Concrete made of 100% recycled materials - Feasibility study

• Use of exclusively recycled materials to replace all concrete components. • Binder composed of GGBS or fly ash, activated by slaked lime and concrete wash water. • Aggregates made of recycled concrete, bricks, sediments and glass. • Admixture composed of used cooking and engine oils . • Strength of up to 37 MPa, but low workability due to water absorption of aggregates. The main purpose of this paper is to study the feasibility of producing concrete made of 100% recycled materials, by using coal fly ash (FA) or granulated blast-furnace slag (GGBS) activated by waste water coming from concrete production and with lime residue coming from the waste of a slaked lime factory as the binder, instead of conventional Portland cement binder. Conventional aggregates were replaced by various percentages of recycled concrete, crushed brick, recycled bottle glass and sediments. Used cooking oil was incorporated as an admixture to improve the fresh properties of the concretes. Several formulations of concrete were tested in order to evaluate their fresh and hardened properties. The results show that it is feasible to formulate concretes containing only recycled materials. The binder composed of GGBS and slaked lime could lead to quite high performance in the long term, especially when used with recycled concrete aggregates. The dry concretes obtained could reach compressive strengths of up to 37 MPa at 9.5 months. Attempts to improve the workability by the use of admixture (e.g. used oil) or less absorbent aggregates (e.g. waste glass) gave limited results and still need to be developed in order to limit the loss of strength. Before any generalization of the results, the variability of the wastes used should be taken into consideration.