CHARACTERIZATION OF NIGERIA'S NATURAL BITUMEN

By

Professor A. S. Adedimila, FNSECivil Engineering Department, University of Lagos

Lagos, Nigeria

Paper Presented at the National Engineering Conference and Annual GeneralMeeting of the Nigerian Society of Engineers

Theme: Local Content Development in the Nigerian Economy

Venue: Petroleum Training Institute, Effurun, Warri, Delta State

Date: 6th - 10th December 2004

CHARACTERIZATION OF NIGERIA'S NATURAL BITUMEN

By

Professor A. S. Adedimila, FNSECivil Engineering Department, University of Lagos

Lagos, Nigeria

ABSTRACT

There is widespread deposit of bitumenin southwestern Nigeria, which comparesfavourably, in quantity, with other depositselsewhere. One should note, however, that notall natural bitumen meet road constructionrequirements. So far, extensive geologicalstudies had been conducted on the naturalbitumen while engineering studies had beenvery limited. In this paper, an attempt is madeto create awareness to the need for engineeringinvestigations for establishing the best ways toutilize the materials and to evolve adequatespecifications for construction. Availablestudies so far conducted are presented andrecommendations towards effective utilizationof the materials are made.

1. . INTRODUCTION

Nigeria'S economy is significantlydependent on highway transportation, the mostflexible mode in providing for mass andindividual movements. Table 1 shows the roadsystem in Nigeria in 1996, with a total of39,500 km of bituminous surfaced roadsrepresenting 20 percent of the total roadnetwork [5].

The major road construction materialsin Nigeria are lateritic soils, gravel andbitumen. One of the problems commonlyassociated with road construction is theshortage of bitumen and good qualityaggregates within economic haulage distances.Fortunately, there is widespread deposit ofbitumen in the southwestern part of Nigeria,which compares favourably, in quantity, withother deposits all over the world.

It has to be noted, however, that not allnaturally occurring bitumen meet therequirements for use in road construction. Toensure that roads give long-lasting andsatisfactory performance, standards andspecifications for construction materials havebeen developed by organisations such as theAmerican Society for Testing and Materials(ASTM), American Association of StateHighway and Transportation Officials(AASHTO), Asphalt Institute and BritishStandards Institute (BSI).

It is also worth noting that while seriousefforts are being made for the continuousexploitation and evaluation of the naturallyoccurring bitumen deposits of other countriessuch as the United States of America andCanada, it appears Nigeria, until recently, paidrelatively little attention to her vast depositsand continued to expend millions of dollars ofher limited foreign exchange to import rawmaterials in the form of asphalt yielding crudepetroleum mostly from Venezuela for themanufacture of bitumen. With the frequentbreakdown of the Kaduna refinery, it hasbecome expedient to import asphalt directly toNigeria.

So far, extensive geological studies hadbeen conducted on the natural bitumen whileengineering studies had been very limited.Consequently, efforts should be made tocharacterize these materials, particularly inrelation to their use for road construction, aseventual utilization of the materials can beexpected to have a significant pay-off potentialon cost reduction and foreign exchangepreservation on the long run.

The objective of this paper, therefore, isto create awareness to the need to carry outengineering investigations that will assist inestablishing the best ways to utilize thematerials and to evolve adequate specificationsfor construction. Available studies so farconducted will be presented andrecommendations that will promote effectiveutilization of the materials will be made.

2. ONDO STATE NATURALBITUMEN DEPOSITS

The natural bitumen deposits of OndoState are found in two basic forms, namely;

(i) Soft and low viscosity bitumenseepages from wells. This is'plain' bitumen and is notnoticeably associated with sand.

(ii) Seepages and outcrops ofbitumen-impregnated sandsfrom which bitumen can beextracted by suitable processes.This is generally referred to as"tar sands" but should moreappropriately be called"bitumen sands" since tar doesnot occur in nature.

Geological Studies on the Bitumen Deposits

According to Onoh [7], the NigerianBitumen Company, a German Company,started exploration for bitumen in 1908 alongthe coastal region stretching from Okitipupa inOndo State to Lagos. Amongst the more recentworkers are the geological survey team fromthe University of Ife (now Obafemi AwolowoUniversity), Ile-Ife led by Professor O. S.Adegoke between 1974 and 1985. Their effortshad led to several reports and publications.

According to Adegoke and his team,the natural bitumen deposits are located withina belt spanning across from east of Ijebu-Odein Ogun State, through Okitipupa andIfesowapo areas in Ondo State to the westernmargin of Delta State. The asphalt-bearingzone is 120 km long and about 6 km wide, andthe thickness ranges from 0.5m to over 40m

with an average of about 6m [4]. Aconservative estimate of the recoverableasphalt from the bituminous sands was alsofound to be of the order of 270 million metrictonnes, which compares favourably with othermajor deposits elsewhere as shown in Table 2.

Engineering Studies

A few engineering studies have alsobeen carried out to appraise the quality ofmaterial from the bitumen-rich areas.Unfortunately however, the effectiveness andreliability of most of these attempts and thecorresponding findings and assessments havebeen adversely affected by one majorconstraint or the other notable among whichhave been the seemingly recurring inability toobtain sufficient quantity and variety ofsamples from the bitumen-rich zones and anoften severe limitation of specializedequipment for core-sampling, and for in-situand laboratory testing.

a) Bitumen Sands

One of the engineering studies carriedout and for which findings and results werepublished is that by Adedimila in 1987.Laboratory tests were performed in order toanalyse the major components of thebituminous sands as well as investigate variousengineering properties relevant to roadconstruction such as stability, stiffness, indirecttensile strength and compressive modulus ofrecovered samples, amount, viscosity andpenetration of recovered asphalt and gradationof recovered aggregates [1].

From the test results, it was observedthat the characteristics of the bituminous sandssuch as aggregate gradation and asphalt typeand amount appear to vary with location in thebituminous sand horizon, while the Marshallstability and stiffness, indirect tensile strengthand compressive modulus vary with locationand coring depth. Finally, it was concludedthat the bituminous sands could form excellentbase course or asphalt concrete wearing coursematerials for flexible pavement constructionprovided there is proper mixture design.

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Plain Bitumen'

In a tudy conducted by Adedimila and01 go re in 1990 to investigate the basicengineering characteristics of the plain bitumen

a view to ascertaining the extent ofla ility for use in flexible pavement

onstruction in its natural state [2], relevantla oratory tests were performed on samplesobtained from two of the bitumen wells in theitumen-rich area of Ondo State.

The results of the physicalcharacteristics and consistency tests indicatedthat while some of the bitumen samples aredirectly suitable for use in road works in theirnatural state, some others require suitabletreatment or modifications. Such treatmentmay, as in the case of Trinidad Lake asphalt,and, according to Adegoke [4], and Krebs andWalker [6], take the form of refining byheating to sufficiently high temperatures todrive off water and entrapped gases responsiblefor the crackling sounds and foaming of theparticular samples during heating.

It is therefore strongly recommendedthat elaborate engineering studies on both plainbitumen and bitumen sands covering widerareas of the bitumen horizon be conducted toevolve adequate design and specifications forthe construction.

Other Uses

Asphalt is an extremely versatilematerial and its usage, which can be likened tothat of the agricultural palm tree, iswidespread. Besides paving and road building,asphalt is also used for protective coating andhydraulic structures, roofing, and otherpurposes such as automobile brake lining,undercoating of automobiles, tyre manufacture,joint filling and sealing, especially concretepavements and bridge decks, insulating andsoundproofing, tunnel grouting, battery cases,polymer and petrol-chemical industries for theproduction of resins, plastics and fibres, treesurgery, etc.

The major uses of asphalt are specifiedby BSI, AASHTO, ASTM and other Agencies

worldwide. The possibility of using thebitumen deposits in some of these areas shouldbe examined.

3. TEST INDICES

A good understanding of the propertiesof any given mixture is essential for its properuse in pavement construction. Laboratory andfield tests are used to set broad limits to theprobable behaviour of mixtures, and thusestablish basis for the use of experience andingenuity in formulating sound engineeringsolution to design and construction problemsinvolving the use of the materials. Factors thataffect the selection of such tests include:

i) Relationship to the basic elementsof pavement design

ii) Relationship to the fundamentalproperties governing mixturestrength

iii) Suitability for routine work

iv) Economy.

A test commonly used in asphaltmixture design is the Marshall stability test.The indirect tensile test (ITT) is a method thathas gained acceptance increasingly. The ITTinvolves loading a cylindrical specimen withcompressive loads along two oppositegenerators, thus developing a relativelyuniform tensile stress perpendicular to thedirection of the applied load and along thevertical diametrical plane. Failure occurs bysplitting along the loaded plane. Both theMarshall and the ITT are relatively simple.However, in actual field condition, pavementmaterials have a confining pressure, which isnot duplicated in the Marshall test. The ITTconforms to a biaxial stress condition. Also, theITT has the additional advantage of its abilityto predict fracture strength and to evaluate theelastic characteristics of asphalt mixtures.Studies had indicated strong correlationsbetween Marshall stability and indirect tensilestrength [3], suggesting a possible substitute ofthe ITT for Marshall stability test in the designof asphalt mixtures.

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Although additional studies had beenrecommended in this regard [3], highwayauthorities in Nigeria should consider thepossibility of using the indirect tensile test forthe design and evaluation of asphalt mixtures.

4. RECOMMENDATIONS

From previous limited studies on thenatural bitumen deposits of Ondo State, it hasbeen observed that many of the deposits areexcellent construction materials while thosethat are not as good in their natural form can bemodified to produce adequate materials forroad construction. Consequently, extensiveengineering studies must be conducted on thematerials with a view to adequatelycharacterizing them and also evolving suitablespecifications for construction.

Bitumen can be used in a number ofareas besides road works. The possibility ofusing the natural bitumen in the other areasshould be examined.

Bitumen is a major road constructionmaterial. However, it is sad to note that atpresent, laboratories in Nigeria are notadequately equipped to conduct meaningfuland reliable research on bituminous materials.Many of those available can best be used forteaching and demonstration purposes.Therefore, there is need to establish standardlaboratories in some of the Universities,Polytechnics and other Research Centres suchas the Nigerian Building and Road ResearchInstitute (NBRRI). The indirect tensile testshould be used for asphalt mixture design andevaluation.

5. CONCLUSION

Natural bitumen is commerciallyavailable in Nigeria. However, the engineeringcharacteristics of the bitumen deposits had notbeen established. This paper has createdawareness to the important need to characterize

the bitumen deposits with a view to makingeffective utilization of the materials and todevelop adequate construction specifications.

REFERENCES

1. Adedimila, AS.: "OkitipupaBituminous Sands: New ConstructionMaterials for Flexible Pavements?" TheNig. Eng. Vol. 22, No. 3, 1 - 14, Lagos,1987.

2. Adedimila, A S. and Olagoke, A A:"Basic Engineering Characteristics ofOndo State Bitumen Deposits," Unpub.Report, Dept. of Civ. Eng., Univ.ofLagos, 1990.

3. Adedimila, A S. and Oti, D. 0.: "AComparison of the Marshall and theIndirect Tensile Tests in Relation toAsphalt Mixture Design," Proceedings,Institution of Civil Engineers, Part 2,TN 461, Vol. 81, London, 461-469,1986.

4. Adegoke, O. S. (Ed): "GeologicalGuide to Some Nigerian Cretaceous-recent Localities," 16th Annual Conf.Nig. Mining and Geos. Soc., 27-36,1980.

5. Fadaka, B.: "An Agenda for GoodRoads in Nigeria in the 21st Century,"2nd Distinguished Lecture inEngineering and Technology, Univ. ofLagos, 1996.

6. Krebs, R. D. and Walker, R. D.:"Highway Materials," McGraw - HillBook Co., New York, 1971.

7. Onoh,1. K.: "The Nigerian OilEconomy," St. Martins Press, N. Y.,1983.

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TABLE 1: NIGERIA'S ROAD SYSTEM IN 1996 [4]

Road Class Road Length, kmPaved Unpaved Total Percentage

Federal 26,500 5,600 32,100 16State 10,400 20,100 30,500 16Local 2,600 128,000 130,600 68Total Network 39,500 153,700 193,200 100Percentage 20 80 100

TABLE 2. ESTIMATED RESERVES FOR MAJOR BITUMEN DEPOSITSIN THE WORLD [3]

EstimatedCountry Bitumen Deposit Reserves

(metric tons)Canada North Alberta Deposits 388x10~

MalagasyRepublic Bemolangu Deposits 246 x 106

Nigeria South Western Nigeria Tar Sand Deposits 270 x 106 (min.)

United Statesof America Utah, Kentucky and California Deposits 351 x 106 (min.)

773 x 106 (max.)Venezuela Orinoco-Guarico Deposits 281 x 108

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