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Degradation of elastomeric parking garage membranes
Mailvaganam, N. P.; Collins, P.
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De gra da t ion of e la st om e ric pa rk ing ga ra ge m e m bra ne s
N R C C - 3 4 0 6 8
M a i l v a g a n a m , N . P . ; C o l l i n s , P .
O c t o b e r 1 9 9 3
A version of this document is published in / Une version de ce document se trouve dans:
oncrete International: Design and Construction,
15, (10), pp. 58-62, October-93
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Degradation Of Elastomerlc ·
Parking Garage Membranes
by Noel P. Mailvaganam and Peter G. Collins
, .
he protection that parking garage membrane systems pro-vide is contingent upon how well and for how long they function in service. They should not show any detrimental aging effects,
such as an increase in brittleness, and
should be unaffected by exposure to freeze-thaw cycles, salt spray, and the variety of chemicals found in service. Durability of such membranes is de-pendent on the interaction of the mate-rial with the various factors involved in the parking garage environment.
Therefore, it is important to under-stand the impact of the various envi-ronmental conditions as well as the properties and limitations of the mate-rials so that degradation problems can he avoided. Also, an understanding of the mechanism of degradation is re-quired to improve and predict mem-brane durability.
Typical defects that result from the deterioration of membranes include chalking, peeling, blistering, alliga-toring·, checking and wrinkling.' The cause may he due to premature solvent evaporation, improper surface prepara-tion, chemical attack by aggressive liq-uids and atmospheric pollutants, heat and light aging, membrane incompati-bility, or moisture problems.
Membrane systems
Most of the waterproofing systems used in parking garage decks are cold liquid-applied self adhering elastomers. These systems are usually applied in relatively thin coats, bonded continuously to the substrate and cured to form a seamless elastomeric waterproof barrier. Typi-cally, the systems consist of a primer, followed by a cold liquid-applied mem-brane (thickness of 30-60 mils [0.75-1.50 mm]) which is then overcoated with an abrasion resistant 60 mil thick wear coat. The wear coat consists of a high modulus material seeded with ag-gregate and bonded by a sprayed on tie coat. A cross section of the various coats of a typical thin adhesive membrane system is shown in Fig. I.
58
Membrane systems vary in chemical composition, types of wear resistant top coats, and method of application. Indi-vidual properties of membranes are gov-erned by the many factors peculiar to each material. The various types in-clude: one component urethanes, two component urethanes, two component solvent borne epoxy-urethrane blends, one component water borne neoprertes, and rubberized asphalt mastics. Mem-brane systems discussed in this paper are three urethanes (S I, S2, S3 ), an epoxy-urethane blend (S4), a neoprene (S5), and an asphaltic mastic (S6).
Modes of degradation
Membrane degradation consists of changes in physical properties caused by chemical and physical processes in-volving the breakdown of the ordered structure of the polymer in the formula-tion. The degradation processes of these materials are quite complex as they re-sult from a series of elementary phe-nomena which are dependent on a va-riety of factors including composition and structural defects produced during the compounding of the finished product. 2 Damage to the product may
result in the formation of some defects which will act as weak sites during its subsequent service life, promoting its deterioration. Thus, degradation in-volves a deterioration in the function-ality of the membranes.
The main degradation agents to be considered for elastomeric parking garage membranes are oxygen, auto-motive and deicing chemicals, water, oxidizing agents (especially ozone), heat, ultraviolet (UV) radiation, and abrasion.
The types of degradation can be sub-divided for convenience according to their various modes of initiation. These are: thermal degradation, chemical degradation, photodegradation and me-chanical degradation.
There is a strung relationship between the different modes of membrane degra-dation. Often, circumstances prevail that permit the simultaneous occurrence
of various modes of degradation.' A typical example is environmental processes, which involve the simulta-neous action of ultraviolet light, oxygen, and harmful automotive chemicals, and oxidative deterioration of elastomers based on the simultaneous action of heat and oxygen.
Thermal degradation - heat
aging
Heat aging characteristics are important because temperature changes drastically alter the properties of membranes. High temperatures may change their structure or cause the basic polymer to melt. Thermal degradation occurs when the polymer, at relatively elevated temper-atures, starts to undergo chemical mod-ifications. It can cause purely physical phenomena (plasticizer migration or change of morphology) or can promote chemical reactions like oxidation. Loss of plasticizer would decrease flexibility of the material, .and reduce its capability to accommodate low temperature move-ment. This is exemplified in the de-crease of elongation and tensile strength values (illustrated in Tables I and 2) on heat aging.
Most exterior decks of parking garages attain high surface temperatures
in summer, particularly if the membrane wearing course is black. Furthermore, car tires, depending on the distance trav-elled, can further increase the surface temperature well in excess of 100 C.' Therefore, it is essential that products used in the field should remain stable at these temperatures to retain their me-chanical properties.
Resistance to heat aging is deter-mined by the heat aging test (ASTM D 573). Heat aging effects determined on.
free films at two temperatures ( 40 C and
I 00 C) are shown in Table 2. The results are presented as a percentage of the original unexposed value given in Table I. At 40 C there is a moderate, overall decrease in mechanical properties, pri-marily due to a loss of elongation capa-bility. Exposure to I 00 C produced
TABLE 1 - Tensile strength and
elongation of free film samples.
Fig. 1 - Schematic of a typical membrane system.
TABLE 2 - Resistance to heat aging, 28
day exposure.
FZ:lj 7 daya 40"C
• 28 daya40"C • 7dlya IOO"C • 28 .UyJIOO"C
drastic reductions in the percentage of elongation in most membranes. At 100 C most samples showed a weight re-duction (Fig. 2), indicating a possible loss of volatile components or water. One of the samples (S6) melted when exposed to temperatures of 100 C.
Chemical degradation -effect
of automotive chemicals on
tensile strength and elongation
Chemical degradation. of membranes occurs when they are brought into con-tact with certain chemicals encountered in the parking garage environment. De-pending on the nature of the chemical, this type of degradation can be oxida-tion, hydrolysis, etc. Reactions start spontaneously and are temperature de-pendent. The time scale over which the degradation processes occur is depen-dent on microstructure of the polymer used in the membrane as well as the type and amount of additives present in the formulation.z
Many of the membrane systems based on epoxies, polyurethanes and neoprenes are resistant to most inor-ganic chemicals except for highly oxi-dizing agents such as nitric and sulfuric
October 1993
Sl S1
"
..
"
"
Fig. 2- Resistance to heat aging, weight changes (per-cent).
acids. In general, polymeric products re-sist freon, alcohol, animal fats, and oils.z.•.s Aromatic solvents, with a few exceptions, will soften and swell most compositions.
On a parking deck, the automobiles drip antifreeze, gasoline and water. To detennine resistance to these chemicals, 14 day cured free film coupons are im-mersed in water, ethylene glycol, and motor oil. After immersion, retention of both tensile strength and elongation ca-pacity are detennined. ASTM standard C 957 requires a retention of tensile strength of at least 70 percent for spec-imens immersed in water or ethylene glycol. No requirements for retention of elongation are stipulated. Percent reten-tion of tensile strength or elongareten-tion ca-pacity is calculated by the equation:
TR = P,/P, ·100
Where:
TR =percent retention of property
p, = value of property after testing
P, = value of same property when tested on control samples
Fig. 3 and 4 show the effects of auto-motive chemicals on the mechanical properties of free film specimens.6
Exposure to motor oil produces small changes in tensile strength and elonga-tion in four of the membranes tested. Similar reductions in elongation capac-ities are noted for S4 and S6 ( 68 percent and 7 4 percent reference value). Four of the membranes immersed in ethylene glycol (S I, S2, S4, S5) showed signifi-cant tensile strength reduction. How-ever, these changes do not appear to af-fect the elongation characteristics of all the membranes.'
Immersion in water produces signif-icant tensile strength reductions but little change in elongation capacity for most membranes. Most polymer based products absorb water. In the gaseous or liquid state water may be involved in different processes: it induces the break-down of the molecules by hydrolysis, plasticization, and solubilization. Ten-sile strength and elongation are ad-versely affected and the consequences depend upon the severity of the expo-sure and the service demands. Swelling is the predominant effect observed when absorption of water has occurred. Com-pounding ingredients are the principal factors in detennining water resistance, rather than the basic elastomer.
TABLE 3a - Effects of UV exposure on
free film mechanlca.l properties; results
after 1000 hours exposure.
TABLE 3b - Effects of UV exposure on
composite system mechanical properties;
results after 500 hours exposure.
drophilic (water attracting) com-pounding materials readily absorb water and the use of water soluble com-pounding ingredients may result
in
degradation of physical properties.M The results presented in Fig. 3 and 4 show that only some membranes meet the requirements of ASTM C957 for re-tention of tensile strength (>70 percent retention)
in
both ethylene glycol andwater.
Photodegradatlon -effect of UV
exposure on tensile strength and
elongation
Photodegradation consists of physical and chemical modifications produced by irradiation with UV or visible light. Degradation processes involve the for-mation of chemical groups due to the breakdown ofpolymer structure (chain-scission), creation of new chemical bonds (crosslinking), oxidation, or a combination of these processes. Energy absorbed from the light induces photo-chemical reactions at sites
in
the mole-cule which contain unsaturated groups. The products that result from theinitial
reactions easily break down under the effect of light. Principal environmental factors that determine the extent of the photochemical degradation in polymers are the wavelength and intensity of light, the ambient temperature and the presence of oxidizing agents in the at-mosphere. Photodegradation depends on the nature of the polymer, on the con-centration of defects, on unsaturated sites, impurities, and on the quantity of light energy absorbed by the material.' The chief effect produced by pho-todegradation is an increase in the glass transition temperature (T6) resulting in
80
the compounds changing from elas-tomers to less flexible materials,
Such changes
in
state can be detectedby
determining
the variation inme-chanical properties such as tensile strength and elongation
in
conjunction with fourier transform infrared spec-troscopy (Ff!R). The effects of UV ra-diation on the tensile strength and elon-gation of the waterproofing membrane are presentedin
Tables 3a and 3b. Marked reductions in the elongation ca-pacities of most membrane films are shown, some retaining just 29 percent of reference value. In general,there ap-pears to be a lossin
tensile strength for polyurethane based membranes (S I, S2, S3) and increases in tensile strengths for the epoxy-urethane (S4), asphaltic based (S6), and neoprene (S5) film specimens.•The decrease in elongation capacity of certain membranes warrants concern. However, tests done on the composite samples (membrane
+
wear course) show that the wear course provides a shielding effect which reduces the dam-aging effects of UV radiation. ASTM C 957 specifies a tensile strength retention at 80 percent and a retention ofelonga-tion
of90 percent for the full systemex-posed to 500 hours UV radiation. Most systems meet the requirement for re-tained tensile strength, but some, (SI and S4) do not meet the requirements for retention of elongation (Table 3b)ft Fourier transform infrared analysis of free specimens exposed to 1000 hours of UV radiation are consistent with those of the mechanical tests. Mem-branes subjected to oxidative degrada-tion show chain scission and modifica-tions
in
the polymer backbone (Fig. 5).ｾｾｾ＠
This was manifested in a loss of tensile strength and/or elongation capacity (see Sl to S3, Tabie 3a). Membrane S2 shows a good retention of mechanical properties after exposure to UV radia-tion. This result was corroborated by the FTIR spectral traces obtained which showed little difference between the UV exposed samples and the controls. Marked changes are noted for S5 (neo-prene). Here, the degradation process may have promoted crosslinking, em-brittling the polymeric structure. Con-sequently, a noticeable loss in
elonga-tion
capacity of the membrane isob-served (i.e., 29 percent retained elonga-tion). 6 Further degradation may also be
attributed to the combined action of water and UV radiation.
Mechanical degradation
-abrasion resistance
The wearing course (both integral and separate) of a membrane on a parking deck must withstand heavy abrasion, and it is expected to do so long after ap-plication. Wear characteristics of the wearing course are tested with a Taber abrader. Abrasion resistance results are usually presented in terms of the wear index and the depth of abrasion. Wear index
is
defined as the mass in grams of material worn away by the action of a rotating wheel after 1000 cycles.' Theresults in Table 4 show that the depth of abrasion values generally correlate well with values obtained for the wear index; the membranes with the lowest wear index and the least abraded depth are the most wear resistant. Although CS-17 wheels are normally used to determine the abrasion resistance of polymeric coatings, the increased wear resistance
"
..
"
..
"
..
ｾ＠ Rd"mnce .MotorOU lll!1ill ｅｬｬｬｹｬｯｩｩｩＡｃｬｬｹｾｯｬ＠ Ill Wtter"
"
"
"
"
Fig. 3 -Effect of automotive chemicals on direct tensile
strength. Fig. 4 -Effect of automotive chemicals on elongation.
of certain membranes required the use
TABLE 4 - Abrasion resistance of free film specimens . .
of a more abrading wheel (H-10) toob-tain comparative values.
These values representing only the waterproofing membranes resistance to abrasion, give a relative index of the de-gree to which it may be eroded in situ-ations where the wear course is pried loose by delamination. They clearly in-dicate that the membranes can be eroded by even light vehicular traffic.
Conclusions
The use of cold liquid-applied elas-tomeric membrane systems offers sig-nificant advantages in the waterproofing of parking garage decks. For example, they have excellent adhesion and pro-vide continuous watertight protection that is fully bonded to the substrate. However, it is important to appreciate their limitations and to understand how and to what extent environmental fac-tors and in-service conditions affect their durability.
• Heat aging tests show a deficiency in the heat stability characteristics of some waterproofing membranes (S3, S4 ). Loss of material due to high tempera-tures (Fig. 2) attained on exposed decks in summer may well influence mem-brane capability to accommodate move-ment at low temperatures.
• The significant tensile strength re-ductions, swelling, and softening effect of ethylene glycol could result in the rupture of the membrane by a shearing action caused when cars brake sharply on the membrane.
• Increase in tensile strength, significant reductions in elongation capacity, and FTIR spectroscopy results show that
October 1993
PAS
Units (b) (a) 4000 3600 3200 2800 2400 2000 1600 1200 800 400 Exposed Control Exposed ControlFig. 5-FTIR spectral differences for two samples exposed to UV radiation: (a) membrane S2 which showed little loss of mechanical properties and (b) mem-brane SS produced more drastic changes. Wavenumbers are at bottom of graph.
sustained UV radiation on the un-shielded membrane causes embrittle-ment, seriously impairing long term per-formance. The wearing course acts as a shield and reduces significantly such damaging effects. In order to protect the membrane, it must retain its integrity.
• The wear course in a composite
mem-brane system provides adequate protec-tion from abrasion as long as the mem-brane system remains intact. Most often, the wear course, like the membrane, em-brittles upon exposure to heat and UV radiation. Subsequent cyclic movement of the substrate and exposure to shear loads results in the delamination and flaking of the wear course. As shown by the abrasion tests results, the unpro-tected membranes can then be eroded by even light vehicular traffic. There-fore, careful vigilance and timely repair is necessary to ensure the integrity of the membrane system and preserve its waterproofing characteristics.
References
I. Feldman, D., ''Durability of Polymers Used
in the Building Industry," Canadian Building
Congress, Nov. ＲＷｾＲＹＬ＠ 1988, pp. 167-174. 2. Mailvaganam, N.P, editor, ''Repair and
Pro-tection of Concrete Structures," CRC Press,
Florida, January 1992, pp. 182-185.
3. Mailvaganam, N.P., "Elastomeric Parking
Deck Membranes,'' Concrete International: De-sign and Construction, V. 5, No. 10, October !986, pp. 5!-58.
4. Monroe, D.C., "Reflective Cracking and
Cold, Liquid-Applied Elastomeric Deck Coating and Membrane Systems: Practical Considerations
from Field Observations," Building Deck Water· proofing, ASTM STP I 084, ed. L.E. Gish, Amer-ican Society for Testing and Materials, 1990, pp. 121-131.
5. Evans, R.M., ''Test Methods Used in ASTM Specifications for Liquid·Applied EID.stomeric Membranes for Waterproofing Concrete,"
Building Deck Waterproofing, ASTM STP I 084, ed. L.E'. Gish, American Society for Testing and
Materials,l990, pp. 107-118.
6. ''Evaluation of Elastomeric Membrane
Sys-tems used in Parking Garage Protection,''
Insti-ttHe for Research in Construction, National Re-search Council of Canada, Client Report CR
6145.3, February 1992.
Selected for reader interest by the editors.
Currently Director of Research for Construction Prod-ucts Research, Inc., in the United States, ACI mem-ber Noel P. Mallva· ganam was previ-ously Head of the Polymer Products G
rials Laboratory at the Na-tional Research Council's Institute for Research in Construction. He is also for-mer chairman of the CSA Committee on Admixtures and a member, as well, of other CSA, ACI, and RILEM commit-tees. He has co-authored twobooks on admixtures.
Peter G. Collins is also with the Insti-tute for Research in Construction in Ot-tawa and is in-volved in the evalu-ation of repair ma-terials. He has a Bachelor's degrE)e
in chemistry from the University terloo, Ontario, Canada.
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