To make the concrete stronger and last longer under tension, companies add materials to the concrete during various stages of the process.
Nano-concrete
Molecular materials are poured into the concrete to add strength while the concrete is being mixed. Some of the nano-concrete mixtures are comprised of polyethylene or ethylene particles such as being developed by The Massachusetts Institute of Technology. Other nano-concrete, like that developed by the University of Florida, use the silicates from finely ground clay. According to MIT's "Technology Review Magazine," nano-molecules work their way into the microscopic holes found in the cement. As a concrete slab is poured, the nano-molecules inside the holes make it harder for salt and other contaminants to enter the holes and cause the concrete to break.
Post Tensioning (Rebar or Cable)
Another way to strengthen concrete is to incorporate steel into the mix. This is not done using fine particles. Instead, the concrete is poured over steel bars or cables that are woven into a mesh. The mesh is completely encapsulated into the concrete. The steel adds reinforcement to the concrete, providing extra help in handling tension. The concrete slabs made in this manner are called post tensioning slabs.
Fiber Reinforcement
Fibers applied to the concrete during the mixing stage are yet another strengthener. Steel, polypropylene and other polymers are mixed into the concrete to reinforce it after drying. The fibers help absorb the tension that leads to cracking, adding to the durability of the concrete.
Availability
Not all of these concrete mixes or their additions are available for purchase at your local hardware. Nano-concrete is not available until the product has undergone further testing. Post tensioning is a technique that has been used for quite some time, however. You can purchase steel rebar and cable materials at any large hardware store. The fiber additives are also available as well as concrete pre-mixed with fibers. You can find these with retailers who specialize in concrete.