ASPHALT FOCUS AREA
Craig Naiker, Ten Logistics and Civils
Abstract
Asphalt contractors are given a set of specifications to adhere to when constructing asphalt layers. This includes the specification of thickness layers where the minimum and maximum tolerances are defined. However, the estimation of what loose layer thickness a contractor should commence with is left to the contractor.
Traditionally compaction factors are used to guide the construction of an asphalt layer, from loose volume, to meet both compacted thickness and density. These factors have thus far been mostly empirical, with a high degree of personal bias. It can, however, be seen that the technical characteristics of the mix, as well as environmental and mix temperatures, play key roles when combined with the mechanics of the construction process to achieve the specified layer or lift thickness.
This study endeavours to delve into these variables and more, with a view to recommending a standardized, practical, and scientific approach to determining compaction “factors” for constructing asphalt layers using currently available mixes and equipment in South Africa.
About the author
Craig Naicker graduated from the University of KwaZulu Natal with a B.Sc. Hons Degree in Mathematics and Statistics in 2007. Before starting his own company, he worked on numerous finance projects in the banking industry where he gained experience in project coordination, financial modelling, as well as designing and implementing an outcome-based remuneration (OBR) project. The OBR project was recognised by the South African Remuneration Association as a leading productivity tool to drive employee motivation.
Craig established Ten Logistics and Civils in 2008 and went on to obtain his MBA at the North-West University. Ten Logistics and Civils has grown into one of the leading asphalt contracting companies in KwaZulu-Natal, with clients such as ACSA, SANRAL and many local municipalities.
A commitment to excellence and professionalism, along with a deep-rooted connection to the KZN region, has enabled Craig to become a well-recognised and respected name in asphalt contracting.
Avi-Nash Sukuram, Joanne Muller
Abstract
The importance of air voids in hot-mix and high modulus asphalt cannot be underestimated. Mixtures exhibiting sub-optimal air voids can adversely affect pavement performance and subsequently its ability to perform suitably over its desired design life.
To ensure not only compliance and consistency of the mix, but also to work towards achieving the required performance in accordance with the design, lab voids and in-situ quality control are statistically assessed against the density requirements as set forth in the overarching project specification. For the current paper, the eThekwini Go! Durban Project - C9 Corridor, Phase 2A - Phoenix Highway to Industrial Park, has been used as a case study with specific focus placed on the 150mm thick Bitumen Treated Base (BTB) and Enrobé à Module Élevé (EME) base courses used.
The main aim is to establish the potential relationship that exists between lab and field voids using the Vacuum Sealing (VS) voids. The pavement structure under review may not attain the 100 MESA traffic design life it is set to if the as-constructed voids in the layer do not satisfy the required criteria.
The current paper further aims to obtain a risk-centred view of the project through statistical means of voids analysis. The differences in outcome that may result between application of the current project specification in comparison to that which may be obtained when COTO DS is applied, will also be highlighted.
About the authors
Avi-Nash Sukuram - Nankhoo Engineers
Avi-Nash Sukuram likes to believe he is a geriatric millennial. He is a qualified and registered professional civil engineering consultant who has 13 years of design and contract administration experience related to roads and civil infrastructure in the private sector. In 2017 he won the national award for Young Professional Technologist of the Year. Avi-Nash is an aspiring poet with recent publications in magazines spanning the African continent. Recently he has been driven by the discovery and assimilation of knowledge pertaining to life, with a passion for discovering one’s true purpose.
Joanne Muller - AECI Much Asphalt
Joanne completed her Bachelor and Honours Degrees in Civil Engineering, followed in 2015 by her Master’s in Engineering Management, at the University of Johannesburg. She is an ECSA registered Candidate Engineer.
She began her career with AECI Much Asphalt in 2008 as a part-time Trainee, followed by two years as a Graduate Trainee in the company’s Gauteng Regional Laboratory. In 2013 Joanne was promoted to Quality Assurance Supervisor at the Benoni plant and in 2016 to Regional Laboratory Manager. In this role she strives to improve quality and cost metrics to meet strategic objectives and customer requirements.
Joanne’s experience in asphalt manufacturing, testing and design, together with her zest for problem solving, is also put to good use on working groups reviewing SANS standard test methods, Sabita manuals and protocols for industry.
Craig Naiker, Ten Logistics and Civils
Abstract
This paper assesses the degree of variability between South African asphalt specifications and international asphalt specifications relating to construction tolerances. Cross-country comparisons avoid poor equilibrium and give insight into common project tolerances.
A comparative statistical analysis will be done between international benchmarks and COTO, which was approved by the Committee of Transport Officials and issued as a specification manual for all road and bridge works in South Africa, with a notable preference to ANOVA testing (analysis of variance) which will guide our discussions.
This comparison study endeavours to delve into these international benchmarks with a view to recommending suitable benchmarks within the South African context.
About the Author
Craig Naicker graduated from the University of KwaZulu Natal with a B.Sc. Hons Degree in Mathematics and Statistics in 2007. Before starting his own company, he worked on numerous finance projects in the banking industry where he gained experience in project coordination, financial modelling, as well as designing and implementing an outcome-based remuneration (OBR) project. The OBR project was recognised by the South African Remuneration Association as a leading productivity tool to drive employee motivation.
Craig established Ten Logistics and Civils in 2008 and went on to obtain his MBA at the North-West University. Ten Logistics and Civils has grown into one of the leading asphalt contracting companies in KwaZulu-Natal, with clients such as ACSA, SANRAL and many local municipalities.
A commitment to excellence and professionalism, along with a deep-rooted connection to the KZN region, has enabled Craig to become a well-recognised and respected name in asphalt contracting.
Dr. Ing. Gonzalo Oroz
Abstract
SMA asphalt mixtures have proven to be an excellent solution for the design of roads and high traffic motorways. Although SMA technology has been around for more than 50 years, it has undergone changes that have enhanced its positive characteristics in terms of durability and resistance.
This paper begins with a brief overview of the historical development of SMA mixtures, initially used exclusively as wearing courses. It then moves on to the latest developments in the use of Stone Mastic Asphalt in binder layers the latest developments in creating a green asphalt that decreases rolling resistance and emissions, saving fuel and reducing greenhouse gas emissions. Experiences gained in many regions of the world have demonstrated the versatility of SMA mixtures, regardless of the prevailing climatic conditions.
Finally we focus on some international cases and on the African reality, and outline future developments from a technical perspective, describing concrete aspects of design adapted to local realities.
INDUSTRY DISRUPTORS
Cameron Munsamy
Abstract
In South Africa, the implementation of labour-based construction techniques is beneficial in that it creates opportunities and assists with the development of small contractors whilst upgrading the transportation network. The performance of a road pavement is primarily a function of the material selected, as well as the testing and quality control of the constructed layer. This is a challenge in remote rural areas with limited access to laboratories.
To ensure quality and provide a solution to this lack of access to testing facilities, the CSIR has been developing mobile laboratories. These self-contained units do not depend on the availability of electricity or running water, as they use technologies that make use of local water, batteries, solar energy, and specialised accessories/equipment. Field test kits to evaluate both pavement surfacing and borrow materials for use as wearing course on unsealed roads ensure that the quality of the construction is appropriate.
The technologies have been successfully demonstrated in South Africa and there are also potential applications elsewhere on the African continent. The fact that such technologies give remote areas with a lack of resources the opportunity to maintain and produce quality road infrastructure has received positive feedback.
Morné Labuschagne
Abstract
With the global implementation of IMO 2020 regulations for marine fuels, as well as the move to green energy, international bitumen supply has been negatively impacted. In South Africa this is also true, with all but one crude oil refinery having closed due to the high capital cost of upgrading to comply with low sulphur limits imposed on marine fuels. The heavy crudes that have good bitumen residues are not fit for the manufacture of low sulphur marine fuel unless the refineries are upgraded to extract excess sulphur.
The move towards more environmentally friendly manufacturing processes to reduce emissions has necessitated the development of alternative binders for flexible pavements that have less impact on the environment, lower emissions, and capture CO2.
"Instant Bio Bitumen" is a carbon-negative alternative to bitumen derived from refining crude oil. It combines asphaltenes extracted from naturally occurring hydrocarbon resins with a maltene component derived from waste cashew nut shells. “Instant Bio Bitumen” can be produced by either blending these components or by individually introducing them during the asphalt manufacturing process. Apart from providing a convenient solution for the use of bitumen in remote locations, "Instant Bio Bitumen" dramatically reduces the SHEQ risks associated with bitumen traditionally derived from crude oil as well as total CO2 emissions.
The test results produced during a preliminary laboratory study by AECI Much Asphalt indicated that the properties of an asphalt mixture prepared using a traditional 50/70 penetration grade bitumen (using the wet blend process), were comparable to that of an asphalt mixture prepared from "Instant Bio Bitumen" (using the dry blend process).
Although limited laboratory work has been conducted to date, this research publication aims to create awareness and share AECI Much Asphalt's experience.
Keywords: Instant Bio Bitumen, IMO 2020, Asphaltenes, Maltene, SHEQ, Asphalt
About the Author
Morne Labuschagne holds a Chemical Engineering qualification and started his career in Colas South Africa’s Central Laboratory in Cape Town in 2004. He spent 14 years testing, evaluating and developing bitumen emulsions, polymer modified binders, slurry- and micro surfacing seals and related bituminous road binders. During the last five years of his career at Colas, Morne headed the Research and Development Department and was also responsible for all technical and related matters within the group in the Southern and East Africa region. In 2018 Morne joined AECI Much Asphalt, where he holds the position of Technical Manager. He is at the helm of the Central Laboratory and oversees Research and Development activities within the organisation. Morne’s key responsibilities include bituminous binder- and hot mix asphalt related research and product development.
Dr Haleh Azari and Dr Alaeddin Mohseni
Superpave introduced a Performance Graded (PG) system for bitumen selection. The high and low temperature PG requirements for any location, based on climatic conditions, are specified by LTPPBind. The PG of the bitumen in any location should match the PG requirement from LTPPBind. The low-temperature PG of bitumen is determined using a device called Bending Beam Rheometer (BBR) and the procedure is outlined in AASHTO T 313 and ASTM D6648. However, the BBR test is very time consuming and laborious and involves several hazardous liquids as listed in Section 8 of D6648. The Incremental Creep for Cracking at Low Temperature (iCCL) test is a low-temperature binder test procedure for determining low-temperature properties equivalent to those of BBR; however, significantly faster, safer, more reliable and less costly. iCCL provides continuous low-temperature grade (Low PG), as well as m-value, S, and delta Tc equivalent to those of BBR using PAV or RTFO aged binder. The test takes 30 minutes and has 2-3 times better between-laboratory precision than BBR. The iCCL test is performed using a Dynamic Shear Rheometer (DSR), which is significantly more advanced, in terms of load and temperature control, than the BBR device. The test may be conducted using a portable DSR that does not require compressed air or a water bath. AASHTO has recognized iCCL as a surrogate test for the BBR by the new Standard Practice PP 112 (2021). This paper outlines comparison of over two thousand pairs of iCCL and BBR test results from testing 367 RTFO aged and 635 RTFO/PAV aged binders from 23 U.S. laboratories, 13 of which performed the tests in house. The results show that iCCL provides low-temperature properties within the allowable limits of the BBR test in AASHTO T 313.
About the Authors
Dr Azari is the president of Pavement Systems in the USA, specializing in research and development in field of pavement materials. She and her colleagues have developed UPTiM test methods, including iCCL and iRLPD, for unified characterization of asphalt binder, mixture, and mastic. Dr Azari has also managed the AASHTO Research Program for eight years, as the principal investigator of several NCHRP projects for improving AASHTO specifications. She earned her Ph.D. in Pavement Materials Testing from the University of Maryland at College Park.
Dr Mohseni has been involved in the SHRP project since 1992 and contributed to the development of current PG asphalt binder grading system for Superpave. Dr Mohseni founded Pavement Systems LLC in 1994. He introduced a new Low-Temperature model for Superpave in 1997 to replace the SHRP model and a new model for High Temperature PG in 2004 based on Degree-Day concept. Since 2005, Dr Mohseni has worked on several new test methods based on an incremental concept, namely UPTiM. Dr Mohseni earned his Ph.D. in Civil Engineering (Pavements) from the University of Illinois at Urbana-Champaign in 1990.
Maurice Arbelaez
Abstract
Coming soon
Matthew Fisher, Amanda Padotan, Nico Herbst & Philip Snyman
Abstract
Our journey started with a vision to digitise laboratory processes from start to finish. Off-the-shelf products were available, but they could not provide a holistic solution. We were after a product that could take our current systems and transfer them into a digital space without changing our procedures, reduce human error and improve our delivery time.
The first step we took was to digitise the in-field testing by incorporating an already established solution; although the software was outdated, it provided the necessary service. Concurrent with the in-field testing, we began the development of our own mobile app, which allowed clients to book testing services and stay up to date on test results.
Phase 2 included developing our LIMS system, which would be tailor-made to our specific needs and processes. The system allowed all lab procedures to be digitised and would serve as the central hub for all our information from the field service app and laboratory testing.
The lessons learned from our journey were significant. We realised that we had to take a step backwards before we could move forward again at pace. We are now building solutions 10x faster, reducing implementation and maintenance costs by 50% while gaining superior functionality compared to traditional development. We are able to achieve this by leveraging industry-leading low-code automation platform capabilities.
This paper will discuss our journey, lessons learnt and plans for the future.
SEALS FOCUS AREA
Hlo Mthiyane
Abstract
Anionic emulsions are not used widely in South Africa for construction of chip seals. The main reason reported is that most of the aggregates are negatively charged, resulting in the opinion that the negatively charged anionic emulsion will not adhere properly. However, the slow setting characteristics of the anionic emulsions produced locally could be advantageous for labour intensive works.
This paper presents the results of an experimental study that was conducted, firstly, to investigate the effect of aggregate mineralogy on the degree of adhesion (the bond) between the aggregate and the bitumen using anionic bitumen emulsions. Secondly it evaluated the potential development and use of new adhesion agents/anti-stripping agents for anionic emulsions used in chip seal applications. For this purpose, the degree of adhesion achieved between the emulsions used and a range of selected aggregates was measured by means of a series of internationally recognised laboratory adhesion tests (such as the Boiling Water as ASTM 3625 and Plate–Stripping Test as AS1141.50 Australian Test Method).
The experimental laboratory work confirmed that the degree of adhesion between the aggregate and emulsion is governed to a large extent by aggregate mineralogical composition, and particularly its associated electrostatic interaction with a given emulsion.
Based on the result obtained in this study, it is concluded that the addition of adhesion agents to the anionic emulsion facilitated a greater degree of adhesion (stronger bond) between the residual binder of the anionic emulsion and the negatively charged aggregate.
About the Author
Hlo Mthiyane is Product Development Manager at AECI Specialty Chemicals. She is an inquisitive and passionate chemist specialising in road additives. Hlo has a Chemistry Degree and has worked as a chemist in research and development for more than 15 years.
Cara Mari Prinsloo
Abstract
The use of precoating fluids is standard practice in South Africa to improve adhesion between aggregate and hot bituminous binders and to minimise the risk of aggregate loss. Pull-out load tests provide an indication of the load required to dislodge a stone from a bituminous binder surface (bond strength).
Method MB-8: Pull-out test method for surfacing aggregate provides repeatability challenges such as raising a scale at a constant rate whilst simultaneously reading the value from the scale and monitoring the exact moment that the stone dislodges from the surface. Ambiguity is also a concern in the MB-8 method as the use of glue may influence load readings, adding an additional adhesive element.
The first objective of this study was to develop an apparatus to improve the existing pull-out test method. The second objective was to test the effectiveness of different precoating fluids available in South Africa, to improve the bond strength between different aggregate and binder types.
The paper firstly describes the newly developed apparatus and highlights the improvement in accuracy and repeatability. Secondly, the effects of different precoating fluids containing kerosene, water and/or specific chemicals are discussed. Depending on the base binder, the study indicated that similar results can be obtained when using bitumen emulsion pre-coated material to their cutback counterpart.
About the Author
Cara Prinsloo is a third-year student in B Eng Civil Engineering at the University of Pretoria. This year she undertook an internship at TOSAS which involved shadowing and assisting with laboratory work and experimental testing of a newly automated pull-out test for the adhesion abilities of different precoating materials. She is passionate about the environment and the potential of civil engineering to further sustainability.
Herline van der Spuy
Abstract
The intermediate temperature (construction and operating temperature) response of a binder influences the initial and longer-term performance of a seal. The creep and recovery characteristics of a binder during construction, initial trafficking and with ageing, at these temperatures, influence the resistance to stone orientation (loss of macro texture) and ability to retard crack reflection.
The goal of this study was to evaluate different types of binders used in South Africa and their performance at various temperatures, with the focus on intermediate temperatures. The properties of original and short-term aged binders were determined to evaluate changes from the refinery to the initial stage after construction. The creep and recovery characteristics were analysed to determine the behaviour of the binder, and how it could link to stone orientation.
The materials used in this study were an unmodified binder and four modified binders. The modified binders consisted of two elastomers and two rubber binders. The Bending Beam Rheometer was used to obtain data at cold temperatures, and the Dynamic Shear Rheometer for intermediate and high temperatures. The Multiple Stress Creep and Recovery (MSCR) test was used to obtain the non-recoverable creep compliance (Jnr) and the recovery (%R).
Results showed that the type and degree of modification significantly influences the performance of binders at intermediate temperatures. The modified binders demonstrated characteristics which affect stone orientation in the surface layer and could be utilised in adjustment of conversion factors used in the seal design process.
About the Author
Herline van der Spuy completed her Bachelor’s in Engineering (Civil) in 2019 and has recently received her Master’s in Engineering (Road) degree from the University of Stellenbosch. In her final year as an undergraduate student, Herline created a successful predictive model as to which type of person would be more likely to recycle and why. She has gained student experience analysing transport data with SMEC and assisting in site investigations for the Kommetjie Road Upgrade Project and the Strand Seawall Project with the City of Cape Town.
Nokuthula Mazibuko
Abstract
Flushing of a chip seal occurs when the binder rises to the top of the seal layer relative to the stone, mainly due to the penetration of the seal aggregate into soft substate, orientation of the stone, binder rise, over-application of binder, or use of soft binder. A flushed seal poses a safety risk to the road user due to the loss of macro-texture of the surfacing, which plays a key role in providing skid resistance in wet conditions.
On the N2 section 9, the surfacing was treated with texture slurry and resealed using a 20/7 double seal with a S-E1 polymer modified binder in both the tack coat and penetration coat, and with the final application of a diluted cat 65 spray grade emulsion. During an extreme hot spell, severe bleeding with bitumen bubbles appeared in certain sections of the road, which also caused pick- up of the seal in the wheel tracks.
The phenomenon of binder rise with bubbles was first reported in 1972 and later investigated in New Zealand. The investigations concluded that the small bubbles appearing even outside the wheel path were not caused by volatiles. The bitumen bubbles were caused by vaporisation of moisture in the base or at the bottom of the seal, which either enters the layer from above or the bottom layer was saturated prior the seal being placed.
This study presents the investigation process and results of moisture contents obtained in good and failed areas. It further highlights the effects of vaporisation due to increases in moisture content and temperature in the cores extracted from the abovementioned road section. The results will assist in improving the current specification by providing a measurable parameter before seal work can commence after rain (COTO 2020, A10.1.3.5).
About the author
Nokuthula Mazibuko is a Candidate Engineer with SANRAL, based in the Gqeberha office. Her current focus is preliminary assessment and design work for the R62 section 7 between Joubertina and Kareedown in the Eastern Cape. Nokuthula began her career as a Graduate Engineer at Aurecon on completing her Bachelor’s Degree in 2014 and gained experience in various locations, including 18 months on the site of the SKA project in Carnarvon working on engineering solutions for road and drainage structures. Nokuthula graduated cum laude with a Master’s in Civil Engineering at the University of Stellenbosch in 2020.
Thomas Modise
Abstract
Slurries are used in South Africa as overlays, thin texture treatments, for rut filling, and within the structure of Cape seals and slurry bound macadam seals. It is considered a low-risk application and ideal for labour intensive projects. However low binder film thickness, resulting in a poor ability to retard crack reflection, and initial permeability often result in slurries not being selected as surface treatments.
The use of anionic organofunctional New-age Modified Emulsions (NME), without the addition of cement, to improve marginal road building material is considered highly successful. Treatment with properly formulated and scientifically designed modified emulsions results in significant Unconfined Compressive Strength (UCS) and Indirect Tensile Strength (ITS) being obtained and improves compact ability (ease of densification) and water proofing.
Following a successful field trial with an anionic organofunctional silane modified emulsion slurry (with no cement filler), a project was initiated to compare the properties with conventional slurry. The introduction of ITS and permeability testing in the slurry design process proved to be a significant advancement.
This paper discusses the process followed and results obtained comparing the properties of conventional and modified emulsion slurries, as well as a recommended protocol for future slurry designs.
BINDERS FOCUS AREA
The exponential growth of the pavement industry over the decades, together with increasing traffic loads and volumes, are the main contributors to the need for binder modification. For this reason, polymers such as styrene butadiene rubber (SBR) and styrene butadiene styrene (SBS) have long been utilized as binder performance modifiers.
Even so, researchers have continued seeking more affordable alternative modifying materials due to the high cost of these polymers. Nanotechnology is a field that could make it possible to achieve impactful modifications to the asphalt binder. Accordingly, nanoclay has been put forward as a suitable alternative by researchers because of its natural abundance and economic benefits. The addition of small amounts of nanoclay has been reported to enhance properties such as stiffness, rutting resistance, low-temperature cracking resistance and storage stability. Oxidation, ageing susceptibility reduction and further advantages are expected in the long-term performance of the asphalt.
This study assesses the effects of nanoclay modification on the short- and long-term performance of the binder and the effects of macro vs. nanoclay modification on the rheology of the binder.
About the Author
Mookgo Sephooko completed her B Tech: Engineering Civil in 2011 and her N Dip: Civil Engineering in 2012, both at the Central University of Technology. She is currently completing her MSc degree on the topic of Nanomaterials modification of asphalt binders and Mastic Asphalt at the University of KwaZulu-Natal. Mookgo has been a Junior Lecturer at the University of South Africa for the past two years. Prior to that she obtained experience in the field at eThekwini Municipality, Sam’s Mega Connections, and Bigen Africa Services, as well as standards writing at the SABS, and working as a Technical Assistant at the Central University of Technology.
Francois Engelbrecht
Abstract
The parameters of the Bending Beam Rheometer (BBR) test give an indication of an asphalt binder’s ability to resist low temperature cracking. The standard test procedure of the ASTM D 6648-08 (2012) was used to determine the flexural creep stiffness of bituminous binders using the BBR. The method specifies two test specimen moulds fabricated from either aluminium/stainless steel or silicone for low-temperature testing.. Bituminous binders were evaluated at various ages to analyse their changes to rheological behaviour.
This research included several degrees of laboratory simulated ageing: Unaged, Rolling Thin Film Oven (RTFO) and with the Pressure Ageing Vessel (PAV) at 20 hr, 40 hr and 80 hr. The unaged and aged binders were tested with the BBR ranging from -36°C to 0°C, using rubber and steel moulds, and Dynamic Shear Rheometer (DSR) at temperatures ranging from 10°C to 70°C.
Due to noticeable differences resulting from each mould type, the dimensions of the BBR beams were measured before and after testing. The rubber moulds appeared to be at the lower limit of the specification tolerance and the steel moulds at the upper limit. In some cases the rubber-moulded beams did not meet the ASTM requirements, and the results were unusable. The tests done with the steel moulds resulted in less fluctuation in the results of bituminous binder stiffness.
The research concludes that the steel moulds are more accurate during the BBR testing to evaluate the binder’s behaviour in low temperatures. The standard test method of the ASTM prescribes that both moulds may be used.
About the author
Francois Engelbrecht obtained his BEng degree (2015) and MEng degree (2017) in Pavement Engineering at Stellenbosch University. He gained specialised experience in the rheology of bituminous binders while undertaking his Masters research on “Age related performance of typical seal binders in South Africa” and presented a paper on this research at CAPSA 2019. Francois works for the Western Cape Government Department of Transport and Public Works.
Many researchers have demonstrated the evidence of a changing climate. It’s also been shown that climate change will have negative impacts on agriculture, health, water and food supply to name a few sectors. This presentation is based on a study conducted at the CSIR on the effects of climate change on roads, with particular focus on the effects of rising temperatures on bituminous binders used for building asphalt roads in South Africa.
The study is important because it presents a practical solution to making South African roads more adaptable to the inevitable impacts of a changing climate. The interdisciplinary study incorporated climate model projections with algorithms used for road material selection to quantify the effects of climate change on bituminous binder selection.
Rising temperatures as a result of climate change were investigated by incorporating climate model projections and geographical information systems into current road material selection practices. Current design methods incorporate performance-graded (PG) specifications which were introduced in 2019 by the Road Pavement Forum and now form part of a South African National Standard. The investigation on adapting asphalt pavements for climate change intends to guide best practise on how to incorporate climate change effects into current specifications for bituminous binder selection.
The temperature of a road surface is dependent on the climate in the area and plays an important role in determining the stiffness of the asphalt layer. Most climate models predict an increasing rate in the rise of average air temperatures in the near future. As the average air temperatures increases, it is expected that the frequency and duration of extreme temperatures will also rise. This will have a direct impact on asphalt pavement performance by increasing the potential for permanent deformation of pavements and the rate of age hardening of asphalt binders. Interpolated maps of minimum and maximum pavement temperatures were generated using climate model data for two 20-year periods, up to the years 2040 and 2060. The same model was used to generate two historic 20-year periods, going back to 2000 and 1980. The maps produced from the study can eventually be used to identify adaptation measures which may include modifying current design and maintenance practices.
The overall objective is to assist engineers and urban planners build roads that can withstand evolving demands in order to build climate resilient infrastructure that can inform adaptation policies for industry.
About the Presenter
Refiloe is research civil engineer in the Pavement Design and Construction Research Group within the Smart Mobility Cluster and Transport Infrastructure Engineering Impact Area at the CSIR. Her research interest and application is concerned with sustainable development in the field of transport infrastructure, in particular adaptation and resilience of South African roads against the impacts of climate change. Her work is aimed towards providing cost-effective and sustainable solutions to road design and construction. Refiloe graduated from the University of the Witwatersrand in 2011 with her undergraduate degree in civil engineering. She joined the Council of Scientific and Industrial Research (CSIR) in 2014 as a candidate researcher where her research work has focussed on the use of industrial by-products as an alternative road and rail construction material. Her recent work has focussed on incorporating climate change strategies into transport infrastructure design and adaptation.
Dr Elaine Goosen
Abstract
Bituminous material failure manifests distinctively in specific ranges of the binder behaviour spectra. Permanent deformation, and fatigue and non-load-associated cracking, are associated with high, intermediate, and low-temperature behaviour. Additionally, premature oxidation of bitumen in low-stiffness ranges during plant processing may complicate and hinder the quality of in-field asphalt compaction.
Ageing ratios are included in the South African Performance Grade Specification to control ageing in the intermediate stiffness range. In the context of abundantly available performance parameters, transitioning engineering knowledge from penetration-viscosity to performance grades and the increasing prevalence of bitumen importation, this paper investigates whether the ageing rates are consistent over the binder behaviour spectra.
Performance parameters in the distinct behaviour ranges are analysed for neat, laboratory-aged and recovered binders. Ageing and the mechanisms influencing relative susceptibility throughout the behaviour spectra are explored. Modified and unmodified binders are evaluated using Dynamic Shear and Bending Beam Rheometers to develop ageing ratios for DTc, Gvet, wc, Gint, G-R and Tmax,cont. The relative ageing represented by each parameter is examined.
It is observed that ageing over the binder behaviour spectra is influenced by the initial performance grade, source, and type and degree of modification. These trends may assist in selecting suitable binders and premature failure investigations.
Elaine is a Pavement Engineer and Lecturer in Civil Engineering at Stellenbosch University, specialising in Pavement Engineering and Bitumen Rheology. Elaine completed her BEng in Civil Engineering in 2011 and her PhD in 2021, with the award of various bursaries and scholarships testifying to her talent and dedication.
She spent a semester at Technische Universiteit in Delft, Netherlands, as an Exchange Student in Civil Engineering, and worked for WorleyParsons RSA as a Graduate Civil Engineer and then Assistant Resident Engineer in Roads and Stormwater.
Elaine is establishing her research career focusing on sustainable pavement materials and applying numerical models and machine learning to materials datasets.
RECYCLING FOR FLEXIBLE PAVEMENTS
Salome Naicker and Krishna Naidoo
Abstract
Project-specific quarrying of aggregate for asphalt manufacture has numerous advantages. With aggregate making up almost 95% of the materials that go into asphalt, the capital costs can balloon significantly when consequential costs such as additional trips generated by haulage are an uncontrolled variable. However, even with all this optimally resolved, there are still many considerations with degrees of varying influence that need to be managed and leveraged to fully realise the advantages of project-specific quarries.
The Upgrade of National Route 3 project by the South African National Roads Agency aims to achieve value through project-specific quarrying. The paper sets out the many considerations to achieve balance and sustainability in the initial selection of aggregate for asphalt for future use in asphalt recycling.
About the Authors
Salome Naicker is a registered Professional Engineer with 15 years of experience in the civil engineering Industry. She focuses on road construction and is employed as a Project Manager at SANRAL. Salome has vast experience in design and construction and is currently managing several large projects in KwaZulu-Natal, including the flagship Upgrade of National Routes 3 and 2. She is also making headway in the aggregate industry with her management of the provision of crushed materials for the N3 upgrade.
Carl Bierman
Abstract
Asphalt, the surfacing layer for most of our urban roads, consists of high-quality aggregates mixed with very expensive bitumen. To mix the aggregate and bitumen, the bitumen is heated to temperatures exceeding 160°C. This makes asphalt a very expensive material in terms of economics and environmental impact. Each year, thousands of tons of asphalt are milled off and replaced to maintain the roads in our major cities, producing huge stockpiles of reclaimed asphalt waiting to be recycled.
Foamed bitumen technology provides a solution to recycle 100% of this high-quality material with a few additional benefits.
Jakes Gerwel Drive connects South Africa’s two major highways, the N1 and N2, making it one of the most congested roads in Cape Town. Rehabilitating this road is challenging as closing lanes during peak hours will result in major traffic issues throughout the city. Recycling asphalt using foamed bitumen technology presented an environmentally friendly solution that allowed for deep road rehabilitation to a depth of 340mm during a single night shift, with the road open before the morning traffic arrived.
About the Author
Carl Bierman graduated from Stellenbosch University with a Civil Engineering degree in 2016, and a Masters in Pavement Engineering with a focus on the design of Bitumen Stabilised Materials (BSM) in 2018. He went on to spend three years learning the ins and outs of the construction industry with Roadmac Surfacing Cape, and then moved to BVi Consulting Engineers Western Cape, where he works as an Assistant Contracts Engineer and a BSM application engineer.
Thembalethu Mhlanga and Wynand van Niekerk
Abstract
The growing worldwide implementation of pavement recycling and bitumen stabilisation technologies has led to an increased need for reliable performance evaluation techniques for bitumen-stabilised materials (BSMs). Laboratory compaction has seen an evolution in the equipment and methods used, with the objective of achieving laboratory compaction that adequately simulates field compaction. While using compaction equipment and methods for granular materials may seem to be the sensible approach to achieving the required compaction of BSM specimens, the following challenges were faced:
- Inadequate energy of existing equipment to achieve required specimen densities
- A large variability of particle sizes created by variability in composition of RA used for BSM mixes, leading to inconsistent results on standard specimen sizes with large aggregates
- Inconsistent specimen densities achieved from existing compaction methods.
This paper describes the stages in the evolution of laboratory compaction equipment for BSM specimens in trials that were conducted over a 10-year period. Test results from the trials show a great reduction in variability of the specimen densities. An additional benefit was an improvement in ITS results, adding to the reliability of the performance evaluation of BSM mixes.
Thembalethu Mhlanga holds a BSc in Civil Engineering which she completed at Wits University in 2018. She works as a Civil Engineer in the Pavement and Materials Department at ROMH Consulting. Since completing her degree, she has acquired experience in road condition assessment, pavement design, materials sourcing and design and contract administration for new projects, periodic maintenance and road upgrade projects. She has also been extensively involved in SANRAL Routine Road Maintenance projects for various national roads.
Wynand van Niekerk is Managing Director of BSM Laboratories. He started working in the soils laboratory industry in 2002 as a field technician at LABCO in Port Elizabeth and joined Contro Lab in 2005 as Laboratory Manager on several site laboratories in the Eastern Cape. In 2009 Soilco Material Investigation approached Wynand to join BSM Laboratories focusing on bitumen stabilised material testing. His contribution to the revision and replacement of TG2 2009 with the TG2 2020 document has been vital to the industry.
Jannie Hattingh, Riaan Burger, Prof. Kim Jenkins
Abstract
The maintenance, rehabilitation and upgrading of a road network can be expensive, and high-quality materials are not always available. The re-use of materials is also an important consideration, as the long-term sustainability of non-renewable resources is questionable.
In recent studies, researchers from the Council for Scientific and Industrial Research (CSIR), University of Pretoria (UP), and others used nano-modified bitumen emulsions to construct base and sub-base layers with materials that are not typically suitable, or marginal at best. However, they showed promise in potential cost savings, shorter construction times and longer pavement life, in most cases at significantly lower bitumen content than typical, and without the addition of cement.
South Africa began using reclaimed asphalt (RA) in the early 2000s. By 2014, approximately 10% of all asphalt used was RA. Several recent projects in the Western Cape have successfully designed and constructed Bitumen Stabilised Material (BSM) base layers using 100% RA, bitumen, and cement. While the previous studies focused on the use of nano-polymer modified bitumen emulsion to improve marginal, or conventionally unsuitable material, the use of nano-polymer modified bitumen in conjunction with RA has not been investigated in South Africa, to the knowledge of the authors.
A typical RA sample contains around 5% residual binder and 95% high-quality aggregate, two highly valuable non-renewable resources. The correct utilization of these resources can result in significant savings. A typical mix of bitumen and cement for BSM base layers in current practice is approximately 2% bitumen and 1% cement. Bitumen and cement are expensive materials that can significantly increase the cost of pavement construction.
The purpose of this article is to evaluate the suitability of using 100% RA and nano-modified bitumen to construct a BSM base layer, and to demonstrate that using 100% RA and nano-modified bitumen can not only provide financial benefits but also at least match the performance of existing BSMs.
About the Author/Presenter
Jannie Hattingh is a Resident Engineer with AECOM. He has a N.Dip Civil (CUT), BTech Civil (CUT), BSc (Hons) Applied Science: Transportation planning (University of Pretoria), and is currently in the final year of his M.Eng (Civil) in pavement and materials engineering at the University of Stellenbosch.
CHEMISTRY FOR ROADS FOCUS AREA
Phindile Mathenjwa
Abstract
There are several factors that affect the performance of the emulsion such as the acidity in Anionic emulsions. Asphalt from varying crude oil sources (such as Paraffinic and Naphthenic) and processes impact the ability of a slow setting emulsified asphalt to mix with a finely divided high surface area material such as Portland Cement and crusher dust.
The acidity in Naphthenic bitumen is beneficial in Cationic emulsions, but it has a negative impact on Anionic slow set emulsions. It influences the slow setting properties to rapid setting.
Water can also possess chemical ionic constituents that can be detrimental when calcium ion attack from the cement mixes with the slow set emulsion, which can lead to breaking the emulsified asphalt.
The exercise was done to illustrate the structural build-up of a continuous calcium polymer that forms thixotropic properties in Anionic slow set emulsion by propagation of the calcium soap gel polymer, which is beneficial for slurry seal and waterproofing sealant applications. The effect of having the chain-stopper in the emulsion system introduced by the presence of an acid (e.g. Naphthenic acid), can be detrimental when mixing cement with slow set asphalt emulsion.
About the Author
Phindile Mathenjwa is a Technical Manager at AECI Specialty Chemicals. She has BTech in Chemistry, BSc Environment Management, and BCom in Management. In 2015 she received an award as one of the top three students in the Foundational Management Development Programme at the Gordon Institute of Business Science. Phindile was employed by NCS Resins prior to joining AECI in 2014. She works with distributors in Asia, Australia and the US, developing new business opportunities and troubleshooting in road science for customers worldwide.
Mikhil Ranka
This research uses laboratory experiments and molecular modelling to represent the optimum dosage and conditions at which a specific organosilane modifier (called OS1 in this work) enhances the resistance to moisture at the bitumen-aggregate interface. The OS1 forms a coating layer on stone aggregates and bridges between the aggregates and bitumen molecules.
Moisture-induced shear-thinning index (MISTI) measurement found the best moisture resistance for a sample with an optimum dosage of 0.6% OS1 on highly susceptible acid rich binders. The performance of the optimum OS1-modified bitumen was not reduced after being exposed to short-term and long-term aging, indicating low susceptibility to thermal and oxidative degradation. MISTI testing clearly demonstrates the moisture resistance that OS1 can provide to tack coats and make them impermeable to moisture induced delamination.
Keywords: organosilane, durability, moisture damage, adhesion, bitumen, aged bitumen, tack coat, silica surface.
About the Author
Mikhil Ranka, Ph.D., is a Director for Zydex Industries and is responsible for new technology development and R&D in the area of polymers, emulsifiers, and colloidal systems. Mikhil received his Ph.D. in Chemical Engineering, with an emphasis in polymer chemistry, from the Massachusetts Institute of Technology, Boston, USA.
Shane Woods
Abstract
For many years people have worked on ways to make our roads more durable to prevent potholes and other road damage. The goal of this experiment is ultimately to gain a better understanding of the chemical elemental composition of materials used in the manufacturing of asphalt final-products (roads/tar).
For this I would like to look at microwave digestion in combination with ICP-analysis. Microwave digestion can break down tough materials (such as asphalt) into their chemical-elemental composition through acid oxidation/reduction at high temperatures. The sample can then be analysed using ICP-analysis, which will result in the chemical-elemental composition together with its concentrations of each.
This information must be interpreted and could ideally lead to optimisation of the binding of the different raw materials that can enhance the strength and durability of the final product (pavement).
About the Author
Shane Woods obtained his BSc (Hons) in Biochemistry from the University of Johannesburg and started his career as a lab analyst, later progressing into a research and development role and eventually sales. He joined the sales team at Anton Paar Southern Africa in 2019 as part of the Measurement Department, responsible for the sales and support of the Analytical and Synthetic Chemistry (ASC) product range. He was appointed as ASC Product Manager in July 2020, with the main focus of providing solutions for R&D and quality control laboratories in South Africa.
Jocelyne Abreu
In a world where the supply of bitumen and other road building materials is continually changing and the quality and chemical makeup is not consistent, it becomes ever more important to understand how these materials will interact with one another.
Electrophoretic Light Scattering is a powerful tool used to understand the surface interaction between the dispersed and continuous phases of an emulsion or suspension, by means of zeta potential. We can understand and optimise concentrations of emulsifiers and additives that may affect the stability of bituminous emulsions, allowing a high-quality product with minimum use of these expensive additives.
The streaming potential technique allows us to measure the zeta potential of aggregate and other road building materials. Quantifying the cationic or anionic state of an aggregate can also assist in designing the most suitable bituminous emulsion for strong adhesion to the aggregate. Quantitatively understanding how each layer of the pavement interacts with the other layers can allow us to understand overall performance, as we would be able to predict potential repulsive and adhesive properties between the layers.
About the Author
Jocelyne has a BSc (Hons) in Applied Chemistry from the University of Pretoria. She joined Anton Paar Southern Africa in 2013 as a Sales Specialist for Rheology and was promoted to Product Manager for Rheology in 2015. Since 2018 she has overseen the Characterization team as Business Unit Manager.
Sinethemba Mkhize
Abstract
Silane additives undergo three crucial mechanisms, namely hydrolysis, re-esterification and condensation. These reactions are influenced by soap phase pH levels. The cationic emulsion soaps are prepared with hydrochloric acid to reach pH 1.5- 3. Sodium hydroxide is generally used for anionic emulsions to produce a soap phase at pH 10.5 – 12.5.
Two types of silane additives, namely, cationic based surfactant silane and anionic based surfactant silane, were tested in solutions at various pH levels. Further tests were conducted to use these differently charged silane additives in cationic and anionic emulsions. The incompatibility between silane additive surfactant charge and emulsion charge led to premature self-reactions, observed as additive crystals (silane converted to polysiloxanes) in solution. The application tests on emulsions showed good performance where there was good compatibility between similar charges of silane additive chemistry and emulsion charge or type.
PAVEMENT DESIGN FOCUS AREA
Aubrey Shabangu & others
Abstract
There is a need for additives to improve the strength, maintenance, and performance of the unsealed South African road network, especially under inclement weather conditions. Agrément SA certified Permazyme is an alternative soil stabiliser whose fitness for purpose as an additive has been tested on four pilot sites in Pretoria, Gauteng.
The study is focused on assessing the post-treatment behaviour of Permazyme-treated roadbeds on the four pilot sites - Mamelodi West, Soshanguve Cemetery, Mamabolo Street and Catherine Street. In-situ Direct Cone Penetrometer (DCP) tests were chosen as the appropriate method of characterising the long-term performance of Permazyme-treated roadbeds, where scheduled testing occurred every 2-3 years.
Permazyme’s effectiveness as an alternative road stabiliser is best demonstrated by its ability to improve the bearing capacity of the subgrades. Performance monitoring DCP tests conducted on the four sites revealed high resistance capacities with in-situ bearings greater than 400 kPa for the first 300 mm depths.
While performance data continues to be collected, the results presented indicate that Permazyme could be adopted as an alternative road stabiliser solution for low volume trafficked pavements, especially rural gravel roads.
About the Author
Aubrey Shabangu is qualified with a B.Eng in Civil engineering Sciences and currently finalizing an M.Eng in Structural Engineering from the university of Johannesburg. His area of research is focused on investigating the effects of loading on flexible storm water pipes subjected to light traffic and geostatic soil stresses through an Finite Element Analysis (FEA) study. Aubrey is employed at Experts On The Go (EOTG) as a technical engineer and has gained vast experience in traffic, transportation engineering, capex infrastructure planning, road safety and project management.
Joanne Muller & Deolon Moodley
Abstract
The uptake of performance-property-based mix designs in South Africa has seen many laboratories equip themselves to meet industry requirements in recent years. Though the testing regime for Sabita Manual 35 has many intricacies that need to be navigated, gearing up for fatigue life testing has been by far the most cumbersome.
The challenges that testing facilities across the country have faced regarding four-point-bending testing are numerous and range from equipment limitations to inconsistencies in results and everything in between. Resolving these challenges without causing delays to projects or having incomplete or inconsistent data supplied to stakeholders is not always easy.
This paper highlights the challenges faced in providing credible fatigue data that can underpin balanced mixes. The ideal culmination of these balanced mix designs would further optimise asphalt pavement designs to facilitate more sustainable road infrastructure development.
About the Author
Joanne Muller
Joanne completed her Bachelor and Honours Degrees in Civil Engineering, followed in 2015 by her Master’s in Engineering Management, at the University of Johannesburg. She is an ECSA registered Candidate Engineer.
She began her career with AECI Much Asphalt in 2008 as a part-time Trainee, followed by two years as a Graduate Trainee in the company’s Gauteng Regional Laboratory. In 2013 Joanne was promoted to Quality Assurance Supervisor at the Benoni plant and in 2016 to Regional Laboratory Manager. In this role she strives to improve quality and cost metrics to meet strategic objectives and customer requirements.
Joanne’s experience in asphalt manufacturing, testing and design, together with her zest for problem solving, is also put to good use on working groups reviewing SANS standard test methods, Sabita manuals and protocols for industry.
Herman Mostert
Abstract
With ever-increasing transport needs, accessibility requirements and construction costs, the implementation of Low Volume Sealed Roads (LVSR) has increased in Namibia. Namibia’s Road Authority has launched a 5-year LVSR strategy for 2021 – 2025 to construct about 1 600 km of LVSR.
According to the Road Authority's Integrated Road Asset Management System (IRAMS), 82.9% of the road network is unsurfaced, with more than 90% carrying between 100 and 300 vehicles per day. The upgrading to LVSR reduces routine maintenance actions required on the unsurfaced roads, which in turn preserves increasingly scarce road building materials.
Several guidelines and manuals exist within southern Africa, but no formal document for the design and construction of LVSR has been adopted by Namibia’s Road Authority. The current practice in the design of LVSR uses these reference guidelines. Still, it leaves room for variability in designs between practitioners, leading to mixed performance and success in the field.
The general pavement design approach conducts DCP testing of the in-situ materials to determine the implicit strength expressed as a DN/penetration value (mm/blow) rather than a converted CBR (%) value. The typical outcome in Namibia is to rework the existing wearing course as a subbase layer and add a new gravel base layer before surfacing. Many LVSRs are surfaced with 14mm Cape seals, while 20mm Cape seals have also been widely adopted in Namibia to consider traffic volumes and the associated embedment. Geometric adjustment and drainage improvement are considered as needed to adhere to safety requirements.
About the author
Herman Mostert is a Transportation Engineer with Element Consulting Engineers Namibia. He has a N.Dip Civil (CUT), BTech Civil (UNISA), BSc (Hons) Applied Science: Transportation Planning (University of Pretoria), and an M.Eng Civil (University of Stellenbosch).
Carl Bierman
Abstract
The development of cold recycling technology using bitumen stabilisation is driven by ever-increasing economic and environmental pressures. The first best practice manual focused on foamed bitumen technology, the original TG2, was released in South Africa in 2002. This document provided a standardised methodology for mix design, structural pavement design and construction of foam bitumen treated materials.
The second edition of the TG2 was published in 2009, introducing a generic guideline for Bitumen Stabilised Materials (BSM) produced using either bitumen emulsion or foamed bitumen. In addition to providing a robust guideline for the industry, TG2 2009 also identified the shear properties of BSM as the key performance indicator.
Since 2009, researchers have interrogated data from more than 300 BSM mix designs and 69 long-term pavement studies. These considerable studies have led to developments in the performance properties of BSMs, a refined mix design process and improved pavement design methods. The latest TG2, published in August 2020, incorporates the previous decade’s research. The existing Pavement Number heuristic design system was further calibrated, and a mechanistic design function was developed specifically for BSMs. The improved design methods for BSMs allow the effective design of long-term road recycling solutions with many environmental and economic benefits.
This study covers the evolution of the structural design methods for BSM through an increased understanding of the material behaviour. Focus is placed on the various factors influencing the long-term performance of BSM and how they are incorporated into the latest design function.
About the Author
Carl Bierman graduated from Stellenbosch University with a Civil Engineering degree in 2016, and a Masters in Pavement Engineering with a focus on the design of Bitumen Stabilised Materials (BSM) in 2018. He went on to spend three years learning the ins and outs of the construction industry with Roadmac Surfacing Cape, and then moved to BVi Consulting Engineers Western Cape, where he works as an Assistant Contracts Engineer and a BSM application engineer.
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