iesl journal october 2013 web file

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October 2013VOL: XXXXVI, No. 04

Commemorating40 years of publication


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From the Editor ... III

SECTION I

Factors Influencing the Service Life ofBuildingsby: Eng. (Prof.) W P S Dias

Potential and Viability of Rice Husk BasedPower Generation in Sri Lankaby: Eng. (Dr.) Asanka S Rodrigo and Eng.

Shantha Perera

Investigation on Efficiency of Repairing andRetrofitting Methods for Chloride inducedCorrosion of Reinforced Concrete Structuresby: Eng. B H J Pushpakumara, Eng. (Dr.)

Sudhira De Silva and Eng. (Dr.) (Mrs.)G H M J Subashi De Silva

Productivity in Construction A CriticalReview of Researchby: Eng. (Dr.) D A R Dolage and Dr. Paul

Chan

Stream flow, Suspended Solids andTurbidity Characteristics of the Gin River,Sri Lankaby: Eng. (Mrs.) T N Wickramaarachchi,

Eng. (Dr.) H. Ishidaira and Eng. (Dr.) TM N Wijayaratna

Peak Electricity Demand Prediction Modelfor Sri Lanka Power Systemby: G V Buddhika De Silva and Eng. Lalith

A Samaliarachchi

SECTION II

Floating Wetlands for Management of AlgalWashout from Waste Stabilization PondEffluent: Case study at Hikkaduwa WasteStabilization Ponds

Notes: ENGINEER, established in 1973, is a Quarterly

Journal, published in the months of January,April, July & October of the year.

All published articles have been refereed inanonymity by at least two subject specialists.

Section Icontains articles based on EngineeringResearch while Section II contains articles ofProfessional Interest.

ENGINEERJOURNAL OF THE INSTITUTION OF ENGINEERS, SRI LANKA* Completed 40 Years of Publication *

EDITORIAL BOARD

Eng. Tilak De Silva -President(Chairman)

Eng. W. Gamage - Chairman, Libraryand PublicationCommittee

Eng. (Prof.) K. P. P. Pathirana - Editor TransactionEng. (Prof.) T. M. Pallewatta - Editor ENGINEEREng. (Dr.) U. P. Nawagamuwa - Editor SLENEng. (Prof.) (Mrs.) N. RathnayakaEng. (Dr.) D. A. R. DolageEng. (Miss.) Arundathi WimalasuriyaEng. (Dr.) K. S. Wanniarachchi

The Institution of Engineers, Sri Lanka

120/15, Wijerama Mawatha,Colombo - 00700Sri Lanka.

Telephone: 94-11-2698426, 2685490, 2699210Fax: 94-11-2699202E-mail: [email protected] (Publications): [email protected]: http://www.iesl.lk

COVER PAGE

Colombo Katunayaka Expressway (CKE)Constructed addressing a long felt need for expedientaccess from Katunayaka International Airport to the city ofColombo, CKE was declared open by H E the President ofSri Lanka on 2013 October 27. Construction commencedon 2009 August 18 on the 25.8 km four lane expresswaywith a segment from Kelani Bridge to Peliyagodainterchange having six lanes. With three interchanges andoption to connect to Outer Circular Highway (OCH) atKerawalapitiya this expressway reduces 90 minute traveltime through route A-003 to 20 minutes.

Courtesy of the Road Development Authority

The statements made or opinions expressed in the

Engineer do not necessarily reflect the views of the

Council or a Committee of the Institution ofEngineers Sri Lanka, unless expressly stated.

October2013VOL: XXXXVI, No. 04

Commemorating40 years of publication

CONTENTSVol.: XXXXVI, No. 04, October 2013

ISSN 1800-1122

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by: Eng. (Mrs.) Sujatha Kalubowila, Dr.Mahesh Jayaweera, Eng. Chandrika M.Nanayakkara and Eng. Dhanesh N. DeS. Gunatilleke

The above Paper was placed First in the Over 35 years ofage Category at the Competition on Water Resources

Development and Future Challenges- Role ofEngineering meeting Future Challenges of WaterResources Development in Sri Lanka 2012/2013Sponsored by: International Water ManagementInstitute (IWMI)

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FROM THE EDITOR..

Reducing the travel time of a 30 km route by as much as 75% is what has beenachieved by the newly opened Colombo Katunayaka Expressway (CKE). Aftersuccessfully defeating terrorism that had been plaguing the country for a long period,we are on the way to development with ambitious targets. In this scenario, the fact thattransportation infrastructure becomes a prerequisite launch board, has not escaped ourEngineers, political decision makers as well as funding agencies. It is a fact that hinderfree expedient access from the first international airport to the commercial city of thecountry will facilitate corporate activities, industry and tourism.

Emergence of better highways and expressways has been the highlight oftransportation infrastructure in this country for the past few decades. However, in the

development of any infrastructure in this era of fast depleting natural resources, veryspecial considerations need to be granted to economy and sustainability in a globalsense. When it comes to transportation, the primary consideration should be tominimize the cost per unit per unit distance, be it people or goods, without neglectingsustainability, environmental and social impacts. When above factors are givencognizance under a technical viewpoint, it would become very clear to you that Railtransport naturally comes to the lead. As a mass land transport mode with the lowestrolling resistance and predefined right of way, rail transport has the aptitude to keep theburden posed by travel and transport needs of an ever growing populace on our planet,at bay. This fact is amply endorsed by the so called Developed countries of the worldthat have adopted rail as the primary land transport mode.

It can not be denied that, our country has in fact, retracted pre independence railtrack infrastructure and given undue prominence to roads. Though drastically late, weshould at least now direct our energies at improving and expanding the railwayinfrastructure in this land. In support of this argument, suffice to say that, it could be theonly way in a future devoid of abundant fossil fuels.

Eng. (Prof.) T. M. Pallewatta, Int. PEng (SL), C. Eng, FIE(SL), FIAE(SL)Editor, ENGINEER, Journal of The Institution of Engineers.

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Factors Influencing the Service Life of BuildingsW.P.S. Dias

Abstract: The service life of a building depends mainly on its chief structural materials and theenvironment it is placed in. This paper collates the evidence from condition surveys conducted onsome buildings with ages of up to 125 years set in a humid tropical environment, and seeks to arriveat some generalizations. Load bearing masonry walls and timber floors had performed well, as hadexposed steel sections that were well maintained. Buildings with such elements could be expected tolast well beyond the normal design life of 60 years. If a reinforced concrete building had beenexposed to a chloride source, major repairs were required after just half this design life. Carbonationdepth was found to broadly obey a correlation with the square root of time. However, it is shown thatboth depths of carbonation and surface chloride levels can vary considerably in different parts of thesame building. These findings have direct implications for both construction (in the choice ofmaterials) and inspection (with respect to sampling and use of multiple test methods).

Keywords: Service life, durability, chlorides, carbonation, corrosion

1. Introduction

1.1. The Service Life of Buildings

The service life of structures depend on avariety of factors, such as (i) their purpose; (ii)socio-economic considerations; (iii) materials ofconstruction; (iv) surrounding environment;and (v) degree of maintenance (Dias, 2003).

Very long service life of even up to 500 years ormore would be desired for monumentalbuildings such as temples and churches. Publicbuildings such as town halls and parliamentbuildings could be expected to last for 100 to200 years, whereas private structures such asoffices and dwellings for perhaps 50 to 60 years.BS 7543 (1992), defines the normal life of abuilding as 60 years. The new Eurocodes, e.g.BS EN 1992-1-1 (2008), assume this period to bea lower one of 50 years.

Socio-economic considerations impinge on theabove durations, some of which tend to reducethe lifespans of buildings, while others increasethem. The changing needs of various owners,and indeed the changing face of the city or areain which the building is located, may cause abuilding to be obsolete even before it ceases tobe serviceable. In the context of the aboveproneness to change, most investors or buildersmay not want to invest in a building with anexcessive service life. On the other hand,owners sometimes try to use an existing

building over and above its service life, becausedemolition and reconstruction may force themto comply with new planning regulations. Also,once a building exceeds a certain lifespan, the

owner, or even other interested parties, maywish to prolong its life further, if it isconsidered a national heritage.

The different materials of construction that areused in a building will give rise to differentrates of deterioration. In general, steel andreinforced concrete will tend to deterioratefaster than masonry; and timber in internalenvironments. Heat and moisture are

environmental factors that tend to acceleratedeterioration. Where steel embedded concreteand structural steel are concerned, a chlorideenvironment, inclusive of proximity to thecoast, will significantly enhance corrosion.

The factors affecting service life can vary, notonly from building to building, but even withina given building. For example, (i) The quality ofthe substructure, superstructure and even roofstructure in a building may vary if differentsubcontractors were responsible for them; (ii)

the environment a building is subjected to willvary from external elements to internalelements and also from seaward side tolandward side (if it is near the coast); and (iii)different building elements may receivedifferent degrees of maintenance, depending ontheir accessibility and inspectability.

1.2. Changes in Construction Technology

From a historical perspective, we can identify

Eng. (Prof.) W.P.S. Dias, BScEng(Hons), PhD(Lond),DIC, CEng, MIStructE, FIE(Sri Lanka), Senior Professor ofCivil Engineering, Department of Civil Engineering,University of Moratuwa, Sri Lanka.

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1945 as a point at which there was a worldwideshift in building materials usage i.e. moststructural steel used for beams and columns,and timber used for floors, was replaced withreinforced concrete.

We can also identify a time around 1975 as a

point at which there were a more subtlechanges in the quality of building materials.There was a worldwide change in cementmanufacturing processes, resulting in cementsthat developed greater strengths quicker (dueto the increased percentage of tricalcium silicatein cements). This meant that a given strength ofconcrete (normally tested at an age of 28 days)could be achieved with less cement. However,concretes were now made not only with lowercement contents, but also with lowerpercentages of the ingredient in cement (i.e.

dicalcium silicate) that contributed to longerterm strength development. This resulted in alowering of the durability properties of theconcrete. There was also a worldwide scarcityof timber for construction, causing less durablespecies of timber to be used for construction.Although such species were chemically treatedto improve durability, the efficiency oftreatment may not always have been adequate.

The passage of time (especially since 1975) hasof course seen increasingly greater awareness ofdurability issues, and these have been reflectedin codes of practice, especially in those forreinforced concrete. It can therefore be arguedthat the greater awareness of durability issueshas compensated for some of the detrimentalimpacts on durability described above. In thissame period, building durability has beenimproved through the availability of goodquality waterproofing materials, performanceenhancing admixtures for concrete andspecialist repair materials (e.g. repair mortars).However, building longevity may havedecreased due to the modern practice of hidingmost of the structural elements behind ceilings,paneling and facades, thus making inspection(and hence the early arresting of deterioration)more difficult.

2. Objectives and Methodology

The first objective of this paper is to analyse aset of condition evaluations carried out onbuildings from the ages of 7 to 125 years, and to

draw various lessons from that analysisregarding the factors that either increase ordecrease the longevity of buildings. Theseevaluations have not been carried out in a

random fashion, but rather in response toclients. At early ages, such evaluations aregenerally made only due to changes of buildingownership. In mid life a need for evaluationoften occurs due to unexpected deterioration.At older ages, clients request evaluationsbecause of concern regarding the continued

safety of their buildings. Many of theseevaluations are based largely on visualinspection, but some of them are backed up bya reasonable degree of sampling for materialproperties, inclusive of durability indices (e.g.Dias, 1994; Dias and Jayanandana, 2003; Diasand Sivasubramaniam, 1989).

The second objective of this paper is to analysesome data regarding the depths of carbonationand surface chloride levels of some reinforcedconcrete elements or structures, because

carbonation and chloride ingress are the twomain mechanisms that lead to the deteriorationof such structures. Considerable focus is placedon variations of such indices within thestructure itself.

The carbonation depths have been obtained byspraying a 1% phenolphthalein solution ontofreshly cut surfaces and noting the depth thatremains colourless. The fresh cuts were madeeither by coring (where the core is used for avariety of other purposes such as strengthtesting) or by advancing a drill bit into thesurface in increments of 5 mm, spraying thephenolphthalein solution into the hole at eachincrement and noting the depth at which theoutflowing liquid is pink in colour. Thecarbonation depths in a structure at a given agewill help us to estimate how much longer it willtake for the carbonation front to reach thereinforcement (i.e. for the incubation phase tobe completed), after which the likelihood ofcorrosion increases significantly. If the front hasalready passed the level of the reinforcement, itsignals the need to take stringent measures forensuring that the reinforced concrete elementsare waterproof.

Procedures for determining the chloride profilewithin the concrete cover zone are welldocumented (e.g. see de Rooij and Polder,2004). This can be done by using extractedcores, slicing them and obtaining the chloridecontents at various depths. It is then possible topredict the time at which the chloride content atthe level of the reinforcement will reach acertain threshold value for corrosion initiationby using the surface chloride concentration andthe diffusion coefficient obtained from the

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chloride profile. However, obtaining thediffusion coefficient in this way is difficult andtedious (de Rooij and Polder, 2004).

As such, the above modeling can also be doneby using values published in the literature (e.g.Bentz and Thomas, 2012). These depend on the

water/cement ratio (which affects the initialdiffusion coefficient) and type of cement (whichaffects the age dependent variation of thatcoefficient). Whatever method is used, thesurface chloride content must be obtained fromthe structure being examined. Publishedliterature also gives guidance regarding therates of surface chloride build-up. However,such broad generalizations may not beaccurate, and there could also be variationsdepending on the micro environment.

The surface chloride contents for the casestudies in this paper have been obtained bytaking the surface layer of the element, whethera plaster coating (of around 10 mm thickness)or a surface slice of 5 mm from extracted cores,and determining either the total or watersoluble chloride content in that layer by acid orwater extraction respectively.

3. Case Studies of Deterioration

Table 1 gives a few cases of buildings that wereinspected for condition evaluation over aperiod ranging from 1988 to 2011, with the ageof the building at inspection given inparentheses. They are listed in inverse order ofyear of construction, which also happens tocorrespond to increasing age when theinspection was made. The cases can be dividedinto three broad categories, separated by boldhorizontal lines in Table 1. The 7 and 12 yearold buildings, which do not show any visibledeterioration, fall into the first category.

In the next category are buildings of ages 25 to30 years where distress of varying degree hasoccurred in reinforced concrete elements, dueto chloride induced corrosion. The chloridesource for both the Hotel Sunflower andBuddhist Girls School is sea spray. It should benoted that the much greater corrosion in thelatter is due to poor construction. For thePuttalam Cement Works, the chloride sourcewas the groundwater used during construction(Dias and Jayanandana, 2003), and for the

Bandaranaike Wing of the Colombo GeneralHospital, contamination from the toilets (Diasand Sivasubramaniam, 1989). This suggests thatserious repair work may become necessary

after around 30 years if reinforced concreteelements of a building are exposed to a chloridesource.

In the last category are buildings that havesurvived for 65 to 125 years. It should be notedthat the main structural elements are not of

reinforced concrete in these buildings; note thatthese have been constructed prior to the year1945, alluded to before. Two of the 100 year oldbuildings had masonry loadbearing walls andtimber floors too - i.e. no steel at all. Thiscombination is arguably the best combinationfor ensuring long service life. The rest of thebuildings in this category are steel framed, withreinforced concrete floors or roofs. In almost allcases the reinforced concrete elementsexperienced significant corrosion, especiallyroofs and toilet areas. The Grand Hotel

displayed only minimal deterioration in theslabs above the kitchens, which are moist andhumid environments. In general hotel buildingstend to be well maintained, with defectsattended to promptly. Steel columns and beamsthat were exposed (and hence easily painted)performed very well, as seen in the 125 year oldGaffoor Building (Figure 1), where the contrastwith the reinforced concrete slab is stark. Onthe other hand, encasing the columns inconcrete (Figure 2) and the beams in a meshand plaster covering (Figure 3) resulted inundetected corrosion of the structural elements.

Figure 1 Exposed steel columns and beamsin the 125 year old Gaffoor Building

4. Depths of Carbonation

Apart from a chloride environment, referred toabove, reinforced concrete in all environmentswill experience carbonation. When thecarbonation front reaches the reinforcement, thechemical protection given to it by the concrete

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Table 1 Analysis of Condition Evaluations

Building Year &Age (yrs)

BuildingType

Deterioration Comments

Smart ShirtsFactory,Katunayake

1991(7)

RC frameand slabs

Not apparent

Tourist BoardBuilding,Colombo 4

1982(12)

RC frameand slabs

Not apparent

Buddhist GirlsSchool, Mt.Lavinia

1977(25)

RC frameand slabs

Columns and sunshadesbadly corroded

Location close to coast;poor quality construction

Hotel Sunflower,Negombo

1974(25)

RC frameand slabs

Some corrosion Location close to coast

Puttalam CementWorks

1970(28)

RC frameand slabs

Some buildings badlycorroded

High chloride levels ingroundwater used forconcreting

BandaranaikeWing, ColomboGeneral Hospital

1958(30)

RC frameand slabs

Severe corrosion in toiletarea slabs

High chloride levelsthrough operation

BaursTenemants,Grandpass Road

1936(65)

Steel frame;RC slabsand roof

RC roof badly corroded;also open corridor andtoilet slabs

Poorly maintained

Angoda MentalHospital

1925(72)

Steel frame,RC slabs

Toilet area slabs badlycorroded

Poorly maintained

Grand Hotel,Nuwara Eliya

1911(100)

Masonry;timber & RC

floors

Some deterioration inslabs above kitchens

Generally coolenvironment; wellmaintained.

Central Point,

Colombo Fort

1911

(100)

Steel frame;

RC slabsand roof

Corrosion in internal

cased columns and roof

Institute ofAesthetic Studies,Colombo 7

1899(100)

Masonry;timber floor;

RC roof

All RC componentscorroded

Gaffoor Building,Colombo Fort

1886(125)

Steel frame& roof; RC

slabs

Severe corrosion in slabs

Figure 2 Significant corrosion in concreteencased steel internal column inCentral Point building

Figure 3 Corrosion in steel floor beamcovered by wire mesh and plaster inCentral Point building

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will be lost, and corrosion will take place,especially in a moist or wet environment. Thedepth of carbonation is considered to be afunction of the square root of time. Figure 4gives a relationship for these two entities (thetrend line is not forced through the origin) forsome of the buildings in Table 1 together with a

few others. Such a universal relationship willnot strictly be possible for concretes of variousqualities, and even moisture conditions.However, since most of the concretes are ofaround grade 20 quality, Figure 4 could be usedto obtain approximately the likely carbonationdepths in concretes of various ages.

y = 4.924x

R = 0.850

0

10

20

30

40

50

60

70

80

0 2 4 6 8 10 12 14DepthofCarbona

tion(mm)

Age ^ 0.5 (years ^ 0.5)

Figure 4 Carbonation depth as a function of

the square root of time

The slope of a logarithmic plot between depthof carbonation (d) and time (t) will give anestimate of the exponent n, in the relationshipd = k(t)n, where k is a constant. Such a plot inFigure 5 gives the exponent as 0.69, somewhathigher than the usually adopted value of 0.5(i.e. the square root of time law). This may bedue to the possibility that the older concreteshave a higher k value than the more recent ones(Richardson, 1988). A plot using only the firstfour data points in Figure 5 (corresponding to amaximum age of 30 years and years of

construction from 1958 to 1991) gives theexpected slope of 0.52. It should be noted thatthese four data points all fall below theregression line in Figure 4.

Figure 5 is based on the average carbonationdepths from the buildings surveyed. There canhowever be significant differences betweenvarious areas in a building. For example, Figure6 shows the differences in depths ofcarbonation for toilet areas compared tocorridor ones in the 30 year old Bandaranaike

Wing of the Colombo General Hospital (Diasand Sivasubramaniam, 1989). The corridorareas were more carbonated because the

concrete was dry, whereas the toilet areas wereless carbonated because the concrete was wet,with 4 zero values too. However, there isgreater scatter in the values for the toilets,inclusive of some high values these regionswould be very susceptible to corrosion if thecarbonation depth exceeds the cover provided,

because of the wet conditions. The phenomenaof zero carbonation depths and widespreadvariation in such depths within a building havebeen reported before (Roy et al, 1996).

Figure 5 Determining the exponent n in theexpression d = ktn

0

5

10

15

20

25

30

35

40

1 2 3 4 5 6 7 8

DepthofCarbonation(mm)

Toilet areas

Corridor areas

Toilet average

Corridor average

Figure 6 Carbonation depths atBandaranaike Wing, Colombo GeneralHospital

5. Surface Chloride Levels

Figure 7 gives the variation in the rate ofsurface chloride build up for different elementsin 3 coastal hotels of varying ages. There is aclear difference between the rates for interiorand exterior elements, with the former beingsignificantly less than the latter and displayingmuch less scatter. It should be noted that theserates have been obtained from the water solubleaverage chloride contents in plasters of

thickness around 10 mm. The publishedliterature for total surface chloride build uprates on concrete surfaces can range from0.004% to more than 0.1% by weight of concrete

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per year, depending on the proximity to thecoast (Bentz and Thomas, 2012).

0.0000

0.0010

0.0020

0.0030

0.0040

0.0050

Interior

slabs

Exterior

slabs

Exterior

beams

Exterior

columns

Chloridebuildupra

te(%/year)

21 yrs

28 yrs

34 yrs

Figure 7 Surface chloride build up rates at 3

coastal hotels of different ages

Another example of within structure surfacechloride level variations is given in Table 2 forthe 100 year old Central Point building inColombo Fort, a capital port city. These total(i.e. acid soluble) chloride levels were obtainedfrom 5 mm thick slices cut from the bottomsurfaces of 4 cores taken at each floor level. Thevery high levels in the fourth and fifth floorscompared to the lower ones may be due to theshielding of the lower floors by surroundingbuildings. It may also be due to sea spray

contaminated rainwater entering the upperfloor levels through observed leaks in theconcrete roof. The evidence for the chloridelevel variation is confirmed by the degree ofcorrosion observed in the mesh reinforcementembedded in those cores. Figures 8(a), 8(b) and8(c) give examples of the degree of corrosiondefined as low (L), medium (M) and high (H).

6. Concluding Discussion -Implications for Practice

The case studies in Table 1 indicate that if verylong service life is required, considerationshould be given to using construction materials

such as masonry for walls, timber for floors andexposed (not encased) steel sections forcolumns and beams. Such materials, especiallythe steel sections, will however requirecontinuous maintenance. Reinforced concrete,although very popular after around 1945, isgood for normal life buildings (i.e. 50 to 60

years) that need little maintenance.

If reinforced concrete is used for buildings inchloride environments, provision will have tobe made for improved design (e.g. greatercover and better quality concrete); else thebuildings may reach only around half theirexpected service life.

Table 2 Surface chloride content variationsin Central Point building

Floor Chloride content(w/w %)

(range, average)

CorrosionLevel

(H, M, L)

Ground 0.02 - 0.04 (0.03) L, L, L, LFirst 0.03 0.05 (0.04) L, L, L, LSecond 0.03 0.04 (0.038) L, L, L, MThird


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similar environment. For example, the estimatefor the carbonation related incubation phaseduration can be obtained both from thebuilding concerned and also from an overallcurve for buildings of varying ages

References

1. Bentz, E. C. and Thomas, M. D. A. (2012).Life-365 Service life Prediction Model forReinforced Concrete Exposed to Chlorides:Computer Program and user manual, v. 2.1.Life-365 Consortium II, January.

2. BS 7543: 1992. Guide to Durability ofBuildings and Building Elements, Productsand Components. British StandardsInstitution, Milton Keynes.

3. BSEN 1992: Part 1-1: 2008 Eurocode 2:Design of concrete structures: General rules

and rules for buildings. British StandardsInstitution, Milton Keynes.

4. de Rooij, M. R. and Polder, R. B. (2004).What Diffusion Coefficient is used forChloride Diffusion Modeling? In Advancesin Concrete through Science and Engineering.RILEM International Symposium, March.

5. Dias, W. P. S. (1994). StructuralAppraisal of Reinforced ConcreteBuildings from In-Situ MaterialProperties - Some Issues and Insights.Transactions, Institution of Engineers, SriLanka, pp. 129-145.

6. Dias, W. P. S. (2003). Useful life ofBuildings. University of Moratuwa,Moratuwa, June.http://www.slaasmb.org/USEFULLIFE OF BUILDINGS.doc. Accessed23/03/2012.

7. Dias, W. P. S. and Jayanandana, A. D.C. (2003). Condition Assessment of aDeteriorated Cement Works. ASCE

Journal of Performance of ConstructedFacilities. Vol. 17, No. 4, pp. 188-195.

8. Dias, W. P. S. and Sivasubramaniyam, S.(1989). Assessment of Floor Slabs in theBandaranaike Wing of the ColomboGeneral Hospital. Engineer (Sri Lanka).September, pp. 27-36.

9. Richardson, M. G. (1988). Carbonation ofReinforced Concrete: Its Causes and

Management. Citis, London.

10. Roy, S. K., Northwood, D. O. and Poh,K. B. (1996). Effect of Plastering on theCarbonation of a 19 year old ReinforcedConcrete Building. Journal ofConstruction and Building Materials, Vol.10, No. 4, pp. 267-272.

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Potential and Viability of Rice Husk Based PowerGeneration in Sri Lanka

Asanka S. Rodrigo and Shantha Perera

Abstract: Due to intense fuel dependency on energy production in the world, cost of energy isnow heavily depends on the prices of fossil fuels. Most of the countries in the world are suffering dueto this and Sri Lanka is no exception. It is in this context promotion of biomass, as a renewable source,is so vital to the country. Rice being the staple food of the country as well as the crop with highest landarea under cultivation, rice husk (RH) generated in paddy processing was found to have a significantpotential in power generation. This paper investigates the possibility of using rice husk as a viablesource of power generation in Sri Lanka. It is clearly seen that there is a significant potential in thedistricts of Ampara, Polonnaruwa, Anuradhapura and Kurunegala for power generation using ricehusk. It was found that 30% of excess RH can be exploited for power generation with an annualenergy potential of 180 GWh. This potential can be exploited by (1) Commercial scale RH power

plants, (2) Small scale power plants under net metering scheme and (3) Off grid RH power plants.

Keywords: Rick husk, power generation, viability, gasification, combustion.

1. IntroductionSri Lankas energy sector has been ailing for thelast two decades due to its excessivedependency on petroleum and lack of diversityin energy sources in the energy supply mix. In

year 2011, the primary energy share in SriLanka was 46% from biomass, 42% frompetroleum, 12% from Hydro and rest from thenon-conventional renewables [1, 2]. Initially,almost entire electricity requirement of thecountry was met by hydropower whilst gradualincrease in demand for electricity during thelast decade of the 20th century shiftingelectricity generation more towards thermalpower.

There are no proven fossil fuel resources in Sri

Lanka. Therefore, there is a high emphasis onintroducing non-conventional renewablesources to the electricity sector. Having realizedthis fact, the government of Sri Lanka set atarget of achieving 10% of electricity demandfrom non-conventional renewable energysources by 2015 as set out in the national energypolicy of Sri Lanka [3]. It is expected to connectfeasible renewables to national grid asdistributed generators, which can also be usedto optimize the network use [4]. Biomass hasbeen identified as one of the most potential

sources of renewable energy for powergeneration in Sri Lanka [3]. At present, biomassis confined to domestic cooking and to someindustrial thermal applications.

In Sri Lanka, rice being the staple food of thecountry as well as the crop with highest landarea under cultivation, produces substantialquantity of rice husk (RH) as a waste product inpaddy processing. Part of RH produced is usedas a source of thermal energy in a fewapplications while the balance is burnt ordumped in the open air, causing a lot ofenvironmental hazards. If this excess RH can beexploited for power generation that can be usedto displace part of oil used in power generationand can add more security to energy supply.

RH is converted to energy using differenttechnologies such as direct combustion, co-firing, gasification, pyrolysis, and anaerobicdigestion [5]. However, the two most provenand common technologies are the directcombustion and the gasification [5, 6, 7]. Mostof todays biomass power plants are direct-firedsystems where the biomass fuel is burnt in aboiler to produce high-pressure steam, which isused to power a steam turbine driven powergenerator.

Eng. (Dr.) Asanka S. Rodrigo, Ph.D., M.Sc.(Eng),B.Sc.Eng.(Moratuwa), MIEEE, MIEE, AMIE(Sri Lanka),Senior Lecturer, Department of Electrical Engineering,,University of Moratuwa.Eng. Shantha Perera, M.Sc., B.Sc.Eng.(Moratuwa), CEng,MIE(Sri Lanka), Chief Engineer, Ceylon Electricity Board.

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Gasification is another commonly used optionthat can be used to generate electricity usingRH. This technology is now widely being usedin rice growing countries for driving small scalepower plants of the order of 10 kW- 100 kW,though the technology can be used for highercapacities of several Mega Watts [9, 10].

Therefore, RH is considered as one of thepotential sources of power generation in SriLanka as it is renewable, sustainable andindigenous, as the rice is the staple food of thecountry as well as the crop with highest landarea under cultivation. Furthermore, RH isconsidered as a waste material with negligiblecommercial value at the moment. Since it beinga local fuel, it will provide financial benefits tothe local community as well. Therefore, themain objectives of this study were to assess the

potential of rice husk based power generationin Sri Lanka and to analyze the economics ofharnessing this resource.

2. MethodologyFirst, the paddy production data of the countryover last twenty years were collected andanalyzed to determine the potential of rice huskproduction at national level. From the initialinvestigations, highest RH generation districtswere identified by analyzing paddy productioncapacity and milling capacity. As a case study,one of the highest potential districts wasconsidered for detailed study. In order tocollect data pertaining to availability anddistribution of rice mills, their capacities andaverage rice production, type of rice beingprocessed, a survey was conducted among therice mills in the selected district. During thissurvey, data from 650 rice mills were collectedand 338 mills were identified as the mills thathave significant milling capacity. Using the

data, the maximum size of the RH based powerplant and the conversion technology to be usedare identified. Finally, a financial analysis forthe plant was performed to ensure the viabilityof the power generation using RH. Even thoughthe case study was confined to a limited area ofthe country, the results obtained were used toassess the potential at the national level.

3. Paddy Cultivation in Sri LankaThe total land area under paddy cultivation in

Sri Lanka is estimated to be about 870,000hectares [8] at present and this is the highestland area occupied by any single cropaccounting for almost 34% of total agricultural

lands in the country [10]. As paddy is a wetlandcrop that needs a lot of water for its growth, it iscultivated seasonally in Sri Lanka so that it getsenough water from rainy seasons. The twoseasons in the year that the paddy is cultivatedare known as Maha and Yala which fallsduring North-East monsoon (November to

February) and South-West monsoon (May toSeptember) respectively. Figure 1 shows theseasonal variation of the paddy production inSri Lanka.

Figure 1- Paddy production in two seasons from

1952 to 2010 (Source:Paddy Statistics,Agriculture andEnvironment Statistics Division, Department of Censusand Statistics-Sri Lanka [10])

Accordingly, it can be seen that production ofMaha season is almost double that of Yala

season. Since rice is the staple food of thecountry, demand for rice remains almostconstant throughout the year. Therefore, paddyis stored and released to the market as rice at aconstant rate. Rice production of the countryhas increased from about 2.2 million tons toabout 4.5 million tons over a period of 20 years.This clearly shows that there is a continuousgrowth of paddy production in the country. Inorder to find the paddy production trend in SriLanka, paddy production data was fitted into atrend line as shown in Figure 2.

Figure 2- Annual paddy production inthousand tons from 1980 to 2010

0

5001000

1500

2000

2500

3000

3500

4000

4500

5000

1952

1959

1966

1973

1980

1987

1994

2001

2008

Padd

yProduction(000Mt.)

Cultivation Year

Maha Season

Yala Season

R = 0.833

0

1,000

2,000

3,000

4,000

5,000

6,000

7,000

1975

1980

1985

1990

1995

2000

2005

2010

2015

2020P

addyProduction,

P(000Mt.)

Cultivation Year, t

ENGINEER 10


19/84

3 ENGINEER

It is clear that there is an increasing trend inpaddy production. After liberating the countryfrom 30 year long civil war, most of the paddylands which had been abandoned in theNorthern and the Eastern provinces are nowbeing added to paddy farming and this too willhave a considerable impact on the paddy

production in the future.

4. Availability of Rice HuskThe outer cover of paddy grain is called as theRH which accounts for about 14%-27% of itsweight [11]. The gross energy content of the RHcan be determined using Husk to Paddy Ratio(HPR) and calorific value (CV) of RH. CV of RHhas been reported by various research works tobe in the range of 12.1-15.2 MJ/kg [7, 12]. SriLanka cultivates different variety of paddy.HPR values for most common paddy veritiesare given in Table 1. Since HPR varies between18% and 23% for different varieties of paddy,an average value of 20% was taken for thefuture analysis. Similarly, average CV value of13.6 MJ/kg is considered for the analysis.

Table 1- Husk to Paddy Ratio values ofcommon local paddy varieties

Paddy Variety HPR

H4 0.1972

BG 3-5 0.1816Podiwee A8 0.2166

Pachchaperumal 0.2065

BW 78 0.2274

BG 400-1 0.2012

LD125 0.2300

BG33-2 0.1898

BW 170 0.2170

MI 329 0.2045

(Source: National Cleaner Production Centre, Sri Lanka[11])

Even though paddy is cultivated all over thecountry, paddy is not grown at same scaleeverywhere. It was found that Ampara,Polonnaruwa, Anuradhapura and Kurunegaladistricts show a greater potential due to theirhigher production compared to the rest of theareas in the country (see Figure 3). However,paddy production is not the only indicator thatshows the real RH availability; instead thepaddy processing/milling capacity of eachdistrict will be a better criterion. Table 2 showsthe milling capacity of highest paddy

production districts.

Figure 3- Annual Average Paddy Productionin Different Areas (Year 1999 to 2010) (Source:

Paddy Statistics,Agriculture and Environment StatisticsDivision, Department of Census and Statistics-Sri Lanka

[10])

Table 2- Milling Capacity of Higest PaddyProduction Districts

No. of Mills

Milling Capacity(kg/Day)

Notfunctioning

Total

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