As one major application of crumb rubber, rubber modified asphalt could
have the largest market for waste tire recycling. Moreover, this application
could result in an important improvement for road construction technology.
Rubber modified asphalt has been known to improve the rheological properties
at low and high temperatures and provide a life up to three times longer
than conventional asphalt. Even though rubber modified asphalt may cost
up to 100 % more than regular asphalt, the advantages may justify the added
cost.
Recent studies have shown that chemically-modified crumb rubber asphalt
can overcome several problems with rubber modified asphalt and improve
the required properties for road construction.
Conventional Rubber Modified Asphalt
Market :
In 1991, the Intermodal Surface Transportation Efficiency Act (ISTEA) section 1038 was passed into law. This act required that starting in 1994, 5 % of the roads built with federal funds use a pavement made with crumb rubber, processed recycled tires, or modified asphalt. By 1997, 20 % of the roads built with federal funds would be required to use recycled tires in the pavement. In order to meet ISTEA's 1997 requirements, about 100 million scrap tires would need to be used each year.
Manufacture :
The traditional manufacturing process for rubber modified asphalt is a simple blend of heated asphalt, over 400 degrees Fahrenheit, and crumb rubber particles, 15 to 25 weight %. The resulting product has a higher viscosity over a wider range of temperature compared to conventional asphalt.
Advantages :
Blending with crumb rubber expands the useful temperature range of the asphalt and increases impermeability. Rubber modified asphalt has shown better rheological performance over a wider range of temperature.Disadvantages :
Normal high quality Canadian asphalt has a rating of 58 -28, indicating a temperature range of 58 degrees C (136.4 F) at the high end and -28 degrees C (-18.4 F) at the low end. The rubber modified asphalt has a rating of 64 -34 (147.2 to -29.2 F)4). Generally, to improve the low temperature performance without using rubber modification, high boiling point petroleum oil is added to make the asphalt softer. This is both economically and ecologically undesirable.
The improvements using rubber modified asphalt include decreased thermal cracking, potholing, deformation, reflective cracking and ice formation, and have extended road life up to three times longer than normal asphalt.
The disadvantage of rubber modified asphalt is associated with the preparation process during heated storage. The crumb rubber and asphalt separate into two or more phases, because of the weak interaction between the rubber particle surface and the asphalt. Normal asphalt shows a separation of between 2 to 4 % during heated storage. Rubber modified asphalt yields a non-homogeneous blend with up to 25 % separation. This non-homogeneity reduces the reliability of the product properties. Separation decreases the expected life of the rubber modified asphalt.Chemically Modified Crumb Rubber Asphalt
Several studies have shown that a chemical bonding between the rubber
and the asphalt would radically reduce separation and create a homogeneous
product less susceptible to deterioration. Compared to a separation of
25 % for conventional rubber modified asphalt, chemically modified crumb
rubber asphalt exhibits a separation range of 5 to 7 %. This is due to
the formation of a chemical bond instead of a physical mixture.
The increased stability of the mixture and homogeneity contributes
to reduce storage cost and improved life of the paved road.
It is also known that some polymers increase the low and high temperature
rheological properties, more than conventional rubber modified asphalt.
The cost of chemically modified crumb rubber asphalt is usually 60
% higher than that of conventional asphalt. However, storage cost is reduced.
Reference Web Site: Rubber Modified Asphalt Binders Blacklidge Emulsions, Inc.
A layer of rubber tire chips under a road surface will help minimize
frost penetration, and therefore minimize the road 'heaving' that takes
place in northern areas of the United States during winter.
The 2 to 3 inch pieces of chipped tire, including steel, are spread
to a layer of 6 to 12 inches in thickness. The layer is covered with
12 to 24 inches of gravel. This layer will provide insulation that reduces
frost heave formation at low cost.
Subjects
Recycling Technology