Petrographically quantifying the damage to field and lab-cast mortars subject to freeze-thaw cycles and deicer application

• Published in: Journal of infrastructure preservation and resilience Vol. 2; no. 1; pp. 1 - 12
• Main Authors: Qiao, Chunyu, Hosseinzadeh, Nima, Suraneni, Prannoy, Wei, Sihang, Rothstein, David
• Format: Journal Article
• Language: English
• Published: Cham Springer International Publishing 14.04.2021; Springer Nature B.V; SpringerOpen
• Subjects: Calcium chloride; Calcium hydroxide; Calcium hypochlorite; Calcium oxychloride; Cement; Cement paste; Chloride; Civil Engineering; Cold; Concrete mixing; Concrete pavements; Concrete petrography; Cracking (fracturing); Cracks; Damage; Deicers; Engineering; Ettringite; Experimental methods; Freeze thaw cycles; Freeze-thaw durability; Freeze-thawing; Image analysis; Image processing; Leaching; Light microscopy; Micrography; Mortars (material); Optical microscopy; Photomicrographs; Portland cement; Portland cements; Preferred orientation; Research methodology; Scanning electron microscopy; Slaked lime; Snow; Spectrometry; Substrate mortar; United States > US; Deicers; Substrate mortar; Concrete petrography; Freeze-thaw cycles; Calcium oxychloride
• ISSN: 2662-2521; 2662-2521
• DOI: 10.1186/s43065-021-00024-3

Although calcium oxychloride (Ca-Oxy) is known to damage cementitious materials exposed to calcium chloride (CaCl 2 ) deicers, there is little direct observation of Ca-Oxy in the field due to its instability. This paper uses optical microscopy (OM) and scanning electron microscopy coupled with energy dispersive X-ray spectrometry (SEM-EDX) to detect the formed Ca-Oxy and quantify its associated damage in a field mortar subject to freeze-thaw cycles and deicer application. The characterized damage in the field mortar is compared to that in lab-cast portland cement paste and mortar which are submerged in a CaCl 2 solution of 25 wt.% under freeze-thaw cycles (− 8 to 25 °C). The field and lab-cast mortars show similar cracking patterns that are parallel to the exposure surface with a variation of 30–45° in the preferred orientation due to the constraints of sand particles. During each lab-controlled freeze-thaw cycle, the high CaCl 2 concentration of 25 wt.% stabilizes the formed Ca-Oxy, which continually damages the mortar and eventually results in 3–4 times higher crack density compared to that in the field mortar. SEM-EDX analysis confirms the presence of secondary deposits including Friedel’s salt, ettringite and Ca-Oxy. Image analysis on thin section photomicrographs shows a reduction of 86.4% in calcium hydroxide (Ca(OH) 2 ) content in the damaged field mortar compared to the undamaged field mortar, suggesting significant leaching of Ca(OH) 2 to form Ca-Oxy due to the deicer application.