Unlike clay, concrete hardens through a chemical process known as curing. When water (which is crystalline in nature) is added to concrete, the microscopic crystals in the cement react and begin to grow. As the crystals continue to grow, they intertwine tightly with the sand, aggregate and other crystals in a strengthening process that continues throughout the life of the concrete. In a manner of speaking, through a process that could be called "crystal fusion", you end up with a crystalline structure that can amplify or magnify the energy & intent with which it's imbued.