One way to increase the strength and durability of concrete is to add stretch edit bars before pouring, and then pull out the rebar to compress the material when the concrete solidifies. But now scientists have found new pre-stress technology that makes concrete lighter without sacrificing strength and reduces carbon emissions.
As the world’s most commonly used building material, the carbon footprint of concrete is huge, and the billions of tons of concrete produced each year require a lot of energy. To this end, scientists around the world are looking to adapt production processes to make them more environmentally friendly, and even small improvements can have a big impact.
Current prestress technology is mainly used for concrete materials that need to withstand particularly high loads (e.g. beams or bridges) and the forces produced by pulled rebar are compressed from the inside. But one drawback of this technique is its susceptibility to corrosion, which means that the concrete poured around them requires a certain thickness and is made with carbon fiber-reinforced polymers (CFRP) instead of corrosion-resistant rebar.
However, using CFRP as a tendon involves expensive equipment and anchoring them to complex processes at both ends of the component. This, coupled with their limitations, means that pre-stressed CFRP-enhanced concrete is not used as widely as it is through rebar.
The swiss team at the Swiss Federal Laboratory of Materials Science and Technology (EMPA) has found a new breakthrough, developing a special formula for CFRP reinforced concrete that expands when hardened. This means that there is no need to anchor and stretch the rebar, as the material swells itself when hardened. The tendonwill to maintain this state permanently, exerting a counterforce on the concrete and creating pressure stress.
“If you pre-stress these CFRP reinforcement materials for the sake of being able to build thinner structures and higher load-bearing capacity, you will reach your limits,” said Dr. Mateusz Wyrzykowski, a member of the project. It’s like a person wrapping a rubber band around his arm and trying to stretch them, the rubber band will be in a state of tension, and a person’s arm will experience the compression of the rubber band, which, by analogy, allows the bloated concrete to experience compression. “
This opens the door to leaner concrete components and provides great strength, and the team’s tests show that self-stressed materials can withstand loads comparable to conventional prestressed concrete, about three times higher than non-prestressed CFRP concrete components.
“Our technology opens up new possibilities for lightweight buildings,” says Wyrzykowski. “Not only can we build more stable structures, but we can also significantly reduce the amount of material used. We can easily pre-stress in several directions at the same time, e.g. for thin concrete slabs or prismatic curved concrete housings. “