Properties of structural concrete with high-strength cement mixes containing waste paper sludge ash

This paper studies the use of wastepaper sludge ash (WPSA) for structural concrete in binary and ternary mixes with high-strength cement and two industrial by-products, ground granulated blast-furnace slag (GGBS) and pulverised fuel ash (PFA). The potential use of WPSA in this type of concrete and its combination with other supplementary cementitious materials has not been established; thus, further research is needed prior to industrial-scale applications. A series of tests investigated the soundness and setting times of the resulting cements, the fresh concrete workability, cube compressive strength at various curing times, tensile splitting strength, flexural strength, static modulus of elasticity, water absorption and carbonation of the resulting concrete. Good binary WPSA mixes were achieved with high early strength gains, but workability reduced; binary mixes with 15% WPSA, were overall the best in terms of strength and durability, whilst maintaining pumpability. An improvement in the carbonation resistance of ternary GGBS and PFA mixes was also indicated upon addition of WPSA although their strengths were lower than those of binary WPSA mixes. Further mix optimisation can lead to other robust and durable high-strength cement systems with WPSA, allowing for higher cement replacements in structural concrete, for improved environmental impact.