Effects of Curing Conditions on Pore Structure of Ultra-High-Strength Shotcrete (UHSSC) Based on X-ray Computed Tomography
Abstract
:1. Introduction
2. Materials and Methods
2.1. Materials and Mix of UHSSC
2.2. Preparation of Concrete Specimens
2.3. CT Analysis Methods
2.3.1. Principles of CT Image
2.3.2. CT Image Processing Method
3. Results and Discussion
3.1. Porosity
3.2. Pore Size Distribution
3.3. Pore Morphology Analysis
3.4. Anisotropy Analysis
3.5. Analysis of the Influence of Pore Parameters on Compressive Strength
4. Conclusions
- (1)
- The new spray process significantly reduced the porosity and pore size, so the concrete became denser and the compressive strength was significantly improved. The curing conditions affected the hydration and porosity of UHSSC. Under natural curing conditions, the hydration degree was the highest, the maximum pore size was the smallest, and the compressive strength was the highest, reaching 95.8 MPa, but the porosity was the highest.
- (2)
- The sphericity of pores was closely related to pore size. The sphericity tended to decrease as the pore size increased. The new spray process would reduce the sphericity of the large pores. The curing condition had a certain influence on the sphericity distribution of UHSSC pores. Under the film curing, the proportion of special-shaped pores (S < 0.4) was the largest, and its compressive strength was the smallest.
- (3)
- There was a good correlation between pore characteristic parameters and the compressive strength of UHSSC under different curing conditions. In particular, the large pore size (D ≥ 5000 µm) and special-shaped pores (S < 0.4) had obvious effects on the strength of UHSSC, and the grey correlation coefficients were 0.8539 and 0.8080, respectively.
- (4)
- The pores of UHSSC were obviously directional, the parameter θ was concentrated in a certain direction, and the parameter φ was significantly reduced compared with the poured specimen. In addition, there were differences in the parameter φ of UHSSC under different curing conditions. This indicated that the anisotropy of UHSSC may be more prominent than that of the poured specimen and was affected by the curing conditions at the same time. Further research is needed on this issue.
Author Contributions
Funding
Institutional Review Board Statement
Informed Consent Statement
Data Availability Statement
Conflicts of Interest
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Water | Cement | SF | FA | AS | Superplasticizer | PP | VE |
---|---|---|---|---|---|---|---|
0.295 | 1.0 | 0.128 | 0.103 | 1.282 | 0.005 | 0.1% | 0.077 |
No. | Forming Process | Curing Regime | Curing Conditions |
---|---|---|---|
SC | Spraying | Standard curing | In curing room (20 ± 2 °C and relative humidity ≥ 95%) |
NC | Natural curing | Indoors, continue sprinkling water curing for 13 days and then placed for 14 days | |
FC | Film curing | Indoors, samples were sealed with plastic film to prevent moisture evaporation | |
MC | Pouring | Standard curing | In curing room (20 ± 2 °C and relative humidity ≥ 95%) |
Parameter | MC | SC | NC | FC | |
---|---|---|---|---|---|
Compressive strength/MPa | A | 74.9 | 88.7 | 100.7 | 80.9 |
B | 77.3 | 93.5 | 96.9 | 83.2 | |
C | 64.1 | 92.2 | 89.9 | 90.4 | |
Average | 72.1 | 91.5 | 95.8 | 84.8 | |
Porosity/% | 2.634 | 0.212 | 0.260 | 0.189 | |
Dmax/µm | 8719 | 6303 | 6221 | 6664 | |
Df/µm | 629 | 568 | 570 | 551 | |
Sf | 0.642 | 0.638 | 0.643 | 0.639 |
Characteristic Parameter | Porosity | Dmax | Df | Sf |
---|---|---|---|---|
Correlation | 0.6837 | 0.6689 | 0.7472 | 0.7827 |
Pore Sphericity Distribution | Proportion of Pores/% by Volume | Correlation | ||
---|---|---|---|---|
SC | NC | FC | ||
0–0.4 | 0.018732 | 0.013535 | 0.018917 | 0.8080 |
0.4–0.5 | 0.037657 | 0.027366 | 0.025949 | 0.6569 |
0.5–0.6 | 0.068311 | 0.097745 | 0.060358 | 0.6467 |
0.6–0.7 | 0.086530 | 0.120322 | 0.083490 | 0.7021 |
0.7–0.8 | 0.000501 | 0.000549 | 0.000439 | 0.7311 |
0.8–1 | 0.000034 | 0.000045 | 0.000031 | 0.6826 |
Pore Sphericity Distribution/µm | Proportion of Pores/% by Volume | Correlation | ||
---|---|---|---|---|
SC | NC | FC | ||
≥5000 | 0.0180 | 0.0112 | 0.0193 | 0.8539 |
5000 > d ≥ 4000 | 0.0148 | 0.0186 | 0.0077 | 0.6864 |
4000 > d ≥ 3000 | 0.0153 | 0.0188 | 0.0095 | 0.7105 |
3000 > d ≥ 2000 | 0.0303 | 0.0565 | 0.0391 | 0.6636 |
2000 > d ≥ 1000 | 0.0887 | 0.1054 | 0.0779 | 0.7930 |
1000 > d ≥ 0 | 0.0447 | 0.0490 | 0.0352 | 0.7935 |
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Xiao, S.; Yang, J.; Liu, Z.; Yang, W.; He, J. Effects of Curing Conditions on Pore Structure of Ultra-High-Strength Shotcrete (UHSSC) Based on X-ray Computed Tomography. Materials 2024, 17, 4094. https://doi.org/10.3390/ma17164094
Xiao S, Yang J, Liu Z, Yang W, He J. Effects of Curing Conditions on Pore Structure of Ultra-High-Strength Shotcrete (UHSSC) Based on X-ray Computed Tomography. Materials. 2024; 17(16):4094. https://doi.org/10.3390/ma17164094
Chicago/Turabian StyleXiao, Shijie, Jianyu Yang, Zelin Liu, Weijun Yang, and Jiangang He. 2024. "Effects of Curing Conditions on Pore Structure of Ultra-High-Strength Shotcrete (UHSSC) Based on X-ray Computed Tomography" Materials 17, no. 16: 4094. https://doi.org/10.3390/ma17164094