混凝土泵送性能的流变学表征及预测综述

自1933年美国首次使用泵送的方式输运混凝土以来,泵送已成为现代混凝土施工的主要方式。随着建筑高度的不断攀升,混凝土泵送技术难度越来越高。虽然我国采用混凝土泵送技术建设了大量的钢筋混凝土(超)高层建筑,但混凝土的成功泵送是基于耗时、耗财的盘管试验结果,而现行技术规范中的经验公式与现场实测值也完全不符,这表明混凝土泵送性能的理论研究严重滞后于应用技术。随着精细化工程管理及混凝土质量控制要求的提高,粗放的经验性方法及耗财的盘管试验已不能适应行业发展的新趋势,因此,为混凝土的泵送行为提供科学的理论基础是土木行业亟需解决的问题。流变学理论是研究混凝土泵送性能的有效工具,国外的研究者从泵管中混凝土的流动行为、润滑层性能与表征、泵送性能预测等方面展开了较为系统的研究工作,取得了良好的成果,但国内在流变理论与泵送技术方面的研究成果极少。研究表明,屈服应力不同的混凝土在管道中表现出不同的流动形态。基于混凝土及润滑层的流变参数建立的模型可准确预测水平直线管道中混凝土的泵送压力。虽然普遍认为润滑层是影响混凝土泵送性能的重要因素,但混凝土润滑层流变参数的表征方法较多,包括滑管仪、摩擦仪和等效砂浆法,研究者还开发出了不同的摩擦仪和测试程序来表征混凝土润滑层的流变性能。基于混凝土及润滑层的流变性能,研究者建立了混凝土在泵管中流动的数学模型,解析出了泵送压力-混凝土流变性能-泵送速率间的关系,为准确预测混凝土的泵送行为提供了科学工具。但不同混凝土及润滑层流变参数的测试结果存在一定差异,哪种方法更能真实反映混凝土在泵管中的流动行为仍是一个问题;并且对于弯管、软管及垂直管道中混凝土的泵送行为也缺乏研究。亟需开展相关理论与技术研究,推动流变学理论在泵送混凝土方面的应用。本文从混凝土在泵管中的流动行为、润滑层性能与表征、泵送性能预测等方面综述了国内外关于泵送混凝土的最新研究成果,分析了各种方法及理论的优缺点,以期为流变理论在混凝土泵送技术中的应用与研究提供参考。

An Overview on the Prediction and Rheological Characterization of Pumping Concrete

Since the first application of pumping concrete in the US in 1933, pumping has become the most important construction technology of concrete. With the continuously increasing height of building, concrete pumping has become more difficult. Although pumping technique has been used to build many high-rising buildings in China, successful pumping was based on the time-consuming and expensive large scale pumping test, and the empirical equations in the code or standard do not fit the measured data on job site. This indicates that theoretical research far lags behind the application of pumping concrete. Since fine management of engineering and high requirement of quality control of concrete has been required in most cases, extensive empirical method and expensive large scale test cannot adapt to the new development trend of the industry. Thus, it is necessary to provide theoretical foundation for concrete pumping technology. Rheological theory is an effective tool to study the pumping of concrete. Foreign researchers have carried out comprehensive researches on the flowing behavior of concrete in pumping pipe, characterization of lubrication layer, and prediction of pumping, and some good results has been obtained. However, there are very limited researches conducted in China. Results show that concretes with different yield stresses flow in pumping pipe in different patterns. The model based on the rheological parameters of concrete and lubrication layer can precisely predict concrete pumping pressure. It is generally believed that the lubrication layer is the most important factor affecting pumping, and many methods have been developed to characterize lubrication layer, including sliding pipe rheometer, tribometer, and equivalent mortar. Different tribometers and testing programs have also been developed. Based on the rheological parameters of concrete and lubrication layer, analytical numerical model for describing the flow of concrete in pipe has been developed, and the relationship among pumping pressure, rheological properties of concrete and pumping rate has been established. This provides theoretical bases for predicting the behavior of concrete pumping. However, different rheological characterization methods of lubrication layer give different results, and which method can reflect the real situation of concrete pumping is still an open question. In addition, concrete flows in bending pipe, vertical pipe and soft pipe are seldom studied. In order to predict concrete pumping in practice, it is necessary to develop appropriate rheological tools based on the characteristics of concrete in China and real engineering. The most up-to-date researches on the flowing behavior of concrete in pumping pipe, characterization of lubrication layer, and prediction of pumping are reviewed in this paper, and the advantages and disadvantages of different methods and theories are analyzed.