Bone matrix as an example for pumped concrete: lightweight and solid
In cooperation with a long-standing partner, Franz Oberndorfer GmbH & Co. KG has developed an additive for an EPS concrete being of a very low bulk density and suitable for transportation over long distances by means of quite normal pumps for ready-mixed concrete. Furthermore, the almost free-flowing concrete is easy to process. The lightweight building material made of EPS recycling granulate and porous hardened cement paste is solid, frost resistant and is distinguished by its excellent fire protection. The hardened structure of the material being similar to the structure of bones, is lightweight, tough and at the same time especially efficient.
The additive, which was developed in the course of a research project, is a concentrated active substance in powder form of organic origin. This additive forms solid air voids within the cement paste, which in turn ensure together with the aggregate EPS a homogenous, cement-bound, pumpable lightweight material.
During the process of treatment the cement paste is produced in conventional concrete mixing plants and discharged directly into a truck mixer. High-quality EPS granulate and a special additive for the porosity of the cement matrix – packed in batch sizes of 1 kg/m3 – are externally filled and mixed in the ready-mix truck.
In this way, a homogenous, cement-bound lightweight building material is produced being similar to the internal bone substance of a human bone – called cancellous bone – a spongily structured scaffold consisting of fine beams. This kind of structure provides for a high strength both in case of concrete and bones at a relatively low weight. “It is not possible to copy nature, but it provides us with a lot of good ideas. Leonardo da Vinci made already use of natural sciences in order to proceed in his technical projects. Right from the beginning, our idea for the project was to orientate ourselves by the setup of the structure of human bones in order to achieve finally an optimum result. As to transport the lightweight concrete by means of pumps to the upper stories as well as the attics, the requirement was to be lightweight, solid and homogeneous. As we are still talking about concrete, the material has to meet the requirements concerning lightness and strength in its ready-made condition,” stated Christian Grill from the research and development department of Franz Oberndorfer GmbH & Co. KG.
The test series
Numerous pumping trials carried out in the plant by means of various pumps for ready-mixed concrete, engineers, pipe lines as well as the reduction to a hose line of 65 mm have revealed that the pumpable EPS lightweight concrete retains its efficiency even over discharge distances of more than 80 m and without the occurrence of any kind of problem. Even pump test runs over a distance of 60 m and retention times of up to 45 minutes (conducted at summery temperatures) have impressively proven the suitability for practical application of the material.
Excellent fire protection
The special structure of this lightweight concrete gives the material an excellent fire protection property. The fire resistance trial of the EPS concrete carried out with slabs having dimensions of 500 mm x 500 mm x 100 mm and a density of 400 kg/m3 has tested the efficiency criteria “E”… enclosing components as well as “I” thermal insulation according to the test conditions of the Austrian standard ÖNORN EN 1364-1 and ÖNORN EN 1363-1 respectively over a test period of 120 minutes (assessment EI 120).
The advantages
As no sand is needed for this kind of pumped concrete, it is possible to discharge an EPS concrete being very light, almost free-flowing and easy to process with the aid of pumps via hose lines up to the upper stories and attics. The outstanding fresh concrete properties allow for easy processing and a surface concrete design similar to normal concrete. Owing to the low transport weight and the excellent properties in terms of building physics such as frost resistance, fire resistance (EI 120), a thermal conductivity of 0.13 W/m k, a compressive strength of 2.0 N/mm2 and a dry bulk density of 400 kg/m3 the EPS pumped concrete is suitable for a great variety of applications.
Range of application
The concrete developed is suitable for both new buildings and the refurbishment of old buildings, especially for attics and loft conversion. The building material is excellently suitable if there are relevant requirements in relation to fire protection or a good thermal insulation is required. Furthermore, the EPS pumped concrete is also used for swimming pool backfill and as leveling insulation layer.
Address/Anschrift
Franz Oberndorfer
GmbH & Co. KG
Lambacher Straße 14
4623 Gunskirchen/Austria
Tel.: +43 7246 7272-0
Fax: +43 7246 7272-1000
office@oberndorfer.at
www.oberndorfer.at
