Flow conditions of fresh mortar and concrete in different pipes

Cement and Concrete Composites, 2016

Finding the critical factors that influence the pressure during pumping of concrete has been investigated for years. From fluid mechanics, the relationship between pressure and flow rate, radius or viscosity is known. In the practical guidelines for pumping of conventional vibrated concrete (CVC) the viscosity term is replaced by the concrete yield stress. However, recently, the influence of viscosity on pumping pressure has been reevaluated for self-consolidating concrete (SCC). In this paper, the influence of concrete rheology, tribology, flow rate and pipe radius on pumping pressure are discussed, based on full-scale pumping tests. The concrete mixtures varied from pumpable CVC to segregating SCC. The influence of flow rate and viscosity on pumping of concrete has been confirmed. It is also shown that with a 20% decrease in pipe radius (from 125 to 100 mm), the pumping pressure can be roughly doubled. An increase in yield stress also increases the pumping pressure, but its influence is only visible when the viscosity is approximately constant. The total flow resistance in the tribometer also appears to correlate well with the pumping pressure, proving that the developed tribometer mimics quite well the flow of concrete in a pipe.

Doboku Gakkai Ronbunshu, 1993

This is to report on the resistance to deformation of fresh concrete when the rearrangement of constituent particles of fresh concrete, i. e. , gravel, sand and cement, is introduced. For realizing the simple deformation field in shear, bent and tapered pipe units were adopted in test and stable flow of fresh concrete through them was produced. Herein, the pressure at the inlet of deformed pipes was measured as an indicator of deformability of fresh concrete, which is regarded as the particulate assembly with different sizes. The effect of volume fraction of gravel, sand and cementitious powder on the resistance to deformation was mainly focused in the series of test based upon the multiphase concept of hydrodynamics. The sensitivity of volume fractions to the total deformational resistance of concrete was of experimental interest to the authors.

Transporting fresh concrete constitutes a significant part of the production process. Transferring ready-mixed concrete on-site is done using concrete pumps. Recent developments in concrete technology, and in mineral and chemical additives, have resulted in new developments in pumping techniques and the use of different concrete mixtures and equipment. These developments required further knowledge of the behavior of fresh concrete under pressure. Two criteria were determined for the pumpability of concrete: the power required to move the concrete or of the repulsive force; and the cohesion of the fresh concrete. It would be insufficient to relate pumpability to these two criteria; the values of segregation pressure, diffusion ability, water retention capacity, and side friction of the mixture are significant parameters in ensuring that concrete is pumped freely along the pipe. To solve the pumpability problem, friction stresses should be determined as a function of the linear pressure gradient, the pressure leading to segregation of the fresh concrete should be determined, and tests for the bleeding of concrete under pressure should be examined. The scope of the research is the examination of the behavior of fresh concrete under pressure. To determine the segregation pressures, a test apparatus was designed for the bleeding of concrete under pressure. The main purpose of the study is to determine whether the concrete can be pumped easily and whether it will lose its cohesion during the pumping, based on tests of concrete workability and bleeding of concrete under pressure. Int J Thermophys (2012) 33:885-894

The transport of fresh concrete by pumping is an important process and widely used in practical concrete technology. This process has been applied since the beginning of the twentieth century. More recent developments of pumping equipment and findings on mineral and chemical admixtures have prompted more sophisticated research on pumping concretes. While they do not elaborate upon standard specifications, many recommendations for the composition of pumping concretes which are very useful in applications, such as ACI-304.2R reports, are available. This paper reports the results of an experimental study into the effects of concrete components, namely cement content, aggregate type, mineral, fiber, and plasticizer admixtures, on the rheology of pumping concretes. The rheological properties of concretes are examined by the Two Point Workability Test Apparatus (CTPT) originally proposed by G. H. Tattersall. The present study shows that concrete workability is improved by increasing cement content and also shows that the aggregate type only effects the rheological parameters in low cement content mixtures. In addition, yield stress and plastic viscosity are generally lower in concrete mixtures that contain natural stone rather than crushed aggregates. In addition, this study shows that the effect of mineral, plasticizer and fiber admixtures depends on cement content and admixture type.

Materials and Structures, 2015

The rheology of concrete is predominant for the required pressures in a pumping pipe. However, more detailed information is required on the formation and the properties of the lubrication layer near the pipe surface, in order to be able to accurately predict the pressure-discharge relation. By means of experimental research in combination with advanced numerical simulations, the lubrication layer near the surface of the concrete pipe has been studied in this paper. The research confirms the existence and the effects of the lubrication layer on the movement of concrete in a pumping pipe. By means of the particle image velocimetry technique, the velocity profile along the cross section has been accurately determined for different types of concrete. There is no real slip at the surface of the pipe, however the velocity profile steeply grows in a thin layer, called lubrication layer, showing a thickness of about 2 mm. The mortar in this layer, with lower yield stress and lower viscosity than the bulk concrete, is highly sheared. The bulk of the concrete is sheared and/or shows a plug flow, depending on the yield stress of the concrete. The stiffer the concrete, the more important the effect of the lubrication layer on the overall velocity profile. In most cases, the lubrication layer is the dominant effect for pumping of concrete. Shear of the bulk concrete only plays a significant role for more fluid concretes.

… and Building Materials, 2009

In this work we have studied the performance of simple concrete pipes produced with the incorporation of rubber tires with contents of 10, 15 and 20 kg/m³ of concrete. The experimental program included diametral compression strength and water absorption tests. Twelve pipes were tested and divided into four sets of three pipes of nominal diameter (ND) of 600 mm and length of 1500 mm. Each series consisted of three pipes stub and bag (SB), one control (without rubber tires), and three sets incorporating rubber pipes on the trace (TB1, TB2 and TB3). All test results showed diametrical compressive strength values higher than that specified the NBR 8890 standard, with respect to simple concrete pipes PS2 class: type SB with ND 600 mm, which is 36 kN/m. In the water absorption test all pipes had absorption values less than the maximum established in the NBR 8890 standard, which is 8%. It can be concluded from the results and specific conditions of the tests conducted, that the tire rubber has the potential to be incorporated into the manufacture of simple concrete pipes. However, it is stated that it is necessary to increase the knowledge about the behavior of concretes incorporating rubber tire.

Particulate Science and Technology, 2010

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Construction and Building Materials, 2017

h i g h l i g h t s New method for measuring water permeability by tests on hollow cylindrical specimens. The water flows through the walls of the sample under a constant pressure of 5 bar. The proposed process provides a high-volume flow of water. The study consists of 12 types of concrete with variable E/C ratio. The water permeability of the concrete decreases with the W/C ratio decreasing.

Scientific Bulletin of Valahia University - Materials and Mechanics

The method of transporting cement with the help of an air jet through pipes is very practical and reliable. However, improper dimensioning of the constructive and functional parameters can lead to improper functioning, to cement agglomerations in certain areas of the route configuration. In order to be able to know the problem areas and geometries, in this paper a comparative, analytical and virtual study of cement transport through a pipeline route, known as geometry and dimensions, was made. Analytical calculation showed that a floating speed of cement particles of 23.45 m/s, with an air flow rate of 0.155 m3/s, is needed to be able to transport a quantity of 40 t/h (11.11 kg/s) of cement. The virtual study done in Flow Simulation showed the behavior of cement particles during transport. The virtual behavior is similar to the real one, with cement particles tending to settle in bends and on long stretches of horizontal pipes. The behavior of the air-cement mixture in the separatio...