Feasibility of using recycled concrete aggregates to produce ultra high performance concrete: A preliminary study

This paper presents a preliminary feasibility study on the utilisation of a high quality recycled concrete aggregates (RCA) to manufacture ultra high performance concrete (UHPC), which represents a new type of cementitious material having superior workability, mechanical performance and durability properties in comparison to conventional concrete. The particle size of the RCA used in this paper ranges from 4 to 8 mm. A total of 4 mixtures are made in the test program, which include a reference mixture with natural coarse grains and 3 mixtures with RCA as coarse aggregates. Since the RCA has high water absorption, the incorporation of this material in producing concrete requires a compensation of the water demand to achieve the desired workability. In the 3 concrete mixtures with RCA, different compensation water amounts are added. Laboratory tests on the workability, compressive strength, modulus of elasticity and four point bending behaviour of the concrete mixtures are carried out. The test results indicate that it is possible to use RCA to produce UHPC despite that its incorporation results in some reductions in the mechanical properties of the concrete mixture in comparison to the reference UHPC mixture with natural coarse aggregates.