Abstract
This study evaluates the chloride binding capacity and the migration of chloride in sodium carbonate-activated slag cements and mortars. The effect on chloride mobility and binding of adding a calcined layered double hydroxide (CLDH) to the binder mix was also assessed. Significantly improved durability characteristics can be achieved for sodium carbonate-activated slag mortars by the addition of small fractions of CLDH, as a consequence of a higher degree of reaction, higher chloride binding capacity, and the refined pore structures present in these modified materials, in comparison with alkali-activated cements produced without CLDH. The addition of CLDH enables the production of sodium carbonate-activated slag cements with notably reduced chloride ingress compared to silicate activated slag cements.
Highlights
Alkali-activated materials have recently gained significant interest as an alternative to Portland cement in many applications [1,2,3]
As for calcined layered double hydroxide (CLDH) modified samples, the incorporation of CLDH in sodium carbonate-activated slag cements increases the content of hydrotalcite-like phases in the binder
A higher degree of reaction has been observed in CLDH modified sodium carbonate-activated slag paste, indicating that there are more reaction products available to potentially bind chloride [14]
Summary
Alkali-activated materials have recently gained significant interest as an alternative to Portland cement in many applications [1,2,3]. Alkali-activated slag (AAS) cements can be produced with much lower global warming potentials than Portland cement (PC) [4], the use of sodium hydroxide and sodium silicate as activators can bring higher impacts than that of PC in other environmental aspects, including human toxicity, fresh water and marine ecotoxicity [4,5,6]. In the search for more cost-effective, low-toxicity and environmentally friendly alternatives, the use of nearneutral salts such as sodium carbonate as activators for blast furnace slag has attracted the attention of academia and industry [7,8,9,10,11,12,13,14]. The factors controlling the durability and mechanical performance of sodium carbonate-activated slag cement are not yet fully understood. The phase assemblages of AAS cements are mainly controlled by the chemistry of the slags and activators used [7, 15,16,17,18], and the microstructures and mechanical properties of AAS cements are strongly influenced by the type of activator [19,20,21,22].
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