Evaluation of Recycled Concrete for Use as Aggregates in New Portland Cement Concrete Pavements

Spencer Ray Boyle

The primary objective of this research is to evaluate the suitability of incorporating recycled concrete produced from demolished concrete pavements in Washington State as an aggregate in new portland cement concrete pavements. Three variables were used to evaluate the effects of recycled concrete aggregate (RCA) in this study: the rate of replacement of a natural coarse aggregate with processed coarse RCA, the source of the RCA, and the inclusion of a 20% substitution of cement with fly ash. In total, 20 concrete batches were created and used to perform a series of tests on fresh and hardened concrete from which the performance of concretes incorporating RCA could be evaluated. Fresh concrete samples were tested for slump, air content, and density. Hardened concrete samples were tested for compressive strength, modulus of rupture, coefficient of thermal expansion, drying shrinkage, and freeze-thaw durability. Additional tests performed to evaluate the RCA as an aggregate included absorption capacity, specific gravity, Los Angeles abrasion loss, degradation value, and alkali-silica reactivity. v Fresh concretes incorporating RCA have a reduced workability. The substitution of cement with fly ash counteracts the effects of RCA and increases workability. Higher RCA substitution rates result in lower fresh concrete density. The effects of a 45% replacement of coarse natural aggregate with coarse RCA on hardened concrete properties are insignificant: compressive strength increases 0-5% with fly ash and decreases 0-5% without fly ash, modulus of rupture decreases 0-10%, coefficient of thermal expansion decreases 0-10% but remains typical of that for ordinary concrete, drying shrinkage increases 0-30% but remains typical of that for ordinary concrete, and freeze-thaw durability is relatively unaffected. RCA should be sieved and washed to remove fine materials prior to use in order to meet WSDOT degradation limits. All concrete mixtures and processed RCAs tested in this study met WSDOT requirements for use in PCCP. As a result, coarse RCA was determined to be viable for use as aggregate in new PCCP for up to a 45% replacement of coarse natural aggregate.

Evaluation of Recycled Concrete for Use as Aggregates in New Portland Cement Concrete Pavements

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