Explosive Spalling Mechanism and Modeling of Concrete Lining Exposed to Fire
Abstract
:1. Introduction
2. Experimental Procedure
2.1. Preparation of Concrete Samples
2.2. Fire Test
3. Experimental Results
3.1. Spalling Phenomenon
3.2. Spalling Mechanism
4. Analytical Prediction of Layered Spalling of Tunnel Lining
- (1)
- Governing equation of heat condition and boundary condition
- (2)
- Equilibrium equation and stress boundary conditions:
- (3)
- Laplace Transformation and series solution
5. Discussions
5.1. Model Validation
5.2. Temperature Field and Stress Field
5.3. Spalling Depth
6. Conclusions
- (1)
- The spalling characteristics of concrete under tunnel fire are summarized from the heating tests. Based on the experimental test results, the moisture content of concrete is one of the key factors of spalling. Obvious layered spalling characteristics of concrete samples without drying could be observed under the unidirectional heat conduction system. The critical temperature of spalling is 600 °C, and the thickness of the spalling layer is 2 cm~2.5 cm.
- (2)
- Based on the spalling characteristics, a multilayer model considering the spalling of concrete lining under tunnel fire is established. Time-dependent temperature, stresses, and spalling depth of tunnel lining relating to the fire temperature could be obtained by using the model proposed. This is the basis of the damage assessment of tunnel lining after fire.
- (3)
- The spalling depth increases nonlinearly with time. Before entering the cooling stage, a total of three spalling failures occurred. The temperature and the stresses induced by fire could be obtained at every time based on the model proposed in this paper.
- (4)
- It is thus clear that heat transfer analysis without considering the effects of spalling can be erroneous at high temperatures. It is therefore imperative that the estimation of the fire resistance of a secondary concrete lining at high temperatures needs to consider its spalling and cross-sectional loss.
Author Contributions
Funding
Conflicts of Interest
Appendix A
Appendix B
References
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Concrete | w/c Ratio | Mass (kg/m3) | ||||||
---|---|---|---|---|---|---|---|---|
Cement | Water | Sand | Aggregate | Fly Ash | Expansive Agent | Admixture | ||
C40P8 | 0.427 | 331 | 183 | 734 | 1057 | 83 | 22 | 7.8 |
Number | ||||
---|---|---|---|---|
Specimen | Maximum Temperature of 800 °C | Maximum Temperature of 1000 °C | ||
Without Drying | With Drying | Without Drying | With Drying | |
5 monitoring holes in specimen | 3 | 3 | 3 | 3 |
0 monitoring hole in specimen | 3 | 3 | 3 | 3 |
1 monitoring hole in specimen | 3 | 0 | 3 | 0 |
Heating Rate | Maximum Temperature | Holding Time | Cooling Mode | |
---|---|---|---|---|
Case 1 | 40 °C/min | 800 °C | 30 min | Natural cooling |
Case 2 | 40 °C/min | 1000 °C | 30 min | Natural cooling |
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Qiao, R.; Guo, Y.; Zhou, H.; Xi, H. Explosive Spalling Mechanism and Modeling of Concrete Lining Exposed to Fire. Materials 2022, 15, 3131. https://doi.org/10.3390/ma15093131
Qiao R, Guo Y, Zhou H, Xi H. Explosive Spalling Mechanism and Modeling of Concrete Lining Exposed to Fire. Materials. 2022; 15(9):3131. https://doi.org/10.3390/ma15093131
Chicago/Turabian StyleQiao, Rujia, Yinbo Guo, Hang Zhou, and Huihui Xi. 2022. "Explosive Spalling Mechanism and Modeling of Concrete Lining Exposed to Fire" Materials 15, no. 9: 3131. https://doi.org/10.3390/ma15093131