Rui Micaelo

Asphalt Compaction Study

ABSTRACT Asphalt mixtures compaction is considered to be one of the most important factors that influence bituminous layers durability. However, it is still not clear how compaction should be carried out. In this paper a numerical tool, based on the Distinct Element Method (DEM), is developed and applied to asphalt compaction studies. Asphalt mixtures were modelled in 2D as an assemblage of circular rigid particles that interact with each other at soft contact points. The methodology was applied to three asphalt mixtures with different compactabilities: Asphalt Concrete 0/16 and 0/5, and Porous Asphalt 0/8. It is shown a good agreement between the static compaction laboratory tests results and the results obtained with the proposed numerical model. Despite the 2D limitations, the obtained results clearly indicate the viability of the proposed numerical tool.

Cracking Models for Use in Pavement Maintenance Management

With the recent approval of the Portuguese Law No. 110/2009 of 18 May, within the scope of road concession contracts, the concessionaires need to submit to the Portuguese Road Infrastructures Institute a Quality Control Plan (QCP) and a Maintenance and Operation Manual (MOM). These documents require the revision of current Pavement Management Systems to consider pavement performance prediction models for each pavement state parameter so that it permits time definition of maintenance and rehabilitation (M&R) interventions for the fulfilment of the values defined in the QCP in each year of the concession period. The QCP presents the admissible values for each pavement state parameter (cracking, rutting, roughness, etc.) that a concessionaire of highways needs to verify.

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.

Discussion of “Viscoelastic-Plastic Model of Asphalt-Roller Interaction” by Fares Beainy, Sesh Commuri, Musharaf Zaman, and Imran Syed

This paper presented an attempt to model an asphalt-roller interaction using Burger’s model, namely, the roller dynamic behavior and asphalt layer compaction evolution. Although the work of the authors is valuable and desired for better asphalt compaction understanding and the development/improvement of current intelligent compaction systems, there are some inconsistencies in the adopted methodology and a lack of information in the published paper. 1. First, the authors state that intelligent compaction techniques derive from the hypothesis that the roller vibrations and layer stiffness are related. Although the statement is not false, the view is rather limited. The concept of intelligent compaction includes on-time information about compaction and the variation of roller operation conditions as a function of the layer characteristics, which change along the compaction process, aiming for faster and/or better compaction (Briaud and Seo 2003; Intelligent Compaction 2013).Minchin et al. (2008) present a literature review of techniques developed for intelligent compaction and not all techniques are based on roller vibrations. 2. Regarding the methodology adopted in the study, the first issue is the spatial representation of the problem. The authors affirm that it is two-dimensional, although the numerical calculus only considers stresses and strains in the vertical direction and does not take into account the effect of the longitudinal and lateral flow of the asphalt mixture and the confinement effect at the edges. Only the variation of the roller (vertical) actionwith the roller longitudinal position for the single point of pavement that is being modeled is represented. Asphaltmix layer compaction is obtained via rearrangement of the mineral structure, with air voids being driven out, which results from both normal and shear stresses (Chadbourn et al. 1998; Dynapac Compaction Equipment 2007; ter Huerne 2004). Fig. 1 illustrates, conceptually, the deformation of finite plane elements in front of, under, and behind the roller drum (Micaelo 2009). 3. The key issue for the simulation of roller compaction is the mechanical model adopted for the asphalt mix: Burger’s model. The authors state that it is simple and often adopted to model the mechanical behavior of asphalt mixtures in pavements under traffic loads at the in-service temperature range and not to the roller-asphalt interactionmodeling.During roller compaction, the aggregate matrix changes toward a stable, deformation-resistant, aggregate packing, which most important mechanical properties rely on. In general, the compaction degree (design density) increases from 80–85% to 97–99% or air voids reduce from 18–22% to 6–4%. The major part of the deformation is almost instantaneous, with the nonrecoverable part being the most important during first passes, which makes problematic the use of the Burger’s model, or the assumption of permanent deformation solely on the dashpot in series (time-dependent permanent deformation) (Masad et al. 2010; Micaelo 2009). There are alternatives that may give appropriate results: (1) inclusion of a slider in the rheological model (Kim 2009); (2) use of amodel based on the critical state theory as implemented by ter Huerne (2004); and (3) use of a micromechanical model that can reproduce particle structure evolution during compaction (Chen 2011; Micaelo 2009). For layer-drum contact in the normal direction (only compression), the Kelvin model (spring and dashpot in parallel) has been used by several researchers, mainly with unbounded materials (Adam 1999; Anderegg and Kaufmann 2004; ter Huerne 2004; Yoo and Selig 1979). In the longitudinal direction, there is a stick-slip phenomenon due to high shear stresses, which may be modeled with the Coulomb friction law (ter Huerne 2004). 4. Regarding the input values for the simulation, it is noted that Burger’s parameters were estimated from complex modulus valuesmeasured according to theAASHTOTP-62 (AASHTO 2007) standard procedure at different experimental conditions (temperature, frequency, and air voids). This information is insufficient for correct analysis of the described study, and Beainy et al. (2012) do not give additional information about the laboratory test conditions. 5. The contact area of the drum-asphalt interaction is assumed to be constant for all passes and equal to 1:63 1023 m2. For the drum width (2 m) (Table 1 of the paper), the contact length is 83 1023 m. This value is too low to be realistic. For a simple calculation, the asphalt-drum static interaction presented in Fig. 2 is considered, in which the contact length can be determinedwith Eq. (1). In Fig. 5 of the paper, it is concluded that with the first drum pass, there is a 0.3% air voids decrease. The same layer thickness reduction corresponds to 2:23 1024 m (76:23 1023 m layer thickness). For a 1.400-m drum diameter, and considering that the thickness reduction is equal to full vertical displacement (not considering the recoverable deformation), the contact length is 35:13 1023 m. To sum up, the drum-layer contact length varies (reduction with roller passes) as a function of the bearing capacity, which increases due to a temperature drop and the compaction degree increase, and the value adopted in the study is considered unsatisfactory

Cyclic Loading Behaviour of Double Strap Bonded Joints with CFRP and Aluminium

The adhesively bonded joints behaviour under cyclic loading is not yet well understood due to its inherent complexity. Numerical approaches appear, therefore, as the easiest way to simulate such mechanical behaviour. In this work, double strap bonded joints with Carbon Fibres Reinforced Polymers (CFRP) and aluminium are numerically simulated and subjected to a cyclic loading history. In the numerical simulation, the Distinct Element Method (DEM) is used and it is assumed cohesive bi-linear bond-slip models with local damage of the interface. The evaluation of the bonded joints under cyclic loading is made by comparing the results with those simulated with a monotonic loading.

A Different Perspective on the Production and Application of Warm Mix Asphalt Under Unfavorable Temperature Conditions

Warm mix asphalt (WMA) is produced by a variety of technologies at lower temperatures that enable to gain important environmental and social benefits and, in consequence, to contribute to a more sustainable transportation infrastructure. The producer usually defines the temperatures used in WMA production. However, some references suggest the increase of temperature in order to allow a longer time to transport or to compact in cases of unfavourable weather conditions, mainly under low temperatures. The objective of this paper is to analyse the feasibility of producing WMA at the same temperatures of hot mix asphalt (HMA) guaranteeing an adequate compaction, and final performance in service. The paper describes a laboratory study to investigate the properties of a WMA using different additives and varying the mixing and compaction temperatures. The effect of production temperatures on the performance of the WMA was evaluated through binder drainage (production phase), volumetric properties (compaction phase), and resistance to permanent deformation (service phase). The paper also presents a numerical study on the time available for paving WMA under unfavourable climatic conditions. Results demonstrated that it is possible to produce WMA at high temperatures without problems of binder drainage, during transport, and of performance in service if adequate compaction is achieved. In fact, the production temperatures influenced the compaction phase. However, it is possible to increase the temperature without negatively affecting the required volumetric properties. The rut depth of the permanent deformation test was mostly influenced by the air-voids of the compacted WMA and the binder. From the numerical study, it was concluded that the time available for in situ compaction increased substantially when WMA was paved at higher temperature. However, in cases of low air temperature and thin layer, the increase of temperature may not be sufficient to obtain the desired level of density or air-voids.

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.