The Impact of High-Alkali Biofuel Fly Ash on the Sustainability Parameters of Concrete

The results of this research show that high-alkali biofuel fly ash (BFA) had a significant influence on the mechanical characteristics, microstructure, porosity, freezing–thawing cycle resistance, and ASR resistance of cementitious materials. Different amounts of BFA (varying from 0 to 30%) were used as a substitute for cement in concrete mixes. The impact of substituting cement with BFA on the cement hydration products was analysed. Slump behaviour, mechanical properties, water absorption, porosity, freeze–thaw cycles, and ASR resistance were studied. The analysis of the mechanical and physical characteristics of the developed sustainable concrete revealed that a better structure, higher compressive and flexural strength and density values, and better freeze–thaw and ASR resistance as well as lower water absorption values were achieved when as much as fifteen percent of cement was substituted with high-alkali BFA. The calculations indicate that the substitution of cement with different quantities of high-alkalinity BFA (from 0% to 30% BFA) increased the SiO2/CaO ratio from 0.32 to 0.51 and the Na2O + K2O/CaO ratio from 0.02 to 0.067 in the composition. An evident higher quantity of the hydration products, reflected in the reduction of porosity by up to 27%, the improvement in compressive strength by up to 19.3%, and the calculated freeze–thaw resistance value of up to 51.50%, was observed when the Na2O + K2O/CaO ratio did not exceed 0.044. The ASR resistance of the concrete improved with the increase in the Na2O + K2O/CaO ratio. This study shows that BFA with high alkalinity is beneficial in the development of sustainable building materials.

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