Civil Engineering Reference
In-Depth Information
The asphalt is a complex mixture of organic and inorganic com-
pounds and their complexes. Some of the organic compounds are aliphatics,
aromatics, polar aromatics, and asphaltenes. Polar aromatics are respon-
sible for the viscoelastic properties of asphalts.
[5]
Over the years, multilayers of tar-based waterproofers replaced the
hot asphalt used in roofing. In early 1900, asphalt became available from
petroleum refining, and it was followed by oxidized bitumen interlaid with
roofing felt and then alternated with a mineral base sheet.
[4]
Asphalt-based
materials are used extensively as binders, sealants, and waterproof coatings
in diverse applications because of their low cost, inherent cohesive nature,
weather-resistant properties, and ease of processing in the molten state.
[6]
Despite its natural viscoelastic properties, asphalt cannot be used
as such in roofing applications because of its inherent limitations, such as
brittleness at low temperature and flow properties at high temperature.
Therefore, studies have been done to improve the properties of bitumen.
Combining bitumen with natural or synthetic rubbers or lattices, new
materials with higher elasticity, low temperature flexibility, higher strength,
and better fatigue resistance can be obtained.
Polymer-modified bituminous membranes were developed in Eu-
rope in the mid-1960s and have been in use in North America since 1975.
The polymeric systems have varied from natural rubber to more complex
synthetic systems such as block copolymers and polymer blends. Most
common polymers used as modifiers are polyisobutylenes, polybutadienes,
polyisoprenes, styrene-butiene-monomer, styrene-butadiene-rubber, butyl
rubber, ethylene-vinylacetate (EVA), atactic polypropylene (APP) as well
as natural rubber. Polymers, such as atactic polypropylene or styrene-
butadiene-styrene (SBS), impart flexibility and elasticity, improve cohe-
sive strength, resist flow at high temperatures, and toughness.
[7]
They are
the most widely used modifiers of bitumen-based roofing materials.
3.0
SYNTHETIC ROOFING MEMBRANES
Polymers such as poly(vinyl chloride) (PVC), ethylene-propylene-
diene monomer (EPDM), chlorosulfonated polyethylene, ketone ethylene
ester (KEE), reinforced polyurethane, butyl rubbers, and polychloroprene
(neoprene) have proven to be suitable for roofing membranes.
[4]
In the last
ten years, a new synthetic roofing material (thermoplastic polyolefins)
