Future cements will require new constituents in order to become a more sustainable construction product.Therefore, the durability of the cements made with them must be checked.In this respect, coal bottom ash is proposed as a new Portland cement constituent and thus chemical durability as well as mechanical strength have been tested in mortar and concrete to evaluate its capability to be an adequate cement constituent.Coal bottom ash is tested in mortars made of mixes of coal combustion bottom and fly ashes.The results are compared to those performed in mortars made of CEM I 42.5 N (EN 197-1:2011).These bottom ash-fly ash mixes are incorporated in the common Portland cement in the needed proportions to produce CEM II/A-V,CEM II/B-V and CEM IV/A (V) cements according to the European standard EN 197-1:2011.Natural carbonation is the only durable property considered in the present work.Blended cements perform well with regard to the chloride diffusion.On the contrary, the higher amount of ashes, the deeper carbonation fronts regardless of the type of ash, bottom ash, fly ash or mixes of them.This effect could be explained because the bottom ash has a content of Fe2O3, TiO2, P2O5, SrO2 and so on, quite similar to that of the fly ash.The presence of such oxides might have a significant effect on pore solution concentration and then it is expected that they will play a significant role in the cement properties related to mortar and concrete durability.Summing up, it is possible to say that the utilization of bottom ash, in comparison to fly ash, does not modify the compressive strength, carbonation resistance and pozzolanicity characteristics of the mortars studied in the present work.