So this is my idea: make concrete using iron sand, preferably one with a decent ferromagnetic interaction. As the concrete sets, apply a magnetic field. The ferromagnetic particles align to the field creating a structure within the concrete. Possible to coat the iron sand in a retarding agent, like sugar, to slow the development of bonds which has an effect of improving strength. Hopefully this will produce a concrete that is still cheap with good tension performance, particular in bending.