Date of Award

5-2008

Document Type

Thesis

Degree Name

Master of Science in Material Science Engineering (MSMatSE)

Department

Materials Science

First Advisor

Dr. Mahmood Allawy Mohsin

Second Advisor

Dr. Abdallh AI-Khanbashi

Third Advisor

Dr. Abdel- Hamid Mourad

Abstract

As in most industrial sectors, today there is a growing preoccupation about product quality. Since waterproofing systems are intended to have the longest possible service life, one of the most critical quality features is their aging performance. As a result, the importance of aging tests is steadily growing, especially in the hot-dry climate zones.

Polymer-modified bituminous waterproofing membranes are normally exposed to solar radiation and various weathering conditions when used in residential and commercial buildings. They are attacked and deteriorated to some degree by environmental factors such as heat, radiation, especially ultraviolet, moisture and gases. The weathering (aging) consequences commonly result in chemical and physical changes to the membranes.

Several varieties of waterproofing membranes are locally manufactured and currently used in the UAE. Each of which has different applications, quality and prices. Three different types of membranes were selected for this study based on their popularity and wide-spread use in the UAE. They are, type (A): atactic polypropylene (APP)-modified bituminous membrane covered with polyethylene film; type (B): atactic polypropylene (APP)-modified bituminous membrane covered with green slate flakes and type (C): styrene-butadiene-styrene (SBS)-modified bituminous membrane which is covered with polyethylene film. All membranes are reinforced by spun bond non-woven polyester sheet (membranes (A) and (B) are reinforced by 180 g/m2 and (C) by 200 g/m2). The effects of natural and accelerated aging on the mechanical and thermal behaviors of these membranes were investigated.

Membrane samples were exposed to both accelerated and natural weathering conditions. In accelerated weathering, an accelerated weathering chamber (Ci3000 Xenon Weathering-Ometer) was used to simulate the Al Ain town weather. The membrane samples were subjected to accelerated weathering of 3600 hours in total, which is equivalent to 5 years in real time. The samples were examined at intervals of 180, 360, 720, 2160 and 3600 hours, which simulates 3, 6, 12, 36, and 60 months of natural weathering, respectively. In the natural weathering, the samples were subjected to direct solar radiation, rain, dust, sand storm and other substances in the air at Al Ain town in the (UAE). Samples were examined after three, six and twelve months of exposure time. Furthermore, samples of imported membrane (type B) were obtained from a demolished building in Al Ain town after twelve years of service, were also subjected for testing.

The long-term performance of these membranes was investigated through studying the effect of the previously mentioned aging conditions on the mechanical and thermal behaviors in terms of tensile testing and thermogravimetric analysis (TGA), respectively. The tensile testing results include peak load, percent elongation, strain energy (energy to break), percent retained factional strain energy (PRFSE) and modulus of elasticity. Thermogravimetric analysis results include the first onset temperature. The condition of the sample's surface was also visually examined after each aging cycle. Moreover, the results obtained for the three membranes were also compared.

The results illustrated that, both mechanical and thermal behaviors of membranes were affected by aging process and severity of the aging depends on the membrane type. Membrane type C (SBS-modified bituminous membrane) is the most susceptible membrane to degradation; because of its sensitivity to UV -radiation. It loses about 26%, 21 %, 34% and 42% of its initial peak load, percent elongation, strain energy to break and PRFSE values, respectively, after the final stage (3600 hrs.) of accelerated aging. Membrane type A (APP-modified bituminous membrane) showed a better resistance to degradation than membrane type C. Its resistance to UV -radiation renders it more suitable to the hot-dry zones. After 3600 hrs. of accelerated aging it loses about: 10%, 28%, 29% and 35% of its initial peak load, percent elongation, strain energy to break and PRFSE values, respectively. On the other hand, the presence of granule covering (green slate flakes) on the membrane type B improves substantially the APP-modified bituminous membrane resistance to UV -radiation and reduces the rate of the degradation and protects it from progressive aging. Unlike the two other membranes, membrane type B is the less affected one by the aging. It loses (only) about 1.4%, 18.4%, 13.7% and 17% of its initial peak load, percent elongation, strain energy to break and PRFSE values, respectively after 3600 hrs. accelerated aging. The value of the first onset temperature obtained from TGA was found to correlate to the changes in the mechanical properties of the membranes. Moreover, the accelerated aging was found to be more severe than natural aging and could not simulate the real conditions perfectly. Correlation between the two aging conditions was found to be a bit difficult. In general the membranes type A and B show a reasonable tolerance to both accelerated and natural weathering conditions. Based on the results of investigation, it maybe concluded that the warranty (10 years) given by the local manufacturer is overestimated and required re-thinking especially for membrane type C.

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