Salinas Alexis, Feys Dimitri
Department of Civil, Architectural and Environmental Engineering, Missouri University of Science and Technology, Rolla, MO 65409, USA.
Materials (Basel). 2020 Apr 11;13(8):1799. doi: 10.3390/ma13081799.
During concrete pumping, a lubrication layer is formed near the pipe wall. Extensive research has been performed on measuring and modeling the properties of this layer and using these values to predict pumping pressures. However, there are numerous discussions in the literature about the composition and thickness of this layer: can it be considered mortar, a micromortar, or is it cement paste? In this paper, possible solutions for the thickness and composition of the lubrication layer are derived from interface rheometry tests. It is assumed that the lubrication layer is composed of one or more concentric layers of paste or micromortar. To accomplish this determination, the rheological properties of the composing paste, mortars with different maximum particle sizes and concrete need to be known. Challenges arising from using different rheometers and from the sensitivity of the paste rheology to shearing are addressed in this contribution. The results show that, mathematically, a single layer of homogeneous paste or mortar with different maximum particle sizes can be responsible for the formation of the lubrication layer. Physically, however, the composing material should contain sand particles to some extent, as particle migration is proportional to the size squared. If the literature results from pumping are applicable to the results obtained in this paper, it seems that the lubrication layer is composed of a mortar with a maximum particle size of around 1 to 2 mm.
在混凝土泵送过程中，管壁附近会形成一层润滑层。关于测量和模拟该层的特性并利用这些值来预测泵送压力，已经开展了大量研究。然而，文献中对该层的组成和厚度存在诸多讨论：它可被视为砂浆、微砂浆，还是水泥浆体？在本文中，润滑层厚度和组成的可能解决方案源自界面流变测试。假定润滑层由一层或多层同心的浆体或微砂浆层组成。为完成此测定，需要了解组成浆体、不同最大粒径的砂浆及混凝土的流变特性。本文探讨了使用不同流变仪以及浆体流变学对剪切的敏感性所带来的挑战。结果表明，从数学角度看，具有不同最大粒径的单层均质浆体或砂浆可导致润滑层的形成。然而，从物理角度讲，组成材料应在一定程度上含有砂粒，因为颗粒迁移与粒径的平方成正比。如果文献中的泵送结果适用于本文所得结果，那么润滑层似乎由最大粒径约为1至2毫米的砂浆组成。
