Evaluation of Chloride Diffusion in Concrete Using Bulk Diffusion Test and Scanning Electron Microscopy

Reinforced concrete is one of the most widely used construction materials in the world with many bridges and other major infrastructure consisting of such structural elements. A primary concern impacting the durability of concrete is chloride penetration in aggressive environments such as marine or coastal areas. In such environments, chloride ions can penetrate into the pores of concrete leading to the corrosion of embedded steel reinforcement which compromises the structural integrity of concrete. To investigate the issue, a comprehensive experimental program was designed and implemented which involved the preparation and testing of 31 different concrete mixes, each incorporating varying proportions of SCMs and w/cm ratios. Concrete samples were mixed, poured, and cured according to ASTM standards and then subjected to exposure in an extremely aggressive environment for 6 months. The standardized Bulk Diffusion, BD, test according to ATSM C1556 was conducted to obtain concrete powder samples which underwent chemical analysis according to FDOT criteria, FM5-516. The research project team experienced the significant time, resources, and labor required to conduct the tedious testing. Scanning Electron Microscopy, SEM, equipped with Energy Dispersive X-ray Spectroscopy, EDS, proved to be the most promising alternative which directly quantifies the chloride content of a sample. A research study was conducted to develop a sound, sustainable SEM-EDS test methodology aiming to produce results more efficiently while maintaining accuracy. It was concluded that the SEM methodology requires minimal resources, besides access to SEM-EDS equipment, and reduces the time to test a layer of concrete by at least 90% through simple and automated procedures. In comparing the BD and SEM test methods, the coefficients of determination, R², for the chloride content and apparent chloride diffusion coefficient results of the study were 0.91 and 0.83 which proves the application of the SEM-EDS test method as a viable alternative to the BD test.