Concrete technology and functional construction materials

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Autoclaved aerated concrete (AAC)

The aim here is to significantly increase the stability of AAC without compromising its heat-insulating properties. By adding a variety of solid admixtures to the initial low-viscosity suspension, it should be possible to substantially increase the load-bearing capacity of the resulting AAC products. This has led to the construction of a porous concrete laboratory facility. It has been designed to enable testing on a wide range of parameters and to ensure that laboratory scale practice can be directly transferred to production.

Porous materials absorb noise and can positively influence indoor conditions so that people’s health, well-being and performance are stimulated. They are very cost-effective materials, providing both good acoustic dampening properties and sufficient stability, while at the same time being easy to produce. Testing revolves around how the autoclaving / compacting process, particle size distribution and the amount of binding agent affect the properties of this heat-insulating / sound absorbing building material.

Fiber-reinforced concrete

Numeric simulation techniques can be applied to calculate the distribution and orientation of fibers in a test concrete block. Using these forecasts it should be possible to develop new components that contain significantly fewer fibers thanks to improved fiber distribution and a reduced number of fiber misplacements.

For the automated and production-integrated determination of steel fiber content, distribution and orientation in concrete parts a non-destructive test system is under development. The system is based on active thermography, an innovative testing technology that should significantly improve manufacture and quality assurance of precast concrete components – thereby generating cost savings for steel fiber reinforced concrete.

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Recycling and obtaining building materials from waste products

Using mechanical methods to process composite materials does break them up – but it cannot separate them into their individual components. Electrodynamic fragmentation relies on ultrashort, high-voltage electrical pulses to selectively break down and separate composite materials into their individual components. It can be used on waste concrete, for instance, to regain raw materials for the cement industry as well as valuable admixtures for use in concrete. In the case of composite materials such as carbon fiber reinforced plastics (CFRP), fibers can be separated from the polymer matrix. The technique can also be applied to break down complex mixes of waste such as waste incineration slag or electronic scrap – so that valuable components such as metals can be taken out for reuse. Selective separation through electrodynamic fragmentation is therefore an extremely promising alternative to the conventional processing methods currently used for recycling.

New technologies designed to integrate waste products into the production of sustainable concrete products are also under development as part of an effort to reduce consumption of non-renewable natural resources. Processed waste materials are transformed into innovative, lightweight, ecological and cost-effective building materials. Low energy consumption and reduced CO2 emissions in production make these materials particularly appealing. Further work is to be carried out on improving key characteristics such as mechanical and heat-insulating properties of this construction material.

© Fraunhofer IBP

Concrete laboratory equipment

The concrete laboratory is fully equipped to produce both concrete and mortar samples as well as for subsequent testing: Tests encompass the properties of fresh and hardened concrete as well as mechanical testing in accordance with DIN standards, including bending tensile strength, compressive strength and modulus of elasticity.

The analytical laboratory is equipped with an X-ray diffractometer and an X-ray fluorescence spectrometer. The D2 PHASER X-ray diffractometer features a LYNXEYE (1D) detector and offers qualitative and quantitative phase analysis of both powder and small-scale solid samples. Samples are prepared using a McCrone micronizing mill. Powder data is of sufficient quality to carry out a Rietveld refinement aimed at quantitative phase analysis. An external standard can additionally be used to determine the X-ray amorphous component of a powder sample without contaminating it. The energy-dispersive X-ray fluorescence spectrometer, complete with silicon drift detector, allows the qualitative and quantitative determination of the chemical composition of samples. The equipment has been specially designed to analyze bulk samples and liquids in addition to powder samples. There is also an automatic titration device for conducting tests on leaching from soils, waste or landfill material at constant pH values (pH-stat). In a special oven cement can be produced in the lab.