Incinerator ash characterization – Implications for elevated temperature landfills

•Relative Heat Potential (RHP) (kJ/kg) was predicted for 16 MSWI and coal ashes.•Coal ashes were predicted to generate 15% more heat than MSWI ashes after disposal.•Ashes proved to be highly alkaline (pH > 10) which may encourage exothermic reactions.•Reactions involving Al and Fe are predicted to be primary heat-generating mechanism.•Greater Cl in MSWI vs coal ashes which may promote exothermic metal corrosion.