The Freeze-Thaw Strength Evolution of Fiber-Reinforced Cement Mortar Based on NMR and Fractal Theory: Considering Porosity and Pore Distribution
Abstract
:1. Introduction
2. Experimental Materials and Procedures
2.1. Material Selection and Sample Preparation
2.2. Freeze-Thaw Treatment
2.3. NMR Analysis
2.4. Uniaxial Compression Tests
3. Experimental Results and Analysis
3.1. NMR Microscopic Pore Distribution Characteristics
3.1.1. T2 Spectrum and Porosity Cumulative Distribution Curve
3.1.2. Changes of NMR Curves under Freeze-Thaw Cycles
3.2. UCS of Cement Mortar under Freeze-Thaw Cycles
4. Discussion
4.1. Relationship between UCS and Porosity
4.2. NMR Fractal Characteristics
5. Freeze-Thaw Strength Degradation Prediction Model
5.1. Proposal of the Model
5.2. Validation of the Model
6. Conclusions
- (1)
- Fiber dispersed in cement mortar can fill the gaps between particles, so the addition of fiber can effectively improve the frost resistance of cement mortar. When the fiber content exceeds 0.5%, the fibers are easily entangled into clusters. The macropores inside the fiber clusters and the micropores at the interface between fiber and cement increase, resulting in the weakening of freeze-thaw resistance of cement mortar;
- (2)
- Cement hydration causes the UCS evolution curve of cement mortar to present the ‘upward convex’ shape under freeze-thaw conditions. Hydration reaction leads to the increase of UCS, while freeze-thaw leads to the decrease of UCS. The substances produced by the chemical reaction between fibers and clinker will prolong the hydration reaction time, resulting in UCS of samples with fiber content less than 0.5% starting to decrease after 25 freeze-thaw cycles, while that of samples with fiber content more than 0.5% starting to decrease after 50 freeze-thaw cycles;
- (3)
- Based on fractal theory, it is found that the fractal dimension of micropores Dmin has a negative correlation with UCS under freeze-thaw conditions. The freeze-thaw strength prediction model considering both porosity and pore distribution can accurately reflect the strength evolution law of cement mortar under freeze-thaw cycles.
Author Contributions
Funding
Institutional Review Board Statement
Informed Consent Statement
Data Availability Statement
Conflicts of Interest
References
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Group | Cement (kg/m3) | Sand (kg/m3) | Water (kg/m3) | Water Reducing Agent (%) | Polyester Fiber (%) |
---|---|---|---|---|---|
A1 | 360 | 760 | 162 | 0.5 | 0 |
A2 | 360 | 760 | 162 | 0.5 | 0.25 |
A3 | 360 | 760 | 162 | 0.5 | 0.5 |
A4 | 360 | 760 | 162 | 0.5 | 0.75 |
Group | Porosity Change Rate | Standard Deviation | ||||||||
---|---|---|---|---|---|---|---|---|---|---|
0 | 25 | 50 | 75 | 100 | 0 | 25 | 50 | 75 | 100 | |
A1 | 0 | 6.826 | 20.408 | 66.106 | 97.085 | 0 | 1.767 | 0.306 | 0.447 | 3.896 |
A2 | 0 | 5.243 | 13.738 | 25.989 | 47.391 | 0 | 0.587 | 0.954 | 0.435 | 1.132 |
A3 | 0 | 5.290 | 11.696 | 21.214 | 28.268 | 0 | 1.324 | 1.496 | 0.768 | 0.952 |
A4 | 0 | 12.111 | 23.658 | 59.083 | 93.528 | 0 | 0.943 | 1.996 | 2.357 | 1.413 |
Fractal Dimension | Freeze-Thaw Cycles | ||||
---|---|---|---|---|---|
0 | 25 | 50 | 75 | 100 | |
Dmin | 1.249 | 1.189 | 1.197 | 1.252 | 1.284 |
Dmax | 2.979 | 2.977 | 2.977 | 2.985 | 2.949 |
Freeze-Thaw Cycles | |||||
---|---|---|---|---|---|
0 | 25 | 50 | 75 | 100 | |
W | 0 | −5.03 | −4.31 | 0.23 | 2.61 |
UCS (MPa) | 24.91 | 29.57 | 28.59 | 24.27 | 20.44 |
Model | Formula | Note |
---|---|---|
This study | Related to total porosity and micropore fractal dimension | |
Gao et al. [35] | Related to the change in porosity | |
Deng et al. [29] | Related to macropore porosity and macropore fractal dimension |
Sample | UCS(MPa) | Porosity (%) | Dmin |
---|---|---|---|
A | 1.427 | 15.245 | 1.637 |
B | 1.247 | 14.431 | 1.718 |
C | 1.122 | 16.634 | 1.829 |
D | 1.090 | 14.187 | 1.943 |
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Zhang, C.; Liu, T.; Jiang, C.; Chen, Z.; Zhou, K.; Chen, L. The Freeze-Thaw Strength Evolution of Fiber-Reinforced Cement Mortar Based on NMR and Fractal Theory: Considering Porosity and Pore Distribution. Materials 2022, 15, 7316. https://doi.org/10.3390/ma15207316
Zhang C, Liu T, Jiang C, Chen Z, Zhou K, Chen L. The Freeze-Thaw Strength Evolution of Fiber-Reinforced Cement Mortar Based on NMR and Fractal Theory: Considering Porosity and Pore Distribution. Materials. 2022; 15(20):7316. https://doi.org/10.3390/ma15207316
Chicago/Turabian StyleZhang, Chaoyang, Taoying Liu, Chong Jiang, Zhao Chen, Keping Zhou, and Lujie Chen. 2022. "The Freeze-Thaw Strength Evolution of Fiber-Reinforced Cement Mortar Based on NMR and Fractal Theory: Considering Porosity and Pore Distribution" Materials 15, no. 20: 7316. https://doi.org/10.3390/ma15207316