On the Correlation between Air-Borne Chloride and Durability of Concrete in Coastal Region of North Taiwan
Date Issued
2011
Date
2011
Author(s)
Chen, Yu-Sheng
Abstract
This research focused on the study of air borne chloride in the coastal region of northern Taiwan, and experiments of on-site exposure tests and chloride content on the surface of old reinforcement concrete (RC) structures, to investigate the correlation between air borne chloride and chloride content of RC structures. Through the theoretical analysis and experiments, the partition of the salt injury to RC structures and the method to estimate the design thickness of covering were proposed in this research.
There were 45 sampling sites to investigate the air borne chloride in the northern Taiwan. The instrument of Japanese air borne chloride sampler was used and the sampling and analysis procedure had followed the steps proposed in this study. The testing period started from December 2006 to August 2010. The testing results have shown the obvious difference of air borne chloride distribution among the testing sites, and the apparent influence of the seasonal monsoon. However, the tests also indicate the considerably well seasonal reproducibility of the air borne chloride content. Based on the environmental factors of effective wine direction, effective wind speed, effective precipitation, and distance from the shore, a domestic empirical prediction model for air borne chloride content was established.
The study of the durability of RC structures in marine atmosphere had been conducted using RC exposure tests and on-site samplings, to investigate the durability of concrete and the behavior of corrosion of rebar. The exposure tests were performed at NTOU(Keelung), Chu-Wei Fishing Port(Taoyuan), and Lung-Fong Fishing Port( Miaoli). The tests included the mechanics performance of concrete, permeation of chloride, the chloride content on the concrete surface, and the corrosion rate of rebar. The results had shown that the mechanical properties and the resistance to chloride ions increased as the water binder ratio deceased. Furthermore, the addition of pozzolan mineral mixture had effectively reduced the diffusion coefficient of chloride. The chloride on the concrete surface and the square root of time had good linear relationship, and thus an exponential expression with the distance from the shore can be used to estimate the mixture proportion.
By the test results, the relationship between the chloride content on the concrete surface and the air borne chloride had also been studied. Depending on the effective precipitation, an empirical equation can be applied based on either total air borne chloride (Cair) or adhesive air borne chloride (Cadh). Besides, the diffusion coefficient of chloride obtained from exposure tests can be used to correct the one from the indoor accelerated tests, and can be applied to the diffusion formula of chloride, to estimate the required thickness of covering in various conditions of mixing proportion and chloride content.
The study results from this research can be used to initially define the distribution of salt injury in each county, and to provide adequate design thickness of covering for RC. The procedures and recommendations of this research can helpfully assist the engineers on designs of chloride-resistant and economic costal structures.
Subjects
air borne chloride
chloride ion
diffusion coefficient
exposure test
corrosion rate of rebar
SDGs
Type
thesis
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