Microspheres can improve concrete's mechanical properties

Researchers have developed micron-sized calcium silicate spheres that could increase concrete's strength and reduce its environmental footprint.

Concrete is the most-used synthetic material worldwide and its improvement could be highly beneficial. Rouzbeh Shahsavari, an assistant professor of materials science and nanoengineering in Rice University and Sung Hoon Hwang, a graduate student, explain that spheres are formed in a liquid mixture around nanoscale seeds of a common detergent.

The spheres can be assembled to create solids that have better mechanical properties (strength, hardness, elasticity and durability) than Portland cement, the most common binder used in concrete. Authors state that their cost is low and their production requires less energy than cement. "These are very simple but universal building blocks, two key traits of many biomaterials. They enable advanced functionalities in synthetic materials. Previously, there were attempts to make platelet or fiber building blocks for composites, but this works uses spheres to create strong, tough and adaptable biomimetic materials. Sphere shapes are important because they are far easier to synthesize, self-assemble and scale up from chemistry and large-scale manufacturing standpoints," Shahsavari said.

Professor Shahsavari highlights the benefits of the spheres utilization: "Cement doesn't have the nicest structure. Particles are amorphous and disorganized, which makes it a bit vulnerable to cracks. But with this material, we know what our limits are and we can channel polymers or other materials in between the spheres to control the structure from bottom to top and predict more accurately how it could fracture." He also adds that the microscopic particles can be used for other engineering purposes like insulation or composite applications.

The diameter of the spheres can range from 100-500 nanometers, controlled by the selection of surfactants, solutions, concentrations and temperatures during manufacture. According to Shahsavari, shape and size of particles influences the mechanical properties of materials like concrete. "It is very beneficial to have something you can control as opposed to a material that is random by nature. Further, one can mix spheres with different diameters to fill the gaps between the self-assembled structures, leading to higher packing densities and thus mechanical and durability properties," he said.

If the utilization of spheres is realized in industry, manufacturers could use less concrete reducing the cost and the energy required to complete a construction.