Damage development in cementitious materials exposed to magnesium chloride deicing salt. (15th September 2015)

• Record Type: Journal Article
• Authors: Farnam, Yaghoob; Wiese, Andrew; Bentz, Dale; Davis, Jeffrey; Weiss, Jason
• Is Part Of: Construction & building materials. Volume 93(2015)
• Page Start: 384
• Page End: 392
• Publication Date: 2015-09-15
• Subjects: Brucite -- Concrete -- Deicing salt -- Freeze–thaw -- Damage -- Magnesium oxychloride -- Magnesium silicate hydrate (M–S–H) -- Phase change -- Calcium oxychloride; Building materials -- Periodicals; 624.18
• DOI: 10.1016/j.conbuildmat.2015.06.004
• Languages: English
• ISSNs: 0950-0618

Abstract

Highlights: Concrete exposed to MgCl2 follows the Ca(OH)2 –CaCl2 –H2 O phase diagram. MgCl2 interacts rapidly with concrete developing damage and degradation. MgCl2 causes a significant decrease in fluid ingress into exposed concrete. Abstract: Magnesium chloride (MgCl2 ) is used in deicing applications due to its capability to depress freezing temperatures to a lower point than other salts such as sodium chloride (NaCl). The constituents of concrete (i.e., pores solution, calcium hydroxide, aluminate phases, and calcium silicate hydrate gel) can alter the MgCl2 –H2 O phase diagram when it is used to interpret the performance of concrete. Different chemical reactions may concurrently occur between MgCl2 and cementitious constituents to form brucite, Friedel's salts, magnesium silicate hydrate, magnesium oxychloride, and/or secondary calcium oxychloride. In this study, it was observed that MgCl2 can be entirely consumed in concrete by the chemical reactions and produce CaCl2 . As such, it was found that MgCl2 interacts significantly with a cementitious material and it follows a response that is more similar to the Ca(OH)2 –CaCl2 –H2 O phase diagram than that of the MgCl2 –H2 O phase diagram. Mortar samples exposed to low concentration MgCl2 solutions (<10% by mass) for a short duration of freezing and thawing showed damage due to ice formation, while for higher concentrations (⩾10% by mass), the damage was most likely due to the chemical reactions between MgCl2 and cementitious constituents at room temperature (23 °C). These chemical reactions occurred rapidly (within 5–10 min) and caused a significant decrease in subsequent fluid ingress into exposed concrete.