Evaluating Time-Cost-Carbon Emission Trade-Offs in Construction: A Study of Onsite Optimization and Offsite Prefabrication Methods

Abstract

This research investigates strategies to accelerate construction projects while balancing cost and environmental considerations, using a single-family house construction project in Edmonton, Canada, as a case study. Two strategies are examined: onsite trade-off optimization and offsite prefabrication. The first strategy employs a Non-dominated Sorting Genetic Algorithm (NSGA-II) to optimize the time, cost, and carbon emissions of a stick-built construction process. By inputting data on activities, costs, and carbon emissions at normal and crash levels, the model generates optimal trade-off solutions through iterative selection, crossover, and mutation, offering a range of shortened project durations based on budget and sustainability goals. The second strategy focuses on scheduling the offsite construction process, where portions of the project are prefabricated in a factory and installed onsite. This method enhances schedule predictability and reduces build time, resulting in an 18% reduction in project duration, a 24.89% decrease in costs, and a 31.67% reduction in carbon emissions. Combining these strategies can significantly improve project efficiency in terms of time, cost, and environmental impact, even under construction uncertainties. These findings highlight the potential for improved construction project management through innovative optimization and prefabrication techniques.