Performance evaluation of nano-silica and silica fume on enhancing acid resistance of cement-based composites for underg
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Performance evaluation of nano-silica and silica fume on enhancing acid resistance of cement-based composites for underground structures WU Lin-ping, HUANG Guang-ping, LIU Wei Victor Department of Civil and Environmental Engineering, University of Alberta, Edmonton, Alberta T6G 2E3, Canada © Central South University Press and Springer-Verlag GmbH Germany, part of Springer Nature 2020 Abstract: This study aims to evaluate the performance of silica fume (SF) and nano-silica (NS) on enhancing the sulfuric acid resistance of mortar mixtures. The NS and SF were added as substitutions for cement at various dosages. The cured samples were immersed in the sulfuric acid solution with a pH of 2 for 75 d. A compressive strength test and absorption and voids tests were conducted before sulfuric acid immersion. It was found that the addition of SF and NS reduced the volume of permeable voids and increased compressive strength. A thermo-gravimetric analysis was carried out to investigate the hydration of mixtures. The mixtures with SF showed a higher level of pozzolanic reaction compared with mixtures with NS. After the 75 d of immersion, the mixtures with 5% SF and 1% NS showed the best resistance against sulfuric acid because they showed the lowest mass change and length change. Key words: acid resistance; nano-silica; silica fume; mortar Cite this article as: WU Lin-ping, HUANG Guang-ping, LIU Wei Victor. Performance evaluation of nano-silica and silica fume on enhancing acid resistance of cement-based composites for underground structures [J]. Journal of Central South University, 2020, 27. DOI: https://doi.org/10.1007/s11771-020-4473-0.
equations below) [5].
1 Introduction For underground structures, a proper support system is essential to ensure their stability within the service life [1]. Of the underground support systems, cementitious material is an indispensable component for their application in grouting, shotcreting, and tunnel lining [2, 3]. For example, North American and Australian mines alone could consume 700000 m3 of shotcrete per year [4]. However, the cementitious materials are susceptible to attacks by acids, which can be naturally generated around underground structures. For example, when sulfide-bearing rocks such as pyrites expose to air and water, the sulfur content in rocks can be oxidized, generating sulfuric acid (see
2FeS2+7O2+2H2O→2Fe2++4SO2−4+4H+
(1)
4Fe2++O2+4H+→4Fe3++2H2O
(2)
3+
4Fe +3H2O→Fe(OH)3+3H
+
(3)
As the generated sulfuric acid contaminates groundwater, the pH of the groundwater can be reduced to as low as 2 [6]. In such acidic environments, the cement hydration products (e.g., calcium hydroxide and calcium silicate hydrate) are decomposed via the following reactions [7]. CH+H 2SO 4 ® CSH
(4)
CSH+H 2SO 4 ® CSH+SiO 2 +H 2 O
(5)
where CH is calcium hydroxide, CSH denotes calcium silicate hydrate, and CSH is the gypsum
Foundation item: Project(NSERC RGPIN-2017-05537) supported by the Natural Sciences and Engineering Research Council of Canada Received date: 2020-05-27; Accepte
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