. In the mechanical tests, by the tensile test, the samples do not reach the minimum elongation and the limit of resistance prescribed in the standard. Thus, it is believed after 70 years of natural aging, the samples are in advanced process of corrosion, with edges worn out, and no comply with the minimum mechanical requirements.

Abstract

Nanjing City Wall, one of the most important cultural heritages in China, has been damaged in a natural environment for centuries. Plants can be a candidate to regulate the micro-environment and mitigate the influence of local climates, which cannot be easily controlled by human efforts. Therefore, we examined the potential of the roadside trees along the City Wall to buffer the hygrothermal cycles that can deteriorate the City Wall. We surveyed the deteriorated state and measured the temperature and moisture content of the City Wall. Measured results showed smaller temperature fluctuation at shaded surface than the unshaded with a maximum temperature difference of 10.9 ℃ in summer. The measured water content decreased with height. A coupled two–dimensional hygrothermal ‘City Wall–plant’ model was proposed to clarify the influence of the roadside trees on the hygrothermal distribution of the City Wall. The proposed city wall-plant hygrothermal model could predict the surface temperature and water content well.