Effect of nano-SiO2 and polypropylene fibers on the mechanical properties and microscopic properties of all coal gangue aggregate concrete
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摘要: 煤矸石作为工业固体废弃物，替换全部骨料制备混凝土，是对煤矸石二次利用的有效途径。本文将破碎后的煤矸石骨料替换混凝土全部粗细骨料，利用不同掺量的纳米SiO2和聚丙烯纤维(PPF)对其改性，通过宏观力学和微观分析相结合的方法，研究了纳米SiO2和PPF单独作用与复合作用下对混凝土力学性能、微观结构的影响。研究结果表明，纳米SiO2与PPF复掺，其掺量分别为1.5wt%与0.6 kg·m−3时混凝土的性能最好。与对照组相比，龄期为7天时，混凝土抗压强度、抗折强度和抗劈裂强度分别提高21.8%、43.5%和44.4%；龄期为28天时，其抗压强度、抗折强度和劈裂强度分别提高20%、44.9%和43.6%。微观结构分析表明，煤矸石混凝土孔隙率减少，水化过程加速，混凝土中大孔的分形维数从2.9975提高至2.9990，而小孔的分形维数从2.9852降低至2.9827，小孔分形维数降低，大孔的分形维数增加，使空间填充能力越强，内部孔隙越少。Abstract: Coal gangue as industrial solid waste, replacing all aggregates to produce concrete, is an effective way to reuse coal gangue. In this paper, all the coarse and fine aggregates of concrete were replaced by crushed coal gangue aggregate, and modified by different amounts of nano-SiO2 and polypropylene fiber (PPF). Based on the combination of macro mechanics and micro analysis, the effects of the single and combined action of nano-SiO2 and PPF on the mechanical properties and microstructure of concrete were studied. The results show that the performance of concrete is the best when the mixture of nano-SiO2 and PPF is 1.5wt% and 0.6 kg·m−3, respectively. Compared with the control group, the compressive strength, flexural strength and splitting strength of the concrete at 7 days increase by 21.8%, 43.5% and 44.4%, respectively. Besides, the compressive strength, flexural strength and splitting strength at 28 days increase by 20%, 44.9% and 43.6%, respectively. The microstructure analysis shows that the porosity of coal gangue concrete decreases, the hydration process is accelerated, the fractal dimension of large holes of the concrete increases from 2.9975 to 2.9990, while that of small holes decreases from 2.9852 to 2.9827, the fractal dimension of small holes decreases, and the fractal dimension of large holes increases, so that the stronger the space filling capacity, the fewer internal pores.
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Key words:
- coal gangue /
- nano-SiO2 /
- PPF /
- concrete /
- mechanical properties /
- microscopic characteristics
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图 1 煤矸石重金属沉淀和自燃对生态环境的影响
Figure 1. Effects of heavy metal precipitation and spontaneous combustion of coal gangue on ecological environment
图 3 反击式破碎机对煤矸石的破碎过程
Figure 3. Breaking process for coal gangue with counterattack crusher
图 5 煤矸石矿物组成和粒度分布
Figure 5. Mineral composition and particle size distribution of coal gangue
图 6 改性材料及分散装置
Figure 6. Modified materials and dispersing devices
PPF—Polypropylene fiber
图 8 不同纳米SiO2和PPF掺量混凝土的抗压强度
Figure 8. Compressive strength of concrete with different nano-SiO2 and PPF contents
图 9 不同纳米SiO2和PPF掺量混凝土在压缩试验中的破坏模式
Figure 9. Failure patterns of concrete with different nano-SiO2 and PPF contents during compressive test
图 10 不同纳米SiO2和PPF掺量混凝土的抗折强度
Figure 10. Flexural strength of concrete with different nano-SiO2 and PPF contents
图 11 不同纳米SiO2和PPF掺量混凝土在弯曲试验中的断裂
Figure 11. Fracture of concrete with different nano-SiO2 and PPF contents during flexural test
图 12 CGAC和1.5wt%N/CGAC断裂面图
Figure 12. Fracture surface diagram of CGAC and 1.5wt%N/CGAC
图 13 纳米SiO2和PPF掺量对混凝土劈裂强度的影响
Figure 13. Splitting strength of concrete with different nano-SiO2 and PPF contents
图 14 不同纳米SiO2和PPF掺量混凝土劈裂试验过程中的断裂裂缝
Figure 14. Fracture crack of concrete with different nano-SiO2 and PPF contents in the process of splitting test
图 15 CGAC和1.5wt%N-0.6PPF/CGAC混凝土的孔隙分布
Figure 15. Pore distribution of CGAC and 1.5wt%N-0.6PPF/CGAC concrete
图 16 不同掺量的纳米SiO2和PPF混凝土的XRD图谱
Figure 16. XRD patterns of concrete with different dosages of nano-SiO2 and PPF
图 17 不同掺量的纳米SiO2和PPF混凝土在养护7天和28天后的SEM图像
Figure 17. SEM images of concrete with different dosages of nano-SiO2 and PPF after 7 days and 28 days curing
AFt—Ettringite
图 18 混凝土大孔与小孔径范围内lg(1-V)和lg(lk/L)的线性拟合关系
Figure 18. Concrete big hole and small aperture within the scope of lg(1-V) and lg(lk/L) of the linear fitting relationship
lk/L—Number of parting holes remaining after k times removal processes; V—Total volume of the removed holes after k times removal processes
表 1 水泥和粉煤灰的化学成分
Table 1. Chemical composition of cement and fly ash
Composition Na2O MgO Al2O3 SiO2 SO3 K2O CaO Fe2O3 Loss on ignition Compressive
strength/MPaFlexural
strength/MPa3 d 28 d 3 d 28 d Cement/wt% 0.79 1.02 4.93 17.63 3.01 0.47 63.22 3.99 3.95 21.2 46.7 5.7 8.3 Fly ash/wt% 0.33 0.23 38.01 46.44 0.69 0.88 7.5 3.12 2.79 — — — — 
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表 2 煤矸石的物理性质
Table 2. Physical properties of coal gangue
Coal gangue Bulk density/
(kg·m−3)Performance
density/(kg·m−3)Water
absorption/wt%Poriness/
wt%Moisture
content/wt%Crushing
value/wt%Coarse aggregate 1507 2740 6.9 45 2.0 22.4 Fine aggregate 1475 2620 2.7 44 0.9 10.2
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表 3 纳米SiO2活性试验结果
Table 3. Activity testing results of the nano-SiO2
Code Concrete mix design/(kg·m−3) Compressive strength/MPa Activity index/% Cement Sand Water Nano-SiO2 7 d 28 d 7 d 28 d MTB 450 1350 225 0 34.5 44.3 — — 2wt%N/MTB 441 1350 225 9 41.8 49.1 121.1 110.8 Notes: MTB—Mortar test block; N—Nano-SiO2.
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表 4 混凝土配合比设计
Table 4. Concrete mix design
kg·m−3 Code Cement Fly ash Water Sand Aggregate Water reducer Nano-SiO2 PPF CGAC 400 100 240 720 880 15 0 0 0.75wt%N/CGAC 400 100 240 720 880 15 3.75 0 1.5wt%N/CGAC 400 100 240 720 880 20 7.5 0 2.25wt%N/CGAC 400 100 240 720 880 22.5 11.25 0 0.3PPF/CGAC 400 100 240 720 880 15 0 0.3 0.75wt%N-0.3PPF/CGAC 400 100 240 720 880 15 3.75 0.3 1.5wt%N-0.3PPF/CGAC 400 100 240 720 880 20 7.5 0.3 2.25wt%N-0.3PPF/CGAC 400 100 240 720 880 22.5 11.25 0.3 0.6PPF/CGAC 400 100 240 720 880 15 0 0.6 0.75wt%N-0.6 PPF/CGAC 400 100 240 720 880 15 3.75 0.6 1.5wt%N-0.6PPF/CGAC 400 100 240 720 880 20 7.5 0.6 2.25wt%N-0.6PPF/CGAC 400 100 240 720 880 22.5 11.25 0.6 0.9PPF/CGAC 400 100 240 720 880 15 0 0.9 0.75wt%N-0.9PPF/CGAC 400 100 240 720 880 15 3.75 0.9 1.5wt%N-0.9PPF/CGAC 400 100 240 720 880 20 7.5 0.9 2.25wt%N-0.9PPF/CGAC 400 100 240 720 880 22.5 11.25 0.9 Notes: CGAC—Coal gangue aggregate concrete; Example: 0.75wt%N-0.3PPF/CGAC is that the control group was added with 0.75wt% nano-SiO2 and 0.3 kg·m−3 PPF.
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表 5 煤矸石混凝土孔隙特性参数
Table 5. Pore characteristic parameters of coal gangue concrete
Code Total pore
area/(m2·g−1）Median pore diameter
(volume)/nmMedian pore diameter
(area)/nmAverage pore
diameter/nmPorosity/wt% CGAC 16.123 32.68 10.03 21.51 17.58 1.5wt%N-0.6PPF/CGAC 10.843 26.56 9.23 18.99 12.36
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表 6 不同孔径范围内混凝土孔隙占比
Table 6. Proportion of concrete pores in different pore size scopes
wt% Code CGAC 1.5wt%N-0.6PPF/CGAC d≤20 nm 35.6 40.6 20 nm≤d≤50 nm 25.2 28.8 50 nm≤d≤200 nm 18.6 20.8 d>200 nm 20.3 10.3
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表 7 混凝土多孔结构的分形维数参数
Table 7. Fractal dimension parameters of porous structures in concrete
Code Demarcation points/nm Great pore Small pore RMSE Fractal dimension Correlation Fractal dimension Correlation CGAC 102.40 2.9975 0.99 2.9852 0.99 0.00057 1.5wt%N-0.6PPF/CGAC 64.70 2.9990 0.90 2.9827 0.97 0.00144 Note: RMSE—Evaluation index of transition aperture.
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