Paper sludge, an environmentally sound alternative source of MK-based cementitious materials. A review

•A complete review and update of all work related to these industrial wastes.•Influence of activation conditions on the pozzolanic properties.•Study of reaction kinetics in function of reaction time and contents of APS.•Study of technical properties of APS blended cements matrices.•Behaviour of APS blended cements on the durability. This review compiles the main scientific and technical findings on the viability of using paper sludge waste as a supplementary cementitious material in the manufacture of future eco-efficient cements. It contains a detailed analysis of the scientific (characterisation, activation conditions, pozzolanic activity, system reaction kinetics) and technical (rheology, physical and mechanical properties, and resistance to chlorides, sulphates, sea spray and CO2) properties of this type of waste when used as a supplementary cementitious material. On the grounds of the literature reviewed, paper sludge waste can be confirmed to be an environmentally sound source of recycled metakaolinite, a conclusion with significant social and economic benefits.