Removal of asbestos as an intrusive contaminant from concrete construction waste

The construction industry is the world's largest and fastest‐growing industry due to the increase in population, standards of living, and the higher demand for infrastructure. This fast growth generates huge amounts of construction and demolition waste (C&D waste), which amounts to more than 25% of the total generated waste, which has become a serious environmental challenge that needs to be addressed. The asbestos content in C&D waste poses a health risk and is entitled to special care, however, disposal of asbestos as hazardous waste is the only option by law. The present paper suggests the selective demolition of asbestos‐containing demolished waste rubble to be disposed of in compliance with all local and state regulations and proposes non‐asbestos rubble fraction to be recycled as an alternative sustainable management option that mitigates different adverse environmental impacts of the presently used conventional C&D waste management method.


Introduction
To consummate the necessity of a growing world population, the need for urban expansion, the connection between cities, and demand for the construction of buildings, residences, paving, urban maintenance, roads, and train lines are the least.The existing constructions need to be updated according to the updated and environmentally friendly construction laws, therefore rebuilding is often observed.The execution of such extensive engineering works requires the usage of millions of tons of natural resources, for example, aggregates, cement, water, wood, and various metals to name a few.To manage the need, exploration of natural resources reserve is carried out however, with this large amount of natural resource extraction, potential environmental impacts must be considered.At the same time, the scarcity of virgin raw materials has enhanced the importance of recycling building materials manyfold.The fast-growing need for construction and demolition generates huge construction and demolition waste (C&D waste).In general, the C&D waste amounts are more than a quarter of the total generated solid waste [1] [2].To manage huge amounts of C&D waste and to be able to be reused back in material flow is the absolute need of the current time.
Since the demolition of buildings and other infrastructure produces much more waste than construction activities, demolition projects often create 20 to 30 times as much waste as construction projects [3], the development of processes to effectively reuse and recycle demolition materials is important for reducing landfilled C&D waste as well as promoting circular economy.In the context of demolition waste, Crushed Concrete in particular is a popular recycling material.Recycling of concrete is often restrained due to the hazardous impurity contents, that are hard to separate as well as to recycle.Particularly, asbestos contamination came into focus after law enforcement and as an impact of various studies worldwide.Asbestos is found in various mineral products such as wall reinforcements, spacers, and tile adhesives, and poses unusually difficult to detect and separate as they form a strong bond with concrete.
As asbestos is categorized as carcinogenic and thus dangerous for human health therefore a ban is imposed on asbestos use since 1993 in Germany.The complete exclusion of asbestos must be observed in any new construction, as well as the rejection of asbestos in any of its fibrous configurations from the recycling route of concrete is mandatory.Eliminating asbestos in concrete recycling will result in increased concrete recycling with a better circular material flow cycle.
Using the deconstruction of the quay wall as an example, this paper presents different life cycle assessments for practicable sustainable options that focus on the potential CO2 footprint of the entire process from detection to the

Abstract
The construction industry is the world's largest and fastest-growing industry due to the increase in population, standards of living, and the higher demand for infrastructure.This fast growth generates huge amounts of construction and demolition waste (C&D waste), which amounts to more than 25% of the total generated waste, which has become a serious environmental challenge that needs to be addressed.The asbestos content in C&D waste poses a health risk and is entitled to special care, however, disposal of asbestos as hazardous waste is the only option by law.The present paper suggests the selective demolition of asbestos-containing demolished waste rubble to be disposed of in compliance with all local and state regulations and proposes non-asbestos rubble fraction to be recycled as an alternative sustainable management option that mitigates different adverse environmental impacts of the presently used conventional C&D waste management method.
removal of asbestos and recycling of concrete.The application of Life Cycle Assessment in the building sector has improved a lot in recent years [4].The increased interest is due to the comprehensiveness of the LCA method for considering many aspects of the environmental impacts of a building [5].This paper uses the ReThiNK EPD app (developed by Kiwa Deutschland) to quantify the potential CO2 footprint and other environmental impact factors.

Life cycle assessment
There are different ways to gauge the amount of pollution emitted during every step of the life cycle of a building, however, the current paper focuses on the demolition and end-of-life stage in the construction industry.The Life Cycle Assessment (LCA) is an internationally standardized methodology for environmental assessment, applied to evaluate the environmental impact of a product or system [6][7].
This methodology can be used for modeling and simulation of waste management scenarios, in the present paper the ReThiNK app [8] is used for the assessment, while the required data for the life cycle inventory is either from the literature, the lab-scale experiments or surveying the recycling facilities [9][10].

Goal and Scope
The present study aims to quantify different environmental impact factors in the process of recycling the demolition waste produced, to assess impact categories for the two scenarios: selective demolition of asbestos-containing segment followed by wrecking the whole structure and recycling the non-asbestos part whereas the asbestos parts end up in controlled landfills; compared with asbestos contained construction that demolished at once and ends up at landfill that deal with hazardous waste: the scenarios are pictorially described in Fig. 1.The focal point is the selective demolition to restrict asbestos content to go further in material flow.

System Boundary
In the first step of LCA, the boundaries of systems are defined to identify inputs and outputs, to consider all processes, the input data on energy flows and material flows, and output data related to specific issues.In the present work, the system boundary falls into the end-of-life category, which comprises the demolition phase and evaluation of the recycling possibilities.

Inventory analysis
The inventory phase is collecting all sorts of information using surveys, calculations, and analyzing comparatively with studies from literature, for all the sectors involving materials, energy, and fuels.After data inventory collection and data normalization to the functional unit, the environmental impact was evaluated.
The designated demolition company and recycling facility were interviewed, and a survey was carried out, moreover, machine specifications and construction guidelines for specific asbestos-containing parts used were referenced for the literature data needed for the analysis.

Life cycle impact assessment
Life cycle impact assessment is the phase in the LCA aiming at understanding and evaluating the magnitude and significance of the potential environmental impacts of a product system.The life cycle of a product ranges from resource extraction via material processing, manufacturing, and product use or service delivery, to recycling, and the disposal of any remaining waste [11].In the present paper Global warming potential, ozone layer depletion, acidification of soil and water, eutrophication, and human toxicity are the environmental impact factors that are taken into account and assessed in the case of demolition and disposal or recycling of asbestos-contained construction.

Result and Discussion
Fig. 1 illustrates the two different scenarios with their system boundaries addressed and discussed in this paper.Scenario 1 depicts the demolition of a concrete structure that contains asbestos, after the inspection, the majority of dismantled concrete rubbles were landfilled in different landfill sites as per their hazardous nature.Whereas the second scenario describes the demolition of asbestos-contained parts after inspection that is disposed of in a controlled landfill designated for hazardous wastes leaving the non-asbestos concrete rubbles to be further recycled and reused.
Traditional demolition practices in which all building materials are mixed create a waste stream that is difficult and costly to recycle, in contrast, the separation of materials at the demolition site through selective demolition or other means is often the most effective way to ensure a clean, uncontaminated product [12].Since carcinogenic asbestos is involved in the present work, precise separation is obliged and proper handling is imposed by the law.

Global Warming Potential
Global warming potential, abbreviated as GWP, is a term used to describe the relative potency of a greenhouse gas, taking into account how long it remains active in the atmosphere.
Fig: 2 shows the global warming potential of both addressed scenarios, as calculated with the help of ReTHiNK web-based LCA software.The global warming potential for scenario 1 is 68,190876 kg CO 2 eq whereas for scenario 2 it is 87,7916149 kg CO 2 eq.It is evident that the recycling of a non-asbestos fraction of the demolished waste contributes an additional amount of GWP, however, a more circular material can be achieved with the recycling and reuse of non-asbestos demolished waste rubble i.e in scenario 2.

Ozone layer depletion
The ozone-depleting potential is a measure of how much damage a chemical can cause to the ozone layer compared with a similar mass of trichlorofluoromethane (CFC-11).CFC-11, with an ozone-depleting potential of 1.0, is used as the base figure for measuring ozone-depleting Potential [13].landfilling of huge C&D waste has an adverse effect on ozone layer depletion as one of the foremost environmental impacts.With a huge percentage of the pollution that can be attributed to the construction industry on a global scale reaching 50% in landfill waste, ozone depletion, and climate change gases, it is pivotal that the construction and demolition industry move forward in implementing preventive measures to decrease catastrophic effects [14].With a little high ozone layer depletion potential Scenario 2 limits landfill activities by choosing to recycle non-asbestos concrete rebel fraction to be reused further in the building industry, leaving behind only the asbestos part to be landfilled in a controlled, designated facility, and thus scenario 2 is a better situation to opt and practice.

Acidification of soil and water
Soil acidification is a process where the soil pH decreases over time and effect adversely soil and subsoil.The process is accelerated by human activities, unconscious agricultural activities, uncontrolled waste management, and dated landfilling actions to name a few.
Fig. 4 shows the soil and water acidification potential of both scenarios assessed in the present work.Scenario 1 has the value 0,45689576 Kg SO2 Equivalent, whereas a small increased value of 0,68325713Kg SO2 Equivalent is for scenario 2. Scenario 2 comprises a recycling activity and therefore it has a slight increase in acidification potential, however, in scenario 1 almost all the concrete rubble ends up in landfill sites that deal with asbestos and other hazardous material.It has been reported that more than 50% of construction and demolition waste is deposited in landfill sites, which forms a real environmental challenge for every country, that needs to be addressed [15].The enormous requirement of land for landfill purposes for growing demolition waste is a previously pointed problem, in addition, the probability of high pH leachate leaching from these landfill sites is another threatening issue to handle over time.Therefore, it is beneficial to recycle concrete rubble to enhance circularity rather disposing at a landfill site.

Eutrophication
An overabundance of nutrients, primarily nitrogen, and phosphorus in a water body leads to a process called eutrophication that has harmful health and environmental effects.
Figure 5 Eutrophication The eutrophication potential is presented in Fig. 5.The eutrophication potential for scenario 1 is 0,10328768 Kg PO4 Equivalent whereas for scenario 2 it is 0,14671303 Kg PO4 Equivalent.The difference in eutrophication potential for both scenarios is negligible even though the second scenario steps up substantially in circularity and as a result, the asbestos-free material flow can be achieved.

Human toxicity
The human toxicity potential (HTP), is used to weigh emissions inventoried as part of a life-cycle assessment, a calculated index that reflects the potential of a unit of chemical released into the environment.As asbestos exposure has carcinogenic potential and is thus banned from a major fraction of the developed world, quantifying the human toxicity associated with both scenarios is needful to perform.fraction, however, the recycling of non-asbestos fraction i.e, the asbestos-free material flow orients well with the aim of the present work as well as satiate the growing need for production of energy incentive construction materials.

Conclusion
Life cycle assessment with the help of the ReTHiNK app of asbestos-containing concrete demolition waste was done and demonstrated based on the primary data collected, for five main environmental impact categories.The study demonstrates two different scenarios, where in the first the major fraction of demolished waste ends up in a controlled landfill while the second one fosters the recycling of non-asbestos fraction and landfill only the asbestoscontaminated rubble.The five environmental impact factors that are assessed in the present study are slightly increased for the second scenario, however, the increased value corresponds to the recycling activity which facilitates better circularity in a bigger perspective.
The removal of carcinogenic asbestos content from the material flow can be achieved by selective demolition and disposal in compliance with all local and state regulations followed by the recycling of non-asbestos C&D waste contributes significantly to achieving sustainable development through the following gains: • Reducing the demand for primary materials by replacing them with secondary recycled (asbestosfree) materials.

•
Cut down energy consumption that corresponds to primary materials extraction, transport, and production energy costs, and reuses waste that can otherwise be lost to landfills and may lead to the severe environmental problem over an extended period such as toxic leachate leaches to soil, or water.Consequently, the land used, and several long-term adverse environmental effects can be avoided by limiting the landfilled waste quantity.

•
Although landfills will continue to be an important disposal option, especially for the asbestos-contained fraction until the proper recycling technique is developed and practiced for the same, the recycling of C&D waste will reduce the possible environmental risk by minimizing the amounts going to landfilling.

Figure 1
Figure 1 System boundaries for the scenarios

Figure 2
Figure 2 Global warming potential

Fig. 3
Fig.3shows the ozone layer depletion potential of both scenarios assessed in the present paper.Scenario 1 has the value of 1,32E-05 Kg CFC-11 Equivalent while scenario 2 has a little potential of 2,72E-05 Kg CFC-11 Equivalent.The slight increase in the second scenario is given the fact of the additional recycling process.

Figure 3
Figure 3 Ozone layer depletion

Figure 4
Figure 4 Acidification of soil and water

Figure 6
Figure 6 Human toxicityFig.6illustrates the human toxicity (cancer) potential for scenario 1 is 4,91E-07 CTUh while a slight increase is evident for scenario 2 and the value is 5,92E-07CTUh.The slight increase in toxicity potential resulting from the various activities involved in recycling and transporting the nonasbestos demolished