With concrete being the world’s leading construction material, it is important to always be investigating ways to improve its inherent durability. What better direction to navigate than to protect it from its nemesis – water. Water can break down concrete, pool on its surface and infiltrate tiny cracks. Especially in climates that endure many freezing and thawing cycles, it comes as no surprise that roads are in constant need of repairs. Thankfully, researcher Konstantin Sobolev, a UWM professor of civil engineering, has designed water-repelling concrete.
It is noted that this water-resistant variety of concrete causes water that is poured over it to form beads on the surface that then rush away. Along with other high-performance concrete composites that Sobolev has developed, his materials are designed to last - with some of the creations having such impressive crack control that their service life is estimated to be about 120 years. Considering the average lifespan on Wisconsin roads are around 40 or 50 years for instance, this is clearly a massive improvement!
The main composite that Sobolev uses to battle against water damage is dubbed “superhydrophobic engineered cementitious composite” and it has two ways that it fights against moisture. The first involves the use of nano-additives that change the concrete on a molecular level once hardened. This results in a spiky surface at a microscopic level which leads to the beading and rolling off of water on contact. Think of a leaf with tiny little hairs across the surface that too leads to beading of water.
The other method involves millions of tiny bubbles that contain air and siloxane oil that are blended throughout the concrete. Cracking causes the bubbles to break upon which then releases the oil and keeps water out.
Though neither method completely waterproofs the concrete on their own, Sobolev combines them together with a fiber reinforcement strategy that addresses both the brittleness found in high-strength concrete and elimination of large cracks. How this works is that strong polyvinyl alcohol fibers or high density polyethylene fibers are mixed into the concrete. When cracks begin to accumulate, the fibers prevent them from becoming larger gaps.
With this method, tiny cracking is not being eliminated. Rather, it results in evenly distributed microcracking while the materials superhydrophobic properties form a water barrier. Sobolev states that this architecture increases ductility or flexibility under stress by over 200 times. It also enables the material to withstand four time the compression in comparison to traditional concrete!