冻融循环后蒸汽养护混凝土的损伤—声发射特性

Damage-Acoustic Emission Characteristics of Steam-Cured Concrete after Freeze-Thaw Cycles

为研究冻融循环对蒸汽养护混凝土力学性能演化规律的影响,通过开展蒸汽养护混凝土试件冻融循环试验和单轴压缩-声发射试验,分析了冻融循环作用后不同蒸汽养护制度下混凝土加载损伤破坏声发射过程,依据声发射特征参数建立了冻融循环后蒸汽养护混凝土受压损伤本构模型,探究了损伤变量与冻融循环次数的变化关系.结果表明:60、80℃蒸汽养护对混凝土抗冻性能不利,40℃蒸汽养护混凝土与标准养护混凝土抗冻性能无明显差异;混凝土受压破坏过程的声发射振铃计数变化呈现出明显的接触期、平静期、陡增期三阶段变化规律,平静期-陡增期分界点随冻融循环次数的增加在时间上发生后移;受压过程前期,蒸汽养护混凝土损伤发展较为缓慢;相对峰值应力达到0.8以后,蒸汽养护混凝土损伤发展较为迅速,直至受压破坏.

To study the influence of freeze-thaw cycles on the evolution of mechanical properties of steam-cured concrete, the freeze-thaw cycles test and uniaxial compression-acoustic emission test of steam-cured concrete specimens were carried out to analyze the damage characteristics of concrete under different steam-curing systems after the action of freeze-thaw cycles. According to the characteristic parameters of acoustic emission, a constitutive model of steam-cured concrete compression damage was established under freeze-thaw cycle, and the relationship between damage variables and the number of freeze-thaw cycles was discussed. The results show that steam-curing temperature of 60 ℃ and 80 ℃ is inconvenient for the frost resistance of concrete, and there is no significant difference between steam-cured concrete at 40 ℃ and standard-cured concrete in frost resistance. The change of the cumulative acoustic emission(AE) ringing count in the process of concrete compression failure shows obviously changes in three-stages, i.e., in contact stage, quiet stage and spike stage. The demarcation point between quiet stage and spike stage shifts backward in time with increase of freeze-thaw cycles. In the early stage of the compression process, the damage of steam-cured concrete develops slowly. After the relative peak stress reaches 0.8, the damage of steam-cured concrete develops more rapidly until it fails under compression.