International Journal of Sustainable Built Environment (2013) 2, 27–40

Gulf Organisation for Research and Development

International Journal of Sustainable Built Environment

ScienceDirectwww.sciencedirect.com

Original article

Physiochemical characterization of coarse aggregatesin Qatar for construction industry

Marwa Al-Ansary a,⇑, Srinath R. Iyengar b

a Qatar Shell Research and Technology Centre, Department of Sulphur utilisation, Qatar Science and Technology Park, PO Box 3747, Doha, Qatarb Texas A&M University at Qatar, Department of Mechanical Engineering, PO Box 23874, Doha, Qatar

Received 25 March 2013; accepted 20 July 2013

Abstract

Due to the sheer volume of construction activities in Qatar, the market of building materials including aggregates is stressed. Thecommercially available natural aggregates are either local limestone aggregate or imported limestone as well as gabbro aggregates fromthe United Arab Emirates. In addition, recycled concrete aggregates (RCA) are produced since 2009 as a result of the extensive construc-tion and demolition activities. It is estimated that around 20,000 tons of construction and demolition (C&D) wastes are produced daily inQatar; half of which are converted daily to RCA. Imported limestone and gabbro aggregates are widely employed for various construc-tion activities in Qatar; however the use of local limestone aggregates are limited due to their substantial heterogeneity, uncontrolledwater absorption and abrasion quality. Although, the specification of RCA for concrete applications has recently been introducedthrough the revised Qatar construction standards (QCS) in 2010, their commercial use is under experimental evaluation. However,the properties of the aforementioned virgin and recycled coarse aggregates were hardly ever systematically published. Hence, this studypresents the initial physiochemical characterization and comparison of the virgin aggregate properties, with those of locally availableRCA as a sustainable alternative. The physiochemical properties were bench marked against the stipulated thresholds of QCS (2010)and other characterization properties.

It was observed that both local limestone and RCA have inferior water absorption and porosity characteristics in comparison toimported gabbro and limestone aggregates. Previous international standards and studies have demonstrated the successful partialRCA replacement of imported virgin aggregates in concrete applications; and if implemented, could potentially offer significant economicand environmental benefits to the State of Qatar.

However, it was recommended to undertake further laboratory studies to assess the mechanical performance and durability of suchreplacements prior to practical implementations within the construction industry in Qatar.

Keywords: Construction and demolition (C&D) waste; Limestone aggregates; Gabbro aggregates; Recycled concrete aggregates (RCA); Qatar

� 2014 The Gulf Organisation for Research and Development. Production and hosting by Elsevier B.V.Open access under CC BY-NC-ND license.

2212-6090 � 2014 The Gulf Organisation for Research and Development. Prod

http://dx.doi.org/10.1016/j.ijsbe.2013.07.003

⇑ Corresponding author. Tel.: +974 44599863; fax: +974 44599859.E-mail addresses: m.al-ansary@shell.com (M. Al-Ansary), sri-

nath.iyengar@qatar.tamu.edu (S.R. Iyengar).

Peer-review under responsibility of The Gulf organisation for Researchand Development.

Production and hosting by Elsevier

1. Introduction

Qatar is witnessing a rapid growth in the constructionand building industry sector in the past few years. Massivequantities of building materials are needed to accommo-date the wide expansion as well as the rapid speed of theconstruction activities. In 2005, the construction and real

uction and hosting by Elsevier B.V. Open access under CC BY-NC-ND license.

Fig. 1. C&D waste processing to RCA at Rawdat Rashid site, Qatar.

Table 1Different grading of RCA produced at Rawdat Rashid site.

Grading Possible usage

0–100 mm Storage0–75 mm Backfilling materialPowder 0–5 mm Filler and fines in asphalt5–10 mm (also known as 5 mm) Aggregates in asphalt10–15 mm (also known as 10 mm) Aggregates in concrete and asphalt15–20 mm (also known as 20 mm) Aggregates in concrete and asphalt20–25 mm Aggregates in concrete and asphalt5–50 mm Subbase Class A5–37.5 mm Subbase Class B5–25 mm Subbase Class C

Table 2Current approximate market costa of different types of aggregates in Qatarfor Q2–2012.

Aggregate type Approximate cost in USD/ton

Local limestone 3–4Imported gabbro 20Imported limestone 20RCA 7–8

a These rates have been compiled based on personal communicationswith the various aggregate vendors in Qatar.

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estate sector in Qatar contributed to 5.7% and 2.3% of theGDP respectively (Al-Khatib, 2009). The state of Qatar hasrecently been awarded the 2022 football world champion-ship. Related construction and renovation of 12 world classstadiums as well as massive investment in infrastructure areplanned which include a new international airport, aninternational harbor, an integrated rail network and metrosystem projects (Qatar 2022, 2011). Moreover, the govern-

ment of Qatar has set aside USD 17 billion for the con-struction of hotels and other tourism relatedinfrastructure (Qatar 2022, 2011). Consequently, a vastamount of building material is needed to accommodate thisrapid industrialization and infrastructure expansion.

Due to this sheer volume of construction activities, themarket of building materials including aggregates isstressed. The commercially available natural aggregatesare either local limestone aggregate or imported limestoneas well as gabbro aggregates from the United Arab Emir-ates (UAE). According to the Qatar Customs database

Table 3Tests and permissible limits for physical and chemical properties of coarse aggregates for concrete as stipulated by QCS (2010).

QCS requirement QCS standard will be based on QCS 2010 Permissible limits

British standards/EuropeanNorm. (BSEN)

American Standards for TestingMaterials (ASTM)

Grading (dry) BSI (2012b) ASTM (2006a) Standarda

Material finer than 75micronsb BSI (2009a) ASTM (2004b, 2006a) 2% maxClay lumps and friable particles – ASTM (2010a) 2% maxLightweight pieces – ASTM (2012a) 0.5% maxOrganic impurities – ASTM (2004a) color standard not darker than plate No.3Water absorption (saturated

surface dried)BSI (2000) ASTM (2012b) 2.0% max

Specific gravity (apparent) BSI (2000) ASTM (2012b) 2.6 minShell content BSI (1998b) – 3% maxParticle shape:

Flakiness IndexElongation Index

BSI (2012a) ASTM (2010c)30% max RCC & 40% PCC35% max RCC & 45% PCC

Acid soluble chlorides BSI (2006) – 0.03% max for reinforced and massconcrete0.01% max for pre-stressed and steam curedstructural concrete

Acid soluble sulfates BSI (2009b) – 0.3% maxSoundness (loss by magnesium

sulfate 5 cycles)– ASTM (2005b) 15% max

Mechanical strength:10% fines value (dry condition) BSI (1990b) 150kN minAggregate Impact value BSI (2010) ASTM (2006b) 25% maxLoss by Los Angeles abrasion BSI (2010) ASTM (2012c) 30% maxAggregate crushing value BSI (1990a)Drying shrinkage BSI (2008) 0.075% maxPotential reactivity of aggregates: –Alkali –silica reaction ASTM (2007b)Alkali-carbonation reaction ASTM (2005a) Not reactiveOf cement-aggregate

combinationASTM (2010b) 6 month expansion 0.10% max

a There were no lower and upper permissible limits specified in QCS (2010), therefore QCS (2007) limits were used and are plotted in Fig. 3.b Natural, uncrushed/crushed rock, wet sieve analysis.

M. Al-Ansary, S.R. Iyengar / International Journal of Sustainable Built Environment 2 (2013) 27–40 29

(2010), the aggregate imports1 in Qatar have increasedfrom 9.5 million tons in 2006 to 21.5 million tons in 2008.Geologically, most parts of Qatar are covered by karstifiedcarbonates, i.e. limestone deposits, of the Mid EoceneDamman Formation (Al-Ansary et al., 2012). In Qatar,there is a limitation on the use of local limestone aggregatesdue to its substantial heterogeneity thus leading to uncon-trolled quality, mainly for water absorption and abrasionvalues. The reported high water absorption and abrasionvalues of local limestone showed inferior performancewhen used in Portland and asphalt concrete mixes. Hence,local limestone aggregates are only used in restricted appli-cations, such as in some subbase layers of the road. Gabbroaggregate is geologically an igneous rock, which is chemi-cally equivalent to basalt. Gabbro is formed when moltenmagma is trapped beneath the Earth’s surface and coolsslowly; while, limestone is a sedimentary rock composedlargely of calcium carbonate or calcite (Vernon, 2000).

1 Figures include aggregates such as pebbles, gravel, broken or crushedstone, of a kind commonly used for concrete aggregates, for roadmetalling or for railway or other ballast, shingle and flint, whether or notheat-treated.

On the other hand, vast amount of construction anddemolition (C&D) wastes are produced as a result of theextensive construction and demolition activities generallyfrom the Gulf Cooperation Council (GCC) countries;including Qatar. It is estimated that around 120 milliontons per year of waste is produced by GCC countries ofwhich little is recycled or even managed (Landais, 2008).This figure is expected to be reaching 350,000 million tonsby 2014. Of the 120 million tons of waste, 55% is C&Dwaste, 20% is municipal waste, 18% is industrial wasteand 7% is hazardous waste (Qatar Today News, 2010).

Little data is available on the quantity or scale of theC&D wastes in Qatar. Nevertheless, C&D wastes havebeen generated from various extensive construction activi-ties undertaken all over the State of Qatar from early 2000to date, as well as from demolition and renovation worksthat are taking place as part of Qatar Vision 2030s develop-ment and expansion aspiration to transform Qatar into adeveloped country. Such wastes typically comprise of awide range of materials, such as Portland and asphalt con-crete debris, bricks, steel scraps, plastics, paper and wood.In 2007, a landfill for dumping C&D waste in Qatar was

Fig. 2. Classification of coarse aggregates used in this study.

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constructed in Rawdat Rashid,2 off Abu Samra road with asurface area of 8 square kilometers. In Mid 2009, QatarConstruction and Development Company (QCDC) wasawarded the bid for managing the C&D waste from theMinistry of Municipality and Urban Planning. Many inter-national municipalities are reusing and recycling the C&Dwastes in various applications. One of these applications isthe recycling of concrete debris into construction aggre-gates, which are called recycled concrete aggregates or sec-ondary aggregates.

Recycled concrete aggregates (RCA) have been pro-duced since 2009 as a result of the extensive C&D activitiesin Qatar. It is estimated that around 20,000 tons of C&Dare produced daily (�7.3 million tons/year); half of whichare converted daily to RCA. Currently, around 3 milliontons of RCA are commercially processed following theprocess summarized in Fig. 1. Table 1 summarizes differentgradings of RCA produced at Rawdat Rashid site andtheir potential usage.

The specification of RCA for concrete applications hasrecently been introduced through the revised Qatar con-struction standards (QCS) in (2010) (Section 5: part 2.9(concrete)). This section stipulated that recycled concrete

2 There are few C&D dumping sites outside the urban expansion circleat Qatar such as Rawdat Rashid and Dokhan. Rawdat Rashid isconsidered the largest dumping site in terms of C&D waste volumes.

should confirm to BS 8500 part 1 and part 2 specifications(BSI, 2002a, 2002b) or ACI 555R (ACI, 2001). Moreover,in part 6 (i.e. property requirements) subsection 6.2.3, Port-land cement concrete, with recycled aggregates was speci-fied as one of the concrete types to be used in Qatar. Itwas stated in QCS (2010) that ‘concrete with recycledaggregates shall be generally approved once the source ofrecycled aggregates is identified and approved by the engi-neer’. However, the commercial use of RCA in Qatar isunder experimental evaluation. Currently, the approximatemarket cost of different types of aggregates in Qatar forQ2–2012 is presented in Table 2.

2. Methodology

The objective of this paper is to provide an initial phys-iochemical characterization of the virgin aggregates com-mercially available and utilized in Qatar’s constructionindustry, and to compare them with the locally availableRCA as a sustainable alternative. The physiochemicalproperties of studied coarse aggregates were bench markedagainst the stipulated thresholds of QCS (2010); apart fromparticle size distribution which was compared to QCS(2007) limits. The requirements and permissible limits ofQCS (2010) are summarized in Table 3. The testing pro-gram can be classified as requirement property tests inaccordance to Qatar Construction Standards and othercharacterization properties tests. Moreover, the micro-

Fig. 3. Type of coarse aggregates used in this study.

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0 102030405060708090

100

0 5 10 15 20 25 30 35 40

Cum

ulat

ive

per

cent

age

pass

ing

Sieve opening in mm

Imported Gabbro 20mm

Imported Limestone 20mm

Local Limestone 20mm

RCA 20mm

Lower limit (QCS, 2007)

Upper limit (QCS, 2007)

0 102030405060708090

100

0 2 4 6 8 10 12 14

Cum

ulat

ive

per

cent

age

pass

ing

Sieve opening in mm

Imported Gabbro 10mmImported Limestone 10mmLocal limestone 10mmRCA 10mmLower limit (QCS, 2007)Upper limit (QCS, 2007)

Fig. 4. Particle size distribution for 10 and 20 mm aggregates used in this study.

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structure characteristics (viz. scanning electron micros-copy,3 X-ray fluorescence4 and X-ray diffraction5) of thevarious types of aggregates were also studied. Scanningelectron microscope was used to study the surface mor-phology of the aggregates, the X-ray diffraction was usedto identify the crystalline phases and the correspondingintensities of various compounds of the aggregates; whilethe X-ray fluorescence was employed to analyze the majorand trace elements present in the aggregates.

The different aggregates studied in this paper, their sizesand sources are summarized in Figs. 2 and 3. In this study,all imported aggregates (limestone and gabbro aggregates)

3 Scanning electron microscope model Quanta 400 by FEI Companywas used. SEM of samples was employed by firstly being vacuum driedand then mounted on an aluminum stub using a strong double-sidedadhesive tape. The microscope accelerating voltage ranged between 2 and5 kV to compromise between the sample charging and capturing high-resolution images. A working distance between 9 and 12 mm was used,whilst the magnifications used ranged from 30 to 6000 times.

4 ZSX PrimusII wavelength-dispersive X-ray fluorescence spectrometermanufactured by Rigaku Corporation was used in this study. Quickqualitative analysis is done and automatic peaks identified. The SQXsoftware provided by Rigaku enabled for more accurate semi-quantitativeanalyses of substances including light elements.

5 Theta-Theta type X-Ray Diffractometer model Ultima IV manufac-tured by Rigaku Corporation fitted with a copper anode diffraction x-raytube operating at 40 kV and 40 mA was used in this study. The PeakSearch and Qualitative Analysis software provided by Rigaku wasemployed to identify the peaks of the raw XRD data and subsequentlylinked with the Joint Commission on Powder Diffraction Standards-International Centre for Diffraction Data (JCPDS-ICDD) library carddatabase (PDF-2 Release 2007).

are exported from the United Arab Emirates via local sup-pliers in Qatar i.e. Construction Materials Co. L.L.C.(Qatar Quarry Company); while indigenous coarse aggre-gates (i.e. local limestone) are quarried from Qatar andcrushed and graded at Qatar Quarry Company. Only 10and 20 mm aggregates’ fractions are studied in this paper,as they are the most commonly used fractions in the pro-duction of Portland concrete ready mix and precast units.Other manufactured aggregates such as Lytag6, which arecommercially used in limited scale in Qatar, are not cov-ered in this study.

3. Experimental results and discussion

3.1. Results

� Fig. 4 presents particle size distribution for 10 and20 mm aggregates used in this study and compare themwith the upper and lower limits stipulated by QCS(2007).� Table 4 presents the results of physical and chemical

properties required by QCS (2010). The permissible lim-its as per QCS (2010) as well as the employed testingStandard are also presented in Table 4.

6 Lytag is the major commercial light weight aggregates (LWA)produced in the UK, which is manufactured from the pelletisation ofpulverised fuel ash in dishpans (Al-Ansary, 2007).

Table 4Results of physical and chemical QCS (2010) requirement properties for commercially utilized coarse aggregates in Qatar.

Test/Sample type Virgin aggregates Recycledaggregates

Permissiblelimits as perQCS 2010

Testing standard

Importedgabbro

Importedlimestone

Local limestone RCA

20 mm 10 mm 20 mm 10 mm 20 mm 10 mm 20 mm 10 mm

Physical properties

Water absorption (%) 0.45 0.645 0.37 0.46 3.5 1.7 3.3 5.5 2.0% Max BSI (2000)Clay lumps and

friable particle0.16 0.26 0.38 0.49 4.9 8.2 3.4 11.8 2.0% Max ASTM (2010a)

Relative density Oven dry 2.86 2.85 2.69 2.68 2.46 2.60 2.49 2.36 – BSI (2000)SSDa 2.88 2.87 2.70 2.69 2.54 2.64 2.57 2.48 – BSI (2000)Apparent 2.90 2.90 2.72 2.71 2.69 2.67 2.71 2.70 2.6 Min BSI (2000)

Shell content (%) Nil Nil Nil Nil Nil Nil Nil Nil 3.0% Max BSI (1998b)Light weight pieces (%) Nil Nil Nil Nil Nil Nil Nil Nil 0.5% Max ASTM (2012a)Flakiness index (%) 11.25 16.50 10.00 19.0 10.0 19.0 12.0 19.0 30.0% Max BSI (2012a)Elongation index (%) 20.25 12.75 19.0 25.0 19.0 24.0 20.0 23.0 35.0% Max BSI (2012a)Aggregate drying shrinkage

(%)0.027 0.027 0.010 0.010 0.020 0.020 0.020 0.020 0.075% Max BSI (2008)

Mechanical properties

10% fines (Dry) KN 336.0 339.3 340.0 420.0 330.0 400.0 320.0 380.0 150KN Min BSI (1990b)Aggregate impact value (%) 11.5 12.5 12.0 9.0 12.0 9.0 13.0 10.0 25% Max BSI (2010)Loss by Los Angeles

abrasion (%)10.3 11.8 11.0 15.0 13.0 16.0 14.0 17.0 30% Max BSI (2010)

Chemical properties

Injurious organic impurities Lighter than color standard plate No.3 color standard not darkerthan plate No.3

ASTM (2004a)

Loss by MgSO4 soundness(%)

0.60 0.91 1.30 2.08 1.39 2.26 1.54 2.51 15% Max ASTM (2005b)

Acid soluble chloride (%) 0.02 0.02 0.01 0.01 0.02 0.01 0.11 0.16 0.03% Max BSI (2006)Acid soluble sulfate (%) 0.12 0.15 0.20 0.20 0.35 0.30 0.89 1.48 0.30%Max BSI (2009b)

a SSD = saturated surface dry

Table 5Results of physical and chemical characterization properties for all studied aggregates.

Test/sample type Virgin aggregates Recycled aggregates Testing standard

Imported gabbro Imported limestone Local limestone RCA

20 mm 10 mm 20 mm 10 mm 20 mm 10 mm 20 mm 10 mm

Physical properties

Median diameter (D50) mm 17.5 7.6 15.5 7.6 12.5 8.2 16.5 7.0 ASTM (2011)Coefficient of Uniformity (Cu) 1.5 1.5 1.5 1.6 1.3 1.7 1.3 2.2Coefficient of Curvature (Cz) 1.0 1.0 1.0 0.9 1.0 1.0 1.0 1.1Classification according to USCS Poorly-graded gravels, gravel-sand mixtures, little or no finesPorosity (%) 1.3 1.9 1.0 1.2 8.6 4.3 8.2 12.9 ASTM (2007a)Bulk Density (kg/m3) 1658 1594 1472 1563 1442 1490 1305 1344 ASTM (2009)Inter-aggregate Voids (%) 0.421 0.440 0.452 0.416 0.413 0.427 0.476 0.429 BSI (1998a)

Chemical properties

aggregate pH 9.72 9.76 9.01 9.05 9.18 9.15 9.32 9.37 ASTM (2007c)

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� Table 5 presents the results of the other physical andchemical characterization properties for all studiedaggregates.� Fig. 5 presents scanning electron micrograph (SEM) of

all studied aggregates at �1000 magnification.� Fig. 6 presents the X-ray powder diffractograms (XRD)

of imported gabbro aggregates.� Fig. 7 presents the X-ray powder diffractograms (XRD)

of local and imported limestone aggregates.

� Fig. 8 presents the X-ray powder diffractograms (XRD)of RCA.� Table 6 presents the qualitative analysis of studied

aggregates based on XRD investigations. The abbrevia-tions employed for the major phases detected in XRDanalysis are also presented in Table 6.� Table 7 presents the semi-quantitative analysis of the

major and minor elements of studied aggregates basedon X-ray fluorescence (XRF) investigations.

Aggregate Size Aggregate Type

10mm 20mm

(a) Imported Gabbro

(b)Imported Limestone

(c) Local Limestone

(d)RCA

Fig. 5. Scanning electron micrographs of the different studied aggregates at �1000 magnification.

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3.2. Discussions

� Overall it was observed that all four types of studiedaggregates and their 10 and 20 mm fractions passedthe physical, mechanical and chemical limits of QCS(2010). However, local limestone and RCA failed tomeet the limits for water absorption, clay lumps and fri-able particles, and acid soluble sulfate. Additionally,RCA failed to meet the limits for acid soluble chloride.� Most of the aggregates complied with (QCS, 2007) upper

and lower limits for particle size distribution (apart from10 to 20 mm local limestone and 20 mm for imported gab-

bro aggregates). Nevertheless, according to the UnifiedSoil Classification System (ASTM, 2011), all aggregatescan be classified as poorly graded gravels.� Imported gabbro and imported limestone:– Both aggregates have passed the physical, mechanical

and chemical limits of QCS (2010); such as waterabsorption, clay lump specific gravity, shell content,light weight pieces, flakiness and elongation index,aggregate drying shrinkage, 10% fine (Dry) KN, aggre-gate impact value, loss by Los Angeles Abrasion, injuri-ous organic impurities, loss by MgSO4 soundness, acidsoluble chloride and sulfate percentage.

Fig. 6. X-ray diffractogram of imported gabbro aggregate.

Fig. 7. X-ray diffractograms of local and imported limestone aggregates.

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– Both aggregates have the lowest low water absorption aswell as clay lumps and friable material percentages andmeet QCS (2010) specifications.

– Both aggregates have the least value of Los AngelesAbrasion percentage, which indicates their highmechanical strength.

– Imported limestone has the lowest porosity of all aggre-gates which was in the range of 1.0–1.2%.

– From SEM (as per Fig. 5), imported gabbro aggregatesare having a dense sealed surface morphology whichexplains their low water absorption and porosity per-centage. The imported limestone also exhibited a similardense microstructure; and thus displayed low absorptionand porosity percentage as well.

– From XRD, imported gabbro aggregates are rich withmagnesium and calcium silicate compounds (as perFig. 6). The imported limestone is rich in calcite andquartz (as per Fig. 7 and Table 6). Dolomite was alsopresent but in small proportions only.

– From XRF, the surface elemental analysis for the gab-bro and imported limestone were in agreement withthe qualitative analysis results from XRD (as perTable 7).� Local limestone:– It has the highest water absorption among all nat-

ural aggregates, which are variable and can beabove the stipulated maximum 2% limit by QCS(2010).

Fig. 8. X-ray diffractogram of RCA.

Table 6Qualitative analysis of studied aggregates based on XRD investigations.

Mineral/phase Notation Chemical formula Relative % composition of sample

Imported gabbro Imported limestone Local limestone RCA

Antigorite a Mg3Si2O5(OH)4 28.54 – – –Clinopyroxene x Ca(Ti,Mg,Al)(Si,Al)2O6 14.06 – – –Edenite e NaCa2Mg5AlSi7O22(OH)2 11.24 – – –Plagioclase p Ca0.63Na0.37(Al1.63Si2.37O8) 28.81 – – –Fosterite f Mg2SiO4 16.35 – – –Dolomite d CaMg(CO3)2 – 6.08 55.01 43.74Calcite c CaCO3 – 45.73 34.15 42.41Quartz q SiO2 – 48.19 10.77 13.8

Table 7Semi-quantitative analysis of the major and minor elements of studied aggregates based on XRF investigations.

Element Component Mass %

Imported gabbro Imported limestone Local limestone RCA

Boron B2O3 – – – 4.01Carbon CO2 8.25 41.6 40.8 41.5Sodium Na2O 1.32 – 0.176 0.383Magnesium MgO 13.1 1.03 16.3 15.3Aluminum Al2O3 13.2 0.799 1.11 1.82Silicon SiO2 39.4 2.31 11.0 3.64Phosphorous P2O5 0.0685 0.094 0.0114 0.0108Sulfur SO3 0.0858 0.253 0.0875 1.57Chlorine Cl 0.110 0.0131 0.108 0.179Potassium K2O 0.0558 0.183 0.0219 0.0658Calcium CaO 12.4 53.6 29.8 31.3Titanium TiO2 0.810 – – –Chromium Cr2O3 0.104 – – –Manganese MnO 0.191 – 0.0315 0.0301Iron Fe2O3 10.9 0.235 0.343 0.218Nickel NiO 0.0655 – – –Strontium SrO 0.0209 0.0356 0.0109 –Barium BaO – – 0.0972 –

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– The clay lumps and friable material percentage wasabove the 2% max limit stipulated by QCS (2010).

– 20 mm local limestone has failed to comply with the lim-its specified by QCS (2010) in terms of the maximumpercentage for acid soluble sulfate; 10 mm local lime-stone was exactly on the border line with the samestandard.

– The porosity was 4–9% higher than those of otherimported virgin aggregates.

– From SEM (as per Fig. 5), it was observed that the sur-face morphology is relatively highly porous and dis-played larger particle sizes which, is in agreement withthe porosity values. From XRD and XRF, local lime-stone aggregates are rich in magnesium, with high pro-

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portions of dolomite with some presence of silica andcalcite (as per Fig. 7 and Tables 6 and 7). This resultwas in agreement with published results from Al-Kuwari(2008), which confirmed that these aggregates can alsocause alkali-aggregate reactions in concrete.

– All the above results can confirm the durability concernswith local limestone aggregates which limit its applica-tion as a building material in Qatar.� RCA:– Water absorption for RCA is significantly higher than

those imported aggregates from UAE. This can beattributed to the high percentage of clay lumps and fri-able particles present in the RCA.

– RCA is a very heterogeneous material and their qualityis dependent on the quality of the C&D concrete debris.Both the porosity and water absorption of RCA arehigher than those of the natural aggregates as being con-firmed with the Portland Cement Association (PCA,2012).

– RCA has failed to comply with the limits specified byQCS (2010) in terms of the maximum percentage foracid soluble chloride and sulfate.

– From XRD (see Fig. 8 and Table 6), it was revealed thatRCA comprised predominantly of calcite and dolomitewith a small proportion of quartz.

– From XRF, (see Table 7) the surface oxide distributionwas more similar to those of local limestone and is inagreement with the XRD results (as per Table 6)obtained.

– From SEM (as per Fig. 5), it was revealed that an extre-mely porous microstructure is one which supports theobserved porosity values.

4. Usage of RCA in other parts of the world

RCA is a very heterogeneous material wherein its qual-ity is highly dependent on the quality of the C&D debris.RCA quality is inferior to those of virgin materials, interms of water absorption and porosity. Although, the rel-evant properties of concrete which contain RCA are gener-ally lower than those of conventional concrete, but are stillsufficient for practical applications in civil engineering. Theconcrete produced using RCA can be employed in variousstructural applications; even as a high performance con-crete by adopting proper mix designs and suitable pozzola-nic additives. This has been confirmed by various studieswhich investigated a range of physical, chemical, mechani-cal and field investigations (Topcu et al., 2004; Poon et al.,2004; Xiao et al., 2005; Tu et al., 2006; Eguchi et al., 2007;Fonteboa et al., 2007; Rao et al., 2007; Xiao et al., 2007; Li,2008, 2009; Cabo et al., 2009).

Both the porosity and water absorption of RCA arehigher than those of the natural aggregates as being con-firmed with Portland Cement Association (PCA, 2012).Therefore only partial replacement of 20–30% of virginaggregates with RCA can be permitted for Portland cement

concrete applications as being confirmed by many pub-lished researches (Barritt, 2007; PCA, 2012). A researchreport launched by the UK WRAP (Waste Resourcesand Action Program) showed that using 20% recycledaggregate blended with natural aggregate has no negativeimpact on concrete performance (Barritt, 2007). AlsoUSA Portland Cement Association (PCA, 2012) confirmedthat replacement up to 30% of natural aggregates withRCA has no significant effect on the mechanical propertiesof concrete. However, replacement of higher percentagescan increase the drying shrinkage without significantlyaffecting the strength or the freeze–thaw resistance.

For concrete pavement applications, numerous studieshighlighted that concrete containing up to 50% of RCAcan be successfully employed for pavement construction(Bekoe et al., 2010; Gress et al., 2009; Smith and Tighe,2009; Vancura et al., 2009; Smith and Tighe, 2008; Kameland Abou-Zeid, 2008; Cuttell et al., 1997). Furthermore,such RCA-based Portland cement concrete (PCC) pave-ments have been reported to perform comparably withthe conventional PCC pavements (if not better) not onlyin the laboratory studies but also in real-field scenarios.In addition to the cost savings, utilizing large proportionsof RCA in PCC for pavements was reported to have noadverse effects on the flexural strength, splitting tensilestrength, the coefficient of thermal expansion, unconfinedcompressive strengths and the stiffness modulii of the pave-ment. Nevertheless, it has been recommended that theinclusion of reclaimed mortar be minimized (i.e. througheffective separation techniques) and the maximum size ofcoarse RCA employed to be 19 mm.

Although, only a few related short-term laboratoryinvestigations for hot-mix asphalt have been undertaken,it has been revealed that it is viable produce to asphalt con-crete using RCA as partial aggregate substitution whichcould meet the requirements of Marshall mix-design speci-fications (Wong et al., 2007; Aljassar et al., 2005). More-over, it has been reported by many transportationdepartments that using 100% coarse recycled aggregatesin concrete, performance similar to those with naturalaggregates have been achieved (Chini et al., 2001).

5. Conclusions and recommendations

Based on the results of the physiochemical characteriza-tion of coarse aggregates, imported gabbro was found tomeet all the physical, mechanical and chemical limits ofQCS (2010). Hence, it comes as no surprise that importedgabbro is the main source of coarse aggregates in Qatar,prevalently used in the construction industry. Furthermore,the data from this study suggests that the characteristics ofimported limestone are comparable with the gabbro aggre-gates and if required, can be employed as a compatiblereplacement of gabbro aggregates.

Alternatively, this study demonstrates that local lime-stone and RCA have inferior water absorption and poros-ity characteristics in comparison to imported lime stone

38 M. Al-Ansary, S.R. Iyengar / International Journal of Sustainable Built Environment 2 (2013) 27–40

and gabbro aggregates; thereby failing to meet at least fourof QCS (2010) prescribed limits. Hence, local limestonecannot be recommended directly for construction usageas virgin aggregates in concrete. However, based on theresults and in accordance to QCS (2007), it can be sug-gested that the local limestone of size above 25 mm couldbe employed as subbase material for pavementconstruction.

However, according to prevalent international guide-lines adopted for concrete mix design, the partial replace-ment of 20–30% of virgin aggregates by RCA is allowed.Also, the previous global research on a range of physical,chemical, mechanical and field studies have confirmed thesuccessful usage of RCA in concrete and asphalt; suchpractices being increasingly widespread in many countriessuch as USA, Germany, UK, The Netherlands andSingapore.

Despite international practices, QCS (2010) specifiesthat the concrete with recycled aggregates shall be generallyapproved once the source of recycled aggregates is identi-fied and ratified by the engineer. Since, RCA in Qatar isknown to be a heterogeneous material, the aforesaid rec-ommendation from QCS (2010) is still pertinent for thelocal construction industry and the same is fully supportedby the experimental data in this study.

Currently in Qatar, RCA above 25 mm is only used as asubbase material while the remaining fractions are stillstock piling in Rawdat Rashid site. Although, someresearch endeavors for RCA applications in concrete andasphalt mixes are underway, there is only very limited com-mercial use for RCA currently in Qatar. According to theQatar Customs database (2010), the aggregate imports ofQatar were 21.5 million tons in 2008. Hence, based onthe 7.3 million tons/year C&D waste generated, it can beinferred that up to one third of the natural imported aggre-gates could potentially be replaced by RCA.

Use of RCA in concrete applications could provide sig-nificant environmental and economic benefits to the Stateof Qatar; especially with its booming construction activi-ties. The economic advantage can be realized by partiallysubstituting the relatively expensive imported aggregateswith the cheaper and locally available RCA. Moreover, sig-nificant environmental impact will be achieved due toreduction in the demand of virgin aggregates by findingtechnically viable use of the rapidly growing local supplyof C&D waste.

However, it is recommended that further laboratorystudies should be undertaken to investigate the partialRCA replacements of virgin aggregates in concrete (viz.the mechanical performance and durability) and to assessthe viability of such practical implementations within theconstruction industry in Qatar.

Acknowledgments

The authors are grateful to the Construction MaterialsCo L.L.C. (Qatar Quarry Company) and in particular to

Mr. Stephen Ward and Mr. Salim Kutty; and to Mr. Mus-tafa Al Omanifrom Qatar Construction and DevelopmentCompany (QCDC) for providing access to their site andsharing their knowledge. Texas A&M University at Qatar(TAMUQ) is thanked for permitting the use of their testingfacility and Qatar Shell Research and Technology Centre(QSRTC) for sponsoring this study. The authors wouldlike to thank Dr. Eyad Masad (TAMUQ), Dr. MohammedYousuf (TAMUQ), Dr. Reginald Kogbara (TAMUQ),Mr. Sunifar Abobacker (QSRTC), Mr. WillemScholten (QSRTC) and Mr. Yousuf Saleh (QSRTC) fortheir support and guidance while carrying out this analysiswork.

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