Scientists from the Brno University of Technology have advanced in the development of flexible concrete

Brno - Scientists from the Brno University of Technology have made significant progress in the development of so-called flexible concrete. The team from the Material Research Center has particularly improved its resistance to moisture, which has long presented a seemingly unsolvable problem. The material will find future applications, for example, in construction in earthquake-prone areas. The foundations of buildings containing flexible concrete can withstand ground tremors, said Jitka Vanýsková, spokesperson for Brno University of Technology.
Although new materials are still emerging in construction, cement and concrete, according to experts, remain the essentials even in the new millennium. However, their form and properties are changing. One of the innovations is also MDF composites, sometimes referred to as flexible concrete. "Don’t picture a spring or something that bounces like a trampoline. The advantage of flexible concrete is its tensile strength in bending," explained one of the members of the research team at the Material Research Center, Tomáš Opravil.
Although many studies have addressed improving the mechanical properties of concrete, the results have long only led to an increase in compressive strength. A breakthrough in this area came only with an unconventional method of processing cement pastes, which allows for the creation of an almost defect-free structure, meaning a material without porosity that limits strength.
The mixture of cement and water is combined in a special mixer composed of two differently sized cylinders that mix at the same speed with high shear mixing, along with a water-soluble polymer, usually based on polyvinyl alcohol. Its proportion in the mixture is only about five percent, but that is enough for the resulting mass to boast up to ten times higher tensile strength in bending. In practice, this means, for example, that a panel with the same load-bearing capacity made of flexible concrete will be several times thinner than a panel made of conventional concrete. Unlike the latter, it is not "poured" into prepared forms but is processed similarly to plastics through molding or extrusion.
The construction material can then be used, for example, for building structures in seismically unstable areas. "We do not expect that entire foundations will be made of flexible concrete. Statics would need to calculate which specific construction elements to use flexible concrete for and in which locations at risk from vibrations to place it," stated František Šoukal from the Material Research Center. Further proposals for the application of MDF composites are quite broad - ranging from fire-resistant doors to thermal insulation, armoring, and even cryogenic vessels.
The small resistance of flexible concrete to moisture had long seemed an insurmountable problem. Many foreign institutions thus stepped back from further developing MDF composites in recent years. However, the Brno scientists managed to solve the issue. "We modified the polymer so that the MDF composite retains more than 90 percent of its original strength even with long-term storage in water," specified Šoukal.