Utilization of recycled waste concrete aggregates in structural concrete

Abstract

One of the biggest environmental problems in the majority of the world today is a generation of huge amounts of waste. Amongst various types of waste, construction and demolition (C&D) waste makes almost the half of the total industrial waste. On the other hand, consumption of natural aggregate as a largest concrete component is constantly and rapidly increasing with increasing of the production and utilization of concrete. Recycling of demolished concrete is one of the sustainable solutions for growing waste disposal crisis and depletion of natural aggregate sources. As a result of the recycling process, recycled concrete aggregate (RCA) is produced and it is used so far mostly in low-value applications such as for pavement base. But from the viewpoint of promoting resource and energy savings and environmental preservation, it is essential to study if a concrete made of recycled aggregates-recycled aggregate concrete (RAC) can be effectively used as a structural material. This chapter presents a review of traditional and advanced demolished concrete recycling technologies for RCA production. The mechanical, rheological and durability properties of RAC based on up-to-date research and on own experimental investigation are discussed from the point of the potential of its utilization in structural concrete. It is concluded that utilization of RAC for low-to-middle strength structural concrete and nonaggressive exposure conditions is technically feasible. However, for that to be fulfilled it is necessary to use quality recycled concrete coarse aggregate and to follow the specific rules for design and production of this new concrete type. The behavior of structural elements-beams made of RAC has been investigated also. Own test results and other authors test results of flexural and shear behavior of reinforced concrete beams made of RAC and NAC (natural aggregate concrete) are compared. On the basis of rather limited reported experimental evidence, it is concluded that the behavior of RAC beams made of concrete with only coarse recycled aggregate is satisfactory comparing to the behavior of NAC beams, for service and ultimate shortterm loading both. This conclusion points also to the fact that the utilization of RAC in structural concrete elements is possible from the technical point of view. Environmental benefits from recycling are investigated within specific case study which comprises a comparison of RAC and NAC production environmental impacts using LCA methodology. Results of this specific case study performed on the basis of the local Serbian LCI data show that the impacts of aggregate and cement production phases are slightly larger for RAC than for NAC. But with transport phase included, the total environmental impacts depend on the natural and recycled aggregates transport distances and on transport types. It is possible to determine the limit natural aggregate transport distances above which the environmental impacts of RAC can be equal or even lower than the impacts of NAC for each specific case study.