Magnesium Sulfate Attack and Deterioration Mode of Metakaolin Blended Cement Matrix

Abstract

In this study, experimental findings on the resistance to magnesium sulfate attack of portland cement mortar and paste specimens incorporating metakaolin (MK) are presented. Specimens with four replacement levels of metakaolin (0, 5, 10 and 15% of cement by mass) were exposed to solutions with concentrations of 0.424% and 4.24% as MgSO 4 at ambient temperature. The resistance of mortar specimens was evaluated through visual examination and linear expansion measurements. Additionally, in order to identify the products formed by magnesium sulfate attack, microstructural analyses such as XRD, DSC and SEM/EDS were also performed on the paste samples incorporating metakaolin. Results confirmed that mortar specimens with a high replacement level of metakaolin exhibited lower resistance to a higher concentration of magnesium sulfate solution. It was found that the negative effect of metakaolin on the magnesium sulfate attack is partially attributed to the formation of gypsum and thaumasite. Conclusively, it is necessary to pay a special attention when using metakaolin in concrete structures, particularly under highly concentrated magnesium sulfate environment.

High Sulfate Attack Resistance of Reinforced Concrete Flumes Containing Liquid Crystal Display (LCD) Waste Glass Powder

“…This result can be attributed to the reaction between the Mg 2+ ions and the hydrates formed in the matrix. According to Lee [4,32], the OH − and Mg 2+ ions in the pore water reacted to form magnesium hydroxide (Mg(OH) 2 ) at early exposure periods, as well as the formation of gypsum and ettringite, filling the voids within the matrix (i.e., micro-filler effect). Therefore, the penetration resistance of ions into the concrete substituted by the LWGP increased with exposure duration to MgSO4 solution, which is validated by the time-dependent behavior of concrete deterioration, implying change of the pore structure.…”

“…In particular, reinforced concrete flumes are most commonly used in flow water, sewage, and wastewater plants. The durability of such flumes reduces because of various pollutants contained in water [4,5,6,7,8,9].…”