L. Quaresma

Production of Hot-Mix Asphalt with PMB: Compactability and Mechanical Behaviour Characterization

The traditional approach used to select production (mixing and compaction) temperatures for hot-mix asphalts (HMA) with polymer modified bitumens (PMB) often lead to extremely high temperatures, which increase energy consumption and may cause bitumen-polymer bond degradation. Moreover, field experience indicates that lower temperatures can be used without compromising aggregate coating with bitumen and on-site compaction. This paper presents a lab study aiming to assess the influence of production temperatures in the on-site paving operations and the in-service performance of asphalt pavements. An AC 14 Surf PMB 45/80-65 (EN 13108-1) was produced and compacted at three different mixing-compaction temperatures groups, based on the suppliers’ recommendation and the temperatures determined with the traditional (Superpave) and the high-shear rate viscosity (HSRV-E) methods. The results showed an important effect of the production temperatures in the asphalt behaviour. Minimum compaction resistance value was obtained with the Superpave temperatures while HSRV-E produced the highest resistance. The water sensitivity test values and the rutting resistance values were very similar for the three temperatures groups. Independently of the test frequency, the stiffness modulus was always higher for the HMA produced at the suppliers’ recommended temperatures. The resistance to fatigue is very similar for the Superpave and HSRV-E temperatures, and higher than with the suppliers’ recommended temperatures. Fatigue resistance was not affected by the use of a higher mixing temperature, recommended by the Superpave method. The best performance was not obtained with any single temperatures group tested and the results show that both mixing and compaction temperatures are very important for the HMA behaviour.

Evaluation of Different Methods for the Estimation of the Bitumen Fatigue Life with DSR Testing

Asphalt fatigue cracking is one of the phenomena that contribute most to degradation of road pavements and it may initiate within the bitumen or at the bitumen-aggregate interface. The cohesive cracking resistance can be evaluated with bitumen testing. Commonly, the Dynamic Shear Rheometer (DSR) is used for bitumen testing. This paper presents an evaluation of different methods proposed in literature for the estimation of the bitumen fatigue life. A neat and a polymer modified bitumen (PMB) were tested with time sweep tests (continuous and discontinuous loading) and with incremental load amplitude (linear amplitude sweep test). The results are analysed with the traditional approach (Nf,50 corresponding to 50 % initial modulus reduction) and other methodologies, namely the Ratio of Dissipated Energy Change (RDEC) and the Viscoelastic Continuum Damage (VECD) approach. The results obtained showed, as expected, that the PMB has a higher resistance to fatigue than the neat bitumen. The test conditions and the method used to evaluate the fatigue resistance lead to significant differences in the estimated bitumen fatigue life. The plateau value (RDEC) shows very good correlation with Nf,50 obtained from constant strain amplitude tests, regardless of the type of bitumen or test conditions. The fatigue life parameters obtained from the linear amplitude sweep test is very sensitive to the analysis method. Healing during non-loading periods has a large effect on the PMB fatigue life while no effect in the neat bitumen fatigue life for small to intermediate rest periods.

Comparative Analysis of Interlayer Bonding Behaviour of Different Types of Pavement Interfaces

The rehabilitation of flexible pavements aims the recovery of its characteristics and is usually accomplished either by the application of additional bituminous mixtures (reinforcement), or by removing the layers whose function is compromised and subsequent placement of new bituminous layers, seeking to increase load capacity, serviceability and extend its life cycle. The bonding between the applied layers is one of the key aspects in pavements performance, reflecting the capability of pavements to work as a whole. A comparative study of the behaviour of the interface between the bituminous top layer and an underlying layer by applying different reinforcement elements has been developed. In order to evaluate the interface bonding behaviour for national conditions, namely in what concerns the type of actions, applied materials and construction techniques, a laboratory study was made with destructive tests such us pull-of test and shear type test allowing the proposition of reference values.

Maintenance and Rehabilitation Programming of the Portuguese Road Network: Development of a Cracking Prediction Model

This paper describes the development of a cracking prediction model for Portuguese conditions which is expected to integrate the Pavement Management System (PMS) of Estradas de Portugal. The World Banks highway development and management (versions III and 4) and PARIS models are used as reference for the development of a deterministic (mechanistic-empirical) model, using pavement condition data from sections of the main road network. A two-phase distress evolution model is proposed where the initiation of cracking (1st phase) is ruled by a different equation than the progression of cracking (2nd phase). Cracking initiation is predicted on a traffic basis, from the annual traffic load and the structural capacity of the pavement. An absolute model is presented and recommended for the maintenance and rehabilitation (M&R) programming in the long-term and for the analysis of non-cracked segments. Absolute and relative type models were obtained for cracking progression. The relative model shows better agreement to data and is proposed for short- to medium-term analysis on segments with cracking history, while the absolute model is proposed for the M&R programming in the long-term and the analysis of non-cracked segments. Finally, the recommended model is evaluated based on the application to a set of pavement structures defined in the Portuguese pavement design guide.