Mechanical Strengths, Durability, and Corrosion Resistance of Concrete with Recycled Sand

The reuse of construction and demolition waste is undoubtedly one of the main research focuses today for reducing waste and preserving the environment within the framework of sustainable development. The objective of this work is to study the effects of varying the dosage of unbaked clinker waste sand (CWS) and recycled concrete sand (RCS), at an age of approximately 28 days, previously to produce compressed pipes, on the physical properties of the fresh and hardened states, as well as the corrosion resistance of ordinary concrete. The analysed concrete mixes contain recycled sand in percentages of (0, 5, 10, 15, and 20) %, in addition to limestone crushed sand. The tested concrete characteristics include density, workability, compressive and flexural strength, splitting tensile strength, water absorption by immersion and capillarity, and resistance to chemical attacks by 5 % CH₃COOH and 5 % NaCl. The corrosion behaviour of steel bars in 3.5 % NaCl solution is monitored using electrochemical methods, including potentiodynamic polarisation and electrochemical impedance spectroscopy. The results obtained show that the use of recycled sands leads to a reduction in concrete workability, improvement in compressive, flexural, and splitting tensile strength, and a reduction in water absorption capacity, which could be directly related to modifications in the microstructure. The electrochemical results indicate that the addition of CWS and RCS in concrete greatly affect the corrosion resistance properties of concrete. The corrosion resistance increases with increasing immersion time up to 40 days, after which it decreases, indicating a loss of protective ability.