TITLE:
Tracking chloride and metal diffusion in proofed and unproofed concrete matrices using ablative laser technology (ICP-MS)
AUTHORS:
Avin Pillay, Mirella Elkadi, Fadi Feghali, Sai Cheong Fok, Ghada Bassioni, Sasi Stephen
KEYWORDS:
Concrete; Cl–, Na+; Mg2+; Laser Ablation; Depth-Profiling; ICP-MS
JOURNAL NAME:
Natural Science,
Vol.2 No.8,
August
25,
2010
ABSTRACT: Depth profiling studies (laser ICP-MS) of ions (Cl-, Na+, Mg2+) in concrete-based material can be used to provide useful information on the migration paths of these ionic species. In particular, deterioration of concrete through infiltration of chloride could lead to costly corrosion problems with serious impact on the environment. Many modeling studies on concrete matrices depend on the tortuosity of these transport paths. Our work showed that dispersion paths of ionic species in concrete are intermittent and sporadic, suggesting that applications of simplifying assumptions in treatment of such data could lead to appreciable perturbations in related mathematical models. This paper examines the capability of using a high resolution ICP-MS laser ablation technique to track Cl– migration in concrete samples in the presence of other ions such as Na+ and Mg2+. Cationic migration in such materials is underexplored and data in this particular area could contribute to modeling studies. Concrete bricks (with and without surface coatings) were specially prepared in cubic configurations and allowed to saturate in a ponding medium (sea water). The study subsequently examined the distribution of Cl– , Na+ and Mg2+ with depth in protected (epoxy coated) and unprotected cored concrete slivers (5 mm diameter; 2 mm thick) using an 80 μm- diameter laser beam coupled to an ICP-MS instrument. The laser (213 nm) was programmed to ablate a total depth of 50 μm at each point at 5-μm intervals. The results in unprotected samples indicated that chloride intensity showed a general decline with depth, suggesting that mobility of the chloride is a function of its interaction with the concrete matrix. In some cases ‘hotspots’ were observed at certain points indicating that transport of the intruding ion was limited. No significant mobility was observed in coated samples. The depth-profiling results for Na+ and Mg2+ were somewhat unexpected. Strong similarities in their spectra purported that the matrix was indifferent to charge and size of the ion. Our experimental data further showed that the matrix itself offers natural protection to the reinforced steel rebars by limiting chloride and metal diffusion at certain locations. Clearly, if the composition of these protective environments within the concrete could be simulated on a larger scale and introduced into the matrix it would offer scope for extended research in this area. Our work would be of definite interest to materials and environmental research; and mechanistic studies on aggregates.