Summary The strength developments of hydrothermally cured blends comprised of ordinary Portland cement (OPC) and clay-brick waste (CB) and treated at 180°C under saturated steam for 6 h were studied. Two types of CB, of different chemical and mineralogical make-up, were used to make OPC-CB blends where 10 to 80 mass% CB replaced OPC. The nature of the hydration products formed after autoclaving were subsequently investigated by using a combination of DTA, DTG, TG, X-ray diffraction, and wet chemical techniques. The modes of the hydrothermal reactions between OPC and the two types of CB, as well as the nature of the main binder belonging to the tobermorite family, are discussed and related to the development of the strength of the autoclaved articles.