Using the nanostructure of sea urchin spines as a guide, the physical chemistry research team at the University of Konstanz (Konstanz, Germany) has developed a cement that is significantly more fracture resistant bysynthesizing it at the nanoscale using a “brick and mortar principle.” Sea urchin spines are mostly made of calcite, usually a very brittle and fragile material; however, the sea urchin spines are much more durable than the raw material alone because the material is optimized with a brick wall-style architecture.
In nanoscience, brick wall-style architecture can be compared to masonry where the guiding principle is to layer hard, then soft, hard, then soft materials. This principle makes sea urchin spines resilient—crystalline calcite blocks in an orderly structure are surrounded by a softer amorphous area comprised of calcium carbonate. When force is applied to the brittle calcite, its crystalline block does crack, but the energy is transferred to a soft disordered layer with no cleavage planes to tear, so further cracking is prevented.
Cement has a disordered structure—each component sticks to all the others. For cement to benefit from the increased stability provided by brick wall-style architecture, its structure would need to be reorganized at the nanoscale with a material that bonds only with cement nanoparticles and nothing else in the cement. The researchers identified macro molecules during the cement synthesis process that take on the function of mortar and affix the crystalline blocks to each other at the nanoscale, with the blocks assembling themselves in an ordered manner.
The team used an ion beam under a scanning electron microscope (SEM) to cut a 3-µm, bar-shaped microstructure out of the nanostructured cement, and bent it with a micromanipulator. As soon as the microstructure was released, it returned to its original position. Mechanical values calculated based on its elastic deformation indicate the optimized cement achieved a value of 200 MPa. The concrete commonly used today has a value of 2 to 5 MPa.
The nanostructured cement provides completely new construction possibilities, the researchers note. A pillar made with this cement could be built 8,000-m high (ten times as high as the current tallest building in the world) before the material at its base would be destroyed by its weight. Normal steel could only reach 3,000-m in height.
Source: University of Konstanz, www.uni-konstanz.de.