Energy Dispersive X-ray Spectrometry for Determining Chloride Concentration Profiles in Concrete

Liam Holloway¹ and Nimue Pendragon²

¹Principal Engineer, MEnD Consulting

²Lead Consulting Scientist, Microanalysis Australia

Abstract: Assessing the condition or durability performance of existing reinforced concrete infrastructure can involve a broad range of investigation techniques. Investigations during the life of the structure can be used to inform the asset management process. A typical test reg ime will involve visual inspection, cover meter surveys, electrochemical testing, strength assessments, and the collection of core samples for a range of analytical chemical testing. In cases where there is a perceived risk of Alkali ‐ Silica Reaction occurr ing, the testing regime may also include uranyl acetate fluorescence screening, or petrography. Petrography can be done using optical microscopy or Scanning Electron Microscopy (SEM). While petrography can be used to determine the likelihood of ASR, it is also able to give an indication of other concrete properties including, porosity, cement content, and strength. SEM petrography with the combination of Energy Dispersive X – Ray Spectroscopy (EDS) can also provide semi quantitative assessment of other proper ties including but not limited to; aggregate cement ratio, and chloride content. In this paper, we propose that the use of SEM petrography and EDS can provide a more efficient and cost effective way to gather most of the information required to perform dur ability assessments of existing structures. While the use of SEM petrography is not a new concept , using EDS to determine chloride concentration profiles is a novel approach. In this paper, we compare chloride profiles from SEM – EDS against those gained fr om conventional wet chemistry. The results from both assessment techniques were fit to estimate the apparent chloride diffusion coefficients .