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- Springer Journals
- Copyright
- Copyright © The Author(s) 2023
- ISSN
- 1563-0854
- eISSN
- 2522-011X
- DOI
- 10.1007/s42107-023-00617-1
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Abstract
A large proportion of today's building projects are realized in existing buildings. This almost always requires the sensitive deconstruction of existing building fabric. Deconstruction technologies have to fulfill high requirements particularly in inner-city residential areas and during ongoing building use, both for construction projects in the existing building stock and for new construction activities. Currently used demolition technologies rarely meet the growing requirements in building practice. Common demolition and separation methods are characterized by high emissions, such as vibrations and noise, large quantities of blasting material, slow performance progress or high physical effort. An alternative technology is the electrodynamic Electric-Impulse-Technology (EIT). The process technology, initially developed for applications in mining and special civil engineering, is based on the destruction of solid materials by high-voltage pulses. On the basis of large-scale tests in mining dimensions, it was possible to demonstrate high dissolving capacities with low energy input. The research project aimed to investigate the basics for transferring the EIT to low-emission and selective material removal in civil and structural engineering. Extensive laboratory tests were conducted on sand-lime and concrete specimens to verify the adap- tation of the EIT. It was found out that the technology is suitable for use in the construction industry. Further research is to be conducted to investigate the identified areas of application in greater depth and to further develop EIT for practical use. Keywords Electric-impulse-technology (EIT) · Building in stock · Selectivity · Deconstruction method · Recycling Introduction urban areas (Dorffmeister, 2019). This is usually associated with the deconstruction of buildings. Due to changes in plan- The handling and management of construction and demoli- ning and faulty construction, deconstruction work is also tion (C&D) materials is currently playing an increasingly required for new buildings (replacement of faulty concrete important role, and will continue to do so in the future, due structures, subsequent construction of openings, geometric to an increase in raw material problem worldwide. Over 60% correction of existing building components). In both cases, of building in stock account for a considerable share of the deconstruction methods are to be applied that can be used total German construction volume and will continue to gain within existing or newly built structures. This sometimes in importance in the future due to limited building land in results in very strict requirements for the type and method of deconstruction technology, especially with regard to reduced emission values for noise, vibration and dust generation. At present, two basic demolition methods are available * Lukas Hammel lukas.hammel@tu-dresden.de for this purpose: mechanical destruction of the structure by external application of force (caulking, milling, drill- Faculty of Civil Engineering, Institute of Construction ing, sawing) or media-transporting blasting methods (high- Management, Technische Universität Dresden, pressure water jetting, solid-state blasting). The vibrations 01062 Dresden, Saxony, Germany 2 of the mechanical demolition methods also damage, above Faculty of Mechanical Engineering, Institute of Mechatronic all, the surrounding building fabric to be preserved. Another Engineering, Chair of Construction Machinery, Technische Universität Dresden, Dresden, Saxony, Germany problem is health hazards for workers (noise, dust, vibration) and thus occupational health and safety concerns. Blasting Texulting GmbH, Chemnitz, Saxony, Germany Vol.:(0123456789) 1 3 Asian Journal of Civil Engineering methods, on the other hand, are relatively low in vibra- waste. An interesting overview of the perceptions, deci- tion and wear, but especially in the case of high-pressure sions and motivations of various stakeholders regarding water jetting, they introduce a large amount of water into the use of recycled C&D waste is provided in Shooshtarian the building fabric. Both demolition methods are therefore et al. (2020) in general and in Shooshtarian et al. (2022) only suitable to a limited extent for construction in sensitive specifically for Australia. environments. Furthermore, some dismantling processes are A targeted and material-selective demolition as well as operated with an internal combustion engine, which releases a downstream sorting of mixed construction waste could pollutants. ensure that the materials are reused in an equivalent man- Another perspective of future developments in the Ger- ner. The aim should, therefore, be to produce new recy- man construction market focuses on the quality of recycling cled building materials in significant quantities through reclaimed building materials. The supply and flow of raw targeted processing of mineral construction waste. The materials in Germany have been the subject of political, sci- importance of the circular economy and its effect on the entific and corporate activities for several years. The first raw entire construction industry is elaborated in detail in Hos- materials strategy of the Federal Republic of Germany was seini (2021) and Shooshtarian et al. (2022). The basis of published in 2010 with a focus on raw materials supply and the circular economy is to win building materials sepa- has since been updated at regular intervals and reviewed by rately after their use and to use them as equally as pos- a raw materials policy compass of the Federal Government sible. To ensure this, suitable processes must be devel- (Hartz et al., 2018). The extraction of raw materials in Ger- oped for new construction, conversion and demolition of many was 1041 million tons in 2015 (Löschel et al., 2020). buildings and the raw materials they contain. A separate With 517 million tons, construction materials represent the extraction of the individual building materials is of great largest group of raw materials (Löschel et al., 2020). importance (Hillebrandt, 2021). The circular economy will In this context, the extraction of raw materials for new continue to gain in importance and is already playing an building materials is accompanied by significant land con- important role for investors. sumption and high energy consumption. Consequently, the In most cases, there is a lack of machine-based demoli- recovery of existing building materials and the recycling tion technologies that meet these selective requirements for of mineral construction waste have become significantly demolition and processing in an urban context. Common more important. These are produced in large quantities, for demolition and separation methods are characterized by example, during demolition, renovation and remodeling high emissions (noise, vibration, dust) and low selectivity. work on existing building structures. Results of investi- Third parties are negatively affected to a high degree by gations have shown that in the Federal Republic of Ger- acoustic pollution, which emanates both from the equip- many, the amount of material bound in buildings can be ment and from the mechanical destruction of the structure. estimated at about 15 billion tons (Vogdt et al., 2016). Often, users / tenants / residents in the immediate vicinity It will, therefore, be one of the most important tasks of are disturbed by demolition procedures to such an extent that the future to make systematic use of this secondary raw simultaneous use of neighboring premises is not possible or material reservoir, the so-called anthropogenic material only possible to a limited extent. The mechanical structural store (Schiller et al., 2015). In the German construction destruction of structural facilities by means of demolition industry, more than 200 million tons of construction and procedures also leads to notable vibrations in addition to demolition (C&D) waste are generated annually (Nelles acoustic impairments. These often lead to unintentional et al., 2016; Umweltbundesamt, 2022). With a total damage to neighboring building components or neighboring waste volume of just over 400 million tons in Germany, buildings. In addition, exposure to dust not only affects the this represents approximately half (Nelles et al., 2016). occupational safety and health of workers but also causes a Statistically, 90% of this waste is recycled, but most of nuisance to residents of neighboring properties, particularly it is "downcycled", i.e., the material is made available in inner-city areas. In most demolition work, dust generation again in reduced quality and functionality (Zhang et al., is unavoidable and is usually caused by the breaking apart 2020). An example of this is C&D waste, which is used of mineral building materials. as low-quality secondary material in the unbound layers Only a controlled interaction of new selective demoli- of road construction. The background to this fact is usu- tion technologies, separation of the construction waste and ally the lack of single-variety processing of the demoli- a modern and efficient processing technology will make it tion material as well as the mechanical destruction of the possible in the future to demolish buildings in the urban building materials or their individual components during environment, obtain high-quality recycling products and deconstruction (Müller, 2018). In addition to the points reduce the land requirement as well as the energy consump- mentioned above, there are a number of other aspects that tion in the extraction of raw materials (Basten, 2018; Stroh motivate individual stakeholders not to use recycled C&D et al., 2020). 1 3 Asian Journal of Civil Engineering the impulse causes the material to be subjected to tension Research aim and objectives instead of compression. An electric field is built up between the two electrodes, which leads to ionization of the process This is the starting point for the EIT (Electric-Impulse-Tech- nology) described here, which can separate mineral materi- environment, i.e., the rock and the surrounding dielectric. Ionization is the release of charge carriers from their bond als with the aid of high-voltage pulses without significant vibrations, dust generation and noise (Meetz et al., 2015; by a strong electric field. The force effect within the field ensures that the free charge carriers are stimulated to move, Müller, 2018). Existing demolition processes often have one or more negative emissions and do not dissolve the mate- collide with other particles and release new charge carri- ers from their bond (Küchler, 2009). The resulting abrupt rial by type, which does not favor the circular economy of building materials. The goal of EIT-Technology is to fill increase in temperature and pressure in the breakdown channel causes the tensile strength of the rock to be over- the aforementioned gaps of established deconstruction tech- nologies and thus promote the circular economy. The aim of come, resulting in a brittle fracture with associated material removal. Under normal conditions, the tensile strength can the investigations carried out is the utilization of new tech- nology for the low-emission and selective deconstruction be overcome with very low specific energy, since it is only about 10 percent of the compressive strength (Biela, 2009). of structural facilities. The study demonstrates by a large number of tests that selective deconstruction in sensitive Structural building materials in civil engineering have sig- nificantly lower tensile strength compared to their compres- areas can be implemented with low emissions by means of deconstruction using EIT. The EIT operates on a power sive strength. EIT makes use of this property of building materials, but this property is not a basic requirement for the connection, therefor, no pollutants are released. Compared to established demolition methods, which often run on die- process. The prerequisite for material removal is discharged within the rock to be dissolved. For this, it is necessary that sel, this is a significant advantage of the EIT. The aim of the research project was to investigate the extent to which the two electrodes rest directly on the rock and that the pro- cess space above the rock is enclosed by a medium that has the EIT can be adapted for use in the construction industry. In addition to extensive literature research for a compari- higher electrical strength (dielectric strength) than the rock. Electrical strength defines the electric field strength that a son of the EIV with the established demolition methods, the EIT was modified for use in the construction industry. material can withstand without electrical breakdown occur- rence. In general, the electrical strength of solids is greater Jens Otto (Institute of Construction Management) and Frank Will (Chair of Construction Machinery) played a key role than that of liquids, which in turn is greater than that of gaseous substances. However, the electrical strength of sub- in supervising the research project through interdisciplinary cooperation at Technische Universität Dresden, Germany stances changes depending on the loading time. In general, substances have higher electrical strength at short loading (TUD). The “EIV-Bau” research project (Otto et al., 2021) was completed at the beginning of 2021, and the main results times. This behavior is more pronounced for liquids than for solids. If the voltage exposure occurs in sufficiently small are summarized in this article. Here, some of the results of the research project, such as the study of the electrode gap, times, i.e., in the nanosecond range, the electrical strength of the liquid increases rapidly and exceeds that of solids. In the number of pulses and the pulse energy are presented and then discussed. this way, a discharge in the solid can be realized. Since there is only a loose contact between the electrodes and the solid, no mechanical forces are necessary for the EIT compared to conventional methods. Literature review: basic applications of EIT‑technology To ensure a targeted breakthrough in the material, the following basic requirements must be met (Fig. 1a): The EIT was researched and developed in the former Soviet two electrodes with different potentials, Union in the middle of the twentieth century. The potential of the technology for hard rock processing was discovered the rock itself and an ambient fluid (dielectric) that acts as an insulator. and research in this field was intensified (Kunze et al., 2007). EIT can be used to economically pre-damage, remove One of the two electrodes is grounded and, therefore, has and crush particularly hard materials, such as granite, ore or high-strength concrete, in drilling, processing and construc- a potential of zero. A high pulse voltage is applied to the other electrode. As a result of the potential difference that tion applications (Anders, 2021; Lämmerer, 2017; Lehmann, 2017; Lehmann, 2021; Voigt et al., 2017). The destructive now prevails, an electric field is formed (Fig. 1b). If the strength of the electric field exceeds the dielectric strength effect is not based on the application of mechanical force, but on high-voltage pulses that are applied to the material via an of the rock, a breakdown channel is formed (Fig. 1c). This expands suddenly and tears the rock from the inside out. electrode arrangement. Contrary to conventional methods, 1 3 Asian Journal of Civil Engineering Fig. 1 Basic principle of the EIT (1 High voltage electrode, 2 Grounding electrode, 3 Dielectric, 4 Rock, 5 Electric field, 6 Plasma channel, 7 Dissolved materials, 8 Cracks) (a basic requirements, b electric field, c electric field exceeds, d dissolving process) Rock fragments are blasted from the formation. Small cracks for use in deep drilling in hard rock for geothermal energy and previous damage form in the surrounding formation (Anders, 2021; Lehmann et al., 2017, Lehmann, 2021). The (Fig. 1d). researchers at the TUD succeeded for the first time in the In order for a discharge to occur in the material and not in consistent implementation of the electrodynamic EIT under the surrounding fluid, the dielectric strength of the material practical conditions of mining and special civil engineer- must be significantly lower than that of the fluid. As already ing. High dissolution rates with low energy input and high mentioned, the dielectric strength is not a constant value, selectivity were demonstrated. In further projects, the pulse but depends on the rise time. Figure 2 shows schematically voltage generators and drill heads for shallow drilling were the characteristics of the dielectric strength as a function of also developed. Another field of application of the EIT is the rise time. It can be seen that, in general, the dielectric the processing, damaging and crushing of ores to support strength of rock and water has an intersection at 500 ns. This means that the dielectric strength of rock is lower than that of water when rise times of less than 500 ns are achieved. In this case, common industrial water is suitable as a dielectric for the EIT. If, on the other hand, it was possible to use oil as the ambient medium, breakdown would occur even with comparatively long rise times in the rock. Figure 2 also shows that as soon as air or air bubbles are in the vicinity of the electrodes, the breakdown always occurs through the air and thus there is no breakdown in the rock anymore. The EIT has been researched and developed for sev- eral years at the Chair for Construction Machinery at the Technische Universität Dresden (TUD) (Anders, 2021; Lämmerer and Flachberger, 2017; Lehmann et al., 2017; Lehmann, 2021; Voigt et al., 2017). Based on the investiga- tions, various fields of application have already been devel- Fig. 2 Electric strength of various substances according to Bluhm oped. In some research projects, the EIT was developed et al., (2000) 1 3 Asian Journal of Civil Engineering Fig. 3 Electrode pairs A, B and C with different geometries energy-intensive mechanical processes (Anders, 2021; be carried out in such a way that selective loosening of min- Lehmann, 2021). eral rock is possible with geometric precision at very low The interdisciplinary research project "Basic Investiga- emissions. After a brief description of the test rig, important tion for the Adaptation of an Innovative Demolition Process results of the individual tests are described below. from Mining (EIT) as a New Construction Technology for Selective Deconstruction in Sensitive Areas" of the Chair of Construction Machinery and the Institute of Construction Methodology and basic experiments Management (TUD) deals with the adaptation of EIT as an alternative deconstruction technology in the construction The basic tests were intended to investigate the influence of industry (Otto et al., 2021). The environmental conditions essential parameters of the EIT and to evaluate them with of a construction site and the application scenarios differ regard to typical construction-specific conditions. For this significantly from the aforementioned application scenarios. purpose, the parameters electrode geometry, electrode spac- For example, while the process chamber in a vertical deep ing, pulse energy and number of pulses were varied singu- borehole is closed by the surrounding solid rock, a sepa- larly at the existing test rig of the TU Dresden and the effects rate process chamber seal must be developed for use on the on the type and size of the dissolved mineral substances construction site for selective dismantling. If the remaining were investigated. technological prerequisites are solved, EIT promises highly In a first step, selective tests were carried out on test sam- interesting areas of application for the construction industry ples made of sand-lime brick using the EIT. The aim was as well. to maximize the measurements of dissolved solid rock per pulse by varying the electrode spacing, electrode geometry, number of pulses as well as pulse energy of the electro- Methodology dynamic EIT. Three geometrically different electrode pairs A, B and C were designed for the basic experiments (see Aims of testing Fig. 3). In the application of EIT in construction, the electrodes The large number of tests carried out as part of the pro- are to be guided continuously over a component, ensuring ject aimed to be able to assess the influences of individual contact between the component and the electrodes. The elec- parameters on the performance of the EIT and the selectivity trode geometry selected was used to investigate the extent of the process. The calculated specific energy for dissolving to which the contact surface has an influence on the dissolu- the material as well as the measurement of the test samples tion process. The pulse parameters are adjusted by design- before and after the tests further enable comparability with ing the electrodes and the pulse voltage generator. For this other demolition and separation processes. With regard to purpose, tests were carried out on samples made of sand- selectivity, the nature of the detached material as well as the lime bricks as well as on samples made of concrete. Due nature of the remaining surface play a role. With the electro- to the industrial production and the resulting homogeneous dynamic EIT, the deconstruction process should ultimately nature, the first basic tests were carried out on sand-lime 1 3 Asian Journal of Civil Engineering Fig. 4 Experimental setup for basic experiments (1—Pulse voltage generator in the pres- sure vessel, 2—Sample holder, 3—Container for water bath, 4—Sand-lime bricks sample, 5—Grounding) bricks. Subsequently, it was investigated whether the find- the horizontal repositioning are presented as a part of the ings obtained could be transferred to concrete test samples. series of experiments within the research project. The tests were carried out using a simple experimental setup consisting of an encapsulated pulse voltage genera- tor, a sample container with a tub of water and the sample Results holder for the pair of electrodes (see Fig. 4). Figure 5 shows a typical result image of the achievable breakout area of a In this section, some results are presented. The parameters sand-lime brick sample. electrode gap, number of pulses, pulse energy and electrode As to the experimental procedure: the samples were guidance are addressed. A variation of these parameters placed in the sample holder, and the pulse and ground elec- results in a change of the solvable volume and the required trodes were placed on the sample and fixed. The sample specific energy. The results are illustrated graphically. holder and sample were then placed in the water container. After the grounding was removed, the experiments could Electrode gap be started. Based on the tests from mining and special civil engineering, it was determined that a dissolving process In a first series of experiments, we investigated to extent can be realized with 5 pulses, which is why this determina- to which electrode geometry and electrode spacing affect tion was also made for this experimental design. The entire the dissolved measurements as well as the required specific test procedure with the associated evaluation can be seen in energy. The inner distance between the electrodes (EA) were Fig. 6 below. All steps that were necessary for a successful varied between 8 and 45 mm (see Fig. 3). This determination and complete test implementation are summarized on the was based on results from previous research with hard rocks basis of the figure. Steps 1–14 concern the preparation and such as granite (Anders, 2021; Lehmann, 2021). The follow- execution of the experiments and steps 15–22 concern the ing graphs (see Fig. 7) show the experimentally determined follow-up of the experiments for a comprehensive evaluation relationship between electrode spacing (EA) and dissolved of the experiments. To generate reliable results, each test mass (in cm ) as well as between electrode spacing (EA) was repeated at least 3 times and the measured values were subsequently evaluated. Based on the fundamental tests, the influence of site-spe- cific influencing criteria was also investigated, such as the influence of the degree of contamination from the dielectric (service water) on the dissolution process or the effect of interfering points made of plastics (e.g., spacers) or steel (e.g., reinforcing steel). In the following, the results of the variation of the electrode spacing, the number of pulses and During horizontal repositioning, the electrodes are laterally dis- placed along the surface on the specimen in one plane. Fig. 5 Typical breakout area (sand-lime brick) 1 3 Asian Journal of Civil Engineering Fig. 6 Scheme of the experimental design Fig. 7 Sand-lime brick: dissolved mass (left) and specific energy (right) depending on the spacing between the electrodes (EA) and the electrode geometry (EG) (Otto et al., 2021) and required specific energy (in J/cm ) on samples made in each case the mean value of the test results as well as of sand-lime brick. The experiments were carried out with their minimum and maximum values. For all three elec- three geometrically different electrodes (EG A, EG B and trodes, you could see that the dissolved mass increases EG C, see Fig. 3). significantly up to an electrode spacing of about 25 mm Already at the beginning of the tests, it became clear and then remains approximately constant. You can also see that the electrode gap on a sand-lime brick could be that the dispersion of the dissolved mass up to an electrode selected significantly higher than on a natural brick. This spacing of approximately 25 mm is significantly smaller is due to the lower material strength of industrially manu- than for larger electrode spacing. The specific energy is factured sand-lime bricks. The results in Fig. 7 represent also almost constant from an electrode spacing of 20 mm. 1 3 Asian Journal of Civil Engineering Fig. 8 Sand-lime brick: dissolved mass (left) and specific energy etry A, therefore only individual values are shown in the diagrams, no (right) depending on the number of impulses and the electrode geom- progression.) (Otto et al., 2021) etry (EG) (Only a few test were carried out with the electrode geom- individual components of the already dissolved material will Number of impulses be crushed, which would have a negative effect on energy efficiency. In a second series of tests, the effects of the number of pulses The generator used for the experiments has 5 stages, each on the dissolved mass and the required specific energy were with 10 capacitors. The charging voltage is about 40 kV. investigated. Here, a series of tests were carried out to allow This results in a discharge voltage of about (5 × 40 kV =) extrapolation of the demolition performance. The elec- 200 kV. Depending on the number of stages in connection trodes were not moved during the dissolving process itself, with the capacitors, the charging voltage and thus also the but were displaced by a distance of 10 mm on the sample discharging voltage can be changed. The pulse energy was only after the pulses of different numbers had been released. reduced by removing one capacitor from each stage. For the Varying the number of pulses showed that the most efficient generator used (about 80 J), this is about 8 J (10%) less per result could be obtained in tests with five pulses. The follow - capacitor removed. The charging voltage was kept constant ing Fig. 8 show the results of the tests. (Fig. 9). While a constant increase in the dissolved measurements It could be seen that the dissolved mass decreases with could be recorded up to a number of five pulses, the increase the reduction of the pulse energy. The specific energy, on the in the dissolved mass is only very slight for more than five other hand, is not influenced by the pulse energy. It follows pulses. When considering the specific energy required per that the dissolved measurements and the pulse energy have number of pulses, an increase in specific energy could be a constant relationship to each other. Furthermore, it can be observed from five pulses onwards. This also confirmed confirmed by the experiments that a reduction of the impulse experimental results from other research areas of the EIT. energy reduces the probability of dissolving rock. Further- During the experiments it was also observed that the acous- more, it can be concluded that reducing the pulse energy tics of the pulse changed with an increasing number of decreases the probability of successful breakthrough. For pulses. This gave further reason to assume that after a certain the configuration considered, it is, therefore, recommended number of pulses the material is no longer dissolved from to work with an impulse energy of 80 J. Figure 10 illustrates the composite, but the already dissolved material is merely this fact. further comminuted. Due to the required number of pulses for loosening the material, a first approach for the prediction Transient electrode guidance of the working speed for the EIT can be derived. In addition to the previously described tests, a number of Impulse energy other investigations were carried out on various parameters of the EIT. Among other, tests were carried out on the ver- With a third series of experiments, the influence of dif- tical and horizontal repositioning of the electrodes during ferent pulse energies on the dissolved measurements and the process to determine the release performance of the EIT the specific energy was investigated. The pulse energy is with a continuously moving mold. For the horizontal reposi- of great interest for selective deconstruction. If the energy tioning of the electrodes, the best experimental results were is too low, the material is not dissolved from the compos- achieved by the following parameters: ite. If the pulse energy is too high, on the other hand, there is a risk that the material will not only be dissolved from Electrode spacing of 15 mm, the composite along the grain boundaries, but also that the 1 3 Asian Journal of Civil Engineering Fig. 9 Sand-lime brick: dissolved mass (left) and specific energy (right) depending on the impulse energy and the electrode geometry (EG), elec- trode spacing EA = 25 mm (Otto et al., 2021) Fig. 11 Schematic test procedure with horizontal repositioning of the Fig. 10 Sand-lime brick: proportion of attempts with a successful electrode pair (Otto et al., 2021) breakdown for different impulse energies (Otto et al., 2021) Discussion • pulses per position and offset of the electrodes by 10 mm. Extrapolation The electrodes of the EIT were not moved over the The results obtained so far, are to be transferred to practi- samples in an ideally continuous manner during the tests. cal construction application scenarios by scaling. The aim Rather, they were placed on the sample, subjected to 5 of the extrapolation is to determine a comparative value of electrical pulses, and then placed on the sample again off- the demolition performance to the established demolition set horizontally by 10 mm. The procedure was repeated and separation methods for the surface removal, the surface a total of 7 times, so that a total of (7 × 5 =) 35 electrical removal and the separation of mineral building materials. pulses were applied to the samples. A distance of 60 mm For this purpose, the previously experimentally determined was realized from the first position to the last position. demolition performance of the EIT in m /h and the separa- The following Fig. 11 illustrates the test sequence with tion performance in m [separation area]/h must be extrapo- horizontal repositioning. lated. The extrapolation of the demolition and separation The tests with horizontal repositioning were carried out performance is carried out on the basis of the test configura- with electrode geometry B. The preliminary series of tests tion listed in Sect. 3.3.4 and the test results listed in Table 1. showed that electrode geometry B is better suited for mass With this test setup, it was possible to dislodge 26.4 removal on the surface than electrode geometry A and C. cm from an unreinforced concrete sample. The dimen- The electrode geometry C, on the other hand, is better sions of the dislodged cavity/cone were approximately suited for mass removal in depth by vertical repositioning. 4.1 cm × 8.1 cm × 0.83 cm (widt h × lengt h × dep t h). The results of the tests are summarized in the following By multiplying the length of the excavation cone by section. The tests carried out form the basis for determin- the mean depth, the separation area after 35 pulses of ing the demolition performance of the EIT when removing (8.00 cm × 0.83 cm =) 6.6 cm can be calculated. mineral building materials over a large area. 1 3 Asian Journal of Civil Engineering Table 1 Test results horizontal repositioning concrete (Electrode Table 3 Extrapolation of the demolition performance based on the geometry B, Offset by 10 mm after 5 pulses) (Otto et al., 2021) laboratory test by repositioning electrode B; hand-held EIT device; 10 Hz and 25 Hz (Otto et al., 2021) Required energy for 35 impulses [J] 2800.00 Demolition Demolition performance [m /h] Dissolved mass of mineral material [cm ] 26.40 process Masonry Concrete Reinforced Reinforced Specific energy [J/cm ] 107.00 concrete (20% concrete (50% Width of the breakout cone [cm] 4.10 reduction) reduction) Length of the breakout cone [cm] 8.10 Mean depth of the breakout cone [cm] 0.83 EIT, 10 Hz 0.030 0.027 0.022 0.014 Dissolved amount after 5 impulses [cm ] 3.77 EIT, 25 Hz 0.074 0.068 0.054 0.034 Dissolved amount after 35 impulses [cm ] 26.40 Separating area after 35 impulses [cm ] 6.60 Table 4 Extrapolation of the demolition performance based on the Laboratory test by repositioning electrode B; EIT attachment; 10 Hz Table 2 Extrapolation concrete; repositioning electrode B; 10 Hz; and 25 Hz (Otto et al., 2021) 25 Hz (Otto et al., 2021) Demolition Demolition performance [m /h] Designation 10 Hz 25 Hz process Masonry Concrete Reinforced Reinforced Duration per pulse [s] 0.10 0.04 concrete (20% concrete (50% Duration for 35 impulses [s] 3.50 1.40 reduction) reduction) Dissolved amount per minute [cm /min] 452.60 1131.40 2 EIT, 10 Hz 0.120 0.108 0.086 0.054 Separation area per minute [cm /min] 113.10 282.90 EIT, 25 Hz 0.296 0.272 0.218 0.136 dissolved amount per hour [cm /h] 27,154.30 67,885.70 Separation area per hour [cm /h] 6788.60 16,971.40 Dissolved amount per hour [m /h] 0.027 0.068 Separation area per hour [m /h] 0.679 1.697 electrode contacts the reinforcement, a short circuit occurs and no material is dissolved. Tests on reinforced concrete test samples were only carried out qualitatively as part of the As a result of the technical properties of the testing facil- research project. It was investigated whether the reinforce- ity, a maximum pulse frequency of 25 Hz can be achieved. ment can be detached from the concrete matrix by the EIT. A higher frequency cannot be realized so far, because the In the absence of concrete test results, it is assumed for the capacitors of the testing facility heat up too much and thus following consideration that the demolition performance of a constant use of the system is not possible. The following the EIT is 20–50% lower for reinforced concrete than for extrapolation was, therefore, carried out at a frequency of unreinforced concrete. Table 4 summarizes the results and 10 Hz and 25 Hz. assumptions for the demolition performance corresponding Depending on the frequency with which the high-voltage to the device used in the laboratory. This device could be pulses are conducted into the building material, a different the starting point for the development of a hand-held EIT demolition performance can be realized. At a frequency of device in the future. 10 Hz, 3.5 s are required for the 35 pulses, and only 1.4 s By increasing the contact area between the electrodes and at 25 Hz. At 10 Hz 1028 pulses are generated in one hour the component to be demolished by several pairs of elec- and at 25 Hz 2571 pulses and a separation area of 6788 trodes (e.g., 4 pieces), the demolition performance of an 2 2 and 16,971 cm per hour (= 0.679 and 1.697 m per hour, EIT attachment can be increased by four times the demoli- respectively) can be realized. Table 2 summarizes the results tion performance determined for one pair of electrodes if of the extrapolation for a frequency of 10 Hz and Table 3 the the arrangement is optimal. Since the adaptation of the EIT results of the extrapolation for a frequency of 25 Hz. leads to an increase in the total weight of the EIT device, The demolition performance demonstrated experimen- such an EIT device is no longer suitable for hand-held use, tally with the EIT on an unreinforced concrete sample must but only as an attachment to a carrier device. Table 5 sum- be reduced for the demolition of reinforced concrete. The marizes the results of the extrapolation for an EIT attach- degree of reduction depends on the degree of reinforcement ment consisting of a total of 4 pairs of electrodes. of the reinforced concrete. Demolition of reinforced con- As a result, it can be stated that the determined perfor- crete with the EIT requires specific positioning of the elec- mance values of the EIT are significantly lower than the trodes along the reinforcement. If the grounding electrode performance values of established hand- or machine-guided comes into contact with the reinforcement, the function of demolition processes. The advantageousness of the EIT the process is hardly affected. However, when the pulse can be explained here exclusively by the selectivity and 1 3 Asian Journal of Civil Engineering Table 5 Extrapolation of the separation performance based on the Table 7 Drilling performance diamond-set drill bit by core drilling laboratory test by repositioning electrode B; 10 Hz and 25 Hz (Otto (Schröder et al., 2015) et al., 2021) Drill bit diam- Concrete strength Separation process Separation performance eter [mm] 2 Low High [m -separation area/h], concrete Drilling performance [m/h] 80 4–6 3–4 150 4–6 4–5 EIT, 10 Hz 0.679 200 4–6 4–5 EIT, 25 Hz 1.697 300 5–8 4–6 Drilling performance 80 0.3–0.5 0.2–0.3 m -separation area per h 150 0.6–0.9 0.6–0.8 Table 6 Cutting performance diamond saws (Schröder et al., 2015) [m /h] 200 0.8–1.2 0.8–1.0 Cutting performance in m separation area/h 300 1.5–2.4 1.2–1.8 Masonry Concrete Rein- forced concrete Table 8 Drilling performance hand-held drill hammer (Schröder Circular blade saw 1.6–2.0 0.5–1.5 0.5–1.2 et al., 2015) (up to 0.4 m cutting Building material Strength (N/mm ) Drilling performance depth) upon demolition (m Chain saw (up to 1.8–2.0 0.5–1.0 0.3–0.9 separation area/h) 0.6 m cutting depth) d < 0.3 m d > 0.3 m Wire saw 1.0–4.0 Concrete (vertical) Low (< 30) 4.241 8.168 High (> 30) 3.299 6.912 the reduced emissions of the process. It must be taken into Concrete (horizontal) Low (< 30) 2.121 4.084 account that the extrapolation is based on assumptions and High (> 30) 1.649 3.456 must be substantiated by concrete tests. In addition to the extrapolation of the demolition perfor- mance of the EIT, the pure separation performance of the EIT for concrete is summarized in Table 6. A performance which is why it is commonly used in sensitive areas. Sawing specification for the demolition of reinforced concrete com - allows for high precision. Saws of different sizes and types ponents is not possible, since the EIT cannot cut through the can be used. A basic distinction is made between circular reinforcement located in reinforced concrete, but can only blade sawing, chain sawing and wire sawing (Schröder et al., expose it without damage. The comparison with established 2015). Table 7 summarizes the most important performance cutting methods is given in the following section. values of these three sawing methods. In drilling, a general distinction is made between core Comparison of the separation performance of EIT drilling and solid drilling methods. As with sawing, the with established separation processes use of water must be planned for this cutting method. This method has proven successfully in renovation and construc- Basics tion in existing structures, since the components to be pre- served in the immediate vicinity remain undamaged and the The basis of the comparative investigations was a full-scale vibrations introduced into existing structures are usually analysis of the established demolition and cutting methods negligible. Noise pollution is significant with this method for selective deconstruction in sensitive areas. In the fol- and must, therefore, be taken into account during planning. lowing, the established cutting and drilling methods are Table 8 summarizes the most important performance values presented and their cutting and separation performance is for core drilling. clarified. With a solid drill rig, a rotating and percussive motion In general, cutting (= sawing) is used for the execution of transfers the force into the borehole via a drill head (Schröder partial demolitions or as a preparatory measure for a subse- et al., 2015). Due to this power transmission, a large part of quent demolition technology. Sawing methods are suitable the material in the borehole is crushed and discharged in for demolition in existing structures, as they are accurate coarse and fine components compared to the diamond core and low in vibration. Process water is required as rinsing or drill. Solid core drill rigs are used as hand-held rotary ham- cooling water and for dust binding. Emissions from this cut- mers (up to 20 kg) or as machine-guided tracked rotary ham- ting process are relatively low except for high noise levels, mers. Table 8 summarizes the most important performance 1 3 Asian Journal of Civil Engineering Table 9 Comparison of cutting performance Table 10 Drilling performance of established drilling methods and the EIT (Otto et al., 2021) Cutting methods Cutting performance [m separation area/h], concrete Drilling method Drilling performance [m -separation area/h], Blade saw 1.000 concrete Chain saw 0.750 Core drill (d = 80 mm) 0.325 Wire saw 2.500 Core drill (d = 150 mm) 0.725 EIT, 10 Hz 0.679 Core drill (d = 200 mm) 0.950 EIT, 25 Hz 1.697 Core drill (d = 300 mm) 1.725 Drill hammer vertical (d < 300 mm) 3.770 Drill hammer horizontal (d < 300 mm) 1.885 values for manually executed solid drilling. It must be noted EIT 10 Hz 0.679 that drilling operations are usually associated with massive EIT 25 Hz 1.697 noise emissions, vibrations and dust generation. Comparison with the cutting methods be seen. In some cases, significantly higher drilling rates can be achieved with the EIT (25 Hz). Several pairs of electrodes When comparing the cutting methods with the EIT, the pure can also be connected to a Marx generator, but only one cutting performance is considered without taking secondary active electrode is reached with each electrical pulse. The operations into account. Table 9 compares the cutting perfor- pulse repetition rate for the Marx generator should be limited mance of the common cutting methods with the extrapolated to 25 Hz to ensure continuous use on a construction site. cutting performance of the EIT. The results show that the EIT in particular produces a Emissions cutting performance at 25 Hz that is comparable to that of the established cutting methods. The quality of the cut sur- Compared to mechanical demolition and cutting processes, face is flat for the established cutting methods and rough the acoustic impact of the EIT is only caused by the electri- for the EIT. cal flashover in the material and the generation of the voltage pulse in the pulse voltage generator. Other emission sources, Comparison with the drilling methods such as water pump or voltage supply, are classified as low. The electrical flashover is acoustically shielded by the pro- In the case of the drilling processes, the separation is not cess chamber sealing with a dielectric located around the achieved by a continuous cut in the part or component, but electrodes. As a result, it can be stated that the acoustic by the complete or partial detachment of parts of the part impact of the EIT is comparatively quiet and significantly or component. lower than that of established dismantling processes. There The results of the extrapolation of the EIT do not include is no transmission of sound waves over the entire building any pre- or post-processing. The aim is to use the process structure analogous to mechanical deconstruction methods. immediately after connection to the power supply and ensur- The same applies to vibrations in comparison to mechani- ing a sufficient amount of dielectric. Consequently, a very cal demolition methods, since the material is not subjected small amount of preparatory and finishing work, comparable to compression but to tensile stress during the EIT. This to the use of a hammer drill, can be assumed. Table 10 com- means that the process is virtually vibration-free. Conse- pares the drilling performance of the EIT with the drilling quently, in terms of emissions, EIT is comparable to the performance of the established drilling methods. established drilling and sawing processes. Due to the process, a higher drilling performance can With regard to dust generation, it can be stated that be achieved with a hammer drill for vertical work than for the use of water as a liquid dielectric means that the dis- horizontal work as a result of the higher contact pressure. solved material is bound directly in the process chamber. With the EIT, the same cutting performance can be achieved As a result, a virtually dust-free demolition process can be for both vertical and horizontal work, since the dead weight assumed. of the device has no influence on the cutting performance. Table 10 shows that at a frequency of 25 Hz, 45% of the Electricity consumption at EIT drilling performance of a vertical hammer drill and even 90% of a horizontal hammer drill can be achieved. If the A sufficient supply of electricity must be ensured for the drilling performance of the EIT is compared with that of operation of the Marx generator. To determine the actual core drilling, the clear comparability of the two methods can power requirement of the EIT, the measurements of the 1 3 Asian Journal of Civil Engineering Table 11 Extrapolation specific energy and electricity consumption of the EIT by dissolving sand-lime samples (Otto et al., 2021) Frequency Duration for Dissolving Energy per Dissolving Energy per Specific Electricity Electricity EIT 5 impulses performance minute [J] performance hour [J] energy per consump- consumption 3 3 3 [s] per minute per hour [cm ] hour [J/cm ] tion per hour per m [kWh] [cm ] [kWh] 10 Hz 0.5 495.00 59,400.00 29,700.00 3,564,000.00 120.00 0.99 33.33 25 Hz 0.2 1237.50 148,500.00 74,250.00 8,910,000.00 120.00 2.48 33.33 Table 12 Extrapolation specific energy and electricity consumption of the EIT by dissolving concrete sample (Otto et al., 2021) Frequency Duration for Dissolving Energy per Dissolving Energy per Specific Electricity Electricity EIT 5 impulses performance minute [J] performance hour [J] energy per consump- consumption 3 3 3 [s] per minute per hour [cm ] hour [J/cm ] tion per hour per m [kWh] [cm ] [kWh] 10 Hz 0.5 452.40 122,902.00 27,144.00 7,374,120.00 271.67 2.05 75.46 25 Hz 0.2 1131.00 307,255.00 67,860.00 18,435,300.00 271.67 5.12 75.46 laboratory tests were used and extrapolated for continuous incompatibility) carried out as part of the research project use on a construction site. Based on the laboratory tests it have shown that in the direct near field (distance of 1 m) to became clear that with 5 pulses 4.13 cm of a sand-lime the pulse electrode, the electric and magnetic fields are not brick sample and 3.77 cm of a concrete sample can be dis- critical for humans. Nevertheless, the operating personnel solved with one pair of electrodes. Assuming a continuous of a hand-held EIT unit as well as an EIT attachment should dissolving process, a dissolving capacity of 1237.5 cm of a always maintain a minimum distance of 1 m from the elec- sandstone and 1131.0 cm of a concrete can thus be achieved trodes. The distance can be ensured by a design solution on in 1 min (cf. Tables 11, 12) (Otto et al., 2021). The specific the device. energy for the dissolving power is 120 J/cm for the sand- lime brick sample and 272 J/cm for the concrete sample. These results from the basic tests were used to extrapolate Conclusions and outlook the electricity consumption. Table 11 extrapolates the spe- cific energy and electricity consumption of the EIT for dis- Within the framework of the research project, it was possible solving sand-lime brick and Table 12 for dissolving concrete. to demonstrate on the basis of basic tests that the EIT can As the frequency of the EIT increases, so does the spe- be used in the construction industry. The limits of the tech- cific energy required. Due to the higher strength of concrete, nology for use in the construction industry were also made a higher specific energy is required for deconstruction com- clear. When considering the results, it is important to keep in pared to sand-lime bricks. mind that they only address a limited scope of investigation. The experiments were limited to the laboratory environment. Safety and health conditions In addition, when considering the results, it should be noted that they only cover a limited scope of the investigation. Safety and health protection are of immense importance, The experiments were performed in a laboratory setting. The especially in dismantling operations, as the field of activity boundary conditions and the building materials used were is one of the most hazardous in the construction industry. limited as a result. However, it is becoming clear that EIT It has already been made clear that EIT can be considered technology still has great research potential. advantageous in terms of emissions compared to established The subsequent findings form an important basis for demolition and separation methods. In addition, the effects further research projects and a concomitant concretization of the electrical current and high-voltage pulses must be of the EIT technology for applications in the construction considered in terms of safety and health. industry: All electrical components of a hand-held EIT device or an EIT attachment for a mini-excavator or demolition robot • The construction site environment, especially for build- must be EMC-tested by the manufacturer (EMC = elec- ing projects in existing structures, as well as the cost tromagnetic compatibility). A corresponding certificate aspect only allow the use of industrial water as a dielec- must be available for each electrical component. The EMC tric. Service water is available in sufficient quantities on and EMCU measurements (EMCU = electromagnetic construction sites, a closed water circuit allows only a 1 3 Asian Journal of Civil Engineering small amount of water to escape, and subsequent treat- A third aspect is the utilization of the selectivity of the EIT. ment of the service water is easily possible using estab- Here, the focus is on the selective removal of mineral layers, lished processes. e.g., plaster layers, or the separation of already broken-off rock According to previous investigations, the electrode spac- according to the individual components, e.g., masonry and ing should be 25 mm. This distance ensures that the elec- plaster. Thus, the subsequent effort for separating and recy - trical flashover takes place in the mineral building mate- cling the building material is reduced and can be automated. rial. With a larger electrode spacing, the probability of Finally, it can be summarized that the results of the electrical flashover in the material decreases (based on research project show interesting potentials of EIT for use punctual tests with 5 pulses). A lower electrode spacing in the construction industry and form the basis for further increases the specific energy. research and development for the elaboration of application- The maximum number of pulses at one point should not ready solution concepts in different areas of the construction exceed five pulses for an efficient dissolution process. A industry. EIT will not be a fundamental substitute for estab- higher number of pulses increases the specific energy lished demolition methods for massive mass structures, but requirement. With a lower number of pulses, the over- will rather be considered as a demolition technology that can cut, which is important for repositioning the electrodes be used for special boundary conditions. The continuation of (horizontally as well as vertically), cannot be ensured. the research work is considered to be promising. For the most energy-efficient removal of mineral build- Acknowledgements Authors express their sincere gratitude to the ing materials, the pulse energy should be between 72 and Federal Institute for Research on Building, Urban Affairs and Spatial 80 J (based on the selected test setup). At lower pulse Development (BBSR) at the Federal Office for Building and Regional Planning (BBR) for funding the preceding research project (SWD- energy, no dissolution process of mineral building mate- 10.08.18.7-18.18) through the research initiative ZukunftBau. We also rials can be ensured. thank our industrial partners: EUROVIA Verkehrsbau Union GmbH, EBF Dresden GmbH, Thomas Werner Industrielle Elektronik e. Kfm. Overall, the basic tests made it clear that EIT can be used (WIE), homilius bohren & umwelttechnik, Institut für Angewandte Bauforschung Weimar gGmbH (IAB), Institut für leichte elektrische as a deconstruction method in the construction industry. The Antriebe und Generatoren e. V. (ILEAG), Institut für Arbeitsschutz economic field of application of the process does not lie in der Deutschen Gesetzlichen Unfallversicherung e. V. (IFA) and Beruf- large-measurement removal (total demolition, mass removal), sgenossenschaft der Bauwirtschaft (BG Bau), Germany. but in drilling and cutting processes as well as in surface Author contributions All authors contributed to the study conception treatment. and design. Material preparation, data collection and analysis were Automation of the EIT is conceivable for uniform surface performed by LH, FL, EA and MV. The first draft of the manuscript removal. Conventional demolition methods often do not allow was written by LH and all authors commented on previous versions of for automation, because the mechanical demolition causes the manuscript. All authors read and approved the final manuscript. vibrations in the carrier. With the EIT, the material is only Funding Open Access funding enabled and organized by Projekt DEAL. subjected to tensile stress and only a low contact pressure on The research project was funded by the ZukunftBau Research Initiative the material has to be ensured by the carrier device or a frame. of the Federal Institute for Research on Building, Urban Affairs and The results of the research project provide many start- Spatial Development. The authors declare that no funds, grants, or other support were received during the preparation of this manuscript. ing points for further research and development. On the one hand, the further development of a hand-guided device Data availability The authors declare that the data can be made for small applications in the field of sawing, slitting or also available. damage-free exposure of reinforcement is recommended. On the other hand, the use of higher pulse energies, pulse volt- Declarations ages and the simultaneous parallel use of a large number Conflict of interest All authors certify that they have no affiliations of electrode pairs can create the possibility of significantly with or involvement in any organization or entity with any financial increasing the productivity of the process and approaching interest or non-financial interest in the subject matter or materials dis- the performance values of competing processes. Further cussed in this manuscript. The authors have no relevant financial or research is needed at this point with regard to the technical non-financial interests to disclose. implementation of the equipment. The dissolving perfor- Open Access This article is licensed under a Creative Commons Attri- mance can be improved through a technological improve- bution 4.0 International License, which permits use, sharing, adapta- ment, but it must also be taken into account that use on the tion, distribution and reproduction in any medium or format, as long construction site and the prevailing conditions there can have as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes a negative effect. were made. The images or other third party material in this article are included in the article's Creative Commons licence, unless indicated otherwise in a credit line to the material. 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Journal
Asian Journal of Civil Engineering – Springer Journals
Published: Mar 6, 2023
Keywords: Electric-impulse-technology (EIT); Building in stock; Selectivity; Deconstruction method; Recycling