Production of hot mix asphalt recycling at BMT
Nowadays, despite extensive development for a long time in many countries around the world, but in our country, asphalt pavement recycling in plant is a new and strange technology for the project owners or consultants and contractors. So that most of people worry about the quality of hot mix asphalt (HMA) containing RAP.
According to scientific researches and practical experiences of prestige organizations on over the world such as Europe Asphalt Pavement Association (EAPA), National Asphalt Pavement Association (NAPA), Federal Highway Administration (FHWA), National Highway Cooperative Research Program (NHCRP), etc., It’s necessary to confirm that the use of processed RAP to produce HMA at plant is the most common type of asphalt recycling and is now considered standard asphalt paving practice. There are abundant technical data available indicating that properly specified and produced recycled hot mix asphalt is equivalent in quality and structural performance to traditional hot mix asphalt in terms of rutting, raveling, weathering, and fatigue cracking. Recycled hot mix asphalt mixture also generally age more slowly and are more resistant to the action of water than traditional hot mix asphalt. Recycling in plant is able to produce hot mix asphalt containing up to 100% RAP depending on kinds of plants and RAP quality.
Fig. 1 – Dynamic modulus test of HMA containing RAP with various percentages [Prof. Mogawer, 2007]
Research results according to the program “Application of reclaimed asphalt pavement in Vietnam” leaded by Dr. Vo Dai Tu also prove the quality of products using this technology. Most of concerns about asphalt recycling focus on aged bitumen of RAP, aggregate quality and gradation, performance of HMA containing RAP. This article will shed light on concerns that impede the application of useful technology in our country.
Fig. 2 – Photo of specimens of traditional HMA12.and HMA12.5 containing 30% RAP
Aggregate quality control: RAP is considered an aggregate fraction after process consisting of milling, testing, sorting, crushing, remixing and re-classifying uniformly. It’s absolutely easy to design and mix RAP with virgin materials to produce HMA if we accurately control above processes.
Fig. 3 – Gradation curve of HMA 12.5 containing 30% RAP
Aged bitumen of RAP: The study of changes in the chemical composition of asphalt through the aging process of the BMT researchers make major cause of aging is as follows: loss of oily components by volatility or absorption, oxidation forming high molecular fractions (resins, asphaltenes) from lower molecular fractions (oils, saturates), molecular structuring that produces thixotropic effects (steric hardening). Understanding listed causes of aging, Dr. Vo Dai Tu has found recycling agent, which is able to make bitumen “younger”. We can absolutely recover bitumen characteristics by using recycling agents.
Fig. 4 – Recycling agent reduce viscosity of aged bitumen
According to the performance testing the quality of HMA containing RAP is equivalent to traditional HMA and is even better than in some characteristics. Typically, the Marshall stability of HMA containing RAP is higher than traditional HMA when produced by the same designs.
Fig. 5 – Marshall stability of traditional HMA12.5 and HMA 12.5 containing 30% RAP