The annual global production of fly ash is estimated at about 780 million tons per year and has been used successfully in the cement industry for more than 50 years, mainly as a mineral additive in Portland cement and also as a component of mixed cement. In this work, the ash reactivity from hazardous waste as supplementary cement material was evaluated. For this, the ashes reactivity in lime pastes was analyzed, centered on thermogravimetric tests as a characterization technique to determine the phases present. Part of the ashes of hazardous waste was pretreated, in order to eliminate chlorides and sulfates from the incineration process. The ashes were characterized by means of DRX and FRX, finding low content of SiO2 and Al2O3 in the ashes of hazardous residues. The pastes were prepared according to the ASTM C-305 standard, using a water/lime ratio of 0.4. The hydration process was stopped with acetone at the ages of 1, 3, 7, 14, 28 and 56 days. It can be concluded that only mixtures of untreated hazardous waste ash are more attractive to be used as replacements in the production of construction inputs.