the influence of bitumen on plastic roof and sealing membranes · leopold glück: the influence of...

Special edition:

The Influence of Bitumen on Plastic Roof and Sealing Membranes

Dipl.-Ing. (FH) Leopold Glück

Translation of a publication in the special magazine „Bauphysik“ (26th year, April 2004, Issue 2 ISSN 0171-5445)

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Leopold Glück: The Influence of Bitumen on Plastic Roof and Sealing Membranes

In future, bitumen compatibility will be checked according to the European standard DIN EN 1548 and assessed according to DIN EN 13956. The results show that the procedures and assessments stipulated by the above standards in their current version are not suitable for providing a reliable assessment and classification of the membranes as bitumen-compatible or not bitumen-compatible. Some current classifications provided by manufacturers should also be regarded as questionable.

1 Introduction

If plastic roof or sealing membranes are in direct contact with bituminous building materials, these membranes need to be bitumen-compatible. Bitumen-compatible means that even in the long term these membranes must not change such as to compromise their functionality (sealing effect).The procedure for determining the influence of bitumen on plastic roof and sealing membranes is described in DIN 16726 [1]. The Technical Committee CEN/TC 254 „Sealing Membra-nes“, Sub-Committee SC2 „Plastic and Rubber Sealing Memb-ranes“ worked out E DIN EN 1548 [2] as a European standard and submitted a draft version to the public. The objective of the standard is to provide criteria for the characterisation and classification of plastic and elastomer membranes - after their production or delivery and before their use.

2 Test procedures

Table 1 summarizes the most important test criteria of the two standards mentioned above. The tests were carried out on commercially available roof and sealing membranes listed in Table 2.

Performance of tests

The tests were carried out in the test laboratory of SKZ–TeCo-nA GmbH, a test laboratory accredited according to DIN EN ISO/IEC 17025 [3].The bitumen was stored in compliance with E DIN EN 1548 [2] and according to the following test principle: the membranes have rear side contact with a bitumen layer of 3 mm thickness at a temperature of 70 °C. The test quality used was commer-cial standard bitumen 85/25.The membrane properties were determined both before and after a contact storage time of 7, 28 and 90 days under stan-dard climatic conditions according to DIN 50014-23/50-2, after allowing the membranes to adjust to ambient temperature for at least 24 hours.

As bitumen is exposed to higher temperatures during storage, additional reference samples were stored at 70°C to allow a comparison of the temperature influence. The following measurements were carried out to determine the influence of temperature and bitumen on the properties of membranes:– Determination of mass changes according to

DIN EN 1849-2 [4]– Determination of dimensional stability according to

DIN EN 1107-2 [5]– Determination of changes in appearance according to

E DIN EN 1548, par. 8.7 [2]– Determination of foldability at low temperature according to

DIN EN 495-5 [6]– Determination of tensile properties according to

procedure B of DIN EN 12311-2 [7].

Dipl.-Ing. (FH) Leopold Glück studied plastics technologies at the University of Applied Sciences of Würzburg-Schweinfurt. From 1981 to 2003, he worked as a research associate at the „Süddeutsche Kunst-stoff-Zentrum“ (SKZ) in Würzburg. Since 2003, he has worked from his own expert‘s office as an official technical consultant in the specialist field of sealing technology. www.svglueck.de

Leopold Glück

The Influence of Bitumen on Plastic Roof and Sealing Membranes

Table 1: Most important test criteria of standard tests carried out on plastic roof and sealing membranes

Test criteria DIN 16726 [1] E DIN EN 1548 [2]

Type of bitumen Bitumen 85/25 Standard type; in case of doubt 95/25 from a Vene-zuelan source

Test principle Rear side contact with 3 mm bitu-men, membrane is loosely laid on top

Rear side contact with 3 mm bitu-men, membrane is loosely laid on top

Storage temperature

70 ± 2 °C 70 ± 2 °C

Exposure time 28 days Standard test: 28 days, any other time possible depending on requirement

Determination of property changes due to bitumen contact storage

8 days after con-tact with bitumen (conditioning at standard atmos-phere)

Not specified

Assessment criteria

Secant modulus E

1-2

a) Change in massb) Dimensional

changec) Change in

appearanced) Change in

physical properties: - foldability at low temp. - other properties by agreement

© 2004 Wilhelm Ernst & Sohn Verlag für Architektur und technische Wissenschaften GmbH & Co. KG, Berlin • Bauphysik 26 (2004), Heft 2

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The tensile strength properties were determined on a minimum of five test specimens of type B, taken from the membrane in transverse direction. Tensile strength at break and elongation at break were measured at a test speed of 100 mm/min. The secant modulus E

1-2 was determined between 1 and 2 %

elongation at a test speed of 1.25 mm/min.

3 Test results

Under the influence of bitumen contact different reactions result, depending on the type of polymer used. Depending on their chemical composition, the membranes are subject to certain changes which may either be of a reversible or irreversible nature. When the roof membrane is in contact with bitumen, two processes can be observed: first, the physical process of wetting, followed by the low-molecular bitumen components diffusing into the interior of the roof membrane. This penetration causes the membrane to swell. As the chemical structure of the plastic material becomes increasingly similar to that of the penetrating bitumen, its solubility increases, resulting in a higher degree of swelling. As a rule, this swelling leads to a softening of the material. Apart from the sorption of bitumen components, it may also oc-cur that components of the roof membrane, or reaction products resulting from the interaction between the plastic and the penet-rating bitumen, exude. If, for instance, the monomeric plasticizer migrates from the membrane into the bitumen, this causes the material to stiffen and sometimes even leads to embrittlement.If and to which extent the application properties of roof and

sealing membranes change under this influence, depends on the type of polymer, on the composition (fillers, plasticizers, fire-proofing agents and other additives) as well as on the conditi-ons of exposure. A rise in temperature during storage causes an exponential increase in reaction speed, while at the same time facilitating the bitumen‘s diffusion into the plastic.

3.1 Changes in mass

Figure 1 shows the different influence of bitumen on the weight of plastic roof and sealing membranes. The mass changes of the membrane types are plotted in relation to time. While PVC-P-BV shows the smallest change, a steady increase in mass can be observed with EVA and PE-C-E-PW membranes which even after 90 days of storage is not finished. The highest incre-ase in mass was measured for FPP, the highest loss in mass for PVC-P-NB.Figures 2 to 6 illustrate the behaviour of the individual mem-brane types even more clearly. For each type of membrane the mass change is plotted over the time of bitumen contact storage, as well as the reverse drying behaviour after a contact storage time of 7, 28 and 90 days. Over a period of 90 days, the mass of PVC-P-BV slightly incre-ases by about 1 % (figure 2). With increasing storage time, the mass decreases after reverse drying at standard atmosphere (by about 2 % after 90 days). It can thus be said that during contact storage the membrane takes up a low amount of bitu-men while a low amount of components is dissolved from the membrane.

Table 2: Tested materials

Type of membrane Short name

Nominal thickness

Material standard

BV3) Market launch

Plastic sealing membrane made of plasticized polyvinyl chloride, bitumen-compatible, black

PVC-P-BV 1.5 mm DIN 16937 yes 1963

Plastic roof membrane made of plasticized polyvinyl chloride, not bitumen-compatible, light grey

PVC-P-NB 2.0 mm DIN 16730 no 1972

Plastic roof membrane made of flexible polypropylene, grey

FPP 1)

(TPO/FPA)2)

1.2 mm - yes about 1994

Plastic roof membrane made of ethylene-vinyl acetate, white

EVA(EVAC) 1)

1.2 mm - yes 1978

Plastic roof membrane made of chlorinated polyethylene with a fabric inlay, grey

PE-C-E-PW 1.5 mm DIN 16737 yes 1976

1) Name according to prEN 13956 [8] 2) Name given by manufacturer 3) BV = „bitumenverträglich“ (bitumen-compatible) acc. to manufacturer

Figure 1: Mass change after up to 90 days bitumen contact storage at 70 °C and subsequent reverse drying at standard atmosphere

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Figure 2: Mass change of PVC-P-BV after 7, 28 and 90 days of bitumen contact storage at 70 °C and sub-sequent reverse drying at standard atmosphere

Figure 4: Mass change of FPP after 7, 28 and 90 days of bitumen contact storage at 70 °C and subsequent reverse drying at standard atmosphere

Figure 3: Mass change of PVC-P-NB after 7, 28 and 90 days of bitumen contact storage at 70 °C and sub-sequent reverse drying at standard atmosphere

Figure 5: Mass change of EVA after 7, 28 and 90 days of bitumen contact storage at 70 °C and subsequent reverse drying at standard atmosphere

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In the case of not bitumen-compatible membranes made of PVC-P, a continuous loss of mass can be observed (figure 3). After bitumen contact storage, the weight remains constant. The most important effect is thus attributable to monomeric plastici-zer migrating from the PVC-P membrane into the bitumen.FPP membranes show a substantial increase in mass which is reversible only to a small extent (figure 4). Even after 90 days‘ mass increase by approx. 30 %, the process is not yet finished.EVA and PE-C-E-PW show a similar behaviour (figures 5 and 6). While the mass constantly increases (even after 90 days no state of equilibrium is reached), it rapidly decreases after end of contact storage.All reference samples showed a mass loss of clearly less than 0.5 % after being stored at 70 °C in the compa-rative storage test.

3.2 Dimensional changes

If plastic sheeting or membranes are exposed to higher tempe-ratures, inner stress - frozen-in during the production process - is released, causing the material to shrink. This shrinkage is

usually determined after 6 hours of storage at 80 °C. With non-reinforced roof membranes it is less than 2%, in the case of reinforced membranes under 0.5 %. The membranes dimensional change in longitudinal direc-tion after bitumen contact storage basically reflects the results measured for the changes in mass (figure 7).

While the substantial mass loss of PVC-P-NB shows itself in a strong shrinkage by nearly 8 % after 90 days bitumen contact storage, the considerable mass incre-ase of FPP results in a longitudinal change by approx. 2 % (elongation). PVC-P-BV, EVA and PE-C-E-PW shrink only marginally; the amount of shrinkage hardly changes over the period of storage. On taking a closer look at the individual membrane types, it can be observed for PVC-P-BV that there is no difference between the bitumen contact storage and the comparative heat storage (figure 8). With membranes made of PVC-P-NB, the amount of shrin-kage steadily increases over the period of bitumen contact storage (figure 9). In the case of FPP, it is the length that continuously increases (figure 10). The homogeneous EVA roof membrane tends to increase in mass when stored in contact with bitumen, whereas its amount of shrinkage tends to decrease over time (figure 11). Due to a fabric insert, there is virtually no change in length (figure 12). In this case, the increase in volume caused by bitumen contact can only result in the membrane‘s increase in thickness as there can be no dimensional changes in the membrane plane.

Figure 6: Mass change of PE-C-E-PW after 7, 28 and 90 days of bitumen contact storage at 70 °C and sub-sequent reverse drying at standard atmosphere

Figure 7: Longitudinal change after 7, 28 and 90 days of bitumen contact storage at 70 °C

Figure 8: Dimensional change of PVC-P-BV in lon-gitudinal and transverse direction after 7, 28 and 90 days of bitumen contact storage and comparative heat storage at 70 °C

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Figure 9: Dimensional change of PVC-P-NB in lon-gitudinal and transverse direction after 7, 28 and 90 days of bitumen contact storage and comparative heat storage at 70 °C

Figure 10: Dimensional change of FPP in longitudinal and transverse direction after 7, 28 and 90 days of bitumen contact storage and comparative heat storage at 70 °C

Figure 11: Dimensional change of EVA in longitudinal and transverse direction after 7, 28 and 90 days of bitumen contact storage and comparative heat storage at 70 °C

Figure 12: Dimensional change of PE-C-E-PW in longitudinal and transverse direction after 7, 28 and 90 days of bitumen contact storage and comparative heat storage at 70 °C.

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3.3 Changes in appearance

A considerable change in appearance could only be detected on the not bitumen-compatible PVC roof membrane (PVC-P-NB). The FPP membrane had a tacky surface after storage.

3.4 Foldability at low temperature

Table 3 shows the results produced when folding the memb-ranes at low temperature. In their as-delivered state (Alz), the membranes‘ foldability at low temperature was measured both in longitudinal and transverse direction. After storage, the mem-branes were folded at a 10 °C higher temperature than deliver-ed. This test criterion had been stipulated by the EN 13956, but was changed again in the Formal Vote version [8].The PVC-P-NB membrane was the only type where after bitu-men contact storage - namely after as many as 90 days - the cold foldability temperature rose by more than 10 °C.((Table 3))

3.5 Tensile properties

In the DIN material standards for roof and sealing membranes, the E

1-2 modulus was introduced as a test criterion for bitumen

resistance. It indicates the membrane‘s resistance to minor deformations. If the E

1-2 modulus increases, the membrane

becomes more rigid; if the modulus decreases, this indicates a softening of the membrane.It is therefore not astonishing that the loss in mass after bitumen contact storage, measured for PVC-P-NB, results in a conside-rable modulus increase by more than 400 %. By contrast, the increase in mass determined for FPP causes the modulus to decrease by more than 60 % (figure 13). The changes measu-red for the remaining roof membranes (PVC-P-BV, EVA and PE-C-E-PW), classified by their manufacturers as bitumen-com-patible, amount to ± 25 % (figure 14). The E

1-2 modulus can be

regarded as a very sensitive measurement category. For this reason, changes in the range of ± 25 % can quite justifiably be classified as minimal.

Tensile strength at break and elongation at break are also frequently quoted categories to assess ageing processes under the influence of heat, weather or exposure to chemicals such as aqueous solutions. Figure 15 (tensile strength at break) and figure 16 (elongation at break) illustrate that - at least for PVC - this assessment is highly questionable as only very little dif-ference can be observed between the bitumen-compatible and the not bitumen-compatible membrane. What is striking in the

case of FPP membranes is the very rapid drop to a nearly con-stant level over time, and the steady increase in tensile strength at break observed for EVA membranes (figure 15).

3.6 Summary

The procedure stipulated in E DIN EN 1548 [2] for determining the influence of bitumen on roof and sealing membranes allows only a very rough comparison of the behaviour of different ma-terials when in contact with bitumen. This applies in particular when testing is limited to the specified test period of 28 days. According to prEN 13956 [8], plastic membranes can be classi-fied as bitumen-compatible if after 28 days of bitumen contact storagea) the loss in mass is smaller or equal to 5 % in the case of membranes equipped with a reinforcing layer or fabric backing;b) the change in the E

1-2 modulus is smaller or equal to 50 % in

the case of homogeneous membranes.Based on this definition, Table 4 provides an assessment of the different membrane types. According to the two criteria above, the not bitumen-compatible PVC-P membrane and the FPP membrane are classified as not bitumen-compatible since the 56 % increase of the modulus for the PVC-P-NB resp. the 60% decrease of the modulus for the FPP membrane only slightly exceed the permissible deviation of ± 50 %. It is therefore quite conceivable that with this „single-point method“ also not bitu-men-compatible membranes can be classified as bitumen-com-patible. The dubious nature of this assessment also shows itself in the fact that if a test had been carried out for a reinforced or fabric-backed variant of the FPP membrane, this would have resulted in the classification „bitumen-compatible“ as the weight loss after bitumen contact storage is in any case less than 5 %.

In order to allow a valid assessment of membrane resistance, it is therefore necessary - as is also general practice with other customary resistance tests - to prolong the period of contact storage until the point of constant weight is reached, and after storage to allow the material to dry back to constant weight as well. Only in this way is it possible to detect all processes that take place during contact with bitumen and to distinguish bet-ween reversible and irreversible phenomena.Apart from the change in mass, the

E1-2 modulus should always

be used as a test and assessment criterion since it is the most sensitive criterion for describing changes in the membrane‘s physico-mechanical properties. If possible, tests should be performed on homogeneous membranes. It is permissible to transfer the test results to membranes of identical formulation equipped with reinforcing inserts (nonwovens, scrims or fleeces) or to membranes of greater thickness.

Table 3: Influence of bitumen contact storage on foldability at low temperature

Storage time (d)

Cold foldability temperature (°C) (longitudinal / transverse)

PVC-P-BV PVC-P-NB FPP EVA PE-C-E-PW

0 (Alz)3) -25/-25 1) -35/-30 < -40/< -40 -35/-35 < -40/< -40

7 < -15/< -15 2) < -25/< -20 < -30/<- 30 < -25/< -25 < -30/<- 30

28 < -15/< -15 < -25/< -20 < -30/ < -30 < -25/< -25 < -30/<- 30

90 < -15/<-15 Cracks/Cracks < -30/< -30 < -25/< -25 < -30/<- 30

1) -25/-25 = longitudinal break at -25 °C / transverse break at -25°C 2) < -15/< -15 = no longitudinal break at test temperature of 15 °C (increased by 10° C compared to as-delivered state) / no trans-

verse break at 15 °C 3) Alz = as-delivered state

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Figure 13: Change of the E1-2 modulus after 7, 28 and 90 days of bitumen contact storage

Figure 14: Change of the E1-2 modulus after 7, 28 and 90 days of bitumen contact storage for the mem-brane types classified as bitumen-compatible by their manufacturers

Figure 15: Change in tensile strength at break after 7, 28 and 90 days of bitumen contact storage for homo-geneous membrane types

Figure 16: Change in elongation at break after 7, 28 and 90 days of bitumen contact storage for homogene-ous membrane types

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4 Discussion

Although it is not possible to transfer the lab results directly onto the behaviour of roof membrane materials under practical conditions of use, it is nevertheless possible to draw material-specific conclusions concerning the assessment of bitumen compatibility.To sum up, the PVC roof membrane (PVC-P-BV), classified as bitumen-compatible, shows the smallest changes. Restrictions for its use when in constant contact with bitumen can therefore not be derived for this membrane type.Membranes made of PVC-P, which have been classified as not bitumen-compatible and usually contain monomeric plasticizers, must not come into contact with bitumen since the monomeric plasticizer rapidly migrates into the adjoining bitumen, causing the PVC-P roof membrane to stiffen and eventually to embrittle.A somehow astonishing result is the considerable mass increa-se (swelling) of the FFP membrane which even after 90 days of storage was not finished, linked with an extremely low degree of reverse drying. After 90 days of storage, approx. 25 % (absolu-te) of the absorbed bituminous matter remained in the FPP. Ob-viously responsible for this effect are the elastifying, non-cross-linked elastomeric ingredients of the FPP membrane which virtually absorb the bitumen and do not release it any more. As

the swelling process also causes considerable changes in the membrane‘s physico-mechanical properties (material softening), a direct contact of bitumen and FPP is not recommendable in practice. Apart from the formation of waves on the roof due to the swelling, a longer contact with bitumen could also make welding of the membrane more difficult. Membranes made of EVA and PE-C show the same effects of a time-related increase in weight as FPP, only at a substantially lower speed. After 90 days of storage, these materials as well have not yet reached a state of equilibrium. A final assessment of their fitness for practical use would only be possible after reasonably prolonging the test period and/or after long years of practical use.It must be considered, however, that there are further criteria which influence the contact of plastic roof and sealing membra-nes and bitumen in practical use. These include in particular the membrane‘s special design or finish (fabric backing, separation layer) as well as the amount of bitumen components capable of migration (age of the bitumen membrane to which contact exists).

Bibliography

[1] DIN 16726:1986-12 Kunststoff-Dachbahnen; Kunststoff-Dichtungs-bahnen; Prüfungen

[2] E DIN EN 1548:2001-01 Abdichtungsbahnen; Verfahren zur Bestim-mung der Einwirkung von Bitumen; Kunststoff- und Elastomerbah-nen für Dachabdichtungen

[3] DIN EN ISO/IEC 17025:2000-04 Allgemeine Anforderungen an die Kompetenz von Prüf- und Kalibrierlaboratorien

[4] DIN EN 1849-2:2001-09 Abdichtungsbahnen; Bestimmung der Dicke und der flächenbezogenen Masse; Teil 2: Kunststoff- und Elastomerbahnen für Dachabdichtungen

[5] DIN EN 1107-2:2001-04 Abdichtungsbahnen; Bestimmung der Maßhaltigkeit; Teil 2: Kunststoff- und Elastomerbahnen für Dachab-dichtungen

[6] DIN EN 495-5:2001-02 Abdichtungsbahnen; Bestimmung des Ver-haltens beim Falzen bei tiefen Temperaturen; Teil 5: Kunststoff- und Elastomerbahnen für Dachabdichtungen

[7] DIN EN 12311-2:2000-12 Abdichtungsbahnen; Bestimmung des Zug-Dehnungsverhaltens; Teil 2: Kunststoff- und Elastomerbahnen für Dachabdichtungen

[8] prEN 13956 Abdichtungsbahnen; Kunststoff- und Elastomerbahnen für Dachabdichtung; Definitionen und Merkmale“, Formal Vote-Fas-sung Dezember 2003

Table 4: Assessment of bitumen compatibility according to prEN 13956 (yes = bitumen-compatible, no = not bitumen-compatible)

Type of membrane

Assessment criteria

Mass loss ≤ 5 %

(criterion for reinforced membranes)

Change in E1-2

modulus≤ 50 %

(criterion for homogeneousmembranes)

PVC-P-BV - yes

PVC-P-NB - no

FPP - no

EVA - yes

PE-C-E-PW yes

Dipl. Ing. (FH) Leopold Glück

Expert for

plastics technologies

publicly appointed and sworn by the Chamber of Industry and

Commerce of Würzburg-Schweinfurt, Germany.

Sheeting, roof and sealing membranes, floor and sports flooring, water protection

by means of coatings, lining and sealing work.

Enheim 45 97340 Martinsheim

Telefon: +49 (0) 9332 4930 Telefax: +49 (0) 9332 4972

Email: [email protected] Internet: www.svglueck.de

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