Construction and Building Materials xxx (2014) xxx–xxx

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Construction and Building Materials

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Assessment of gaseous emissions produced on site by bituminousmixtures containing crumb rubber

http://dx.doi.org/10.1016/j.conbuildmat.2014.03.0300950-0618/� 2014 Elsevier Ltd. All rights reserved.

⇑ Corresponding author. Tel.: +39 0110907696; fax: +39 0110907699.E-mail addresses: mariachiara.zanetti@polito.it (M.C. Zanetti), silvia.fiore@

polito.it (S. Fiore), barbara.ruffino@polito.it (B. Ruffino), ezio.santagata@polito.it(E. Santagata), michele.lanotte@polito.it (M. Lanotte).

Please cite this article in press as: Zanetti MC et al. Assessment of gaseous emissions produced on site by bituminous mixtures containing crumbConstr Build Mater (2014), http://dx.doi.org/10.1016/j.conbuildmat.2014.03.030

Maria Chiara Zanetti ⇑, Silvia Fiore, Barbara Ruffino, Ezio Santagata, Michele LanotteDepartment of Environment, Land and Infrastructure Engineering, Politecnico di Torino, 24, corso Duca degli Abruzzi, 10129 Turin, Italy

h i g h l i g h t s

� Gaseous emission of bituminous mixtures were sampled at several construction sites.� Laboratory analyses were carried out for the evaluation of the contents of potentially hazardous compounds.� Experimental data were evaluated in differential terms in the framework of a sanitary-environmental risk analysis model.� Possible toxicological and carcinogenic effects on workers were assessed.

a r t i c l e i n f o

Article history:Received 14 August 2013Received in revised form 21 March 2014Accepted 24 March 2014Available online xxxx

Keywords:Crumb rubberBituminous mixturesGaseous emissionsSanitary-environmental riskConstruction workers

a b s t r a c t

Crumb rubber (CR) derived from the grinding of end-of-life tires (ELTs) can be employed, either by meansof the ‘‘wet’’ or of the ‘‘dry’’ process, in the production of high-performance bituminous mixtures for roadpaving applications. Nevertheless, when Administrations consider possible implementation of such tech-nologies in pavement construction and rehabilitation, they are often concerned with the potential impactthat the use of CR may have on environment and on workers operating at laying sites. This paper providesa specific contribution to this area of technical knowledge, focusing on the assessment of gaseous emis-sions which workers may be potentially exposed to in the framework of a sanitary-environmental riskanalysis model which considers possible toxicological and carcinogenic effects.

� 2014 Elsevier Ltd. All rights reserved.

1. Introduction

Based on several years of experience worldwide, it has beenproven that crumb rubber (CR) obtained from the grinding ofend-of-life tires (ELTs) can be employed in the production ofhigh-performance bituminous mixtures for road paving applica-tions [1]. Available technologies are known as the ‘‘wet’’ and‘‘dry’’ processes. In the ‘‘wet’’ process, CR is preliminarily mixedwith bitumen, thus obtaining a very ductile and elastic modifiedbinder, also known as ‘‘asphalt rubber’’ (AR) [ASTM D6114-09],that is then combined with aggregates in the hot mix plant. Inthe ‘‘dry’’ method, CR is introduced in the production flow of bitu-minous mixtures as a supplementary component, substituting partof the aggregates and providing enhanced elastic response underloading [2,3].

Research has focused on a number of performance-relatedissues of bituminous mixtures containing CR, including the assess-ment of resistance to permanent deformation, fatigue cracking,oxidative ageing and water damage [4]. Moreover, several aspectsto be taken into account during mix design and quality controloperations have been addressed, with the consequent definitionof reliable technical specifications [5,6]. Nevertheless, the effectsof the use of CR on gaseous emissions produced during laying oper-ations have not been subjected to extensive investigations, with alimited number of experimental studies which have not yieldedquantitative information on the potential health risks which work-ers are exposed to on site [7–9].

The study carried out in the United States by the National Insti-tute for Occupational Safety and Health (NIOSH) in cooperationwith the Federal Highway Administration (FHWA) was based ondata gathered at several pavement construction sites, where occu-pational exposures among asphalt workers were evaluated bycomparing conventional and AR bituminous mixtures [7]. Workers’medical data were related to results of chemical analyses carriedout on fumes sampled at paving sites in different positions. In

rubber.

Table 2Construction sites considered in the investigation – bituminous mixtures containingCR.

Mixture code Mixture type Site type Layer thickness (cm)

BV-W Gap-graded Provincial road 3SF-W Gap-graded Urban road 5AO-W Dense graded Motorway 4AL-D Dense graded Provincial road 4

2 M.C. Zanetti et al. / Construction and Building Materials xxx (2014) xxx–xxx

particular, tests focused on the assessment of potentially harmfulsubstances such as total particulate, benzene soluble particulate,polycyclic aromatic hydrocarbons (PAHs), organic sulphur-con-taining compounds and benzothiazole. It was found that the high-est exposures were from jobs near the paver or asphalt deliverytrucks and it was concluded that exposure to emissions of bitumi-nous mixtures containing CR may be potentially more hazardousthan that associated to conventional paving materials.

In the personal exposure monitoring study carried out by Wattset al. [8], gaseous emissions of bituminous mixtures containing CRand of the standard type were analysed by considering fine respi-rable particles (<2.5 lm) and PAHs. Even though experimentalresults highlighted a greater potential carcinogenic PAH exposureof road workers in the case of AR mixtures, from a statistical pointof view no significant differences were found with respect to stan-dard mixtures.

Evaluation of stack emissions at production plants was the sub-ject of the investigations reported by Stout and Carlson [9], whoreviewed the results of analyses carried out in the case of bitumi-nous mixtures prepared with and without CR. The studies wereperformed with different approaches and methods, but in all casesthe effects of CR, if any, were reported to be relatively small.

With the goal of filling a significant gap in technical knowledge,the issue of health risk assessment was given a prominent role intwo research projects which were recently launched in Italy onthe use of CR in bituminous mixtures (‘‘wet’’ and ‘‘dry’’ technolo-gies): POLIPNEUS (2012-16), funded by Ecopneus, a non-profitcompany which has the mission of managing the entire flow ofELTs in Italy, and TYREC4LIFE (2011-14), supported by the Euro-pean Commission as part of the LIFE + funding program [10,11].The work presented in this paper is based on monitoring activitieswhich were carried out within these projects on several construc-tion sites in which bituminous mixtures were laid for the forma-tion of wearing and binder courses both of the standard type andcontaining CR (‘‘wet’’ and ‘‘dry’’ mixtures). The main goal of theinvestigation was to assess the potential health impact on workersof gaseous emissions produced during paving operations. For sucha purpose, fumes were sampled at the paver and were then sub-jected to laboratory analyses for the determination of the concen-tration of Volatile Organic Compounds (VOCs) and PolycyclicAromatic Hydrocarbons (PAHs). Results were used within a proce-dure for the assessment of health risks which workers are exposedto. In such a context, the influence of CR was highlighted in differ-ential terms, comparing calculated risks associated to the laying ofmixtures with and without CR.

2. Experimental

2.1. Construction sites

Experimental investigations were carried out on several construction siteswhich involved the laying of a wide range of bituminous mixtures, including stan-dard ones and several types of ‘‘wet’’ and ‘‘dry’’ mixtures containing CR. A syntheticdescription of considered sites and mixtures is given in Tables 1 and 2.

Standard mixtures (identified with ‘‘S’’ as final letter in code names) weredesigned according to available technical specifications for binder courses [12].They contained aggregates of different origin and, as shown in Table 1, were pre-pared by employing both neat and polymer-modified bitumen. Mixture QU-S alsoincorporated 13% (b.w. on dry aggregates) of Reclaimed Asphalt Pavement (RAP)material.

Table 1Construction sites considered in the investigation – standard bituminous mixtures.

Mixture code Binder type Site type Layer thickness (cm)

QU-S Neat bitumen Urban road 7BR-S Polymer-modified Trial section 9AL-S Neat bitumen Provincial road 4

Please cite this article in press as: Zanetti MC et al. Assessment of gaseous emiConstr Build Mater (2014), http://dx.doi.org/10.1016/j.conbuildmat.2014.03.03

Mixtures containing CR were both of the gap-graded and dense-graded type.Those containing asphalt rubber (identified with ‘‘W’’ as final letter in code names)were conceived for the formation of wearing courses and were produced in threedifferent hot-mix plants by employing binders which were prepared by the sameCompany according to an undisclosed recipe. No information was available on com-ponent materials (base bitumens and CRs) employed for each production batch.Mixture AL-D was of the ‘‘dry’’ type and was used as a binder course material. Itsjob-mix formula was obtained from that of a standard reference mixture (AL-S),also included in the investigation, by simply adding 1% CR (b.w. of aggregates)and by slightly increasing target bitumen content to take into account additionaladsorption effects due to CR.

Mixtures SF-W and QU-S were produced in the same day and in the same plantby employing a common base bitumen. Mixtures AL-D and AL-S shared these samecommon aspects (day and plant of production, employed bitumen) and were alsolaid in the same site.

During pavement construction operations, temperature of the mixtures wascontinuously monitored behind the paver’s screed by means of hand-held immer-sion thermometers. Site-specific conditions were also recorded by measuring airtemperature.

Samples of bituminous mixtures taken at the construction sites were subjectedto laboratory tests for the determination of binder content and aggregate size dis-tribution. Binder content was determined by means of ignition tests carried outaccording to EN 12697-39. Size distribution of aggregates recovered from ignitiontests was evaluated in wet conditions by employing the standard set of sieves indi-cated in technical specifications.

A synthesis of mixture composition data is provided in Tables 3 and 4. Bindercontent (%B) is expressed as a percentage b.w. of dry aggregates. Aggregate size dis-tributions are described by referring to maximum diameter (Dmax, corresponding to100% passing), percentage of fine aggregates (%P2, passing the 2 mm sieve) and offiller (%P0.075, passing the 0.075 mm sieve). Both tables also contain average air(TA) and mixture (TM) temperature values recorded on site during laying operations.

2.2. Test methods

Fume samples were taken at the driver’s seat of the paver, in the most severeexposure conditions during mixture discharge operations from trucks, and at thescreed, immediately after discharge of the hot mixture and during the forwardmovement of the paver along the construction site. Sampling was carried out byemploying a pump (0.5 l/min flow rate, 5 min total sampling time) by means ofwhich fumes were adsorbed on active granular carbon cartridges which were thenstored at freezing temperature until analysis. These matrixes were subjected to sol-vent extraction (with methylene chloride, Fluka, HPLC grade) in an ultrasound bathfor 60 min [EN 13649, 13] and were then analysed with an Agilent 7890/5975 gaschromatograph, equipped with a HP5-MS capillary column (30 m �0.25 mm � 0.25 lm), for the determination of the concentration of Volatile OrganicCompounds (VOCs) and Polycyclic Aromatic Hydrocarbons (PAHs) [2,14].

3. Results and discussion

Results of analyses performed on gaseous emissions sampled atthe test sections are given in Tables 5–8 (mean values derived fromtwo independent replicates). Listed compounds are those whichare considered toxic or carcinogenic among all substances poten-tially detectable by means of gas-chromatographic techniques.These are also the compounds which were considered within thesanitary-environmental risk analysis procedure described inSection 4.

Table 3Mixture composition and laying conditions – standard bituminous mixtures.

Site code %B (%) Dmax (mm) %P2 (mm) %P0.075 (%) TL (�C) TA (�C)

QU-S 4.8 25 29.0 6.3 165 28BR-S 5.5 20 31.5 6.1 165 28AL-S 4.7 20 35.5 5.4 170 15

ssions produced on site by bituminous mixtures containing crumb rubber.0

Table 4Mixture composition and laying conditions – bituminous mixtures containing CR.

Site code %B (%) Dmax (mm) %P2 (mm) %P0.075 (%) TL (�C) TA (�C)

BV-W 8.5 16 19.4 3.9 170 9SF-W 8.0 16 16.0 4.0 170 24AO-W 6.8 16 19.5 5.5 190 25AL-D 6.3 20 34.5 6.5 170 15

Table 5VOCs of gaseous emissions (lg/m3) at the paver (D: driver’s seat; S: screed) –standard bituminous mixtures.

QU-S BR-S AL-S

D S D S D S

Benzene 3.99 8.40 10.80 3.55 0.67 0.88Toluene 29.40 8.31 5.70 8.75 1.36 0.96Ethylbenzene 10.69 16.08 3.40 1.64 7.07 4.66p-Xylene 0.90 1.47 5.69 10.59 28.01 12.95Styrene <0.10 <0.10 <0.10 <0.10 0.23 0.25Bromo-benzene 0.93 0.69 <0.10 3.62 4.36 3.591,3,5-Trimethyl-

benzene70.37 66.19 78.04 54.86 9.16 39.26

1,2,4-Trimethyl-benzene

14.21 32.99 29.61 4.67 15.31 5.72

p-Isopropiltoluene 24.50 14.65 3.02 1.97 2.99 1.66Butyl-benzene 16.35 14.28 3.08 3.75 41.07 15.681,3,5-Trichloro-

benzene<0.10 <0.10 <0.10 <0.10 <0.10 <0.10

1,2,4-Trichloro-benzene

<0.10 <0.10 <0.10 <0.10 <0.10 <0.10

Total VOCs 171.33 163.08 139.33 93.41 110.23 85.62

Table 6PAHs of gaseous emissions (lg/m3) at the paver (D: driver’s seat; S: screed) –standard bituminous mixtures.

QU-S BR-S AL-S

D S D S D S

Naphthalene 2.17 2.04 1.78 2.25 1.00 0.70Acenaphthylene 1.04 0.99 1.17 0.76 0.22 0.101-bromo-naphthalene 8.73 8.68 8.89 7.44 0.76 0.56Acenaphthene 1.44 1.81 1.50 1.05 0.15 0.07Fluorene 1.56 1.86 3.14 1.25 0.43 0.78Phenanthrene 0.78 0.84 0.89 0.90 1.79 0.53Anthracene 0.19 0.65 0.86 0.68 0.14 0.63Fluoranthene 0.20 0.32 0.43 0.09 0.17 0.15Pyrene 0.24 0.38 0.21 0.12 0.28 0.18Triphenylene <0.10 <0.10 <0.10 <0.10 <0.10 <0.10Benzo[a]anthracene <0.10 <0.10 <0.10 <0.10 <0.10 <0.10Benzo[b]fluoranthene 8.27 4.01 6.63 6.14 19.78 32.30Benzo[a]pyrene 9.69 24.32 9.58 19.68 12.98 27.73Indeno[1,2,3-cd]pyrene <0.10 <0.10 <0.10 <0.10 <0.10 <0.10Dibenzo[a,h]anthracene <0.10 <0.10 <0.10 <0.10 <0.10 <0.10Benzo[ghi]perylene <0.10 <0.10 <0.10 <0.10 3.03 0.51

Total PAHs 34.31 45.91 35.08 40.37 40.73 64.24

M.C. Zanetti et al. / Construction and Building Materials xxx (2014) xxx–xxx 3

Interpretation of the data listed in Tables 5–8 is not a trivial tasksince composition of fumes is affected by several material-specific(i.e. mixture composition, CR type and base bitumen type) and site-specific (i.e. layer thickness, laying temperature, air temperature,wind, air pressure) factors. Moreover, significant differences maybe found depending upon considered compounds (being VOCsmuch more volatile than PAHs and therefore more sensitive totemperature variations) or on sampling position (D or S).

In general terms it can be observed that mixtures containing ARprepared with the ‘‘wet’’ process (BV-W, SF-W, AO-W) show higherPAH values in the driver’s position (D) than at the screed (S), pos-sibly as a result of the higher mixture temperature while being dis-charged into the paver. The opposite condition occurs for VOCs,

Please cite this article in press as: Zanetti MC et al. Assessment of gaseous emiConstr Build Mater (2014), http://dx.doi.org/10.1016/j.conbuildmat.2014.03.03

since total (and most individual) values are higher at the screed.This is probably due to the fact that VOCs are light compoundswhich are therefore more strongly influenced by external environ-mental conditions (temperature, wind, air pressure) at the higherelevation of the driver’s seat. This does not occur for PAHs, whichin comparison to VOCs are heavier compounds, less sensitive tochanges of external conditions.

A totally different scenario was recorded for standard mixtures(QU-S, BR-S, AL-S) and for the mixture which incorporated CR bymeans of the ‘‘dry’’ technology (AL-D): PAH values were higher atthe screed sampling point while VOCs were higher in the driver’sposition. Such a difference may depend upon the different layingtemperature (which was slightly lower for these mixtures, asshown in Tables 3 and 4) and on the fact that for such mixtureschanges to bitumen composition did not occur as a result of thepartial absorption of aromatic fractions which is typical of ARbinders.

As expected, absolute values of all chemical compoundsdetected by means of gas-chromatography in both sampling posi-tions were characterized by a very high variability from site to site(and from one mixture to another). This is due to the fact that, aspreviously mentioned, composition of fumes is affected by severalmaterial-specific and site-specific factors.

Even though the Authors have observed that the PAH and VOCcontents of CRs can significantly change from one ELT processingplant to another, in a previous research project it was observedthat the contribution of bitumen to gaseous emissions of mixturesappears to be comparatively more relevant, with a high depen-dency upon its type and quantity [15]. This is due to fact that forall mixtures, produced either with the ‘‘wet’’ or ‘‘dry’’ process,the total quantity of incorporated CR is very small when comparedto total bitumen. Moreover, during site operations the abovemen-tioned compounds are more easily released from bitumen ratherthan from CR, in which they are contained within a cross-linkedvulcanized matrix.

This general observation is confirmed by the data reported inTables 5–8, which allow comparisons to be made between siteswhich share common factors. In particular, when considering mix-tures QU-S and SF-W, prepared in the same plant with the samebase bitumen and then laid in similar external conditions (sameday and short distance between the two sites), gaseous emissionsexpressed in terms of PAHs seem to be controlled by amount oftotal binder, respectively equal to 4.8% and 8% (see Tables 3 and4), with total and individual values significantly higher in the caseof mixture SF-W. On the contrary, for the two sites VOC emissionsare quite similar, being the concentration of these lighter com-pounds, as previously discussed, more strongly influenced bysite-specific factors. Such an explanation is coherent with the caseof mixtures AL-D and AL-S, prepared in the same plant with thesame bitumen and laid on the same site: PAH values in gaseousemissions are approximately equal, probably as a result of thesmall binder content difference (respectively equal to 6.3% and4.7%) and once again even the VOC values are very similar.

Finally, it should be noticed that PAH and VOC contents offumes sampled at the AO-W site were extremely low when com-pared to all other cases. This is due to the fact that constructionwas carried out in very windy conditions which significantlyaffected the diffusion and dispersion of gaseous emissions, espe-cially for the case of the lighter VOCs.

4. Sanitary-environmental risk assessment

Assessment of toxicological and carcinogenic risks which work-ers are exposed to on site as a result of the presence of gaseousemissions coming from hot bituminous mixtures containing CR

ssions produced on site by bituminous mixtures containing crumb rubber.0

Table 7VOCs of gaseous emissions (lg/m3) at the paver (D: driver’s seat; S: screed) – bituminous mixtures containing CR.

BV-W SF-W AO-W AL-D

D S D S D S D S

Benzene 2.6 <0.10 0.94 2.21 0.29 0.22 0.75 0.62Toluene 5.4 13.4 12.27 13.04 0.10 0.24 0.81 1.32Ethylbenzene <0.10 <0.10 5.24 6.41 0.15 0.19 8.26 5.13p-Xylene 11.8 157.3 32.66 41.08 0.42 7.75 25.66 52.61Styrene <0.10 <0.10 1.71 <0.10 0.11 0.19 0.26 0.39Bromo-benzene <0.10 <0.10 1.38 1.68 0.07 0.30 5.90 3.221,3,5-Trimethyl-benzene 5.9 17.1 45.88 81.27 0.11 0.12 9.68 37.151,2,4-Trimethyl-benzene 7.6 6.1 18.68 40.15 0.17 0.33 16.35 5.79p-Isopropiltoluene 1.4 57.3 4.16 12.25 0.03 0.02 2.70 2.86Butyl-benzene <0.10 3.1 2.66 9.64 0.18 0.09 37.62 20.091,3,5-Trichloro-benzene <0.10 <0.10 <0.10 <0.10 <0.10 <0.10 <0.10 <0.101,2,4-Trichloro-benzene <0.10 <0.10 <0.10 <0.10 <0.10 <0.10 <0.10 <0.10

Total VOCs 34.70 254.30 125.58 207.75 1.62 9.44 108.00 129.18

Table 8PAHs of gaseous emissions (lg/m3) at the paver (D: driver’s seat; S: screed) – bituminous mixtures containing CR.

BV-W SF-W AO-W AL-D

D S D S D S D S

Naphthalene 7.90 5.20 1.28 1.41 1.11 1.40 1.16 0.90Acenaphthylene 1.80 1.20 1.84 2.45 0.22 0.21 0.17 0.141-Bromo-naphthalene 10.30 9.20 17.81 11.94 1.21 1.16 1.10 0.77Acenaphthene 2.30 1.40 23.73 3.78 0.33 0.26 0.09 0.06Fluorene 1.30 1.00 15.70 8.12 0.70 0.57 0.43 1.07Phenanthrene 2.00 1.10 4.44 0.53 1.72 1.38 0.73 0.79Anthracene 1.80 0.60 2.72 0.38 1.64 0.91 0.13 0.84Fluoranthene 3.10 0.90 2.32 0.22 4.23 3.04 0.20 0.28Pyrene 3.00 0.90 2.38 0.96 4.05 2.48 0.33 0.27Triphenylene 6.10 2.20 <0.10 <0.10 <0.10 <0.10 <0.10 <0.10Benzo[a]anthracene 3.60 0.80 <0.10 <0.10 <0.10 <0.10 <0.10 <0.10Benzo[b]fluoranthene 5.30 3.50 4.14 3.09 9.68 9.76 15.78 29.31Benzo[a]pyrene 3.60 0.80 15.96 27.07 9.88 10.02 15.84 27.28Indeno[1,2,3-cd]pyrene <0.10 <0.10 <0.10 <0.10 <0.10 <0.10 <0.10 <0.10Dibenzo[a,h]anthracene 8.90 2.15 <0.10 <0.10 <0.10 <0.10 <0.10 <0.10Benzo[ghi]perylene 3.60 5.78 68.87 19.88 <0.10 0.33 0.51 <0.10

Total PAHs 64.60 36.73 161.19 79.84 34.77 31.52 36.45 61.70

4 M.C. Zanetti et al. / Construction and Building Materials xxx (2014) xxx–xxx

was carried out by means of a sanitary-environmental risk analysisprocedure [ASTM E1739-09, ASTM E2081-00]. This was developedbased on previous work carried out for the evaluation and remedi-ation of contaminated sites [16,17] and for the approval of the useof CR in artificial turf sports fields [18].

Given that the contaminant source (i.e. bituminous mixture)and the potential receptors (i.e. paving workers) were clearly iden-tified and that direct measurements were performed (i.e. fumesampling and analysis), risk evaluation was developed by compar-ing experimental data with threshold values (the so-called ‘‘level1’’ of analysis) and by analytically modelling them in each localscenario (‘‘level 2’’). Analysis at ‘‘level 3’’, based on numerical sim-ulation models capable of fully reproducing contamination dynam-ics, was not included in the investigation.

With respect to ‘‘level 1’’ analysis, reference can be made to lim-its which have been defined by the American Conference of Gov-ernmental Hygienists [19] and by the German regulation system[20]. In the first case, the maximum exposure limit is fixed by con-sidering the benzene-soluble fraction of inhaled aerosol, whichcannot exceed 0.5 mg/m3 (by assuming 8 h/day, 5 days/week). Ger-man regulations refer to a maximum concentration of total hydro-carbons in emissions equal to 10 mg/m3, without distinguishingbetween compounds characterized by different degrees of toxicity.

Data collected at the test sections cannot be directly comparedto the limits illustrated above since measurements were carriedout by focusing on potentially harmful VOCs and PAHs. Neverthe-less, by considering the sum of total VOC and PAH contents, and by

Please cite this article in press as: Zanetti MC et al. Assessment of gaseous emiConstr Build Mater (2014), http://dx.doi.org/10.1016/j.conbuildmat.2014.03.03

conservatively assuming a worst-case scenario of continuous expo-sure, composition of analysed emissions seems to be compatiblewith the two abovementioned thresholds.

Risk analysis developed at ‘‘level 2’’ required the choice and useof an adequate model for exposure evaluation and of dose–response curves relative to toxic and carcinogenic substances.These two key elements of risk assessment are given in Eq. (1)and Fig. 1, respectively.

EM ¼ CR � EF� EDBW� AT

ð1Þ

where EM is calculated exposure (or effective exposure flow, in m3

kg�1 day�1), CR is the so-called contact factor (dependent on thetype of exposure, in this case inhalation and therefore assumedequal to 3.6 m3/day), EF is exposure frequency (in days/year,hypothesized equal to 250 for construction workers), ED is exposureduration (in years, assumed equal to 25 years), BW is average bodyweight (in kg, fixed at 70 kg), AT is the average mediation period ofexposure (corresponding to ED in the case of non-carcinogenic sub-stances, equal to 70 years in the case of carcinogenic substances).

As shown in Fig. 1, the shape of the dose–response curves is dif-ferent when comparing toxic (non-carcinogenic) and carcinogenicsubstances. In the first case, a dose threshold can be identifiedbelow which it has been experimentally verified that there areno harmful effects of that substance. However, risk calculationsrequire the use of a ‘‘reference dose’’ (RfD) which is obtained byreducing the threshold in order to take into account uncertainty

ssions produced on site by bituminous mixtures containing crumb rubber.0

Res

pons

e

Dose [mg·kg-1·d-1]

Carcinogenic substance

Toxic (non-carcinogenic) substance

SF

RfD Threshold

Fig. 1. Dose–response curves of carcinogenic and toxic (non-carcinogenic)substances.

M.C. Zanetti et al. / Construction and Building Materials xxx (2014) xxx–xxx 5

in the extrapolation of dose levels from animals to humans and toconsider specific characteristics of human response. In the case ofcarcinogenic substances, the concept of a threshold is no longervalid since health of human beings is damaged at any considereddose. For the description of such effects it can therefore beassumed that in a wide dose range the response curve is linear,with the consequent identification of a single gradient value, alsoknown as ‘‘slope factor’’ (SF).

In the investigation described in this paper, RfD and SF values ofcompounds listed in Tables 5–8 were retrieved from the databaseof the Istituto Superiore di Sanità [21], the leading technical andscientific public body of the Italian National Health Service. Thedose value (D, in mg kg�1 d�1) to use as an input in risk analysisevaluations was calculated, for each compound, by means of Eq.(2), where C is compound concentration (in mg/m3) measured inthe gaseous emissions sampled on site (Tables 5–8).

D ¼ C � EM ð2Þ

Toxicological and carcinogenic risks were quantified by respec-tively considering the so-called Hazard Quotient (HQ) and the Indi-vidual Excess Life Cancer Risk (IELCR), calculated as indicated inEqs. (3) and (4).

HQ ¼ D=RfD ð3Þ

Table 9HQratio and IELCRratio values for the BV-W, SF-W, AO-W and AL-D construction sites.

BV-W SF-W AO-W AL-D

D S D S D S D S

HQratio (min HQ) 2.84 3.25 6.77 4.03 0.76 0.76 0.91 1.31HQratio (max HQ) 0.95 1.03 2.26 1.27 0.25 0.24 0.30 0.41HQratio (mean HQ) 1.43 1.62 3.40 2.01 0.38 0.38 0.46 0.65IELCRratio (min

IELCR)0.44 0.06 1.62 1.35 1.05 0.54 1.67 1.47

IELCRratio (maxIELCR)

0.31 0.04 1.14 0.90 0.73 0.36 1.17 0.98

IELCRratio (meanIELCR)

0.38 0.05 1.41 1.09 0.91 0.43 1.46 1.18

Table 10HQratio and IELCRratio values for the SF-W/QU-S, AL-D/AL-S construction sites.

SF-W/QU-S AL-D/AL-S

D S D S

HQratio 3.43 1.27 0.91 1.31IELCRratio 1.59 1.11 1.17 0.98

IELCR ¼ D� SF ð4Þ

HQ or IELCR contributions due to each compound (or group ofcompounds) were summed together, thus obtaining final HQ orIELCR values which provide a synthetic description of the potentialimpact of a specific paving site on workers’ health, both from a tox-icological and carcinogenic viewpoint. However, these valuesshould be considered with caution since they were calculated byreferring to emissions sampled in the most critical conditions(i.e. during mixture discharge from trucks) which occur only in alimited number of occasions within a typical working day on site.For such a reason, HQ and IELCR values are not listed in this paper,nor are they compared with ASTM recommendations, which, forthe purpose of guaranteeing acceptable working conditions,require HQ be lower than 1 and IELCR be lower than 10�4 [ASTME1739-09, ASTM E2081-00].

Since the focus of research was to highlight the effects of CR onworkers’ health, for the construction sites with mixtures producedby means of the ‘‘wet’’ and ‘‘dry’’ technologies (BV-W, SF-W, AO-Wand AL-D), risk parameters were expressed in differential terms byconsidering their ratio (HQratio and IELCRratio) with respect to refer-ence values. These were calculated for the three paving sites withstandard mixtures (QU-S, BR-S and AL-S) (containing neat or poly-mer-modified bitumen). In particular, as shown in Table 9, ratios

Please cite this article in press as: Zanetti MC et al. Assessment of gaseous emiConstr Build Mater (2014), http://dx.doi.org/10.1016/j.conbuildmat.2014.03.03

were calculated with respect to the minimum, maximum and aver-age value of HQ and IELCR, both at the driver’s seat (D) and at thescreed (S).

Data listed in Table 9 clearly indicate that HQratio and IELCRratio

change significantly depending upon which reference parametersare adopted for their calculation. However, it is interesting to notethat with the exception of few outlier values they are comprisedwithin a single order of magnitude (ranging from 0.24 to 6.77). Thismeans that the sanitary-environmental risk associated to the useof bituminous mixtures containing CR is comparable to that ofstandard paving materials (produced by employing neat or poly-mer-modified bitumen).

In order to carry out the relative risk evaluation in the mostconservative conditions, analysis needs to focus on HQratio andIELCRratio values obtained by comparing risk parameters of sitesBV-W, SF-W, AO-W and AL-D to the those of the paving sites inwhich HQ and IELCR were found to be the smallest in all the data-base. In such a case, values of HQratio and IELCRratio are all greaterthan 1 only for site SF-W and in three out of four values for siteAL-D. For the other sites (BV-W and AO-W) values of HQratio andIELCRratio in the most conservative conditions are generally lowerthan 1 and highly variable. However, this seems to indicate thatthe reference database (constituted by only three sites: QU-S,BR-S and AL-S) is too limited and is too strongly influenced byenvironmental conditions.

In order to perform a more objective evaluation of the trueeffects of CR on the potential health risks which workers areexposed to, without biasing effects of variable environmental con-ditions and bitumen composition, supplementary values of HQratio

and IELCRratio need to be calculated. These are found by relatingactual HQ and IELCR values of homologue sites which, as alreadyhighlighted above, share common factors (SF-W and QU-S; AL-Dand AL-S).

Results obtained from these calculations are reported inTable 10. It can be observed that all calculated ratios are close tothe unit value, with the only exception of the HQ value calculatedin the driver’s position for site SF-W. This indicates that the use ofCR, both in the ‘‘wet’’ and ‘‘dry’’ technology, does not significantlyalter the risk scenario which workers are exposed to. However, byconsidering the set of ratios associated to each couple of homo-logue sites, in very general terms it can be stated that a slightincrease of toxic and carcinogenic risk is registered for the ‘‘wet’’process site (SF-W), probably as a result of the greater binder

ssions produced on site by bituminous mixtures containing crumb rubber.0

6 M.C. Zanetti et al. / Construction and Building Materials xxx (2014) xxx–xxx

content. Such an effect, as expected, is not recorded in the case ofthe ‘‘dry’’ technology (AL-D).

5. Conclusions

Results obtained in the investigation described in this paperrepresent a contribution to the assessment of health risks whichworkers may be exposed to on site during paving operationsinvolving the use of bituminous mixtures containing crumb rubber(CR). Even though more research is certainly needed on this topicin order to develop a sound and fully validated know-how, severalconclusions can already be drawn.

Sampling of gaseous emissions at paving sites and subsequentlaboratory analyses are the key elements of workers’ health riskassessment. Thus, it is crucial that codified procedures are followedin order to have reliable data to feed into evaluation models.Results obtained on the sites described in this paper, and thosealready available from previous and ongoing research projects,show that composition of fumes is affected by several material-specific (i.e. mixture composition, CR type and bitumen base type)and site-specific (i.e. layer thickness, laying and air temperature,wind, air pressure) factors. Nevertheless, relative contributions ofbitumen quantity, type and composition seem to be the mostrelevant.

Modelling of the experimental data within a sanitary-environ-mental risk analysis procedure requires conservative assumptionsto be made, mainly with respect to the work load of paving oper-ators. As shown in this paper, in order to highlight health-relatedeffects caused by the use of CR, it is convenient to express toxicand carcinogenic risk parameters (Hazard Quotient, HQ, and Indi-vidual Excess Life Cancer Risk, IELCR) in relative terms. This canbe done by comparing absolute values with analogous dataobtained in other paving sites where no CR was employed.

Results of the sanitary-environmental assessment indicate thatthe toxic and carcinogenic risk to which workers are exposed onsite in the case of bituminous mixtures containing CR is compara-ble to that of standard paving materials (produced by employingneat or polymer-modified bitumen).

Future research will be focused on overcoming current limita-tions of the reference database which, as a results of the numberof considered sites, is too strongly influenced by environmentalfactors and therefore yields results which in some cases are incon-sistent and too variable. Further activities will also be carried outfor the development of a laboratory test procedure for the preli-minary evaluation, in controlled conditions, of the maximum emis-sion potential of bituminous mixtures (of the standard type andcontaining CR).

Acknowledgements

The investigation described in this paper was carried out as partof the POLIPNEUS and TYREC4LIFE research projects, respectivelyfunded by Ecopneus S.c.p.A. and the European Commission.

Please cite this article in press as: Zanetti MC et al. Assessment of gaseous emiConstr Build Mater (2014), http://dx.doi.org/10.1016/j.conbuildmat.2014.03.03

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