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Test analysis of effects of cushion on concrete specimen's elastic modulus and creep under biaxial compression
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摘要: 混凝土双轴受压弹模和徐变试验加载应力控制在相应龄期棱柱体强度的30%~40%，相比混凝土抗压强度试验，试件表面轻微不平整和倾斜以及钢承压板与试件承压面的摩阻对混凝土双轴弹模和徐变试验结果的影响更大。为减小混凝土试件承压面轻微不平整和倾斜以及钢压板与混凝土试件间的摩阻对混凝土双轴弹模和徐变试验结果的影响，提出适用于混凝土双轴弹模和徐变试验、能使混凝土试件在弹性变形阶段整体应力应变均匀性好的垫层。通过棱柱体混凝土试件单轴受压时不同材料和组合的垫层对应变偏差率、应变曲线及弹性特征影响的比较，筛选3种组合垫层进行双轴弹模验证试验。结果表明聚四氟乙烯薄膜(PTFE)夹土工布的组合垫层能在双轴受压弹模试验中有效降低试件竖向和横向应变偏差率，使混凝土试件应力分布均匀，2层1.0 mmPTFE夹1.2 mm土工布的组合垫层总体效果最好。Abstract: The stress of concrete in the biaxial compression elastic modulus and creep tests is controlled at 30%~40% of the prism specimen's strength at the corresponding age. Compared with the concrete compressive strength testing, the slight unevenness and inclination on the concrete specimen surface as well as the friction between the steel load-bearing board and the concrete specimen have a greater influence on the concrete biaxial elastic modulus and creep tests. In order to reduce the above adverse effects and make the stress and strain of the concrete specimens uniform during the elastic deformation stage, proposing a suitable cushion for the concrete biaxial elastic modulus and creep tests is necessary. By comparing the effects of different materials and composite cushions on the strain deviation rates, strain curves and elastic characteristics when the prismatic concrete specimens are uniaxially compressed, three kinds of composite cushions are choosen and verified in the biaxial elastic modulus tests. The testing analysis results show that the composite cushion with PTFE and geotextile can effectively reduce the vertical and lateral strain deviation rates of the concrete specimen in the biaxial compression elastic modulus tests, uniforming the stress distribution of the concrete specimen. The overall effect of the composite cushion with two layers of 1.0 mm PTFE and 1.2 mm geotextile is optimal.
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Key words:
- concrete /
- biaxial creep /
- composite cushion /
- deviation /
- antifriction
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图 2 不同厚度PTFE垫层混凝土试件各荷载级应变增量偏差率
Figure 2. Strain deviation rate of concrete specimens with different-thickness PTFE cushions under all load levels
图 3 不同厚度PTFE垫层的混凝土试件应变曲线
Figure 3. Strain curves of concrete specimens with different-thickness PTFE cushions
图 4 不同垫层组合棱柱体试件应变曲线
Figure 4. Strain curves of prism specimens with different cushions
图 5 不同垫层组合立方体试件应变曲线
Figure 5. Strain curves of cubic specimens with different cushions
图 6 不同垫层组合各荷载级弹模和泊松比及其标准差
Figure 6. Standard deviation of elastic modulus and Poisson's ratio with different cushions under all load levels
图 7 PTFE夹1.2 mm土工布组合垫层应变曲线
Figure 7. Strain curves of composite cushion with PTFE and 1.2 mm geotextile
表 1 不同厚度PTFE垫层混凝土试件竖向和横向总应变偏差率
Table 1. Vertical and lateral total strain deviation rates of concrete specimens with different-thickness PTFE cushions
% 编号 垫层厚度/mm eVf, Vb eH1，H2 eH2, H3 eH A1 0(无垫层) 9.31 14.17 31.48 22.83 A2 0.1 8.12 10.43 31.28 20.86 A3 0.2 13.14 18.06 17.04 17.55 A4 0.3 15.23 11.78 20.31 16.05 A5 0.5 5.53 7.96 26.47 17.21 A6 1.0 4.86 7.56 19.90 13.73 
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表 2 不同厚度PTFE垫层各荷载级弹模及泊松比试验结果
Table 2. Elastic modulus and Poisson's ratio test results for different-thickness PTFE cushions under all load levels
垫层编号 不同荷载级的E/GPa和μ 平均值 标准差 1 2 3 4 5 A1 47.1(0.04) 40.9(0.07) 38.9(0.20) 39.9(0.17) 39.3(0.22) 41.2(0.14) 3.36(0.081) A2 47.1(0.07) 40.7(0.09) 39.3(0.19) 41.9(0.25) 40.7(0.23) 41.9(0.17) 3.01(0.082) A3 44.7(0.03) 38.2(0.15) 38.0(0.19) 37.9(0.17) 40.4(0.15) 39.9(0.14) 2.90(0.062) A4 45.2(0.10) 40.2(0.31) 37.3(0.22) 38.7(0.14) 37.9(0.03) 39.9(0.16) 3.10(0.107) A5 45.4(0.05) 38.9(0.29) 38.0(0.20) 37.1(0.03) 44.1(0.20) 40.7(0.15) 3.78(0.112) A6 48.0(0.07) 38.6(0.04) 39.2(0.16) 40.8(0.20) 44.0(0.28) 42.1(0.15) 3.90(0.098)
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表 3 组合垫层混凝土试件横竖向总应变偏差率
Table 3. Horizontal and vertical total strain deviation rates of concrete specimens with different composite cushions
% 垫层组合 棱柱体试件 立方体试件 编号 eVf, Vb eH1, H2 eH2, H3 eH 编号 eVf, Vb eV1, V3 eH1, H2 无垫层 A1 9.31 14.17 31.48 22.83 / / / / 2层1.0 mm PTFE B1 7.12 7.39 17.51 12.45 C1 11.64 13.12 19.66 2层1.0 mm PTFE夹氯丁橡胶 B2 4.52 17.41 30.43 23.92 C2 0.26 24.26 10.35 2层1.0 mm PTFE夹瓦楞纸板 B3 16.46 21.40 34.33 27.86 C3 3.38 31.63 13.81 2层1.0 mm PTFE夹0.6 mm土工布 B4 3.83 7.28 16.97 10.46 C4 0.91 11.96 4.30 2层1.0 mmPTFE夹1.2 mm土工布 B5 12.46 8.20 11.65 12.59 C5 2.00 10.25 14.42 2层1.0 mmPTFE夹(1.2+0.6)mm土工布 B6 11.83 3.89 8.55 6.22 C6 2.53 14.87 5.64
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表 4 PTFE夹土工布组合垫层双轴受压试验结果
Table 4. Biaxial compression test results of composite cushion with PTFE and geotextile
加载方式 组合垫层 eVf, Vb/
%eVl, Vr/
%eH1, H2/
%EV/
GPaEH/
GPaμV μH 先竖向分4级加载
至400 kNPTFE夹0.6 mm土工布 1.83 3.66 0.90 36.2 36.3 0.27 0.38 PTFE夹1.2 mm土工布 0.49 0.45 0.24 36.1 36.1 0.24 0.36 后横向分4级加载
至400 kNPTFE夹(0.6+1.2)mm土工布 0.31 4.99 3.16 40.7 35.9 0.25 0.39 先横向分4级加载
至400 kNPTFE夹0.6 mm土工布 3.48 3.72 0.17 38.5 31.3 0.28 0.35 PTFE夹1.2 mm土工布 2.80 2.63 0.96 34.7 33.3 0.25 0.33 后竖向分4级加载
至400 kNPTFE夹(0.6+1.2)mm土工布 1.34 6.90 3.69 38.1 31.4 0.24 0.34 横竖向100 kN
交替加载PTFE夹0.6 mm土工布 10.13 9.57 3.02 38.0 32.5 0.28 0.32 PTFE夹1.2 mm土工布 9.86 9.83 7.98 32.1 32.7 0.22 0.43 PTFE夹(0.6+1.2)mm土工布 8.22 10.07 1.90 36.5 34.7 0.25 0.45
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