© 2012 ISCOWA and SGI. All rights reserved.
Risk Assessment and Life Cycle Assessment of Reclaimed Asphalt
Yue HUANG1, Tony PARRY1, Matthew WAYMAN2, Ciaran MCNALLY3, Yvonne ANDERSSON-SKÖLD4, Ola WIK4, Anja ENELL4, Roman LICBINSKY5
1University of Nottingham, UK, y.huang@nottingham.ac.uk, tony.parry@nottingham.ac.uk
2Transport Research Laboratory, UK, mwayman@trl.co.uk
3University College Dublin, Ireland, ciaran.mcnally@ucd.ie
4Swedish Geotechnical Institute, Sweden, yvonne.andersson-skold@swedgeo.se, ola.wik@swedgeo.se, Anja.Enell@swedgeo.se
5Transport Research Centre, Czech Republic, roman.licbinsky@cdv.cz
Abstract
The use of reclaimed asphalt (RA) in pavement construction can conserve natural resources and reduce impacts (e.g. CO2 emissions) on the environment. However, old pavements exposed to vehicle exhaust, tyre and brake wear, and fuel spillage over many years, potentially contain hazardous substances. The contamination rate can be higher in urban areas where a large part of RA derives from utility works, and the problems with contaminated RA can be greater in Eastern Europe where the use of tar binder continued into the 1990´s. Uncertainties regarding the performance of RA (environmental, mechanical, etc) currently results in a substantial part of it being mixed into unbound granular layers or other low-grade applications.
In order to use RA in high value applications such as surface course asphalt, one must be able to scientifically quantify the health and environmental risks associated with such applications. Re-Road, a European FP7 project, is developing tools that can be used to assess these risks. The assessment will encompass the whole life cycle of RA such as production (e.g. milling), processing and handling (e.g.
crushing, screening and storage), mixing, use in pavement, and recycling.
Risk Assessment and Life Cycle Assessment (LCA) are used to understand the potential health and environmental impacts of the processes involved. The main tasks include:
1) Modelling the release, transport and distribution of contaminants (e.g. particles, fumes, water- borne emissions) to conduct exposure assessments;
2) A number of laboratory experiments (e.g. leaching and ecotoxicity tests) and field studies (at different stages of the life cycle of RA) will be conducted to produce the inventory of emissions from RA;
3) Compiling and characterising the results from the laboratory and field studies for further usage in the risk assessment models and in the LCA study; and
4) Sensitivity analysis as to how these impacts would vary across Europe and the relative importance of different stages in the life cycle.
This paper outlines as a baseline scenario, the experiments that will be conducted, the datasets that will be compiled and how they will be used in the assessment of risk and environmental impacts, such as global warming potential, human health and ecotoxicity.
Keywords: Risk Assessment; Life Cycle Assessment; Reclaimed Asphalt; Pavement Surface Course
1 Introduction 1.1 Background
The use of reclaimed asphalt (RA) in pavement construction can conserve natural resources and reduce impacts (e.g. CO2 emissions) on the environment. However, studies (Legret et al., 2005) have found contaminants present in RA, such as polycyclic aromatic hydrocarbons (PAH) from gasoline or tar binder, zinc, copper and nickel from tyres and brake lining. This is compounded by the deposition of further contaminants from wear of road furniture (e.g. crash barriers). Abraded RA particles due to traffic wear contain such contaminants. These particles may be transported by wind, road run-off or by water infiltrating the pavement; and the risk could be higher if ravelling is to occur (e.g. during recycling). The contamination rate can be higher in urban areas where a large part of RA derives from utility works, and the problems with PAH contaminated RA can be greater in Eastern Europe where the use of coal tar binder continued into the 1990´s. Tar contaminated asphalt is classified as hazardous waste (EC, 2000) and reuse is restricted throughout the European Community, although limit values and restrictions on reuse vary by country. Incorrect handling of RA may result in contamination of otherwise high quality pavements and thus hinder the preservation of binders and aggregates for future use. Uncertainties regarding the performance of RA (environmental, mechanical, etc.) currently results in a substantial part of it being mixed into unbound granular layers or other low- grade applications (Mollenhauer, 2011, EAPA, 2010). In order to use RA in high value applications such as surface course asphalt, the decision makers must be able to scientifically quantify the health and environmental risks (if any) associated with such applications over the service life of a pavement.
This includes understanding what the critical points are and identifying where a potential benefit becomes a drawback.
1.2 Life cycle assessment
Life cycle assessment (LCA) allows quantification of environmental benefits (and burdens) of using RA in bound layers, and comparison with other waste management options. An asphalt pavement‟s life cycle (Figure 1) can be defined to have the following four stages:
Figure 1. Life cycle of asphalt pavement
1) Asphalt production from new raw materials; 2) paving and in service use (including maintenance);
3) dismantling of the pavement (waste generated) and, 4) production of RA-material (crushing, sieving, high/low grade use applied).
Activities or processes taking place at different stages will result in interactions with the environment, in the form of resource consumption (energy, raw material, etc.) and/or emissions of hazardous substances to human health and the environment. The LCA results, either as an input- output inventory or characterised impact indicators, can be presented against these stages and enable sensitivity analysis of the „hot spot‟ areas, and reduction measures can be prioritised accordingly.
1.3 Risk Assessment
When asphalt is recycled, two sources of contaminants are prominent: 1) chemicals intrinsically present as constituents of bituminous materials may be available for leaching from the broken bound materials, 2) contaminants that build up over the service life of the pavement may be transferred into any new pavement. Previous research by Münch has shown that bituminous layers can release potentially significant quantities of PAH (Münch, 1993). Some PAH are known to be carcinogenic to
New material
Paving, In service use RA
production
Asphalt production
Resource consumption
Emissions
Dismantling
Waste Downgrading
humans. Exposure to heavy metals such as arsenic, cadmium, lead and mercury can also have adverse health effects. Coal tar is classified in the CERCLA (Comprehensive Environmental Response, Compensation and Liability Act) National Priority List (NPL) of Hazardous Substances (CERCLA, 2007). Bitumen has now replaced tar as the asphalt binder, even so, other additives such as crumb rubber (Azizian et al., 2003), organic substances and concentrations of less harmful metals such as vanadium, nickel, iron, magnesium and calcium have been identified (Lindgren, 1996).
The CERCLA list is based on the following algorithm, which takes into account: 1) frequency of occurrence of the substances at NPL hazardous waste sites and facilities, 2) toxicity of the substance, and 3) concentration of the substance and the potential for human exposure to the substance.
SCORE = NPL Frequency + Toxicity + Potential for Human Exposure
This paper reviews the knowledge gap of LCA and risk assessment undertaken for road pavement using RA, outlines a European collaborative research project that aims to fill this knowledge gap, experiments that will be conducted, datasets that will be compiled and how they will be used in the assessment of risk and environmental impacts, such as global warming potential, human health and ecotoxicity. Some preliminary results of LCA on baseline construction scenarios are also presented.
2 Gap analysis
LCA studies have been undertaken in the past 20 years to investigate the impacts associated with pavement construction; most such studies concentrated on energy consumption, air emissions and waste from other industries (Birgisdóttir et al., 2006, Hakkinen and Makela, 1996, Huang et al., 2009, Stripple, 2001). These studies provide a useful framework for undertaking LCA research on road pavements. However, they do not cover all aspects of the use of pavement across its life cycle, especially in the end-of-life scenarios. Non-energy related impacts (e.g. leaching, fuming) are typically excluded. The health and safety aspects of bitumen and asphalt handling have been studied; most of these studies are based on point of compliance (POC). In other words, no account is taken to study where the RA is put back to use, or the confinement/release of contaminants to humans and the environment. The challenges of expanding current LCA/risk assessment studies to include the RA use in asphalt are summarised below.
Material characterisation: If data on the total content of the substances in extracts of RA are available, predictions of emissions potential and environmental fate can be made, although this may overestimate the bio-accessible fraction of the contaminants, especially in large particles. Nowadays, two main methods are used to study such emissions. The first evaluates exposure to asphalt fumes at road sites during construction, by measuring the semi-volatile organic compounds (SVOC), total particulate matter (TP), benzene soluble matter (BSM) and PAH concentrations (Deygout and LeCoutaller, 2010, Cirla et al., 2007, Ruhl et al., 2007, Hugener et al., 2009). This type of measurement is necessary to assess the occupational hazards to workers on sites, but they are largely influenced by uncontrollable variables such as weather conditions (Kenny et al., 1997) or the proximity to road traffic. Moreover, fume measurements on site cannot be used as prediction tests to forecast the emission potential of different asphalts (hot/warm mix). The second method analyses emissions from laboratory fume generators (Kurek et al., 1999, Brandt and deGroot, 1999, Bonnet et al., 2000, Brandt et al., 2000, Binet et al., 2002, Hugener et al., 2007, Gasthauer et al., 2007). Brandt (Brandt and deGroot, 1999) demonstrated the influence of temperature on bitumen volatility and BSM emissions. However, these laboratory studies concerned the fumes from bitumen, not asphalt mixture.
Compositional change: Ageing of binders during hot mix production and pavement life may alter their chemical and toxicological properties, which complicates the assessment of RA. Contamination of RA with metals and organic substances during pavement life is another important factor, especially for porous asphalt pavements where more deposits can find space in the open graded mixture. The inclusion of complex additions with unknown or unidentified substances such as vehicle exhaust, tyre and brake wear, and fuel spillage represents a major challenge. In this case, analytical screening
methods can be of value, which if used alongside toxicological tests, can provide basic information on properties of the substances that are incorporated in or emitted from RA (Azizian et al., 2003).
Pathway modelling: Fumes from hot mix asphalt manufacturing contain a particulate fraction and a gas fraction (Gaudefroy et al., 2010). The rate of emission of fumes and vapours from binders during hot mix manufacturing is principally related to the heating temperature. Leaching of organic substances from asphalt can be expected to be controlled by the concentration and rate of diffusion in the binder phase, which is related to molecular size of the substances, viscosity of the bitumen, and the RA particle size and exposure to precipitation. This is compounded by the unknown fate of the RA, its storage and secondary use, although this can be modelled using typical scenarios.
3 Re-Road methodology
Re-Road, a European Framework Program (FP7) project (2009-2012), is looking at the use of RA in pavement surface course. Work package 3 (WP3) is developing tools that can be used to assess life cycle impacts and risks of using RA to humans and the environment. The assessment will encompass the whole life cycle of RA such as production (e.g. milling), processing and handling (e.g. crushing, screening and storage), mixing, use in pavement, and recycling. The purpose is to supplement existing modelling of such impacts with state of the art experimental data on all aspects of the RA life cycle.
The majority of the data will be sourced from the project‟s other technical work packages (Table 1).
The life cycle attributes will then be assessed relative to conventional asphalt pavements made from virgin materials and other end-of-life options for RA.
3.1 Work Package 3 outline
Table 1 summarises the data that will be sourced from Re-Road WPs. The key actions include: 1) a thorough risk assessment that considers the range of ways in which contaminants can be introduced to the environment, e.g. vapours, fumes and water-borne contaminants; 2) variables that influence the risk assessment, e.g. RA content, particle size of RA, liquid to solid ratio (L/S), will be tested in the laboratory to investigate their effects. Analytical methods have also been identified for quantifying these parameters; and 3) results from selected field experiments, e.g. dust, leaching, will feed into the LCA study, and will be equated to established impact assessment indicators.
Table 1. Summary of data expected from Re-Road work packages
RA parameter Data format Re-Road source Material
consumption
Constituent quantities (kg) per tonne of asphalt
WP2 mix recipes Energy
consumption
Energy consumption by fuel type per tonne of RA/asphalt
WP4 energy consumption at plant WP3.2 energy consumption of extraction, processing and transportation
Particulate emissions
kg per tonne of pavement milled WP1.3 milling off and handling WP3.2 in use wearing
Fumes and vapours (type & quantity)
mg of carbon equivalent per kg of bitumen or asphalt
WP1.3 emitted vapours from hot mix manufacturing WP3.2 stack emissions
Leachates (type &
quantity)
mg per litre, mg per square metre of sample surface or mg per kg of dry matter
WP1.3 unbound RA in stockpile WP3.1 RA in the road structure Pavement
durability
Estimates of durability (years) of the pavement with RA
WP5 performance modelling
3.2 Life cycle assessment in Re-Road
LCA in Re-Road follows the four-phase approach prescribed by ISO 14040 (ISO14040, 2006). The aim of the LCA is to investigate the environmental impacts of using RA in pavement surface asphalt.
The functional unit for this study is defined as a 1m2 of road surface over a 60-year service life.
Material quantities, to provide this function in different applications (e.g. foundation, base, binder or
surface course), are calculated. The full life cycle of the pavement is included but impacts associated with traffic use are excluded, assumed to be identical for pavements with and without RA. The pavement will be designed to traffic levels established by national guidance of participating countries.
An important task is to obtain the best possible data and confirm its relevance, i.e. to verify that the data is obtained on representative material recipes and construction processes.
Life cycle inventory analysis: A baseline scenario is established; 15% RA in SMA surface course (11mm maximum coarse aggregate size and a polymer modified bitumen) using typical quarry materials, representative average transport distances and energy consumption. Initial scenarios will be new build rather than maintenance, to allow for the impact of recycling RA to the sub-base to be evaluated in the model. The initial model is prepared in SimaPro (a commercially available LCA software program). The model will go through validation and refinement as new datasets become available from other WPs. For comparison, the principal variations are summarised below:
Materials:
o RA rate: 0%, 15% and 30%, to find optimal content in practice.
o Additives in the mixture to facilitate RA use, e.g. binder rejuvenators.
o Country specific recycling levels.
Transport:
o Mode and distance: dependent on the material source.
o Tipping points: where is the benefit of using RA countered by excess transport?
Energy consumption:
o Plant efficiency if altered to accommodate RA, mainly to counter the higher moisture content typically present in RA as opposed to virgin aggregates.
o Effect of using warm mix asphalt that uses less energy and liberates less volatile hazardous substances but requires additives.
o Country specific energy mixes.
Lifetimes:
o Durability: the life time performance of RA asphalt compared to virgin asphalt;
o End-of-life scenarios: RA for surface course asphalt compared to unbound layers or other low-grade applications.
Life cycle impact assessment: The Institute of Environmental Sciences impact assessment method (CML2001), which is built-in SimaPro, is used that includes the following impact categories:
Abiotic depletion Human toxicity
Acidification Marine aquatic ecotoxicity
Eutrophication Ozone layer depletion
Fresh water aquatic ecotoxicity Photochemical oxidation Global warming potential (GWP100yrs) Terrestrial ecotoxicity
Interpretation: So far, a tonne of surface course asphalt (3% SBS + 6% fibre modified binder) containing 15% RA is modelled in SimaPro using assumptions and data found from literature:
Transport distance (>16t lorry) for ingredient materials: 30km aggregates, 100km limestone filler, 10km RA and asphalt mixture, 200km bitumen, SBS and emulsion, 750km fibre;
Asphalt mixing is based on an 85kWh plant with output capacity of 160t/hour and waste gas 5,000m3/hour (VDI-RICHTLINIEN, 2008). Rate of emissions of PAH is sourced from a study using the closest available data for 10% RAP with a 100t/hour capacity (Ventura et al., 2007);
Eurobitume inventory data for base bitumen (Eurobitume, 2011);
Data on PAH and heavy metals leaching from RA incorporated asphalt in place is available from a study by LCPC: column test, 4L, density: 2.4t/m3 (Legret et al., 2005); Data on PAH leaching from bitumen (representing the worst case scenario for bituminous materials in place) is available from a study in USA: GC-MS test, average of six paving materials (Kriech et al., 2002);
Data for bitumen storage is available (VDI-RICHTLINIEN, 2008), but not used in this study, since the Eurobitume inventory for bitumen includes the storage (Eurobitume, 2011);
Particulate emissions from asphalt placement are sourced from a LCPC study (Jullien et al., 2006) assuming a 50m3/hour output for surface course (using the average of 10% RAP and 20% RAP);
Energy consumption for asphalt placement is sourced from the ECRPD project (ECRPD, 2010), and the emulsion (0.2kg/m2) for tack coat from Akzo Nobel (James and Thorstensson, 1996) and Swedish Environmental Research Institute (IVL) report (ramp width: 2.5m) (Stripple, 2001);
Leaching from RA stockpile: data available from LCPC column (L/S: 0.5, day 2, density: 1.6t/m3) and batch (L/S: 10, density: 1.6t/m3) tests (Legret et al., 2005), Chalmers column (L/S: 0.05) and batch (L/S: 100) tests (Norin and Strömvall, 2004); leaching from asphalt: data available from Dutch batch (L/S: 10, density: 1.6t/m3) tests (Brandt and de Groot, 2001).
The full LCA model was run to compare the influence of the data from different sources for leaching from RA stockpile, and using the LCPC results for asphalt in place. It should be noted that these literature data are based on tests of varying conditions (e.g. L/S) and on different samples (e.g.
bitumen, asphalt, RAP) and thus any comparison between the results must be made with care.
1. Leaching from asphalt in place is negligible in all impact categories when the LCPC column method results are used.
2. The results are not sensitive to the method chosen for RA in stockpile, except the „fresh water aquatic ecotoxicity‟ category, where the Chalmers batch method gives the highest results (15%
higher compared to other leaching test methods). In other words, leaching from RA in stockpile is negligible in the full pavement life cycle unless the Chalmers batch method result is used.
3. Benzo(k)fluoranthene contributes to 49% of the „fresh water aquatic ecotoxicity‟ category in the Chalmers batch test. In general, batch tests will overestimate concentrations of PAHs with high molecular weights compared to percolation (column) tests. This is due to the fact that there are often more particles left in the eluates from batch tests compared to the percolation eluates, after separating the solid phase from the liquid phase. The similar “effect” was discovered in Re-Road WP3.1 batch tests with RA (Enell et al., 2012). Thus the concentration of B(k)F measured from Chalmers batch test, which belongs to the PAH-H group, may not be the true dissolved fraction, but a fraction adsorbed to particles.
3.3 Risk assessment in Re-Road
Contaminants can be leached from RA stockpiles or RA-incorporated pavements in place. The RA handling can lead to new types of emissions, e.g. fuming, dust. In order to determine which substances to focus on, the CERCLA rankings and the substances in Annex II of Directive 2008/105/EC are considered. The emissions considered can be divided into three categories based on the pathway medium (i.e. release in a solid, gaseous or liquid phase):
Emission of Particles: Particulates and dust can be released as a result of wear of the road surface, or during handling of RA. Released particles can be of various sizes, from small breathable particles (PM10, PM2.5) to RA aggregates of several centimetres. Breathable particles are in general considered toxic, independent of their content and level of contamination and thus the amount (or concentration) of such particles in ambient air is often regulated, e.g. Council Directive 1999/30/EC. Large particles tend to settle to the ground by gravity whereas small ones (less than 1 micron) can stay in the atmosphere for weeks and are mostly removed by precipitation.
Emission of Fumes and Vapours: Several measurement campaigns have been conducted to assess the occupational exposure to hot mix asphalt and fumes (Allison et al., 2006). These studies usually revealed a low hazard level associated with the pollutant emissions, although detection of carcinogenic compounds such as benzo(a)pyrene has shown the need to remain cautious and to continue monitoring. The frequent updates of carcinogenic compound classifications, the decrease in threshold exposures and the advent of REACH (Registration, Evaluation, Authorisation & restriction of CHemicals) and CPR (Construction Products Regulation) regulations require both responsiveness and
the proactive use of effective devices for asphalt fume studies. The road industry is concerned, since bitumen is often used at temperatures of around 160°C. Asphalt fumes contain a particulate fraction and a gas fraction, see Figure 2 (Gaudefroy et al., 2010). The organic part is called Total Organic Compounds (TOC), which contains two groups: an organic aerosol contains all the airborne organic particles (the BSM), and a volatile and semi-volatile organic compounds (VOC, SVOC). Both groups contain PAH, which are detected as particles in the BSM fraction or as gas in the SVOC fraction. In general, emission of fumes and vapours during milling and crushing is assumed to be negligible compared to emissions during heating and paving.
Figure 2. Composition of fumes emitted during hot mix asphalt manufacture (Gaudefroy et al., 2010).
Emission of leachate: Emissions of substances due to leaching are assessed when: 1) RA is stored in stockpiles, and 2) RA is in place in the pavement. The mode of water contact with RA (e.g.
percolation through a RA stockpile or leaching from the surface of a road) is of special importance and depends both on material properties (e.g. porosity, particle size) and design (e.g. bound or unbound).
The risk assessment will be based on leaching data obtained from both laboratory and field studies to cover both of these scenarios. Only chemicals with toxicity data or limit/guideline values, e.g. PAH, heavy metals, are assessed.
4 Re-Road testing program
4.1 Airborne emissions from the mixing process
Researchers at IFSTTAR (French Institute of Science and Technology for Transport, Development and Networks) have developed a laboratory fume generation system (Paranhos, 2007, Viranaiken et al., 2010) which eliminates the fume condensation risk by adding heating devices, and a specific sampling system dedicated to the SVOC and BSM fractions, so as to forecast the amount and nature of fumes generated by bituminous mixtures in different emission scenarios. The system is designed to mimic the different steps of hot or warm mix asphalt emissions from manufacture to laying on road sites. It consists of an asphalt mixer which allows preparation of 80kg of asphalt mixtures to the EN 12697-35 standard. Aggregates and bitumen are mixed at the required temperature, at a defined stirring speed, for a specific time. A stainless steel stack has been linked to the mixer in order to collect fumes emitted from the mixture (see Figure 3) (Gaudefroy et al., 2010, Paranhos, 2007).
After generation and transport in the stack, fumes reach the sampling area at the top of the stack where two probes are linked. The first probe enables staff to sample the TOC with a portable measuring equipment. The second probe is dedicated to the SVOC and BSM fractions. The PAH trapped on sorbents are measured by Gas Chromatography Mass Spectro- metry (GC-MS) or High Perfor- mance Liquid Chromatography (HPLC) after extraction of the
sorbent. Figure 3 View of IFSTTAR mixer and stack for asphalt
4.2 Laboratory testing of leaching
The laboratory testing of leaching comprises evaluation of three different leaching tests: percolation test (CEN/TC351, 2009), batch test (CEN-ISO/TS21268-1) and percolation test with recirculation (Gamst et al., 2007). The percolation test is conducted from an L/S ratio of 0.1 to 10 L/kg in order to study how the leached concentrations of metals and PAHs will change over time (i.e. during increased infiltration of water). Several different types of RA are being characterised with this test to cover a broad spectra of materials and the leachates are further characterised by ecotoxicological tests (Enell et al., 2012).
4.3 Field testing of leaching
Leaching from stockpile: The experiment was designed to sample seeping water from repository where milled RA is stored for limited time and prepared for reuse. RA repository was chosen as the best environment for characterisation of possible leaching of harmful compounds under real conditions. Specific sampler that represents an upgrade of the device referred to in the literature was used for sampling seeping water from an unsaturated zone, by injecting pressure gas. This sampler joins together two different approaches for soil porous water and ground water sampling, namely square lysimeter and Gillham principle of pneumatic sampler. Meteorological conditions including temperature, relative humidity, solar radiation and the amount of rain fall were monitored during the whole period of experiment. Chemical composition of rain fall was also determined to eliminate input of observed compounds from rain fall for proper characterization of leaching processes in the repository. Collected samples of seeping water, rainfall water and bulk material composition were analysed by ICP-MS (inductively coupled plasma mass spectrometry, for metals) and GC-MS (for organic compounds), to identify the content of selected organic and inorganic compounds, and to characterise possible effects of water on living organisms with ecotoxicological test.
Seeping water collected during the first sampling campaign was typical with very high concentration of Zn and high concentrations of Sb, Ni and Ba. It also contained high concentrations of dissolved organic carbon (DOC) and TOC, which indicates high pollution by organic compounds. Seeping water from the second sampling campaign contained in many cases different concentrations of substances compared to the first sample. Only concentrations of Cu, Mo, Pb, V, Cd and DOC were roughly similar in both samples. Concentrations of Ba, Cr, Zn, TOC and the value of turbidity were substantially lower in the second sample. Seeping water collected from the first sample contained higher concentrations of almost all analysed PAH. Total PAH concentration was nearly fivefold higher in the first sample. Concentrations of some PAH, such as acenaphtene, fluoranthene and pyrene, were found orders of magnitude higher. Seeping water was found of low impact on living organisms from performed ecotoxicity tests since limited values for all measured parameters were observed.
Asphalt mixer
Heated stack Sampling plan TOCe heated sampler
Asphalt mixer
Heated stack Sampling plan TOCe heated sampler
Rainfall simulator testing of RA: A specially designed rainfall simulator to mimic Irish rainfall conditions will be used to evaluate the transport of contaminants through pavement and in road runoff In reality, natural precipitation is the hydrological force controlling the actual loss and transport of contaminants from RA. It is thus essential in the research environment that the hydrological conditions be both controllable and repeatable. Such experimental control can only be attained using physically simulated precipitation. By analysing the water collected for some or all of the contaminants detected in the laboratory leaching experiments, testing will enable the examination of the effects of rainfall characteristics such as intensity and volume, on the types and quantities of contaminants released from RA. The different polluting potential of RA stockpiles and pavements with varying RA content could also be investigated using the rainfall simulator.
5 Conclusions and future work
Old pavements exposed to vehicle exhaust, tyre and brake wear, and fuel spillage over many years or contaminated by additives, potentially contain hazardous substances in particular PAH and heavy metals. Risk Assessment and LCA are used to understand the potential health and environmental impacts of the recycling process. Baseline models for LCA and risk assessment of pavement have been established for the Re-Road project, with literature data. This forms the basis of the conceptual model for assessing the reuse of RA, although it will be refined through the application of new experimental data gathered throughout the project. It is anticipated that the main output of this work will be a model capable of describing the physical and chemical processes involved in the migration of contaminants from the RA material into air and water, as both dissolved and particle-bound contaminants will be considered. Re-Road aims at exploring the use of RA in high value applications such as asphalt and pavement surface. The main tasks of work package 3 include:
1) Modelling the release, transport and distribution of contaminants (e.g. particles, fumes, water- borne emissions) to conduct exposure assessments;
2) A number of laboratory experiments (e.g. leaching and ecotoxicity tests) and field studies (at different stages of the life cycle of RA) will be conducted to produce the inventory of emissions from RA;
3) Compiling and characterising the results from the laboratory and field studies for further usage in the risk assessment models and in the LCA study; and
4) Sensitivity analysis of how these impacts would vary across Europe and the relative importance of different stages in the life cycle.
Whereas several studies have dealt with fumes from bitumen, there are no conclusive results found on the emissions from hot bituminous mixture. A special fume generation and sampling system has been developed to identify mixing parameters that could influence the fume and particulate emissions. From this, the organic compounds concentrations on site could be forecast by considering the thermal and mixing history of asphalt. Studying the impact of manufacturing parameters such as temperature, bitumen additives, RAP content and mix design will be the next step towards the understanding of the emissions from asphalt mixing process.
Leaching scenarios of pavement containing RA are defined; laboratory and field experiments are designed to simulate the movement of leachate in RA stockpile and pavement in use. Similar to fuming, parameters that affect leaching will be tested and modelled in a controlled manner that lead to prediction of future leaching behaviour. Initial LCA results of using RA in asphalt surface indicated that the leaching from asphalt in place is negligible, whilst the leaching derived from a RA stockpile is sensitive to the testing method. This will be verified when more parameters are tested and the primary data from Re-Road are fed into the LCA model.
Acknowledgements
This project is funded under European Community‟s Seventh Framework Programme (FP7/2009- 2012) under grant agreement no218747.
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