Effect of Composite Impregnation on Properties of Recycled Coarse Aggregate and Recycled Aggregate Concrete
Abstract
:1. Introduction
2. Materials and Methods
2.1. Materials
2.2. Impregnation Treatment Methods
2.3. Preparation of Concrete
2.4. Physical Properties Test of RCA
2.5. Concrete Slump and Mechanical Properties Test
2.6. Microstructure Performance Test
3. Results and Discussion
3.1. Physical Properties of RCA and Slump
3.2. Basic Mechanical Properties of Recycled Aggregate Concrete
3.3. The Enhancement Coefficients
4. Micro–Analysis of RCA and Recycled Aggregate Concrete
4.1. Surface Microstructure of RCA
4.2. Analysis of the Internal Microstructure of Recycled Aggregate Concrete
5. Conclusions
- (1)
- Composite impregnation treatment can comprehensively improve the physical properties of RCA and show higher stability. Among them, the composite impregnation treatment of sodium silicate and silane has the best repair effect on the cracks and holes on the surface of RCA, and the increase of apparent density and the decrease of the crushing index is the most obvious. Using PVA solution single impregnation, sodium silicate, and PVA composite impregnation treatment, the surface of RCA formed a hydrophobic membrane to isolate water molecules, which improved the water absorption of RCA best.
- (2)
- All composite impregnation schemes can effectively improve the working performance of recycled aggregate concrete, in which the composite impregnation of sodium silicate and silane can increase the slump of fresh recycled aggregate concrete slurry by 9.8%.
- (3)
- After impregnation strengthening treatment, the enhancement coefficient of basic mechanical properties of each specimen is greater than 1.0, which shows that three chemical strengthening agents and different impregnation treatments can effectively improve the basic mechanical properties of recycled aggregate concrete. According to the composite effect coefficient, only the composite impregnation of sodium silicate and silane can produce a positive composite effect, which can effectively improve the basic mechanical properties of recycled aggregate concrete specimens. The cubic compressive strength, split tensile strength, and flexural strength are improved by 26.53%, 21.70%, and 14.72%, respectively. The analysis results of the standard deviation of the strength of recycled aggregate concrete show that the treatment of three chemical strengthening agents and different treatment methods have a certain improvement effect on the strong dispersion of recycled aggregate concrete.
- (4)
- According to the analysis of scanning electron microscopy images, the ITZ of recycled aggregate concrete with sodium silicate and silane composite impregnation has rich hydration products and compact accumulation, and the interfacial strengthening and toughening effects are the most obvious. The strengthening effect of sodium silicate and PVA and silane and PVA composite impregnation treatment is not obvious because the hydrophobic film formed by PVA is covered on the surface of aggregate so that the hydrolysis product of sodium silicate and the residual alkoxy group of silane cannot fully contact with cement mortar, and the interface hydration is less and the structure is loose. Compared with single impregnation, the proper composite impregnation scheme can better repair the original defects of RCA and form a denser ITZ, thus improving the mechanical properties of recycled aggregate concrete.
Author Contributions
Funding
Institutional Review Board Statement
Informed Consent Statement
Data Availability Statement
Conflicts of Interest
References
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Sample NO | Strengthening Method | Strengthening Type |
---|---|---|
R0 | RCA | Untreated |
S1 | Sodium silicate solution | Single impregnation |
S2 | Silane slurry | |
P1 | PVA solution | |
S1S2 | Sodium silicate solution + silane slurry | Compound impregnation |
S1P1 | Sodium silicate solution + PVA solution | |
S2P1 | Silane slurry + PVA solution |
Cement | Water | Coarse Aggregate | Fine Aggregate | Admixture | Water Reducing Agent | |||
---|---|---|---|---|---|---|---|---|
NCA | RCA | Machine–Made Sand | Sand | Fly Ash | Mineral Powder | |||
220 | 160 | 787.5 | 262.5 | 370 | 455 | 57 | 104 | 7.4 |
Physical Property | Class I | Class II | Class Ⅲ |
---|---|---|---|
Apparent density (kg/m3) | >2450 | >2350 | >2250 |
Water absorption (%) | <3 | <5 | <8 |
Crushing index (%) | <12 | <20 | <30 |
Sample NO | Compressive Strength/MPa | α1 | Split Tensile Strength/MPa | α2 | Flexural Strength/MPa | α3 |
---|---|---|---|---|---|---|
R0 | 29.920 | 1.000 | 2.553 | 1.000 | 4.300 | 1.000 |
S1 | 32.387 | 1.082 | 2.647 | 1.037 | 4.367 | 1.016 |
S2 | 34.757 | 1.162 | 2.920 | 1.144 | 4.733 | 1.101 |
P1 | 33.630 | 1.124 | 2.723 | 1.067 | 4.633 | 1.077 |
S1S2 | 37.857 | 1.265 | 3.107 | 1.217 | 4.933 | 1.147 |
S1P1 | 33.807 | 1.130 | 2.850 | 1.116 | 4.533 | 1.054 |
S2P1 | 35.560 | 1.189 | 2.830 | 1.108 | 4.700 | 1.093 |
Sample NO | β1 | β2 | β3 |
---|---|---|---|
S1S2 | 1.006 | 1.026 | 1.025 |
S1P1 | 0.929 | 1.009 | 0.963 |
S2P1 | 0.910 | 0.908 | 0.922 |
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Zhong, C.; Tian, P.; Long, Y.; Zhou, J.; Peng, K.; Yuan, C. Effect of Composite Impregnation on Properties of Recycled Coarse Aggregate and Recycled Aggregate Concrete. Buildings 2022, 12, 1035. https://doi.org/10.3390/buildings12071035
Zhong C, Tian P, Long Y, Zhou J, Peng K, Yuan C. Effect of Composite Impregnation on Properties of Recycled Coarse Aggregate and Recycled Aggregate Concrete. Buildings. 2022; 12(7):1035. https://doi.org/10.3390/buildings12071035
Chicago/Turabian StyleZhong, Chuheng, Peng Tian, Yuhua Long, Jinzhi Zhou, Kun Peng, and Chengxin Yuan. 2022. "Effect of Composite Impregnation on Properties of Recycled Coarse Aggregate and Recycled Aggregate Concrete" Buildings 12, no. 7: 1035. https://doi.org/10.3390/buildings12071035