The building material fly ash brick (FAB) is made out of class C or class F fly ash and water. It's employed in the construction of masonry units. The bricks can withstand more than 100 freeze-thaw cycles after being compressed at 28 MPa (272 atm) and cured for 24 hours in a 66 °C steam bath before being toughened using an air-entrainment agent. Because of the high concentration of calcium oxide in class C fly ash, the brick is considered "self-cementing.". The process saves energy, minimizes mercury pollution in the environment, and is often 20% less expensive than traditional clay brick production.