報告題目：Cementitious materials exposed to NaCl, CaCl2 and MgCl2 solutions: Damage and Chloride Binding
報告摘要：Chemical attack occurs in cementitious materials exposed to de-icing salt solutions. Friedel’s salt forms in cementitious materials exposed to NaCl solutions. Additionally, CaCl2 can react with calcium hydroxide (Ca(OH)2) from hydrated cement paste to form an expansive product, calcium oxychloride. MgCl2 can lead to calcium leaching from cementitious materials by the formation of Mg(OH)2 and M-S-H. Volume change measurement, thermal analysis and the ball-on-three-balls (B3B) test are used to characterize the chemical attack in cement pastes exposed to NaCl, CaCl2 and MgCl2 solutions. In the case of NaCl solution, Friedel’s salt causes damage to the cement pastes and the flexural strength reduction of the cement paste is proportional to the amount of Friedel’s salt. Moreover, in the case of CaCl2 solution, there is a larger flexural strength reduction, and the flexural strength reduction primarily results from the formation of calcium oxychloride. In the case of MgCl2, the flexural strength shows a two-stage reduction. The initial and second reduction belongs to the formation of Mg(OH)2 and M-S-H, respectively. The addition of fly ash can help to mitigate the chemical attack in cementitious materials exposed to de-icing salts. Chloride binding of cementitious materials exposed to different Cl based salt solutions are also compared and discussed.
Dr. Chunyu Qiao is a senior petrographer at DRP, A Twining Company. He received his bachelor degree from Central South University and his PhD from University of Science and Technology Beijing. He was a visiting scholar in Prof. Jason Weiss’ group at Purdue University from 2013 to 2015. He was a postdoctoral researcher at Oregon State University from 2016 to 2018. He is an associate member of ACI Committee 201 (Durability) and 365 (Service Life). He has published 23 peer-reviewed journal papers, 5 peer-reviewed conference papers and 1 book chapter. His research interests include transport (chloride diffusion, moisture absorption, and wicking) and durability (deicer damage, free-thaw damage and chloride corrosion) of concrete and other cementitious materials, numerical simulation of transport process, chemical admixtures (SRA and SAP) and fluorescence microscopy of cementitious materials.