SUSTAINABLE CONSTRUCTION MATERIALS AND STRUCTURAL ANALYSIS FOR EARTHQUAKE-RESISTANT INFRASTRUCTURE: A MULTI-METHOD ASSESSMENT OF LOW-CARBON CONCRETE MIXES IN A MID-RISE REINFORCED-CONCRETE FRAME

Abstract

Reinforced-concrete buildings in seismic regions must be both safe and low in embodied carbon, yet material studies and seismic studies are rarely combined. This paper links four concrete mixes (an OPC control, 30% fly ash, 50% ground granulated blast-furnace slag, and a ternary fly-ash/silica-fume blend) to the seismic assessment of a five-storey, three-bay reinforced-concrete frame. Material properties and emission factors are assumed within literature ranges; the structure is idealised as a five-degree-of-freedom shear building and analysed by modal response-spectrum analysis (Eurocode 8, ground type C, a_g = 0.30 g, q = 3.9), elastic time-history analysis with 24 synthetic records, pushover analysis, fragility analysis and Monte Carlo simulation, followed by cost estimation and multi-criteria ranking. Cement replacement lowered the embodied CO₂ of the concrete by 28.7%, 44.6% and 36.5%, and the embodied CO₂ of the whole frame (450 mm columns) by 19.5%, 30.2% and 24.8%. The fundamental period varied only between 0.572 and 0.588 s, so base shear was identical across mixes, and the code relation chosen for the elastic modulus (Eurocode 2 versus ACI 318) changed peak drift by about 16%, far more than the mix. Column size, cracked stiffness and storey height dominated drift sensitivity. For a section sized near the drift limit, strength variability (COV 15%) gave exceedance probabilities of 56.6%, 73.0%, 56.6% and 16.6% for the four mixes, and the slower strength gain of the fly-ash mix lengthened the time to reach 70% of the 28-day strength from 3.6 to 7.5 days. A TOPSIS ranking favoured the ternary blend under all three weighting scenarios. All strengths, emission factors, costs and structural parameters are assumed or simulated, so the findings describe relative trends for a representative frame, not a specific building.