Abstract
This paper investigates the development of the alkalinity and its impact on carbon steel reinforcement embedded in alkali-activated fly ashes (AAFA) and alkali-activated fly ashes with ten percentage mass (wt%) of blast furnace slag (AAFAS)-based materials (geopolymer–GP). The pH analysis of eluates indicates a remarkable decrease of alkalinity in AAFA and AAFAS in the first hours of the geopolymerization process. Phenolphthalein solution and pore solution tests on concretes also show a sharp decrease of alkalinity with increased Ca content in the binder due to carbonation. Micro X-ray computer tomography (µXCT) and electrochemical techniques indicate that the changed pH in the GP systems was accompanied by a decrease in the corrosion rates of steel reinforcement when compared to ordinary Portland cement (OPC) systems. In contrast to calcite and vaterite, which were detected in OPC and AAFAS after a carbonation process, only sodium carbonate natron was determined at lower levels in AAFA by X-ray diffraction (XRD).
Highlights
Alkali-activated binders (AABs)/geopolymer binders (GPs) are increasingly in the focus of research and development
Study was carried out by combining geopolymer durability investigations and microstructure changes ◦ with reinforcement electrochemical
Layer was observed in the AAB and ordinary Portland cement (OPC) concrete samples
Summary
Alkali-activated binders (AABs)/geopolymer binders (GPs) are increasingly in the focus of research and development (one in ten articles in the best-known cement and concrete journals refers to AABs or GPs [1]). AABs/GPs show advantageous properties with regard to environmental protection (air pollutant reduction, resource and energy conservation, reuse of waste materials [2,3,4,5]), improved chemical resistance [6,7,8,9,10], and adequate mechanical performance [2,11,12]. GPs are defined as low Ca AABs with high Al and Si content (e.g., fly ash, metakaolin). (very high Ca and low Al content) phases will be formed (see STAR [2]). The threshold of the Ca content can be defined based on the chemical composition of the raw material, for example fly ash
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