Sizing and Assigning Construction Robots Under Skilled-Labor Scarcity: A Bi-Objective Scheduling Model with Safety-Driven Zone Exclusivity

Construction robots for repetitive trades have moved beyond demonstration, yet fleet size and task assignment are still decided by rule of thumb. This study formulates the human–robot collaborative resource-constrained project scheduling problem, which chooses execution modes, fleet size, and start times together and renders the speed-and-separation requirement as a static zone-exclusivity constraint. A heuristic, repair-augmented evolutionary method is validated against exact bi-objective fronts and two established heuristics. In computational experiments on 30 generated apartment-finishing instances of 64 to 128 activities, the minimum-cost schedule reduced cost by 3.7% relative to a human-only plan, whereas robotizing every eligible activity cost 7.8% more than using no robots at the calibrated day rate and paid off only below about 649 thousand KRW per machine-day. As skilled-labor availability fell to 40%, the cost effect of a two-machine fleet moved from −2.2% to +17.0%, and a factorial design attributed more of the variance in cost saving to labor availability than to machine productivity. Static zone exclusivity lengthened the schedule by 11.0%, an upper bound on the cost of dynamic separation. Under duration noise and downtime the schedule advantage persisted while the cost advantage narrowed. All results are model-based estimates conditional on the calibrated assumptions.