Recent rain and flooding events in the southwest have demonstrated the damage that water can cause to asphalt roadways. But in reality, it does not take a flood to cause Hot Mix Asphalt (HMA) pavements to fail. The fact is that moisture susceptibility is a primary cause of distress in HMA paved roadways. Moisture damage is the result of moisture interaction with the asphalt binder and thereby reducing adhesion of the binder, to the aggregate; which in turn can lead to rutting and fatigue cracking.
Without going too deep into the chemistry and science; the design of a proper asphalt mix that is suitable for withstanding intended traffic use and climate zone weather conditions, is critical to the safety of the traveling public. Perhaps nowhere else in the country is this more crucial than here in Southern Nevada, due to the flurry of new roadway improvement projects funded by the Fuel Revenue Index (FRI), program.
The FRI is a tax approved by the Board of County Commissioners, based on fuel pump sales from January 2014 to December 2016. This funding measure is expected to raise $700 million in bonding capacity, create more than 9,000 jobs and result in 199 completed projects. For motorists, this averages out to about a dime a day over the three year period.
However, while the FRI program is creating job opportunities and improving our transportation infrastructure, it is also important that the roadways built with this money, last well into the future. And that is where proper asphalt mix design plays an important role.
To assist in achieving the needed quality asphalt mix designs, GES has invested in new TSR testing equipment that is key to analyzing the effects of moisture on specific mix designs.
Most people don’t realize that asphalt roadways are not exactly hard surfaces, oh they feel hard when you stand on them, but they actually are designed to have an elastic quality that allows the asphalt to recover under the strain of repeated loads. This recovery is called the “resilient modulus.” Over time, moisture combined with freezing temperatures and excessive heat can cause asphalt to become less resilient and more susceptible to rutting and fatigue cracking.
To test for the effects of moisture on a specific asphalt mix design, a number of asphalt core specimens, which look like large hockey pucks, are created. Using tensile strength ratio (TSR) testing equipment, the resilient modulus test characterizes the pavement construction materials under a variety of temperatures and stress levels that simulate the conditions of a pavement that is subjected to moving wheel loads. One test is performed by applying pressure on a specimen that has not been exposed to moisture, heat, or freezing conditions and measuring the results. Subsequent pressure tests are performed on identical specimens that have been “conditioned” through emersion in water, overnight freezing, and high heat. The difference in the ability of the unconditioned and the conditioned asphalt to respond to pressure during the tests, called the “modulus ratio,” is recorded and provides engineers with key information as to how well a roadway using that specific asphalt mix design will perform in Southern Nevada.
GES is proud to be a member the Nevada Economic Development Coalition (NEDCO), an organization formed to propose a change in the Nevada Revised Statute to allow Clark County to implement the Fuel Revenue Index. By investing in our community, highly qualified employees, and technology; GES can continue to provide high performance services.
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