A Single Depot Concrete Delivery with Time Windows Model Using Integer and Assignment Variables

We address the logistics and planning problem of delivering Ready Mixed Concrete (RMC) to a set of demand customers from a single depot while respecting time-windows induced restrictions. The RMC Dispatching Problem (RMCDP) is closely related to the Vehicle Routing Problem (VRP) with the difference that demand nodes in the RMCDP may be visited more than once by a truck. This class of routing and scheduling problems can be represented using Mixed-Integer Programming (MIP), however the joint decisions involved often lead to hard-tosolve formulations, due to either the number of variables required or the number of constraints imposed in the models. In this work, we propose a novel formulation for the single-depot RMCDP that attempts to integrate time windows restrictions by assigning vehicles to feasible delivery slots and uses integer variables to represent repeated trips between depot and customer nodes. We show that the proposed formulation is able to provide promising computational results on a realistic dataset representative of an active RMCDP in the region of Adelaide, Australia.