Physical salt attack on concrete: field case study and innovative mitigations

Physical salt attack (PSA) is a physical damage that affects elements associated with extensive sources of deleterious salts and exposed to cyclic environmental conditions. Although this topic has caught the attention of several researchers, some areas still need to be addressed (e.g., using surface treatments for protecting concretes prepared with supplementary cementitious materials [SCMs]). In this thesis, previously repaired friction piles were selected in Winnipeg, Manitoba, Canada, to investigate the associated damage consequences and recommend effective repair techniques. In addition, an experimental program was designed to examine the efficiency of some innovative treatments (nanocomposites) for mitigating/preventing deterioration resulting from PSA; also, the developed treatments were tested in salt-frost scaling conditions to examine their functionality for a wider range of applications. It was found that the field case suffered from destructive PSA consequences, which might compromise the structural ability of some elements (i.e., piles), although it was repaired previously. Also, signs of chemical sulfate attack were detected in the cores of piles as an accompanied damage mechanism (minor effect). Maintenance procedures were recommended to protect the damaged piles from any further deterioration, including removal of deteriorated concrete from the surface, confining the affected piles with high-performance concrete (HPC) with a low water-to-binder ratio (0.30 to 0.40) and appropriate thickness up to the grade beams level and applying an effective surface treatment (e.g., epoxy, ethyl silicate, or experimentally investigated nanocomposites. The results of the experimental study showed that using a high water-to-binder ratio produced vulnerable concretes against PSA, especially with high replacement ratios (e.g., 40% and 60%) of SCMs. The application of ethyl silicate or high-molecular-weight methyl methacrylate did not provide adequate protection against either PSA and salt-frost scaling exposures; however, incorporating nanoparticles (i.e., halloysite-based nano-clay or montmorillonite-based nano-clay) resulted in moderate to superior performance compared to neat coatings. Ethyl silicate-based nanocomposites were efficient in mitigating or fully protecting specimens exposed to both exposures, especially the one prepared with halloysite-based nano-clay at the lowest dosage (i.e., 2.5%). High-molecular-weight methyl methacrylate-based nanocomposites only succeeded in mitigating the consequences of PSA; however, they failed to show the same performance in the salt-frost scaling exposure.

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