Full scale pumping tests on SCC: application of the modified Hattori-Izumi theory

Studying the flow of fresh concrete is influenced by time dependency of the rheological properties of the concrete. This time dependency can be divided into two parts : the non-reversible part, being loss of workability and the reversible part, called thixotropy. Loss of workability can be neglected in some cases, when comparing with the effect of thixotropy, but it is advised to keep track of it, especially in case of SCC for precast industry. Several attempts have been made to characterize the thixotropic properties of concrete, but no general test procedure is known at this moment to universally describe thixotropy. In most cases, the study of the thixotropic properties is restricted to the area of interest of the authors, mostly the variation of static yield stress. Only one theory takes into account the influence of thixotropy on both viscosity and yield stress : the Hattori-Izumi theory, modified by J.E. Wallevik. This theory will be used to provide a qualitative description of the observed phenomena occurring during pumping of SCC, but due to the large complexity of both the theory and the practical application, a quantitative approach is beyond the scope of this study

Influence of demoulding oil on the rheological properties of fresh SCC

In concrete research centers, the determination of the rheological properties of concrete is becoming a daily business, easy to perform when the proper apparatus (and staff) are available. On the building site, rheometers are still absent, although some portable rheometers have been developed. Instead, the slump (flow) test is the only one performed to characterize the "workability" of the concrete. On the other hand, the rheological properties are very important on site, especially in case of self compacting concrete (SCC), in order to know whether the concrete can provide proper filling of the formwork, which pumping pressures will be needed, how long the concrete can wait before placement, ... The difference between laboratories and building sites is not only noticeable by the test equipment, there is also another mentality and way of thinking. In a laboratory, the scientist tries to eliminate every disturbing factor as much as possible. On site, workmen prefer to work more easily, and if necessary, they apply some "tools" to ease their jobs, sometimes not being aware of the negative consequences. Specifically in the domain of rheological characterization of concrete and its application, there is a large difference between lab and building site. In the lab, thorough cleaning of the testing materials is obtained by washing with water, but on site, as the water availability is restricted, releasing agents are applied so that the concrete does not stick to the equipment. Although these releasing agents are applied daily, very few scientific reports have been made on their influence on the rheological properties. This paper describes the influence of one type of demoulding oil on the rheological properties of SCC. No research has been performed on the causes of the differences between SCC with or without oil, so the only purpose of this paper is to show the resulting differences. Secondly, the results have been obtained in steady state, thixotropy and loss of workability have not been investigated explicitly

Full scale pumping tests on SCC: test description and results

Pumping of concrete is a daily applied process, providing the possibility of continuously filling a formwork. Reports have been created dealing with the composition and the workability of the concrete, with the maximal discharge and pressures, with the characteristics of pumps and pipes, ... On the other hand, only a very few fundamental scientific studies on this topic are available. In case of self compacting concrete (SCC), the same rules, valid for traditional concrete (TC), are applied. On the other hand, the verification of these rules, or new rules, are not reported (yet). SCC is considered as a special case of TC, having an advantageous composition for the pumping process, which should simplify the pumping and reduce the problems. This paper shows the results from a series of pumping tests. After a description of the equipment is provided, a set of surprising results is presented : SCC causes higher pressure losses, compared to TC. Further results will prove the existence of a less viscous layer near the wall, a temperature increase inside the concrete equivalent to the pressure loss and the importance of thixotropy

Pipe flow velocity profiles of complex suspensions, like concrete

The flow of different suspensions has been studied in literature in order to maximize the transport capacity or to minimize the needed pressure. For concrete, several research projects have been performed, but the question remains if the results for one type of concrete are applicable to another type. This paper deals mainly with the flow of self-compacting concrete in pipes. It is shown that the flow of this type of concrete is not influenced by friction between the aggregates, but that the material does not remain homogeneous during the flow. By means of full scale experiments, it is shown that the measured pressure losses are lower than the theoretically calculated pressure losses, due to three effects lowering the viscosity near the wall. The results have been compared with the available literature dealing with traditional concrete, showing some major points of difference. Finally, it is assumed that the velocity profile of concrete in a pipe consists of a plug with uniform velocity in the centre, a lubrication layer with a large velocity gradient near the wall and possibly, a part of the homogeneous concrete also being sheared, depending on the rheological properties and the type of concrete. Unfortunately, no direct velocity profile measuring equipment is available

Numerical modelling of the filling of formworks with self-compacting concrete

This paper describes the numerical modelling of the flow of self-compacting concrete (SCC) in column and wall formworks during the filling process. It is subdivided in four main parts. In the first part, the rheological properties of SCC and the theory regarding the pressure exerted by the SCC on the formworks are shortly described. In the second part, the formwork filling tests, that have been carried out at the Magnel Laboratory for Concrete Research of the Ghent University, are presented. The general layout of the tests and the measurement set-up are clearly described. In the third part, the numerical modelling of the flow of SCC using a commercially available solver is explained as well as the obtained results from the CFD simulations. Finally in the last part, a comparison is made between the measurements and the simulation results. The formwork pressures are hydrostatic for SCC pumped from the base of the formworks

Validation of the STRIVE model for coupling ecological processes and surface water flow

The 1D model package STRIVE is verified for simulating the interaction between ecological processes and surface water flow. The model is general and can be adapted and further developed according to the research question. The hydraulic module, based on the Saint-Venant equations, is the core part. The presence of macrophytes influences the water quality and the discharge due to the flow resistance of the river, expressed by Manning's coefficient, and allows an ecological description of the river processes. Based on the advection–dispersion equation, water quality parameters are incorporated and modelled. Calculation of the water quantity parameters, coupled with water quality and inherent validation and sensitivity analysis, is the main goal of this research. An important study area is the River Aa near Poederlee (Belgium), a lowland river with a wealth of vegetation growth, where discharge and vegetation measurements are carried out on a regular basis. The developed STRIVE model shows good and accurate calculation results. The work highlights the possibility of STRIVE to model flow processes, water quality aspects and ecological interaction combined and separately. Coupling of discharges, water levels, amount of biomass and tracer values provides a powerful prediction modelling tool for the ecological behaviour of lowland rivers