The Trouble with Sealants Sealant Technology Conference, Oxford Brookes University, School of Technology, Wednesday 13 October 2004

Durability Testing of Sealants

A.T. Wolf

Dow Corning GmbH, Global Construction Industry, Science and Technology, Rheingaustrasse 34, 65201 Wiesbaden, Germany

ABSTRACT The paper discusses the work carried out over the past decade within ISO TC59/SC8 and RILEM TC139-DBS committees towards the development of a durability test standard for sealants. In 2001, RILEM TC139-DBS published a RILEM Technical Recommendation (RTR) on a durability test method for curtain wall joint sealants. The paper discusses the development of this test method as well as results obtained in the evaluation of sealants. Results of initial evaluations indicate that the test method is able to differentiate between products with regard to their resistance to accelerated ageing and mechanical cycling. The type of failure and the changes in surface appearance observed during the test regime are similar to those observed in actual service conditions. Sealant degradation resulting from durability cycles without fatigue cycling was slower than had been anticipated for most sealant systems. KEYWORDS Durability, Sealant, Test Method, Curtainwall, RILEM. INTRODUCTION Over the past two decades, the sealants industry has undergone rapid technological and structural changes. On the one hand, advancements in technology have enabled the launch of a multitude of new sealant products based on novel polymers, cure chemistries and formulations. On the other hand, increasing competitive pressure and customers that are more demanding have required shorter product development cycles. Unlike the well-established sealants, which have been sold for more than twenty years based on the same formulation, the new sealant products do not have documented long-term performance histories. At present, generating a reliable performance history for a new sealant product still requires long-term outdoor testing and extensive in-service field evaluations. Attempts at avoiding these tasks, by employing various forms of short-term laboratory-based ageing tests, have had limited success and are viewed with suspicion by construction specifiers, mainly because of the lack of an established correlation with actual in-service performance of sealants. The sealants industry, therefore, urgently needs a method for generating long-term performance data rapidly and with assured reliability. Accelerated laboratory ageing experiments are the most promising method for acquiring durability information within the shortest possible time; however, a methodology for conducting and interpreting these experiments needs to be developed that improves the predictive value of this technique. The need for improved longevity of sealed joints is well recognised. Work towards an accelerated durability test method was started in 1989 within the International Standardisation Organisation Committee ISO TC59/SC8 (Work Group 6). Later, in 1994, the activity was transferred to RILEM TC139-DBS Durability of Building Sealants, when the ISO committee realised that the task was too

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complex to be completed within the five-year time frame allowed for the development of an ISO standard. The RILEM committee has now developed a Technical Recommendation (RTR) (RILEM 2001), which will be considered by ISO for the development of a future durability test standard. The purpose of this technical recommendation is to provide a framework for assessing the effects of cyclic movement and artificial weathering on curtain-wall sealants in a laboratory-based procedure. DEVELOPMENT OF A DURABILITY TEST METHOD FOR SEALANTS During their entire service life, joint seals are exposed to cyclic mechanical strain and environmental degradation factors. Cyclic joint movement, sunlight, temperature variations (heat, cold) and moisture (water) are considered to be the primary environmental and service degradation factors leading to sealed joint failure. Weatherproofing joint seals in building faades are exposed to frequent cyclic movements. This joint movement imposes cyclic mechanical strain on the seal, which, depending on the exposure conditions and the construction design, can vary substantially in rate and amplitude. Work on the durability test method started with the premise that the accelerated testing regime should incorporate only the following four key ageing factors: solar radiation, moisture, temperature and joint movement. With this limitation, the committee realised the impossibility of incorporation all possible combinations of weathering and service factors into a single laboratory-based testing regime. Weathering and service factors, which the committee specifically did not intend to address, were: Dirt accumulation Acid rain Cleaning solvents Microbial growth Incompatibility with other building materials. Joint movement is the preponderant service factor in the ageing of sealants, since it has a damaging effect both while the sealant is curing and after completion of the cure. Depending on the type of joints, sealants are exposed to various types and degrees of movement. Joint movements are induced by various factors, such as: Thermal expansion/contraction of construction components Shrinkage of construction components Settling of buildings Wind loads Service loads. Some of these factors may occur simultaneously, exposing the sealed joint to a rather complex, stochastic, often three-dimensional movement pattern of overlapping shear and extension/compression movements. Such complex movement patterns are difficult to simulate and the analysis of its effect on the sealant properties is an even more challenging task. Therefore, for the purpose of developing an accelerated durability test standard, the RILEM TC139-DBS committee decided to consider only the following three simple movement types: One single large movement followed by essentially no further movement One large movement followed by some cyclic movement Cyclic movement (in shear or tensile). The above movement types can be roughly correlated with the movement patterns occurring in settlement joints, settlement joints with some movement, and glazing or weatherproofing joints, respectively.

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Considering the frequency with which sealants are being used for the various applications, expansion and glazing joints represent the majority of sealant usage. Therefore, the development of a test method based on cyclic movement was prioritised by the committee. Obviously, the type of movement (tensile or shear) as well as the amplitude and rate of movement still depend on the type of application. A joint in a monolithic concrete faade, for instance, is likely to see slower and smaller movements than a joint in an aluminium curtain wall faade. For simplification, the committee had to narrow the scope of the initial test method again, and it decided to initially focus on cyclic tensile movements. Even joints that are predominately exposed to cyclic tensile movement still show a rather complex movement pattern (see Hutchinson et al. 1999 and literature cited therein). However, based on experience with the development of movement capability tests (ISO 1989, Wolf 1999 and literature cited therein), it was assumed that the actual joint movement could be approximated by using idealised cyclic movements, such as trapezoidal, V-shaped, or sinusoidal movements. Research, comparing the performance of sealants exposed to various waveforms, suggested that trapezoidal movement waveforms provide the best correlation with simulated in-service performance (Jones et al. 1999). Therefore, trapezoidal movement waveforms were selected for the accelerated durability test method.

]2 weeksDay 1 Day 2 Day 3 Day 4 Day 5 Day 6 Day 7

Extension

Compression

-20C

+70C

-20C

+70C

-20C

+70C

-20C

+70C23C, no movement

+x%

-x%

rated movementcapability[ISO 9047 Movement Cycle (2 weeks)

]x 28 days[4 8 12 16 20 240

UV-A

Condensation

UV-A UV-A

Condensation Condensation

62 C 42 C 62 C 62 C42 C 42 C

hours

Tem

pera

ture

Weathering Cycle (4 weeks)

Figure 1. Initial proposal of an accelerated durability test method (1993). A further narrowing of the scope of the initial test standard occurred when the committee decided to consider only elastomeric sealants, as defined by the ISO 11600 classification scheme (ISO 2000). Since ISO 9047 (ISO 1989) is the relevant test standard for determining the movement capability of cured elastomeric sealants, it was the most obvious candidate to consider as movement cycle for the future durability test standard. A first proposal of a test method (ISO 1993) suggested exposing the cured sealants to consecutive durability cycles. Each durability cycle consisted of a two week movement cycle as defined in ISO 9047 and a four week weathering period consisting of repeated cycles of four hours fluorescent lamp UV-A exposure followed by four hours moisture condensation

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(see Fig. 1). The proposal suggested that the durability cycles should be continued, until failure occurred, which was to be detected by visual inspection of the specimens after each durability cycle (see Fig. 2). The procedure proposed for the inspection was to extend the specimens to their rated movement capability and to place the extended specimens over a light.

P rep ara tion ofS p ecim en s

C o n ditio n in g

D u rability C y cling

In spectio nP ass

C y cles to F a ilu re

F a il

Figure 2. Proposed concept for accelerated durability testing (1993). Much discussion revolved around the question of how the sealants should be conditioned prior to exposing them to the durability cycles. The proposal to use the same conditioning methods as defined in ISO 11600 was widely supported, based on the assumption that this approach allowed direct comparison of the result of the durability cycles with the initial properties as determined by the other test methods referenced in ISO 11600. On the other hand, previous testing had clearly demonstrated the negative impact of mechanical cycling during cure on the properties of sealed joints (Jones & Lacasse 1999, Wolf 1999 and literature cited therein). Therefore a dynamic cure procedure was proposed (Jones & Hutchinson 1998), in which the sealed joint is mechanically cycled while the sealant cures. Weathering of a sealed joint during cure also has an effect on its initial properties (Beech & Turner 1983); the effect is especially noticeable for those weathering factors that either accelerate or retard the cure of the sealant. However, the effect appeared to be smaller than that of joint movement. The committee, therefore, agreed that it would be sufficient to consider only the effect of movement during cure to establish the initial reference state. SUMMARY OF THE RTR DURABILITY TEST METHOD The RILEM Technical Recommendation Durability test method - Determination of changes in adhesion, cohesion and appearance of elastic weatherproofing sealants for high movement faade joints after exposure to artificial weathering (RILEM 2001) specifies a laboratory procedure for determining the effects of cyclic movement and artificial weathering on laboratory cured, elastic weatherproofing joint sealants (one- or multi-component) for use in high movement building faade applications. In this method, test specimens are prepared in which the sealant to be tested adheres to two parallel contact surfaces (substrates). Sealant specimens are conditioned either statically (no movement) or

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dynamically (exposed to cyclic movement). The conditioned sealant specimens are then exposed to repetitive cycles of artificial weathering (light, heat and moisture) and cyclic movement under controlled environmental conditions (degradation cycles). Weathering is carried out for eight weeks (default value) in an artificial weathering machine. This is followed (optionally) by rapid mechanical fatigue cycling (default: 200 cycles). The specimens are then exposed to two thermo-mechanical cycles as defined in ISO 9047 (section 8, first week), using the full amplitude suggested as the movement range of the sealant under test. After completion of each degradation cycle, the specimens are extended to their full rated extension and held there as the sealant beads are visually examined for changes in appearance, cohesion and adhesion. The depth of any cohesive or adhesive flaw is determined according to the rules provided in ISO/DIS 11600 and the general condition of the sealant is reported. The weathering exposure, the cyclic movement, and the examination for failures constitute a degradation cycle and the degradation cycle is repeated as often as desired to achieve a certain exposure. A schematic representation of the test procedure is shown in Fig. 3.

Figure 3. Schematic representation of RILEM RTR test procedure. Default test parameters and, for some procedures, alternative options are defined in the technical recommendation (see Table 1). In cases of dispute, the default method is the reference method. The experimenter is allowed to deviate from the default values for the following test parameters, however, is required to highlight any deviation from the default values in the test report: a) Substrate default: anodised aluminium as specified in ISO 13640 (ISO 1996) b) Support dimensions default: 75mm x 12mm x 6mm as specified in ISO 8339 (ISO 1984)

Start

Conditioning A B C

Accelerated Weathering XenonFluorescent

UV

Fatigue Cycling (optional) Fatigue Cycling

Thermomechanical Cycling Cycling

Examination for Defects Examination

a

Stop

OptionalDefault

ProcedureStart

Conditioning A B C

Accelerated Weathering XenonFluorescent

UV

Fatigue Cycling (optional) Fatigue Cycling

Thermomechanical Cycling Cycling

Examination for Defects Examination

a

Stop

OptionalDefault

Procedure

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c) Conditioning method (A, B or C) default: A as specified in ISO 11600 d) Artificial light source (xenon-arc, fluorescent UVA-340 lamp) default: xenon-arc as specified in

ISO 4892-1-3 (ISO 1998a) e) Weathering procedure: duration of artificial weathering, type of moisture exposure (spraying or

immersion), the temperature of light exposure, the temperature of moisture exposure, the timing of light and moisture/water cycle default values are specified for xenon arc/water-spray, xenon-arc/water immersion and fluorescent UVA-340/water-spray weathering;

f) Rapid fatigue cycling (optional): inclusion of fatigue cycling, amplitude and duration (number of cycles) of fatigue cycling, default: 200 cycles as specified in JIS A 1439 (JISC 1997);

g) Thermo-mechanical cycling (ISO 9047 type): amplitude and duration (number of cycles) default values are specified in the test procedure.

Table 1. Overview of default and alternative choices of key test parameters

Procedure Default Alternative option Conditioning A B or C Movement parameters for Conditioning C

1 cycle/day 7.5% amplitude 2.4 hour periods trapezoidal waveform extension/compression rate 7020 mm/min 1st stroke in tension

Accelerated weathering Xenon arc light and water spray 102 min. light at 655C black standard thermometer and 60 10 % rel. humidity 18 min. light with water spray 672 cycles (8 weeks) or Xenon arc light and water immersion 102 min. light at 65 +//-5oC black standard thermometer; 18 min. light during water immersion 672 cycles (8 weeks)

Fluorescent ultraviolet radiation and water-spray (FL/UVA-340 lamps) 8h UV at 655C black panel thermometer 4h UV with water spray 112 cycles (8 weeks)

Fatigue degradation ----------------------------------------------- Isothermal cycling Movement parameters for isothermal cycling

5 cycles/min at rated movement capability amplitude 200 cycles total

Thermomechanical cycling

2 cycles at rated movement capability amplitude (ISO 9047, 1st week)

The use of this method is intended to induce property changes in sealants associated with typical end use conditions, i.e. to simulate a natural weathering environment of sealants installed in curtain-wall joints exposed to high joint movement. Exposures are not intended to simulate the deterioration caused by localised environmental conditions, such as atmospheric pollution, biological attack or salt-water exposure. It should be noted that the use of this method as a predictor of the service life of a sealed joint for a given climate and location and on a given building has not been demonstrated yet. In the future, it is hoped that the test parameters can be linked with specific climatic zones and actual exposure conditions on site. RESULTS OBTAINED WITH RTR DURABILITY TEST METHOD Oxford Brookes University study (1999-2000) As the committee started to converge towards the final test method in 1999, the importance of evaluating the behaviour of a set of sealants under comparative conditions became apparent in order

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to validate the proposed durability test method. A first study was completed by Oxford Brookes University (Jones et al. 2001), in which a total of fifteen different high quality sealant products, supplied by twelve manufacturers, were tested, including five silicones, four polyurethanes, three silicon-modified polyethers, two polysulfides, and one solvent-borne, silicon-modified acrylic. Anodised aluminium as specified in ISO-DIS 13640 (ISO 1998b) was used as a substrate material. Primers were used on the anodised aluminium substrates as recommended by the manufacturers. All test specimens were subjected to four durability cycles. A durability cycle consisted of the joints being subjected to eight weeks of artificial weathering in a fluorescent UV/condensation device followed by two full ISO 9047 movement cycles (4 days). Following the fourth durability cycle, it became apparent that the durability cycles did not accelerate sealant degradation as quickly as originally thought. It was therefore decided to incorporate 1000 fatigue cycles with amplitude of 25% at a rate of 5 cycles/minute into the experimental programme following the fourth durability cycle. The results from the fatigue cycling were intended to give insight into the possibility of including fatigue into later draft versions of the durability test method. Figure 4 shows photos of representative test specimens at the discontinuation of the test.

Figure 4. Representative test specimens at discontinuation of test. Exposing the silicone sealants to the durability cycles showed no effect for the first three cycles. After the fourth durability cycle, some silicone sealants showed a minor loss of adhesion, primarily at the ends of the joints, where stresses are highest. For these sealants, further loss of adhesion occurred during the fatigue cycling phase, but it proceeded at a different rate for each sealant. In general, no substantial differences were observed in the performance of dynamically and statically conditioned specimens, except for slight bead deformation resulting from the dynamic conditioning. The surface appearance of the silicone sealants tested was not affected by the durability cycles; no cracking, crazing, or visible discoloration occurred.

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Large differences in the performance of the tested polyurethane sealants were observed. Except for taking a slight compression set, a one-part polyurethane sealant exhibited few signs of deterioration following the durability cycles. Another one-part polyurethane sealant lost adhesion at the ends of the joints, discoloured and developed surface crazing. The three-component polyurethane sealant showed severe discolouration soon after the first durability cycle and extensive blisters and cohesive cracks developed after the second cycle. The cohesive cracks propagated into the sealant and finally led to complete cohesive failure after the fatigue cycling. The silicon-modified polyether sealants tested were little affected by the first two durability cycles. Surface crazing was observed for one sealant after the second cycle; the other two sealants started to craze after the third cycle. Two sealants survived four durability cycles, exhibiting no or only minor adhesion loss. All silicon-modified polyether sealants started to fail adhesively during the fatigue cycling. The one-part polysulfide sealant cured very slowly and remained incompletely cured even after being exposed to three durability cycles. Due to the incomplete cure, the sealant developed major folds in the sealant bead, which further developed into cohesive cracks that finally resulted in complete cohesive failure after the second and third durability cycle for the dynamically and statically cured specimens respectively. Clearly, this sealant was not able to withstand the large and rapid movements that may occur in a curtain wall joint, due to its slow cure. The two-part polysulfide sealant performed better, although cracks developed on the bead surface after the second durability cycle, which continued to propagate into the depth of the sealant during the following cycles. The silicon-modified polyacrylate sealant performed better than the other silicon-modified sealants. Very little deterioration was observed for the first three durability cycles. After the fourth durability cycle, some loss of adhesion occurred along the edge and the ends of the joints. The area of adhesion loss increased because of the fatigue cycling. In general, the Oxford Brookes study found that the RILEM durability test method was able to differentiate between products with regard to their resistance to accelerated ageing and mechanical cycling. The type of failure and the changes in surface appearance observed during the test regime were similar to those observed in actual service conditions. The study confirmed that the initial modulus of a sealant is not a good indicator of the performance in the durability test; apparently more important are the property changes that occur because of the ageing (hardening, reversion, etc.). The dynamic conditioning procedure reduced joint durability for some of the tested products, but increased it for others. Sealant degradation resulting from the durability cycles was slower than had been anticipated for most sealant systems. The fatigue cycling clearly accelerated sealant degradation. It was therefore proposed to include fatigue cycling as part of each durability cycle. The RILEM TC139-DBS committee followed this recommendation and included the fatigue cycling as an option in the final technical recommendation. Tokyo Institute of Technology study (2001-2002) A further study was initiated by the Japan Sealant Industry Association (JSIA) after the RILEM Technical Recommendation (RTR) on the durability test method had been finalised. This study, carried out by the Tokyo Institute of Technology in Yokohama (Miyauchi et al. 2004), comprised eleven sealants, two silicones, two silicon-modified polyethers, two polysulphides, two polyurethanes each as one- and two-part products one two-part silicon-modified polyisobutylene, one two-part urethane cure acrylic, and a one-part water-borne acrylic. The two-part polysulphide sealant was based on a new type of polysulphide/polyether/polysulphide co-polymer and employed isocyanate cure chemistry. Test specimens were prepared using anodised aluminium and mortar as specified in ISO-DIS 13640 as substrate materials; primers were used for all sealant/substrate combinations as recommended by the manufacturers. The two-part polyurethane, the two-part urethane-cure acrylic

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and the one-part water-borne acrylic were also evaluated after painting the sealant surface with a highly elastic paint. All sealant specimens were conditioned according to method A. Weathering was conducted in a fully automated weathering machine using a Xenon-lamp light source. Durability cycles were carried out with and without inclusion of the 200-cycle fatigue ageing. Table 2 displays a summary of the interim results after the second durability cycle.

Table 2. Interim results of Japanese study after second durability cycle

Sealant Substrate Surface painting

Fatigue cycling

Chalking1 Crazing2 Test result

SR-1 Aluminium No Without With

1 1

0 0

Pass Pass

SR-2 Aluminium No Without With

1 1

0 0

Pass Pass

MS-1 Aluminium No Without With

2 2

0 0

Fail (1st cycle) Fail (1st cycle)

MS-2 Aluminium No Without With

3-4 3-4

4-5 4-5

Pass Pass

PS-1 Aluminium No Without With

3 3

3-4 3-4

Pass Pass

PS-2 Aluminium No Without With

4 4

5 5

Pass Fail (2nd cycle)

PU-1 Aluminium No Without With

2 2

0 0

Pass Pass

PU-2 Aluminium No Without With

5 5

5 5

Fail (1st cycle) Fail (1st cycle)

IB-2 Aluminium No Without With

1 1

2 3-4

Pass Pass

PU-2 Mortar No Without With

5 5

5 5

Fail (1st cycle) Fail (1st cycle)

Yes Without With

- -

- -

Pass Fail (1/3) (2nd cycle)

UA-2 Mortar No Without With

2-3 2-3

5 5

Pass Pass

Yes Without With

- -

- -

Pass Pass

AC-1 Mortar No Without With

3 1

1 1

Pass Fail (2nd cycle)

Yes Without With

- -

- -

Pass Fail

Table legend: XX-1, XX: chemical type, 1 or 2: one- or two-part

SR: Silicone, MS: Silicon-modified polyether, PS: Polysulphide, PU: Polyurethane, IB: Silicon-modified polyisobutylene, UA: Urethane-cured acrylic, AC: water-borne Acrylic; Chalking: 1 (none) 5 (strong); Crazing: 0 (none) 5 (strong)

Figure 5 shows the surface appearance of the test specimens exposed to additional fatigue cycling after the third durability cycle (specimen PU-2 is shown after the first durability cycle, since it failed in the first cycle).

1 Chalking was assessed according to ISO 4628-6 (ISO 1990) 2 Crazing was assessed according to ISO CD 4628-4 (ISO 1994)

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Figure 5. Surface appearance of the test specimens exposed to additional fatigue cycling after the third durability cycle (specimen PU-2 is shown after the first durability cycle).

The silicone sealant specimens survived the first and second durability cycles without any signs of degradation no cracks, no crazing, no chalking and no loss of adhesion were observed. Both silicon-modified polyether products showed signs of moderate chalking after the first durability cycle. The one-part silicon-modified polyether sealant took a strong compression set during the ISO 9047 thermo-mechanical cycle (3 mm set based on 12 mm joint width after 25% compression), resulting in

SR-1

SR-2

MS-1

MS-2

PS-1

PS-2

PU-1

PU-2

IB-2

PU-2With painting

UA-2Withpainting

With painting

AC-1

Withoutpainting

PU-2

Without painting

UA-2

Without painting

AC-1

SR-1

SR-2

MS-1

MS-2

PS-1

PS-2

PU-1

PU-2

IB-2

PU-2With painting

UA-2Withpainting

With painting

AC-1

Withoutpainting

PU-2

Without painting

UA-2

Without painting

AC-1

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adhesive failure during the first durability cycle. However, for this sealant, there is a possibility of an experimental mistake during the preparation of the test specimens. In spite of exhibiting moderate to strong chalking and crazing as well as a 2 mm compression set, the two-part silicon-modified polyether sealant passed both durability cycles. The one-part polysulphide sealant also passed both durability cycles, despite a 2.5 mm compression set and signs of moderate chalking and crazing. Showing strong chalking and crazing, the two-part polysulphide sealant passed both durability cycles, when no fatigue cycling was included, however, two out of three test specimens failed the second durability cycle, when fatigue cycling was included. The one-part polyurethane sealant passed both durability cycles and showed some chalking, but no signs of crazing, regardless whether or not the sealant was exposed to fatigue cycling. The two-part polyurethane sealant chalked and crazed badly already after the first durability cycle. Due to the depth of the surface cracks (2-3 mm), this sealant failed the ISO 11600 pass criterion both on aluminium and mortar substrates. When the same sealant was painted with a highly elastic paint prior to weathering, the sealant passed the first durability cycle on mortar substrates with and without fatigue cycling without problems, but failed the second durability cycle, when fatigue cycling was included. The silicon-modified polyisobutylene sealant passed both durability cycles, but showed signs of moderate crazing after the second cycle. The urethane-cured acrylic sealant passed both durability cycles, with and without fatigue cycling, regardless whether it was painted or not. Without surface paint, it developed moderate chalking and severe crazing during the second durability cycle. The water-borne acrylic sealant passed two durability cycles, when no fatigue cycling was included, but failed in the second durability cycle, when the specimens were exposed to fatigue cycling. This behaviour was observed, regardless whether the sealant surface was painted or not prior to weathering. Based on the above findings, at the meeting of ISO TC59/SC8 in 2001, the Japanese delegation recommended the RTR method for development as an ISO standard. With the exception of the urethane-cure acrylic sealant, they considered the degradation of the various chemical types of sealants observed after exposure to the two durability cycles to be similar to the one observed in outdoor weathering. The study conducted by the Tokyo Institute of Technology will continue until completion of the third durability cycle. Further studies are planned by the Architectural Institute of Japan in order to investigate the correlation of the results observed in the RILEM accelerated durability test method with those obtained in outdoor exposure. Also, the test standard is in-line with the recommendations of the Japan Architectural Standard Specification, Volume 8 - Waterproofing and Sealing. A distinct difference in the results can be observed depending on whether or not the fatigue cycling is included in the test procedure. It is important to include the fatigue cycling in order to evaluate the performance of sealants according to actual service conditions. It is assumed that adjustments in the balance between accelerated weathering, fatigue cycling and thermo-mechanical cycling will allow tailoring of the RTR test method to specific outdoor climate and exposure conditions. CONCLUSIONS Both studies found that the RILEM durability test method is able to differentiate between products with regard to their resistance to accelerated ageing and mechanical cycling. The type of failure and the changes in surface appearance observed during the test regime are similar to those observed in actual service conditions. Since different sealant products were evaluated in both studies, their results cannot be compared directly; however, it appears that the Japanese study, using a Xenon-light source, yields faster degradation than the British study, which employed a fluorescent light source. Fatigue cycling substantially accelerates sealant degradation, as found by both studies. Finally, the dynamic cure procedure can be used to simulate movement during cure. However, a discussion of the British test results within RILEM TC139-DBS suggests the results depend critically on the relation between the duration of the movement cycle (2.4 hours) and the speed of cure (e.g. pot-life) of the product.

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REFERENCES Beech, J.C. and Turner, C.H.C. 1983, Cure of elastomeric building sealants, Journal of Chemical

Technology and Biotechnology, 33A, pp. 63-69. Hutchinson, A.R., Jones, T.G.B. & Atkinson, K.E. 1999, Building joint movement monitoring and

development of laboratory simulation rigs, in Durability of Building Sealants, RILEM Proceedings, ed A.T. Wolf, E & FN Spon, London, pp. 99-116.

ISO 1984, ISO 8339 - Building Construction - Jointing Products - Sealants - Determination of Tensile Properties, International Standardisation Organisation, Geneva.

ISO 1989, ISO 9047 - Determination of Adhesion/Cohesion Properties at Variable Temperature, International Standardisation Organisation, Geneva.

ISO 1990, ISO 4628-6 - Paints and varnishes - Evaluation of degradation of paint coatings -- Designation of intensity, quantity and size of common types of defect, Part 6: Rating of degree of chalking by tape method, International Standardisation Organisation, Geneva.

ISO 1993, Proposed Test Method for Durability of Sealants Subject to Outdoor Weathering as Simulated in an Artificial Weathering Machine, ISO TC59/SC8 Committee Document, International Standardisation Organisation, Geneva.

ISO 1994, ISO CD 4628-4 Paints and varnishes - Evaluation of degradation of paint coatings - Designation of intensity, quantity and size of common types of defect, Part 4: Designation of degree of cracking, International Standardisation Organisation, Geneva.

ISO 1996, ISO 13640 - Building Construction - Definition of Test Substrates, International Standardisation Organisation, Geneva.

ISO 1998a, ISO 4892-1-3 Plastics - Methods of Exposure to Laboratory Light Sources - Part 1: General Guidance, Part 2: Xenon Lamps, Part 3: Fluorescent UV Lamps, International Standardisation Organisation, Geneva.

ISO 1998b, ISO-DIS 13640 Building Construction Jointing Products Definition of Test Substrates, International Standardisation Organisation, Geneva.

ISO 2000, ISO/DIS 11600 - Building Construction - Sealants - Classification and Requirements, International Standardisation Organisation, Geneva.

JISC 1997, JIS A 1439 Test Methods of Sealants for Sealing and Glazing in Buildings, Japanese Industrial Standards Committee, Technical Regulation, Standards and Conformity Assessment Policy Unit, Ministry of Economy, Trade and Industry, Tokyo.

Jones, T.G.B. & Hutchinson, A.R. 1998, Building Construction - Sealants - Dynamic Conditioning of Sealants used in High Movement Curtain Walling Systems (Jones Cycle), Attachment to Letter from A.R. Hutchinson to J.M. Klosowski, October 19th.

Jones, T.G.B. & Lacasse, M.A. 1999, Effect of joint movement on seals and sealed joints, in Durability of Building Sealants, RILEM Report 21, ed A.T. Wolf, RILEM Publications, Paris, pp. 73-105.

Jones, T.G.B., Hutchinson, A.R. & Lacasse, M.A. 1999, Effect of movement waveforms on the experimental performance of newly sealed joints, in Durability of Building and Construction Sealants, RILEM Proceedings PRO 10, ed A.T. Wolf, RILEM Publications, Paris, pp. 211-227.

Jones, T.G.B., Hutchinson, A.R. & Wolf, A.T. 2001, Experimental results obtained with proposed RILEM durability test method for curtain wall sealants, Materials and Structures, 34(5), pp. 332-341.

Miyauchi, H., Enomoto, N., Sugiyama, S. & Tanaka, K. 2004, Artificial Weathering and Cyclic Movement Test Results Based on the RILEM TC139-DBS Durability Test Method for Construction Sealants, Durability of Building and Construction Sealants and Adhesives, ASTM STP 1453, A. T. Wolf, Ed., ASTM International, West Conshohocken, PA, 2004.

RILEM 2001, RILEM TC 139-DBS: Durability test method - Determination of changes in adhesion, cohesion and appearance of elastic weatherproofing sealants for high movement faade joints after exposure to artificial weathering, Materials & Structures, in print.

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Wolf, A.T. 1999, Progress towards the development of a durability test method for sealants, in Durability of Building Sealants, RILEM Report 21, ed A.T. Wolf, RILEM Publications, Paris, pp. 365-380.