Influences of EVA and methylcellulose on mechanical properties of Portland cement-calcium aluminate cement-gypsum ternary repair mortar

Portland cement-calcium aluminate cement-gypsum ternary repair mortar has the problems of poor toughness, low flexural strength and later strength retrogression in the process of road repair. The effects of ethylene-vinyl acetate (EVA) copolymer and methylcellulose on the mechanical properties of Portland cement-calcium aluminate cement-gypsum ternary repair mortar were investigated. The flexural strength of mortar increases with increasing content of EVA powder by less than 1.5% and the modified mortar with 1.5% EVA has better toughness but the late strength did not grow or was even lower than early strength. The combination of EVA and methylcellulose can effectively improve the flexural and compressive strengths and ensure the development of late strength. The acetic group of EVA copolymer consumes calcium hydroxide to produce calcium acetate under the basic condition, thus forming fine ettringite (AFt) crystal, which can improve the flexural strength with the filling effect of EVA particles. The methylcellulose has good water retention ability, which improves the stability of AFt and thus ensures the late strength. The combined addition of EVA and methylcellulose into the ternary system can improve the stability of AFt, optimize the crystal morphology of AFt, and increase the compressive strength and flexural strength, so as to ensure the development of strength in the later stage. (C) 2020 Elsevier Ltd. All rights reserved.