Concrete with 100% recycled mineral aggregates – A precast production case study

Adding recycled mineral aggregates to concrete mixes commonly used in building construction appears to be a promising approach to conserving natural resources. This paper focuses on the bond behavior of reinforcing steel in concrete mixes with a high ratio of recycled aggregates from crushed concrete, including those designed for use in precast production. To investigate the potential influence of the aggregate characteristics, five different aggregate sizes in 12 concrete mixes were tested, and a precast concrete mix containing 100% recycled aggregates of type 1 was designed. In addition, design bond stresses were determined based on the pull-out tests conducted. The tests revealed a tendency for the maximum absorbable bond stress to decrease in line with the increase in the recycled aggregate ratio. However, design bond strength values exceeded those specified in Eurocode 2. The decrease in design bond stress appears to be predictable both by the percentage by volume of recycled aggregates and by the bulk density of the concrete. The precast concrete mix designed with 100% recycled aggregates of type 1 reaches a compressive strength equivalent to concrete class C40/50 after 28 days and meets the requirements for exposure classes XC4 and XF3 according to its verified performance. This paper also summarizes the design recommendations on which the project-related approval was based.