Effects of a simulated freezing construction environment on the mass concrete performance
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摘要: 模擬大體積混凝土在凍結法施工環境的狀態，將混凝土澆筑7 h后施加?5/60 ℃和?5/70 ℃溫差，測試施加模擬環境后混凝土的超聲波參數、抗壓強度、劈裂抗拉強度、氯離子擴散系數和沖擊傾向性，分析混凝土的掃描電鏡微觀形貌。結果表明，凍結施工環境對于混凝土內部會造成一定的損傷，且平行于加溫方向的損傷要大于垂直方向，C50混凝土的損傷大于C70混凝土，溫度梯度會加劇混凝土內部的損傷。模擬凍結環境會對混凝土抗壓強度、劈裂抗拉強度、氯離子滲透性能和沖擊傾向性造成不利影響，溫差與性能降低率正相關，且這種影響對于低強度混凝土更加顯著。模擬凍結環境造成混凝土試塊的內部微觀結構不均勻，低溫端混凝土結構比較疏松，高溫端結構比較致密，導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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圖 1 試驗儀器。（a）主控機箱；（b）循環管線和加溫模具
Figure 1. Experiment instrument: (a) main control cabinet; (b) circulation pipeline and heating mold
圖 3 混凝土的抗壓強度和劈裂抗拉強度。（a）抗壓強度；（b）劈裂抗拉強度
Figure 3. Compressive strength and splitting tensile strength of concrete: (a) compressive strength; (b) splitting tensile strength
圖 4 混凝土的氯離子擴散系數。（a）C50；（b）C70
Figure 4. Chloride diffusion coefficient of concrete: (a) C50; (b) C70
圖 5 C50混凝土的掃描電鏡圖片。（a）冷端；（b） 熱端；（c）中溫；（d）標準養護
Figure 5. SEM images of C50 concrete: (a) cold side; (b) hot side; (c) medium temperature; (d) standard curing
圖 6 C70混凝土的掃描電鏡圖片。（a）冷端；（b）熱端；（c）中溫；（d）標準養護
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水泥性能指標
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 不同強度等級的混凝土配合比
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 混凝土在不同條件下的超聲檢測結果
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 混凝土在不同溫差模擬條件下的超聲檢測分析結果
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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中文字幕在线观看表 5 混凝土的沖擊傾向性指標
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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