Abstract

Bitumen Rubber binders have been used in Chip seals in South Africa since the early 1980’s. Over the past 3 decades the use thereof has extended to southern Africa, including Namibia where it has been extensively incorporated into the recent reseal program of approximately 3,200km of roads, of which approximately 700km roads have been surfaced using Bitumen rubber between 2016 and 2019. A Total of 340km of these rubber seals were done using the S-R2 bitumen binder, instead of the conventional S-R1 bitumen rubber.

According to the TRH3 design manual of 2007, no data for the adjustment for the non-homogenous S-R2 binder to conventional binder is available. The common practice was to use the S-R1 conversion factors. This use of the S-R1 conversion factor led to extensive bleeding in some cases on Namibian roads. One of the key benefits of using rubber bitumen is that due to the stiffness of the binder which provides resistance to the orientation of the surfacing stone, higher bitumen application rates can be applied compared with conventional binders, normally in the range of 1.8 – 2.3 l/m² hot for a 14mm seal. It was observed that the stone orientations rates differed between the conventional S-R1 and S-R2 bitumen rubbers resulting in early bleeding, subsequently justifying different binder application rates and conversation factors.

The rate of stone orientation was observed using two different S-R2 products sprayed at different application rates in the same direction of travel on a trial section. The use of two SR-2 products from different suppliers was used to established if there is any significant difference in the behavior in the SR-2 binders itself and to established the rate of stone orientation. Application rates ranged from 1.8 l/m² to 2.1 l/m².

Texture depth measurements were taken directly after surfacing prior to traffic and rechecked every day for a week, thereafter weekly for a month and finally monthly over a period of four months. The location of the texture depth measurements was strategically placed in and between the wheel tracks to observe the sensitivity of the S-R2 bitumen rubber to early stone orientation due to traffic. No marked difference in rate of texture loss due to traffic compaction was observed between the two S-R2 products, but it was noted that S-R2 has a lower viscosity specification at a lower temperature than S-R1 which leads to a less stiff bitumen at the time of application. Higher application rates can thus be achieved with S-R1 than with S-R2 binder which reverts to a stable condition at around 5000 vehicle passes. The outcome of the S-R2 trials in Namibia lead to the provisional conversion factors for S-R2 binders, as published in the recently released SABITA Manual 40 / TRH3 2021

Abstract

The purpose of this paper is to illustrate the process of selecting and prioritizing surface treatments such as reseal, in Namibia. Roads Authority of Namibia has an IRMS (Integrated Road Management System) of which the PMS (Pavement Management System) is a subsystem. PMS is a software tool that assists decision makers in identifying and prioritizing potential projects and optimum maintenance strategies. Once potential projects for reseal are identified by the system, the system generates a reseal priority list of projects at network level, which is then circulated to Regional Engineers, PMS Manager and appointed Consulting Engineers (responsible for reseal projects) for scrutiny. The team then evaluates the PMS recommended action, priority and confirms the project start and end. Results of these panel inspections form the basis of a three-year reseal work program.

The data that feed the PMS is collected through standardised Visual Assessments, conducted with a Cloud-based Tablet application; mechanical surveillance measurements that collect road roughness and rut depth using a laser road surface profiler and; Pavement strength measurements using a Falling Weight Deflectometer. The PMS module uses the pavement structural condition, pavement performance and prediction method through historical deterioration to determine both the Surfacing and Structural remaining life.

The reseal type selection process uses the type of distress, their degrees and extents, traffic volume and turning actions, the coarseness or variation of the existing macro texture and road importance, using decision trees. The cost-effectiveness of different reseal types are then evaluated using costs and benefits through an “area under the curve” approach.

During the panel inspections, Regional Engineers share their experience of previous work under various condition in their areas and in some cases, question the selection of correct pre-treatment and reseal types. These comments are then fed back into the PMS and used to improve the PMS models through its adjustable rule sets.

Panel inspections, facilitated by experienced practitioners, are also used for capacity building, allowing young engineers to carry out ball penetration and sand patch testing with explanation of how all gathered information is used to select and prioritise appropriate actions.

Abstract

The video, Chip Seal Construction Process, summarizes the construction process of a triple seal in South Africa. A triple seal has three layers of aggregate; 20mm + 7mm + 7mm; and three spray coats of binder, typically but not restricted to; S-R1 + S-E1 + Cat65%. The second video, Abaqus 3D Chip Seal Model, is a digital copy of the chip seal construction process. The chip seal model was developed in Abaqus, has a load consisting of a 20 kN truck wheel inflated to 800 kPa, rolling at 10 km/h. Stress and strain results were obtained at the aggregate-binder interface as an approach to quantify the environment conducive for ravelling.

Chip Seal Construction Process:

Abaqus 3D Chip Seal Model:

Abstract

In South Africa, the Marvil apparatus (SANS 3001-BT12:2012) is the primary method used to determine the permeability of a seal. The Marvil apparatus, however, does not consider the influence of the magnitude of pressure generated between the wet road and the wheels of the traffic, which led to this research study with three objectives. Firstly, design and build an apparatus able to test the permeability of seals under a pressure of up to 300 kPa. Secondly, introduce a preliminary test protocol, and thirdly conduct pressurised permeability testing on seals.

The objectives were achieved based on the successful testing of 26 cored seal specimens with newly designed High Pressure Permeability (HPP) test apparatus. The permeability was calculated by means of measuring the amount of water seeping through the 100mm seal core over a set time, under a constant pressure. Five different seal types were tested and permeability within the wheel tracks were compared to permeability between the wheel tracks and on the shoulder.
The data from the study suggests the following:

• Permeability increases with the increase in applied pressure; In comparing traffic data to permeability, a trend is recognised which suggest permeability increases as traffic loading increase. There are however exceptions within the data, that does not follow the suggested trend and more testing is recommended;
• Isolated defects, such as cracked stone or small holes, greatly influences the permeability which highlights the negative influence such as aggregate crushing or cracked stones found in seals;
• Aged cores recovered are more permeable in the wheel tracks as opposed to between the wheel tracks, and on the shoulder. This suggests that ageing combined with fatigue damage caused by traffic increases the permeability of the seal;
• Permeability was also compared to binder content, but there is no clear relationship between bitumen content and the permeability.
  An overview of permeability rates measured for each seal type is presented in the paper. It is however important to highlight that each seal functioned under different circumstances and that the number of cores tested per seal type varied. These permeability values should be viewed as preliminary test values and not exact seal type specific values, as more testing is recommended.

Cape Seals had the highest average permeability of 31.54 ml/min at 300 kPa. The other three seals were found to have an average permeability close to each other. The Single Seals was found least permeable with 2.50 ml/min at 300 kPa. The Double Seal had a permeability of 2.75 ml/min and the Multiple Seal a permeability of 2.81 ml/min at 300 kPa. For each seal type these values are the average values found within the wheel track only.

This study did not result in an ultimate measurement for permeability of seals under pressure. It did however produce a meaningful test apparatus and method which will serve as platform for further investigation into permeability of seals and asphalt under pressure.

Abstract

A major behavioural characteristic of surfacing seals includes aggregate re-orientation which involves the re-orientation of seal aggregates, onto their respective least dimensions, during and after construction, to ensure a lower risk of aggregate loss and adhesion problems.

The purpose of this investigation is to gain an understanding of the effect that traffic has on the re-orientation of surfacing seal aggregate. Variables that affect aggregate re-orientation include different binder types, rheological properties, different pavement temperatures and different aggregate matrices. The combination of these variables is measured and discussed to determine the optimal binder adjustment factors and conditions for aggregate re-orientation. This investigation tests eight different binders including 70/100 penetration grade bitumen, Cat65 emulsion, SC-E1, SC-E2, S-E1, S-E2, S-R1 and S-R2 at three different trafficking temperatures (10°C, 20°C and 30°C), two different aggregate matrices (shoulder-to-shoulder and over application) and simulated traffic going up to five thousand load repetitions per combination of variables. To simulate traffic, the Model Mobile Load Simulator Mk. 3 is used, after which a Laser Profilometer is used to record texture readings. The time between construction and testing was kept constant throughout. This study provides a better understanding of different factors that influence aggregate re-orientation, which could be implemented in practice immediately.

Abstract

Infrastructure maintenance and preservation are important activities for any developing city. Microsurfacing is a well known slurry seal surface maintenance technique that leverages the use of cationic quick setting slurry. The technique is considered by some practitioners to be more economic than other conventional surface treatment methods such as asphalt and chip seal. Micro surfacing seals could correct rutting defects, restore skid resistance, reduce pavement oxidation, help preserve water ingress, and in turn extend the surface life span. Quick setting slurries are preferred when working on urban roads where the specialised modified emulsion allows the seal to set quickly, building good cohesion and allowing opening to traffic within 2hrs (weather dependent). Work performed in urban areas during winter poses various challenges for micro surfacing seals due to shades on residential streets (low surface temperature). These conditions are usually mitigated through adjustment of the emulsion formulation to allow different setting/breaking times of the quick set product.

The success of a microsurfacing seals depends on careful pre-planning (using digital logging), surface preparation (sealing of cracks, potholes repairs, etc.); raw materials selection (emulsion and crusher dust); workmanship and fit for purpose equipment. The system can only be placed with a purpose designed microsurfacing machine and spreader box capable of continuously feeding accurate raw material proportions to ensure a consistent, high quality surfacing layer. The application process of quick set slurries is a complex and specialised operation requiring skilled supervision, specialised machine operators and skilled squeegee operators who understand quality requirements, on site trouble shooting, breaking times and time constraints with regards to workability and hand work.

Careful seal design & application techniques are critical for successfully achieving a quick setting slurry seal capable of accommodating light to medium traffic. This presentation addresses onsite challenges & solutions for laying microsurfacing systems.

Abstract

Bitumen is one of the most used materials in the world, constituting most road designs and applications. Given the extensive use of bitumen, it is important to understand the material and limit all possible drawbacks for better utilisation.

Although bitumen has many desirable properties, one disadvantage that bitumen has is its susceptibility to the action of fuel and other petrolic substances. This can be fatal to the pavement as the bituminous binder dissolves when exposed to fuel, leaving behind only loose aggregate, resulting in a failed pavement.

This study compares the fuel resistance of different polymer modified binders commonly used in South African roads and identifies the best polymer modifier from those tested. This was done by subjecting the test specimens to the Fuel Immersion and Brush Test, Indirect Tensile Strength and the Hamburg Wheel Tracker Test. The test was done on conditioned (diesel saturated) and unconditioned samples and the results were compared.

Abstract

Surface treatments are the most commonly used bituminous binder products for roads in Southern Africa. This is mainly because with comparison to other types of surfacing are found to be inexpensive. Although there have been great strides in the improvements of bituminous emulsions, where the ever changing or expansion in the variation of their formulations plays a great role in that development.

The current testing methods of emulsions are empirical and show very little in their in-service. The quality of the bituminous emulsion is affected by many factors, such as particle size, base binder and formulation ingredients, which in turn affect their in-service performance.

There are several test methods that have been suggested and developed in the possible evaluation of bituminous emulsion rheological properties with relation to the in-service conditions. The performance based methods that were found to correlate with the failures experienced by the slurry sealed pavements were identified and verified, using the standard bituminous emulsions already used in industry of South Africa.

The primary objective of this study was to evaluate the possible effects of emulsifiers have on the rheological properties of the emulsion and its residue. These are during storage and in-service of anionic slow-setting bituminous emulsions used in slurry seals.

This was studied by evaluation of their change in viscosity through storage. The strain resistance of their residue through determining their elastic resistance and non-recoverable (J_nr) compliance. The evaluation of the fatigue resistance was carried out by the prediction of failure using time-temperature superposition (TTS) principle. All performance evaluation was carried out using the readily used dynamic shear rheometer (DSR) in industry.

Results showed the performance of the emulsion and residue in-service may be observed with limited observation on the effect of the varying emulsifiers used.

Abstract

Environmental considerations and increased traffic demands make the use of rubber-modified bitumen an attractive alternative to polymer-modified bitumen. Bitumen-rubber as a binder in both seals and asphalt is used extensively in South Africa with a track record of excellent performance. It was decided to use a bitumen-rubber open graded asphalt (BRAOG) as a wearing course for the N3 corridor upgrade project. Bredenhann et al (2019) reported on the appropriate application of the new performance grade (PG) specifications with regards to bitumen-rubber modified bitumen to the 2019 CAPSA Conference. This paper will report on further work done with bitumen-rubber characterisation to be used in the BRAOG design for the N3 corridor project.

Currently there are two types of bitumen-rubber binders available in South Africa namely A-R1 (traditional and A-R2. The longer shelf life and lower emissions during manufacture are the primary benefits of A-R2 over A-R1. However, past experiences together with desktop level studies highlighted the varied performance of bitumen-rubber binders from various suppliers.

In order to ensure that the performance of the rubber modified binders supplied for the N3 corridor upgrades are within compliance limits, testing was carried out on the rubber modified binders with the objective of tightening up the existing binder specifications. Binders for testing were provided by participating suppliers. Each binder was tested for its empirical, PG and chemical properties. This paper will focus on the PG testing conducted to understand the rheological behaviour of the binders in relation to loading and temperature variations.

The rheological properties were assessed at three ageing conditions i.e. unaged, short term aged (rolling thin film oven test (RTFOT)) and long term aged (pressure ageing vessel (PAV)). The low service temperature behaviour of the rubber modified binders were evaluated using the bending beam rheometer (BBR) and high service temperature behaviour using the dynamic shear rheometer (DSR). The multiple stress creep-recovery (MSCR) test was also conducted on the RTFOT aged binders to gain an understanding of the stress / loading resistance of the binders at high service temperatures.

PG test results were stored in comma separated value (csv) format for ease of incorporation during assessment and analysis. Analysis of the data involved various modelling techniques utilised locally as well as internationally. With the simplest of digitisation modelling tools, the metadata collated from the tests conducted were simulated into graphical relationships, relationships predetermined and prescribed through the current ASTM standards and research drives in the binder testing industry.

Prior to data analysis, quality and acceptance control of the data was carried out using the validation and precision estimate requirements in accordance with the relevant ASTM standards. In addition, black space diagrams were utilised for the identification and removal of bad data points. Rheological index trend lines were overlaid onto the black space diagrams to aid in the assessment of the data points in relation to known bitumen trends.

Analysis of the results currently include the construction of master curves. Various shape defining functions, including the Christensen-Anderson (CA) and Christensen-Anderson-Marasteanu (CAM), were utilised depending on the suitability to the data points. In order to assess the data at the various temperatures, a reference temperature was set, and the various isotherms shifted to the reference utilising shift functions. The shift functions include the Arrhenius function and Williams Landel Ferry (WLF) function. The primary objective of this research is to assess the performance of various industry available rubber modified binders with the intention of tightening up the current specifications in preparation for the use thereof on the upcoming road upgrades.

Bio

Babalwa is a hardworking, enthusiastic, young technician who values understanding and knowledge transferal. She started her journey in the Civil Engineer working industry as a Trainee Technician at Naidu Consulting, and later got appointed as Civil Technician in the Pavement Engineering unit, having worked on a few projects as an Assistant Technician. She completed her National Diploma in Civil engineering at the Durban University of Technology, in 2018 and is currently progressing towards completing her Bachelor of Technology studies, specializing in Transportation.

Abstract

As performance grades are developed for South African bituminous binders, the need arises to expand the related engineering knowledge and understanding in the context of local technology and materials. The Dynamic Shear and Bending Beam Rheometers are commonly applied to evaluate fundamental viscoelastic material behaviour by measuring properties such as the shear complex modulus and phase angle. The isotherms are subsequently shifted to form master curves and Black Space diagrams. Focusing on high, intermediate and low-temperature load-displacement responses, examining these behavioural curves leads to the identification of primary stiffness and relaxation ranges. Changes and the evolution of parameters in response ranges can indicate ageing-related developments in binder rheology. The progression of binder rheology may vary significantly depending on the modification, seal type and origin of the binder. For various seal binders, performance-related testing is conducted. The principles and modelling of shift and master curves are reviewed as an introduction to the influences on and development of rheology with increased age. The implications of these changes are discussed with regard to expected performance. An overview of current research is presented.

Abstract

As the asphalt industry moves forward, emphasis continues to shift from volumetric properties to performance tests. The quest for suitable performance tests goes back more than 100 years, pre-dating development of Marshall mix design. Marshall stability, developed in the 1930s as an indication of permanent deformation resistance, was used until research in the 1980s indicated a poor correlation between rutting resistance and Marshall stability. In the Strategic Highway Research Program (1987 to 1993) a newly developed mix design method included measurement of engineering properties and prediction of performance. As implemented in the late 1990s, Superpave included only the base level of volumetric design because the engineering property tests were too complex and not ready for implementation. Since SHRP the asphalt industry has grappled with performance-related tests such as wheel track testers and various cracking tests seeking to relate the test results with anticipated performance. Results have been mixed. Engineering properties of asphalt depend on the property of bitumen and aggregates, their proportions in the mixture and their final in-situ compaction. On a separate path, work has occurred in the last 20 years to identify the relationship of engineering properties and volumetric properties. The vision is to measure engineering properties during design and then during construction use the relationship to volumetric properties to estimate engineering properties. These properties can be used to predict performance from fundamental, engineering-based models rather than empirical relationships.

Bio

Originally from the Province of Saskatchewan in Canada, Mr. Huber obtained a degree in civil engineering and joined Saskatchewan Highways and Transportation where he worked on highway construction and design.

During his tenure in Saskatchewan, he obtained a Master's degree from the University of Texas that led him to the Asphalt Institute, an industry association in the U.S. At the Asphalt Institute’s research center, he helped develop a new method to design of asphalt pavement called Superpave. Mr. Huber now works as Associate Director of Research for the Heritage Research Group, a private asphalt research office based in Indianapolis. He works with transportation and research agencies at the state, national and international level. He is active in the Transportation Research Board, is Past President of the Association of Asphalt Paving Technologist and is Past Chairman of the International Society of Asphalt Pavements.

Abstract

The hot mix asphalt mix design process and testing technology are moving at such a rapid pace that it may create different challenges than the current benchmarks used for mix analysis. It is as important as ever to be able to review and track where the local industry is currently and where it may be heading. To accomplish this, the analysis and data gathering using software outputs between Contractors and localized agencies will be reviewed as well as some current testing specifications and requirements. The specific software outputs to look at for the state of Indiana include the Illinois Flexibility Index (IFIT), IDEAL-CT and Hamburg Wheel Tracking Test. It will be discussed how determining a baseline for Contractor mixes is imperative to collect using these software outputs from both laboratory and plant mixtures. By analysing overall data for these Performance Testing methods, Indiana Contractors will be able make sustainable and economic decisions on mix designs and as-produced mixtures.

Bio

Elizabeth holds a Bachelors Degree in Civil Engineering from Michigan State University and a multitude of industry-based qualifications including Superpave and Balanced Mix Design methodology. She has been active in industry for 18 years starting in Indiana Department of Transport to her role today in the Contractors’ fraternity. She is the co-chair for the Women of Asphalt branch in Indiana and participates in several industry committees surrounding technical analysis and performance testing.

Abstract

Much emphasis is usually placed on getting the asphalt mix design correct, running the relevant trials and agreeing on a final approved mix design for construction. Proper quality management in terms of monitoring and acceptance, which ensures consistency and achieving the desired result, is however often overlooked in practice.

A background will be provided in terms of the design and construction processes with reference to the specific manual guidelines and specifications available. High-level information to assist in the transition between the COLTO and COTO Standard Specifications that the industry now faces, including the influence of aspects such as testing, personnel competency and equipment requirements, will be addressed.

The need for making full use of test results in terms of risk mitigation is paramount. In practice, making use of purpose-built spreadsheets or programs to aid in displaying, analysing and interpreting results correctly is vital. The significance of using sound engineering judgement and relating what can be seen on site to the test results, identifying pitfalls and implementing the corrective actions cannot be disregarded. Notwithstanding the importance of the above, the need for open communication amongst all Stakeholders and the value gained in working as a team is highlighted.

Bio

Leanne is a Civil Engineering Technologist and Associate at Royal HaskoningDHV, Woodmead. She holds a BTech in both Water Engineering and Transportation Engineering and is a member of ECSA, SAICE, SAT and IPET. She has worked in the Civil Engineering Industry for over 15 years in the Water Engineering, GIS and Transportation Engineering environments.

Her experience includes Pavement and Materials Design (Roads and Airports), Documentation, Project and Contract Administration, and Project Management where more recently, she is the Project Manager of multi-disciplinary projects within the Organization including provincial wide Road Asset Management System projects.

Leanne also has several years of Construction Site Supervision experience in the fields of Pavement and Materials. She has held site and contract administration positions on various SANRAL projects including GFIP Package B and the R104 Experimental Test Section.

Abstract

Linking the Technical Standards, Guidelines & Manuals can be the difference between the (un)successful implementation of a project. The importance key role players in understanding the link of appropriate information into the project specifications cannot be understated.

The current COTO Standard Specification aims to incorporate the latest design requirements for asphalt mixes, referencing all the latest design Guidelines and Manuals as part of the Specification. This ensures that all contract parties are required to comply with the latest information and technology pertaining to Asphalt.

The current Frankenstein approach of combining multiple Technical Standards, Guidelines & Manuals can lead to the specification requirements which is on opposite sides of the performance specification spectrum, for example, N₃₀₀ Gyration Parameter specification for a Level III Manual 35 mix.

This presentation discusses the new specification, focusing mainly on the implementation of the new COTO specifications in specifying asphalt mixes in line with the proposed design. The linkages between structural pavement design and specification thereof, asphalt mix design and field performance are discussed and debated extensively. The outcome of this presentation therefore highlights the roles, responsibilities, and in particular, the relationship between the Client, Consultant, Supplier and Contractor in as far as project specifications extend.

Abstract

With all the waste generated by humanity on a daily basis, the roads industry has a responsibility to find sustainable applications for materials re-use and recycling whilst maintaining product quality and performance at the required standards.

In recent times, the recycling of glass, plastic, slag aggregates, ground tyre rubber and reclaimed asphalt in fresh asphalt has been on the rise with several research projects coming to fruition to show not only what is possible, but also what the caveats are surrounding the use of each. This will be presented using several case studies, both at laboratory and in-service scales.

In order for recycling of materials to be more viable, databases on road construction materials that are being used at present need to be comprehensive and informative during the design stage of recycling projects. Prospective ways and benefits of digitising such databases are explored and presented, aiming at promoting efficient strategies for recycling in the roads industry.

Bio

Tafadzwa completed her BSc Eng degree in Civil Engineering at UKZN in 2013 and is currently completing her M-Eng in Pavement Engineering at SUN. She has extensive experience from both contractors’ experience and on the quality and technical focus from an Asphalt suppliers’ perspective. She currently holds membership of ECSA, SAICE and SAT.

Abstract

Our world is rapidly changing. Globally we are experiencing the effects of developments in technology but also a change in the character of our society. As a people we have understood for example that we have to be more respectful to our surroundings, to become more environmentally aware, be less wasteful. And well, if one is a part of the pavement industry a small inner conflict might occur there. On the one hand asphalt pavements worldwide are constructed with secondary materials like concrete and masonry rubble in foundation layers. Even the bitumen binder in our asphalt is the waste material from oil refineries. On the other hand, our asphalt production still contributes to pollution and paving processes are quite artisanal and operating based on implicit knowledge.

To do better QRS* presents H.O.P.E., a Holistic Ontological Pavement Endeavour. H.O.P.E. considers the asphalt process from a holistic point of view and focuses on the interrelations instead of on its individual parts. By appointing and classifying these relations they can be optimized and/or (re)designed using of both theory and practice. And in this way further the pavement industry’s transition from implicit craftsmanship to explicit industrialization, from empirically based to functionally driven and from linear processes to circular strategies. In this paper H.O.P.E. is explained and its application is illustrated with special focus on the design-production-processing interrelations of the paving process.

Bio

Born and raised in the Netherlands, Natascha achieved her master’s degree in Road and Railway Engineering at Delft University of Technology. During her study she discovered her fascination for materials, their behaviour, and the fundamental challenges therein, especially for bitumen and asphalt. Now, Natascha works as a Research Consultant at the R&D department Quality, Research & Support, or QRS in short, at the Road and Infrastructure division of Royal Boskalis Westminster. Natascha combines knowledge of both theory and practice to design and optimize research projects, processes, and their interrelations.

Abstract

Plastic strain causes non-recoverable, permanent deformation in pavement layers. The effect of plastic strain is generally referred to as rutting. Rutting may occur throughout the pavement structure in granular, stabilised and asphalt layers. Granular materials exhibit plastic deformation when loading occurs outside the elastic limits. The fatigue life evaluation of granular layers during design is generally sufficient to ensure adequate strength and rut resistance. Asphaltic materials may behave visco-plastically, whether as a surfacing or lower layer. Additional to the degree of loading, such materials' susceptibility to permanent deformation depends on the traffic speed, operational temperature, layer thickness and bitumen age. Opposite to granular material, asphalt is generally more susceptible to permanent deformation during its early life. During design, evaluating the effective vertical strain imposed on the layer is essential to specify an appropriate layer and mix type. Other interventions to counteract compliance under loading include the selection of high modulus bitumen. The theory of permanent deformation is linked to relative rutting in the pavement structure by observed plastic strain during triaxial testing. The influence of bitumen age and environmental factors on expected performance is discussed.

Bio

Elaine completed her PhD in Pavement Engineering at SU in 2021. She has experience in road consulting and construction supervision and is currently a lecturer at SU. Her research focusses on binder rheology and ageing.

Abstract

Traditionally, pavement designs consisted of considering the design traffic loading over the structural life of the road together with a single conservative estimate of the layer moduli in order to estimate the bearing capacity of the pavement using mechanistic analysis. Only a single point in time is considered ignoring the changes in layer characteristics with time and temperature. Research for the South African Roads Design System (SARDS),the recent implementation of a performance-grade (PG) binder specification in South Africa and advances in computational capacity presents an opportunity to expand on the pavement design philosophy and consider environmental influences on pavement behaviour in the form of temperature.

In order to simulate these changes in pavement design, an incremental model based on time and consequently the material changes with time may be utilised. Time increments are chosen to represent appropriate variations in terms of material characteristics, one such characteristic is the dynamic modulus.

A temperature model based on temperature prediction algorithms developed by Viljoen (2001) has been automated for ease of calculation. The output provides a prediction of the pavement temperature for design purposes. Dynamic modulus models involve the generation of master curves. There are a variety of shape defining models and shift functions available for master curve generation. The master curve developed is based on a sigmoidal model, in accordance with SABITA Manual 35 (2020), with an appropriate solver function utilised for optimisation purposes. The resultant dynamic modulus model allows for the identification of asphalt layer moduli at the predetermined temperature and loading frequencies.

The predetermined temperature and loading frequencies are considered the design increments. Considering the life of a pavement as a series of time increments will highlight potential premature failures, allow for an improved prediction of pavement durability. Furthermore, the outcomes of the analysis may allow for the development of an optimised design solution which may lead to reduced initial capital investment and life cycle costs.

This purpose of this presentation is to create awareness and inform on the processes involved in carrying out the recursive, incremental design approach for asphalt layers.

Bio

Semeshan is a young Engineer who obtained his Bachelor of Science Degree in 2016. He joined Naidu Consulting in 2017 and currently holds the position of Engineer with four years of industry experience specialising in Pavement Engineering.

Abstract

EME are used for pavements which require a high stiffness modulus, high resistance to rutting, good fatigue resistance and good durability. This technical solution has been already used with great success in South Africa and more projects are currently being developed. But EME quality is also dependent on its key components. One of the key components is bitumen 10/20 being a contributor to achieve the desired high stiffness and fatigue resistance.

After having been through recent EME projects in South Africa, we will demonstrate the importance of using 10/20 bitumen which keeps the balance between good low temperature behavior, fatigue performance and high stiffness modulus.

To further build on the importance of controlling the quality of the binder, we will present the context and results of a study done in Europe where a specific polymer modified hard grade bitumen has been developed to answer to specific EME constraints when used at higher elevation.

Bio

After a first experience with ExxonMobil, Jean-Nicolas joined Shell in 2003. For 15 years, he specialized in base oils working in various refineries located in France, The Netherlands and Singapore. In 2018, he joined Shell Specialties (Bitumen and Sulphur) as Bitumen Senior Application Specialist for France and BENELUX. In this position, he is supporting Shell customers on bitumen and asphalt mix design. During these years, he also provided several trainings on bitumen manufacturing and bitumen special products. Jean-Nicolas is also a member of several normalization working group.