Characterization of Concrete with Recycled Aggregates Produced from Returned Concrete

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Title: Characterization of Concrete with Recycled Aggregates Produced from Returned Concrete

Author(s): Giorgio Ferrari, Alberto Brocchi, Luca Torelli, Gilberto Artioli, Michele Secco Luca Valentini, and Maria Chiara Dalconi

Publication: Special Publication

Volume: 303

Issue:

Appears on pages(s): 147-166

Keywords: aggregates; durability; ITZ; permeability; recycling; returned concrete; sustainability

Date: 6/1/2015

Abstract:
Returned concrete is the residual amount of fresh concrete that is not placed at the job site and returns to the ready-mix plant in the truck mixer. According to local conditions, returned concrete may range from 1 to 5 per cent of the overall concrete production, representing a serious burden for the ready-mix plant. Recently, a new sustainable technology has been developed to convert returned concrete into aggregates. The aggregate product consists of size-graded material, for the most part formed by a core of coarse original aggregate with a shell consisting of a finer composite of sand and hydrated cement. The characteristics of the new aggregate depend on many factors, including the compressive strength class of the original concrete. In the present paper, the influence of the class strength of returned concrete on the performance of new concrete made with recycled aggregates produced with the new technology has been investigated. The compressive strength measurements and the permeability tests confirmed that it is possible to produce high quality concrete mixtures with recycled aggregates obtained from returned concrete by a new technology. Results indicate that in no case the properties and the nominal strength class of the concrete are downgraded by a substantial substitution (30% by weight) of recycled concrete in place of the natural coarse aggregate. Also water permeability of concrete mixtures is improved by the use of the new aggregates. These results are supported by the microstructural characterization of the material performed by electron microscopy.