Influence of steel fibres and silica fume on mechanical properties and shrinkage of recycled aggregate concrete

This study investigates the performance enhancement of recycled aggregate concrete (RAC) produced with 100% recycled coarse aggregates through the incorporation of 10% silica fume, 0.5% hooked steel fibres, and their combined use. Compressive strength, flexural strength, elastic modulus, stress-strain behaviour, and shrinkage were evaluated, while shrinkage predictions were compared using Eurocode 2 (EC2), MC2020, and B4 models. The results showed that RA reduced 90-day compressive strength and elastic modulus by 24% and 33.7%, respectively, and increased 180-day shrinkage by 38.4% compared with natural aggregate concrete. Silica fume improved compressive strength and elastic modulus by 29% and 33.4%, respectively, although it increased early-age shrinkage. Steel fibres increased flexural strength by 178% and reduced shrinkage by about 20%. The combined mixture enhanced compressive strength, flexural strength, and elastic modulus by 23.8%, 201%, and 18%, respectively. Two-way ANOVA confirmed significant individual effects of silica fume and steel fibres, whereas their interaction was not statistically significant (p > 0.05). MC2020 showed the best prediction accuracy for most RAC mixtures, with RMSE values between 59.85 and 233.99 µm/m. The findings demonstrate that combining recycled aggregates, silica fume, and steel fibres improves RAC performance and supports sustainable construction practices by reducing natural resource consumption.