Anhydrite cellular concrete composite building elements and their method of manufacture

Method of producing composite building elements comprising a cellular central layer sandwiched between two non-cellular facing layers which comprises pouring into the bottom of a mold a first facing layer comprised of an insoluble anhydrite binder containing an anhydrite setting catalyst and capable of being set to form a non-cellular layer, pouring onto said first layer a central layer comprised of an insoluble anhydrite binder, an anhydrite setting catalyst and containing a porogenic system comprising aluminum powder and an alkaline agent which produces a gas by reaction with the aluminum powder, and pouring onto said central layer before it sets and after it has expanded a second facing layer comprised of an insoluble anhydrite binder containing an anhydrite setting catalyst and capable of being set to form a non-cellular layer, said anhydrite binders comprising at least about 15% by weight of particles having a diameter of less than about 10 .mu.m and at least about 20% by weight of particles having a diameter in excess of about 20 .mu.m and having a mean or average diameter of between about 5 and 30 .mu.m, the anhydrite likewise being characterized by a Blaine surface area between about 1000 and 8000 sq. cm./g, and permitting the layers to harden into a strong unitary composite building element.