Performance of concrete with blended binders in sulfuric acid and ammonium sulphate solutions
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Date
2016-06
Authors
Amin, Mahmud
Journal Title
Journal ISSN
Volume Title
Publisher
Canadian Society for Civil Engineering
Abstract
Acid attacks on concrete impart unique set of damage mechanisms and manifestations compared to other durability issues of concrete. Up to date, there are still research gaps and conflicting data regarding the effects of supplementary cementitious materials (SCMs) at improving the resistance of concrete to acidic exposures. Hence, this thesis aims at understanding the role of SCMs in the performance of concrete under two different acidic environments (sulfuric acid and ammonium sulfate solutions) that produce similar reaction products while their damage mechanisms and manifestations are completely different.
Concrete has long been the most popular choice for constructing key infrastructural elements such as sewer pipes, water treatment facilities, industrial floors and foundations, which can be chemically vulnerable to damage by sulfuric acid attack. Since high alkalinity is required for the stability of the cementitious matrix, concrete is susceptible to attack by acidic media, which may disintegrate the hydrated cement paste to various levels based on the prevailing exposure conditions and key mixture design parameters of concrete. The aim of this part of research was to investigate the response, in terms of phyico-mechanical and microstructural features, of concrete comprising different types of cement (general use or portland limestone cement [PLC]) with various combinations of SCMs (fly ash, silica fume and nano-silica) to a severe sulfuric acid exposure. The project comprised 13 weeks (90 days) of immersing test specimens in 5% sulfuric acid solutions with a maximum pH threshold of 2.0. The results revealed that the surface degradation (mass loss) of concrete under severe sulfuric acid attack was independent of its penetrability (physical resistance), since very dense cementitious matrices (low penetrability) suffered from severe deterioration. Portland limestone cement [PLC] may slightly improve the resistance of concrete to sulfuric acid attack, whereas among the blended binders tested, binary binders comprising 30% fly ash showed increased resistance of concrete to sulfuric acid attack due to an inert filler effect at the exposed surface.
On the other hand, concrete elements in agricultural, wastewater treatment, mining and industrial applications can be vulnerable to chemical attack by ammonium-based solutions. In particular, ammonium sulfate (commonly used as a fertilizer) is extremely deleterious to concrete due to its dual acid-sulfate action, which may disintegrate the hydrated cement paste to various levels based on the prevailing exposure conditions and key mixture design parameters of concrete. The aim of the second part of research was to investigate the response, in terms of physico-mechanical and microstructural features, of concrete comprising different types of cement (general use or PLC) with various combinations of SCMs (fly ash, silica fume and nano-silica) to a severe ammonium sulfate exposure. This part comprised 12 months of immersing test specimens in 5% ammonium sulfate solutions with a pH level of 6.0-8.0. The results revealed that the type of binder along with the dosage and nature of SCMs dictated different modes and levels of deterioration, and in turn physico-mechanical trends of concrete characterised by softening with (single binders) or without (blended binders) significant expansion. PLC may slightly improve the resistance of concrete to ammonium attack, whereas among the blended binders tested, binary binders comprising 5% silica fume, 5% nano-silica, or 30% fly ash particularly improved the resistance of concrete to this type of chemical attack.
Description
Keywords
Durability of concrete, Acid attack, Sulfuric acid, Ammonium sulphate, Supplementary cementitious materials
Citation
Amin, M. and Bassuoni, M. T. 2016. “Resistance of Concrete Incorporating Portland Limestone Cement to Sulfuric Acid.” 5th International Materials Specialty Conference, Canadian Society for Civil Engineering, London, Ontario, Canada.