Effect of curing conditions on the alkali-activated blends: Microstructure, performance and economic assessment

Abstract

To enhance the application of alkali-activated materials in engineering, this study investigates the influence of cast-in-place and prefabrication by steam curing and autoclaved curing on alkali-activated materials with different slag-fly ash mass ratios. The selection of the three curing methods is based on current construction techniques: onsite construction (ambient curing), production of prefabricated cement-based components (steam curing), and production of aerated concrete blocks (autoclaved curing). In this paper, the dissolution ability of CaO, SiO2 and Al2O3 in fly ash and slag was first evaluated. Subsequently, the hydration products of the samples were analyzed using X-ray diffraction, thermogravimetric analysis, and a scanning electron microscope. Additionally, the degree of hydration of the samples was quantitatively analyzed using the selective dissolution method combined with 29Si NMR. The results showed that compared to ambient curing, autoclaved curing, which provides a high-temperature and high-pressure environment, enhances the reactivity of slag and fly ash. This enhancement is reflected in the increase in their solubility and the degree of reaction from 28.3% to 14.6%–69.9% and 63.7% respectively. The pore structure, compressive strength, and shrinkage of the samples were also evaluated. The results demonstrate that autoclaved curing enhances the formation of hydration products, reduces porosity, and increases compressive strength. Compared to ambient curing, steam curing can reduce the shrinkage rate from 64.8% to 68.4%, while autoclaved curing can decrease it from 87.9% to 95.1%. Based on the economic analysis, autoclaved curing can offset the total costs by reducing the usage of slag and lowering raw material expenses, demonstrating its cost-effectiveness. The obtained results can provide a theoretical foundation for the large-scale application of alkali-activated slag-fly ash materials in civil engineering construction.