Research

Using Recycled Demolition Aggregates in the Production of Structural Concrete Panels

Project Details

Abstract

This study investigates the feasibility of using recycled demolition aggregates (RA) from war-damaged structures in South Lebanon as partial or full replacements for natural aggregates in the production of reinforced concrete panels. Virgin and recycled aggregates were processed and characterized through sieve analysis and water absorption testing. The recycled aggregates exhibited significantly higher absorption values (5.95% for coarse and 7.59% for fine) compared to virgin aggregates (1.51% and 1.56%, respectively), indicating increased porosity and the presence of adhered mortar. A control concrete mix prepared with natural aggregates achieved an average compressive strength of 41.45 MPa and a split tensile strength of 3.09 MPa, validating the adopted mix design and testing procedures. An experimental mix incorporating 100% recycled coarse aggregate and 50% recycled fine aggregate was attempted using the same mix proportions. However, severe segregation and instability occurred during mixing and casting, preventing the production of viable test specimens on the first trial. This behavior is attributed to chemicals in the Recycled aggregates, which reacted with the acid-based superplasticizers. For the second mix, an naphthalene-based superplasticizer was used, which did not react with the recycled aggregates. The recycled concrete mix, on the other hand, showed lower mechanical performance, with an average compressive strength of 26.17 MPa. This reduction is mainly attributed to the higher porosity, water absorption, and weaker interfacial transition zone associated with recycled aggregates. In addition, workability issues were observed, as reflected by the low slump value, indicating the need for mix design adjustments when using recycled materials.

Regarding the structural behavior of the panels, normal concrete panels demonstrated higher load-carrying capacity, with an average ultimate load of 13.9 kN, compared to 8.967 kN for recycled concrete panels. This confirms that the use of recycled aggregates negatively affects the structural performance under bending. Furthermore, cracking patterns differed significantly: normal concrete panels exhibited X-shaped cracks typical of better stress distribution, whereas recycled panels showed single-line cracks, indicating more brittle behavior and weaker internal bonding. Despite these limitations, the results confirm that recycled demolition aggregates can still be used in structural concrete applications, provided that proper modifications are made to the mix design. These may include adjusting the water content, using suitable admixtures, or partially replacing natural aggregates rather than fully replacing them.