DOI: 10.14457/tu.the.2023.532
title: A study on airborne chloride and surface chloride of concrete in the marine environment

description: Chloride attack has been the main problem in deteriorating concrete structures in the marine environment. Concrete structures were damaged and had a short service life in the marine environment. Therefore, the Department of Public Works and Town & Country Planning (DPT) of Thailand has launched a standard of concrete work that considers the durability and service life of the reinforced concrete structures in Thailand (DPT 1332-55). The surface chloride content, chloride diffusion coefficient, and critical chloride content are three crucial parameters in the durability equation of the DPT 1332- 55 service life design. The primary source of chlorides, which initiates the damage of the structures, comes from the sea. Sea waves create whitecaps that are later transported inland by the wind as airborne chloride. This airborne chloride is gradually deposited on the surface of concrete structures and becomes the surface chloride. However, determining the surface chloride contents requires massive work and time to investigate and get their values. Therefore, this research aims to investigate and find the relationship between airborne chloride deposition and surface chloride content in the coastal area of Thailand. The airborne chloride deposition was collected using the mortar chip and cotton and gauze methods while surface chloride content was determined from the mortar cube specimens and the actual structures. The mortar specimens were cast with different water-to-binder ratios and fly ash replacement ratios to study the effects of the water-to-binder ratio and the fly ash content, respectively. Chloride penetration profiles of the actual concrete structures and the tested mortar specimens were plotted, and Fick’s second law was applied to determine the surface chloride content. The specimens were exposed to the marine atmospheric zone in 10 locations of 5 coastal provinces in the eastern Gulf of Thailand (Chachoengsao, Chon Buri, Chanthaburi, Rayong, and Trat provinces) with different distances from the seashore and elevations above the mean sea level. After the specified period, specimens were collected and the surface chloride contents were investigated. In addition, the surface chloride contents of selected actual structures in the eastern Gulf of Thailand, the southern Gulf of Thailand, and the Andaman Sea were also investigated. From the results, surface chloride contents were influenced by environmental parameters and material properties of the concrete. The prediction model of the surface chloride content was conducted as the function of airborne chloride deposition in different parts of the coastal area of Thailand by also considering the exposure periods, elevations above mean sea level, fly ash content, water-to-binder ratio, and geographical conditions. An effective approach to determine the surface chloride content of the structures at any location in the coastal region of Thailand was proposed based on the airborne chloride map and the equation relating the airborne chloride depositions and surface chloride contents.