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Competition in the field of road construction hasgenerated a continuing debate on the cost-effectiveness of various materials, and this discussion is nowhere morevigorous than in comparisons between asphalt andconcrete pavements.

All too frequently, however, the factual information usedto formulate supportive arguments is distorted, inaccurateor misleading, and a case in point arose recently when the Civil Engineering Contractor magazine published anarticle entitled: Concrete pavements – a viablealternative. Several statements contained in the articleboth misconstrueavailable data andcreate misperceptionsabout key issues suchas life cycle costing,source of constituentmaterials,sustainability,performance andversatility.

To dispel thesemisconceptions, andto ensure thatinfrastructureprovision is based onsound understandingof alternativematerials, Sabita hasundertaken to compile a fact sheet toexamine some ofthese parameters.

Life cycle costing:

It is widely believed (outside of the bituminousproducts industry) that as crude oil prices rise, concretepavements become more competitive vs asphalt forhighly trafficked roads over the life of the pavement.

The facts:

• The price of bitumen (see Figure 1) fluctuates inline with global macro determinants, especiallythe dollar price of crude oil and the rand/dollar

Volume 22 Issue 1 February 2008

3 RPF resolutions establish new task groups 5 BSM: call for industry input on design method 7 Gravel roads under threat as oil price rises 9 Members formulate new road map12 Rut challenge: tests start in 2008

IN THIS ISSUE

Sabita to develop fact sheets to dispel myths about alternative paving materials

Figure 1: Bitumen price fluctuations in line with otherkey materials

exchange rate. Figure 1 makes it clear, however,that increases in the price of bitumen (whichconstitutes only about 5% of asphalt’s total mass)are matched by increases in the prices of cement,aggregate and reinforcing steel;

• Asphalt prices will move proportionately in linewith bitumen prices and inflation attached to other locally produced materials, e.g. aggregates;

• The prices of cement, aggregate and steel and thus concrete are driven by local inflation (steel andcement manufacturing being large consumers ofenergy);

• During an analysis period of, say, 40 years it maybe true that a concrete pavement would onlyrequire limited, periodic maintenance and repairmeasures. An asphalt pavement, on the otherhand, will normally be designed to undergoperiodic rehabilitation or strengthening in theform of overlays. This staged construction, typical of asphalt pavements, is a major financial oreconomic advantage, for both tax payers andinvestors in concessioned highways; expenditurestreams are more closely matched to current roadusage or cash income from tolls.

• Full depth asphalt pavements, known as perpetual pavements, can be constructed (USA and Europe) to ensure longer life and lower maintenance costsover the design life. A perpetual pavement isconstructed so that distress occurs in the top layeronly, and the only rehabilitation required is theremoval of the surface and resurfacing with anasphalt overlay (see Figure 2);

• The perception that concrete pavements have atraffic carrying capacity significantly in excess ofthat associated with asphalt pavements has notalways been vindicated by experience with thistype of pavement in SA. It isalso true that high modulusasphalt technology is currentlyavailable which elevates thetraffic carrying capacities ofasphalt pavements to levelspreviously unattainable;

• Concrete is not economicallyviable as a cost-effectivepavement for low traffickedroads because of its high initialcost;

• Up to 80% of southern Africa’sflexible pavements are surfacedwith bituminous surfacetreatments as opposed to asphalt or concrete due to theircost-effectiveness.

Sabita has undertaken to disseminatethis information in the form ofcomparative graphics such as Figure 1,and to update pavement life cycleanalysis using the latest input costs todetermine comparative break-evencostings for concrete and asphaltpavements.

Local content:

A second misconception is that bitumen is an importedmaterial, since it is a product of refining imported crudeoil. This mistaken impression is exacerbated byconfusion between the terms bitumen and asphalt, which are often used interchangeably.

The facts:

• Crude oil is imported expressly for the purpose of manufacturing fuels such as petrol, diesel andparaffin, as well as lubricating oils. Bitumen is anend product of this process, and is thereforelocally produced. South Africa is in fact a netexporter of bitumen;

• Although cement is locally produced, about 50%of local demand is currently met by imports fromChina;

• Bitumen is the binder that glues the stone andsand together in the mixture ultimately calledasphalt. All the constituent materials are locallyproduced, with bitumen making up only about 5% of the asphalt’s total mass.

To set the record straight, Sabita intends producing ananalysis of supply and demand volumes for bitumen andcement, and a diagrammatic representation of thecomponent materials used in asphalt and concrete.

Sustainability:

The belief that concrete is more environmentally friendly than asphalt because the raw materials used in itsmanufacture are locally produced and recyclable cannotbe defended.

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Figure 2: Conceptual design of a perpetual pavement

The facts:

• Asphalt is 100% recyclable making it the USA’smost recycled manufactured material;

• The recovered bitumen in the reused asphaltremains active in the new mixture;

• The recycling of asphalt becomes moreeconomically viable as the cost of bitumen andaggregates increases;

• It is more cost-effective to overlay distressedconcrete pavements with asphalt than to recycle;

• When making a comparison between asphalt andconcrete to determine their respective energyconsumption and green house gas emissions, lifecycle inventories covering the entire process from the manufacture of the raw component materialsto the construction of the final pavement need tobe carried out. Such inventory studies have shown clearly that flexible pavements are moreenvironmentally friendly than rigid pavements(concrete). (Refer to the study by Gambatese andRajendran, 2005: Sustainable roadwayconstruction: energy consumption and materialwaste generation of roadways. American Societyof Civil Engineers, Proceedings of 2005Construction Research Congress. See website(http:/www.pubs.asce.org/wwwdisplay.cgi?0520020)

• Although the manufacture and construction of aconcrete pavement is a cold process, themanufacture of cement and steel is carried out attemperatures of up to 1600°C.

• Asphalt is mixed and laid at temperatures above130°C, and the bitumen itself is distilled at atemperature below 375°C. However, bituminousmaterials can also be manufactured and placed atambient temperatures by emulsifying the bitumenwith chemically treated water, with significantreduction in GHG emissions;

• Additives can also be added to the bitumen during the manufacture of asphalt to reduce the mixingand paving temperatures by up to 40°C.

• Waste materials such as rubber tyres, steel slagand glass are used in the manufacture of asphalt,and remain viable and available when the asphaltpavement in which they are used is recycled;

• Asphalt surfaces can be designed and built togenerate less vehicular tyre noise than concrete.

“In the environment of diminishing resources andincreasing costs in which the road construction sectoroperates, and given South Africa’s overriding need tofacilitate cost-effective infrastructure provision, a duty of care must be borne by industry associations such as Sabita to ensure that decision makers at all levels have accurate, up-to-date, and relevantinformation,” according to Sabita CEO Trevor Distin.

“Sabita has now undertaken to facilitate a thoroughanalysis of all the issues outlined above. The resultinginformation will be presented in a objective way anddisseminated for the guidance of both government andindustry.” q

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The following resolutions were adopted at the RoadPavements Forum (RPF) in November 2007:

#1: That an RPF task group be established under theleadership of Dennis Rossmann to assess and refinethe input parameters for seal design;

#2: That an RPF task group be established under theleadership of Arthur Taute to coordinate activitiesrelating to hot mix asphalt design, qualityassurance, performance and specifications in linewith the recommendations of CAPSA'07;

#3: That an RPF task group be established under theleadership of Fred Hugo to develop draft protocolsfor MMLS testing to address specific test objectives and to disseminate them to industry;

#4: (i) That the RPF stabilisation working group bereactivated under the leadership of Dr Phil Paige-Green to provide guidelines for theappropriate use of cementitious materials; (ii) That a cement-specific sub-task group beestablished for the development of a draft guidelineon the selection and use of the various cementtypes in road construction;

#5: (i) That the working group led by Piet Myburghfurther investigate the implications for adopting the ASTM/EU standards for bitumen materials asstandard test methods for South Africa, and thentable a firm proposal in this regard at the next RPF; (ii) If adopted, it needs to be supported byuser-friendly bench methods (training manuals) fullyaligned with the ASTM/EU standards;

#6: That an RPF task group be established under theleadership of Elzbieta Sadzik and Rob Lindsay todiscuss a new structure and way forward for theCOTO Road Materials Committee;

#7: That an RPF task group be established under theleadership of Trevor Distin to develop best practiceguidelines for the use of RAP in HMA;

#8: That an RPF task group be established under theleadership of Benoit Verhaeghe to developguidelines for environmentally sustainablepractices in the construction and maintenance ofroad pavements;

#9: That the sponsors of the RPF actively pursue theestablishment of a Roads Academy in line with theRISFSA document approved by Cabinet and obtain a mandate from the DoT to drive the initiative. q

14th RPF establishestask groups to tacklekey issues

The Australian AsphaltPavement Association (AAPA)Conference in Sydney from 21 to 24 October 2007, attended bySabita CEO Trevor Distin,examined a wide range of keyasphalt technology issues.

Organised by Sabita's sisterassociation in Australia and heldevery two years, the AAPA'07conference was also arranged tobid farewell to Ray Farrelly, who has been the incumbent CEO ofAAPA for the past 27 years anda regular visitor to our CAPSAconferences since 1994.

Distin reports that the maintheme of the conference was Innovation toImplementation, with a focus on innovations and theiracceptance. The conference was attended by more than200 industry delegates and the 31 technical paperspresented by both international and local experts covered the following key categories:

• Warm mix asphalt (6);• Spray seals (5);• Testing materials (4);• Polymer modified binders (4);• Stone Mastic Asphalt (3);• Conference & study tour feedback (3);• Sustainability (2);• Special binders (2);• Pavement design (1); and• Hot mix asphalt quality assurance (1).

Judging by the number of papers, the main interest wasin the development of warm mix asphalt technology,with presentations on experiences from as far afield asUSA, Canada, Germany, Norway and of courseAustralia. Essentially warm mix technology isaccomplished by lowering the binder's viscosity throughthe addition of an additive to the bitumen during themixing process. This enables the asphalt to be mixed and applied at temperatures up to 40

oC lower than the

temperature applicable to conventional hot bitumen,without any loss of compactability.

The most commonly used additives reported on wereAlpha Min (Zeolite), Evotherm (DAT process byWestvaco) and Sasobit, which has the added benefit of enhancing the binder's performance properties during itsin-service life. There was also feedback on adevelopment by Astec using a foam bitumen attachmentto a double drum plant, and Shell's WAM process.

In addition to the obviousbenefits that accrue fromreducing the mixing andapplication temperatures (suchas the reduction of emissions,fumes, odours and energyrequirements and improvedworker safety) significant otherbenefits were reported. Theseinclude:

• Improved durability of mixes due to less oxidation of thebinder during mixing;

• Increase in the distance thatHMA can be transportedfrom mixing plants;

• Extension of the workingseason for HMA before the onset of cold weather;

• Longer compaction window for thin asphaltlayers;

• Improved workability of stiff mixes which canfacilitate hand work and patching;

• Allows higher proportion of RAP to be usedbecause of a reduction in steam.

Environmentally friendly

These developments highlight the asphalt industry'spotential to evolve further by extending the conditionsunder which the product can be applied, and by makingit more environmentally friendly.

On the issue of spray seals it was interesting to note theadvances made in New Zealand with the introduction oflong term performance based maintenance contracts forreseals. With surface texture being the main criteria thishas led to the development of:

• variable transverse distribution spray bars toaccommodate varying surface texture;

• water blasting techniques to remove excess binder and improve texture.

This innovation has now led to contractors takingresponsibility for the seal design, but concern wasexpressed that the fixation on surface texture as a keyperformance parameter could result in seals becomingmore permeable to the ingress of moisture. Practitionerswith a particular interest in seals should note thatAustralia will be hosting the first conference on sprayseals in Adelaide in July 2008.

Conference papers can be downloaded from the website:www.halledit.com.au/conferences/2007/AAPA q

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"Down under" conference focusses on asphalt technology and bids farewell to Ray Farrelly

Ray Farrelly with Daniel Mashatoladuring a Sydney Harbour cruise

At the Road Pavements Forum (RPF) meeting inNovember 2007, an invitation was extended topractitioners to participate in the validation process ofthe structural design phase of the research project onbitumen stabilised materials (BSM), jointly sponsored by Gauteng Department of Public Transport, Roads andWorks (GPTRW) and Sabita.

Dr Fenella Long gave a presentation on the progressmade in this phase of the project, particularlydemonstrating the software for the pavement design andthe materials classification methods proposed.

Materials classification

Proper classification of the materials in each pavementlayer is essential to the performance of the structuraldesign method proposed. To meet this need a specificmaterials classification method was developed for theinterpretation of routine materials test data to yield arational, consistent materials classification.

The objective of the materials classification method istherefore to exploit the results of routine tests onmaterials to derive a consistent assessment of pavementmaterials. (Although the method was specificallydeveloped for use in pavements that incorporate BSM,the approach can be used in any pavement rehabilitationcontext.)

Careful consideration of the challenges posed byuncertainty, risk, small sample sizes, the empirical nature of test results and their interpretationindicated that a suitable approachmust incorporate the followingelements:

• Clear and rational formulationof the objective;

• Ability to handle vaguenessand uncertainty ofinterpretation; and

• Ability to work with smallsample sizes.

All these factors have been taken intoconsideration to arrive at a designequivalent (DE) materialsclassification for use as inputs in thestructural design of rehabilitated ornew pavements.

An example of the application of themethod proposed, in this case for DCP values only, is given in the Figure 1.

Structural design

The design method relies on an index to quantify thelong term load spreading capacity of a pavement, termed the Pavement Number (PN). The PN - similar to theStructural Number widely used in the 1986 AASHTOdesign method - is calculated using the layer thicknessesand assigned DE material classes. An empiricalrelationship between the PN and observed performanceof more than 80 pavement structures incorporating BSMincorporating foam or emulsion provides the basis.

The fundamental points of departure for the method are: 1. The structural capacity of a pavement is a function of:

(a) load spreading potential of the pavement layers; (b) quality of the subgrade.

2. The quality and stiffness of the subgrade is the starting point for design;

3. For pavements with thin surfacings, failure in the base effectively constitutes pavement failure;

4. The load spreading potential of an individual layer is a product of its thickness and its Effective Long Term Stiffness (ELTS);

5. The ELTS of a layer is a model parameter, calibrated for use in the PN method, which depends on the material type and on its position in the pavement. It serves as a relative indicator of the average long term in-situ stiffness of a pavement layer. For subgrade materials, the ELTS is determined by the DE material class, climatic region and depth of cover. For the layers above the subgrade, the ELTS is determined by

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Figure 1: Proposed application method for materialsclassification (DCP values only)

Bitumen Stabilised Materials

BSM design method shaping up, but needsinput from practitioners

the DE material class and the ELTS of the supporting layer;

6. A modular ratio regimen is adopted to account for the characteristic stress-dependant stiffness of granular materials and to limit the stiffness values ascribed to unbound layers placed over a weaker support. Higher quality materials can sustain higher modular ratios;

7. In the PN method a Base Confidence Factor (BCF) has been included to reflect proven capabilities of certain base materials and to disqualify unpractical designs which have a high likelihood of failure.

Figure 2 illustrates an overview of the fundamentalelements of the PN method, applied to a "moderate"climatic region.

Professional interaction

To allow designers to test newly developed pavementdesign and evaluation technology, and to providefeedback for improvement, a website has been created -(www.bitstab.roadrehab.com) which provides fulldetails of the methods and of the software used.

Although the PN-based design andmaterials classification methods are fairly complete, refinement is required beforepublication of the new guidelines for thedesign and use of BSM. Comment frompractitioners on the method itself, theapproach to materials classification andreasonableness of results would bevaluable to make the method morerobust, user-friendly and reliable. Those27 practioners who have alreadyregistered on the website are thereforeencouraged to provide constructive,specific feedback that can be used toimprove the method for the benefit ofpavement engineering practice insouthern Africa. All practitioners areinvited to participate in the refinementprocess. q

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Figure 2: fundamental elements of the PN method,

Sabita Manual 5: Guidelines for the manufacture andconstruction of hot mix asphalt has been updated andexpanded to serve as a current and relevant guideline and to assist new entrants to the road industry and students of the subject. The document covers the topic thoroughly,dealing with processes, procedures and activities ranging from the design of project mixes to their application onsite.

Key revisions incorporate:

• the interface of design and manufacture;• project planning;• procedural and legal requirements;• stockpiling of aggregates;• the use of reclaimed asphalt pavement (RAP) and

stockpiling techniques;• sound paving techniques, especially level and

finish controls, to achieve good riding quality;• construction of joints;• various specialised topics related to quality

management and construction; and • plant components, roller type and characteristics,

substrata preparations and the finer points ofpaving, which are covered in the appendices.

In line with Sabita policy on HSE, the reader’sattention is drawn to the hazards associated with themanufacture and construction of hot mix asphalt –from plant to site – and steps to mitigate exposure tothese hazards are suggested. These include properinduction of new employees into the company’ssafety programmes and ongoing training in the safehandling of materials and proper operation of plantand equipment. Reference is made to manuals andcourses developed by Sabita to minimise exposure tothe risks as well asfirst level treatment of injuries and theprevention andfighting of fires.

An electronicversion of therevised manual isavailable on theSabita websitefree-of-charge, and a hard copy of themanual is currently in production. This version may soonbe ordered on the Sabita website. www.sabita.co.za q

Sabita's revised Manual5 now available

The revised 2008 edition ofSabita's Manual 5

The recent increases in oil and bitumen prices could bethe death knell for the ongoing construction andmaintenance of gravel roads.

This is the conclusion reached by Professor Don Rossand researcher Kim Field, both of the Department ofFinance, Economics and Quantitative Methods at theUniversity of Cape Town, following an examination ofthe economic warrants for surfacing gravel roads in aclimate of rising oil and bitumen prices.

Commissioned by Sabita, the study makes it clear that asubstantially higher proportion of the price ofmaintaining gravel roads is driven by the petroleum price

when compared to that for bitumen-surfaced roads.Therefore, as the petroleum price rises, the relativeopportunity costs of gravel and surfaced roadsshould be expected to shift in favour of surfacedroads. The impact of this differential is significantgiven South Africa's extensive network of gravelroads.

The report makes it clear that the largest costcomponent by far in construction and maintenanceof gravel roads is haulage. Gravel is heavy andmust be carried in trucks running on diesel fuel. For maintenance of SA’s current extent of gravel roads, about 30 million cubic metres of aggregate material are required to be hauled each year. At currentdistances between borrow pits, about 30 millionlitres of fuel is consumed. An additional 10 millionlitres is used for grading. This amounts to about0.1% of total SA diesel fuel consumption. Thisexpenditure, unlike increased expenditure on

bitumen, mainly occurs beyond year one of a roadproject, due to the need to replace gravel lost due totraffic. Thus the proportional impact of rising petrolprices on road maintenance goes steadily upward forgravel relative to bitumen as time horizons are extended(see Figure 1).

Gravel supply

A further observation is that over the last twelve years,gravel supply in South Africa has fluctuated withsignificantly greater volatility than bitumen, and therecent trend is one of decline. This means that the impact of oil price changes on a low-volume road with a gravel

base and a bitumen seal presents amore favourable picture than that ofunsealed gravel roads. Savings infuture maintenance costs for this type of road, relative to an unsealed one,principally arise through the fact thatthe seal prevents gravel from beingblown and washed away, needing tobe replaced by newly hauledaggregate.

The report stresses that comparisonsof trends often fail to capture twocrucial aspects of the relationshipsbetween changes in world oil pricesand the economics of road surfacingdecisions. Gravel haulage is by farthe largest cost component ofconstruction and maintenance ofeither surfaced or gravel roads.

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Gravel roads could be the first casualty as oiland bitumen prices escalate

Figure 1: Maintenance costs for gravel and surfacedroads (CoT Chief Engineer Johan Henning, 2007)

Figure 2: Petroleum price impacts on maintenancecosts per km of haulage for different types of road.

Figure 2 illustrates clearly that, when gravel roadconstruction and maintenance are compared with theconstruction and maintenance of a bitumen surfacedroad, the diesel cost component of the total undiscounted cost of an unsurfaced road outweighs the combinedundiscounted bitumen and diesel costs associated withconstructing and maintaining a low-volumebitumen-sealed, or even a hot mix asphalt paved road.The comparison will of course be still more favourablefor sealing an already constructed gravel road.Therefore, as the price of oil rises, the undiscountedopportunity cost ratios between unsurfaced and surfacedroads must shift in the direction of surfaced roads.

Fewer oil-based inputs

The above illustrates clearly that building andmaintaining a bitumen road without aggregate consumesfewer oil-based inputs over 20 years than building andconstructing an unsurfaced road, measured by rand cost,at an average haulage distance of just over 7 km. Sealing a gravel road consumes fewer oil-based inputs, measured

by rand cost, at an average haulage distance of 11 km.This corresponds to findings from South-East Asia asreported in Jahren et al (2005). Given that the oil-basedcost of bitumen is included in this model, it illustratesthe extent to which bitumen, despite being apetroleum-derived product, does not represent anintensive allocation of this ever-costlier commodity toroads relative to its main alternative.Gravel roads also impose a range of negativeexternalities on both drivers and the community at large:

• Each year, more than 30 million cubic metres ofgravel blows or washes off SA’s roads and mustbe replaced (NDoT 2002). Because of the dustthey spread onto crops, wildlife and people,gravel roads impose heavier environmental coststhan surfaced ones. Dust causes allergies andrespiratory illnesses, especially in small children;

• Rougher road surfaces increase vehicle operatingcosts, especially petrol use and tyre wear.Netterberg and Pinard (1991) estimate thatequivalent traffic volumes consume, on average, 6 - 7% more fuel on gravel roads than on pavedones. Dierks (1992) suggests a substantiallyhigher figure of 20%, partly reflecting arestriction to lower quality gravel roads in hissample;

• Surfaced roads are also safer than gravel roadsbecause on paved surfaces vehicles can brake tofaster stops from equivalent speeds and are lessdisposed to skid, and accident statistics concludethat road surface conditions contribute to about8.6% of all accidents in SA, and that surfaceimprovements would prevent 10% of thesealtogether – so, 0.86% of the total. The accidentrate per million vehicle kilometres on gravel roads is more than double that for two-lane paved roads, and the composition of fatalities among accidentson gravel (10.9%) is higher than on 2-lane pavedroads (7.8%), and much higher than on full-speed

freeways (3.2%);• A significant consideration in this debate is

that gravel roads, due to their reliance on large machines for grading and shaping, cannot beconstructed and maintained mainly or entirelyusing small equipment that can be operated by unskilled people. Bituminous surfaces on theother hand, can be constructed and maintained with light equipment that requires littletraining to master (Pinard and Overby, 2006).For example, a recent project which usedmanually operated chip spreaders to constructlow-volume sealed roads near Siyabuswa inMpumalanga resulted in the employment ofmore than 60 mainly unskilled workers for amonth, whereas the alternativecapital-intensive methods that would havebeen required for an unsurfaced road adequate to the relevant AADT level would haveemployed 5 to 6 people for a few days.

Shadow prices

A true estimation of the opportunity cost ofconstructing a gravel road, and of maintaining such aroad as gravel rather than re-sealing it, wouldincorporate shadow prices for all of these externalities. If unsurfaced roads carry a range of shadow costs thatbitumen-surfaced low-volume roads avoid, then thismust affect the break-even point in time: for a given rateof inflation it must grow shorter. Because the negativeexternalities also reduce the supply of gravel, and henceincrease haulage distances, they also reduce thethreshold for gravel use at which expenditure on oil isminimised.

The report reaches several important conclusions:

• As the petroleum price rises, the relativeopportunity costs of gravel and surfaced roads

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Figure 3: Enhanced labour usage in the applicationof a bituminous surface

should be expected to shift in favour of surfacedroads;

• At present oil prices – but given expectations ofrising oil prices – any gravel road that averagesmore than 10 km in haulage distance from nearest sources of adequate aggregate material should nolonger be maintained, and a bitumen surfaceshould be considered;

• Barring a persistent surge in inflation, aninvestment in a bitumen surface seal on any roadthat is worth maintaining at all to meet trafficdemands recoups its value in 5 to 6 years;

• Rural bitumen-surfaced roads constructed andmaintained using labour-intensive methods offerpotential augmentation of human capital, andexploitation of SA’s large gap between shadow

wages of underemployed workers andformal-sector market wages;

• Significant but not quantified negativeexternalities associated with gravel roads make itlikely that the supply of gravel will continue tocontract, the oil-minimising haulage distancethreshold for gravel roads will shrink (over andabove shrinkage caused by rising oil prices), andthe duration between a decision to surface and the break-even point will shorten.

The report concludes: “We think it probable that, whenall of the above conclusions are considered, South Africa should maintain gravel roads only where AADT levelsare too low to normally justify expenditure on any road,but a community’s access to a minimally acceptablequality of life is crucially dependent on it.” q

9

Representatives from 34 Sabita member companiesattended a strategic planning forum at Alpine HeathResort in the Drakensberg on 10 and 11 October 2007to review and update Sabita's current business plan.

The delegates were given an overview of currentissues facing the bituminous product industry throughpresentations by:

• Mike Zacharias of Shell Oil Products Africa: Factorsaffecting bitumen suppliesinto the future;

• Mike Winfield of theSAFCEC Western CapeBranch: Some issues facingthe construction industry;and

• Les Sampson of the Asphalt Academy: Issues emanating from CAPSA'07.

This was followed by facilitatedworkshops designed to allowmembers to discuss, formulate and prioritise key issues and activitiesthat should be addressed by Sabitaover the next three years. Use wasmade of a mind-map tool whichproved invaluable in consolidating the issues into four key focus areas as detailed in the accompanyingtable.

Sabita's activities will be gearedand directed towards achievingthese new goals to provide theindustry with a new direction into

the future and to consolidate the association'sachievements.Members who did not attend the Forum are invited toview the outcomes and the mind-map tool in theMembers' Section of the Sabita website, and to offerany observations and/or comments. q

Sabita's members formulate a new road map for theasphalt industry

Cluster Objective

Sustainable Practices (formerly HSE)

Promote sustainable practices in the constructionand maintenance of roads through:

• Self regulation in occupational health &safety, environmental conservation andquality management; and

• Reducing the industry's carbon footprint

StakeholderEngagement(formerly Contactwith Government)

Interact with all stakeholders who:• Make decisions on the allocation of funds for

roads;• Manage road networks;• Influence and specify the use of bituminous

materials; and• Supply materials for the production of

bituminous products

TechnologyDevelopment

Promote cost-effective road provision through: • Developing best practice techniques to

ensure that our products remain competitive;• Investing in appropriate research and

development; and• Ensuring that our products and practices are

sustainable.

Human CapitalDevelopment

Educate and train the practitioners through supportfor:

• The development of a Roads Academy andCentres of Development; and

• The Asphalt Academy and the Society forAsphalt Technology.

Although the very successful CAPSA'07 conference was held in September 2007 shortens the time available forother offerings, the Asphalt Academy (AsAc) will haveheld 23 courses and seminars by the end of its 2007/08financial year. The courses related to bituminousproducts and their use in the design, construction andmaintenance of surfaced roads using hot mix asphaltand/or surfacing seals have again proved popular andwell supported in all regions. However, the advances inother areas will be the focus of this article.

The international lecture series featuring presentationsby Prof Joe Mahoney of the University of Washingtonon Acceptance control and quality assurance of HMAand by Prof Hussain Bahia on Bitumen performance andclassification in the South African context were wellreceived and kept practitioners updated on currentpractice in the USA in these areas.

The symposium held in association with the GautengDepartment of Public Transport, Roads and Works(GPTRW) to feed back the latest findings from theirtechnology development programme developed as partof their Heavy Vehicle Simulator (HVS) programme,was presented to very positive reviews. Similar symposia will be held on a regular basis to report further findings.

In July/August 2007, AsAc held its first course acrossthe borders in Namibia with over 40 learners attendingthe Design, application and construction of surfacingseals course presented by Gerrie van Zyl. The coursewas presented in association with the NamibianEngineering Professionals Association (EPA) and it ishoped to expand on this alliance for the presentation ofsubsequent bituminous product related courses andseminars in the future.

Launch of revised TG1

It is pleasing to report that AsAc’s first publication, TG 1: The use of modified binders in road constructionhas been completely revised through the RoadsPavement Forum (RPF) task group chaired by DennisRossmann of SANRAL. The second edition wassuccessfully launched at three half-day seminars in theWestern Cape, KZN and Gauteng in November 2007,attracting over 170 attendees.

Establishment of a Roads Academy

At the RPF meeting in May 2007, Les Sampson wasasked to reconvene the Skills Development task group to provide better coordination of several initiatives thathave arisen in this now critical area for the industry.

Among the outcomes of the meeting was the unanimousdecision to investigate the establishment of a RoadsAcademy to provide coordination of all skillsdevelopment initiatives for the road pavement sector. Adraft scope of work is being prepared for presentationand discussion by the task group and possiblesubmission to the DoT, underlining industry support oftheir Road Infrastructure Framework for South Africa(RISFSA) document approved by Cabinet.

Revised materials testers'course

The other important development emanating from thetask group meeting is the agreement to present a muchneeded Materials Testers' Course (MTC) which will now be a combination of the five newly developed testingmodules (Sampling, Soils and Gravel, Aggregates,Bitumen and Asphalt) from the old Asphalt TestersCourse's three.

The course will include a one week concrete testingmodule to be presented by C&CI. The course will bemanaged by Barry Pearce.

Expansion to other areas

As part of its expansion strategy, AsAc has been verysensitive to the need to present courses and seminars inother regional/provincial centres. Hence, as part of the2008/09 course schedule, it is the intention to hold 2-day Bituminous products in practice seminars, in associationwith Sabita, in the Eastern Cape, Mpumalanga and theFree State to update practitioners on the latest bestpractice manuals. It is anticipated that the seminars willinclude presentations on the new TG 1 for modifiedbinders, the revised TRH 3 published by SANRAL, thelatest guide to the design of HMA and other relevantindustry documents that have been published by Sabita.

Course targets new graduates

Finally, the Pavement Engineering course will now bepresented as part of the Gauteng ProvincialGovernment’s programme to develop capacity inpavement engineering in Gauteng, and will be presentedfrom March 2008. New entrants into the roads sectorwith a first tertiary qualification in civil engineering arebeing targeted.

Applicants will be screened from the public and privatesector supporting the Gauteng road construction,rehabilitation and maintenance programme. Privatesector mentorship will be required for successfulapplicants during the 15 months of the course. q

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Comprehensive AsAc courseprogramme tackles skills shortage

For AsAc course programme see the flyer with this publication or the AsAc web site at www.asphaltacademy.co.za

Presenters at the recent CAPSA stressed the importanceof filler/bitumen ratio in continuously graded mixes.This subject is not well understood by manypractitioners and needs to be re-examined.

Filler is the term describing the fines component of themineral aggregate passing the 0.075mm size sieve. Thebitumen absorbs this filler and the resultant mixturebecomes the “mastic”. Logically, the more filler, or thehigher the filler to bitumen (F/B) ratio, the stiffer andmore viscous the mastic becomes.

However, determining the optimum F/B ratio for a mixis no simple matter, given the influence of stiffness oncompactive effort required.

Consider a specific mix e.g. COLTO medium with 13.2maximum size aggregate, mixed at a specific plant.

• The more filler, the stiffer the binder, and themore compaction effort is needed. Therefore there is an upper limit to the F/B ratio in order toachieve optimum compaction;

• The bitumen content will also vary for differentmat thicknesses and maximum aggregate size.• Mat thickness – better lubrication (more

bitumen) is needed for thin mats than thicklifts (That’s another whole topic in itself); and

• Maximum size aggregate – the larger themaximum size aggregate the lower thebitumen content.

• Filler contents do not change significantly forCOLTO mixes from individual plants.

Typical bitumen content

Thus the F/B ratio will change with the above variables.

Filler contents of all COLTO mixes in Cape Town arearound 7.2%. Typical bitumen contents for the differentmixes are as follows:

• 40mm medium wearing course (13.2mm NMAS)= 5.2%

• 90mm LAMBS (37mm NMAS) = 4.2%

• 70mm BTB (26.5mm NMAS) = 4.4%• But for this same BTB mix, when paved 45mm

thick as a COLTO coarse wearing course, thebitumen content must be raised to 4.8% due to the need for better lubrication for the thinner mat.

Thus the F/B ratio is different for all four mixes, evenfor the same mix paved at a different thickness. Thetable below shows a range of typical mixes for CapeTown with recommended F/B ratios. Note the similarityof filler contents of the four COLTO mixes, and the wide range of optimum F/B ratios over the spectrum of mixes(the last two of which include 10% sand).

Tolerances

To complicate things further, the tolerances allowed inCOLTO are:

• + 0.3% for bitumen• + 1.0% for 0.075mm material

Applying these to the extreme to the COLTO mediummix above, means that the F/B ratio could range between 1.1 and 1.6, and still be within specification, but 1.6 for this mix is too high to be able to get goodcompaction.

There may well be a need to reconsider these tolerances.Modern asphalt plants are highly sophisticated with built in controls which should enable the tolerances to befurther reduced to say +0.2% for bitumen and +0.6% for0.075mm material.

There is an upper limit to the F/B ratio for any mix, ifthe required density is to be achieved. Each mix willhave its own unique optimum F/B ratio dependingmainly on: filler grading and harshness, maximum sizeaggregate (generally the smaller the stone, the lower theratio) and mat thickness (generally the thicker the matthe lower the ratio).

These may be determined by laboratory testing, or byexperience with what works and what doesn’t. q

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Thoughts arising from CAPSA'07

A paving contractor's view of filler-binder ratio

MixMax. sizeaggregate

Matthickness

% bitumen % 0.075TargetVIMs

F/B ratio

COLTO medium 13.2 40 5.2 7.0 4.5 1.35

COLTO coarse 26.5 45 4.8 7.5 4.0 1.55

COLTO BTB 26.5 >50 4.4 7.5 4.0 1.65

COLTO Lambs 37.0 >70 4.2 7.0 4.0 1.65

CCC w.c. 13.2 40 4.8 6.2 4.5 1.30

Residential w.c 9.5 25 5.5 6.6 4.0 1.20

The next phase of the so-called “rut challenge” is set tokick off early in 2008 when two mix designs proposedby Much Asphalt from their East and West Rand plantswill be constructed by Roadmac Surfacing.

Originally it was planned that the first rut-resistant mix(East Rand) be laid in early December 2007, and forHVS testing to start at the end of January 2008.Construction of the second rut-resistant mix (West Rand) was to be laid in early February 2008 for testing with the HVS to start in March 2008. Unfortunately, due toinclement weather conditions not conducive to layinghot mix asphalt, the programme has had to be postponedfor commencement early in the new year.

Two categories of trial sections are envisaged – one foraccelated pavement testing (APT) with the GPTRWheavy vehicle simulator (HVS), and the other for longterm pavement performance (LTPP) monitoring andevaluation. The LTPP sections will be constructed 50mlong over 2 lanes at 7.6 or 7.4m width. The APT sectionwill be 60m long and 3.7m wide. The thickness of thetrial layers will be 40mm.

Key objectives

Vela VKE will take responsibility for the on-sitesupervision of the construction in terms ofspecifications drawn up by the CSIR BuiltEnvironment, which will also take responsibility forthe testing programme. Mix designs submitted will bereviewed by both Vela VKE and CSIR prior toconstruction. Sabita will coordinate the mix designprocesses, production and construction of the sections.

As one of the key objectives of the study is to examinemixes made with conventional bitumen and especiallydesigned for a high resistance to permanentdeformation, the test programme provides for hightemperature testing regimens (60°C) as well as toassess the validity of bi- or uni-directional testing.

Dr Wynand Steyn of CSIR commented that there is acommon-sense perception that rut evaluation with APT

should be performed using uni-directional tracking tosimulate traffic more realistically.

While international research has indicated this to be avalid approach in some cases, other studies have shownan insensitivity of the rut performance of asphalt to themode of tracking.

Steyn indicated that these inconsistencies could be partly ascribed to factors such as ageing and, hence, stiffness of the asphalt as well as layer depth. Consequently theresults already obtained with bi-directional tests on agedconventional (reference) asphalt at the test terrain will be supplemented by tests on freshly laid, rut-resistantasphalt. In so doing, the aim is to strike a balancebetween HVS productivity and validity of outputs.

The stage is therefore set to assay the ability of theaggregate structure of asphalt to resist permanentdeformation. Bringing this aspect of asphalt design intosharp focus will facilitate the establishment ofboundaries between conventional binders and bitumenmodification in the interests of cost-effectiveness.

The project will be jointly funded by GPTRW andSabita. q

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The rut challenge is on, and tests begin in 2008

13 Mar Sabita AGM/Council meeting, Cape Town

6-7 May RPF, Mpekweni, Eastern Cape

21-23 May Eurasphalt/Eurobitume Congress, Copenhagen

7-10 July 27th SATC conference, Pretoria

17 July Sabita Council meeting, Durban

27-29 July 1st International AARB Sprayed SealsConference, Adelaide, Australia

6-8 Aug BitSafe Train-the-Trainer course, Gauteng

11-12 Nov RPF, Pretoria

12 Nov Sabita Council meeting, Gauteng q

The rut challenge task team (l-r): Herman Marais,Wynand Steyn, Les Sampson and Elzbieta Sadzik

Events calendar: 2008

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