Impact of RAP as recycled aggregate on durability-related parameters of structural concrete

Abstract

In view of promoting the recycling of construction and demolition waste, the re-utilization of Recycled Asphalt Pavement (RAP) as aggregate in structural concrete has been recently proposed and investigated. Although many studies are available on the physical and mechanical characterisation of concrete containing RAP, little is still known about how medium- to long-term durability performances are affected by the partial or total replacement of natural aggregates with RAP aggregate. In this experimental study, several durability-related properties were assessed, with the aim of investigating the possible use of RAP as partial or total replacement of natural aggregates for reinforced concrete applications. In particular, concretes were obtained with increasing RAP contents (from reference mixtures with natural aggregate only, to complete substitution with RAP aggregate), two different cement types (Portland-limestone and pozzolanic), and two water/cement ratios (0.45 and 0.65), representative of two exposure classes for chloride and carbonation induced corrosion. Water sorptivity through capillary suction and water absorption were investigated, together with the resistance to the penetration of carbonation, both under accelerated and natural exposure, and the resistance to the penetration of chlorides, under natural diffusion. Relationships between physical and mechanical properties, such as total open porosity and compressive strength, and durability-related properties were also investigated. Results showed that sorptivity experienced a neat decrease for increasing RAP contents, due to the hydrophobic nature of RAP aggregate, while water absorption was less affected. Resistance to the penetration of carbonation and chlorides were both more clearly affected by other mix design variables, such as w/c ratio and cement type, rather than RAP content.