Flexural properties of ultra high performance concrete reinforced with steel wire mesh or fiber mesh
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摘要: 为研究钢丝网或纤维网对混杂纤维超高性能混凝土(Ultra-high performance concrete,UHPC)板弯曲性能的影响,进行了四边简支双向板弯曲试验。UHPC中短切纤维为:单掺钢纤维、钢纤维分别与聚乙烯醇纤维、玻璃纤维、玄武岩纤维混掺等。研究参数为:钢丝网与玻璃纤维网层数、孔径、混掺纤维比例等。结果表明,单掺体积分数为1.5vol%的钢纤维时,铺设3层和4层钢丝网的UHPC板的极限承载力和25 mm挠度处的能量吸收值较2层分别提升14.9%、32.3%和14.1%、25.2%;孔径较小的钢丝网对UHPC板承载力和韧性提升明显。当混杂纤维总体积分数为1.5vol%且钢丝网2层时,混掺1.0vol%钢纤维和0.5vol%聚乙烯醇纤维对UHPC板增强增韧效果更好,0.5vol%钢纤维与1.0vol%玻璃纤维或玄武岩纤维混掺较0.5vol%钢纤维与1.0vol%聚乙烯醇纤维混掺对改善板峰后持荷能力更有利,即钢纤维与较高弹性模量非金属纤维混掺有利于提高裂后承载力。与玻璃纤维网相比,铺设钢丝网的UHPC板在峰后延性更好。提出了以素UHPC板峰值荷载挠度作为初裂挠度的韧性指标评定方法,该方法可表征网格和纤维对UHPC板裂后韧性的贡献。基于网格有效利用率概念,建立了板抗弯承载力计算方法,理论值与试验值吻合良好。Abstract: To study the influence of steel wire mesh on the bending properties of ultra-high performance concrete (UHPC) slabs, a bending test of simply supported two-way slabs with four sides was carried out. The chopped fibers in UHPC ware: Steel fiber and steel fiber were mixed with polyvinyl alcohol fiber, glass fiber and basalt fiber, respectively. The research parameters were: Number of layers of wire mesh and glass fiber mesh, pore size and proportion of blended fibers. The results show that when UHPC is single-doped with 1.5vol% steel fiber, the ultimate bearing capacity and energy absorption at 25 mm deflection of UHPC slabs with 3 layers and 4 layers are increased by 14.9%, 32.3% and 14.1%, 25.2%, respectively compared with UHPC slabs with 2 layers of steel wire mesh. When the total volume fraction of hybrid fibers is 1.5vol% and the steel wire mesh is 2 layers, the blending of 1.0vol% steel fiber and 0.5vol% polyvinyl alcohol fiber has better reinforcing and toughening effect on UHPC slabs, and the UHPC slab mixed with 0.5vol% steel fiber and 1.0vol% glass fiber or basalt fiber has a stronger ability to maintain load after peak load than 1.0vol% polyvinyl alcohol fiber, namely the mixing of steel fiber with higher modulus of elasticity non-metallic fiber is advantageous to increase the post-cracking bearing capacity. Compared with glass fiber mesh, UHPC slabs with steel mesh have better ductility after peak load. A method for evaluating the flexibility of UHPC slabs with peak load deflection as initial cracking parameter was proposed, which can characterize the contribution of mesh and fibers to the post-crack toughness of UHPC slabs. Based on the concept of effective utilization of mesh, the theoretical value is in good agreement with the experimental value by calculating the bending capacity.
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Key words:
- steel mesh /
- two-way slab /
- hybrid fiber /
- hardening index /
- toughness index /
- bending capacity
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图 17 UHPC双向板矩形截面受弯承载力计算图
Figure 17. Calculation diagram of bending capacity of rectangular section of UHPC two-way slabs
fc—Axial compressive strength; ft—Axial tensile strength; h0—Effective height of section; Mu−Theoretical bending capacity; a—Distance from the mesh resultant point in the tension zone to the edge of the bottom section of the slab; b—Calculated width of the slab; α1—Equivalent rectangular stress diagram coefficient of compression zone, take 0.88; β—Equivalent rectangular stress diagram coefficient of tensile zone, take 0.35; xc—Height of compression zone; xt—Equivalent rectangular stress height of tension zone; fte—Mesh effective stress; k—Ratio of x to xc; Af—Total section area of grid; h—Height of slab; x—Equivalent rectangular stress height of compression zone
表 1 钢丝网和玻璃纤维网力学性能参数
Table 1. Mechanical property parameters of steel wire mesh and glass fiber mesh
Mesh name Tensile strength/MPa Elastic modulus/GPa Monofilament area/mm2 Elongation/
%SWM 582 200 0.785 2.6 GFM 2200 79 0.290 3.0 表 2 超高性能混凝土(UHPC)基体配合比
Table 2. Composition ratio of ultra-high performance concrete (UHPC)
Matrix type Cement Silica Mineral powder River sand Water
consumptionUHPC 1.000 0.182 0.621 2.182 0.327 表 3 SWM或GFM增强UHPC双向板试件编号与分组方案
Table 3. Specimen number and grouping scheme of UHPC reinforced with SWM or GFM
Group category Specimen number Dosage and type
of fiberNumber of mesh layers The first
groupU1-S2-12 1.5vol% SF 2 U1-S3-12 1.5vol% SF 3 U1-S4-12 1.5vol% SF 4 The second group U1-S2-12 1.5vol% SF 2 U1-S2-20 1.5vol% SF 2 U1-S3-12 1.5vol% SF 3 U1-S3-20 1.5vol% SF 3 U1-S4-12 1.5vol% SF 4 U1-S4-20 1.5vol% SF 4 The third group U1-S2-20 1.5vol% SF 2 U2-S2-20 1.0vol% SF+0.5vol% PVA 2 U3-S2-20 0.5vol% SF+1.0vol% PVA 2 U4-S2-20 0.5vol% SF+1.0vol% GF 2 U5-S2-20 0.5vol% SF+1.0vol% BF 2 The fourth
groupU1-S2-12 1.5vol% SF 2 U1-S2-20 1.5vol% SF 2 U1-G2-5 1.5vol% SF 2 Notes: In specimen number, Un represent UHPC types; Sn/Gn represent SWM or GFM types and number of mesh layers; The next number represents the mesh aperture. Such as, U1-S2-12 represents UHPC slab with 2 layers of steel wire mesh with 12 mm aperture and 1.5vol% steel fiber volume fraction. 表 4 短切纤维性能参数
Table 4. Performance parameters of chopped fibers
Fiber type Diameter/µm Tensile strength/MPa Density/(g·cm−3) Elastic modulus/GPa Length/mm Steel fiber 200 2950 78 205 13 Polyvinyl alcohol 40 1600 1.3 35-40 12 Glass fiber 18 1700 2.68 72 18 Basalt fiber 20 3200 2.6 90-110 20 表 5 SWM或GFM增强UHPC板初裂、峰值荷载及其挠度
Table 5. Initial crack, peak load and deflection of UHPC slabs with SWM or GFM
Specimen number Pcr/kN δcr/mm Pm/kN δm/mm U1-S2-12 61.76 1.50 80.15 3.79 U1-S3-12 64.88 1.84 92.06 7.76 U1-S4-12 72.95 2.50 106.05 8.53 U1-S2-20 57.93 1.44 72.79 3.43 U1-S3-20 61.15 1.64 80.30 7.32 U1-S4-20 68.35 2.05 88.73 8.86 U2-S2-20 51.34 1.48 77.08 3.49 U3-S2-20 52.72 1.53 65.59 3.47 U4-S2-20 45.97 1.57 60.73 13.02 U5-S2-20 43.15 1.39 57.62 11.93 U1-G2-5 30.56 0.85 73.14 6.53 Notes: Pcr—Initial crack load;δcr—Deflection at initial crack load;Pm—Peak load;δm—Deflection at peak load. 表 6 SWM或GFM增强UHPC板不同挠度处能量吸收计算值
Table 6. Calculated values of energy absorption for different deflections of UHPC slabs with SWM or GFM
Specimen
numberQcr/J Qm/J Q2/J Q5/J Q15/J Q25/J U1-S2-12 54.78 226.42 88.71 321.55 1084.37 1769.73 U1-S3-12 74.39 578.58 84.55 329.84 1229.86 2019.31 U1-S4-12 94.82 676.10 60.43 315.28 1332.85 2215.37 U1-S2-20 44.57 180.36 80.03 290.77 934.06 1480.90 U1-S3-20 61.06 490.54 83.62 306.65 1087.16 1762.61 U1-S4-20 82.41 656.36 79.01 320.16 1181.46 1965.45 U2-S2-20 41.32 178.87 71.49 292.22 959.04 1501.36 U3-S2-20 40.85 156.78 66.52 254.19 805.11 1139.25 U4-S2-20 36.30 673.04 56.85 213.34 785.48 1206.25 U5-S2-20 36.15 578.58 63.19 211.76 759.31 1191.33 U1-G2-5 12.83 327.61 52.35 218.20 744.56 − Notes: Qcr and Qm—Energy absorption values at the initial crack and peak load deflection of UHPC slabs, respectively; Q2, Q5, Q15, Q25—Energy absorption value of UHPC slabs with deflection of 2 mm, 5 mm, 15 mm and 25 mm, respectively. 表 7 SWM或GFM增强UHPC板硬化指数和韧性指标
Table 7. Hardening index and toughness index of UHPC slabs with SWM or GFM
Specimen number ISh T15 T25 U1-S2-12 1.30 141.68 231.86 U1-S3-12 1.42 160.82 264.70 U1-S4-12 1.45 174.38 290.50 U1-S2-20 1.26 121.90 193.86 U1-S3-20 1.31 142.05 230.92 U1-S4-20 1.30 154.46 257.61 U2-S2-20 1.50 125.19 196.55 U3-S2-20 1.24 104.94 148.90 U4-S2-20 1.32 102.35 157.72 U5-S2-20 1.34 98.91 155.75 U1-G2-5 2.39 96.97 − Notes: ISh—Hardening index; T15—Toughness index at 15 mm deflection; T25—Toughness index at 25 mm deflection. 表 8 各UHPC板抗弯承载力计算结果
Table 8. Calculation results of bending capacity of UHPC slabs
Specimen
numberfc/MPa ft/MPa h0/mm εc fte/MPa λ/% Mu
/(kN·m)Me
/(kN·m)Me/Mu U1-S2-12 98.81 6.37 43.5 0.00391 3279.73 82.0 9.96 10.02 1.006 U1-S3-12 98.81 6.37 41.0 0.00397 2595.67 64.9 10.95 11.13 1.017 U1-S4-12 98.81 6.37 38.5 0.00401 2199.33 55.0 11.54 13.26 1.198 U1-S2-20 98.81 6.37 43.5 0.00353 3908.73 97.7 7.81 9.10 1.165 U1-S3-20 98.81 6.37 41.0 0.00365 3205.44 80.1 8.82 10.04 1.138 U1-S4-20 98.81 6.37 38.5 0.00385 2740.10 68.5 9.39 11.09 1.227 U2-S2-20 91.12 6.49 43.5 0.00353 3871.35 96.3 7.73 9.64 1.247 U3-S2-20 90.78 6.11 43.5 0.00341 3681.44 92.0 7.36 8.20 1.114 U4-S2-20 86.52 5.95 43.5 0.00339 3570.49 89.3 7.14 7.59 1.064 U5-S2-20 83.06 5.89 43.5 0.00338 3480.91 87.0 6.97 7.20 1.034 U1-G2-5 98.81 6.37 45.0 0.00409 2027.73 78.0 7.24 8.62 1.191 Notes:fc—Axial compressive strength; ft—Axial tensile strength; h0—Effective height of section; εc—Compressive strain of concrete; fte—Mesh effective stress; λ—Effective utilization of mesh; Mu—Theoretical bending capacity; Me—Experimental bending capacity. -
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