Abstract
Durability of binders, mortars and concretes in aggressive environments is of crucial importance for their commercial application. In this paper the resistance to external sulfate attack of two different alkaliactivated binders (AABs), based either on blast furnace slag (BFS) or fly ash/blast furnace slag (FA/BFS) blend, was compared with two different commercially available Portland cement (CEM II) blended either with BFS or with FA and BFS. Comparison of sulfate resistance was based on compressive strength testing (the loss of strength) of mortar samples exposed to sodium sulfate attack up to 180 days and samples cured under controlled conditions for the same period of time. Furthermore, the evolution of microstructure of alkali-activated binders and pH of sodium silicate solution during testing were also analyzed. Despite different gel chemistry being involved, both alkali-activated binders based either on BFS or FA/BFS blend showed excellent resistance to external sulfate attack and even better than selected Portland cements tested under the same experimental conditions.
Highlights
Durability of concrete structures during long-term exploitation is of key importance for their safe and efficient functioning and it is determined by its ability to resist chemical attack, weathering action, abrasion, or any other process of deterioration
Alkali-activated blast furnace slag (BFS) did not show any sign of deterioration after exposure to external sulfate attack over a period of 90 days (Fig. 1a)
The samples of alkali-activated fly ash/blast furnace slag (FA/BFS) blend exposed to sodium sulfate solution showed strength increase but at somewhat slower rate when compared to the reference samples cured in a humid chamber for the same period of time
Summary
Durability of concrete structures during long-term exploitation is of key importance for their safe and efficient functioning and it is determined by its ability to resist chemical attack, weathering action, abrasion, or any other process of deterioration. Chemical reactions that can alter the cement paste properties are one of the fundamental causes of concrete degradation. The external sulfate attack, as an important process of concrete degradation, might occur due the presence of sulfate ions in soils, underground waters, sea water or industrial waste waters [1,2]. In the last few decades alkali-activated binders (AABs) have drawn attention of scientific and professional community as promising alternative to Portland cement. In order to underpin the predicted future role, AABs are expected to meet the requirements specified for Portland cements in terms of quality and durability [4,5]
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