A case study on the flexural behaviour of sustainable recycled lump-aggregate concrete precast beams using inclined-crossed stirrups

Recycled lump-aggregate concrete (RLAC) is produced by combining large-scale recycled lumps (RLs) with newly mixed recycled aggregate concrete, serving as a new type of construction material for effectively recycling construction and demolition waste. A new type of RLAC precast beam with inclined-crossed (I-C) stirrup was proposed in previous research, which successfully resolves the production inefficiencies arising from the challenges when applying RLAC in conventional precast beams. This study experimentally investigates its flexural behaviour, focusing on stirrup type, spacing, compressive bar diameter, and RL substitution rate, and further analyzes compressive bar buckling to develop an optimized I-C stirrup layout. The findings are as follows: (a) For the similar consumption of stirrup steel, precast beams with I-C stirrups exhibit flexural capacity and ductility equal to or slightly greater than those with traditional vertical stirrups, while the former also show smaller average crack spacing and maximum crack width; (b) Increasing stirrup spacing reduces the flexural ductility of beams with I-C stirrups, but their flexural capacity either remains unchanged (with no premature buckling of the compressive longitudinal bar) or decreases by less than 10% (with premature buckling); (c) The use of RLs within the precast part has a limited effect on the flexural capacity and ductility of the beams; (d) The proposed method for judging premature buckling of the compressive longitudinal bar is reasonable, and the maximum allowable stirrup spacing derived from it could be employed as a reference for practical.