Matrix hybridization using waste fuel ash and slag in alkali-activated composites and its influence on maturity of fiber-matrix bond

With growing environmental concerns due to huge carbon foot prints of different industries, particularly, cement industry which is about 7% of the global CO2 emissions, the use of industrial by-products such as fuel ash and slag to replace cement in construction industry has been considered one of the most effective approaches for recycling these waste materials. One alternative is to use these industrial by-products to fully replace cement in the alkali-activated materials. This study is aimed to investigate the feasibility and influence of hybridization of pulverized fuel ash and ground granulated blast-furnace slag at different proportions on maturity of strength properties and bond strength of alkali-activated composites reinforced with different macro fibers cured at ambient temperature. Slag was replaced as 0% (reference), 10%, 20% and 30% of the total binder and activated by sodium silicate and sodium. Working life and strength of alkali-activated composites were determined. Single fiber pull-out tests were conducted with different macro steel fibers (straight, hooked end-deformed, sinusoidal end-deformed, length-deformed) and polypropylene fibers (length-deformed) embedded in dog-bone shaped specimens and cured at ambient temperature for 7 and 28 days to evaluate the bond-slip behavior. In addition, an optimal mix proportion of pulverized fuel ash-slag-based alkali-activated composites was cured at elevated temperature of 60 °C (24 h) for comparison. The results are compared to the bond-slip behavior of the same fibers in alkali-activated composites without slag as control condition. Finally, an improvement in compressive and tensile strengths of pulverized fuel ash-slag-based alkali-activated composites cured at ambient temperature achieved with the effect of hybridization of pulverized fuel ash and slag along with prolonged curing. Results also demonstrate that the maximum fiber-matrix bond strength of pulverized fuel ash-slag-based alkali-activated composites to different fibers was obtained within 7-day ambient curing which is almost the same as the ones obtained after 28-day ambient- and heat curing.