Durability of superficially treated concrete to ammonium sulfate and sulfuric acid solutions combined with cyclic environments
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Date
2023-09-08
Authors
Ibrahim, Amr Magdy
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Abstract
Protecting concrete surface layer is essential for maintaining durability and functionality of concrete infrastructure during their service life. This thesis aimed to investigate the performance of nano-based coatings as superficial treatments for concrete elements exposed to aggravated exposures of ammonium sulfate, commonly found in agricultural, mining, and industrial zones, and sulfuric acid, usually found in wastewater and industrial facilities. Silane (hydrophobic agent) and vinyl ester (membrane-forming polymer) were used as base resins, in which nano-clay and nano-calcium carbonate particulates were dispersed at different dosages (0, 2.5, and 5%). In addition, a colloidal silica solution was used as a surface treatment. These surface treatments were applied to concrete specimens with water-to-binder ratios (w/b) of 0.6 (representing deteriorated concrete) and 0.4 (representing good quality concrete). Firstly, the durability of coated concrete specimens was evaluated under two ammonium sulfate exposures: full immersion and combined with cyclic environmental conditions (freezing-thawing and wetting-drying cycles). Degradation of concrete specimens was monitored by visual assessment and quantified in terms of mass and length changes over time. Secondly, the performance of superficially treated concrete specimens was assessed under two sulfuric acid exposures: full immersion and wetting-drying (W/D). Deterioration of concrete specimens was monitored by visual assessment and quantified in terms of mass changes over time. Furthermore, the degradation mechanisms and coatings’ performance were studied by thermal, mineralogical, and microstructural analyses.
The results showed that colloidal silica could not adequately protect concrete specimens from these exposures. In addition, neat silane did not provide sufficient protection for concrete under sulfuric acid exposures; however, adding nanoparticles to neat silane significantly enhanced its performance under such exposures. On the other hand, silane/nanocomposites improved the durability of concrete under ammonium sulfate exposures, and superior performance was generally observed for concrete specimens coated with vinyl ester/ nanocomposites by the end of all exposures.
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Keywords
Nanoparticles, Coatings, Concrete, Ammonium sulfate, Sulfuric acid, Durability