There are two truths to concrete: 1) it will get hard, and 2) it will crack. There are many others as well, but these are the two that make or break a good concrete project.
The hard winters in the upper Midwest and the common freeze and thaw cycles are increasingly hard on all concrete, as water can become entrapped in cracks of any size and expand when frozen.
The challenge over the years with any concrete product is protection - not from cracking, but how to repair cracking at the early stages before failure. The industry has developed some creative solutions, including “self-healing” concrete.
What is Self-Healing Concrete?
In 2006, a Dutch inventor introduced a mixture that contains a bacterium that will stay dormant inside a concrete slab until a crack develops.
Since the introduction of the bacteria-based mixture, researchers have also had success with sodium silicate and fungus-based products.
This new technology was created to extend the life of infrastructure concrete and is slowly making its way into the commercial construction world.
Why Self-Healing Concrete?
Concrete is one of the most used materials in construction and, while it‘s strong, it is also quite brittle and has a high tendency to crack. These cracks can be broken into two different types:
- Large or structural cracks: These are the large cracks you see in floors, sidewalks, etc. These cracks generally result from improper reinforcement of the concrete. These types of cracks require replacement of the slab or the area that is cracked.
- Micro cracks or fissure cracks: These are small (under 1 millimeter) cracks that develop within the concrete slab. These types of cracks, while not resulting in structural failure like the cracking above, will result in deterioration of the concrete and failure over time. The photos below show a micro crack. Photo A is a crack in regular concrete showing some movement but no reconnection of the concrete. Photo B shows another micro crack with self-healing concrete, showing the micro crack being repaired by the organisms within the concrete mixture.
Of these two types, self-healing concrete is designed for the micro type of cracking, extending the life of properly poured concrete.
How does Self-Healing Concrete work?
The three different types of self-healing systems are similar in the way they are incorporated into the mix and both react from cracking, but the healing is different for each.
The bacteria is incorporated into the concrete mix before it is poured; when a crack develops, the bacteria feeds on the calcium lactate, and converts it into calcite, a mineral in limestone. This limestone seals the crack, preventing air and water from reentering.
Micro-encapsulated sodium silicate is incorporated; as cracks form, the capsules rupture and release the sodium which, in turn, reacts with the calcium within the concrete. This reaction forms a calcium-silica-hydrate gel that repairs the crack and hardens in about a week.
This system relies on spores. The spores remain dormant until the cracks occur and then begin to fill in the areas.
Cost Impact of Self-Healing Concrete
The newness of self-healing concrete technology makes it difficult to identify the relative costs. Some studies are saying that it will raise the overall pricing by 70% per yard, while other studies are saying that there will only be an increase of 20%. However, they all agree that self-healing concrete will reduce maintenance costs by over 50% over the lifespan of the concrete when properly installed and maintained.
The Future of Self-Healing Concrete
Self-healing concrete is in the midst of changing the concrete world. While it is relatively new technology compared to the 2,000 plus years that concrete has been around, it has the potential to increase the life span of structures, roads, driveways, sidewalks, and the list goes on and on.
While this product is still new and developing, you can expect in the near future that it will become the new normal for concrete construction.
Paul Block has been a project manager with Shingobee Builders for one year. He has over 20 years of experience in various facets of the construction industry, including work with concrete construction. In his time with Shingobee, he has managed retail, restaurant, financial, and telecommunications projects.