Reclaimed Asphalt Pavement (RAP)—FAQ
FAQ 1 : How is the asphalt producer maintaining the quality of the RAP at the plant site?
At Lafarge, when our asphalt plants receive the RAP, they can either separate the road millings (grindings) from the bulk asphalt pavements or combine them together in one large pile. Lafarge accepts only clean RAP with no contaminants such as topsoil, brick, and the like. Before we use the RAP, we process it through a crushing process and size the materials based on mix design and market requirements. Lafarge also performs quality control on the processed RAP to ensure the consistency of the asphalt content and gradation used during the mix design process.
FAQ 2 : How much RAP can be used in HMA?
Depending on the quality of the RAP residual asphalt cement, aggregate type, and gradation anywhere from 15 to 20 percent, RAP can be used in a mix design without changing the virgin asphalt cement. Anything greater than 15 to 20 percent RAP will usually require a change in the virgin asphalt cement. Typically, in an HMA mix, one grade of softer asphalt cement is used to overcome the higher quantities of aged residue asphalt cement to meet pavement performance requirements, such as fatigue and low-temperature cracking resistance. Further, the type of asphalt plant will dictate the amount of RAP used in HMA. For a batch plant, usually no more than 30 percent RAP is used. For a drum mix plant, quantities greater than 50 percent have been used successfully.
FAQ 3 : What is the effect of different percentages of RAP on HMA performance?
When more than 15 to 20 percent RAP is used, greater replacement of the virgin asphalt cement occurs with the RAP residue asphalt cement. As a result, a softer virgin asphalt cement is needed to ensure proper pavement performance expectations to resist fatigue and low-temperature cracking.
FAQ 4 : How long has RAP been used in HMA?
RAP has been used in HMA since the 1950s. It has only been since the 1990s, however, that asphalt plant manufacturers have designed plants that will properly recycle RAP, resulting in recycled HMA that is equivalent to conventional HMA.
FAQ 5 : What is the contractor doing to monitor the quality of RAP and recycle HMA?
At Lafarge, we have a strong quality-control system in place that tests the processed RAP at a set frequency. We typically test for gradation and asphalt cement content once per 1,000 metric tons. We also test for RAP aggregate physical characteristics. These are used in the design of recycled HMA. Further, Lafarge tests the produced recycled HMA at the same testing frequency as conventional HMA, ensuring that the quality and consistency of our products meet owner specifications.
FAQ 6 : Why should I be recycling?
The use of RAP in HMA and its long-term performance have been scientifically proven when designed and produced properly, following standard agency mix design procedures. The ability to recycle RAP into HMA saves our natural resources and helps reduce our carbon footprint. Further, any project using recycled HMA is eligible for LEED points.
FAQ 7 : Why should I accept RAP in HMA?
It has been proven that properly designed and produced recycled HMA is equivalent to, if not better than, conventional HMA.
FAQ 8 : I’ve heard RAP makes HMA an inferior product. Is this true?
Too much RAP without adjusting the virgin asphalt cement or the mix design will result in an inferior recycled HMA product. Inconsistent RAP also will result in a poor product.
FAQ 9 : Can you take recycled mix and recycle it again?
Because RAP has been used in asphalt pavements since the 1950s, there has been ample opportunity to recycle existing recycled HMA back into recycled HMA. In the end, the recycled HMA still needs to meet owner specifications.
FAQ 10 : I’ve heard RAP causes segregation on the road. Is this true?
Inconsistency in the RAP processed or millings stockpile, and/or high moisture content may cause segregation on the jobsite.
FAQ 11 : I’ve heard RAP makes mixes difficult to compact. Is this true?
Where a high percentage of RAP is used without adjusting for the impact to the virgin asphalt cement, or where moisture still exists in the recycled mix, it may be difficult to properly compact the recycled HMA.
FAQ 12 : How do I ensure that I have received a recycled HMA that meets my product specifications?
It is very important that the owner test the recycled HMA as if it were conventional HMA.
FAQ 13 : What is the quality of the recycled asphalt pavement (RAP) coming off the road?
The quality of the RAP is generally good. The aggregate is excellent because it had to meet earlier specifications, but the asphalt cement will be a harder (stiffer) product due to aging effects.
FAQ 14 : How do I ensure that the recycled mix will give me the same design life as virgin mix?
Field-tested sections of recycled HMA have proven that long-term field performance is there.