Detection of Microcracking in Concrete Subjected to Elevated Temperature at Very Early Age by Acoustic Emission
Detection of Microcracking in Concrete Subjected to Elevated Temperature at Very Early Age by Acoustic Emission
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DOI：
10.3151/jact.8.201
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发表时间：
2010-06
影响因子：
2
通讯作者：
Ha Ngoc Son;A. Hosoda
中科院分区：
文献类型：
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作者：
Ha Ngoc Son;A. Hosoda
混凝土在早期经受高达约60°C的高温，特别是在低水胶比（0.3）混凝土中，微裂纹显著发展。微观开裂是由于砂浆和骨料之间的变形不协调引起的应力。砂浆与粗集料的热膨胀系数差异、砂浆的自收缩和粗集料粒径是影响劣化的重要因素。混凝土的抗拉强度受微裂缝的影响很大。使用磨细高炉矿渣（GGBFS）的混凝土比仅用普通波特兰水泥制备的混凝土遭受更严重的破坏。尝试应用声发射技术研究微裂纹的形成过程和机理。仔细考虑了在早期和高温下练习AE技术所需的技能。声发射命中与变形和拉伸强度的测试结果一致。大部分的微裂纹发生在温度下降期间，并归类为拉伸模式。使用具有较大CTE的粗骨料、饱和的细轻骨料以及减小骨料的最大尺寸在减少微裂纹和提高用矿渣微粉制成的混凝土的抗拉强度方面是非常有效的。微裂纹对直接拉伸强度的影响大于劈裂拉伸强度。
Microcracks developed considerably in concrete subjected to elevated temperature up to around 60°C at early ages, especially in low water-to-binder ratio (0.3) concrete. Microcracking was attributed to the stresses induced by the incompatibility in deformation between mortar and aggregate. Differences of coefficients of thermal expansion (CTE) between mortar and coarse aggregate, autogenous shrinkage of mortar and size of coarse aggregate were important factors influencing deterioration. The tensile strength of concrete was severely affected by the extent of microcracks. Concrete using ground granulated blast furnace slag (GGBFS) suffered worse damage than concrete prepared from ordinary Portland cement alone. Attempts were made to apply the acoustic emission (AE) technique to study the process and mechanism of microcracking. The skills required to practice the AE technique at early ages and at high temperature were carefully considered. AE hits agreed with the test results for deformation and tensile strength. Most of the microcracks occurred within the descending period of temperature and were classified into tensile mode. The use of coarse aggregate with larger CTE, saturated fine lightweight aggregate, and the reduction of the maximum size of the aggregate were greatly effective in reducing microcracking and improving the tensile strength of concrete made with GGBFS. Direct tensile strength was more adversely affected by microcracking than splitting tensile strength.