This chapter examines different formulations of calcium aluminate cements (CAC) exposed to high temperatures in air environment. The CAC paste samples were heated to 500, 800 and 1000?C in an open-air furnace. The high temperature favors the conversion process and it generates cracks in the material, diminishing its mechanical strength. It was observed that materials with higher alumina content have an increased number of cracks. Cements with higher ratio w/c were observed to favor this conversion process, demonstrated by the increased number of cracks. The compression tests were conducted in a universal Shimadzu Autograhp apparatus at a cross head speed of 1mm /min. Sample dimensions were 19 mm diameter and 22 mm height. Results showed good mechanical strength but poor thermal strength due to structural cracking associated to a reversion process.