Abstract
The paper assesses the durability of one-part alkali-activated slag-based mortars (AAS) in different aggressive environments, such as calcium chloride- and magnesium sulphate-rich solutions, in comparison with traditional cementitious mortars at equal water to binder ratio. Moreover, the freezing and thawing resistance was evaluated on mortars manufactured with and without air entraining admixture (AEA). Experimental results indicate that the alkali content is a key parameter for durability of AAS: the higher the alkali content, the higher the resistance in severe conditions. In particular, high-alkali content AAS mortars are characterized by freeze–thaw resistances similar to that of blast furnace cement-based mixtures, but lower than that of Portland cement-mortars while AAS with low activators dosages evidence a very limited resistance in cold environment. The effectiveness of AEA in enhancement of freeze–thaw resistance is confirmed also for AAS mortars. Moreover, AAS mixtures are quasi-immune to expansive calcium oxychloride formation in presence of CaCl2-based deicing salts, but they are very vulnerable to magnesium sulphate attack due to decalcification of C-S-H gel and gypsum formation.
Highlights
In the recent years, the research concerning the sustainability of cement and concrete industry has greatly increased both in academic and industrial community, following a three-sided approach aimed at reducing the environmental impact of cementitious materials, prolonging the service life of concrete structures and improving the performances of mixtures [1]
The paper assesses the durability of one-part alkali-activated slag-based mortars (AAS) in different aggressive environments, such as calcium chloride- and magnesium sulphate-rich solutions, in comparison with traditional cementitious mortars at equal water to binder ratio
Several studies were conducted in the field of rheology [2,3,4], physical performances [5,6,7,8,9,10,11] as well as microstructure [12,13,14] of AAS-based materials but only a limited number of paper concerning the durability of alkali-activated slag-based mortars and concretes was published
Summary
The research concerning the sustainability of cement and concrete industry has greatly increased both in academic and industrial community, following a three-sided approach aimed at reducing the environmental impact of cementitious materials, prolonging the service life of concrete structures and improving the performances of mixtures [1]. The alkali-activated slag-based materials (AAS) seem to be an effective solution to enhance the sustainability of concrete structures but their success is strictly related with their durability in aggressive environments. Several studies were conducted in the field of rheology [2,3,4], physical performances [5,6,7,8,9,10,11] as well as microstructure [12,13,14] of AAS-based materials but only a limited number of paper concerning the durability of alkali-activated slag-based mortars and concretes was published. Immersion of two-parts alkali-activated slag binders in sodium sulphate solutions, according to traditional test method for Portland cement-based (OPC) concretes, does not promote expansion or cracking of binder paste [15,16]. The presence of magnesium leads to decalcification of the Ca-rich gel phases in alkali-activated materials, promoting the decay of the main binding phases and leading to formation of low-strength M-S-H type phases
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