Rheological behaviour of concrete made with fine recycled concrete aggregates – Influence of the superplasticizer

• The use of FRCA significantly increased the shrinkage and creep deformation.
• The FRCA’s effect on rheological behaviour is influenced by the curing age.
• Superplasticizers increase early-age shrinkage but decrease it in the long-term.
• High-performance superplasticizer decreases creep deformation.
• The incorporation of FRCA partially hindered the effectiveness of the superplasticizers.

This paper evaluates the influence of two superplasticizers (SP) on the rheological behaviour of concrete made with fine recycled concrete aggregates (FRCA). Three families of concrete were tested: family C0 made without SP, family C1 made with a regular superplasticizer and family C2 made with a high-performance superplasticizer. Five replacement ratios of natural sand by FRCA were tested: 0%, 10%, 30%, 50% and 100%. The coarse aggregates were natural gravels. Three criteria were established to design the concrete mixes’ composition: keep the same particle size distribution curves, adjust the water/cement ratio to obtain a similar slump and no pre-saturation of the FRCA. All mixes had the same cement and SP content. The results show that the incorporation of FRCA significantly increased the shrinkage and creep deformation. The FRCA’s effect was influenced by the curing age. The reference concrete made with natural sand stabilizes the creep deformation faster than the mixes made with FRCA. The incorporation of superplasticizer increased the shrinkage at early ages and decreased the shrinkage at 91 days of age. The regular superplasticizer did not improve the creep deformation while the high-performance superplasticizer highly improved this property. The incorporation of FRCA jeopardized the SP’s effectiveness. This study demonstrated that to use FRCA and superplasticizer for concrete production it is necessary to take into account the different rheological behaviour of these mixes.