<p>The demolition of old buildings to renovate them for a growing population causes environmental problems due to construction waste disposal. Meanwhile, the indiscriminate usage of natural aggregates in construction renders them irreplaceable in nature. Therefore, incorporating recycled aggregates in concrete production presents a logical and cost-effective solution to environmental issues. Six concrete mix designs in the C20 and C40 strength classes and with varying percentages of 0%, 50%, and 100% recycled aggregate replacement were used to produce cubic and cylindrical concrete specimens. The mechanical properties of recycled concrete, including compressive strength, tensile strength and modulus of elasticity, have been investigated at both early and long-term ages. In addition, to evaluate the in-situ strength of recycled concrete, cores of 46, 69, and 100mm were extracted from C20 and C40 concrete slabs, which replaced 100% recycled aggregate concrete. The core tests examined the effects of variables including diameter, length-to-diameter ratio, and drilling damage. All samples were tested at both early ages and 365 days to measure changes in behavior and performance over time. Estimating the cubic compressive strength of recycled concrete from core strength and comparing it with proposed code relationships was also examined.</p>