Professor Shahsavari and graduate student Sung Hoon have demonstrated a process for producing a cement that is stronger, lighter, and more durable than the traditional Portland cement.
Tech Briefs: What got you interested in this project?
Professor Rouzbeh Shahsavari: Concrete is the most widely used engineering material. Since such a large amount of concrete is consumed, it has a large energy and environmental footprint. We got the idea that if concrete could be produced that has greater durability, lasts longer, and doesn't need as much replacement or repair, it would have a lower environmental impact. Also, with concrete that is twice as strong, you would need half the amount for construction because it could sustain a load using half the volume. You would then need half the labor, half the transportation, half the rebar — everything becomes half. We decided to attack the problem from a materials perspective. If we could produce cement made up of spherical particles, its porosity would be minimized.
Tech Briefs: Don't particles with different shapes and sizes have fewer spaces between them than spheres?
Shahsavari: The problem in the current cement industry is that there is no control over the size and shape of the particles. Once you mix the cement with water, and it becomes a slurry that hardens, the shapes of the particles are random. You can have porosity up to a centimeter so that water can easily ingress and penetrate to the steel rebar, weakening the structure and reducing its durability. If, however, the spheres were different sizes, the smaller ones would fill the gaps.
Tech Briefs: Are there other possible applications for your process?
Shahsavari: Yes. Calcium silicates like cement can be used as thermal insulators that have good tolerance for high temperatures. Also, bone tissue has a structure similar to cement — tough and inorganic — and importantly, calcium silicates are biocompatible. We're already using artificial bone for making hips and other body parts. There is a general price pressure to stay with Portland cement for building construction, but for medical use, high quality outweighs price as an important factor.
Tech Briefs: What process did you use to form the spherical particles?
Shahsavari: From fields such as epitaxial growth, it is known that if you want to control shape or size, you need some sort of template. Our thought was that we could form micron-sized calcium silicate spheres around micelle surfactant seeds because they are essentially spherical in shape. Although these seed points are very small, their impact is high when it comes to shape.
These cement ingredients are attracted to the small templates and grow on top of each other while retaining the same shape as the seeds. We demonstrated that if we use techniques such as self-evaporation, individual spherical particles come together. Making this self-assembly process more efficient is the subject of our ongoing research.
Tech Briefs: Do you think this process will completely replace Portland cement?
Shahsavari: No, not completely. Portland cement is in high demand — more than three billion tons a year globally; however, it may be mixed with Portland cement to improve its properties. We still have a lot of details to work out to make this process commercially viable.