Flexural Behaviour of Lightweight Concrete Beams Incorporating Expanded Clay Aggregates, Alccofine, and Hybrid Fibres – An Experimental Study

Lightweight concrete offers significant structural benefits due to its low self-weight, but replacing natural aggregates with expanded clay aggregates typically reduces mechanical strength. This experimental study investigates the structural properties of reinforced lightweight concrete beams. Beams of size 150mm × 250mm × 3200mm were used to study the flexural behaviour. Beams were designed as singly reinforced beams with 2 numbers of 12mm diameter bars in the tension zone and 2 numbers of 10mm diameter bars at compression zone with 2 legged 8mm diameter bars at 150mm center-to-center. Overall 9 beams were cast according to mix proportions. Beam specimens were tested under four-point bending. The modified concrete incorporates 20% expanded clay aggregates, 15% Alccofine for matrix densification and 0.3% volume fraction of hybrid polypropylene and glass fibres for crack bridging. Static load testing on the beam specimens revealed that incorporating the hybrid fibres significantly improved the ultimate load capacity, deformation capacity, deflection ductility and energy ductility. The ECAH-5 beam showed an increase of 37.87% in ultimate load, a reduction of 75% in maximum deflection, and an increase of 27.05% and 22.88% in deflection ductility and energy ductility, respectively. The maximum reduction in crack width was 152.93%. Ultimately, the combined effect of Alccofine and hybrid fibres shifted the concrete's failure mode from a sudden, brittle failure to a ductile failure, characterized by better control over fine, welldistributed micro-cracking. The ECAH-5 beam exhibited a highly ductile, gradual failure pattern with better crack containment compared with other beams.