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Title: Chemical Impacts of MgCl2 on OPC and HVFA Concrete

Author(s): He

Publication: Web Session

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Appears on pages(s):

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Date: 4/2/2023

Abstract:
Magnesium chloride (MgCl2) has been increasingly used in snow and ice control operations for roadways enduring cold weather and its detrimental impact on the integrity and durability of concrete infrastructure has gained increasing attention. This laboratory study investigated the mechanism of chemical reactions of ordinary Portland cement (OPC) and high-volume fly ash (HVFA) concrete with concentrated MgCl2 solution under room temperature. OPC and HVFA mortar specimens were immersed in the 29.8 wt.% MgCl2 solution for 14, 28, and 56 days after 28-day moist curing. The evolution of mechanical properties and gas permeability with respect to the MgCl2 immersion duration was studied. The compressive strength of OPC mortar specimens showed a slight decrease while that of HVFA mortar specimens increased by 19%, after 56-day immersion. The splitting tensile strength of OPC and HVFA mortar respectively increased by 136.5% and 47.1% after 56-day immersion. The MgCl2 immersion also resulted in a reduction of 66.1% and 66.6% in the gas permeability coefficient of OPC and HVFA mortars, respectively. Advanced characterizations including TGA, XRD, and SEM-EDX were conducted to further shed light on the change in chemical compositions and microstructure of OPC/HVFA after MgCl2 immersion and on the associated reaction products with MgCl2 and semi-quantify the profile of multiple elements with respect to the depth to the exposed surface. The results revealed that, unlike salt scaling damage under freeze-thaw cycles, MgCl2 could enhance the hydration of OPC and fly ash under room temperature by producing more Calcium-Silicate-Hydrate phases, which is the main reason for the improvement of mechanical properties.




  


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