دراسة تأثير استخدام مخلفات الخرسانة كبديل جزئي للركام الخشن

This study aims to evaluate the possibility of using recycled concrete demolition waste as coarse aggregate for the partial replacement of natural aggregate in concrete mixes. The waste was collected from a demolished building in Al- Qubbah city and crushed to a suitable size. Three concrete mixes were made with 25%, 50%, and 75% replacement levels, along with a reference mix without any replacement. Nine standard concrete cubes (150×150×150 mm) were prepared for each mix and tested for compressive strength, density, and water absorption at 7 and 28 days, then compared to the reference mix. The results showed that water absorption increased gradually with higher replacement levels, likely due to the porous nature of the recycled aggregate and the old mortar attached to it. The overall concrete density decreased as more recycled aggregate was used. Compressive strength at 28 days was highest in the reference mix (22.67 MPa), while the mixes with recycled aggregate recorded ( 20.00, 19.11, and 18.22 MPa ) for ( 25%, 50%, and 75% ) replacement, respectively. Despite the slight drop in compressive strength, all values remained within acceptable limits. These findings show that recycled coarse aggregate can be used successfully to produce concrete with good structural performance, while also providing environmental benefits and supporting sustainability. Keywords: Recycled aggregate, Compressive strength, Water absorption, Density, Sustainability of construction materials.