Abstract
There is a growing demand for alternative low carbon binders. For these relatively new binder systems to be well received in industry it is important that detailed understanding of their durability performance is available. This paper investigates the hydrochloric acid resistance of geopolymer binders containing 100% fly ash and various blends of fly ash and blast furnace slag. Both physical and microstructural properties changes were examined to assess acid resistance and the leaching behaviour was also monitored. As the slag content of geopolymer binders increased, the resistance to hydrochloric acid also increased, evidenced by the reduced mass and strength loss observed. Findings also illustrate that geopolymer binders have hydrochloric acid resistance which exceeds that of traditional Portland cement binders in terms of the mass losses observed. The process of hydrochloric acid attack for each binder is also studied. • Fly ash/slag geopolymers had improved resistance to HCl than Portland cement. • As the slag content increased the resistance of geopolymers also increased. • Neat fly ash mixes had high apparent acid penetration but low surface deterioration. • Fly ash/slag geopolymers underwent decalcification of C-A-S-H type gel. • Neat fly ash mixes experienced dealumination of N-A-S-H gel.
Highlights
It is well documented that the cement and concrete industry is under increasing pressure to reduce its contribution to global CO2 emissions
Findings illustrate that geopolymer binders have hydrochloric acid resistance which exceeds that of traditional Portland cement binders in terms of the mass losses observed
The compressive strength increased significantly. This was caused by the development of calcium aluminium silicate hydrate (C-A-S-H) and C–N-A-S-H gels in systems with more slag whereas N-A-S-H gel was found in unblended fly ash binders
Summary
It is well documented that the cement and concrete industry is under increasing pressure to reduce its contribution to global CO2 emissions. This has led to considerable interest in alternative low-carbon binders such as alkali-activated or geopolymer (GP) systems (Shi et al, 2019). The alkali-activation of fly ash and slag to form GP binders has received significant attention. Fly ash and slag are by-products from coal combustion and steel production, respectively. They are considered as ideal components to produce a low-carbon binder whilst reducing landfilled or stockpiled waste from other industries. To give confidence in their performance and help their uptake become more widespread it is vital their performance is as well understood as traditional Portland cement (PC) based systems
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