Recent Developments in Pavement Design, Modeling and Performance

The concept of ultra-thin seals for pavement was initially a preventive maintenance strategy for deteriorating pavement structure. However, it has currently been considered as an alternative for upgrading unsealed low-volume road to sealed road. Considering ultra-thin seal surfacing in low-volume roads will make these roads to be maintenance cost effective, improve ride quality, reduce noise generated, prevent water ingression to underlying layer, and reduce dust generation and loss of aggregate. Nevertheless, the question remains which pavement surfacing option will give a substantial improvement in terms of bearing capacity and economy. Therefore, this paper examines the performance of sealed low-volume roads using asphalt and concrete. Consequently, a finite element (FE) model was developed in general-purpose FE software Abaqus to simulate the pavement layers under a static loading condition and benchmarked with multi-layered elastic software WinJulea and mePADS. In this study two scenarios of low-volume roads were modelled by varying the thickness of the surfacing layer over the conventional granular base and stabilized base layer. Comparative results of the two surfacing options were measured through the horizontal strains underneath the surface layer, vertical strains on the subgrade layer and the increase in pavement bearing capacities. Thus, this study evaluates and suggests the most viable ultra-thin surfacing option between asphalt and concrete for low volume roads.

The search for new oil and gas deposits worldwide has increased due to the high demand for energy sources needed by industrial development and population growth. Although the industry has developed many processes and technologies to minimize waste generation and to dispose them safely and economically, a significant volume of solid waste from oil and gas drilling is expected in the future. For that reason, it is necessary to study some waste reuse alternatives.

In this work, the potential use of ashes derived from oil drilling cuts (ODC), applied to tertiary roads construction for remote areas in Colombia, is evaluated. To that purpose, ashes exposed to mechanical heat treatment are used as an improvement agent for lateritic clayey soils of low plasticity, predominant in the eastern region of Colombia (extended to Brasil and Venezuela). This region was selected due to its complexity: it has limited resources and large difficulties to obtain suitable materials for road construction, it is exposed to extreme cycles of drought and flood with an 8-month rainy season, and this is one of the areas to be recovered after peace agreements in the country with the guerrilla.

In the experimental plan, basic characterization tests were conducted to the soil, the ash, and mixtures soil-ash, as well as strength and durability evaluation of compacted and cured samples of stabilized soil at 0, 7 and 14 days, considering typical climate conditions of temperature and humidity in the region. Based on successful previous experiences, combination with other nonconventional soil stabilizers, such as salts and waterproofing materials, are also been considered to improve some properties of ash cuttings - soil mixtures. As a result, an economical and viable option is obtained to reduce environmental impacts of wastes and to improve lateritic soils of low mechanical characteristics for road earthworks.

Pavement friction is one of the most important operational requirements to ensure road safety. Adequate pavement friction is a fundamental requirement to perform safe driving, steering, and braking because it affects the interface between the tires of a vehicle and the pavement surface. Pavement friction is determined through a combination of two surface textures, microtexture and macrotexture. In Ontario, Canada, the provincial transportation agency is responsible for monitoring and maintaining adequate pavement friction; however, incorporating friction into the pavement management is still challenging because there is not a specific device that can measure both textures simultaneously at a high speed. This paper provides regression models that can be used to estimate skid resistance for rural roads based on field measurements of macrotexture, type of surface coarseness, aggregate properties, and operational condition of the roads. The models can be used by researchers and practitioners to predict skid resistance for asphalt pavements.

Various concentration of composite nanoclay was studied to determine the physical and rheological properties of three types of asphalt binders. One type of composite Nanoclay in different concentrations (0%, 3%, 5%, and 7%) by weight of bitumen were used and blended with three asphalt binder types (80/100-60/70 and PG-76|) penetration grade. The physical properties of unaged base and nanoclay modified asphalt were characterized using viscosity, softening point, and penetration tests. Dynamic Shear Rheometer were used to determine the rheological properties of unmodified and nanoclay modified asphalt in accordance with AASHTO T315 in order to evaluate the effectiveness of composite nanoclay type and concentration on the physical and rheological properties of asphalt binder. The results indicated remarkable increment in softening point; viscosity and decrement in asphalt binder’s penetration for both types and contents of organic nanoclay and asphalt types as compared with unmodified bitumen. The results of the experiments indicated that the addition of nano particles was helpful in increasing the complex modulus values and in improving rutting resistance of the RTFO binder. The phase angle of the binders generally decreased with an increase in nano content and RTFO aging procedure. Also, the results indicated that modified binders show better rheological properties compared to standard bitumen for all asphalt type. The addition of Nanoclay to base asphalt binder has led to noticeable improvements in aging resistance this may be due to the homogeneous dispersion of nano particles consisting of layer silicate in the asphalt medium. The main objective of this study is to study the effect of nanoclay on the physical and rheological properties for three different type of binder.

This paper deals with the possible reuse of rubber waste such as car tires and plastic bottles in the design of asphalt mixtures in Libya. This work is a continuation to the laboratory research that began in the last year. In the earlier study, the volumetric properties of the traditional asphalt mixture using penetration grade binder (B60/70) were compared with the Superpave mixture using performance grade binder (PG70-10). However, this study is to evaluate the effect of the crumb rubber (CR) on the performance of the asphalt mixture in Libya. Four asphalt concrete mixtures were designed using asphalt-binder B60/70, aggregate and CR and then tested by both Marshall and Superpave mix design procedures. These results were compared with the results obtained from the previous traditional Marshall mix design test using asphalt binder B60/70 and Superpave mix design test using PG70-10. This study clearly showed that asphalt mixtures with CR performed slightly better than the traditional mixtures with binder B60/70. In addition, the results obtained from the Superpave mix design test with asphalt binder PG70-10 have shown a better performance indicator than those obtained with Marshall modifier mixture with CR. These results provide a guide line to improving the production and mechanical properties of the hot mix asphalt (HMA) in Libya by adopting new mix design methods such as Superpave or adding additives such as CR to the traditional mix design method with binder B60/70.

In recent years, software has been developed to calculate aircraft pavement strength ratings from modulus values that are back-calculated from deflections measured by a falling weight deflectometer. Deflection data from a uniform section of consistent runway pavement was analysed for variability to determine the effect of deflection variability on back-calculated modulus and the resulting pavement strength rating. The drop force of the falling weight had a significant influence on the calculated pavement strength, with 50 kN drop force rating the pavement approximately 35% lower than the 100 kN drop force. The number of layers in the nominated pavement structure also had a significant influence on the back-calculated modulus values, but not the resulting pavement strength rating. Compared to traditional design-based evaluation using intrusively measured layer thicknesses and laboratory material characterisation, the falling weight deflection back-calculation underestimated the pavement strength. Consequently, it is recommended that airports do not set their PCN based on back-calculated FWD data unless also supported by intrusive geotechnical investigation and a design-based evaluation.

Asphalt pavement is widely used in the US. The Volatile Organic Compounds (VOCs) volatized and emitted during its life cycle phase, including asphalt production, transportation, pavement paving, operation, as well as the demolition and reclaim, have a great effect on human health and the environment. Many studies have focused on the calculation, collecting, testing, and characteristics of VOC emissions from the asphalt pavement, however, several limitations still exist. For example, the database and the calculation methods are insufficient, as the calculation boundary is limited in the production phase and cannot extend to the lifecycle. To help the government to constrain the VOCs emissions within the legal system and draw more attention to the asphalt pavement reduction, this paper first defines the asphalt type, emission type and VOC category, along with the divided phases of the emissions. Then, a general database of VOCs emissions of asphalt pavement is established based on the data from the Environmental Protection Agency (EPA), European Environmental Agency (EEA) and other resources. Thirdly, a calculation method based on the coefficients is proposed to measure and compare the emissions from different types of asphalt under different conditions. Finally, this paper used an example project to test the reliability and feasibility of the method, as well as come up with suggestions for the related stakeholders, such as government, contractors and owners.

Foamed bitumen base is one method for producing a bitumen stabilised granular material for pavement construction. Foamed bitumen relies on the rapid expansion (foaming) of hot bitumen when introduced to cold water, temporarily reducing the viscosity of the bitumen, allowing mixing, placement and compaction. The resulting material is fast to construct, stiffer than crushed rock, moisture resistant and almost immediately able to support traffic, making it valuable for expedient pavement expansion and strengthening works. Airports with single runways often require expedient pavement construction methods and this paper presents foamed bitumen base through a case study on the runway strengthening at Whitsunday Coast Airport in Australia. Foamed bitumen base was produced ex-situ, initially using new crushed rock, prior to transitioning to the existing pavement materials. Challenges included the inability to recover existing pavement material in a representatively pulverised condition during the mixture design phase and the high sensitivity of the foamed bitumen base to production moisture content. Isolated underlying unsuitable materials were also encountered and this impacted the overall productivity and program. However, the relative density and resilient modulus of all samples exceeded the relevant requirements and foamed bitumen base is recommended to other airports requiring expedient pavement upgrade solutions.

Foamed bitumen stabilised (FBS) materials as non-continuously bound pavement layers are being increasingly used globally in both new road pavement base construction and rehabilitation of degraded pavements. However, the essential research on testing and design methods of FBS materials is still far from complete. In current pavement design practice, the laboratory-derived fatigue criterion of asphalt is used directly for FBS materials. This paper critically discusses the limitations in current pavement design and test methods and proposes a detailed bottom-up study for the characterisation of the flexural fatigue behaviour of FBS materials under both laboratory and field conditions. The numerical results obtained from Circly computer program revealed that the critical pavement response under standard axle loading is below the inner wheel of the standard axle along the vehicle travel direction. The analysis of numerical results showed that the level of interaction between the axles of various axle configurations increases with increasing FBS base layer thickness. Moreover, the ratio of the maximum compressive stress divided by the maximum tensile stress (R) at bottom of the FBS base under standard axle loading was determined to be less than 10% for all the FBS base layer thicknesses employed in this study.

Bituminous concrete is a premix widely used in road construction as a surface course. A high amount of expenditure is required for the construction of pavement structure. Due to increase in the magnitude of commercial vehicles, bituminous mixes are now exposed to greater stresses, and hence the performance of bituminous mixes is not good enough for paving applications. The present investigation, primly emphasizes to study the effect of filler materials and stress levels based on tensile strength on the number of load repetition sustained against the initiation of the first crack of a bituminous concrete mix. At controlled test temperature 25 °C, Indirect tensile fatigue test is conducted on bituminous concrete mix prepared using Stone dust and Cement as filler materials at 10%, 20%, and 30% stress level. Further regression analysis Based on the data obtained from Indirect Tensile Fatigue test and cost estimation per km for the construction of one kilometer of bituminous concrete mix prepared using both types of filler materials is carried out. As per the limited laboratory studies carried out, It can be concluded that no of load repetition varies with the addition of filler content and filler type. Fatigue life against the cracks decreases with an increase in stress level irrespective of filler materials. In the mathematical model Stress level and tensile stress are statistically significant with fatigue life, i.e., no of load repetition of a bituminous concrete mix.

Rif Chain (North of Morocco) is subject of ground instabilities. Several studies analyzed landslides’ triggering factors and confirmed that water is a predominant factor. Once a landslide occurs, it damages the roadway paralyzing traffic especially Mediterranean Bypass Road which links the North of Morocco from East to West. To open up population, recovery maintenance requires a heavy budget. Thus, this paper proposes a preventive solution based on automatic recognition of pavement degradations (cracking and tearing) that allow water penetration through pavement until reaching ground support or even deeper layers destabilizing slopes and then triggering landslides. This study applies deep convolutional neural network using pretrained AlexNet model, to automate image classification of road pavement and recognition of three classes (presence of cracking, presence of tearing and absence of degradation). Then to save more time in training and classifying, a second classifier is trained to simply distinguish between two classes (pavement degraded and pavement not degraded).

In developed countries there is a clear shift from new pavement structures to rehabilitation works which usually use the mill and fill method by replacing some of the asphalt layers. This process on one hand creates material which has to be milled and on the other hand requires new material for producing asphalt mixtures which are used back to the pavement structure. To improve the economic efficiency and reduce environmental impacts reuse or recycling are presently supported in elevated extent. To make the highest possible use of reclaimed asphalt rejuvenation is seen as one of the options. On the other hand excessive heating of reclaimed asphalt should be avoided to not overburn the bitumen or even to avoid additional ageing of already aged material. Combining effects of rejuvenation and warm mix technologies seems as an interesting option. In this respect a trial section was designed including 13 different options of warm mix asphalt with 0–50% reclaimed asphalt. The asphalt mixtures differed in amount of used reclaimed asphalt (RA) 0/11 mm (0%, 30% and 50%), the gradation of used paving grade bitumen (50/70,70/100) and warm mix asphalt additives or used techniques. In asphalt mixtures there were used bituminous binders with selected low temperature additive, which have primarily the function of reducing the production temperature, or the benefit in terms of improving the properties of the asphalt mixture, the adhesion improvement (in some cases) and in at least one of the cases the potential for reducing the characteristic odor of asphalt mixtures. Additives based on organo-silanes and different types of synthetic waxes (FT paraffin, amide wax, PE wax) have been used. Additionally foamed bitumen technology was applied as well. The asphalt mix performance was assessed by term of stiffness, resistance to permanent deformation, water susceptibility and thermal induced as well as fatigue cracking. The key findings will be presented by the paper.

The usage of certain amount of reclaimed asphalt (RA) is a well-established trend, which can be seen in many developed countries. Regrettably there are some countries or regions which still have very strict standard restrictions about RA usage in asphalt mixtures, mainly in surface layers. For example in current technical standards in the Czech Republic the use of RA in stone mastic asphalt mixtures or asphalt concrete for premium surface layers is banned. Recycling of construction materials saves direct primary costs like new material purchasing and at the same time also facilitates savings of other costs like energy, material disposal and transport etc. Those factors are connected to environment-friendly approaches, primarily in the case of emission and greenhouse gas production reduction. Material disposal can subsequently be reduced solely to waste or by-product materials which have no way of further utilization.

In this respect a 5 km trial section was designed including 12 different variants of stone mastic asphalt mixtures. The mixtures contained 0%, 20%, 30% and 50% reclaimed asphalt. The mixtures differed not only in amount of used RA, but also in source of RA (normal and SMA RA), used bituminous binder and used additives. The selected additives were based on cellulose fibers modified by an oil-based rejuvenator and crumb rubber modification in some alternatives of the used rejuvenator.

The performance of the asphalt mixtures was assessed by term of stiffness modulus (IT-CY method), thermal induced crack propagation (SCB test), flexural strength (three-point bending test) and resistance to permanent deformations. The key findings are presented in this paper.

Recent concept of the structure and the mechanics of mechanically stabilized granular layers is described from the point of view of pavement design. Described approach is applied in finite elements model of an example of typical pavement structure. Influence of mechanical properties of mechanically stabilized layer on the range of the strain on the base of asphalt layer is analysed. The results are implemented into pavement performance models using various empirical equations. The consequence on serviceability of the pavement structure is shown. Mechanically stabilized granular layer concept is proven as an effective approach to pavement design.

The ever-increasing requirements on quality and life-span of asphalt layers present a reasonable motivation to explore new approaches and technologies. For many years, the technical options have included modification of regular paving grade bituminous binders. This paper focuses on the possible use of bituminous binders used; both activated and chemically improved by selected modifiers, in mastic asphalt as well as on their potential beneficial effects on selected parameters of the mixtures tested. The modification of reference paving grade bitumen 20/30 involved micromilled (pulverized) recycled crumb rubber as well as a new generation of synthetic waxes or even combination of the two types of additives. Potential benefit can be seen in the improved deformation characteristics and in the possibility to reduce the manufacturing temperature including potential improvements in mix workability. The paper presents the experimental assessment in the form of the indentation test, compression strength test, 3-point bending beam strength test, stiffness and creep characteristics. The properties of mastic asphalt mixtures are complemented by parameters of the bituminous binders applied (complex modulus, viscosity etc.).