Effects of PCI Trigger Thresholds on Construction Carbon Emissions and Pavement Performance in Hot In-Place Recycling of Xinjiang Expressways

This deterministic scenario study examines how PCI trigger thresholds influence treatment timing, pavement condition, and cumulative construction-stage greenhouse-gas emissions for 4 cm hot in-place recycling within a boundary covering material production, transport, mixing, and on-site construction. Using project-derived deterioration parameters for nine Xinjiang expressway sections, annual simulations compared 4 cm hot in-place recycling rules over a 15-year horizon. Thirty-three rules combined pavement condition index (PCI) thresholds of 70–80 with assumed treatment gains of 5, 10 or 15 points. Each rule was evaluated under baseline parameters and twelve one-at-a-time perturbations of ±5% and ±10%. Feasibility required every section to maintain a pre-treatment PCI of at least 70 throughout the horizon. Thirteen rules were feasible at baseline, and eleven remained feasible in all 13 parameter scenarios. The selected thresholds were 76 at a 10-point gain and 75 at a 15-point gain, with baseline mean cumulative construction emissions of 11.8677 and 8.4770 kgCO2em−2, respectively. At a 15-point gain, threshold 74 passed the ±10% endpoint checks but failed when α decreased by 5%. Raising the PCI floor to 71 changed the selected thresholds to 77 and 76 for the two gain scenarios. The methodological contribution is an exhaustive integer-threshold scan coupled with section-wise feasibility screening across both endpoint and intermediate deterministic perturbations. The resulting thresholds are case-specific scenario outcomes, not probabilistic reliability estimates or whole-life carbon savings, and remain conditional on the adopted deterioration parameters, treatment gains, system boundary, and tested scenarios.