The Challenge of Replacing Natural Aggregate with Artificial Aggregate for Structural Concrete

In the last years the use of artificial aggregate as a partial replacement of natural aggregate to produce structural concrete is encouraged. However, the production of concrete with artificial aggregate represents a challenge since the mix design should be properly tailored to guarantee the performances both at the fresh and hardened state. In this study, two different types of artificial aggregate, the re-claimed asphalt pavement and a municipal solid waste incineration slag, were used as partial replacement of natural siliceous aggregate. Several trial mixes, with water/cement ratio ranging from 0.58 to 0.5, were cast to define the optimal mix design, that allowed to guarantee comparable properties at the fresh state (i.e. workability) and at the hardened state (i.e. compressive strength after 28 days of moist curing) of reference concretes made with natural aggregate. On the concrete mixes that satisfied these requirements, durability properties were also evaluated, as the sorptivity, the water absorption and the resistance to carbonation penetra-tion and to chloride penetration, both measured through accelerated tests. Results of the tests showed that the replacement of natural aggregate with artificial aggre-gate allowed to cast concretes characterized by a consistency class of, at least, S4 (slump > 160 mm) and a strength class of C25/30. Durability performances were comparable or even better than those of reference concretes, showing that these types of artificial aggregate are promising to lower the environmental impact of concrete industry.