Demolition and recycling of carbon reinforced concrete

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International HISER Conference on Advances in Recycling and Management of Construction and Demolition Waste

21-23 June 2017, Delft University of Technology, Delft, The Netherlands

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Demolition and recycling of carbon reinforced concrete Peter Jehle1, Jan Kortmann2, Florian Kopf3 and Natalia Bienkowski4

1

Professor, Department of Civil Engineering, Institute of Construction Management, Technische Universität Dresden, Nürnberger Strasse 31a, 01187 Dresden, Germany; PH (0049) 351-46334674; FAX (0049) 351-463 34680; E-mail: peter.jehle@tu-dresden.de

2

Research Associate and Ph.D. Candidate, Department of Civil Engineering, Institute of Construction Management, Technische Universität Dresden, Nürnberger Strasse 31a, 01187

Dresden, Germany; PH (0049) 351-46336315; E-mail: jan.kortmann@tu-dresden.de

3

Dresden Germany; PH (0049) 351-46339287; E-mail: florian.kopf@tu-dresden.de

4

Dresden Germany; PH (0049) 351-46332084; E-mail: Natalia.bienkowski@tu-dresden.de Abstract

Carbon reinforced concrete is an artificially produced composite construction material consisting of two components: concrete and continuous carbon filaments formed as roving fabric or bars. The research project C³-V1.5 “Demolition, Dismantling and Recycling” aims to answer the key questions regarding the LCA. Under the leadership of the “Institute of Construction Technology” (TECHNISCHE UNIVERSITÄT DRESDEN), 5 companies and 4 research institutes are involved in the project. The main goal of the research project is to keep carbon concrete materials in the life cycle and to avoid down-cycling. Furthermore, investigations concerning health and safety will be carried out to make sure that no hazardous emissions are released while working with the material. To reach this goal, laboratory tests will be conducted to set the basis for large-scale experiments. Within these experiments relevant concrete processing and recycling technologies will be assessed. First results of the laboratory tests indicate that the wear on the machines while processing carbon concrete is significantly lower than processing steel reinforced concrete. Furthermore, carbon concrete allows the use of much smaller machines due to the lack of steel reinforcement. Concerning the measurements of emissions, first results show that no dangerous fibre particles (WHO fibres) were released.

Keywords: carbon reinforced concrete, lifecycle, demolition, recyclability, health and

safety.

Introduction

Within Germany’s most expensive construction research project to date funded by the Federal Ministry of Education and Research, the use of carbon fibre reinforced concrete structures has been researched since 2014. Carbon concrete (carbon composite concrete = C³) is a composite material consisting of the concrete matrix and carbon reinforcement in the form of bars or roving fabrics. The carbon material used has a tensile strength of approximately 2,500 N/mm², which is significantly higher than the tensile strength of reinforcement steel (approx. 500 N/mm²), therefore less reinforcement is required. In addition, the amount of concrete can be reduced due to the corrosion resistance of the carbon fibre. In contrast to commonly used concrete elements, carbon concrete consists of

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grained high-strength concrete. Carbon concrete can be used to manufacture new building elements or to reinforce existing structures.

Since March 2016, the research project C³-V1.5 “Demolition, Dismantling and Recycling” has been investigating key issues relevant for the market launch of the new construction material. Five German companies are involved in the research project: KLEBL GMBH from Gröbzig, CARUSO UMWELTSERVICE GMBH from Großpösna, STEINBEISSER GMBH from Landsberg, MÜLLER-BBM from Dresden, and AIB GMBH from Bautzen. The scientific supervision is realized by four institutes of the TECHNISCHE UNIVERSITÄT DRESDEN: the Institute of Construction Technology (Leadership), the Institute of Concrete Structures, the Chair of Business Management especially Environmental Management, and the Institute of Construction Materials.

Goal

Within the project, experiments on test samples made of carbon reinforced concrete were made with commonly used concrete drilling and sawing tools. The goal was to gain information about how the carbon fibre reinforcement influences the emissions generated and how it effects the processing of the carbon concrete test samples. For new construction products or new construction materials to be successful, the material properties have to be at least equal or ideally better than the ones of comparable (in this case, steel reinforced concrete) products already available on the market. In addition, a possible health hazard is an exclusion criteria. Furthermore, it was to be investigated how the carbon fibre reinforcement structures (bars or roving fabric) can be separated from the concrete matrix in order to draw conclusions concerning recyclability and the ability to create joints during reconstruction works. Finally, the laboratory examination of the recycling material was carried out, including dust, concrete fragments, and reinforcement structures.

Preparationof theexperiments

For the experiments, 27 test samples with dimensions of 100 cm x 100 cm x 6 cm and two concrete strengths (normal-strength C45/55 and high-strength C90/105) were created. Five different variants were used for the reinforcement: without reinforcement, steel reinforcement, one and two layers of carbon fibre roving fabric, and carbon fibre bars. In total, 18 m² of carbon fibre roving fabric, ca. 30 m of carbon fibre bars, 750 litres of normal-strength concrete, and ca. 1,000 litres of high-normal-strength concrete were used. The samples received an after-treatment and were stored for 28 days.

For the processing of the test samples with concrete drilling and sawing tools, seven processing methods – thereof 5 dry processes without cooling water and 2 wet processes with cooling water – were chosen:

• core drilling, wet, diameter 200 mm (tool: Hilti DD 350-CA); • core drilling, dry, diameter 100 mm (tool: Weka Dk 32); • sawing, wet, diameter 800 mm (tool: Hilti DS TS20-E); • sawing, dry, diameter 200 mm (tool: Hilti DCH-EX 300); • drilling, dry, diameter 20 mm (tool: Hilti TE 70-ATC); • chiselling, dry with pointed chisel (tool: Hilti TE 905); and • grinding, dry (tool: Hilti DG 150).

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Experimental procedure

During demolition works, especially when cutting, drilling, crushing, and grinding mineral materials, dust is a nearly inevitable by-product (see Figure 1). The dust is unwanted, mainly because it is a potential health hazard, but also due to the risk of material damage. During the small-scale experiments, state-of-the-art measures have been taken to reduce the amount of dust on the workplaces. The last experiment was an exception. The dry grinding without aspiration of dust directly on the separated carbon fibre reinforcement was a simulation the worst case scenario.

The measurement concept varied depending on the expected main emissions and dust concentrations per experiment. As possible main emission components, the following fractions were found to be most relevant to evaluate the risk of exposure:

• alveolar dust fractions (A-dust), • inhalable dust fraction (E-dust), • crystalline silica (quartz), and

• WHO fibres, especially from the carbon fibre reinforcement material.

The exposure measurements were taken in the vicinity of the source of the emissions in the distances of: 1.0 m, 2.0 m; 5.0 m and 10.0 m (see Figure 2). This experimental setup remained unchanged for all experiments. The duration of the measurements was between 45 min and 60 min to ensure that various influencing factors can be taken into account in a statistical evaluation.

Figure 1. Grinding dry on a high-strength concrete

sample with carbon fibre bars as reinforcement

Figure 2. Experimental setup with measurement

equipment

Experimental results

Upon completion of the laboratory experiments, verifiable statements about the processing of C³-construction elements can be made. The results of the emission measurements for each experiment have been evaluated and were made accessible within the C³-consortium. In order to answer the question of whether the processing of carbon fibre reinforced concrete can lead to the formation of harmful fibres (according to the WHO definition), a total of 144 measurements, each with 320 SEM-pictures, had to be evaluated. The 320 SEM-pictures represent 1 mm² and therefore 0.14% of the surface area of the filter of the respective measurement. In none of the SEM pictures were fibres as defined by WHO found. According to the current state of the research, it can be stated that no health hazardous fibres, as is the case with asbestos, appeared during the experiments. The results are consistent with other publications concerning emissions when processing carbon fibre.

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Furthermore, with the evaluation of the test results from the small-scale experiments, the following statements concerning the concrete processing technologies can be made:

• Significant differences in the working speed during the processing of the separate test samples with normal-strength and with high-strength concrete were measured. • Reinforcement structures from carbon fibre can be cut (sawed, drilled, grinded, etc.)

with far less energy input than steel reinforcement of the same dimension.

• The time needed to process carbon fibre reinforced test samples and the wear of the tools used was significantly lower as with the comparable steel reinforced samples. • The separation of the carbon fibre reinforcement and the concrete matrix was

possible with commonly used tools and, therefore, the basic requirement for recyclability is ensured.