Results ofOutdoor Exposure Tests

Surface Condition ofSealed Joints—Fig. 6 shows the surface condition of the sealed joints after 5years of outdoor exposure at the different exposure site loca­tions. In Table 5 results of the aging (staining due to dirt pickup) and degree of cracking from the outdoor exposure tests are presented. As might be expected, the degree of aging (dirt pickup) of test specimens after 5 years of exposure is greater than that at the onset of the exposure period (0 year) and after 2 years exposure, in particular, the degree of dirt pickup of test specimens exposed to the Yokohama climate is the greatest. It is thought that dust is more prevalent on the surface of sealants at the Yokohama exposure site because this site is close to a highway. However, it was not possible to confirm the differences in

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FIG. 4—Location of outdoor exposure test.

FIG. 6—Outdoor exposure test results after 5 years.

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the degree of dirt pickup by the presence or absence of coating applied to the exterior surface of joint specimens. As for the rate of occurrence of cracks on sealed joints, it was evident that test specimens exposed at the Miyako Island and the Yokohama sites were high. The rate of occurrence of cracks of coated sealant products for three-sided adhesion joints was greater than that of prod­ucts in joints having two-sided adhesion.

Hardness Measurement Results of Sealed Joints—The hardness of sealed joints exposed to the different exterior climate conditions is shown in Table 6. The results indicate that the longer the exposure period to which the specimens were subjected, the greater the value of hardness of the sealed joint product. As for the importance of the exposure site with respect to the aging and hardening of the sealant, the results indicate the following order, in decreasing order of hardness value: Miyakojima (52 Shore A hardness) > Yokohama (49 Shore A hardness) > Rikubetsu (39 Shore A hardness). The results also indicated that the hardness of sealed joints without a coating was greater than that of joint products with a coating.

Tensile Test Results—Fig. 7 shows the maximum tensile stress obtained for two – and three-sided adhesion joint specimens that had been coated with paint for outdoor exposure testing. The differences between the two – and three-sided adhesion joint specimens in respect to values achieved for maximum tensile stress and maximum percent elongation arise because three-sided adhesion joints bring about greater internal stress to the joint as compared to two-sided joints. In essence, three-sided joints are capable of accommodating less move­ment as compared to 2-sided joints and, for the same degree of movement, give rise to both higher bond and internal stress. The results revealed that the longer the exposure period, the greater the tensile stress achieved in the sealant speci­mens. The location of the exposure site affected the severity of the exposure conditions and consequently the degree of aging and resulting tensile stress of the aged products. It was determined, on the basis of results from tensile tests, that the order of exposure severity starting with the most severe exposure loca­tion and proceeding toward less severe exposure locations was: Myakojima > Yokohama > Rikubetsu. The tensile stress achieved for three­sided adhesion joint specimens was greater than that of two-sided adhesion joints. Figure 8 shows the maximum elongation achieved of sealed joints in ten­sion; results indicate that the longer the exposure period, the lower the degree of elongation of the sealed joint specimen.

Considering the differences in elongation achieved for three-sided as com­pared to two-sided joint specimens, the degree of elongation of three-sided ad­hesion joint specimens was remarkably smaller after two years exposure and additionally, after 5 years of exposure testing the maximum elongation was less than 50 % at all exposure locations, whereas that of the two-sided joints all exceeded 50 % elongation. The results did not confirm that differences existed amongst the various three-sided adhesion joint specimens and neither were these affected by the severity of conditions at the different exposure sites.

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О: Cohesion failure Д: Adhesion failure peeling failure X :ALC failure

(Sealant and ALC failure)

FIG. 9—Type of fracture of sealed joint.

However, the lower degree of elongation obtained for two-sided adhesion joint specimens varied in relation to the severity of the climate for which the least degree of elongation was obtained for the exposure location having the more severe exposure conditions; specifically, in order of more to least severe effects, this was: Miyakojima < Yokohama < Rikubetsu.

Figure 9 and Table 7 provide information on the type of failure of the sealed joint specimens in tensile tests; these could be classified into four types of fail­ure: (i) cohesion failure (symbol: O); (ii) mixed mode adhesive failure of the sealant and ALC substrate (symbol: A); (iii) failure in peel (symbol: —), and fail­ure of the ALC substrate (symbol: x). The sealed joint specimens used as control specimens and cured indoors in laboratory conditions all failed in cohesion (symbol: O ). On the contrary, the results confirmed that the sealed joint speci­mens after 2 years of exposure testing had mixed mode adhesion failure, exhib­iting both sealant and ALC substrate failure (symbol: A) as well as failure in peel (symbol: —). It was also revealed that a considerable number of the sealed joint specimens after 5 years of exposure testing had failed at the ALC substrate (symbol: x). The value of the 50 % modulus of the sealed joint specimens having three-sided adhesion joints could not be measured because the failure of test specimens had already occurred at an elongation below 50 %.