Constitutive relation of uniaxial compression of hybrid fiber reinforced mortar after high temperature
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摘要: 为建立高温和CaCO3晶须(CW)影响下混杂纤维增强砂浆(HyFRM)的单轴受压本构关系，对不同CW掺量的钢-聚乙烯醇(PVA) HyFRM开展25℃、200℃、400℃、500℃、800℃、900℃六个温度水平的单轴受压性能试验。结果表明：随钢-PVA混杂纤维的引入，高温后砂浆的轴压峰值应力显著提高；随CW的引入，轴压峰值应力进一步提高：800℃以下，1.5vol%钢纤维+0.5vol%PVA纤维+2vol%CW的HyFRM轴压峰值应力均为最优。随温度升高，轴压应力-应变曲线由陡峭趋于扁平，HyFRM轴压峰值应力、弹性模量、应变能总体下降。但500℃以下下降缓慢，甚至还有所提高，以1.5vol%钢纤维+0.5vol%PVA纤维+2vol%CW的HyFRM提高最为明显；800℃及以上，受压性能则急剧劣化。建立了考虑温度和CW掺量的HyFRM受压应力-应变损伤本构模型。损伤本构模型和损伤变量不仅可以较好地体现出多尺度纤维体系在砂浆单轴受压破坏的不同阶段多尺度阻裂、延缓砂浆损伤扩展的作用，而且可以反映高温对砂浆初始损伤的影响。光学显微镜和SEM观测揭示了高温对HyFRM轴压性能的影响机制。Abstract: In order to establish the uniaxial compressive constitutive relation of hybrid fiber reinforced mortar (HyFRM) under the influence of high temperature and CaCO3 whisker (CW), uniaxial compressive tests were carried out on steel-polyvinyl alcohol (PVA) HyFRM with different dosages of CW at six temperature levels of 25℃, 200℃, 400℃, 500℃, 800℃ and 900℃. The results show that with the introduction of steel-PVA hybrid fiber, the peak axial compressive stress of mortar is increased significantly. With the introduction of CW, the peak axial compressive stress of HyFRM is further increased before and after high temperature: Below 800℃, the peak axial compressive stress of 1.5vol%steel fiber+0.5vol%PVA fiber+2vol%CW is the best. With the increase of the high treatment temperature, the axial compressive stress-strain curve becomes flat from steep, and the peak axial compressive stress, elastic modulus and strain energy of HyFRM generally decrease. However, below 500℃, they decrease slowly and even increase, and the increases are most obvious when 1.5vol%steel fiber+0.5vol%PVA fiber+2vol%CW. At 800℃ and above, the compressive performance deteriorates sharply. A stress-strain damage constitutive model for HyFRM under compression considering the effects of high temperature treatment temperature and CW content was established. The damage constitutive model and damage variable can’t only preferably reflect the multi-scale fiber system in the different stages of uniaxial compression crack inhibition and retardation of mortar damage propagation, but also reflect the effect of high temperature on the initial damage of mortar. The observations by optical microscope and SEM reveal the influence mechanism of high temperature on the axial compression of HyFRM.
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Key words:
- mortar /
- hybrid fiber /
- multi-scale /
- high temperature /
- constitutive model
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图 2 HyFRM高温后轴压峰值应力
Figure 2. Compressive peak stress of HyFRM after elevated temperature
图 3 HyFRM高温后轴压应力-应变曲线
Figure 3. Compressive stress-strain curves of heated HyFRM after elevated temperature
图 4 HyFRM高温后轴压应变能
Figure 4. Compressive strain energy of HyFRM after elevated temperature
图 5 高温后HyFRM归一化轴压应力-应变实测曲线与理论曲线
Figure 5. Experimental and analytical normalized stress-strain curves of HyFRM after high temperatures
图 6 不同温度后HyFRM损伤变量D
Figure 6. Damage variable D of HyFRM expose to different temperatures
图 7 高温后不同配比HyFRM损伤变量D
Figure 7. Damage variable D of heated HyFRM with various fiber mixures after high temperatures
图 8 HyFRM中水化产物微观结构的SEM图像
Figure 8. SEM images of microstructures of hydration products in HyFRM
图 9 光学显微镜下HyFRM高温后的微观结构
Figure 9. Microstructures of HyFRM after high temperatures under optical microscope
图 10 HyFRM高温后微观结构的SEM图像
Figure 10. SEM images of microstructures for HyFRM after high temperatures
表 1 混杂纤维增强砂浆(HyFRM)原材料的基本性能
Table 1. Properties of raw materials of hybrid fiber reinforced mortar (HyFRM)
Raw
materialsSize Mechanical property Cement Specific surface
area 356 m2/kg28 days cement mortar strength 46.5 MPa Fly ash 45 μm sieve residue 23.72wt% — Silica sand Fineness modulus
1.9 media sandMoh’s hardness 7 Steel fiber Length 13 mm
Diameter 200 μmTensile strength ≥2 GPa
Elastic modulus 200-210 GPaPVA fiber Length 6 mm
Diameter 31 μmTensile strength 1.1 GPa
Elastic modulus 41 GPaCW Length 20-30 μm
Diameter 0.5-2 μmTensile strength 3-6 GPa
Elastic modulus 410–710 GPaNotes: PVA—Polyvinyl alcohol; CW—CaCO3 whisker. 
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表 2 HyFRM的配合比
Table 2. Mix ratios of HyFRM
kg/m3 Group Steel fiber PVA fiber CW Binder Water Sand M 0 0.00 0.0 1220 366 610 1SF-0.5PVA/M 117 6.45 0.0 1196 359 598 1SF-0.5PVA-1CW/M 117 6.45 28.6 1183 355 592 1SF-0.5PVA-2CW/M 117 6.45 57.2 1171 351 586 Notes: M—Mortar; SF—Steel fiber.
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表 3 高温后HyFRM的孔隙率
Table 3. Porosity of HyFRM after high temperatures
Group Temperature/℃ Porosity 2-5000 nm/% Porosity <50 nm/% Porosity ≥50 nm/% 1SF-0.5PVA/M 25 15.30 10.32 4.98 1SF-0.5PVA-2CW/M 25 16.59 12.48 4.11 1SF-0.5PVA-2CW/M 200 17.10 11.66 5.34 1SF-0.5PVA-2CW/M 400 16.86 11.61 5.25 1SF-0.5PVA-2CW/M 900 24.92 4.99 19.93
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