Effects of a simulated freezing construction environment on the mass concrete performance
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摘要: 模拟大体积混凝土在冻结法施工环境的状态，将混凝土浇筑7 h后施加−5/60 ℃和−5/70 ℃温差，测试施加模拟环境后混凝土的超声波参数、抗压强度、劈裂抗拉强度、氯离子扩散系数和冲击倾向性，分析混凝土的扫描电镜微观形貌。结果表明，冻结施工环境对于混凝土内部会造成一定的损伤，且平行于加温方向的损伤要大于垂直方向，C50混凝土的损伤大于C70混凝土，温度梯度会加剧混凝土内部的损伤。模拟冻结环境会对混凝土抗压强度、劈裂抗拉强度、氯离子渗透性能和冲击倾向性造成不利影响，温差与性能降低率正相关，且这种影响对于低强度混凝土更加显著。模拟冻结环境造成混凝土试块的内部微观结构不均匀，低温端混凝土结构比较疏松，高温端结构比较致密，导致部分混凝土性能的降低。Abstract: Exhausted shallow resources have turned mining into deep mining, with the mining depth of most mines under construction being more than 1000 m. With the continuous increase of the mining depth of mineral resources, the thickness and strength grade of the shaft lining concrete increases, resulting in higher hydration heat. The freezing method is usually used in deep well construction, resulting in a high temperature on one side and a low temperature on the other side of the shaft wall concrete. The influence law of this environment on concrete needs to be studied. It is of great theoretical significance for deep well construction and service safety to find out the change law of the shaft wall concrete performance under a freezing construction environment. The temperature difference between −5/60 ℃ and −5/70 ℃ was applied to simulate the state of the mass concrete in the freezing method construction environment. The ultrasonic parameters, compressive strength, splitting tensile strength, chloride diffusion coefficient, and bursting liability of concrete under the simulated environment were studied, and the scanning electron microscope of the concrete was analyzed. Results show that the freezing construction environment will cause certain damage to the interior of the concrete, and the damage parallel to the heating direction is greater than that in the vertical direction. The damage of the C50 concrete is greater than that of the C70 concrete, and the temperature gradient will aggravate the internal damage of the concrete. The simulated freezing environment will have adverse effects on the compressive strength, splitting tensile strength, chloride ion permeability, and bursting liability of the concrete. The temperature difference has a positive correlation with the performance reduction rate, which becomes more significant for low-strength concrete. The internal microstructure of the concrete block is uneven due to the simulated freezing environment, the concrete structure at the low-temperature end is loose, and the structure at the high-temperature end is dense, resulting in the decrease of the concrete’s performance.
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Key words:
- freezing method /
- mass concrete /
- bursting liability /
- deep shaft lining /
- ultrasonic measure
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图 1 试验仪器。（a）主控机箱；（b）循环管线和加温模具
Figure 1. Experiment instrument: (a) main control cabinet; (b) circulation pipeline and heating mold
图 3 混凝土的抗压强度和劈裂抗拉强度。（a）抗压强度；（b）劈裂抗拉强度
Figure 3. Compressive strength and splitting tensile strength of concrete: (a) compressive strength; (b) splitting tensile strength
图 4 混凝土的氯离子扩散系数。（a）C50；（b）C70
Figure 4. Chloride diffusion coefficient of concrete: (a) C50; (b) C70
图 5 C50混凝土的扫描电镜图片。（a）冷端；（b） 热端；（c）中温；（d）标准养护
Figure 5. SEM images of C50 concrete: (a) cold side; (b) hot side; (c) medium temperature; (d) standard curing
图 6 C70混凝土的扫描电镜图片。（a）冷端；（b）热端；（c）中温；（d）标准养护
Figure 6. SEM image of C70 concrete: (a) cold side; (b) hot side; (c) medium temperature; (d) standard curing
表 1 P.O 42.5水泥性能指标
Table 1. Main properties of cement
Water mass requirement for normal
consistency/%Initial setting
time/minFinal setting
time/minSpecific surface
area/(m2·kg−1)Soundness Flexural strength/MPa Compressive strength/MPa 3 d 28 d 3 d 28 d 29.2 162 226 392 Qualified 4.9 9.9 27.5 50.0 
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表 2 不同强度等级的混凝土配合比
Table 2. Mix proportions of concrete with different strengths
kg·m−3 Strength grade Cement Fly ash Slag powder Silica fume Sand Stone Water PC* C50 320 80 85 0 673 1077 155 5.82 C70 337 100 108 25 555 1126 140 9.69 Note：* is polycarboxylate superplasticizer for concrete.
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表 3 混凝土在不同条件下的超声检测结果
Table 3. Ultrasonic testing results of concrete under different conditions
Strength grade Simulation condition/℃ Direction Amplitude/db Velocity/
(km·s−1)C50 −5/60 Vertical 101.8 5.68 −5/60 Parallel 99.8 5.42 Standard curing — 103.6 5.85 −5/70 Vertical 102.1 5.66 −5/70 Parallel 100.0 5.33 Standard curing — 104.2 5.94 C70 −5/60 Vertical 103.1 6.03 −5/60 Parallel 101.6 5.89 Standard curing — 104.8 6.14 −5/70 Vertical 103.3 6.08 −5/70 Parallel 100.2 5.85 Standard curing — 105.3 6.21
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表 4 混凝土在不同温差模拟条件下的超声检测分析结果
Table 4. Analysis results of ultrasonic testing of concrete under different simulation conditions
Strength grade Temperature difference/℃ Relative variation ratio/% Vertical velocity Parallel velocity Vertical amplitude Parallel amplitude C50 −5/60 2.9 7.4 1.7 3.7 C50 −5/70 4.7 10.3 2.0 4.2 C70 −5/60 1.8 4.1 1.6 3.1 C70 −5/70 2.1 5.8 1.9 4.8
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表 5 混凝土的冲击倾向性指标
Table 5. Bursting liability indexes of concrete
Group Brittleness Dynamic failure time,
TD/ msImpact energy
index, KEC50 Standard 19.6 480 1.78 C50 −5/60 ℃ 20.2 410 2.06 C50 −5/70 ℃ 21.2 380 2.32 C70 Standard 21.9 170 5.81 C70 −5/60 ℃ 22.8 140 6.32 C70 −5/70 ℃ 23.5 120 6.55
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