Wednesday, August 22, 2012

Self Healing Asphalt (Guest Blog)

About a year ago I started following a research project that has got me pretty excited about the possibilities for the future of pavements.   The project is examining an approach to what is lovingly being called "self-healing" pavements.  In other words, pavement, that when cracks start to form...heals itself!  How cool is that!?

California is extremely lucky to have so many great pavement research programs but every once in a while venturing outside of California for the world's view on pavements proves extremely interesting.  I contacted the professor in charge of this project, Erik Schlangen of Delft University of Technology in the Netherlands, and he generously put together the synopsis below for the Quality in California readers. Lucky you!  I'd also encourage you to visit their blog to learn more about the project and keep up to date on their progress and updates.  The blog's link can be found at the end of the post.  Happy Reading!

Induction heating and healing of porous asphalt concrete

An induction heating/healing approach was developed at Delft university of Technology in the Netherlands to enhance the durability of porous asphalt pavement. Steel fibers are added to the porous asphalt mixture and induction heating is used to heat the porous asphalt pavement when micro cracks are expected to occur in the asphalt mastic of the pavement.  In such a way, porous asphalt concrete can repair itself and close the cracks through the healing of the binder (diffusion and flow) at the high temperatures. The closure of micro cracks will prevent the formation of macro cracks. In the end, raveling and cracking can be avoided or delayed .

To prove that induction healing works in porous asphalt concrete, the electrical conductivity, induction heating speed, mechanical properties and healing capacity of porous asphalt concrete with steel fibers were studied in this research.  The following aspects can be outlined from this research:

1.      Adding steel fibers to porous asphalt concrete makes it electrically conductive.

2.      Porous asphalt concrete with steel fibers can be heated with induction energy. It is proven that induction heating doesn’t cause extra aging to the binder.

3.      Addition of a moderate amount of steel fibers reinforces porous asphalt concrete by increasing its the ravelling resistance, indirect tensile strength, fatigue resistance and water damage resistance.

4.      The healing capacity of porous asphalt concrete with steel fibers is greatly increased by induction heating. The completely fractured porous asphalt concrete beams with steel fiber can be healed many times due to induction heating. The stiffness of fatigue damaged porous asphalt concrete samples recovers more and faster when induction heating is applied on them. The fatigue life of porous asphalt concrete samples with steel fiber is significantly extended after induction heating.

5.      The optimal heating temperature is 85 ÂșC. Overheating, causing swelling and drainage problems,  decreases the healing rate of porous asphalt concrete.

6.      Induction heating can be repeated when cracks return. Through multiple times induction heating, the fatigue life of a porous asphalt beam can be strongly increased.

7.      The durability of porous asphalt concrete pavement will be improved with induction heating because of the improvements in the healing capacity and in the fatigue resistance.

8.      A porous asphalt trial section with the concept of induction healing was paved on Dutch motorway A58 in December 2010. The trial section was fully intact after the two winters of 2010-2011 and 2011-2012. The trial section can be heated with induction energy and cores form the trial section show better particle loss resistance than the reference section. It is expected that the durability of the trial section will be enhanced by induction heating.

9.      An induction generator for field heating is being developed.

In further research, the efforts will be focused on the following issues:

1.      Optimization of steel fibers
Steel fibers will be optimized to obtain the highest induction heating speed without affecting the mechanical properties of porous asphalt concrete negatively.

2.      Optimization of the mixing technology
To shorten mixing time and save energy consumed in dispersing steel fiber into porous asphalt concrete, the mixing technology needs to be optimized.

3.      Optimization of induction generator
To enhance the induction speed, the induction generator should be optimized by changing its frequency and the shape/size of the coil.

4.      Modeling of induction healing in porous asphalt concrete
The capillary flow of the Newtonian binder in cracks under surface tension force will be simulated in further research to fully understand the mechanisms involved in induction healing.

More information about this research can be found in the self healing asphalt blog:

The work described above forms also the basis for a PhD-thesis by Quantao Liu at Delft University. He will defend his thesis on October 2nd 2012. After that date it will be possible to download the thesis from the self healing asphalt blog.