High performance and low carbon flowable solidified soil based on construction muck and alkali-activated solid wastes

Area of Science:

• Civil Engineering
• Materials Science
• Environmental Engineering

Background:

• Construction muck (CM) presents disposal challenges, necessitating resource utilization strategies.
• Flowable solidified soil (FSS) offers a viable solution for CM valorization as engineered backfill.
• Developing sustainable and high-performance binders is crucial for effective CM utilization.

Purpose of the Study:

• To develop a low-carbon, high-performance FSS using composite binders derived from cement and alkali-activated solid wastes.
• To optimize FSS mix design considering flowability, compressive strength, and environmental impact (GWP, CED).
• To identify the optimal mixture proportions through multi-objective optimization techniques.

Main Methods:

• Response Surface Methodology (RSM) to model FSS flowability and 28-day compressive strength.
• Life-Cycle Assessment (LCA) to quantify Global Warming Potential (GWP) and Cumulative Energy Demand (CED).
• Non-dominated Sorting Genetic Algorithm III (NSGA-III) coupled with entropy-weight TOPSIS for multi-objective optimization.

Main Results:

• FSS properties (flowability, strength) are controllable via mix design; GWP is sensitive to cement and activator content.
• Microstructural analysis revealed C-S-H gels and AFt phases contributing to matrix densification and strength.
• Optimized mixture (4% LS, 2% cement, 14% GGBFS, 12.3% activator) achieved 279 mm flowability and 6.05 MPa strength with <5% prediction error.

Conclusions:

• The developed FSS provides a sustainable pathway for construction muck utilization.
• The integrated optimization framework effectively balances material performance and environmental objectives.
• The proposed mix design and optimization approach are validated for practical application in engineered backfill.