Interfacial Bonding in Concrete: Effects of Natural, Recycled, and Agricultural Aggregates

The depletion and rising costs of natural aggregates have intensified the search for sustainable alternatives in concrete production. Recycled concrete aggregate (RCA) and lightweight agricultural wastes such as palm kernel shell (PKS) and coconut shell (CS) offer potential for reducing environmental impact and construction waste. This study investigates the flexural and splitting tensile performance of concretes incorporating RCA, PKS, and CS, bonded with either mortar or chemical adhesive (Aqualatex C10). Experimental tests on cylindrical and rectangular specimens were conducted, complemented by numerical simulations using Abaqus CAE with Concrete Damage Plasticity models to capture interfacial transition zone (ITZ) behavior. Results show that experimental strengths consistently exceeded numerical predictions. For RCA, mortar and Aqualatex-bonded, experimental flexural strengths reached 6.73 MPa and 5.25 MPa, compared to 3.00 MPa and 2.10 MPa obtained numerically, respectively. CS concretes recorded 4.66 MPa (mortar) and 4.21 MPa (Aqualatex) versus 3.50 MPa and 2.00 MPa, while PKS concretes achieved 6.55 MPa (mortar) and 5.98 MPa (Aqualatex) against 3.30 MPa and 1.80 MPa numerically. Splitting tensile strengths followed similar trends. The discrepancies highlight the influence of curing conditions, aggregate variability, and pore refinement on ITZ behavior, factors not fully captured by numerical models. Overall, both mortar and Aqualatex C10 exhibited superior real-world performance, emphasizing the need for experimental validation when assessing sustainable concretes. These findings enhance understanding of ITZ behavior in alternative aggregate systems and provide guidance for improving predictive modeling of composite concrete performance.