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Transforming waterworks sludge into controlled low-strength material: Bench-scale optimization and field test
Xiaoliang Fang1, Lei Wang1, Chi Sun Poon1
1Department of Civil and Environmental Engineering, The Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong Kong, China.
This study upcycles waterworks sludge and incinerated sewage sludge ash into controlled low-strength materials (CLSM). Adding triethanolamine (TEA) optimized CLSM properties, creating sustainable construction materials.
Area of Science:
- Civil Engineering
- Environmental Science
- Materials Science
Background:
- Landfill disposal of waterworks sludge and incinerated sewage sludge ash (ISSA) presents environmental challenges.
- Upcycling these waste materials into value-added products is crucial for sustainable development.
Purpose of the Study:
- To develop controlled low-strength materials (CLSM) using waterworks sludge and ISSA.
- To optimize CLSM properties, specifically addressing the delayed stiffening caused by sludge organics.
Main Methods:
- Investigated the impact of waterworks sludge on cement hydration and CLSM stiffening time.
- Utilized triethanolamine (TEA) as an admixture to accelerate the stiffening process.
- Determined optimal CLSM mix design incorporating sludge, ISSA, and recycled fine aggregate.
- Conducted lab-scale and pilot-scale field tests to evaluate CLSM performance.
Main Results:
- Waterworks sludge (5% organics) delayed CLSM stiffening (>10h).
- 0.1 wt% TEA addition reduced stiffening time to 4.5h.
- Optimal CLSM (6% cement, 14% ISSA, 8% sludge, 72% recycled fine aggregate, w/b=1.2) met flowability (>200mm), stiffening time (<5h), and strength (0.3-2.1MPa) standards.
- Field tests confirmed CLSM with sludge had high flowability (220mm), short stiffening (4h), low strength (1.38MPa), and easy re-excavatability.
Conclusions:
- Waterworks sludge can be effectively upcycled into CLSM.
- TEA is a viable admixture for mitigating sludge-induced setting delays.
- Developed CLSM meets performance requirements for sustainable construction applications.
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