EFFECT OF FREEZING AND THAWING ON FRACTURE PERFORMANCE OF CONCRETE AT POLAR LOW TEMPERATURE
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摘要: 为研究混凝土在极地及严寒地区经历冻融循环作用后的耐久性能变化情况，该文通过慢冻法开展了84个三点弯曲梁的冻融循环及加载试验。试验以冻融循环下限温度(低至−80℃)、冻融循环次数、混凝土强度、混凝土类型为研究变量，对比分析了冻融循环前后混凝土基本力学性能和关键断裂参数的变化规律。研究结果表明：随着循环下限温度的降低以及循环次数的增加，混凝土的基本力学性能以及起裂韧度和断裂能均呈下降趋势，但失稳韧度以及特征长度则呈相反趋势，表明混凝土在经历冻融循环后阻裂的能力下降，但混凝土变形性能有明显改善；随着混凝土强度的提高，抗冻耐久性能有一定程度的提升；海水海砂混凝土经受冻融循环后断裂性能不低于普通混凝土；提出冻融损伤累积量的概念，可利用其反映断裂参数的变化情况和不同冻融工况的定量化比较。Abstract: In order to study the durability performance changes of concrete after freeze-thaw cycles in polar and cold regions, freeze-thaw cycles and loading tests of 84 three-point bending beams were carried out by the slow-freezing method. The test was conducted with the lower limit temperature (down to −80 ℃), the number of freeze-thaw cycles, the concrete strength, and the concrete type as the study parameters, and the changes in the basic mechanical properties of concrete and key fracture parameters were compared and analyzed before and after the freeze-thaw cycles. The study results show that: with the decrease of the lower limit temperature of freeze-thaw cycles and the increase of the number of freeze-thaw cycles, the basic mechanical properties as well as the cracking toughness and fracture energy of concrete show a decreasing trend, but the instability toughness and characteristic length show a opposite trend, indicating that the ability of concrete to resist cracking decreases after experiencing freeze-thaw cycles, but the deformation properties of concrete improve significantly; with the increase of concrete strength, the freeze-resistance durability has been improved to a certain extent; the fracture performance of seawater sea-sand concrete after freeze-thaw cycles is not lower than that of ordinary concrete. The concept of freeze-thaw damage accumulation is proposed, which can be used to reflect the variation of fracture parameters and the quantitative comparison of different freeze-thaw conditions.
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Key words:
- concrete /
- double K fracture toughness /
- experimental study /
- freeze-thaw cycles /
- polar low temperature
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图 3 冻融循环后混凝土立方体抗压强度
Figure 3. Compressive strength of concrete cubes after freeze-thaw cycles
图 4 冻融循环后混凝土立方体劈裂抗拉强度
Figure 4. Splitting tensile strength of concrete cubes after freeze-thaw cycles
图 13 断裂能损失率与冻融损伤累积量趋势线
Figure 13. Trend line of fracture energy loss rate and freeze-thaw damage accumulation
表 1 试件详细设计参数
Table 1. Detailed design parameters of specimens
编号 混凝土类型 设计强度 温度下限/(℃) 循环次数 编号 混凝土类型 设计强度 温度下限/(℃) 循环次数 C-2-0-0-1/2/3 普通混凝土 C20 常温 0 C-6-0-0-1/2/3 普通混凝土 C60 常温 0 C-2-3-1-1/2/3 −30 5 C-6-3-1-1/2/3 −30 5 C-2-3-2-1/2/3 −30 10 C-6-3-2-1/2/3 −30 10 C-2-6-1-1/2/3 −60 5 C-6-6-1-1/2/3 −60 5 C-2-6-2-1/2/3 −60 10 C-6-6-2-1/2/3 −60 10 C-2-8-1-1/2/3 −80 5 C-6-8-1-1/2/3 −80 5 C-2-8-2-1/2/3 −80 10 C-6-8-2-1/2/3 −80 10 C-4-0-0-1/2/3 普通混凝土 C40 常温 0 S-4-0-0-1/2/3 海水海砂混凝土 S40 常温 0 C-4-3-1-1/2/3 −30 5 S-4-3-1-1/2/3 −30 5 C-4-3-2-1/2/3 −30 10 S-4-3-2-1/2/3 −30 10 C-4-6-1-1/2/3 −60 5 S-4-6-1-1/2/3 −60 5 C-4-6-2-1/2/3 −60 10 S-4-6-2-1/2/3 −60 10 C-4-8-1-1/2/3 −80 5 S-4-8-1-1/2/3 −80 5 C-4-8-2-1/2/3 −80 10 S-4-8-2-1/2/3 −80 10 
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表 2 混凝土配合比设计
Table 2. Mix proportion design of concrete
/(kg/m3) 设计强度等级 水泥 河砂/海砂 石子 水 水胶比 C20 280.5 812.5 1077.0 230.0 0.82 C40 460.0 598.5 1111.5 230.0 0.50 S40 460.0 598.5 1111.5 230.0 0.50 C60 638.9 459.3 1071.8 230.0 0.36
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表 3 主要试验结果及断裂参数计算结果
Table 3. Main test results and fracture parameters calculation results
试件编号 抗压强度
$ {f_{{\text{cu}}}} $/MPa抗拉强度
$ {f_{\text{t}}} $/MPa起裂荷载
$ {F_{\text{Q}}} $/kN峰值荷载
$ {F_{\max }} $/kN裂缝张开口位移
$ CMO{D_{\text{C}}} $/μm临界有效裂缝
长度$ {a_{\text{c}}} $/m起裂韧度
$ K_{{\text{IC}}}^{\text{Q}} $/(MPa·m1/2)断裂韧度
$ K_{{\text{IC}}}^{\text{S}} $/(MPa·m1/2)断裂能
$ G_{\text{F}}^{} $/(N/m)特征长度
$ L_{{\text{ch}}}^{} $/mmC-2-0-0-1/2/3 33.7 3.6 0.748 2.271 51.33 0.060 0.308 1.326 199.83 546.7 C-2-3-1-1/2/3 30.4 2.7 0.599 1.908 68.37 0.067 0.270 1.661 190.01 1383.4 C-2-3-2-1/2/3 32.3 2.7 0.389 1.518 100.60 0.075 0.219 1.802 187.34 1265.8 C-2-6-1-1/2/3 24.5 2.1 0.240 0.851 106.87 0.080 0.206 1.879 170.41 3309.4 C-2-6-2-1/2/3 19.5 1.5 0.096 0.499 162.15 0.089 0.167 2.855 141.48 5957.5 C-2-8-1-1/2/3 27.6 2.2 0.250 0.978 119.67 0.081 0.181 2.164 161.75 4381.1 C-2-8-2-1/2/3 19.4 1.4 0.102 0.714 173.80 0.085 0.143 2.691 142.62 8535.9 C-4-0-0-1/2/3 39.8 3.7 0.807 2.646 48.40 0.058 0.323 1.374 201.26 491.6 C-4-3-1-1/2/3 36.9 4.0 0.729 2.194 64.80 0.065 0.306 1.564 196.82 518.6 C-4-3-2-1/2/3 39.5 3.3 0.654 2.327 73.67 0.065 0.287 1.874 182.85 924.2 C-4-6-1-1/2/3 33.4 2.9 0.360 1.017 97.77 0.079 0.236 2.191 178.36 2071.2 C-4-6-2-1/2/3 29.3 2.3 0.279 0.886 123.37 0.082 0.189 2.319 172.79 3585.5 C-4-8-1-1/2/3 34.1 3.0 0.417 1.555 102.40 0.076 0.226 2.081 173.16 2864.4 C-4-8-2-1/2/3 26.2 2.0 0.265 0.888 133.70 0.083 0.188 1.963 163.17 4616.3 C-6-0-0-1/2/3 49.6 4.6 0.886 3.351 47.13 0.054 0.347 1.481 215.25 395.2 C-6-3-1-1/2/3 47.1 4.5 0.692 2.552 51.47 0.060 0.335 1.600 196.56 425.2 C-6-3-2-1/2/3 47.6 4.5 0.888 2.637 52.00 0.059 0.321 1.484 192.06 357.9 C-6-6-1-1/2/3 43.2 4.0 0.434 1.303 71.63 0.074 0.255 1.681 165.44 810.1 C-6-6-2-1/2/3 41.4 3.7 0.318 0.953 111.77 0.082 0.218 2.383 156.54 1458.4 C-6-8-1-1/2/3 47.3 4.0 0.414 1.280 78.00 0.075 0.226 2.149 165.30 1491.2 C-6-8-2-1/2/3 40.3 3.5 0.321 1.141 110.57 0.081 0.205 2.310 151.65 1307.6 S-4-0-0-1/2/3 43.1 4.4 0.889 2.946 49.65 0.056 0.344 1.434 198.12 903.9 S-4-3-1-1/2/3 41.9 3.9 0.841 2.638 53.50 0.060 0.334 1.508 196.68 596.3 S-4-3-2-1/2/3 42.6 4.0 0.612 2.110 74.25 0.068 0.299 2.021 182.83 925.0 S-4-6-1-1/2/3 39.2 3.4 0.548 1.652 91.77 0.074 0.259 2.099 178.29 1271.3 S-4-6-2-1/2/3 36.0 3.1 0.296 1.052 122.93 0.082 0.196 2.380 170.50 1513.9 S-4-8-1-1/2/3 41.5 3.6 0.428 1.715 101.00 0.075 0.229 2.114 170.97 1233.3 S-4-8-2-1/2/3 34.7 2.8 0.266 1.115 126.23 0.081 0.189 2.194 166.90 2293.7 注：表中数据为三个平行试件的平均值。本文后续分析中均按照混凝土实际强度进行计算分析，C20、C40、C60等仅起到分组编号的作用。
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