Impact of PCC Pavement Structural Response on Rolling Resistance and Vehicle Fuel Economy

Reduction in vehicle fuel consumption is one of the main benefits considered in technical and economic evaluations of road improvements considering its significance. Surface roughness, texture, and structural response are the main pavement characteristics influencing rolling resistance. This project investigates the increase in vehicle energy consumption caused by the structural response of a cement concrete pavement. The rotation and deformation of the slabs on a viscoelastic subgrade, which is represented as a damped Winkler foundation, cause the vehicle to consume additional energy to overcome the slope formed by the local deflection basin. The structural rolling resistance is calculated on sections with different mechanical characteristics at different speeds, temperature, loading conditions and subsequently converted into fuel consumption excess. The maximum deflection-induced energy consumption is about 0.1% of the total consumption for articulated trucks. Note that the effects of curling and load transfer efficiency (LTE) below 100% were not considered in this study. Considering the stress-strain history, as the energy dissipated in the hysteresis loop of the viscoelastic material, in a finite volume of pavement (Coleri et al. 2016, Pouget et al. 2012, Shakiba et al. 2016). Considering the deflection basin, in terms of the energy required for a rolling wheel to move uphill, facing a positive slope caused by the delayed deformation of the viscoelastic pavement. (Louhghalam et al. 2013, Chupin et al. 2013). All of these studies assumed the asphalt pavement to be a homogeneous continuous viscoelastic medium, which is a valid hypothesis for asphalt pavements but can’t be applied to rigid pavements, due to the discontinuities caused by the joints. The study carried out in this paper investigates the effect of the SRR on rigid pavements, namely the increase of vehicle energy consumption induced by the pavement structural response due to the deformation of subgrade materials and the rotation of the concrete slabs under passing vehicles. This study is part of a research that aims to quantify rolling resistance due only to the structure of the pavement. In parallel with the study shown in the paper, different models are being developed to evaluate the SRR on flexible pavement. The findings of these studies will finally be compared and checked versus field measurements to establish if different types of pavement (rigid or flexible) or different pavement structures could lead to a change in rolling resistance and therefore in fuel consumption. The approach used to estimate the fuel consumption excess of a vehicle caused by the SSR is in three folds: (1) Compute the concrete pavement response due to a moving vehicle of three types of vehicles (car, SUV, truck) at different speeds and positions on the slab using a finite element solution (DYNASLAB). (2) Calculate the energy dissipated in the pavement, which is equal to the energy needed by the vehicle to overcome the additional traction forces caused by the pavement’s deformation. (3) Estimate the fuel consumption excess due to such energy dissipation. 2 CONCRETE PAVEMENT RESPONSE The calculation of the response of the pavement is performed using the 2D finite element software DYNASLAB (Chatti 1992). The program can analyze pavements with one or two layers resting on a damped frequency-dependent Winkler foundation, modeled by uniformly distributed springs and dashpots. The concrete slab is modeled by rectangular medium-thick plate elements. Each node contains three degrees of freedom: a vertical translation in the s-direction and two rotations about the x and y axes, respectively. The program can also analyze multiple slabs with variable load-transfer mechanisms across cracks and joints: a bar element to represent dowel bars or a vertical Kelvin-Voigt element (spring and dashpot connected in parallel) to represent the aggregate interlock. The moving load is simulated using finite-element shape functions at successive time-dependent positions of the vehicle. In this paper, three different concrete pavements sections located in I-5 and US-50 near Sacramento were used (Figure 1). Their mechanical characteristics were backcalculated from falling weight deflectometer tests, which have been conducted during daytime and nighttime, so that the effects of daily temperature change could be accounted for. Figure 1. Pavement sections Figure 1. Pavement sections 2.1 Effects of the joints Any concrete pavement requires joints. Through the joints, the bending and shear stresses are transferred between slabs. When a slab is loaded, the adjacent slabs also deflect, and the Load transfer efficiency (LTE) is defined as