Embodied carbon determination in the transportation stage of prefabricated constructions: A micro-level model using the bin-packing algorithm and modal analysis model

The prefabricated construction generates considerable embodied carbon emissions during the manufacture, transportation, and construction stages. However, the contribution from the transportation stage is usually overlooked, leading to biases in life-cycle sustainability analysis of these projects. This article provides a micro-level transportation CE calculation method that estimates the project-specific emissions according to the features of prefabricated elements. The method simulates the transportation status of prefabricated elements as bin packing (BP) problems. Then, a modal analysis model is employed to calculate the CE of each vehicle based on vehicle type, road condition, and freight weight. Considering the minimum transportation CE as objective, a genetic algorithm is then used to search for the optimal solution and corresponding CE values. The comparative results among different CE calculation methods show that this BP-algorithm-based method provides reliable data across different loading rates, rendering the method suitable for calculating the transportation CE of prefabricated construction projects. Additionally, the BP-algorithm-based method differs the emission characteristics among different element types—the prefabricated floor generates the highest emissions, followed by prefabricated beam, wall, and column—suggesting the need to identify disparate emission factors for different element types and considering the sustainability aspects when selecting prefabricated approaches of projects. The results also highlight the efficiency of considering more prefabricated elements in a single transportation batch and selecting suitable vehicles for the optimisation of embodied carbon emissions. Architects, engineers, and contractors can use the method for project-specific transportation CE calculations and transportation planning. The calculation variables concerning the geometric features of prefabricated elements and vehicles can be adopted in the optimisation of project design and construction management for achieving less embodied carbon.