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Journal of Coatings Technology, 50, 644, pp. 66-69, 1978-09
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New test method for resistance to water immersion: some results
obtained with two-part polysulfide sealant
Karpati, K. K.
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https://nrc-publications.canada.ca/eng/view/object/?id=494fe4a2-2db7-4961-9ef4-b995620bd5f1 https://publications-cnrc.canada.ca/fra/voir/objet/?id=494fe4a2-2db7-4961-9ef4-b995620bd5f1
National Research Council of Canada
Conseil national de recherches du Canada
NEW TEST METHOD FOR RESISTANCE TO
WATER IMMERSION. Some results obtained
with two-part polysulfide sealant
. T ~ ~ ~Reprinted from
.
Journal of Coatings Technology Vol. 50, No. 644, September 1978 p. 66-69
BBR
Paper No. 807
Division of Building Research
Une mithode d'essai de resistance
i
l'irnmersion dans l'eau est decrite et les resultats obtenus avec les polysulfures a deux compos- ants sont exposes. Les eprouvettes de produit d'etanchkite ont i t e coulies sur des substrats d'aluminum et de mortier de ciment, dur- cies, vieillie~i
la chaleur, diposees.dans un sac de plastique conten- ant de l'eau et itireesA
differentes vitesses jusqu'i ce que la rupture se produise, tout en itant continuellement immergkes.New Test Method
For Resistance to Water Immersion
Some Results Obtained with Two-Part Polysulfide Sealant
Klara K. Karpati
National Research Council of Canada'
A test method for resistance to water immersion is de-
scribed and the results obtained with two-part polysulfide sealant are presented. Sealant specimens were cast on aluminum and cement-mortar substrates, cured, heat- aged, then enclosed in a plastic bag containing water and extended at various rates while continuously immersed until failure occurred.
INTRODUCTION
In some applications, such as water reservoirs and swimming pools, sealants are used in joints that are continuously immersed in water. Sealants are usually water resistant materials, their weak point in immersion being the interface between sealant and substrate, especially if the substrate is a porous material such as concrete.
Tests for the performance of sealants in a state of continuous immersion do not exist. The method of test- ing that comes closest to this condition is examination of the specimen after a period of immersion in water1 and, if no failure has occurred, tensile testing it after blotting the water off its surface, thus completely alter- ing the conditions existing in practice.
This work establishes the feasibility of tensile exten- sion tests on continuously immersed specimens using porous and non-porous substrates.
DESCRIPTION
strate when immersed and was, therefore, used to ex- amine the feasibility of the proposed test method.
Most sealants, once cured, are water-resistant mate- rials. The adhesive layer, however, could be water sensitive because water molecules can reach the inter- face by diffusion starting from the edges, or by diffusion through the pores of the substrate, provided the sub- strate is porous. In the building industry, the most common porous materials on which sealants may be used in immersion are concrete and cement-mortar. The latter is a good representative of concrete surfaces for the purpose of this test and was used as a specimen substrate. The preparation of the cement-mortar bars is described later under the Notation section; Grade 65ST6 aluminum was used as the non-porous substrate. After conditioning the substrate bars for a minimum of two days at 72°F (22°C) and 50% relative humidity, 0.5
x
0.5 x 2-in. (1.3 x 1.3 x 5.0cm)sealantbeadswere cast on them. Figure 1 shows a specimen. The speci- mens were left on spacers to cure at the foregoing conditions for two weeks, then subjected to heat aging. The most frequently specified heat aging is four weeks at 158°F (70°C) in a ventilated oven. The cement-mortar substrate, however, presented a problem because under these conditions large internal bubbles of 0.25 to 0.5 in. (1.3 to 0.6 cm) diameter formed inside the seal- ant. In previous investigations2 aluminum bars were used as substrate and bubble formation never occurred. By trial and error, it was found that heat aging one week The material chosen for the test was a two-part at 104°F (40°C) with a subsequent three weeks at 13 1°F (55°C) gave bubble-free specimens on cement-mortar. P ~ ~conforming YCGSBt
~ standard ~ ~Although the specimens had ~ ~ ~ undergone as ~ 19-GP-3. It is recommended for sealing ofjoints contin-heat aging as those used in previous investigations, it uously immersed in water.
Sealants that are not recommended for use in im- was considered sufficient, without unduly lengthening mersed joints usually do not retain any adhesion to a the test procedure, to make the test more realistic than porous substrate after a short immersion in water; ten- one without heat aging.
sile tests, therefore, can not be done on them. Two-part After heat aging, the specimens were conditioned at polysulfide does retain its adhesion to a porous sub- 72°F (22°C) for a minimum of two days, then immersed in distilled water in a glass container (Figure 1) for
*Div. of Building Research, Building Materials Section. Ottawa. Canada K I A OR6. seven days. The minimim amount of wate; to be used
i
tcanadian Government Specifications BOX^ while extending the specimen was determined in ad-Figure 1--Specimen on spacers, dry and immersed; reinforced plastic bag
vance and the same liquid (containing leached salts from the cement) was used for the immersion prior to and during the test. Care was taken to insure that the specimens stayed immersed at about the same depth for the whole time. After the seven days the specimen and the liquid were transferred into a polyethylene bag
about 6 x 6 in. (15 x 15 cm) in size. The bag was closed
(by a lip seal) leaving a vent. Reinforcing tapes were applied to the bag (Figure 1) to avoid piercing by the serrated jaws of the Instron machine when the substrate bars were gripped through the bag.
I I I I I
LEGEND:
----
IMMERSED TEST-
DRY CONTROL TEST0.05 c m l m i n
0.005 c m l m i n 0.0005 c m l m i n
EXTENS ION, %
Figure 2-Average tensile curves; cement-mortar substrate
HOD FOF i RESISTANCE TO WATER I!
To provide the necessary flexibility, the optimum thickness for the bag was found to be 0.002 in. (0.005 cm). Care was taken to again insure continuous immer- sion of the specimen during the test.
The extension rates used were 5.0, 0.5,0.05, 0.005, 0.0005 cmlmin. At each rate six specimens were tested in immersion for both types of substrates and two spec- imens served for dry control tests. The tests were done at 72°F (22°C).
RESULTS
The averaged tensile curves are shown in Figures 2 and 3 for cement-mortar and aluminum substrate, re- spectively. The dashed lines represent the tests in im- mersion, the continuous lines the dry control tests. The rate of extensions are indicated on the curves. For both substrates the stress for a given extension decreases with decreasing extension rates, This is the normal behavior of the material as discussed in reference (2). The decrease of the stress with extension rate is more pronounced for immersed specimens than for dry ones, except for the highest rates where the differences are small, especially at small extensions. This phenomenon occurs on both substrates and seems to be unrelated to the type of break, as will be seen later.
One has to assume that on extension there may be interaction between water and sealant, and the water acts as plasticizer because the tensile curves on immer- sion show lower stresses irrespective of substrate. This occurs despite the fact that, in the absence of strain, water uptake by weighing on analytical balance could not be detected.
LEGEND:
o I I I I I la
U 100 2 300 400 5 0 600
EXTENSION. %
K.K. KARPATI
MINUTES HOURS DAYS MONTHS C - - C I ) - t 0.80 1 I 1 0 I 1I 3I 1 I 7 1 3 6
b.
- 0 . 6 0
o IMMERSED ON CEMENT-MORTAR SUBSTRATE DRY CONTROL ON CEMENT-MORTAR SUBSTRATE
A IMMERSED ON ALUMINUM SUBSTRATE
A DRY CONTROL ON ALUMINUM SUBSTRATE
- 1 . 0 0
-2.00 - 1 . 0 0 0 1.00 2 . 0 0 3.00 4.00 5.00 6.00 LOG TIME, m i n
Figure 4--Average break points of tensile extensions
The percentage extension at break (extensibility) is shown in Figure 4 for both surfaces. The logarithm of the average extension at break is plotted against the logarithm of the time to reach the break. This method of plotting the results was developed in previous investi- g a t i o n ~ . ~ It allows extrapolation to the slower exten- sions that occur in practice. This method of presenta- tion could be useful in the development of new sealants and primers using the test method here described. Each point of Figure 4 represents the average of the exten- sion at break for the six tests at a given rate of exten- sion. On aluminum substrate the difference between immersed and dry specimens could be attributed to experimental error. On cement-mortar, however, the immersed specimens failed at lower extensions than those tested dry.
The average extensions at break of both the dry and immersed specimens attached to the cement-mortar are shown in Table 1, for each rate of extension. In the last column of the table the difference between the extensi- bility of dry and immersed specimens is given. With the exception of the highest rate, the difference is consider- able compared with the extensibility. This demon- strates that the test method can reveal even a relatively small difference in sealant behavior between the dry and immersed conditions.
Table 1-Average Extensibilities of Cement-Mortar Substrate
Rate of Extension Dry Control Immersed Difference
cmlmin YO % %
Figure 5--Typical failure occurring on cement-mortar substrate
As seen in Figure 4, the extensibility at break on aluminum is about the same whether immersed or dry. The difference in the extensibility on porous substrate cannot be explained by the type of failure obtained.
Figures 5 and 6 show the failures for the sealant on
cement-mortar and aluminum substrate, respectively. On cement-mortar the failure is adhesive whether the
TEST METHOD FOR RESISTANCE TO
specimen was extended dry or immersed. On alumi- num, the failure is cohesive starting adhesively at a corner for both dry and immersed tests.
NOTATION
The cement-mortar substrate bars with dimensions of 0.5 x 1
x
3.25 in. (1.3x
2.5 x 8.3 cm) were prepared from one part by volume cement (normal Portland, typeI) and two parts by volume BMK sand. T o 662 g cement and 1667 g sand, 300 g water was added and mixed according t o CSA Standard A8-1956, paragraph B7.8.3 The mortar flow determined by B8.5.1 was found to be 110%. After casting, the blocks were cured for a month at 73°F (23°C) and 95 to 100% relative humidity.
SUMMARY
A new test method was developed for performance testing of sealants while immersed, such a s would occur in swimming pools and water reservoirs. T o achieve this, the sealant specimens were subjected to tensile testing while immersed in water in a plastic bag.
The test can demonstrate a relatively small difference between the behavior of dry and immersed specimens. The results showed that for the sealant tested, the fail- ure for a mortar substrate was adhesive whether the
specimens were tested dry or immersed, and that f a ure occurred at smaller extensions for the immersc condition. No difference in extensibility was found fc
sealant on aluminum substrate where the failure wi cohesive, starting adhesively, on both immersed a1 dry specimens. On both substrates, the stress for a given extension was less for the immersed condition than for the dry indicating that the water may act as a plasticizer.
il- :d
ACKNOWLEDGMENT
The author acknowledges with special thanks the efforts of R.C. Seeley in developing the new technique required for this test method. This paper is a contribu- tion from the Division of Building Research, National Research Council of Canada and is published with the approval of the Director of the Division.
References
(1) Amoroso, G.G. and Pangalos, A . , "Comportement des joints en silicone caoutchouc a I'air et dans I'eau chloree," MatPriaux er
Technique, Jan./Feb., p 41 (1976).
(2) Karpati, K . K . , "Mechanical Properties of Sealants: IV. Per- formance Testing of Two-Part Polysulfide Sealants," JOURNALOF
PAINT TECHNOLOGY, 45, No. 580, 49 (1973).
(3) CSA Standard AS, Masonry Cement, Canadian Standards As- soc., Rexdale, Ont., 1956.
Reprinted from the Sept. 1978 issue of the JOURNAL OF COATINGS TECHNOLOGY Volume 50; Number 644; Pages 66-69.
Copyright 1978 by the Federation of Societies for Coatings Technology, Philadelphia, Pennsylvania, U.S.A.
