Design considerations of high RAP-content asphalt produced at reduced temperatures

In many countries recycling of reclaimed asphalt pavement (RAP) for road surface layers is limited to a maximum of 10–30%. This is due to technical limitation of common asphalt plant but also to specifications that are still restrictive when it comes to increasing RAP in surface courses. The mistrust in this practice is mainly related to uncertainty in performance of these mixes as well as to existing fundamental issues with the mix design, especially when production temperatures are lowered. This paper analyses some of the factors affecting the design of warm asphalt mixtures for surface course layers containing 50% RAP, and suggests a framework to justify the common assumption of full blending by optimising production conditions. A control hot mix asphalt which was manufactured with 49 dmm penetration binder and asphalt mixtures containing 50% RAP produced at temperatures between 95 and 135 °C and at different mixing times were investigated in terms of volumetric properties, indirect tensile stiffness modulus, and indirect tensile strength. The high-content RAP mixtures were produced within the warm mix region by using only a very soft binder as a rejuvenator, which reduces production costs. Statistical analysis was deployed, and different models were developed to estimate degree of blending between RAP binder and rejuvenator binder, and to predict the equivalent penetration of the blend without binder extraction and recovery. The analysis results showed that the selected performance indicators correlate significantly with mixing time and temperature, and provide evidence that only in certain circumstances and if the production conditions are accurately controlled, the practical full blending approach is acceptable

Combined Discrete-Continuum Analysis for Ballasted Rail Tracks

A study on the load-deformation behaviour of railway ballast aggregates subjected to cyclic loadings using a combined discrete-continuum modelling approach is presented. Discrete ballast particles are simulated in the DEM and the continuum-based subgrade is simulated by the FDM. Interface elements are generated to transmit contact forces and displacements between the two domains (i.e. discrete and continuum) whereby the DEM exchanges contact forces to the FDM, and then the FDM transfers the displacement back to the DEM. Distributions of contact forces, coordination number, stress contours on the subgrade and corresponding number of broken bonds (representing ballast breakage) are analysed

Life-cycle economic and environmental assessment of warm stone mastic asphalt

202310 bcchAccepted ManuscriptSelf-fundedPublishe

Three dimensional finite element model for active crack control in continuously reinforced concrete pavement

Crack patterns in continuously reinforced concrete pavements (CRCPs) traditionally have been controlled by continuous longitudinal reinforcement steel. This passive crack control has resulted in the formation of an unfavorable crack pattern with a high probability of clusters of closely spaced cracks, which has eventually led to premature distresses such as spalling and punch-out in the later age of CRCP. In an effort to eliminate the cluster cracking and crack meandering, the standard design concept for CRCP in Belgium underwent several changes over time, mainly addressing the longitudinal reinforcement rate, depth of the reinforcement steel, and thickness of the concrete slab. In the current design concept, the active crack control method in the form of partial surface saw-cuts on side of the concrete slab perpendicular to the axis of the road within 16–24 h after the placement of concrete is being employed to facilitate the formation of a regular spaced crack pattern in CRCP. However, this area needs further investigation and validation. The present study investigates the early-age crack pattern induced by active crack control method under typical Belgian conditions. Therefore, a 3D finite element model of CRCP with induced partial surface saw-cuts is developed using FE tool Diana 10.2. Findings show that active crack control method exhibits the cracking sooner than passive crack control method. Moreover, a more controlled and regular spaced crack pattern is produced

Prediction of Extra Confinement Offered by Cellular Inclusion Under Three-Dimensional Stress State

The granular substructure layers in a ballasted railway track often undergo a large amount of lateral deformation due to insufficient confinement. This deformation results in a loss of track geometry and demands expensive maintenance work to ensure passenger safety and comfort. The cellular inclusions such as scrap tires and geocells can provide confinement to the granular substructure layers and increase their strength and stiffness. It is inevitable to evaluate the magnitude of improvement in strength and stiffness provided by these inclusions before their in-situ application. This article presents a mathematical model to determine the magnitude of extra confining pressure offered by the inclusions under the three-dimensional stress state. The model is validated by comparison with the results of experimental investigations on the cellular inclusion reinforced soils. The parametric study of the variables affecting the performance of cellular inclusions reveals that the magnitude of additional confinement significantly depends on the stress state, inclusion and infill soil properties. The present model can be employed for the selection of optimum material parameters for achieving the desired magnitude of confinement from the cellular inclusions