Geopolymer Concrete and Recycled Aggregate Concrete: Mechanical Performance, Durability Characterization, and Lifecycle Sustainability Assessment for Indian Low-Carbon Construction
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Abstract
The global construction industry's dependency on ordinary Portland cement (OPC) contributing 5–8% of anthropogenic CO₂ emissions at 0.83 kg CO₂ per kilogram of clinker [1] demands transformative material substitution strategies beyond partial OPC replacement. Geopolymer concrete (GPC), produced through alkali activation of industrial by-product aluminosilicates without any OPC, and recycled aggregate concrete (RAC), substituting virgin aggregates with crushed demolition concrete, represent two complementary decarbonisation pathways that have received substantial international research attention but remain inadequately characterised for Indian material conditions and IS code frameworks [2],[3]. This paper presents a comprehensive experimental investigation of: (i) four GPC mixes fly ash/GGBS binary systems at FA: GGBS ratios of 70:30, 50:50, 30:70, and 100% GGBS, activated with NaOH + Na₂SiO₃; (ii) five RAC mixes at coarse RCA replacement levels of 0%, 25%, 50%, 75%, and 100%; and (iii) two hybrid GPC-RAC mixes combining geopolymer binders with 25% and 50% RCA. Compressive strength, flexural strength, split tensile strength, rapid chloride permeability (RCPT per ASTM C1202 [4]), water absorption, sorptivity, and modulus of elasticity are evaluated at 7, 28, 56, and 90 days. Embodied CO₂ is quantified using the ICE database [5] and lifecycle cost analysis (LCCA) over 50 years is conducted per ISO 15686 [6]. GPC-GGBS100 achieves the highest 28-day compressive strength (46.4 MPa, M40 grade), while GPC-FA70:GGBS30 demonstrates 44.6% embodied CO₂ saving relative to OPC concrete at equivalent M35 strength. RAC at 25% RCA with pre-soaking treatment achieves IS 456: 2000 [7] M30 compliance (f'c = 33.8 MPa) with 90.1% OPC concrete strength retention. The hybrid GPC-RAC-25% mix achieves M35 strength with 55.8% total embodied CO₂ reduction the highest sustainability metric in the programme.
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References
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