The Mechanical Properties of Early Aged Shotcrete under Internal Sulfate Attack
Abstract
:1. Introduction
2. Materials and Methods
2.1. Materials
2.2. Sample Preparation
2.3. Test Procedure
3. Results and Discussion
3.1. Failure Modes
3.2. Mass Variation
3.3. Stress–Strain Response
3.3.1. Compressive Strength
3.3.2. Crack Damage Stress Threshold
4. Conclusions
- Regardless of sulfate factors, the failure characteristics of shotcrete did not show objective cracks on the outside. The damaged specimens showed physical sulfate attack damage characteristics, and the efflorescence phenomenon only under high concentrations of sulfate. SEM and energy dispersive X-ray (EDX) analyses of specimens showed that lower sodium sulfate concentration, such as 2%, led to a great deal of ettringite formation. Samples mixed with 5% and 10% concentration sulfate solutions had crystals that appeared on the sample surfaces.
- The curing time significantly affects the stress–strain relationship of early age concrete with a hardening accelerator. Regardless of the stress–strain curve or the ultimate compressive strength law of the shotcrete material, the properties of shotcrete will deteriorate due to the presence of sulfate. Simultaneously, the effect of sulfate on shotcrete should also be differentiated into chemical sulfate attack and physical sulfate attack, according to sulfate concentration.
- The concrete hardening behavior equation expressed by the elastic modulus and the compressive strength can describe the hardening behavior of shotcrete by modification. The fitting result could be accepted according to the correlation coefficients. Meanwhile, the two parameters in the equation of the sulfate attack samples, the ultimate compressive strength and the constant time are related to sulfate concentration.
- In a stress–strain curve, when the volume strain reaches a certain extent, the samples will enter the rapid expansion stage. As the sulfate solution concentration increases from 2% to 5%, the specimen’s lateral strain develops much earlier, which leads to earlier volume strain dilation. Moreover, as the concentration of sulfate solution increases from 2% to 10%, the ratio of samples decreased significantly, which could illustrate the similar trend of the ultimate compressive strength of samples. The ratio of samples under a high concentration, sulfate attack is less than 0.6, which less than the index of rock material. In other words, the sulfate attack caused by the solution with a high concentration leads to an impact on the shotcrete’s durability.
- In practical engineering, we suggest that water quality be tested, and the aggregates should be strictly selected. Sulfate ions in water are not up to standards, which may cause the strength of shotcrete to decline sharply. Moreover, the aggregates can precipitate sulfate ions and increase the sulfate concentration of the overall concrete material. In this case, it may also cause local performance degradation caused by the local sulfate content being too high and then affect the overall performance of concrete.
Author Contributions
Funding
Data Availability Statement
Conflicts of Interest
References
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Physical Properties | Cement | Fly Ash |
---|---|---|
Density (g/cm3) | 3.12 | 2.11 |
Blaine fineness (cm2/g) | 3345 | 4042 |
Loss of ignition (%) | 2.25 | 3.1 |
Main Component | Type | Density (g/cm3) | Usage (Cement × %, Mass Ratio) |
---|---|---|---|
Calcium aluminate | Powder | 2.15 | 1–5 |
S No | Cement | Coarse Aggregate | Fine Aggregates | Superplasticizer | Accelerator | Water | Fly Ash | Sulfate Ion Concentrations (%) | w/c |
---|---|---|---|---|---|---|---|---|---|
(kg) | |||||||||
A (Control) | 486 | 844 | 813 | 4.86 | 12.4 | 235 | 45 | 0 | 0.5 |
B | 486 | 844 | 813 | 4.86 | 12.4 | 235 | 45 | 2 | 0.5 |
C | 486 | 844 | 813 | 4.86 | 12.4 | 235 | 45 | 5 | 0.5 |
D | 486 | 844 | 813 | 4.86 | 12.4 | 235 | 45 | 10 | 0.5 |
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Jin, X.; He, J.; Hou, C.; Luo, W.; He, W. The Mechanical Properties of Early Aged Shotcrete under Internal Sulfate Attack. Materials 2021, 14, 3726. https://doi.org/10.3390/ma14133726
Jin X, He J, Hou C, Luo W, He W. The Mechanical Properties of Early Aged Shotcrete under Internal Sulfate Attack. Materials. 2021; 14(13):3726. https://doi.org/10.3390/ma14133726
Chicago/Turabian StyleJin, Xiaoguang, Jie He, Chao Hou, Wei Luo, and Wenjun He. 2021. "The Mechanical Properties of Early Aged Shotcrete under Internal Sulfate Attack" Materials 14, no. 13: 3726. https://doi.org/10.3390/ma14133726