Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Rock solid: Carbon-reinforced concrete from Augsburg

11.10.2016

Chemists at the University of Augsburg have discovered how to manufacture an extremely strong cement at reasonable cost through use of aligned short carbon fibres

Prof. Dr. Dirk Volkmer and fellow scientists from the Chair of Solid State and Materials Chemistry at the University of Augsburg have published a report in the Journal "Cement and Concrete Research", describing for the first time a simple and resource-efficient technique by which a specific alignment of short carbon fibres in cementitious construction materials can be achieved.


Mortar with parallel aligned short carbon fibres. Inside picture: Schematic sketch of the nozzle technique for the alignment of carbon fibres in construction materials.

© IfP/University of Augsburg


Measurement curves (three-point flexure) of normal concrete; mortar with aligned short carbon fibres, hard bone tissue, and beech wood demonstrate the comparatively low strength of normal concrete.

© IfP/University of Augsburg

The material produced with this process exhibits extraordinary strength, putting cement - which is actually a rather brittle material - into the same league as tough high‐performance structural biomaterials such as bone or shell. The material was developed in cooperation with the construction firm Schwenk KG, with the vision of being able to dispense with steel reinforcement in concrete construction components in the future.

Fibre-reinforced mortars and concretes are attracting ever more interest in the construction industry, as the fibre additives improve the low tensile strength of plain concrete without the need for conventional reinforcement. Carbon fibres in particular combine the advantages of low density and high resistance to corrosion with outstandingly high strength values. Up to now, however, their high manufacturing costs have meant they have not been introduced into concrete construction components on a wider scale.

More strength thanks to specific carbon fibre alignment

When it comes to casting of fibre-reinforced concrete in moulds or formwork, the fibres are always randomly oriented. However, because load-bearing structures in building construction are in most cases subjected to loading in one direction only, a haphazard orientation of the fibres means that a considerable proportion of their potential for strength enhancement goes to waste. As Prof. Dr. Dirk Volkmer points out, “If, instead, all the fibres can be aligned in parallel along the lines of force which affect the structural element, even fibre admixtures would produce a major effect – which will also help to save resources. This was our basic concept, because similar strategies occur in nature, such as in natural bones, where the structure is suitably reinforced by aligned collagen fibres at points which come under heavy stress."

Following on from this, Dr. Volkmer’s Augsburg research group have developed a concept which facilitates specific alignment of short carbon fibres in a mortar mixture. The team have now reported on their results in the highly respected construction industry journal "Cement and Concrete Research" (http://dx.doi.org/10.1016/j.cemconres.2016.08.011).

Nozzles instead of formwork and casting

The scientists adopted a new approach altogether, turning their backs on the traditional technique of casting the mortar mixture in formwork. Instead, they developed the “nozzle technique”, where the fibre-cement compound is squeezed through a narrow nozzle. The key feature here is that by adaptation of the cross section of the nozzle, a preferred orientation of the fibres can be imposed as they pass through, as can be seen in Figure 1. The short carbon fibres are oriented parallel to the direction of travel of the mortar compound as it emerges through the nozzle (see Fig. 1, inside picture).

Extremely tough and strong

“At first we simply worked on getting the most homogeneous possible distribution of the carbon fibres within the mortar mixture”, says Manuel Hambach, a Ph.D. student from Professor Volkmer’s group. “However, we rapidly discovered that homogeneous distribution alone could only achieve a limited increase in strength, because the fibres are oriented in all three spatial directions. It was only with our nozzle technique and the alignment of the fibres along the tensile force lines that we obtained a material which is extremely tough and extremely strong.”

Strength increased by 1340 %

The scientists have been able to prove that samples produced with this nozzle procedure containing 3% by volume of aligned short carbon fibres can achieve flexural strength values of up to 120 Megapascal (MPa). The Pascal is a unit for defining pressure or mechanical stress. By way of comparison, a concrete sample without fibres or steel reinforcement exhibits a flexural strength of only 8 MPa. This means that thanks to the specific fibre orientation, an increase in strength of 1340 % can be achieved, which gives the material extreme tensile strength, as Figure 2 shows.

Buildings without steel-reinforced concrete

The Augsburg researchers have also been able to show that the compressive strength, which is also a very important factor for mortar and concrete, is not adversely affected by the intentional and specific alignment of the carbon fibres. “Our mixture of cement, water, and aligned carbon fibres is the first cementitious construction material to have a flexural strength which is greater than its compressive strength. This is an important milestone in the development of building structures in which conventional steel reinforcement can be reduced, or even dispensed with altogether”, says Volkmer. "Our material exhibits high strength values which are similar to those found in the hard tissue of mammalian bones, which scientists all over the world have been trying for decades to emulate in biomimetic terms."

Implementation by 3D printing

In order for this new material to find a way to practical application, however, it will be essential to develop technical concepts for transfer of the nozzle technique to dimensions which approach the reality of structural building components. The current process is not yet compatible with the conventional processing methods used on construction sites, as Dr. Volkmer admits. But the Augsburg scientists have a potential solution ready to hand: they see 3D printing, which is becoming more and more significant in materials research and development, as a technique with huge potential for the future. "The first prototypes of houses constructed with the aid of 3D printers have been arousing public interest for some years now", says Volkmer. With this he is referring to the recently laid foundation stone for the new Augsburg research building, the "Materials Resource Management" (MRM) facility. This was produced by his team with a 3D printer using FIBRACRETE, the internal designation adopted for the Augsburg carbon-fibre mortar.

Multifunctional applications

As well as its high strength, another characteristic of FIBRACRETE is its huge potential for use in a wide range of different and multifunctional applications. As early as the beginning of 2016, Professor Volkmer and his group were able publish proof that it is possible to heat cement mortar containing short carbon fibres by means of electricity (see http://dx.doi.org/10.1016/j.compositesb.2016.01.043). As Volkmer points out, the new material is therefore ideally positioned to take its place within the range of high-tech solutions already available at Augsburg in the area of functional carbon materials (Carboterials®).

Publications:

• Hambach, M., Möller, H., Neumann, T., & Volkmer, D. (2016). Portland cement paste with aligned carbon fibers exhibiting exceptionally high flexural strength (> 100MPa). Cement and Concrete Research, 89, 80‐86. ‐ http://dx.doi.org/10.1016/j.cemconres.2016.08.011

• Hambach, M., Möller, H., Neumann, T., & Volkmer, D. (2016). Carbon fibre reinforced cement based composites as smart floor heating materials. Composites Part B: Engineering, 90, 465‐470. ‐
http://dx.doi.org/10.1016/j.compositesb.2016.01.043

Contact:

Prof. Dr. Dirk Volkmer
Faculty of Solid State and Materials Chemistry
Institute of Physics at the University Augsburg
D‐86135 Augsburg
Telephone: +49(0)821‐598‐3032
dirk.volkmer@physik.uni‐augsburg.de
http://www.physik.uni‐augsburg.de/chemie/

Weitere Informationen:

http://dx.doi.org/10.1016/j.cemconres.2016.08.011
http://dx.doi.org/10.1016/j.compositesb.2016.01.043

Klaus P. Prem | idw - Informationsdienst Wissenschaft

More articles from Architecture and Construction:

nachricht Smart homes will “LISTEN” to your voice
17.01.2017 | EML European Media Laboratory GmbH

nachricht Designing Architecture with Solar Building Envelopes
16.01.2017 | Fraunhofer-Institut für Solare Energiesysteme ISE

All articles from Architecture and Construction >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Breakthrough with a chain of gold atoms

In the field of nanoscience, an international team of physicists with participants from Konstanz has achieved a breakthrough in understanding heat transport

In the field of nanoscience, an international team of physicists with participants from Konstanz has achieved a breakthrough in understanding heat transport

Im Focus: DNA repair: a new letter in the cell alphabet

Results reveal how discoveries may be hidden in scientific “blind spots”

Cells need to repair damaged DNA in our genes to prevent the development of cancer and other diseases. Our cells therefore activate and send “repair-proteins”...

Im Focus: Dresdner scientists print tomorrow’s world

The Fraunhofer IWS Dresden and Technische Universität Dresden inaugurated their jointly operated Center for Additive Manufacturing Dresden (AMCD) with a festive ceremony on February 7, 2017. Scientists from various disciplines perform research on materials, additive manufacturing processes and innovative technologies, which build up components in a layer by layer process. This technology opens up new horizons for component design and combinations of functions. For example during fabrication, electrical conductors and sensors are already able to be additively manufactured into components. They provide information about stress conditions of a product during operation.

The 3D-printing technology, or additive manufacturing as it is often called, has long made the step out of scientific research laboratories into industrial...

Im Focus: Mimicking nature's cellular architectures via 3-D printing

Research offers new level of control over the structure of 3-D printed materials

Nature does amazing things with limited design materials. Grass, for example, can support its own weight, resist strong wind loads, and recover after being...

Im Focus: Three Magnetic States for Each Hole

Nanometer-scale magnetic perforated grids could create new possibilities for computing. Together with international colleagues, scientists from the Helmholtz Zentrum Dresden-Rossendorf (HZDR) have shown how a cobalt grid can be reliably programmed at room temperature. In addition they discovered that for every hole ("antidot") three magnetic states can be configured. The results have been published in the journal "Scientific Reports".

Physicist Dr. Rantej Bali from the HZDR, together with scientists from Singapore and Australia, designed a special grid structure in a thin layer of cobalt in...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Booth and panel discussion – The Lindau Nobel Laureate Meetings at the AAAS 2017 Annual Meeting

13.02.2017 | Event News

Complex Loading versus Hidden Reserves

10.02.2017 | Event News

International Conference on Crystal Growth in Freiburg

09.02.2017 | Event News

 
Latest News

Start codons in DNA may be more numerous than previously thought

21.02.2017 | Life Sciences

An alternative to opioids? Compound from marine snail is potent pain reliever

21.02.2017 | Life Sciences

Warming ponds could accelerate climate change

21.02.2017 | Life Sciences

VideoLinks
B2B-VideoLinks
More VideoLinks >>>