Stripping of aggregate from mortar in waste concrete heated by microwave: Mechanisms of differential-temperature stress and vapor expansion pressure

IF 7.4 2区 工程技术 Q1 ENGINEERING, CIVIL Journal of Traffic and Transportation Engineering-English Edition Pub Date : 2024-06-01 DOI:10.1016/j.jtte.2022.06.008
Yanping Sheng , Xiao Huan , Peizhen Hu , Liangliang Li , Ahmed Abdulakeem , Zhoujing Ye , Linbing Wang , Yanping Yin
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Abstract

Microwave heating, which is used for pre-treatment of concrete before it is comminuted, stands as a strong candidate for selective liberation of multiphase materials like concrete. This paper is concerned with the selective liberation of concrete's raw constituents (particularly aggregate) for recycling by considering the water content of concrete as a parameter of microwave heating for the first time. The deterioration law of the concrete's performance was characterized by the variation in the splitting tensile strength and relative dynamic modulus after heating by microwave at different water contents. Besides, tests were conducted to evaluate the performance of the interface transition zone (ITZ) between aggregate and mortar as well as to investigate the reasons for the stripping behavior of aggregate-mortar, which included the interface tensile strength test, temperature measurement, and porosity test. The deterioration law of splitting tensile strength and relative dynamic modulus revealed that the performance of concrete was subject to different degrees of damage depending on the water content. Furthermore, experimental results showed that interface bonding strength between aggregate and mortar was dramatically impaired, and a large temperature difference was generated between the aggregate and mortar during microwave heating. Meanwhile, the permeable pores increased considerably even when the specimens were dried. In the presence of water, the intactness of ITZ between aggregate and mortar was destroyed by microwave heating, and its performance was significantly lowered, which led to the occurrence of stripping behavior between aggregate and mortar. This was reaffirmed by the microstructure presented by scanning electron microscopy. Thus, the newly developed microwave pre-treatment improved by providing appropriate water contents for concrete corresponding to different strength grades is a promising method for recycling aggregate from waste concrete.

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微波加热废混凝土中砂浆骨料的剥离:温差应力和蒸汽膨胀压力的机理
微波加热用于混凝土粉碎前的预处理,是选择性释放混凝土等多相材料的有力候选。本文首次将混凝土的含水量作为微波加热的一个参数,研究如何选择性地释放混凝土的原始成分(尤其是骨料),以便回收利用。在不同含水量下,通过微波加热后劈裂拉伸强度和相对动态模量的变化来表征混凝土性能的劣化规律。此外,为评估骨料和砂浆之间界面过渡区(ITZ)的性能以及研究骨料-砂浆剥离行为的原因,还进行了界面抗拉强度测试、温度测量和孔隙率测试。劈裂抗拉强度和相对动模量的劣化规律表明,混凝土的性能会因含水量的不同而受到不同程度的破坏。此外,实验结果表明,骨料和砂浆之间的界面粘结强度显著降低,在微波加热过程中骨料和砂浆之间产生了较大的温差。同时,即使试样被烘干,透水孔隙也会显著增加。在有水的情况下,微波加热破坏了骨料和砂浆之间 ITZ 的完好性,使其性能显著降低,导致骨料和砂浆之间出现剥离行为。扫描电子显微镜显示的微观结构再次证实了这一点。因此,新开发的微波预处理方法通过为不同强度等级的混凝土提供适当的含水量而得到改进,是一种很有前途的从废弃混凝土中回收骨料的方法。
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来源期刊
CiteScore
13.60
自引率
6.30%
发文量
402
审稿时长
15 weeks
期刊介绍: The Journal of Traffic and Transportation Engineering (English Edition) serves as a renowned academic platform facilitating the exchange and exploration of innovative ideas in the realm of transportation. Our journal aims to foster theoretical and experimental research in transportation and welcomes the submission of exceptional peer-reviewed papers on engineering, planning, management, and information technology. We are dedicated to expediting the peer review process and ensuring timely publication of top-notch research in this field.
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