The Effect of Steel Fiber Content on the Workability and Mechanical Properties of Slag-Based/Fly Ash-Based UHPC
Abstract
1. Introduction
2. Materials and Methods
2.1. Materials
2.2. Mix Proportion Design
2.3. Sample Preparation and Curing
2.4. Test Methods
2.4.1. Flowability Test
2.4.2. Compressive and Flexural Strength Tests
2.4.3. Flexural Toughness Test
- ηk represents the toughness at a specific strain level (such as 5%, 10%, or 20%).σ(ε) is the stress at a given strain on the stress–strain curve.ε is the strain.εk is the corresponding strain level (e.g., 5%, 10%, or 20%).
2.4.4. Split Hopkinson Pressure Bar (SHPB) Impact Compression Test
2.4.5. Scanning Electron Microscopy (SEM)
3. Results and Discussion
3.1. Workability
3.2. Compressive Strength
3.3. Flexural Strength
3.4. Flexural Behavior
3.5. Impact Compression Performance
3.6. SEM
4. Conclusions
- (1)
- The flowability of UHPC decreases linearly with increasing steel fiber content. UHPC containing 25% FA exhibits higher flowability than that containing 25% BFS. This indicates that FA-based mixtures are more suitable for applications requiring high workability, such as densely reinforced structural elements or complex formworks.
- (2)
- BFS-based UHPC develops higher early-age compressive strength—ideal for fast-track construction where rapid formwork removal and early load bearing are critical. In contrast, FA-based UHPC exhibits more pronounced strength gains at later ages due to the delayed pozzolanic reaction of fly ash, which contributes to matrix densification after the initial hydration period. Consequently, BFS-based UHPC is recommended for accelerated projects, whereas FA-based UHPC is better suited to applications that prioritize long-term durability.
- (3)
- Adding steel fibers greatly improves UHPC’s mechanical properties. As the fiber content increases, improvements are observed in compressive strength, flexural strength, flexural behavior, and impact toughness. A fiber volume content of 2% provides a good balance between mechanical performance and workability.
- (4)
- The area under the impact compressive stress–strain curve can be used as a quantitative indicator of impact toughness. The addition of steel fibers increases both the peak stress and the total energy absorbed, resulting in improved toughness and energy dissipation capacity. Notably, incorporating 2% steel fibers provides a significant enhancement in energy dissipation, which is particularly beneficial for structural components subjected to impact or dynamic loads, such as bridge expansion joints and seismic isolation bearings.
- (5)
- SEM analysis revealed that after 3 days of curing, small gaps still existed at the fiber–matrix interface. However, in some regions, a good bond had already formed, indicating that steel fibers begin to establish effective connections with the matrix at an early age. As curing progresses, the interfacial zone becomes denser, thereby supporting the continued development of strength.
Author Contributions
Funding
Data Availability Statement
Conflicts of Interest
References
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Cementitious Materials | SiO2 | CaO | Al2O3 | MgO | Fe2O3 | SO3 | Na2O | K2O | Loss on Ignition |
---|---|---|---|---|---|---|---|---|---|
PC | 25.26 | 64.67 | 6.38 | 2.68 | 4.05 | 0.94 | - | - | 0.9 |
SF | 90.82 | 0.45 | 1.03 | 0.83 | 1.50 | - | 0.17 | 0.86 | 4.34 |
BFS | 33.00 | 39.11 | 13.91 | 10.04 | 0.82 | 0.92 | 0.26 | 1.61 | 0.33 |
FA | 54.29 | 1.34 | 32.55 | 2.56 | 5.53 | 0.35 | 0.49 | 1.34 | 1.55 |
PC | Density (kg/m3) | 80 μm Sieve Residue (%) | Specific Surface Area (m2/kg) | Setting Time (h) | Flexural Strength (MPa) | Compressive Strength (MPa) | |||
---|---|---|---|---|---|---|---|---|---|
Initial | Final | 3 d | 28 d | 3 d | 28 d | ||||
P·I | 3150 | 0.3 | 380 | 2.5 | 3.4 | 6.4 | 9.0 | 33.0 | 60.0 |
Sieve Size (mm) | Percentage Retained on Each Sieve (%) | Cumulative Percentage Retained (%) |
---|---|---|
2.36 | 0 | 0 |
1.18 | 15.7 | 15.7 |
0.6 | 33.4 | 49.1 |
0.3 | 33.6 | 82.7 |
0.15 | 14.9 | 97.6 |
Pan | 2.2 | 99.8 |
No. | PC (%) | SF (%) | BFS (%) | FA (%) | High-Efficiency Water Reducer (%) | Steel Fiber Content (%) | Water-to-Binder Ratio | Binder-to-Sand Ratio |
---|---|---|---|---|---|---|---|---|
K-1 | 55 | 20 | 25 | 0 | 2 | 0 | 0.18 | 1:1.1 |
K-2 | 55 | 20 | 25 | 0 | 2 | 1 | 0.18 | 1:1.1 |
K-3 | 55 | 20 | 25 | 0 | 2 | 2 | 0.18 | 1:1.1 |
K-4 | 55 | 20 | 25 | 0 | 2 | 3 | 0.18 | 1:1.1 |
F-1 | 55 | 20 | 0 | 25 | 2 | 0 | 0.18 | 1:1.1 |
F-2 | 55 | 20 | 0 | 25 | 2 | 1 | 0.18 | 1:1.1 |
F-3 | 55 | 20 | 0 | 25 | 2 | 2 | 0.18 | 1:1.1 |
F-4 | 55 | 20 | 0 | 25 | 2 | 3 | 0.18 | 1:1.1 |
No. | Initial Crack Strength (MPa) | Initial Crack Deflection (mm) | Peak Strength (MPa) | Peak Deflection (mm) | Toughness Index | ||
---|---|---|---|---|---|---|---|
η5 | η10 | η20 | |||||
K-1 | 19.0 | 0.30 | 19.0 | 0.30 | 1.00 | 1.00 | 1.00 |
K-2 | 19.2 | 0.31 | 21.7 | 0.36 | 4.79 | 9.08 | 14.56 |
K-3 | 19.3 | 0.32 | 27.8 | 0.53 | 7.86 | 14.95 | 22.05 |
K-4 | 19.9 | 0.33 | 38.3 | 0.80 | 10.17 | 19.78 | 27.10 |
No. | Average Strain Rate (s−1) | Peak Stress (MPa) | Strain Corresponding to Peak Stress (με) | Static Compressive Strength (MPa) | Dynamic Amplification Factor | Impact Compressive Toughness (MJ/m3) |
---|---|---|---|---|---|---|
K-1 | 130.0 | 100.4 | 6010 | 94.3 | 1.06 | 1.76 |
K-2 | 169.8 | 128.4 | 5240 | 94.3 | 1.36 | 1.94 |
K-3 | 206.1 | 146.8 | 7540 | 94.3 | 1.56 | 3.10 |
K-4 | 115.5 | 124.0 | 5320 | 115.1 | 1.08 | 2.62 |
F-1 | 158.2 | 160.6 | 6630 | 115.1 | 1.40 | 3.76 |
F-2 | 195.8 | 177.4 | 6890 | 115.1 | 1.54 | 3.90 |
F-3 | 114.8 | 159.7 | 4060 | 120.8 | 1.32 | 2.72 |
F-4 | 155.7 | 184.3 | 4220 | 120.8 | 1.53 | 3.29 |
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Liao, G.; Wu, R.; He, M.; Huang, X.; Wu, L. The Effect of Steel Fiber Content on the Workability and Mechanical Properties of Slag-Based/Fly Ash-Based UHPC. Buildings 2025, 15, 2350. https://doi.org/10.3390/buildings15132350
Liao G, Wu R, He M, Huang X, Wu L. The Effect of Steel Fiber Content on the Workability and Mechanical Properties of Slag-Based/Fly Ash-Based UHPC. Buildings. 2025; 15(13):2350. https://doi.org/10.3390/buildings15132350
Chicago/Turabian StyleLiao, Gaoyu, Rui Wu, Mier He, Xiangchen Huang, and Linmei Wu. 2025. "The Effect of Steel Fiber Content on the Workability and Mechanical Properties of Slag-Based/Fly Ash-Based UHPC" Buildings 15, no. 13: 2350. https://doi.org/10.3390/buildings15132350
APA StyleLiao, G., Wu, R., He, M., Huang, X., & Wu, L. (2025). The Effect of Steel Fiber Content on the Workability and Mechanical Properties of Slag-Based/Fly Ash-Based UHPC. Buildings, 15(13), 2350. https://doi.org/10.3390/buildings15132350