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WAM
Environmental benefits
of reducing asphalt
production and laying
temperature

Emission and occupational exposure at lower asphalt production and laying
temperatures
M. Lecomte
Shell Bitumen, 307 rue d’Estienne d’Orves, 92708 Colombes, Paris, France
F. Deygout
Shell Bitumen, RD3, BP97, 76650 Petit Couronne, France
A. Menetti
Contech, Italy
Summary
It is well known that reducing asphalt production temperatures has significant
environmental benefits on emissions, occupational exposures and energy
consumption. The hot mix asphalt industry has been aware of this for many years.
The biggest challenge however has always been to achieve adequate asphalt
mixture quality at lower or ambient operating temperatures.
In recent years, new production processes at temperatures between 80 - 120°C have
attracted much interest because of the possibility to approach or even obtain hot mix
quality and having reductions in energy consumption, emissions and occupational
exposures. Results of recent measurements on a site in Florence in Italy show that
decrease in temperature offers a dramatic reduction in greenhouse gases emission
and a considerable reduction of fume emissions and workers exposure, together with
a 30% energy reduction. This confirms the great potential of this solution for the
environment.
1. Introduction
Shell Bitumen is very active in the development of new technologies and in
investigations to properly quantify the environmental benefits [1-5].
This paper describes the results of recent emission and exposure studies carried out
at Conglobit during the production of their new asphalt mixture, Greenfalt,
manufactured at low temperatures and developed on the basis of the Shell patented
warm asphalt mixture (WAM) technology 1 using foam [6]. It must be understood that
in all cases (hot and warm production) the values determined are well below any
occupational exposure or environmental limit. This clearly demonstrates that both hot
mix and WAM Foam production are fully acceptable from an occupational and
environmental point of view.
In October 2006, during a trial on the high speed road Firenze-Pisa-Livorno in Italy,
several air pollutants (CO 2 , CO, NO x , SO 2 , TOC and dust) emitted by the chimney of
the mixing plant were measured by Det Norske Veritas AS. Simultaneously, emission
measurements were carried out at three positions in the asphalt mixing plant. During
the asphalt laying and compaction operations, the paving crew was equipped with
fume collection devices for exposure measurements.
1
WAM is a Shell trademark
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For both emissions and exposures, fume analysis was performed to determine the
total aerosols, the organic aerosols (Benzene Soluble Fraction), the gaseous fraction
and specific polycyclic aromatic compounds.
All measurements were performed during the production of the conventional hot
mixtures and the production of Greenfalt. The mixing temperatures were 180°C for
the conventional hot mixture and 120 to 125 °C for the WAM Foam. The productions
were carried out on different days of the same week, in the same mixing plant, with
the same testing devices and in similar weather conditions in order to get a set of
fully comparable data. In addition, energy consumptions for the two different
productions were compared.
2. Studies in Florence, Italy
Work was conducted on 25 and 27 October 2006 in Florence at a mixing plant that
was modified to produce asphalt according to the WAM foam process. The hard
bitumen used for WAM was a 20/30 pen grade (EN12591 – Table 1) and the soft
bitumen was a V10000 grade (EN12591 – Table 3). The objectives of the study were
the following:
To determine personal exposures for applications for the road contractor
Conglobit. Conglobit uses the WAM Foam process to produce and lay asphalt
mixtures under the name "Greenfalt".
To compare, under field exposure conditions, the type of emissions using
Greenfalt with those using HMA.
To collect and compare emission values from mixing operations in the asphalt
plant during WAM and HMA production.
Exposures to particulate matter were determined and compared with Italian
Occupational Exposure Limits (OEL) for bitumen fumes (petroleum bitumen CAS
number 8052-42-4). Some countries, such as Italy in 2003, have adopted the
American Conference of Governmental Industrial Hygienists (ACGIH)
recommendations [7] into national legislation. In January 2000, ACGIH changed its
Recommended Exposure Limits (REL) for bitumen fumes. The limit was 5 mg/m 3
measured as total aerosols (mineral and organic). The latest REL is 0.5 mg/m 3
measured as benzene-soluble aerosol of the inhalable fraction, i.e. the organic
fraction of total aerosols.
Total aerosols are measured using a closed-faced 37-mm cassette equipped with a
PTFE filter, which is a "total aerosol" sampler (breathable fraction). Total organic
aerosols are then extracted and quantified (Benzene Soluble Fraction or BSF). Note
that the inhalable fraction is regarded as similar to BSF for this work.
Sampling durations for HMA and WAM were between 3 and 4 hours which was
adapted to obtain more than the minimum quantity (BSF > 0.1 mg/m 3 ) required by
NIOSH 5042.
The positions of the samplers are indicated in Picture 1.
Two samplers close to the pugmill; due to the observed saturation of the filters
in the case of hot mixture production, a third filter was added with a 60 minutes
sampling time. No saturation was observed in the case of WAM Foam.
Two samplers set up at the top of the discharge hoppers.
Sampler(s) at the discharge point.
Static sampler, about 50 m away from the mixing plant.
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Picture 1 Emission samplers in the asphalt plant
2.2 Conditions and measurements at the asphalt plant
On 26 October, paving work involved the construction of a structural layer using
Greenfalt. An amount of 870 tons of Greenfalt were laid on the site with a length of
1300 m, 3.5 m width and thicknesses were 90, 50 and 90 mm for the three sections
of this layer.
Recorded air temperatures were 19°C in the morning and 30°C at 3 pm in the
afternoon. Weather condition was cloudy with no wind. Paving crew sampling
duration was around 400 minutes.
Sampling for exposure measurements was performed for the following jobs:
A paver driver
Two screedmen
A skilled labourer / raker
A roller compactor driver
Personal pumps were used for fume sampling with a 2 l/min flow rate. The matter
was collected on PTFE filters (2 µm) placed in the standard 37-mm cassette (see
pictures 2 and 3):
Total aerosols, which represents the mineral and organic aerosols
BSF extracted from the filter with benzene, which represents the total organic
aerosols (the remaining part is regarded as the mineral fraction or MF)
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Picture 2 Picture 3
Two static samples were also taken in order to cover the whole worksite area on the
road and to check whether there were aerosol sources other than the laying train.
During the whole day of sampling, the absence of fumes (visual and smell) during
laying of the warm asphalt mixture has to be noted (Picture 4). Only a little water
vapour was observed from water used for the roller (compactor).
Picture 4
The standard 37-mm filter cassettes containing PTFE were used in series with
adsorbent tubes in order to collect the vapour fraction (gases). The suitable
adsorbent used for trapping volatile compounds is XAD-2 with front and back
adsorbent sections. The front and back sections were separately extracted using
dichloromethane to check for breakthrough. Analysis and quantifications were
performed by means of gas chromatography with flame ionisation detection (GC-
FID).
Sampling and analysis were carried out in accordance with NIOSH 5042 NMAM (MF
& BSF using 37 mm samplers) with some minor changes.
Polycyclic Aromatic Hydrocarbon (PAH) determination and quantification in the
benzene-soluble fractions were conducted on the HMA samplers. This has not been
done in the case of WAM as the amount of collected organic matter was too low for
such analysis. The compound identification is based on the priority 16 compounds
mentioned in the US EPA (Environmental Protection Agency) list. PAH analysis was
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carried out in accordance with Shell’s in-house AMS 1057-1 method (based on the
610-EPA method for wastewater). PAHs were extracted with THF from the organic
part of the collected particulates (BSF) and analysed by HPLC-UV.
3. Results and discussion on measurements in the asphalt plant
3.1 Results on fuel consumption in the asphalt plant
The fuel (gas) consumption was measured at different levels of the plant’s production
capacity in the range from 60-100 %. The results showed a reduction in fuel
consumption of 35%.
3.2 Results gas and dust emissions from the chimney
During the asphalt production for the paving work on the high speed road Firenze-
Pisa-Livorno in Italy, several air pollutants (CO 2 , CO, NO x , SO 2 , TOC and dust)
emitted by the chimney of the mixing plant were measured by Det Norske Veritas AS.
An impression of the set-up is shown in Pictures 5 and 6.
Picture 5 Picture 6
The results obtained at a production rate of 140 tonnes asphalt per hour are
presented in Figures 1, 2 and 3. Lowering the operating temperatures from 180 °C in
the hot mixture production to about 125-130°C in the warm asphalt mixture
production produced a considerable reduction in the amount of gas and dust
emissions.
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Figure 1 CO 2 emission levels at three measurement times in the asphalt plant
5
4.5
M1 M2 M3
4
Emission level (tonnes/h)
3.5
3
2.5
2
1.5
1
0.5
0
HMA
CO2, t/h
WAM foam
In Figure 1 the CO 2 emission is shown in tonne per hour and emission reduction
obtained is about 35%.
Figure 2 CO and NO x emission levels at three measurement times in the asphalt
plant
8
7
M1 M2 M3
6
Emission level (kg/h)
5
4
3
2
1
0
HMA WAM foam HMA WAM foam
CO, kg/h
NOx, kg/h
Figure 2 shows that the CO reductions obtained were about 8% and the NO x
reduction was about 60%.
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Figure 3 SO 2 and dust emission levels at three measurement times in the asphalt
plant
0.1
0.09
M1 M2 M3
0.08
Emission level (kg/h)
0.07
0.06
0.05
0.04
0.03
0.02
0.01
0
HMA WAM foam HMA WAM foam
SO2, kg/h
Dust, kg/h
Figure 3 shows that SO 2 and dust emissions levels are low, but still reductions in the
order of 25 to 30% can be obtained.
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3.3 Results and discussion on emissions in the asphalt plant
A first emission study was carried out in an asphalt mixing plant in 2000 [2]. This
recent study is a more extensive study in an asphalt mixing plant. The results (in
mg/m 3 ) are presented in Figure 4, in which MF indicates the mineral fraction, BSF the
benzene soluble fraction and VF the volatile fraction.
Figure 4 Emissions in the asphalt plant
Pugmill sampler 1 Pugmill sampler 2 Hopper
70
Emissions (mg/m3)
60
50
40
30
20
10
0
HMA WAM HMA WAM HMA WAM
MF BSF VF
It appears that the pugmill discharge is the location where most fumes are
emitted.
The mineral fraction (MF) was found similar.
The organic fraction (BSF) was found significantly higher for HMA (up to 200
times more). Organic aerosols represent a little part of the total emissions for
WAM unlike HMA (up to 4% and 90% respectively).
The volatile fraction (VF) was found higher for HMA (up to 6 times more). Due to
the very low level of emitted BSF with WAM, the volatile fractions can represent
almost all the organic emissions (up to 99%).
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4. Results and discussion on the exposure measurements on the paving site
The exposure values (corrected for field blank) are given in Table 1. There are 8-hour
Time-Weighted Average values (TWA). The 8-hr TWA values correspond to average
exposure over the course of an 8-hour work shift. This value is often preferred
because it is more representative of a full workday.
Table 1
8 h TWA in mg/m 3 WAM laying (day 2)
MF BSF SV
Paver driver 0.22 0.05 3.45
Screedman 1 0.19 0.08 2.40
Screedman 2 0.19 0.07 1.18
Raker 0.16 0.14 2.93
Roller driver 0.13 0.03 0.79
Static 1 0.97 0.02 0.32
Static 2 0.14 0.01 0.23
The main part of the aerosols is inorganic (mineral dust). Relevant exposure data
(BSF) have been compared with Italian OELs. On an 8-hr Time-Weighted Average
basis, no measured values exceed these OELs.
It must be understood that in all cases (hot and warm production) the values
determined are well below any occupational exposure or environmental limit. This
clearly demonstrates that both hot mixture and WAM-Foam production are fully
acceptable from an occupational and environmental point of view.
When compared with Shell’s previous exposure measurements conducted on paving
HMA, these emissions are in the lower range (commonly 0.05-0.60 mg/m 3 in BSF).
The same level of magnitude (< 0.05) was previously recorded when using usual pen
grade binders (e.g. 35/50) at around 150°C.
The BSF data are also consistent with exposure data from our earlier studies (up to
0.05 mg/m 3 ).
Static values were found rather high especially in terms of mineral dust. This is
probably explained by the traffic on the other side of the motorway.
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5. PAHs in BSF
The PAH concentrations are the summed values for both BSFs and VFs. The
analysis results are presented in Figure 5 and the values are expressed in ng/m 3 .
The sum of the 4-6 ring compounds and the sum of 15 detected PAHs are displayed.
The results are consistent with the BSF values: the higher the organic fraction, the
higher the PAH content is. The values for the hot mixture presented in Figure 5 are
typical values derived from previous exposure measurements carried out by Shell.
Figure 5
Paver driver Screedman Raker Roller driver
PAH emissions (ng/m3)
900
600
300
0
HMA WAM (< 0.1) HMA WAM (< 2)
4 - 6 ring Total (15 PAHs)
6. Concluding remarks
In the asphalt production, the WAM Foam technology is significantly more
environmentally friendly in terms of emissions of CO 2 , NO x , dust and organic aerosol.
The organic aerosols, expressed in benzene soluble fraction, emitted with WAM at
around 125°C are in the lower range commonly found for hot asphalt laying when
good product stewardship is used (e.g. the use of lowest recommended
temperature). This is in accordance with a previous Shell Bitumen paper, which
demonstrates that in the temperature range relevant for paving applications (about
140 to 190°C), the fume emission rate increases by a factor of 2 for about every 12°C
increase in temperature [8].
10/11

References
1. B.G. Koenders, D.A. Stoker, C. Bowen, P. de Groot, O. Larsen, D. Hardy, K.P.
Wilms, Innovative process in asphalt production and application to obtain lower
operating temperatures, 2 nd Eurasphalt&Eurobitume congress, Barcelona, 20-22
September 2000, Book 2, session 3, pp. 831-840.
2. P.C. de Groot, C. Bowen, B.G. Koenders, D.A. Stoker, O. Larsen, J. Johansen, A
comparison of emissions from hot mixture and warm asphalt mixture production,
Proceedings IRF congress, Paris, June 2001, paper O022.
3. B.G. Koenders, D.A. Stoker, C. Robertus, O. Larsen and J. Johansen, WAM
Foam, asphalt production at lower operating temperatures, 9 th International
Conference on Asphalt Pavements, ISAP 2002.
4. D. Strickland, Development of WAM Foam technology, paper presented at 2 nd
International Conference: “Addressing Government sustainability and recycling
targets for contruction and related industries, John Moores University, Liverpool,
February 2003, UK.
5. O.R. Larsen, Ø. Moen, C. Robertus, B.G. Koenders, WAM Foam asphalt
production at lower operating temperatures as an environmental friendly
alternative to HMA, 3 rd Eurasphalt&Eurobitume congress, Vienna, 2004.
6. European patent numbers: EP 863 949, EP 977 813 and EP 1 263 885.
7. American Conference of Governmental Industrial Hygienists 2001 TLVs and BEIs
booklet.
8. Brandt, H. C. A. and De Groot, P. C.; A laboratory rig for studying aspects of
worker exposure to bitumen fumes; American Industrial Hygiene Association
Journal (1999), 60(2), 182-190.
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