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Experimental studies and performance analysis of wedge splitting for concrete specimens with cavity defects
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摘要: 为研究空洞缺陷对混凝土楔入劈拉性能的影响，将空洞缺陷等效为相应纵向截面高度的损失量，并推导了含空洞缺陷混凝土楔入劈拉断裂参数的计算式，同时利用改进型测试装置进行了8组共32个试件的楔入劈拉性能试验，分析研究了空洞尺寸及其位置变化对试件楔入劈拉性能的影响规律。结果表明，起裂荷载、失稳荷载、起裂张口位移和失稳张口位移都随着空洞尺寸增大(直径0~120 mm)而降低，降幅分别为43.59%，23.75%，39.85%，54.50%；空洞缺陷对混凝土的起裂韧度影响较小，但却会明显降低混凝土失稳韧度，随着空洞尺寸增大，其降幅达到46.20%；空洞位置对混凝土断裂特性的影响跟裂纹扩展路径相关，当裂纹经过空洞时会降低相关参数，当其远离空洞区域时，则影响较小。Abstract: In order to investigate the defects such as the cavity influences on the wedge splitting performance of the concrete, the cavity is made equal to a loss of the height of the longitudinal section and the calculation formulas for the wedge splitting fracture parameters of the concrete with cavity defects are derived. And then 8 groups including 32 specimens are designed for the wedge splitting tests using the improved testing instrument developed by our team. The influences of different sizes and locations of the cavity on the wedge splitting performance of the concrete are analyzed. The test and calculation results show that along with the increases of the cavity size (diameters from 0 to 120 mm), initial load, instability load, initial CMOD (crack mouth opening displacement) and instability CMOD are respectively reduced by 43.59%, 23.75%, 39.85% and 54.50%. The cavity defects have smaller effects upon the initial toughness of the concrete as their values are stable, but the cavity defects have greater effects on the instability toughness of the concrete, and the instability toughness decreases by 46.20% with a increase in the cavity size. The influences of the cavity location on the wedge splitting performance are relevant to a crack propagation path. When the crack passes through the cavity, the related fracture parameters are reduced; when the crack is far away from the cavity, it has a little effect.
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Key words:
- wedge splitting /
- cavity defect /
- concrete fracture /
- performance analysis
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表 1 试件设计参数
Table 1. Design parameters of specimens
试件标号 高×宽×厚/(mm×mm×mm) 初始缝长a0/mm 空洞直径r/mm 空洞表层离预制缝尖距离c/mm 数量 WS400-040-#1 400×400×200 160 0 0 4 WS400-040-#2 400×400×200 160 20 25 4 WS400-040-#3 400×400×200 160 40 25 4 WS400-040-#4 400×400×200 160 60 25 4 WS400-040-#5 400×400×200 160 80 25 4 WS400-040-#6 400×400×200 160 100 25 4 WS400-040-#7 400×400×200 160 120 25 4 WS400-040-#8 400×400×200 160 60 180 4 注：试件编号中，WS代表楔入劈拉试验；400代表高度；040代表缝高比是0.4；#1是分组序号。 
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表 2 等效高度计算结果
Table 2. Calculated results of equivalent height
试件编号 r/mm c/mm hs1/m h1/m h1降幅/% hs2/m h2/m h2降幅/% WS400-040-#1 0 0 0.240 0 0.400 0 0 0.240 0 0.400 0 0 WS400-040-#2 20 25 0.238 4 0.398 4 -0.393 0.236 6 0.396 6 -0.860 WS400-040-#3 40 25 0.233 7 0.393 7 -1.571 0.227 5 0.387 5 -3.119 WS400-040-#4 60 25 0.225 9 0.385 9 -3.534 0.214 6 0.374 6 -6.341 WS400-040-#5 80 25 0.214 9 0.374 9 -6.283 0.199 4 0.359 4 -10.153 WS400-040-#6 100 25 0.200 7 0.360 7 -9.817 0.189 8 0.349 8 -12.561 WS400-040-#7 120 25 0.183 5 0.343 5 -14.137 0.166 6 0.326 6 -18.353 WS400-040-#8 60 180 0.225 9 0.385 9 -3.534 0.237 7 0.397 7 -0.584
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表 3 断裂参数计算结果
Table 3. Calculated results of fracture parameters
试件编号 Pini/kN Pun/kN Kini/(MPa·m1/2) Kun/(MPa·m1/2) Pini/Pun Kini/Kun WS400-040-#1-1 6.094 16.960 0.453 1.934 0.359 0.234 WS400-040-#1-2 6.233 16.888 0.463 2.170 0.369 0.213 WS400-040-#1-3 6.393 17.504 0.475 2.047 0.365 0.232 平均 6.240 17.117 0.464 2.050 0.365 0.226 WS400-040-#2-1 6.254 16.223 0.473 1.931 0.386 0.245 WS400-040-#2-3 5.970 16.000 0.451 1.899 0.373 0.238 WS400-040-#2-4 6.071 15.810 0.459 1.706 0.384 0.269 平均 6.098 16.011 0.461 1.845 0.381 0.250 WS400-040-#3-2 6.130 15.500 0.485 1.339 0.395 0.362 WS400-040-#3-3 6.121 15.674 0.484 1.857 0.391 0.261 WS400-040-#3-4 5.920 15.500 0.468 1.505 0.382 0.311 平均 6.057 15.558 0.479 1.567 0.389 0.306 WS400-040-#4-1 5.790 15.160 0.492 1.330 0.382 0.370 WS400-040-#4-2 4.410 14.291 0.375 1.316 0.309 0.285 WS400-040-#4-4 5.654 15.108 0.480 1.548 0.374 0.310 平均 5.285 14.853 0.449 1.398 0.356 0.321 WS400-040-#5-1 4.980 15.536 0.465 1.317 0.321 0.353 WS400-040-#5-2 4.360 11.780 0.407 1.120 0.370 0.363 WS400-040-#5-4 6.393 15.418 0.596 1.250 0.415 0.477 平均 5.244 14.245 0.489 1.229 0.368 0.398 WS400-040-#6-1 4.280 12.057 0.430 1.039 0.355 0.414 WS400-040-#6-2 5.140 14.145 0.517 1.361 0.363 0.380 WS400-040-#6-3 5.100 13.526 0.513 1.153 0.377 0.445 平均 4.840 13.243 0.486 1.184 0.365 0.411 WS400-040-#7-1 3.700 12.340 0.443 1.069 0.300 0.414 WS400-040-#7-2 3.160 14.090 0.378 1.181 0.224 0.320 WS400-040-#7-4 3.718 12.726 0.443 1.058 0.291 0.419 平均 3.526 13.052 0.421 1.103 0.270 0.382 WS400-040-#8-1 6.190 16.196 0.477 1.998 0.382 0.239 WS400-040-#8-3 6.530 14.940 0.503 1.817 0.437 0.277 WS400-040-#8-4 5.530 15.480 0.426 1.768 0.357 0.241 平均 6.083 15.539 0.469 1.861 0.391 0.252
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