Influence of Alkaline Activator to Precursor Ratio on the Mechanical and Long-Term Performance of Sustainable Sugarcane Bagasse Ash and Slag-Based Alkali-Activated Recycled Aggregate Concrete

Abstract Portland cement-based concretes produced with natural coarse aggregates contribute significantly to environmental impacts, primarily through the high <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll"> <mml:mrow> <mml:msub> <mml:mi>CO</mml:mi> <mml:mn>2</mml:mn> </mml:msub> </mml:mrow> </mml:math> emissions associated with cement production and depletion of natural resources. The present study aims to study the impact of alkaline activator to precursor (A/P) ratio on the mechanical and long-term performance of sustainable sugarcane bagasse ash (SBA)-based alkali-activated recycled aggregate concrete (ARC). This study emphasizes the crucial role of A/P in designing structural grade SBA-based ARC to attain the required strength and long-term performance. SBA-based ARCs with A/P ranging between 0.3 and 0.8 were developed, and their mechanical and durability properties were monitored over a period of time to study the impact of A/P. This macrobehavior is substantiated by microstructural analysis to validate its performance. The results of this work indicate that by maintaining the A/P at 0.5 or lower, concretes with high compressive strengths in the range of 70–85 MPa can be developed, while maintaining drying shrinkage strains between 490 and 770 μ-strains, considerably within acceptable limits. At these ratios, these concretes showed a volume of permeable voids lower than 13% and negligible weight loss of 0.95%–3.71% when exposed to an acidic environment. Other durability indicators, including water penetration depth, ranged between 5–13 mm, and sorptivity ranged between <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll"> <mml:mrow> <mml:mn>0.86</mml:mn> <mml:mi>–</mml:mi> <mml:mn>2.41</mml:mn> <mml:mtext> </mml:mtext> <mml:mi>mm</mml:mi> <mml:mo stretchy="false">/</mml:mo> <mml:mo>√</mml:mo> <mml:mi mathvariant="normal">h</mml:mi> </mml:mrow> </mml:math> , remained within acceptable ranges irrespective of A/P, although mixes with lower A/P consistently performed better. This superior behavior is ascribed to a compact matrix and elevated Ca/Si and Al/Si ratios, as confirmed by sacanning electron microscopy (SEM) image observations and energy-dispersive X-ray spectroscopy (EDS) analysis. By establishing how A/P influences key properties, this research presents a practical direction for engineers and industry practitioners to optimize mix design to meet specific performance requirements. Moreover, the environmental advantage is significant, as these SBA-based ARCs contribute nearly three times less <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll"> <mml:mrow> <mml:msub> <mml:mi>CO</mml:mi> <mml:mn>2</mml:mn> </mml:msub> </mml:mrow> </mml:math> emissions compared to conventional portland cement concretes.