Study on dynamic mechanical properties of high-temperature concrete with different cooling methods
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摘要: 混凝土材料被大量应用于基础设施及国防设施的建造中。为了研究高温混凝土在不同冷却方式下的动态力学特性，通过
$\varnothing $ 74 mm大口径分离式霍普金森压杆对不同冷却方式处理下不同温度的C30圆柱形混凝土试样进行了动态力学性能试验，得到了其在热、水、力联合作用下的力学特性。研究了冷却方式、温度和加载条件对平均应变率的影响，重点分析了高温混凝土在不同方式冷却后的动态应力-应变曲线，以及冷却方式、温度和加载速率对其破碎形态、动态抗压强度、弹性模量、峰值应变及一系列动态效应的影响。结果表明：水冷混凝土试样的平均应变率受温度的影响更明显，不同冷却方式下加载速度与平均应变率近似呈线性关系；当温度达到400 ℃及以上时，试样颜色发生明显改变，相同温度下，水冷试样比自然冷却试样的颜色更深，出现更多细微裂纹，骨料形态破坏更严重；不同冷却方式下混凝土的动态抗压强度均与加载速度成正比，与加热温度成反比；水冷混凝土试样的弹性模量损伤系数低于自然冷却试样；高温混凝土试样的峰值应变与加热温度成正比，与加载速度成反比，且水冷混凝土试样的峰值应变相对值要高于自然冷却试样；混凝土的动载荷增加因子与温度及加载速度均成正比，且温度越高，混凝土的应变率效应越明显；当温度在200 ℃时，混凝土耗能系数出现反弹现象。Abstract: Concrete materials are widely used in the construction of infrastructure and defense facilities. In order to study the dynamic mechanical properties of high-temperature concrete with different cooling methods, the dynamic mechanical properties of C30 cylindrical concrete samples at different temperatures with different cooling methods were tested by$\varnothing $ 74 mm split Hopkinson pressure bar (SHPB), and their mechanical properties under the combined influence of heat, water and force were obtained, while the effects of cooling methods, temperature and loading velocity on the average strain rate were studied, with the focus on the analysis of the dynamic stress-strain curve of high-temperature concrete with different cooling methods, as well as the effects of cooling methods, temperature and loading velocity on its crushing morphology, dynamic compressive strength, elastic modulus, peak strain and a range of dynamic effects. The main findings are as following. In the static mechanical tests, the peak points of the concrete stress-strain curve are shifted down and to the right with the two cooling methods. The average strain rate of concrete specimens is more obviously affected by temperature during water-cooling, and the loading velocity is approximately varying linearly with the average strain rate under different cooling methods. When the temperature reaches 400 °C or above, the color of the sample changes significantly, and cracking, at the same temperature, the water-cooled sample is darker than the air-cooled color, more fine cracks appear, and the aggregate morphological damage is more serious. The dynamic stress-strain curves of concrete under different temperatures and cooling methods maintain their basic shape, and the dynamic compressive strength of concrete with different cooling methods is proportional to the loading velocity and inversely proportional to the heating temperature. The damage coefficient of elastic modulus of concrete under various loading velocity and temperatures when cooled by water is lower than that under air cooling. The peak strain of high-temperature concrete is directly proportional to the heating temperature and inversely proportional to the loading velocity, and the peak strain under water cooling is higher than that under air cooling. The dynamic increase factor (DIF) of concrete is proportional to temperature and loading velocity, and the higher the temperature, the more obvious the strain rate effect of concrete. When the temperature is 200 °C, the energy consumption coefficient of concrete rebounds. -
图 5 常温和高温处理混凝土的SEM微观形貌
Figure 5. SEM microscopic morphology of concrete at room temperature and after high temperature
图 6 常温及高温冷却后混凝土的外观照片
Figure 6. Photographs of the concrete at room temperature and after high temperature cooling
图 7 不同温度和冷却方式下混凝土的静态应力-应变曲线
Figure 7. Static stress-strain curves of concrete at different temperatures and cooling methods
图 8 不同温度、冷却方式和加载速度下混凝土的破碎特性
Figure 8. Breaking characteristics of concrete at different temperatures, cooling methods, and loading velocity
图 9 不同冷却方式下加载速度与平均应变率的拟合曲线
Figure 9. Fitting curves of loading velocity vs. average strain rate under different cooling methods
图 10 不同温度和不同冷却方式下混凝土的动态应力-应变曲线
Figure 10. Dynamic stress-strain curves of concrete at different temperatures and different cooling methods
图 11 不同冷却方式下各温度混凝土的动态抗压强度曲线
Figure 11. Dynamic compressive strength curves of concrete at different temperatures with different cooling methods
图 12 不同冷却方式下混凝土由常温加热至600 ℃时动态抗压强度下降比例
Figure 12. Proportion of dynamic compressive strength decrease of concrete heated from room temperature to 600 ℃ with different cooling methods
图 13 不同冷却方式下各温度混凝土的动态弹性模量
Figure 13. Dynamic elastic modulus of concrete at different temperatures with different cooling methods
图 14 不同冷却方式下各温度混凝土的弹性模量损伤系数
Figure 14. Damage coefficient of elastic modulus of concrete at different temperatures with different cooling methods
图 15 不同冷却方式下各温度混凝土的峰值应变
Figure 15. Peak strain of concrete at different temperatures with different cooling methods
图 16 不同冷却方式下各温度混凝土静态强度
Figure 16. Static strength of concrete at different temperatures with different cooling methods
图 17 温度、加载速度、冷却方式对DIF的影响
Figure 17. Influence of temperature, loading velocity, and cooling method on DIF
图 18 混凝土耗能计算示意图
Figure 18. Schematic diagram of concrete energy consumption calculation
图 19 不同冷却方式下高温混凝土的耗能系数
Figure 19. Energy consumption coefficient of high-temperature concrete with different cooling methods
表 2 不同加热温度及冷却条件下混凝土试样外观对比
Table 2. Comparison of the appearance of concrete samples under different heating temperatures and cooling conditions
温度/℃ 自然冷却试样 水冷试样 颜色 裂纹 剥落 颜色 裂纹 剥落 20 灰 无 无 灰 无 无 100 灰白 无 无 暗灰 无 无 200 灰白、黄 无 无 暗灰、黄 无 无 400 灰白、浅粉 细微裂纹 无 灰白、浅粉 明显裂纹 少量剥落 600 灰白、粉 明显裂纹 少量剥落 灰白、粉 明显裂纹 少量剥落 
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表 3 加载速度与平均应变率的线性拟合参数
Table 3. Linear fitting parameters of loading velocity and average strain rate
工况 a b R2 20 ℃ 9.17 12.08 0.972 63 100 ℃，自然冷却 5.65 12.31 0.971 85 100 ℃，水冷 17.93 9.25 0.992 31 200 ℃，自然冷却 3.15 14.04 0.982 53 200 ℃，水冷 28.36 9.83 0.953 02 400 ℃，自然冷却 −6.16 15.23 0.993 56 400 ℃，水冷 −2.14 11.29 0.969 76 600 ℃，自然冷却 7.62 12.56 0.982 44 600 ℃，水冷 24.91 10.06 0.974 02
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