Sustainably Protecting Marine Concrete

Sulfate-reducing bacteria are implicated in the rapid degradation of concrete used in marine environments. According to scientists at the Hong Kong Polytechnic University, the solution may be to select a better bug.

“Sulfate attack” is a major cause of cracking and failure in concrete used in retaining walls, boat ramps, and in roads and buildings that are near the ocean. Sulfate-reducing bacteria, which reside in typical biofilms, initiate the conversion of sulfate ions in seawater into sulfuric acid. The acid reacts with the concrete matrix, causing degradation and cracking. One solution is to try to kill the bacteria, but repeated treatments may cause them to become biocide-resistant. Additives can make concrete more resistant, and specialist concrete coatings can provide a barrier – but structures must be regularly re-painted to survive. There is an increasing demand for new “green” and effective alternatives to inhibit the corrosion of marine concrete.

In the latest edition of Environmental Science and Technology, researchers report that by selecting right bacteria the biofilm that inevitably forms on concrete in wet environments can be primed to protect rather than destroy. Biomineralization can provide a natural barrier to seawater and the potentially corrosive salts it contains. This approach, which had been already proposed for metal materials, could provide a more sustainable approach to preserving concrete structures.

Concrete surfaces were coated with bacterial suspension rich in urease-producing bacteria enriched from seawater. The enzyme breaks down urea, providing carbonate ions and an increase in pH that leads to the precipitation of calcium carbonate, CaCO3, using calcium ions from the concrete (the same process as used in geologic CO2 sequestration). The treatment created a stable barrier coating for the concrete and led to a decrease in the abundance of sulfate-reducing bacteria. It provided better protection for the concrete (lower mass loss and strength reduction) than most previously reported methods for inhibiting concrete corrosion.

We love to see such examples of a possible biobased solutions for serious commercial challenges that align with Vireo’s mission to move our world towards a safer and more sustainable future by highlighting and supporting the commercialization of novel and biobased materials and processes.