Cracks and leaks in concrete are history with self-healing concrete

Especially with reinforced concrete combined with water, cracks are a major problem

Concrete is a wonderful building material. It has so many advantages and we make everything from it. From water basins to basements to crucial infrastructure. But it also has a downside: concrete cracks. And that's where Basilisk Self-Healing Concrete has a solution. Time to talk to this fast-growing international company from Delft.

With good design, cracking can be limited, but even so, even small (hair) cracks cause problems. "Especially when reinforced concrete comes into contact with water, cracks are a big problem," says Bart van der Woerd, Managing Director at Basilisk. "When the reinforcement starts to rust, the lifespan of the building's structure is compromised. In addition, the cost of repair at that point is sky-high." 

When self-healing concrete is interesting

Self-healing concrete is particularly interesting for structures where waterproofing plays an important role. "Think for example of constructions where ground or rain water play a role such as parking garages, basements and water tanks. Of course, there are other ways to make concrete waterproof, but they are generally more expensive than self-healing concrete. Moreover, with our self-healing concrete, the CO2 footprint of concrete can be significantly reduced," Van der Woerd said.

40% less shrinkage reinforcement required

Basilisk claims that 40% less shrinkage reinforcement is needed. That results in hefty savings, both in cost and CO2 emissions. How that works. "Two criteria determine the amount of shrinkage reinforcement needed for watertight structures: durability requirements and watertightness requirements. In almost all cases, the watertightness requirements are leading, as they call for the smallest crack width. The smaller the acceptable crack widths, the more shrinkage reinforcement steel is required."

By adding self-healing properties to the concrete, the waterproofing of the concrete increases and waterproofing requirements are met. "This means that the reinforcement design can only be made based on the durability requirements. Usually these allow for a larger crack width. In addition to environmental and cost advantages, we found out in practice that there is another important advantage. Because less steel is incorporated into the structure, the chance of gravel nests is minimal."

How does self-healing concrete work? 

Self-healing concrete works with limestone-producing bacteria. In other words, it is bio-based. Every time the bacteria in the concrete come into contact with oxygen and moisture, they convert certain nutrients to calcium carbonate (limestone). This causes cracks to fill with limestone and eliminates the need to repair or restore concrete through manual maintenance. Every time a crack occurs, the microorganisms repair it autonomously. Basilisk currently has three products on the market: an admixture added in granular form to concrete mortar, a repair mortar and a liquid repair system for cracks in floors. Whether the bacteria also have a negative effect on humans or concrete? "We get that question more often," Van der Woerd says with a laugh. "To that I can answer briefly: it does not. Our bacteria are safe for both humans and concrete."

Less maintenance, longer life

In practice, we see that the market is primarily interested in the short-term benefits of self-healing concrete: waterproofing and steel savings. "I also understand that very well. In construction, despite the increasing focus on sustainability, there is also a strong focus on cost efficiency. That's where these two benefits fit in well," agrees Van der Woerd. "We recently did a project in a basement parking garage. Here the contractor was able to save about 35% on shrinkage reinforcement and the decision to choose self-healing concrete was quickly made. Another great project where the short-term benefits were immediately obvious was a wastewater treatment tank." 

In the long run, however, there are performance differences from regular concrete that are sometimes somewhat understated. "Structures last much longer and also require less maintenance. That's a really important difference. In the Netherlands, we see that this argument does not yet carry much weight. In Japan, it is different. There, on the contrary, they attach great importance to the entire life cycle. In fact, Japan is one of our biggest growth markets. We have also recently seen a lot of interest from the Middle East, another area with a lot of potential. The Dutch market is still a bit more conservative. It will take us a bit more time here, but I am sure that the Netherlands will eventually embrace self-healing concrete as well. The advantages are simply too great not to."