Physical salt attack on concrete: mechanisms, influential factors and mitigation
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Date
2020-07
Authors
Sakr, Mohamed Ramadan Yousef
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Abstract
Physical salt attack (PSA) is a key damage mechanism of concrete serving in salt-rich media under certain environments; yet, there is still lack of essential knowledge in the technical literature regarding different aspects of PSA. This thesis applied the response surface method to assess the influence of perspective- and performance-based parameters on PSA of 52 concrete mixtures. Also, the research program considered additional parameters that may alter the kinetics of PSA in service by adopting a holistic testing approach of concurrently exposing concrete to PSA and carbonation, simulating elements serving in heavy traffic and industrial zones. In addition, several surface treatments of concrete were tested/developed (nanocomposites) for mitigating PSA and also tested under salt-frost scaling to generalize their applicability.
The results suggested limiting the water-to-binder ratio and binder content to a maximum and minimum of 0.40 and 400 kg/m3, respectively, regardless of the binder type. With extended curing, the use of fly ash or slag was beneficial at dosages below 25 and 30%, respectively, for binary binders and 35% for ternary blends combining both. Blended binders (28 to 35% replacement) comprising silica fume (≥ 8%) were capable of resisting severe PSA conditions.
Mutual PSA and carbonation escalated the rate of surface scaling compared to single PSA. The wicking factor of concrete informatively captured the trends of damage for single and combined modes. Thermal, mineralogical, and microscopy analyses elucidated the coexistence of complex degradation processes in concrete subjected to combined PSA and carbonation, which was fundamentally different from salt crystallization in case of single PSA.
Epoxy, ethyl silicate, and acrylic emulsion coatings protected concrete from PSA. Colloidal nano-silica (50% concentration) minimized PSA and salt-frost scaling. Silane mixed with 5% nano-clay or nano-silica mitigated PSA and salt-frost scaling damage of sound and pre-cracked concrete, with relatively better performance for nano-clay. Methyl-methacrylate/nanocomposites, at 5% dosage, were efficient at resisting PSA, but failed against salt-frost scaling.
The synoptic outcomes from this thesis can be used as a basis for updating stipulations on PSA in the current ACI 201.2R document with limits on mixture design variables and suitable surface treatments for concrete protection against PSA.
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Keywords
Physical salt attack, Concrete durability, Surface treatments, Polymeric nanocomposites, Salt-frost scaling, Response surface method
Citation
Sakr, M. R., Bassuoni, M. T., & Taha, M. R. (2019). Effect of Coatings on Concrete Resistance to Physical Salt Attack. ACI Materials Journal, 116(6).
Sakr, M. R., & Bassuoni, M. T. (2020). Effect of Nano-Based Coatings on Concrete under Aggravated Exposures. Journal of Materials in Civil Engineering, 32(10), 04020284.
Sakr, M.R., Bassuoni, M.T., Hooton, D., Drimalas, T., Haynes, H., & Folliard, K.J. Physical Salt Attack on Concrete: Mechanisms, Influential Factors, and Protection. ACI Materials Journal. (Accepted in Jun. 2020, In-press)
Sakr, M.R., Bassuoni, M.T., & Ghazy, A. Durability of Concrete Superficially Treated with Nano-silica and Silane/Nano-clay Coatings. Transportation Research Record. (Accepted in June. 2020, In-press)
Sakr, M.R., & Bassuoni, M.T. Silane and Methyl-methacrylate based Nanocomposites as Coatings for Concrete Exposed to Salt Solutions and Cyclic Environments. Cement and Concrete Composites. (Submitted in Mar. 2020, Under Review)
Sakr, M.R., & Bassuoni, M.T. Modeling of Parameters Affecting Physical Salt Attack of Concrete. ACI Materials Journal. (Submitted in May 2020, Under Review)
Sakr, M.R., & Bassuoni, M.T. Performance of Concrete under Physical Salt Attack Combined with Carbonation. Cement and Concrete Research. (Submitted in July 2020, Under Review)
Sakr, M.R., & Bassuoni, M.T. (2018) Surface Treatments for Concrete Under Physical Salt Attack. 6th International Conference on Durability of Concrete Structures (ICDCS), Leeds, UK, July 2018
Sakr, M. R., & Bassuoni, M. T. (2020). Effect of Nano-Based Coatings on Concrete under Aggravated Exposures. Journal of Materials in Civil Engineering, 32(10), 04020284.
Sakr, M.R., Bassuoni, M.T., Hooton, D., Drimalas, T., Haynes, H., & Folliard, K.J. Physical Salt Attack on Concrete: Mechanisms, Influential Factors, and Protection. ACI Materials Journal. (Accepted in Jun. 2020, In-press)
Sakr, M.R., Bassuoni, M.T., & Ghazy, A. Durability of Concrete Superficially Treated with Nano-silica and Silane/Nano-clay Coatings. Transportation Research Record. (Accepted in June. 2020, In-press)
Sakr, M.R., & Bassuoni, M.T. Silane and Methyl-methacrylate based Nanocomposites as Coatings for Concrete Exposed to Salt Solutions and Cyclic Environments. Cement and Concrete Composites. (Submitted in Mar. 2020, Under Review)
Sakr, M.R., & Bassuoni, M.T. Modeling of Parameters Affecting Physical Salt Attack of Concrete. ACI Materials Journal. (Submitted in May 2020, Under Review)
Sakr, M.R., & Bassuoni, M.T. Performance of Concrete under Physical Salt Attack Combined with Carbonation. Cement and Concrete Research. (Submitted in July 2020, Under Review)
Sakr, M.R., & Bassuoni, M.T. (2018) Surface Treatments for Concrete Under Physical Salt Attack. 6th International Conference on Durability of Concrete Structures (ICDCS), Leeds, UK, July 2018