Limiting the maximum fine and coarse recycled aggregates - Type B used in structural concrete

Abstract

The use of mixed recycled aggregate (MRA) is increasingly being adopted as a sustainable solution to the environmental impact of concrete production. This study investigates the suitability of using varying proportions of fine MRA (FMRA) and coarse MRA (CMRA) classified as type B MRA (MRA with a maximum of 30 % masonry waste) to produce structural concrete suitable for exposure to XC1 to XC4 environments. Two experimental phases were conducted. In Phase 1, an effective water-to-cement ratio of 0.48 was employed, along with up to 100 % CMRA and up to 25 % FMRA, to produce concrete. In Phase 2, the effective water-to-cement ratio was 0.52, with up to 50 % CMRA and up to 15 % FMRA used in concrete production. In the two phases, 300 kg of CEM IIAL 42.5 R cement was used, and the physical properties (density, absorption and accessible porosity), mechanical properties (compressive strength, splitting tensile strength and modulus of elasticity), shrinkage properties and durability properties (sorptivity and water penetration) were assessed. In addition, the criteria stipulated in Eurocode 2 and in the Spanish structural concrete code (SC-BOE) were used to validate the structural MRA concrete produced. The results indicate that the simultaneous combination of up to 40 % CMRA and 15 % FMRA in Phase 1 achieves compressive strength and durability properties similar to those of conventional concrete produced with an effective w/c ratio of 0.52. However, to guarantee mechanical performance of concrete produced with 30 % CMRA and 10 % FMRA satisfies all the specification requirements.