What is High Alumina Cement (HAC)?
It is a special cement which develops its strength very rapidly and has high chemical resistance. It can also be used for refractory concretes, e.g. in steelworks, using the white version. It suffers from a phenomenon known as “inversion”, in which if it gets hot and wet it disintegrates. There were a number of 1960s high-rises which had autoclaved HAC panels and started shedding them in the 1980s. I do not believe that anyone was killed, but a hundredweight panel falling 20 stories was obviously very dangerous. It is also useful in cold regions as it can be laid in sub-zero temperatures. Lafarge, a French company are the principal manufacturer of HAC.
