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Development of economically feasible sustainable and durable concrete mixtures using performance-enhancing admixtures and alternative cementitious materials
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Thesis/Dissertation
Date
2025-08
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Civil Engineering
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https://doi.org/10.34944/0njh-1073
Abstract
The global construction sector relies heavily on concrete, yet the production of its primary binder, Ordinary Portland Cement (OPC), is a significant contributor to anthropogenic CO2 emissions (5-8% globally) and is highly energy-intensive. Addressing this environmental burden necessitates practical and economically viable strategies. This dissertation investigates two primary approaches to developing sustainable concrete: optimizing mixtures with reduced cement content enabled by a higher dosage of high-range water reducers (HRWR), and evaluating Portland Limestone Cement (PLC) as a lower-carbon alternative binder.
The research first focused on developing and characterizing concrete mixtures with reduced cement content (specifically 10% reduction) and low water-to-cementitious material (w/c) ratios (0.37–0.42), facilitated by optimized aggregate gradation and increased HRWR dosages. Experimental results demonstrated that these "low cement + high HRWR" systems, while requiring approximately three times the HRWR dosage to maintain workability (managed with retaining admixtures), exhibited superior performance. Mechanical strengths (compressive and flexural) increased by over 30-50%, while dimensional stability (shrinkage) remained comparable to control mixtures. Crucially, durability was significantly enhanced, evidenced by reduced porosity (up to 26%) and lower water absorption (up to 40%). This translated into a predicted 117% increase in service life against chloride-induced corrosion and a 29% reduction in life-cycle costs compared to conventional concrete.
A subsequent multicriteria assessment, integrating Life Cycle Assessment (LCA), Life Cycle Cost Analysis (LCCA), service life prediction, and mechanical properties, further validated these findings for both non-air-entrained and air-entrained systems. Reducing cement content substantially lowered environmental impacts, including Global Warming Potential and resource depletion. The 10% low cement mixture consistently emerged as the most sustainable option, achieving the lowest environmental footprint and life-cycle costs (28.9% reduction for non-air-entrained, 25% for air-entrained). Overall, the 10% low cement mixture outperformed the control mixture by 30% across the combined sustainability metrics.
Finally, the research specifically evaluated the abrasion resistance of PLC concrete compared to OPC, a critical factor for applications like industrial flooring. Testing according to BS EN 13892-4 revealed that PLC mixtures, across various sources, generally provided comparable or superior abrasion resistance to OPC at similar strength levels, with an average wear depth 21% lower in the tested PLC samples. Performance improved significantly with lower w/c ratios (0.42 vs. 0.52) and when testing formed surfaces versus finished surfaces (25-55% less wear). While PLC proved a viable alternative, higher variability between sources was noted, linked to differences in cement fineness and chemistry affecting HRWR demand and strength. The application of a surface hardener dramatically improved abrasion resistance (80-90% wear reduction for PLC), highlighting the benefit of surface treatments.
This research provides compelling evidence for the efficacy of utilizing optimized low-cement concrete systems with HRWR and adopting PLC as a binder. These approaches yield concrete with enhanced mechanical properties, significantly improved durability and service life, reduced environmental impact, and greater economic feasibility over the life cycle, offering practical pathways towards more sustainable construction practices.
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