This study explores the behavior of blended mortars of low reactive bottom ashes (BA) and ordinary Portland cement (OPC) in an alkaline solution. Mortar mixtures incorporating OPC with different replacement levels (0% to 30% mass) were studied. Isothermal conduction calorimetric analysis was studied and 28-and 60-day mechanical strength values were found. SEM images was used to identifies porosity structures at 28-day. Water absorption was also investigated. The results revealed different behaviors to low (OPC 2.5 and OPC 5) and moderated (OPC 10 and OPC 30) OPC content. Increase in percentage of Portland accelerated hydration kinetics. There is a second peak formation for moderated OPC content, associated with C-A-S-H gel formation. The partial replacement of bottom ash by OPC tend to reduce the absorption. There is a slower initial water absorption to low OPC content. This behavior is due the higher unreacted BA content, that works as a filler. Otherwise, the increase of water absorption for OPC content is due to the coexistence of Portland cement hydrates and alkali activated reactions.