What Is Pumpable Concrete? Factors Affecting Pumpability Of Concrete?
What Is Pumpable Concrete?
Pumpable concrete is a special type of concrete designed for construction purposes which can be pumped through pipelines with ease. To produce pumpable concrete, special attention is given to its formulation so that its friction with the inner walls of the pipelines is minimized and it does not become wedged while flowing through the pipeline.
Understanding the behavior of concrete when pumped through pipelines is crucial in the study of concrete pumping. Pumpable concrete flows in the form of a plug, separated from the pipeline walls by a thin layer of lubricating cement paste, which is hydraulically linked with the interparticle water layer in the plug.
The flow of the concrete is under pressure, and it is crucial that the pressure generated by the flow resistance does not exceed the pump’s pressure rating to maintain the continuous movement of the plug.
A concrete with a high w/c ratio is not pumpable as it is too saturated and may result in water being forced out of the mix increasing flow resistance and possibly causing blockages. On the other hand, a very stiff concrete is also not pumpable.
What Are The Factors Affecting Pumpability Of Concrete?
The pumpability of concrete is influenced by various factors such as the cementitious materials used, aggregate characteristics, admixtures, and material batching and mixing.
In terms of cementitious materials, the use of fine cement helps to prevent bleeding in pumped concrete. Fly ash and silica fume are advantageous for improving the cohesion and pumpability of concrete, while ground granulated blast furnace slag and metakaolin have less obvious effects on pumpability.
Aggregate characteristics such as size, grading, shape, and density also affect pumpability. The maximum aggregate size should not be larger than a quarter of the minimum pumping pipe diameter to prevent segregation.
Well-graded aggregate, produced by blending continuous coarse aggregate and sand, is suitable for pumpable concrete. Round-shaped aggregate is preferable for pumpable concrete, but angular aggregate can also be used with careful consideration of sand proportion.
The density of different particle sizes in a concrete mixture should be consistent to prevent bleeding and segregation. Lightweight aggregate should be soaked in advance or treated with an admixture to prevent water absorption and pipeline blockage.
Heavyweight aggregate can sink to the invert of horizontal pumping pipes and cause blockage.
Admixtures such as water-reducing and high-range water-reducing admixtures, air-entraining admixtures, and retarder admixtures also affect pumpability.
Water-reducing and high-range water-reducing admixtures help to prevent excessive bleeding, while air-entraining admixtures improve cohesion and pumpability. Retarder admixtures are useful in hot environments and during unanticipated delays.
Accurate material batching and adequate mixing are important for pumpable concrete. Batching errors and incorrect mixing can negatively impact pumpability. Mixing should be thorough, and the machines used should be well-maintained.
In conclusion, a careful consideration of the various factors affecting pumpability can lead to the production of high-quality, pumpable concrete.
How Do You Make Concrete More Pumpable?
Using a medium-range water-reducing admixture and/or a superplasticizer (HRWR) is one of the best ways to indirectly improve the pumpability of high-strength concrete.
These admixtures reduce the water–cementitious materials ratio, potentially increasing workability and improving pumpability. Additionally, using adequate amounts of fly ash can help with dispersal and create a more flowable mix that is easier to pump while reducing water demands.
Retarding admixtures should also be used at moderate dosages as they delay set times and may increase displacement capabilities. Lastly, proper proportioning of fine aggregates plays an important role in creating a well-graded aggregate matrix that results in flowable concrete mixes with minimal bleeding or settling issues which are ideal for pumping applications.
What Are The Properties Of Pumpable Concrete?
The pumpable concrete should contain a minimum of 400 kg/m3 of cement and fine aggregate, with particles smaller than 0.25 mm in size; the coarse aggregate maximum size should be no greater than 32mm.
In cases where the aggregate is angular and flaky, the quantity of fine aggregate must be increased by 10%. This ensures that the concrete will remain pumpable without clogging up pumps or hoses.