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摘要: 为降低超高性能混凝土(UHPC)收缩和开裂风险, 进行了5组不同粗集料掺量(质量分数分别为0、12.5%、22.5%、32.5%和42.5%)的UHPC的自收缩、基本材性(抗压强度、抗拉强度和弹性模量)、集料级配和圆环约束收缩等试验, 分析了粗集料掺量和集料级配对UHPC自收缩和基本材性的影响, 并采用提出的收缩开裂应力相对差值评价粗集料的掺入对UHPC收缩开裂的影响; 进行了有、无粗集料UHPC在圆环约束下的开裂性能试验与对比分析, 验证粗集料掺入对减小UHPC收缩开裂的有效性, 并给出UHPC中粗集料掺量和最大粒径限制的建议。研究结果表明: 随着粗集料掺量的增加, UHPC早期自收缩量降低, 最大降幅近20%;粗集料对UHPC的弹性模量、抗压强度和抗拉强度等的影响程度与其掺量和级配有关, 当粗集料掺量为22.5%时, 其级配曲线几乎全部处于富勒氏与泰勃特曲线范围内, 是5组材料中堆积最紧密的一组, 对UHPC弹性模量与抗压强度提高最为显著, 对抗拉强度的降低幅度影响最小; 当粗集料掺量为22.5%时, UHPC收缩开裂应力相对差值最大为1.31 MPa, 为试验中的最合理掺量, 可有效降低收缩开裂风险; 与未掺粗集料的UHPC相比, 圆环约束下掺有22.5%粗集料的UHPC的残余应力与拉应力水平分别降低15.8%和14.7%, 其抗裂性能得到提高; 建议对粗集料UHPC进行紧密堆积设计以获得尽可能优的材性, 对掺有长度为12~20 mm钢纤维的UHPC, 其集料的最大粒径可放宽至9.5 mm。Abstract: To reduce the shrinkage and cracking risk of ultra-high-performance concrete(UHPC), the autogenerous shrinkage, basic mechanical properties(compressive strength, tensile strength and elastic modulus), aggregate gradation and restrained ring shrinkage tests on five groups UHPCs with different coarse aggregate contents(mass fractions are 0, 12.5%, 22.5%, 32.5%, and 42.5%, respectively) were studied. The influences of coarse aggregate content and aggregate gradation on the autogenerous shrinkage and basic mechanical properties of UHPC were analyzed. The proposed relative difference of shrinkage-cracking stress was used to evaluate the effect of coarse aggregate incorporation on the shrinkage-cracking of UHPC. The cracking performances of UHPCs with and without coarse aggregate under restrained ring were tested and compared. The effectiveness of coarse aggregate incorporation on reducing the shrinkage-cracking of UHPC was verified, and the suggestions for the coarse aggregate content and the maximum particle size limitation in UHPC were given. Research result shows that the autogenous shrinkage of UHPC at early age reduces with the increase of coarse aggregate content, and the maximum decreasing amplitude is about 20%. The effect degrees of coarse aggregate on the elastic modulus, compressive strength and tensile strength of UHPC are depended on its content and gradation. When the coarse aggregate content is 22.5%, the aggeregate gradation curve is almost inside the range of Fuller's and Talbot's curves. It is the most closely packed group among the five material groups. The coarse aggregate of this group has the most remarkable effect on the improvement of elastic modulus and compressive strength of UHPC, and has the minimum effect on the reduction of tensile strength. The maximum relative difference of shrinkage-cracking stress of UHPC with the coarse aggregate content of 22.5% is up to 1.31 MPa. It is the optimal content in the tests and can effectively reduce the risk of shrinkage-cracking. Comparing the UHPC without coarse aggregate, the levels of residual stress and tensile stress of UHPC with the coarse aggregate content of 22.5% under the restrained ring decreases by 15.8% and 14.7%, respectively, indicating that its crack resistance improves. The UHPC with closely packing coarse aggregate is recommended to achieve the material properties as high as possible. The maximum particle size of coarse aggregate can relaxes to 9.5 mm for the UHPC with steel fiber length of 12-20 mm.
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图 2 粗集料对UHPC自收缩的影响
Figure 2. Effect of coarse aggregate on autogenous shrinkage of UHPC
图 4 粗集料对UHPC抗压强度影响
Figure 4. Effect of coarse aggregate on compressive strength of UHPC
图 7 试件残余应力随时间发展曲线
Figure 7. Development curves of residual stresses of specimens with time
图 8 UHPC拉应力水平随时间发展曲线
Figure 8. Development curves of tensile stress levels of UHPC with time
表 1 粗、细集料粒径分布
Table 1. Particle size distributions of coarse and fine aggregates
粒径/mm 9.50 4.75 2.36 1.18 0.60 0.03 0.015 累计筛余/% 粗集料 0 86.8 99.6 细集料 0 0 44.8 57.2 91.2 98.5 
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表 2 关键龄期内UHPC的自收缩与基本力学性能指标
Table 2. Autogenous shrinkage and mechanical property indexes of UHPC at key ages
UHPC测试指标 组别 各指标随龄期(d)变化 1 3 7 14 28 60 90 自收缩/10-6 CA000 -313.3 -356.4 -452.4 -537.9 -579.3 -607.9 -615.9 CA125 -259.2 -302.7 -392.2 -485.2 -533.0 -545.7 -556.9 CA225 -264.7 -297.2 -379.7 -471.3 -520.6 -531.8 -543.5 CA325 -255.4 -288.4 -380.2 -470.6 -510.8 -510.5 -516.7 CA425 -267.0 -276.5 -364.1 -449.8 -490.8 -495.6 -496.7 抗压强度/MPa CA000 46.4 88.1 113.9 130.9 141.6 150.2 152.5 CA125 48.5 88.4 110.6 126.6 136.5 143.8 145.4 CA225 43.8 87.0 118.9 130.1 144.6 150.9 153.0 CA325 50.0 87.1 117.4 131.1 145.0 150.2 152.5 CA425 41.0 87.0 109.4 127.9 140.4 145.9 147.8 弹性模量/GPa CA000 33.5 40.1 42.1 43.4 44.4 44.9 45.1 CA125 35.6 40.8 42.9 44.2 45.3 45.4 45.9 CA225 33.7 39.6 44.6 45.9 47.2 47.5 47.8 CA325 35.7 42.2 44.3 45.9 46.9 46.9 47.0 CA425 32.9 39.7 41.9 44.0 45.3 46.4 46.9 直拉(开裂)强度/MPa CA000 8.0(7.3) CA125 7.3(7.1) CA225 7.9(7.2) CA325 6.8(6.4) CA425 5.7(5.4)
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表 3 圆环约束收缩试验参数设计
Table 3. Parameter design of restrained ring shrinkage test
UHPC组别 组别 密闭 干燥 高约束水平 低约束水平 CA225 CA225-S-L √ √ CA225-S-H √ √ CA225-D-L √ √ CA225-D-H √ √ CA000 CA000-S-L √ √ CA000-S-H √ √ CA000-D-L √ √ CA000-D-H √ √
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表 4 各龄期内UHPC自由收缩与基本力学性能指标
Table 4. Free shrinkage and mechanical property indexes of UHPC at each age
测试指标 组别 各指标随龄期(d)变化 1 2 3 7 14 28 60 90 总收缩/10-6 CA225 -291.9 -337.1 -369.9 -451.4 -510.0 -535.6 -545.7 -554.5 CA000 -408.8 -452.4 -500.9 -606.1 -680.0 -698.7 -701.9 -705.7 自收缩/10-6 CA225 -194.6 -208.9 -249.1 -362.3 -453.1 -486.0 -494.2 -496.6 CA000 -289.7 -306.1 -356.4 -489.9 -590.4 -618.7 -615.6 -619.8 抗压强度/MPa CA225 42.2 77.8 101.3 137.1 147.8 151.8 155.0 CA000 45.8 88.8 112.5 133.5 145.6 150.9 153.7 弹性模量/GPa CA225 39.0 45.8 49.4 50.7 51.8 52.0 52.2 52.6 CA000 36.3 41.8 45.0 47.0 48.1 48.9 49.5 49.7 劈裂强度/MPa CA225 11.9 13.4 15.6 16.5 16.5 16.7 17.0 CA000 11.0 12.2 13.8 15.0 15.6 16.2 16.5
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表 5 各龄期钢圆环应变
Table 5. Steel ring strains at each age
UHPC类型 组别 不同龄期(d)的钢圆环应变/10-6 1 3 7 14 28 60 90 CA225 CA225-S-L -56.6 -74.4 -128.3 -165.4 -170.3 -172.6 -173.9 CA225-S-H -31.1 -44.8 -91.7 -130.2 -134.8 -133.1 -133.5 CA225-D-L -51.8 -91.4 -129.4 -151.1 -158.9 -164.7 -160.7 CA000 CA225-D-H -38.3 -67.3 -100.4 -119.8 -120.1 -121.7 -117.1 CA000-S-L -54.0 -78.3 -134.7 -177.8 -184.3 -183.3 -184.0 CA000-S-H -23.7 -47.1 -101.5 -143.1 -145.2 -143.9 -144.7 CA000-D-L -52.4 -93.4 -143.6 -170.8 -172.3 -176.3 -173.8 CA000-D-H -27.6 -72.1 -118.8 -138.5 -137.7 -143.9 -140.2
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