Shrinkage Characteristics and Anti-Crack Technology of Early-Age Concrete under Large Dry-Cold Temperature Difference
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摘要:
为探究干寒大温差下早龄期混凝土收缩变形规律，降低开裂风险，采用3种养护方法对混凝土进行早龄期养护，以抗压强度、劈裂抗拉强度、自由收缩率及最大约束应力为表征手段，设置了基本力学性能试验、自由收缩试验与约束收缩试验，并采用综合型多指标的灰色关联法分析了不同养护方式下混凝土的抗裂性能. 同时，设计了纳米涂层保温性能试验，探究其对混凝土的保温隔热性能. 试验结果表明：在−20.0～15.0 ℃的循环温度中，采用纳米涂层使得圆柱体混凝土试件内部平均温差降低2.95 ℃；相比于标准养护，3种养护方式下混凝土抗压及劈裂抗拉强度均有显著降低，干寒大温差不利于混凝土的强度发展；自由收缩率随温度变化明显，呈现出温度降低，自由收缩率增大，反之，温度升高自由收缩率减小，并在−20.0 ℃与15.0 ℃时出现极值；最大约束应力受到养护方式影响，自然养护下最大约束应力发展最快，终值最大，薄膜养护次之，涂层养护最大约束应力发展最慢，终值最小；涂层养护下灰色关联度高达0.9149，明显高于自然养护与薄膜养护，表现出优异的抗裂性能.
Abstract:In order to explore the shrinkage and deformation laws of early-age concrete under large dry-cold temperature differences and reduce the risk of cracking, three curing methods were used for early-age curing of concrete. The compressive strength, splitting tensile strength, free shrinkage rate, and maximum restraint stress were used as the characterization methods. Basic mechanical performance test, free shrinkage test, and restraint shrinkage test were designed. The comprehensive multi-index grey correlation method was adopted to analyze the anti-cracking performance of concrete under different curing methods. In addition, a nano-coating thermal insulation performance test was designed to explore its thermal insulation performance on concrete. The test results show that the use of nano-coating reduces the average temperature difference inside the cylindrical concrete specimen by 2.95 ℃ in the circulating temperature of ‒20.0–15.0 ℃; compared with those under standard curing, the compressive and splitting tensile strengths of concrete under the three curing methods are significantly reduced, and the large dry-cold temperature difference is not conducive to the strength development of concrete. The free shrinkage rate changes significantly with temperature. Specifically, as the temperature decreases, the free shrinkage rate increases, and as the temperature rises, the free shrinkage rate decreases. In addition, extreme values appear at ‒20.0 ℃ and 15.0 ℃; the maximum restraint stress is affected by the curing method. Under natural curing, the maximum restraint stress develops the fastest, with the largest final value, followed by that under film curing. Under coating curing, the maximum restraint stress develops the slowest, with the smallest final value. The gray correlation degree under coating curing is as high as 0.9149, which is significantly higher than that under natural curing and film curing, showing excellent anti-cracking performance.
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Key words:
- early-age concrete /
- curing method /
- strength /
- shrinkage /
- anti-cracking performance
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图 2 保温性能试验试件及仪器照片
Figure 2. Thermal insulation performance test specimens and instrument photo
图 6 不同龄期3种养护方式下混凝土抗压强度
Figure 6. Compressive strength of concrete under three curing methods at different ages
图 7 不同龄期3种养护方式下混凝土劈裂抗拉强度
Figure 7. Splitting tensile strength of concrete under three curing methods at different ages
图 8 不同龄期3种不同养护方式下混凝土收缩率
Figure 8. Shrinkage rate of concrete under three curing methods at different ages
图 9 3种养护方式下约束应力随龄期的变化曲线
Figure 9. Curves of restraint stress with age under three curing methods
图 10 3种养护方式下最大约束应力随龄期的变化曲线
Figure 10. Curves of maximum restraint stress with age under three curing methods
表 1 涂层保温性能试验设计表
Table 1. Test design table of coating thermal insulation performance
试件编号 循环温度/℃ 保温隔热涂层厚度/mm 测试时长/d 试件个数/个 底涂层 中涂层 面涂层 总厚度 1 −20.0～15.0 0.1 1.0 0.1 1.2 7 2 2 −20.0～15.0 7 2 
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表 2 混凝土各项性能测试结果汇总
Table 2. Summary of concrete performance test results
养护方式 劈裂抗拉
强度/MPa抗压强
度/MPa最大自由
收缩率/ × 10−3最大约束
应力/MPa自然养护 0.91 19.78 1.601 1.06 薄膜养护 1.06 20.81 1.544 0.84 涂层养护 1.20 21.62 1.494 0.72
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