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Geotextiles and Geomembranes 45 (2017) 121e130

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Geotextiles and Geomembranes

journal homepage: www.elsevier .com/locate/geotexmem

Long-term performance and binder chemical structure evolution ofelastomeric bituminous geomembranes

N. Touze-Foltz a, *, F. Farcas b

a Irstea Regional Center, Hydrosystems and Bioprocesses Research Unit, Irstea, 92761, Antony Cedex, Franceb Materials and Structures Department, Ifsttar, F-77447, Champs sur Marne, Marne la Vall�ee Cedex 2, France

a r t i c l e i n f o

Article history:Received 5 May 2016Received in revised form23 December 2016Accepted 27 December 2016Available online 15 February 2017

Keywords:GeosyntheticsGeomembraneBituminousDurabilityWater reservoirs

* Corresponding author.E-mail addresses: nathalie.touze@irstea.fr (N. To

ifsttar.fr (F. Farcas).

http://dx.doi.org/10.1016/j.geotexmem.2017.01.0030266-1144/© 2017 Elsevier Ltd. All rights reserved.

a b s t r a c t

This paper presents the results of uniaxial tensile tests, flow-rate measurements, and size-exclusionchromatography (SEC), which are used to evaluate the ageing of elastomeric bituminous geo-membranes (BGMs) that were installed 6, 10, 15, 20, and 30 years ago in ponds at two different sites inFrance. SEC was used to detect oxidation and the absence of polymer in the bitumen at the surface of the20- and 30-year-old BGMs. The results indicate that, for BGMs exposed less than 20 years, there was nooxidation or degradation of the polymer at the core. However, the elastomeric polymer was altered at thecore of the 30-year-old BGM, resulting in an embrittlement of the bitumen, but this did not affect themechanical properties of the glass veil and nonwoven polyester geotextile in the BGM core. Lastly, theflow rates through the BGM measured according to EN 14150 are still below 10�6 m3 m�2 d�1, whichindicates that the elastomeric bituminous GM is still watertight after 30 years of exposure.

© 2017 Elsevier Ltd. All rights reserved.

1. Introduction

A geosynthetic barrier (GBR) is defined in EN ISO 10318 (AFNOR,2005) as “a low-permeability geosynthetic material, used ingeotechnical and civil engineering applications with the purpose ofreducing or preventing the flow of fluid through the construction.”GBRs are classified in three categories according to thematerial thatfulfills the barrier function: (i) clay geosynthetic barriers (GBR-C)when the barrier function is implemented by clays, (ii) bituminousgeosynthetic barriers (GBR-B) when the barrier function is imple-mented by bitumen, and (iii) polymeric geosynthetic barriers (GBR-P) when the barrier function is implemented by a polymer.

The International Geosynthetics Society (IGS) defines a geo-membrane (GM) as “a planar, relatively impermeable, polymeric(synthetic or natural) sheet used in civil engineering applications”(IGS, 2009). The ISO terminology however dos not refer to geo-membranes but to geosynthetic barriers. However through thispaper the wording geomembrane (GM) which is more common isused. GMs are used around the world in civil-engineering appli-cations, notably for landfills, reservoirs, dams, canals, or tunnels.

Some recent publications report on the durability of GMs in

uze-Foltz), Fabienne.Farcas@

hydraulic applications as a function of the GM (Cazzuffi et al., 2010;Cazzuffi, 2014). These publications discuss, for example, polyvinylchloride GMs (Carreira and Tanghe, 2008; Girard et al., 2002;Newman et al., 2002; Blanco et al., 2012a,b,c), polypropylene GMs(Peggs, 2008; Wallace, 2008), high-density polyethylene GMs(Baldauf et al., 2012; Blanco et al., 2012a), and ethylene propylenediene terpolymer EPDM GMs (Blanco et al., 2012a,d; Blanco et al.,2014; Noval et al., 2014). However, very little information is avail-able for bituminous geomembranes. Touze-Foltz et al. (2010) re-ported the results of EN 14150 (AFNOR, 2006) hydraulic tests doneon oxidized bituminous GMs (BGMs) taken from six sites (pondsand dams). More recently, Touze-Foltz et al. (2015) compared anoxidized bituminous GM with an elastomeric bituminous GM afterboth were exposed in a pond for 15 years. In that work, they clearlystated that the results obtained for oxidized bituminous GMscannot and must not be extended to elastomeric bituminous GMs.The elastomeric bituminous geomembrane exhibited a better hy-draulic performance after 15 years and a better state of conserva-tion (visual) than the oxidized bituminous geomembrane. Indeeddifferences exist between both kinds of bitumen, oxidized orelastomeric. Bitumen is a material obtained through a doubledistillation (atmospheric distillation followed by vacuum distilla-tion) of a heavy crude oil. These two operations result in a materialcalled direct distillation bitumen consisting of two main distinctfractions: (1) the oil fraction, maltenes, and (2) the n-alcane

N. Touze-Foltz, F. Farcas / Geotextiles and Geomembranes 45 (2017) 121e130122

solvents precipitated fraction, asphaltenes. The distilled bitumencannot be directly used to produce geomembranes as it is toosensitive to temperature (Benneton, 2008). It is therefore necessaryto reduce the temperature sensitivity of the basematerial by either:(1) oxidizing it by blowing hot air (260 �C and 320 �C), therebyproducing asphaltenes by consumption of a portion of maltenes, or(2) adding elastomers like SBS (styrene-butadiene-styrene) (Touze-Foltz et al., 2015).

The oxidized bitumen forms a tight mass which flow tempera-ture is about þ80� C, the temperature of low-temperature brittle-ness is 0 �C, the maximum strain is close to 0% and elongation is afew percents. The elastomeric bitumen, mixed with the filler, formsa sealing mass that will exhibit creep at 120 �Ce130 �C; the tem-perature of low-temperature brittleness ranges between �20 �Cand �30 �C, the maximum strain is lower than 10% and the elon-gation at break is larger than 1500% (Touze-Foltz et al., 2015). As aresult the workable temperature range is increased throughoxidation and even more when modified by adding elastomers.

Unfortunately, the single study by Touze-Foltz et al. (2015) isinsufficient to fully understand the durability of elastomeric bitu-minous GMs. Indeed results obtained are valid for a given experi-mental site in a given context. Additional study could becontroversial. To evaluate a potential ageing of elastomeric bitu-minous GMs, the present study analyzes GM samples taken fromponds at two different sites in France: the Bazancourt site and theKronenbourg site. The GM samples were removed from the pondsin 2012 after having been installed there 6e30 years prior.

Section 2 of this paper describes the characteristics of elasto-meric bituminous GMs and presents the testing sites and GMs usedin this study. Section 3 describes the various analytical methodsapplied to the GMs: uniaxial tensile tests, flow-rate measurements,and size-exclusion chromatography (SEC). The results are pre-sented in Section 4, followed by a discussion in Section 5 and aconclusion in Section 6.

2. Materials and sampling sites

2.1. Elastomeric bituminous geomembranes

2.1.1. General features of geomembranesBituminous GMs are multicomponent products made by

combining a waterproof bituminous binder with a reinforcement,and a processing of the surfaces (as detailed below) to produce afinished product. The elastomeric bituminous GM presented in thiswork is made a base pure bitumen converted by adding elastomerssuch as styrene-butadiene-styrene (SBS). Considering the Styrene-Butadiene-Styrene chemical structure (SBS) (Fig. 1) Fourier Trans-formed analysis in attenuated total reflectance mode of the core ofthe 30 years BGM studied (Fig. 2) highlight SBS absorption bands at966 cm�1 corresponding to the butadiene double bond of the SBS

Fig. 1. Styrene-Butadiene-Styrene chemical structure (SBS).

and 700 cm�1 to the monosubstituted aromatic ring.The elastomeric bitumen forms a sealing mass with a creep

temperature from approximately 120 to 130 �C and exhibits low-temperature brittleness between �20 and �30 �C. The maximumstrain is less than 10% and the elongation at break is greater than1500%.

Elastomeric bituminous GMs have gradually replaced the oldertechnology of oxidized bituminous GMs (Touze-Foltz et al., 2015)because of their better resistance to exposure to UVs, as is illus-trated in this paper.

Three types of reinforcement are possible: (1) a glass veil, (2) anonwoven polyester geotextile, and (3) a composite consisting ofglass veil and polyester. The role of the reinforcement is to allow theGM to withstand the mechanical stresses to which it is subjectedduring its installation or during the operation of the facility. Thereinforcement endows the GM with its properties related to trac-tion, static puncture, dynamic puncture, and tear resistance. Thereinforcements typically undergo two treatments to produce abituminous GM: the first treatment consists of impregnating thereinforcement with a bituminous binder which, in the case of thepresent study, is an elastomeric bitumen, and the second treatmentconsists of coating the top of the elastomeric bitumen impregnatedreinforcement layer with a layer of the same bituminous binder.The impregnation consists of saturating the reinforcement to fillthe voids and remove the air and any residual moisture. The coatingconsists of adding bituminous mass underneath or on top of thereinforcement to give the required thickness and to ensure a bondat the overlap between GMs to the final product. The reinforcementis required to store, handle, and install the GM.

Processing the GM surfaces by sanding or by applying film notonly avoids having the turns of a GM roll bond to themselves, butalso performs additional functions, such as increasing the frictionangle (for sanding) and preventing root penetration (for film).

2.1.2. Ageing mechanismsBitumens are highly complex materials because they are

composed of numerous hydrocarbons. As a viscoelastic material,bitumen plays a prominent role in determiningmany aspects of GMperformance. Bitumen mechanical performance (cracking, creep,…) is function of solicitation type and thermal conditions, like forany viscoelastic material. The properties of the elastomericbitumen depend on the polymer characteristics and content, thebitumen nature, and the blending process (Isacsson and Lu, 1999).However, the enhanced properties of the elastomeric bitumen canevolve as a result of ageing during the manufacturing of the ma-terial, storage, and installation (Lu and Isacsson, 1998). Thus,knowledge of the chemical structure of the bituminous bindermakes it possible to characterize its ageing and how it affectsperformance.

The complexity of ageing increases when polymer-modifiedbitumens are involved. The principal cause of ageing of bitumi-nous binders in the field is known to be oxidation of certain mol-ecules (due to atmospheric oxygen) and polymer degradation. Suchoxidation results in the formation of highly polar and stronglyinteracting oxygen-containing functional groups (Petersen, 1998).Polymer degradation results in scission of polymer chains, whichproduces oligomers (Mouillet et al., 2008). Bitumen ageing resultsin an increase of high-molecular-weight compounds (Lesueur,2009; Mouillet et al., 2011). These changes in molecular weightare easily detected by using SEC, which separates molecules from amixture according to their size (Fayolle et al., 2007). The Break ofpolymer chains decreases binder elasticity. Polymer bitumensbecome more sensitive to mechanic and thermic solicitations. Therisks of cracks increase with a possible alteration of GM sealing(Airey, 2004; Mouillet et al., 2011).

Fig. 2. ATR-FTIR spectrum of the core of the 30 years old BGM studied. (Spectrum performed with 32 scans and a resolution of 4 cm�1).

Table 2Thickness and mass per unit area of virgin geomembranes.

Thickness EN 1849-1 (mm) Mass per unit area EN 1849-1 (g/m2)

GMrefK (3.04 ± 0.10) mm (k ¼ 2) (3779 ± 115) g/m2 (k ¼ 2)GMrefB (4.16 ± 0.08) mm (k ¼ 2) (4947 ± 97) g/m2 (k ¼ 2)

B: Bazancourt.

N. Touze-Foltz, F. Farcas / Geotextiles and Geomembranes 45 (2017) 121e130 123

Applied to linear SBS and radial SBS modified bitumen, SEC al-lows distinguishing between elastomer architectures in bitumen(Mouillet et al., 2008). The PmB chromatograms display, for thepolymer part, a bimodal distribution in the case of radial SBS and amonomodal distribution in the case of linear SBS (Mouillet et al.,2011).

K: Kronenbourg.

2.1.3. Geomembranes testedTable 1 presents the various samples used in this study. Samples

GM6B, GM10B, GM15B, GM20B were taken from various ponds at theBazancourt site, respectively after 6, 10, 15 and 20 exposure years(see Section 2.2.2). GMs GM30K1 and GM30K1 were taken from theKronenbourg site (subscript K) (see Section 2.2.1), where the GMhad served for 30 years.

GMs from Bazancourt site (subscript B) GM6B to GM20B contain anonwoven polyester geotextile with a mass per unit area of 235 g/m2 and a glass veil with a mass per unit area of 50 g/m2. These GMsare similar in terms of thickness, mass per unit area and nature ofbinder to GM GMrefB (see Table 2), which was produced in 2014 bythe same manufacturer.

Specimens GM30K1 and GM30K2 from the same GM contain apolyester nonwoven geotextile with a mass per unit area of 180 g/m2, which is similar to the mass per unit area of GM GMrefK, alsoproduced by the same manufacturer in 2014.

Table 1Measurements made on the various samples.

Age of BGM (years) Sample Measurement

SEC

6 BGM6B x10 BGM10B x15 BGM15B x20 BGM20B x30 BGM30K1

BGM30K2 x

The thickness and mass per unit area of GMs GMrefK and GMrefBare given in Table 2.

2.2. Locations and climate

2.2.1. Kronenbourg siteThe Konenbourg site is in Obernai in the Bas-Rhin department in

France, on the industrial site of the Konenbourg company (abrewery). The pond incorporates a levee used to collect rainwaterand also receives releases from process stirring. The pH of theeffluent varies from 2 to 7.

The GMwas installed 30 years prior to the time of sampling (theinstallation was completed in 1981). The samples were taken fromthe top of the slope, face south.

The underlying layer at this site consists of rolled 0/20 mm

Flux (EN 14150) Uniaxial tensile test (EN 12311-1)

xx x

xx x

xx x

Fig. 3. Stainless-steel cell and pressure-volume controllers to measure flow throughBGMs.

N. Touze-Foltz, F. Farcas / Geotextiles and Geomembranes 45 (2017) 121e130124

gravel with the bituminous GM resting directly on this layer. Thepond has a storage volume of 55 000 m3, of which 10% is regularlyused, with peaks up to 35%. The slope is angled at 27� and is 7 mlong.

Over the last 20 years, the air temperature extremesaveraged �15 �C for the colder months and þ38 �C for the warmermonths, with an average annual temperature ranging from 6.6 to15.3 �C. The running average of sunshine hours over a 10 yearsperiod in this region ranged from 1456 to 2198 h. For comparison,the average annual duration of sunshine over the last decade was2113 h.

2.2.2. Bazancourt siteThe Bazancourt site is a sugar refinery located in the Marne

region of France. This site contains nine ponds. Over the last 15years, peak air temperatures in the region averaged �13 �C for thecoldest months and þ39 �C for the warmest months, with anaverage annual temperature ranging from þ6.1 to þ15.1 �C. Duringthe last decade, the average annual duration of sunshine in thisregion ranged from 1274 to 2026 h.

3. Experiments

Table 1 lists the measurements that were made on each GMsampled. In addition, some measurements were made on GMsrecently produced by the same manufacturer (see Table 2). Tofacilitate comparing the evolution of the mechanical properties, thevirgin GMs had the same reinforcement structure as those takenfrom the field sites. The various GM samples were characterized byuniaxial tensile tests (EN 12311-1), flow-rate measurements (EN14150), and SEC.

3.1. Unidirectional tensile characteristics

The tensile characteristics of the GM specimens were deter-mined according to EN 12311-1. The displacement speed used forthese measurements was 100 mm/min. The results of these mea-surements were used to study the tensile force and the corre-sponding elongation of the GM during the tests.

3.2. Flow-rate measurement

The flow-rate measurement was first developed in France(Durin et al., 1998; Eloy-Giorni, 1993; Lambert and Touze-Foltz,2000; Pelte, 1993; Touze-Foltz, 2012) to quantify flows throughGMs destined for applications involving hydraulic gradients. Thiswork led to a French standard and later to a European standard (EN14150) for measuring the steady-state liquid flow through GMs. Byusing this method and the associated apparatus, the flow can bemeasured with confidence down to 10�6 m3 m�2 d�1.

EN 14150 stipulates that the two-part cell used for these mea-surements (see Fig. 3) be made of stainless steel because it mustresist oxidation during long-term immersion. Hydraulic pressuremay be applied over each part of the cell cavity, and a porous discplaced in the downstream cavity prevents the GM from deforming.

The cell was designed to clamp and hold specimen withoutallowing any leaks at the interface between specimen and cell. Thecell has no tightening system; clamping between flat surfaces isusually sufficient (if not, a sealant is added). The minimum diam-eter of the measuring chamber is 0.2 m, and the cell is equippedwith an inlet and outlet to allow liquid to pass through the cell.Finally, each section contains a flushing valve.

The volume of GM specimens was measured by using apressure-volume controller. This device applies a constant pressureto the specimen while measuring the volume. It consists of a

cylinder through which a piston slides. A computer controlledmotor drives the piston to apply the desired pressure, which ismeasured by a pressure sensor. Displacement of the piston corre-sponds to changing the volume of the liquid.

3.3. Size-exclusion chromatography

The bituminous binder of the elastomeric bituminous GM wasanalyzed by SEC, which was done on specimens consisting of about2% (weight/volume) bitumen solution in tetrahydrofuran (THF). Tomake the specimen, about 0.1 g of bitumenwas taken from the GMcore (i.e., at the interface with the reinforcement; see Fig. 4) andimmersed in 5 mL of THF. Once the binder was solubilized, thesolution was filtered through 0.45 mm Wathman polytetrafluoro-ethylene syringe filters to remove any remaining solid elements,following which 50 mL of the filtered solution was injected into thechromatographic system by using a Waters instrument (Saint-Quentin-en-Yvelines, France) equipped with a 610 pump managedby a 600 controller and a 4214 differential refractometer detector.Two series of mixed-gel columns provided by Agilent TechnologiesPolymer Laboratories (Les Ulis, France) were used: a PL Mixed-D5 mm column and a guard column PLgel 5 mm. Data were ac-quired with the AZUR V4.6 software from Datalys (Saint Martind'H�eres, France). A high-performance liquid-chromatography-grade THF solvent from Carlo Erba Reactifs SDS (Val de Reuil,France) was used as the mobile phase at a flow rate of 1 mL/min.

Each sample was analyzed three times. The SBS fraction inbitumenwas calculated from the ratio of the areas of the SBS peakswithin the area of the spectrum of the entire binder (polymer plusbitumen) according to Equation (1):

SBS peak areaðSBSþ bitumenÞ peaks area

� 100 (1)

4. Results

4.1. Unidirectional tensile characteristics

Fig. 5a and b presents an overview of the various results ob-tained in terms of force as a function of deformation in the machinedirection (i.e., strain). For comparison, results obtained from virginGMs are also shown. Detailed data on the strength and elongation

Fig. 4. Schematic drawing of BGM made of bituminous BGM and location from where various samples of bitumen binder were taken.

N. Touze-Foltz, F. Farcas / Geotextiles and Geomembranes 45 (2017) 121e130 125

at maximum force are given in Table 3.Results presented in Fig. 5a correspond to samples GM15B and

GM6B from the Bazancourt site. The characteristics of these samplesare similar to those of the virgin GMrefB. All curves peak at about 4%strain, which corresponds to rupture of the glass veil. The sharpdrop above 40% strain corresponds to the rupture of the geotextile.

Results presented in Fig. 5b correspond to GMs taken from theKronenbourg site (samples GM30K1 and GM30K2), whose responseto uniaxial tensile tests is similar to that of GM GMrefK. No peakcorresponding to the rupture of the glass veil appears because glassveils were not incorporated during manufacturing. For this secondfamily of GMs, the maximum force at rupture is less than that forthe first family of GMs, which is attributed to the smaller mass perunit area of the geotextile used in the second family of GMs.

The results indicate that the relationship between strain andstrength does not significantly change with time, which couldreveal an evolution of the geotextile or glass veil over time in thefield. The results given in Table 3 also indicate that the relationshipbetween force and strain at failure remains essentially constantover the time during which the GM is exposed. The conclusionimposed by these results is that the geotextile and glass veil in theGMs did not change detectably during the time that the GMs wereexposed in this study.

4.2. Flow-rate measurements

Table 4 gives the flow rate measured for GMs GM10B GM20B, andGM30K2. For all GMs, the measurement was done according to EN14150, which means that a 100 kPa difference in hydraulic pressureexisted between the surfaces of the GM. For GMs GM20B and GM10B,the measured flow ratewas less than 10�6 m3 m�2 d�1, which is thethreshold for this standard. In the case of the oldest GM (GM30K2)the flow ratemeasured is slightly larger than 10�6 m3m�2 d�1. Suchvalues have previously been observed with virgin bituminous GMsso that the flow rate obtained cannot be indicative of an effect of anageing phenomenon of the GM.

From a hydraulics point of view, the performance of the testedGMs is thus similar to that of a virgin GM of the same type (forwhich the flow rate is below 10�6 m3 m�2 d�1 or slightly larger(Touze-Foltz and Zanzinger, 2009)). No change in the function ofGMs (i.e., watertightness) is thus detected for the exposed elasto-meric bituminous GMs, even after 30 years of exposure to the cli-matic conditions described above at the two sites.

4.3. Size of polymer chain

SBS degradation was evaluated by considering how the elas-tomerweight evolves as a function of depthwithin the GM. For this,bituminous binder extracted from the top, the core, and the

geotextile of the GM was analyzed (see Figs. 6e8).

4.4. Evolution of polymer in bituminous binder extracted from topof geomembrane

Fig. 6 shows chromatograms of elastomeric bitumen extractedfrom the top of the 6- and 10-year-old GMs, which reveals thepresence of the polymer eluted at two poorly separated peaks(11.80 and 12.5 mL) and at a shoulder at 12.4 mL (residual SBS).Bitumen, which molar mass is smaller than SBS one (Mouillet et al.,2008; Zhao et al., 2016), elutes at 17.3 mL. In contrast, after 15 years,because of ageing the polymer chromatographic peaks becomenegligible.

In addition, the shoulder at 14.8 mL increases for GMs after 15,20, and 30 years of exposure. The increases in the concentration oflarge molecules reveal the formation of large molecular structureslinked by hydrogen links due to oxidation of the bitumen.

The decrease of binder answer with ageing is attributed to a lossof modified bitumen due to erosion. Consequently the part ofbinder is lower than the part sampled from the core of the GM.

Based on the usual polymer ratio incorporated into bituminousGM (about 15% and 13% for linear SBS and 13.5%e11.5% for radialSBS), the small fraction of SBS calculated for GMs exposed for 6 and10 years, considering the SEC peak area of SBS and (SBS þ bitumen)ratio, and the inexistent polymer response at 15, 20, and 30 yearsreveals that the polymer has degraded by chain scission due tophoto- and thermo-oxidation (Table 5). Part of the polymer mayhave cross linked or formed gel, thereby also being retained on thefilter and avoiding quantification.

It is important to note that these results, revealing loss of thepolymer and oxidation of the bitumen, affect only the extremeupper surface of the GM. These results do not apply over the entirethickness of the GM.

4.5. Evolution of polymer contained in bituminous binder extractedfrom core of geomembrane

Chromatograms of elastomeric binders extracted from the coreof 6-, 10-, and 20-year-old GMs show two poorly separated peaks at11.80 and 12.5 mL (Fig. 7), which indicate the presence of polymerin these samples. In the same figure, three peaks (11.4, 11.8, and12.5 mL) indicate that SBS is present in the 15-year-old GM. Thissize distribution reveals a different formulation of the polymer inthis GM than in the other GMs: the binders of the 6-, 10-, and 20-year-old GMs contain linear SBS, whereas the 15-year-old GMbinder was probably manufactured with a mixture of linear andradial SBS.

For all the aged GMs considered, SBS elution peaks appear in thechromatogram zone between 10.0 and 14.7 mL, which means that

Fig. 5. Force as a function of strain obtained from uniaxial tensile tests (a) for geomembranes from the Bazancourt site and (b) for geomembranes from the Kronenbourg site.

N. Touze-Foltz, F. Farcas / Geotextiles and Geomembranes 45 (2017) 121e130126

Table 3Results of uniaxial tensile tests done according to EN ISO 527-3 at maximum force inmachine direction.

Strength (kN/m) Strain (%)

BGM refK 18.3 41.2BGM30K1 17.3 39.8BGM30K2 18.3 44.3BGM ref2 25.4 43.2BGM20B 31.7 54.8BGM15B 26.0 54.2BGM6B 28.7 46.9GM10B 30.2 41.4

Table 4Results of flow-rate measurements.

GM Flow rate (m3 m�2 d�1)

BGM10B 4.46 � 10�7

BGM20B 7.03 � 10�7

BGM30K2 1.12 � 10�6

Fig. 6. SEC chromatograms of elastomeric bitumen extracted from top of aged BGM.

Table 5Fraction of SBS in the bitumen ( SBS peak area

ðSBSþbitumenÞ peaks area � 100) extracted at various locations.

GM6B GM10B GM15B GM20B GM30B

m (%) s m (%) s m (%) s m (%) s m (%) s

SBS fraction of binder extracted from the top of the BGM 4.2 0.091 2.6 0.113 ~0 / ~0 / ~0 /SBS fraction of binder extracted from the core of the BGM 11.2 0.100 11.7 0.040 8.8 0.128 11.4 0.344 7.4 0.04SBS fraction of binder extracted next to geotextile of the BGM 12.9 0.108 12.7 0.232 9.3 0.328 10.6 0.081 8.8 0.206

m: Mean (%).s:Standard deviation.

N. Touze-Foltz, F. Farcas / Geotextiles and Geomembranes 45 (2017) 121e130 127

the polymer is still present in the bitumen of these GMs. No changeis detected based on the SBS elution peaks in the 6-, 10-, and 20-

year-old GMs. From this result we deduce that, for less than 20years of exposure, the polymer in the GMs did not degrade. Incontrast, after 30 years of exposure, the SBS elutes under a largemass between 9.1 and 13.8 mL, with a maximum towards thesmaller molecular weights. The profile of the chromatographyspectrum of SBS from the 30-year-old bituminous GM reveals thatit degraded because of breaks in the polymer chains. Without anybenchmark, it is not possible to judge of the extent of degradationof the radial SBS in the bitumen of the 15-year-old GM. No oxida-tion of the bitumen is detected.

Table 5 lists the polymer ratios of each binder, which are about11.5% after being exposed for 6, 10, and 20 years, 9% after exposurefor 15 years, and 7% after exposure for 30 years. The amount of SBSappears unchanged after 6, 10, and 20 years of exposure in theponds. The lowest polymer ratio calculated for GMs with 15 and 30years of exposure can be attributed either to the retention of thepolymer during the filtration stage of the solution before chro-matographic analysis, to an effective loss of SBS without degrada-tion that can be detected by SEC, or to a different polymer

formulation.The results of SEC show that, after 30 years of exposure in a

Fig. 7. SEC chromatograms of elastomeric bitumen extracted from core of aged BGM.

Fig. 8. SEC chromatograms of elastomeric bitumen extracted near geotextile of aged BGM.

N. Touze-Foltz, F. Farcas / Geotextiles and Geomembranes 45 (2017) 121e130128

N. Touze-Foltz, F. Farcas / Geotextiles and Geomembranes 45 (2017) 121e130 129

pond, the elastomer remains in the GM core. Degradation of thepolymer chains is observed only for GMs exposed for 30 years.

4.6. Evolution of polymer contained in bituminous binder neargeomembrane geotextile

Chromatograms of the binders extracted from the 6-, 10-, and20-year-old GMs are identical (Fig. 8). In a 20-year-old GM, nomodification of the elastomer contained in the binder near thegeotextile is detected. Because of the lack of a benchmark for the15-year-old binder, which differs from the binder in the 6-, 10-, and20-year-old GM, we are forced to conclude that the linear and radialSBSs are still present in the bitumen. Only the chromatogram of the30-year-old GM binder reveals a broadening of SBS peaks, whichindicates smaller molecular weights, meaning that the polymerwas degraded by scission of its chains.

The polymer ratios reported in Table 5 are comparable to thosecalculated for the binder extracted from the core of the GM.

The results of SEC of the binder extracted from three depthswithin the elastomeric bituminous GM aged in ponds indicate thatthe polymer is significantly degraded and that the bitumen at thetop surface of the GM is oxidized. This result, which applies to onlya very small part of the GM, may not be representative of thechemical structure of the entire GM. In fact, the elastomer isdegraded only for the 30-year-old GM and the bitumen for this GMis not oxidized.

5. Discussion

Tensile tests make it possible to study the evolution of themechanical properties of the glass veil and the nonwoven polyestergeotextile located at the core of the GM; our results indicate thatneither was affected even after 30 years of exposure.

SEC makes is possible to separate molecules from a mix ac-cording to their size. By using this technique, changes in molecularweight due either to chain scission in the polymer (intensity ofpolymer peaks diminution and displacement to smaller elutionvolumes) or to oxidation of the bitumen (increase of the bitumenshoulder at 14.3 mL due to formation of large molecular sizestructures) are easily detected.

The results of SEC indicate that the polymer is no longer presentwithin the first fewmicrons of the exposed surface of the GMs olderthan 15 years. In parallel, oxidation is detected. However, thisdegradation at the surface is not representative of the state of thebitumen binder in deeper layers of the GM or at the core, at theinterface of the glass veil and the geotextile. Based on their un-changed mechanical properties, we conclude that the bitumenbinder and glass veil deep within the GM were adequatelyprotected.

According to the literature, an increase in the molecular weightof the bitumen compounds and the degradation of SBS by scissionof the polymer chain after 30 years of exposure results in an in-crease in the rigidity of the bitumen and some brittleness. However,it does not alter the watertightness of the GM. In fact, the flow ratethrough the 30-year-old GM is remains less than 10�6 m3 m�2 d�1,which is the maximum allowed by EN 14150 and is the same as theflow rate of virgin GMs (thicker than 1 mm).

6. Conclusions

This paper presents a study of the evolution of an elastomericbituminous GM installed in ponds at two different sites (Bazancourtand Kronenbourg, France) for periods of 6, 10, 15, 20, and 30 years.The study is based on unidirectional tensile tests, size-exclusionchromatography, and flow-rate measurements.

The results of SEC indicate that, within the first few micronsfrom the surface of GMs exposed for over 15 years, the polymer iscompletely consumed (i.e., transformed into oligomer). In parallel,within the same surface layer, the bitumen is oxidized in GMsexposed for greater than 15 years. However, the disappearance ofthe polymer and the oxidation of the bitumen do not extendthroughout the entire layer of bitumen binder. In fact, at the GMcore, the results indicate that the polymer content is unchanged forGMs exposed between 6 and 20 years.

For the GM exposed for 30 years, the polymer, although stillpresent at the core, has been altered. Nevertheless, this GM stilldelivers the same level of watertightness as virgin GMs. Thus, thehydraulic properties of the GMs are not significantly affected bythese chemical modifications at the GM surface.

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