Graphene- and MWCNT-reinforced magnesium oxychloride composite modified by tannic acid

•MOC composites with graphene, multi-walled carbon nanotubes (MWCNT) and tannic acid.•Tannic acid helped to homogenously distribute the carbon nanoparticles.•Nano-doping and addition of tannic acid significantly improved water resistance of MOC.•Graphene and MWCNT significantly improved mechanical parameters of the composite.•Developed composite is a promising alternative for Portland cement-based materials.