The construction of high-rise buildings and tunnels necessitates pumping concrete over long distances. Concrete pumping is a complex physico-chemical process that results in the formation of different layers with distinct characteristics inside the pipe. A thin cement paste/mortar layer formed at the concrete–pipe interface, called the lubrication layer (LL), is vital for facilitating concrete pumping. Engineering the pumping process involves understanding the origin and controlling the onset, magnitude and velocity of the LL. However, the formation, evolution and characteristics of the LL are still largely unexplored. This paper presents a comprehensive review of the mechanistic origins of the LL, its influencing parameters and measured data on LL thickness using various techniques to date. An attempt is made to find an overall link between different theories (shear-induced particle migration, wall depletion theory etc.) in terms of concrete rheology. The paper also provides a fundamental understanding of the different mechanisms involved in LL formation, with the help of different theories put forth by researchers in the field of particle rheology. Based on the insights derived from the discussions, recommendations are made for future research directions in concrete pumping.

中文翻译：

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混凝土泵送的机械起源：综合展望与前进方向

高层建筑和隧道的建设需要长距离泵送混凝土。混凝土泵送是一个复杂的物理化学过程，会导致在管道内部形成具有不同特征的不同层。在混凝土-管道界面处形成的薄水泥浆/砂浆层，称为润滑层 (LL)，对于促进混凝土泵送至关重要。设计泵送过程涉及了解 LL 的起源和控制 LL 的开始、大小和速度。然而，LL 的形成、演变和特征在很大程度上仍未得到探索。本文全面回顾了 LL 的机械起源、其影响参数以及迄今为止使用各种技术测量的 LL 厚度数据。试图在混凝土流变学方面找到不同理论（剪切诱导颗粒迁移、壁耗尽理论等）之间的整体联系。在粒子流变学领域研究人员提出的不同理论的帮助下，本文还提供了对 LL 形成所涉及的不同机制的基本理解。根据讨论得出的见解，对混凝土泵送未来的研究方向提出了建议。