Early-Strength Controllable Geopolymeric CLSM Derived by Shield Tunneling Muck: Performance Optimization and Hydration Mechanism of GGBFS–CS Systems
The large-scale reuse of shield tunneling muck remains a major challenge in urban construction. This study proposes a geopolymeric-controlled low-strength material (GC-CLSM) utilizing shield tunneling muck as the primary raw material and a novel alkali-activated binder composed of ground granulated...
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| Main Authors: | , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
MDPI AG
2025-07-01
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| Series: | Buildings |
| Subjects: | |
| Online Access: | https://www.mdpi.com/2075-5309/15/13/2373 |
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| Summary: | The large-scale reuse of shield tunneling muck remains a major challenge in urban construction. This study proposes a geopolymeric-controlled low-strength material (GC-CLSM) utilizing shield tunneling muck as the primary raw material and a novel alkali-activated binder composed of ground granulated blast-furnace slag (GGBFS) and carbide slag (CS). Emphasis is placed on early-age strength development and its underlying mechanisms, which were often overlooked in previous CLSM studies. Among the tested mixtures, a GGBFS:CS ratio of 80:20 yielded the best balance between early and long-term strength. Its 1-day UCS reached 1.18–1.75 MPa, representing a 6.3–23.6-fold increase over the low-CS reference (90:10), which achieved only 0.05–0.31 MPa. However, excessive CS content (e.g., 60:40) led to a significant reduction in the 28-day strength—up to nearly 50% compared with the 90:10 mix—due to impaired microstructural densification. Microstructural analyses (pore-solution pH, SEM, EDS, XRD, FTIR, LF-NMR) confirmed that higher CS levels enhanced early C–A–S–H gel formation by increasing OH<sup>−</sup> and Ca<sup>2+</sup> availability while compromising long-term structure. Additionally, the GC-CLSM system reduced carbon emissions by 68.6–70.3% per ton of treated shield tunneling muck compared with conventional cement-based CLSM. Overall, this study offers a sustainable and performance-driven approach for the valorization of shield tunneling muck, enabling the development of early-strength controllable, low-carbon CLSM for infrastructure applications. |
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| ISSN: | 2075-5309 |