By Peter-Shaun Tyrell
Photo courtesy of Joe Loong.
Self-healing concrete is a technology that may revolutionize the cost and process of maintaining our roads in addition to how we build them. Professor Erik Schlangen, a Dutch civil engineer, is the leading researcher at the Delft University of Technology for “Self-Healing Pavement”, which is being commercially used in the Netherlands with some success.
Asphalt concrete is cheap, almost noiseless, and when possible allows rain water to drain into a small reservoir below, which is a big tool for managing storm weather. However it does have its downsides, specifically raveling. Raveling can occur after several years of use and is when smaller stones break away from the main body. This deterioration leads to the roads becoming unusable.
If not treated, issues such as small stones flicking up from tires and hitting windshields as well as major issues like potholes can occur. Combined with the 2.2 million miles of road in America, 93 percent of which are covered with asphalt, this leads to an expensive operation of relaying. To be exact in terms of costs, in 2005 the US Federal Highway Administration was granted $286 billion to provide repairs and maintenance.
The current solution to the roadway deterioration problem is to introduce a dual layer of asphalt. However even with the dual layer the lifespan is only seven years. Schlangen’s team hopes to introduce a new technology that will increase the lifespan of single layered asphalt to 10-14 years, cutting the cost of relaying exponentially.
The asphalt pavement is made up of a symbiotic relationship between aggregate and bitumen. Aggregate are small stones and bitumen is like glue binding them all together. The bitumen can be worn down by rain, UV light, and vibrations when this occurs the aggregate loosens and the consequences previously explained can occur.
The “self-healing” process begins by introducing steel wool and heat induction machines. The first step is to combine the steel wool with the bitumen, then the induction machine heats the steel, allowing it to flow into the micro-cracks of the bitumen, filling them up.
As a result of Schlangen’s research, the Dutch government gave his team the A58 highway to be layered with the self-healing pavement. Which led to the International Union of Laboratories and Experts in Construction Materials, Systems, and Structures (RILEM) launching a five year long report into the use of asphalt. RILEM’s mission is to “promote sustainable and safe construction, and improved performance and cost benefit for society.”
In October 2012, Schlangen presented his work at a TED conference. Schlangen explains that on site and in his laboratory an industrial powered induction machine, not a microwave will be used. The A58 highway has also been a full success.
Self-healing materials are not limited to pavement and steel wool. Bacterial concrete is designed to introduce bacteria into the steel reinforcement of concrete to stop it from corroding. The bacteria, when metabolically activated by calcium lactate, begins to consume oxygen which is a leading ingredient in the corrosion of steel.
Nanotechnology is being used in the form of nano tailored material. It combines several materials with steel at a nano-level so weaknesses such as corrosion from chloride and carbonation prevalent in steel will be eliminated.
So will the self-healing material come to the US? Well, porous asphalt has been demonstrated to work on US roadways. At the moment there may be a lack of international exposure, hence RILEM’s involvement in this new technology, but when their report closes in 2019, Schlangen’s creation may be the foundation to future self-healing roads.