Paving, Asphalt, Tires and Latex Allergies:
What is the Relationship?
By Donald F. Groce, Best Manufacturing Company
Donald Groce spearheads technical services and the analytical testing lab at Best Manufacturing. He is a frequent contributor to Latex Allergy News. This article appeared in the August 1996 edition.
If you are a latex allergy victim and you experience any type of reaction around streets that are being paved, or asphalt that is being added to roof structures, there is a very good reason. Asphalt, when combined with ground up tires in the paving process, contains natural rubber.
Since the very early days of paved-highway construction, rubber has been added to modify asphalt. Natural rubber, styrene-butadiene rubber (SBR) and neoprene are added to improve the temperature sensitivity of asphalt at both low and high temperature extremes.
In addition, these rubbers aid in waterproofing the asphalt and reducing cracking at low temperatures. Many countries use natural rubber to make rubberized asphalt; however, in the U.S., recycled or reclaimed rubber has been used to reinforce asphalt since the early 1960s. The reclaimed rubber is mainly from ground whole-tire rubber and ground tire tread. These tire components contain natural rubber, SBR, and butyl rubber.
Paving with rubberized asphalt consists of the following four steps or layers: Asphalt concrete hot mixes, stress-absorbing membrane interlayer (SAMI), stress-absorbing membrane (SAM) or seal coat, and joint and crack sealers.
Rubber, either in the form of ground up tires or as powdered devulcanized rubber, is added to each of the layers.
The amount of rubber added is up to 25 percent of the weight of the total blend. The rubber components are added to the pug mixer and blended at 425 degrees Fahrenheit. When the asphalt is being mixed or sprayed, natural rubber latex particles are almost certainly being aerosolized.
The latex allergy sufferer also needs to be aware of the rubber found in both passenger car tires and commercial vehicle tires. At least 70-75 percent of the natural rubber produced today is used to manufacture tires. Tires contain natural rubber in two forms: Latex (1.4 percent proteins) and as dry sheet rubber (2.2 percent proteins).
The following outlines the different components of passenger car tires and what blends of rubbers they contain.
This list clearly shows that natural rubber alone or blended with other rubbers such as SBR, butyl rubber and isoprene is used in almost every part of the tire making process. As for commercial vehicle tires, the amount of natural rubber increases with the size of the vehicle. For example, large earth mover tires are made of 100 percent natural rubber.
There is no specific data concerning the exact level of natural rubber proteins in tires or rubberized asphalt.
It is possible that the rubber proteins are denatured by the high temperatures used in the mixing of the asphalt. However, latex allergens have been found in tire dust, roadside dust and air samples from the Los Angeles area. More than 10,000 pounds of rubber tire particles are released into the external air of Los Angeles every day.
A study of blood samples from asthmatics and healthy persons from the Los Angeles area showed a high correlation in the increased incidence of latex allergen antibodies in asthmatics. Victims of latex protein hypersensitivity should avoid areas that are being paved or roofed when asphalt is being used. The airborne particles of natural latex proteins emitted in these processes are known to cause reactions in latex allergic individuals.
Copyright © Latex Allergy News
Reproduced here with permission.