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Journal of Cleaner Production 99 (2015) 59e74

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Journal of Cleaner Production

journal homepage: www.elsevier .com/locate/ jc lepro

Mechanical performance of concrete made with aggregatesfrom construction and demolition waste recycling plants

Miguel Bravo a, Jorge de Brito b, *, Jorge Pontes a, Luís Evangelista c

a ICIST, IST, Universidade de Lisboa, Portugal, Lisbon, Portugalb ICIST, Department of Civil Engineering, Architecture and Georresources, Instituto Superior T�ecnico (IST), Universidade de Lisboa, Lisbon, Portugalc ICIST, Lisbon's Polytechnic Engineering Institute (ISEL-IPL), Lisbon, Portugal

a r t i c l e i n f o

Article history:Received 11 June 2014Received in revised form24 February 2015Accepted 3 March 2015Available online 11 March 2015

Keywords:Recycled aggregatesConstruction and demolition wasteRecycling plantsConcreteMechanical performance

List of abbreviations: CDW, construction and derecycled aggregates; FRA, fine recycled aggregates; ITNA, natural aggregates; RA, recycled aggregates; w/c,* Corresponding author. Tel.: þ351 218419709.

E-mail addresses: miguelnbravo@gmail.com (M. BBrito), jorgempontes@gmail.com (J. Pontes),(L. Evangelista).

http://dx.doi.org/10.1016/j.jclepro.2015.03.0120959-6526/© 2015 Elsevier Ltd. All rights reserved.

a b s t r a c t

This research aims at analysing the mechanical performance of concrete with recycled aggregates (RA)from construction and demolition waste (CDW) from various locations in Portugal.

First the characteristics of the various aggregates (natural and recycled) used in the production ofconcrete were thoroughly analysed. The composition of the RA was determined and several physical andchemical tests of the aggregates were performed.

In order to evaluate the mechanical performance of concrete, compressive strength (in cubes andcylinders), splitting tensile strength, modulus of elasticity and abrasion resistance tests were performed.

Concrete mixes with RA from CDW from several recycling plants were evaluated, in order to under-stand the influence that the RA's collection point, and consequently their composition, has on thecharacteristics of the mixes produced.

The analysis of the mechanical performance allowed concluding that the use of RA worsens most ofthe properties tested, especially when fine RA are used. On the other hand, there was an increase inabrasion resistance when coarse RA were used. In global terms, the use of this type of aggregates, inlimited contents, is viable from a mechanical viewpoint.

© 2015 Elsevier Ltd. All rights reserved.

1. Introduction

Every year 3000 Mt of waste are produced in the EuropeanUnion, of which 90 million are considered hazardous. The con-struction industry generates in the EU around 900 million tons peryear of wastes. Therefore, this waste flow represents around 25%e30% of all wastes produced (Eurostat, 2010).

CDW have a very heterogeneous composition. The mostimportant fraction corresponds to inert material, i.e. between 40%and 85% of the overall waste volume discounting excavation soils(Eurostat, 2010). The main sources of inert material are concreteand ceramic materials. Pereira et al. (2004) and Bergsdal et al.(2007) determined the amount of “concrete, masonry and

molition waste; CRA, coarseZ, interfacial transition zone;water cement ratio.

ravo), jb@civil.ist.utl.pt (J. deevangelista@dec.isel.ipl.pt

mortar” in inert material, which accounts for 58% and 67% inPortugal and Norway, respectively. Costa and Ursella (2003) andReixach et al. (2000) obtained values of approximately 85% in Italyand Spain, respectively.

The amount of waste from the construction industry used asfilling material or illegally dumped in vacant lots has beenincreasing over time. This has led to an increasing lack of landfillareas, useful lands becoming dumping yards and highly increaseddumping costs at landfill sites. So handling wastes has become oneof the most important environmental issues in developed countries(Behera et al., 2014) In 2010, around 75% of all CDWproduced in theEUwere dumped (Ortiz et al., 2010). However, reuse ratios over 80%have already been reached by countries such as the Netherlands,Denmark and Germany (Eurostat, 2010). The Community Directive2008/98/EC establishes that the EU state members must take thenecessary measures to reach until 2020 a minimum of reuse ratio70% (in weight) of the CDW produced.

The use of natural aggregates in concrete leads to high envi-ronmental impacts, both because of the amount of emissions of CO2produced during their extraction and of the depletion of naturalresources that this activity implies. Therefore, the incorporation of

M. Bravo et al. / Journal of Cleaner Production 99 (2015) 59e7460

recycled aggregates from construction and demolition wastesignificantly improves concrete in terms of its ecological footprint,saving ecosystems for generations to come. Considering that asubstantial amount of the environmental impacts of using RA fromCDW comes from their production and that such impacts areintrinsic to the construction and demolition activities, it is possibleto conclude that the use of RA in concrete production has a positiveenvironmental effect.

Adequatewastemanagement and recycling lead to a decrease ofthe consumption of natural resources and of the volume of wastesent to dumping grounds, two measures with effects beneficial tothe environment (Cochran et al., 2007). To that purpose, the use ofwaste in the production of concrete has been analysed. There arevarious researches that evaluate the use of a wide variety of wastesin concrete, such as used tyres (Bravo and de Brito, 2012). Anotherexample is the use of wastes from the quarrying of marble in theproduction of concrete. The quarrying of marble, a well-knownornamental stone, has a substantial positive impact on Portugal'seconomy, but it also generates large environmental impacts. Theamount of waste produced during quarrying can be as much as 80%of all stone/soil extracted (Andr�e et al., 2014). However, CDW arethe waste with the greatest potential of reuse in concrete. TheEuropean Commission identified CDW as a priority waste flow fortreatment and recycling, due to the high amounts produced and itsgreat potential of reuse as raw material. Therefore it is not sur-prising that in the latest years there were various researches withthe objective of evaluating the use of CDW in concrete. The prop-erties of concrete made with RA from concrete, ceramic materials,glass, plastics, among other materials, were analysed in order tofully understand their potential and limitations. However, the re-searches that evaluate the use in concrete of CDW from recyclingplants are still scarce. Most of the previous studies analyse the useof a single RA type from CDW, with no comparisons between CDWtypes with different compositions. On the other hand, there are buta few studies that exhaustively analyse the RA used in concrete,through the characterization of their composition and physical andchemical tests. Furthermore, as described below, studies in whichfine RA from CDW were used are even scarcer.

In this research program, the first step was to collect CDW fromfive recycling plants in different locations in Portugal. Then thecharacteristics of all the aggregates (natural and recycled) used inthe production of concrete were examined. To that purpose, thecomposition of the RA was determined and various physical andchemical tests of the aggregates were performed. In order toevaluate the mechanical performance of concrete, compressivestrength (in cubes and cylinders), splitting tensile strength,modulus of elasticity and abrasion resistance tests were performed.

The main objective of this work is the analysis of concretemixes with RA from various CDW recycling plants, with compo-sitions representative of this type of waste in industrializedcountries. The aim is to analyse the influence of the RA's collectionlocation, and consequently of their composition, on the charac-teristics of the mixes produced. Five types of coarse CDW (CRA)and three types of fine CDW (FRA) were collected, with theobjective of also analysing the influence of the size of the CDW RAon their use in concrete.

2. Literature review

There are various researches aimed at analysing the use ofrecycled aggregates (RA) in concrete. These studies evaluate theproperties of concrete with aggregates recycled from concrete,ceramic materials, glass, plastics, among others. However, studiesevaluating the use in concrete production of CDW from recyclingplants are still scarce.

Kou et al. (2004) produced concrete with coarse RA from CDW,at 0%, 20%, 50% and 100% of the overall mass of the coarse NA. Theyanalysed the concrete compressive strength at 7, 28 and 90 daysand, for full replacement, obtained losses of 33%, 37% and 31%.

Oliveira et al. (2004) studied the compressive strength of con-crete with replacement of coarse NA with coarse RA at 10%, 20%,30%, 40% and 100%. The RA came from CDW, mostly from crushedconcrete. In order to produce a mix with 100% of coarse RAwith thesame strength as the reference concrete, the authors had to in-crease the cement content from 378 kg/m3 to 475 kg/m3.

Poon et al. (2007) studied the influence of the replacement ofcoarse NAwith coarse RA on themechanical strength. They used RAfrom CDW from a recycling plant and produced concrete mixeswith 10%, 20%, 50%, 80% and 100% replacement ratios, keeping thew/c ratio constant. They found that full replacement of the coarseNA led to compressive strength losses of 24%, 16%, 19% and 10% at 3,7, 28 and 90 days.

Medina et al. (2014) analysed the viability of producing 30 MPaconcrete using coarse RA from CDW with a high content of asphaltand floating matter. They found that the use of 50% of these RAcaused a 28-day compressive strength loss up to 18%.

Kou et al. (2004) evaluated the tensile strength at 1, 4, 7, 28 and90 days of concrete with coarse RA from CDW. For full replacementof the coarse NA, they obtained losses of 34%, 26%, 11%, 17% and 8%.They concluded that the negative influence of the use of these RApartially fades over time.

Oliveira et al. (2004) evaluated the influence on concrete'smodulus of elasticity of replacing coarse NA with coarse RA at 10%,20%, 30%, 40% and 100%. These RA came fromCDWandweremostlymade of crushed concrete. The authors found that full replacementof the coarse NA caused an 18% decrease of the modulus ofelasticity.

Kou et al. (2004) also evaluated the 28- and 90-day modulus ofelasticity of concrete with coarse RA from CDWat 0%, 20%, 50% and100% of the overall mass of the coarse aggregates. For fullreplacement of the coarse NA they obtained losses of 40% and 28%at 28 and 91 days.

The Waste & Resources Action Programme (WRAP) developedin the UK to facilitate the use of RA from CDW has concluded thatcoarse RA from UK washing plants are suitable for use in concreteand fine RA are also suitable for use in concrete, with the exceptionof RA with sulphate content above limits of 1.0% (Dhir et al., 2008).

Regarding RA concrete properties, the same programmeconcluded that Eurocode 2's (EC2) relations for concrete propertiescan be used to determine the RA's mechanical properties in termsof compressive strength, with the exception of secant modulus ofelasticity. Regarding that property, the use of the EC2 relation todetermine the secant modulus of elasticity for RA concrete resultedin poorer deformation predictions than those made for standardconcretes. The use of RA resulted in an increase by 14% in the elasticdeformations (Waleed and Canisius, 2007).

In terms of the use of RA from concrete in the production of newconcrete, it is consensual that the replacement of the part of thecoarse natural aggregates (NA) with coarse RA does not signifi-cantly damage the concrete's characteristics. However, there is noconsensus concerning the replacement of fine aggregates. Themainfactor singled out by some researchers against the use of fine RA inconcrete is their high water absorption, which may lead to concretewith worse performance. Nevertheless, recent researches indicatethat the use of fine RA in concrete may be viable, since it does notlead to a significant loss of its properties, both in mechanical(Evangelista and de Brito, 2010) and durability terms (Evangelistaand de Brito, 2014).

Concrete's compressive strength is one of the most importantproperties to evaluate the performance of a structure. Merlet and

M. Bravo et al. / Journal of Cleaner Production 99 (2015) 59e74 61

Pimienta (1994) evaluated the compressive strength of variousconcrete mixes with RA from concrete. They used fine and/orcoarse RA at 0%, 20%, 50% and 100% of the global aggregates'volume and cement contents of 250 kg/m3, 300 kg/m3 and 350 kg/m3. All the mixes analysed showed losses in compressive strength,between 18% and 39%. According to Sanchez and Alaejos (2004),these losses are due to the following factors: less mechanicalstrength of the RA; greater water absorption of the RA; increase ofthe fragile areas within concrete, i.e. the interfacial transition zone(ITZ) between the old cement paste and the original NA and alsothe one between the RA and the new cement paste. Poon et al.(2004) evaluated the microstructure of concrete produced withRA from current concrete and from high-performance concreteusing scanning electron microscopy (SEM) and compared it withthe microstructure of NA concrete. They found that the ITZ be-tween the RA from current concrete and the cement paste had ahigh porosity. The authors refer that the high porosity and waterabsorption of these aggregates, together with their low initialwater content during the constituents mixing process, may haveproduced significant water absorption at the initial stage of themixing. Consequently, this process may have caused the reportedITZ0 high porosity. On the other hand, the ITZ between the RAfrom high-performance concrete and the cement paste is muchdenser. Xiao et al. (2013) also analysed the microstructure ofconcrete with RA from concrete and compared the old and newITZ between aggregates and the cement paste. They concludedthat the average modulus of elasticity of the old ITZ is around70%e80% that of the old cement paste. On the other hand, theaverage modulus of elasticity of the new ITZ is around 70%e80%that of the new cement paste.

Barra (1996) found that concrete with coarse RA from concreteneed greater cement content to reach the compressive strength of aconventional concrete. For mixes with strengths of 45 MPa and57.5 MPa, increases of 7.2% and 17.3% of the cement content werenecessary.

Etxeberria et al. (2007) obtained a loss of 20%e25% of the 28-daycompressive strength of concrete for full replacement of coarse NAwith coarse RA from concrete, keeping constant the effectivewater/cement (w/c) ratio and cement content. When 25% of the aggre-gates were replaced there were no significant effects on thecompressive strength.

Evangelista and de Brito (2007) analysed the compressivestrength of various concrete mixes with fine RA from concrete andfound similar values to that of the reference concrete (60 MPa).They justify these good results with the presence of non-hydratedcement in the fine RA and the better bond between the cementpaste and the fine RA, due to their higher porosity.

Pereira et al. (2012) evaluated the influence of superplasticizers(SP) on the compressive strength of concrete with fine RA. Threefamilies of concrete were produced (without SP, with a current SPand with a high-performance SP) at five replacement ratios of fineRA with fine RA from concrete (0%, 10%, 30%, 50% and 100%),maintaining constant the slump in all the mixes. The authors ob-tained an increase in compressive strength due to the SP's incor-poration up to 34.8% and 69.5%, for mixes with current SP and high-performance. As expected, the strength gain increased as the waterreduction power of the admixtures improved. The authors alsofound that the SP had a greater influence on the compressivestrength of conventional concrete than of concrete with fine RAfrom concrete. The loss of efficiency of the admixtures was justifiedby the increase of the specific surface of the aggregates, due to theincorporation of the RA. Barbudo et al. (2013), in a research parallelto the previous one, analysed the influence of the use of SP inconcrete with coarse RA. They reached similar conclusions to thosedescribed in the Pereira et al. (2012) study.

The results from researches concerning other mechanicalproperties, such as tensile strength and modulus of elasticity, aresimilar to the ones on compressive strength. However, the use of RAfrom concrete seems to allow an improvement of the new con-crete's abrasion resistance.

Matias et al. (2013) performed wear by abrasion tests anddetected a decrease of the worn thickness when coarse RA wereused. They justified this result with a better bond between these RAand the cement paste.

Evangelista and de Brito (2007), even though with results notcompletely conclusive, also found that use of fine RA from concretetends to improve the concrete performance against wear actions.

Finally Pereira et al. (2012) evaluated the influence of the use ofSP on the wear by abrasion resistance of concrete with variouscontents of fine RA from concrete (0%, 10%, 30%, 50% and 100%). Theuse of RA caused increases of the worn thickness up to 21.7%, 395%and 51.3%, for mixes without SP, with current SP and with high-performance SP.

The researches that analysed the use of ceramic RA in concreteare not as consensual as those that evaluated the use of RA fromconcrete.

Gomes and de Brito (2009) analysed the performance of twoconcrete types: with coarse RA from concrete only (full replace-ment) and with coarse RA from concrete and ceramic materials (upto 75% replacement). None of these mixes showed a significant lossin compressive strength. However, the mixes with ceramic RAdisplayed a slightly descending trend of strength as the replace-ment ratio increased.

Medina et al. (2013) evaluated the compressive strength ofconcrete with ceramic RA and found that it increased by 11% inmixes with 25% of RA. Medina et al. (2012) found that the ITZ be-tween the ceramic sanitary ware RA and the cement paste is morecompact and stable than the ITZ between the NA and the paste.Other studies also hint at an increase of compressive strengthwhen30% of NA are replaced by ceramic RA (http://www.sciencedir-ect.com/science/article/pii/S0959652612004660 Pacheco-Torgaland Jalali, 2010).

Alves et al. (2014) analysed the incorporation in concrete ofcoarse ceramic RA from bricks and sanitary ware. They found thatthe decrease of 28-day compressive strength is less than 10% for fullreplacement of NA with coarse brick RA. Full use of coarse sanitaryware RA caused a compressive strength loss of 42.5%.

Zong et al. (2014) refer that the use of brick RA in concretejeopardizes its mechanical performance and increases its perme-ability. They found that this is due to the increase in porosity of theaggregates and their effects on the concrete's microstructure.

In terms of the other mechanical properties of concrete, resultsare similar to the ones relative to compressive strength, except forwear by abrasion resistance.

De Brito et al. (2005) found there is an approximately linearincrease of the abrasion resistancewith the replacement ratio of NAwith ceramic brick RA. They justified this trend with the betterbond between the ceramic aggregates and the cement paste,because of the greater porosity of the RA.

Alves et al. (2014) found an increase in abrasion resistance of31.4% and 49.8% from the use of 100% of coarse ceramic RA frombricks and sanitary ware.

There are also some researches on the use of glass RA in con-crete. Castro and de Brito (2013) analysed the use of coarse and fineglass RA in concrete and found that the incorporation of 20% ofglass RA only led to a decrease in compressive strength of 3% and14% for coarse and fine aggregates.

Park et al. (2004) evaluated the mechanical performance ofconcrete with fine glass RA. They found that the use of 30%, 50% and70% of these RA caused a decrease of the 28-day compressive

Table 1Composition of the reference concrete (RC) (l/l).

Cement 0.115Fine aggregates 0e0.063 0.000

0.063e0.125 0.0160.125e0.25 0.0440.25e0.5 0.0500.5e1 0.0571e2 0.066

Coarse aggregates 2e4 0.0764e5.6 0.041

5.6e8 0.0468e11.2 0.047

11.2e16 0.12116e22.4 0.122

Water 0.182Voids 0.017Total 1.000

Table 2Tests performed to determine the aggregates' properties.

Properties Standard

Physical testsParticles density and water absorption NP EN 1097-6 (2003) and

Rodrigues et al. (2013a) patentBulk density and voids volume NP EN 1097-3 (2003)Shape index NP EN 933-4 (2002)Fragmentation resistance (Los Angeles) NP EN 1097-2 (2002)Chemical testsWater soluble chlorides content EN 1744-1 (2009) Section 7Water soluble sulphates content EN 1744-1 (2009) Section 10Acid soluble sulphates content EN 1744-1 (2009) Section 12Sulphur global content EN 1744-1 (2009) Section 11Light contaminants content EN 1744-1 (2009) Section 14.2Humus content EN 1744-1 (2009) Section 15.1Water solubility EN 1744-1 (2009) Section 16

M. Bravo et al. / Journal of Cleaner Production 99 (2015) 59e7462

strength of 0.6%, 9.8% and 13.6%. The results were justified by thepoorer adherence between the glass RA's surface and the cementpaste.

3. Experimental program

In this chapter the materials used in the production of concreteare presented. The different mixes' composition and the differentprocesses of production are also identified and explained. Finallythe several tests performed with the objective of characterizing themechanical performance of concrete with RA from CDW arepresented.

3.1. Materials

In this research the aggregates used were NA and RA from fiveCDW Portuguese plants (Valnor, Vimajas, Ambilei, Europontal andRetria). In three of them (Vimajas, Ambilei and Europontal) coarseand fine RA were analysed and in the remaining ones only coarseRA. These recycling plants were selected in order to representvarious geographical areas, leading to a wide range of constructionmaterials and processes, as well as geological backgrounds and avariety of recycling procedures. The material used came from theoutput of the plants. Vimajas yielded two products that containmaterial smaller than 4 mm, which were both sampled. TheAmbilei plant processes separately CDW made mostly of concreteand CDW that is a mixture of concrete and ceramics. As for the NA,limestone gravel and alluvial rolled sand were used. In the pro-duction of concrete cement CEM I 42.5 R and tap water were used.

3.2. Mixes' composition

33 concrete mixes were produced: a reference concrete (RC),mixes with replacement ratios of 10%, 25%, 50% and 100% of theoverall volume of coarse NA (with coarse RA from five recyclingplants) and mixes with replacement ratios of 10%, 25%, 50% and100% of the overall volume of fine NA (with fine RA from threeplants).

The aggregates were considered fine when their particlespassed through a 4 mm sieve and coarse when they were retainedin that sieve. The maximum particle size used was 22.4 mm.

The NA were replaced by the RA in volume and by size fraction,in order to keep constant in all the mixes with RA the aggregatessize distribution of the RC. No admixtures or additions were used inthis research.

Every mix was produced with a 125 ± 15 mm slump, for a bettercomparison between them. For that purpose in a preliminary stagethe water content was adjusted, when necessary, to each mix inorder to comply with that requirement.

The RC composition was determined using the Faury's methodwith a C30/37 target strength class. The materials content, in vol-ume, are provided in Table 1. All other mixes were designed basedon this composition with just slight changes in solid volume inorder to comply with the different w/c ratios required to keep of allmixes within target slump.

3.3. Tests

EN 12620:2008 “Aggregates for concrete” specifies the proper-ties required from natural aggregates, mechanically-processed ag-gregates, recycled aggregates and mixtures of aggregates for use inconcrete. It covers the aggregates with dry density higher than2000 kg/m3, to be used in every concrete type, including concretein conformity with NP EN 206-1 (2013).

The characteristics of the aggregates were determined accord-ing to the requirements of the standards and specifications listed inTable 2. Besides these tests, an analysis of the composition of thevarious RC was performed.

With the objective of characterizing the mechanical perfor-mance of concrete with RA from CDW, several tests were per-formed. In the fresh state, the following properties were measured:slump using the Abrams cone based on EN 12350-2 (2002) anddensity according to EN 12350-6 (2002). The characterization of thehardened state included the following properties: compressivestrength in cubic and cylindrical specimens (according to EN12390-3, 2003), splitting tensile strength (according to EN 12390-6, 2003), modulus of elasticity (according to LNEC E-397, 1993)and abrasion resistance (according to DIN 52108, 2010).

4. Results and discussion

4.1. Aggregates' properties

4.1.1. CompositionThe NA used in the production of concrete were crushed lime-

stone gravel and rolled river sand.In order to better know the various RA used in the production of

concrete, their composition was determined by visual observation(Table 3). The RA all have a high content of “concrete, mortar andnatural sand” (between 68% and 86%). The content of “masonry e

clay materials” varies between 1% and 29%. The RA from Ambileiand Vimajas stand out in terms of glass and bituminous materialscontent, respectively.

Table 3Composition of the recycled aggregates (% in mass).

Composition (in %) CRA Valnor CRA Retria CRA Ambilei CRA Vimajas CRA Europontal FRA Ambilei FRA Vimajas FRA Europontal

Concrete, mortar and natural sand 70.8 69.1 85.6 79.8 79.9 83.7 75.2 68.8Masonry e clay materials 28.6 28.6 4.2 11.1 17.1 0.9 11.6 26.5Glass 0.5 2.1 10.2 1.0 0.2 15.4 1.0 3.4Bituminous materials 0.0 0.0 0.0 6.2 2.8 0.0 10.5 1.0Others 0.1 0.2 0.0 2.0 0.0 0.0 1.7 0.3Total 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0

Table 5Results of the physical tests of the fine aggregates.

Physical tests Finesand

Coarsesand

FRAAmbilei

FRAVimajas

FRAEuropontal

Oven-dry particlesdensity (kg/m3)

2583 2581 2112 2070 2063

Water absorption (%) 0.3 0.7 12.9 10.1 10.4Bulk density (kg/m3) 1530 1540 1435 1332 1358

M. Bravo et al. / Journal of Cleaner Production 99 (2015) 59e74 63

4.1.2. Physical propertiesTables 4 and 5 show the results of the tests of characterization of

the physical properties of all aggregates used. The RA, by compar-ison with the NA, have lower particles density and higher waterabsorption. This results from the nature and porosity of the RA. Itdemonstrates that there is a propensity of the RA mixes to requiremore mixing water than the NA mixes. The greater water absorp-tion of the FRA relative to the CRA stands out. In order to determinethewater absorption of the FRA themethod defined in the patent ofRodrigues et al. (2013a) was used. This method solves the problemsthat occur when using NP EN 1097-6 in FRA, namely those asso-ciated to the formation of air bubbles in the sample during theimmersion of the pycnometer and to the particles agglomerationduring the saturation stage, because of the cohesiveness of the FRA.

When comparing aggregates of similar size, it is found that theRA have a lower bulk density than the NA. This is due to the moreporous nature and sharper shape of the RA. The low bulk density ofthe CRA Valnor stands out.

With the exception of the Ambilei aggregates, every RA has ahigher shape index than the NA, which may cause a lower slump ofthe mixes with RA relative to the RC.

It is also found that the RA have a lower fragmentation resis-tance than the NA, possibly due to their composition and crushingprocess, which creates micro-cracks in the particles, making themmore unstable and fragile.

4.1.3. Chemical propertiesTable 6 presents the results of the chemical tests performed on

the RA showing that the light contaminants content in the variousRA is their main problem, in terms of the chemical tests results. Thethreshold value for theses contaminants is 0.5% in mass, accordingto EN 12620 (2008). This value drops to 0.25% when there is specialconcern with the surface finish. Rodrigues et al. (2013b) chemicallyanalysed eight types of RA from CDW recycling plants and alsofound very high contents (between 0.3% and 17.1%).

These chemical tests also indicate that the RA Vimajas havehigher water soluble chlorides content than the threshold. Thechlorides in aggregates that most affect concrete may be found inalkaline salts, namely sodium chloride and potassium chloride,decisively contributing to the overall chlorides content insideconcrete. This limitation is needed tominimize the risk of corrosionof the reinforcement within concrete. It is also important toconsider the chlorides content of the remaining constituent ma-terials of concrete when designing its composition. According to

Table 4Results of the physical tests of the coarse aggregates.

Physical tests Gravel 2 Gravel 1 Granule CRA

Oven-dry particles density (kg/m3) 2599 2609 2522 2091Water absorption (%) 1.5 1.3 2.7 8.6Bulk density (kg/m3) 1360 1350 1348 1095Shape index (%) 15 17 18 24Los Angeles wear (%) 26 28 e 52

APEB (2007), the chlorides content in concrete is expressed inpercentage of chloride ions in cement mass, which means that thechlorides threshold content may not be exceeded if the cementcontent used is high.

All the other results of the chemical tests of the RA fall withinthe thresholds imposed, except for the sulphates content in the FRAVimajas that equal the limit. Internal sulphates present a risk ofchemical attack of concrete (Mehta and Monteiro, 2006).

4.2. Fresh-state concrete properties

4.2.1. WorkabilityAll mixes were produced with a 125 ± 15 mm slump, in order to

bemore fairly compared. This involved a preliminary stage inwhichthe mixing water of each mix was adjusted, whenever necessary, inorder to comply with this requirement.

As Table 7 shows, it was necessary to increase the effective w/cratio as the RA ratio increased. However, this increase was notidentical in all the families of mixes with RA. It was concluded thatthe shape and composition of the various RA influenced the mixes'workability. As referred by De Brito and Robles (2010), the roughershape of the RA, relative to the NA, may contribute to this change ofworkability.

The significant increase of the w/c ratio of the mixes with FRAfrom Vimajas and Europontal stands out. This change is due to thehigh clay content of these RA (Rodrigues et al., 2013b). These fineparticles absorb a great amount of water, forcing an increase of thew/c ratio in order tomaintain the slump of themixes with these RA.

Out of the 33 mixes produced, only one (that with 25% of CRAValnor) had a cone Abrams slump slightly outside the target range(110 mme140 mm). Since the incompliance was only by 4 mm, thiswas not considered relevant for the analysis of the hardened stateconcrete tests.

Valnor CRA Retria CRA Ambilei CRA Vimajas CRA Europontal

2137 1928 2243 22628.4 9.9 6.4 5.51236 1288 1261 128524 14 25 2146 44 39 43

Table 6Results of the chemical tests of the recycled aggregates.

Chemical tests CRA Valnor CRA Retria CRA Ambilei CRA Vimajas CRA Europontal FRA Ambilei FRA Vimajas FRA Europontal Threshold

Water soluble chlorides content <0.010 <0.010 <0.010 0.016 <0.010 <0.010 0.016 0.010 0.010a

Water soluble sulphates content 0.04 0.04 0.04 0.13 0.06 0.11 0.18 0.04 0.20a

Acid soluble sulphates content 0.2 0.3 0.1 0.4 0.3 0.2 0.8 0.1 0.8a

Sulphur global content 0.1 0.1 <0.1 0.2 <0.1 0.1 0.3 <0.1 1.0a

Light contaminants content 1.5 <0.1 0.9 1.5 0.3 1.8 1.7 1.0 0.5a

Humus content Neg. Neg. Neg. Neg. Neg. Neg. Neg. Neg. Neg.Water solubility 1.0 1.2 0.2 1.4 0.8 0.5 2.1 0.8 10.0b

a According to EN 12620 (2008).b According to EN 1744.

Table 7Slump and effective w/c ratio of the concrete mixes.

Aggregates replacement ratio (%)

0 10 25 50 100

Slump (mm) w/c ratio Slump (mm) w/c ratio Slump (mm) w/c ratio Slump (mm) w/c ratio Slump (mm) w/c ratio

CRA Valnor 114 0.51 126 0.52 106 0.53 120 0.53 120 0.53CRA Vimajas 121 0.52 120 0.53 130 0.53 119 0.53CRA Ambilei 125 0.52 110 0.53 120 0.53 126 0.55CRA Europontal 125 0.51 125 0.51 128 0.51 115 0.51CRA Retria 118 0.52 130 0.52 125 0.53 121 0.53FRA Vimajas 119 0.53 121 0.55 124 0.58 121 0.64FRA Ambilei 140 0.52 140 0.52 140 0.53 135 0.55FRA Europontal 120 0.53 118 0.54 125 0.57 140 0.63

M. Bravo et al. / Journal of Cleaner Production 99 (2015) 59e7464

4.2.2. DensityFigs. 1 and 2 show that the fresh-state density of concrete de-

creases as the RA incorporation ratio increases. This is justified bythe lower particles density of the RA, relative to the NA. The figuresalso show that this reduction changes according to the specific RAused, because it depends on the constitution of the RA from eachplant.

Finally, it is clear that there is an approximately linear decreaseof the density with aggregates replacement ratio (determinationcoefficients between 0.90 and 0.99). Gomes and de Brito (2009)reached the same conclusion when they investigated concretewith coarse RA.

Fig. 1. Fresh-state density of the

4.3. Concrete mechanical properties

4.3.1. Compressive strength in cubesTable 8 presents the mixes' average compressive strength at

several ages (fcm,7, fcm,28 and fcm,56), as well as the strength varia-tions (D) relative to the RC. It shows that the 28-day compressivestrength of the RC is 53.9 ± 1.8MPa. This strength level correspondsto the strength class C35/45, higher than the previously set target.

To better interpret the 28-day compressive strength results,they were represented graphically in Fig. 3. Independently of theaggregates' size fraction replaced, the compressive strength isaffected by the incorporation of RA. This is due to the RA's

mixes with CRA from CDW.

Fig. 2. Fresh-state density of the mixes with FRA from CDW.

M. Bravo et al. / Journal of Cleaner Production 99 (2015) 59e74 65

composition and the increase of the effective w/c ratio as the RAincorporation increases. However, the results demonstrate that thescale of the compressive strength's decrease varies with severalfactors.

One of the factors that most influenced the results was the RA'ssource. Because the RA were collected in different plants, spreadout in the Portuguese territory, their composition varies accordingto the source. This was demonstrated in the analysis presented inTable 3. As expected the results varied considerably. In the mixeswith 100% of CRA Ambilei, there was a reduction of 5.2% of the 28-day compressive strength, while in the mixes with RA from Valnor

Table 8Compressive strength of the RA concrete mixes, in cubes, at 7, 28 and 56 days.

fcm,7 (MPa) D (%) fcm,28 (MPa) D (%) fcm,56 (MPa) D (%)

BR 44.8 ± 1.2 e 53.9 ± 1.8 e 61.1 ± 1.6 e

C10C-Valnor 46.4 ± 0.5 3.4 54.1 ± 2.2 0.2 58.8 ± 1.9 �3.8C25C-Valnor 42.8 ± 1.5 �4.6 48.9 ± 1.1 �9.4 55.6 ± 2.0 �9.0C50C-Valnor 41.0 ± 1.4 �8.5 46.2 ± 2.7 �14.3 50.1 ± 2.1 �18.1C100C-Valnor 29.6 ± 1.9 �33.9 35.3 ± 1.4 �34.5 43.2 ± 1.5 �29.4C10C-Vimajas 42.6 ± 0.7 �5.0 52.3 ± 1.7 �3.0 56.7 ± 1.0 �7.2C25C-Vimajas 44.1 ± 0.9 �1.7 54.1 ± 1.3 0.3 57.9 ± 2.8 �5.4C50C-Vimajas 38.1 ± 0.8 �15.0 48.4 ± 0.9 �10.3 49.5 ± 0.6 �19.1C100C-Vimajas 35.7 ± 0.2 �20.3 42.0 ± 1.5 �22.1 44.6 ± 0.5 �27.0C10C-Ambilei 43.6 ± 0.8 �2.8 53.7 ± 2.1 �0.5 55.7 ± 2.7 �8.9C25C-Ambilei 39.3 ± 0.6 �12.4 50.0 ± 2.4 �7.2 50.3 ± 1.2 �17.7C50C-Ambilei 39.6 ± 0.8 �11.7 48.8 ± 2.0 �9.6 51.5 ± 2.6 �15.7C100C-Ambilei 40.7 ± 0.8 �9.3 51.1 ± 1.5 �5.2 49.5 ± 1.3 �19.0C10C-Europontal 41.3 ± 1.6 �7.9 45.4 ± 1.3 �15.9 49.7 ± 0.1 �18.7C25C-Europontal 38.7 ± 0.6 �13.8 46.0 ± 1.8 �14.8 48.8 ± 1.1 �20.1C50C-Europontal 39.1 ± 0.1 �12.9 46.6 ± 1.1 �13.6 47.4 ± 3.2 �22.5C100C-Europontal 32.2 ± 0.2 �28.3 36.2 ± 1.3 �32.9 39.5 ± 1.4 �35.5C10C-Retria 40.4 ± 0.8 �9.9 48.3 ± 2.3 �10.4 53.4 ± 0.9 �12.6C25C-Retria 37.4 ± 0.3 �16.6 44.6 ± 0.8 �17.3 46.2 ± 1.8 �24.4C50C-Retria 36.4 ± 1.6 �18.8 44.9 ± 1.4 �16.8 42.7 ± 1.8 �30.2C100C-Retria 31.8 ± 1.3 �29.1 40.1 ± 1.1 �25.6 33.9 ± 2.6 �44.5C10F-Vimajas 39.9 ± 0.5 �11.1 49.2 ± 1.1 �8.7 52.8 ± 1.9 �13.7C25F-Vimajas 38.5 ± 0.6 �14.2 45.6 ± 1.5 �15.5 48.7 ± 1.2 �20.4C50F-Vimajas 31.1 ± 0.1 �30.6 37.6 ± 1.3 �30.2 40.5 ± 0.1 �33.7C100F-Vimajas 23.0 ± 0.3 �48.7 30.2 ± 0.5 �44.1 30.6 ± 0.9 �50.0C10F-Ambilei 41.3 ± 0.4 �7.9 51.6 ± 1.0 �4.3 52.3 ± 0.4 �14.5C25F-Ambilei 40.0 ± 0.4 �10.8 47.3 ± 1.1 �12.3 48.1 ± 1.4 �21.3C50F-Ambilei 36.5 ± 1.7 �18.6 46.8 ± 1.2 �13.3 48.1 ± 0.9 �21.3C100F-Ambilei 29.1 ± 0.0 �35.1 38.4 ± 1.2 �28.8 40.3 ± 0.1 �34.0C10F-Europontal 38.9 ± 1.4 �13.3 50.3 ± 1.5 �6.8 53.7 ± 2.0 �12.2C25F-Europontal 39.3 ± 1.0 �12.3 44.7 ± 2.0 �17.0 48.1 ± 1.9 �21.3C50F-Europontal 36.7 ± 1.2 �18.1 44.5 ± 1.0 �17.4 46.3 ± 1.2 �24.2C100F-Europontal 26.1 ± 0.5 �41.7 29.9 ± 0.6 �44.6 31.5 ± 0.8 �48.5

this reduction reached 34.5%. In the mixes with CRA, those with RAfrom Valnor, Europontal and Retria showed the highest compres-sive strength loss. These results are justified by the high ceramicscontent of the RA from these three recycling plants (between 17.1%and 28.6%). Hansen (1992) also found that the RA with greaterceramics content cause a greater mechanical strength loss than theRA from concrete. In the mixes with FRA, there was a much greater28-day compressive strength loss in those with RA from Vimajasand Europontal (44.1% and 44.6%), relative to those with RA fromAmbilei (28.8%). This lower compressive strength of the mixes withFRA from Vimajas and Europontal is essentially due to the greatincrease of thew/c ratio of thesemixes, caused by their clay content(Rodrigues et al., 2013b). These fine particles coat the RA grains andabsorb the mixing water, besides hindering an adequate bond be-tween the RA and the cement paste, weakening the cement's innerstructure. Through scanning electron microscopy (SEM), it wasproven that these phenomena caused an increase of the porosity ofthese mixes, leading to a decrease in compressive strength. Figs. 4and 5show that the FRA from Vimajas have greater micro-porosity and macro-porosity than the FRA from Ambilei, as seenboth in the mixes with 50% of RA (Fig. 4a and b) and those with100% of RA (Fig. 5a and b).

The results of the mixes with FRA from Europontal may also beexplained by their high content of ceramic materials (26.5%).

The size of the RAwas another factor influencing the results. Thecompressive strength drop was significantly greater in the mixeswith FRA than in those with CRA. For example the use of 100% of RAfrom Vimajas led to a decrease in 28-day compressive strength of22.1% and 44.1%, for 100% CRA and FRA. In the mixes with RA fromAmbilei, the compressive strength dropped by 5.2% and 28.8% forfull incorporation of CRA and FRA. In the mixes with RA fromEuropontal the corresponding decreases were 32.9% and 44.6%respectively. These differences are partly justified by the clay con-tent of some of the FRA (from Vimajas and Europontal). As statedbefore, the presence of clay makes it necessary to increase the w/cratio in themixes with these FRA, in order to have a slump constantin all the mixes. This increase naturally leads to a reduction of thecompressive strength.

These results are similar to those of Zaharieva et al. (2003). Theyevaluated the performance of concretewith RA from CDW (fine andcoarse), collected randomly from a recycling plant, and found thatfor a constant concrete slump the full replacement of the NA causeda 28-day compressive strength drop from 54.8 MPa to 39.4 MPa(around 30%).

Fig. 3. 28-day compressive strength for RA concretes versus aggregates' replacement ratio.

Fig. 4. Comparison of the micro-porosity of the concrete mixes with 50% of fine RA: a) detail of the ITZ of the mix with FRA from Vimajas; b) detail of the ITZ of the mix with FRAfrom Ambilei.

Fig. 5. Comparison of the micro-porosity of the concrete mixes with 100% of fine RA: a) detail of the ITZ of the mix with FRA from Vimajas; b) detail of the ITZ of the mix with FRAfrom Ambilei.

M. Bravo et al. / Journal of Cleaner Production 99 (2015) 59e7466

Fig. 6. Variation of compressive strength with time for the mixes with coarse RA.

Fig. 7. Variation of compressive strength with time for the mixes with fine RA.

M. Bravo et al. / Journal of Cleaner Production 99 (2015) 59e74 67

Figs. 6 and 7 demonstrate that the evolution of compressivestrength of the mixes with RA is identical to that of conventionalconcrete. Therefore, the older concrete is the lower the increase inconcrete becomes. This general trend is more intense in mixes withRA than in the RC. In other words the compressive strength of the

Fig. 8. 28-day compressive strength in cubes of CRA and FR

RC keeps on increasing after 28 days at a steeper rate than in themixes with RA.

Fig. 8 shows a linear decrease of the compressive strength withthe replacement of NAwith RA. This is confirmed by the high valuesof the determination coefficient of the linear regressions

A concrete mixes versus aggregates' replacement ratio.

Table 928-day compressive strength in cylinders.

Aggregates' replacement ratio (%)

0 10 25 50 100

Compressive strengthin cylinders (MPa)

Compressive strengthin cylinders (MPa)

D (%) Compressive strengthin cylinders (MPa)

D (%) Compressive strengthin cylinders (MPa)

D (%) Compressive strengthin cylinders (MPa)

D (%)

CRA Valnor 37.5 ± 1.3 35.3 ± 2.6 �5.9 32.4 ± 1.2 �13.6 33.5 ± 1.9 �10.8 25.6 ± 0.6 �31.6CRA Vimajas 40.8 ± 1.8 8.9 33.5 ± 1.8 �10.6 30.8 ± 2.3 �17.8 30.5 ± 1.7 �18.6CRA Ambilei 37.4 ± 3.1 �0.2 36.0 ± 1.6 �4.1 33.6 ± 1.0 �10.5 31.1 ± 1.7 �17.1CRA Europontal 35.7 ± 2.2 �4.7 34.6 ± 3.2 �7.8 33.1 ± 2.1 �11.6 25.7 ± 0.8 �31.4CRA Retria 40.5 ± 0.5 �8.1 34.2 ± 3.4 �8.9 32.3 ± 1.7 �13.8 29.4 ± 2.5 �21.5FRA Vimajas 36.2 ± 0.9 �3.5 35.7 ± 0.1 �4.9 30.2 ± 1.3 �19.5 21.8 ± 1.8 �42.0FRA Ambilei 39.1 ± 3.7 4.2 38.9 ± 1.4 3.8 35.2 ± 0.4 �6.1 30.8 ± 0.9 �17.8FRA Europontal 33.8 ± 3.5 �9.9 33.8 ± 2.5 �9.8 33.9 ± 3.1 �9.7 23.3 ± 0.1 �38.0

M. Bravo et al. / Journal of Cleaner Production 99 (2015) 59e7468

concerning the mixes with CRA and FRA tested at 28 days (0.93 and0.97, respectively).

4.3.2. Compressive strength in cylindersTable 9 shows that the replacement of NA with RA caused a

decrease of the 28-day compressive strength in cylinders. This re-sults from the RA's composition and the increase in effective w/cratio as the RA incorporation in concrete goes up.

Fig. 9 represents the 28-day compressive strength in cylinders ofall mixes. As for strength in cubes, the strength in cylinders loss wasgreater when fine aggregates were replaced. The FRA from Vimajasand Europontal are again the ones with the worst results. This ismostly due to the need of increasing these mixes' w/c ratio to keepthe slump constant, caused by the presence of clay in the FRA'scomposition.

Fig. 9 allows confirming that this property varies considerablyaccording to the RA's source. For example, full replacement of thecoarse NA caused decreases of the compressive strength in cylin-ders between 17.1% and 31.6%. This is mostly due to the changes ofthe ceramics content in the RA (between 4.2% and 28.6%). On theother hand, full replacement of the fine NA caused decreases be-tween 17.8% and 42.0%, according to the RA's source. This range ofvalues is mostly due to two factors: the wide range of ceramicscontent in the FRA (between 0.9% and 26.5%); the significant in-crease in effectivew/c ratio of themixes with FRA fromVimajas andEuropontal, due to their clay content. These factors led to an in-crease in porosity of the mixes with RA from these two plants andconsequently a drop in compressive strength in cylinders.

Fig. 9. 28-day compressive strength in

Table 10 shows the compressive strength of themixeswith 100%of RA. For 100% of CRA the mixes reached strength classes C25/30and C30/37. On the other hand, for 100% of FRA the mixes reachedstrength classes C20/25 and C30/37. Four of themixes from Table 10would be classified in a higher compressive strength class if onlythe characteristic value obtained in cubes were considered.

Fig. 10 shows the determination coefficient (R2) of the linearregressions concerning the mixes with CRA and FRA (0.95 in bothcases). It is concluded that the loss of compressive strength incylinders due to the replacement of NAwith RA is linear. Fig. 10 alsoconfirms that this property's loss in cylinders is greater when FRAare used than when RCA are used.

4.3.3. Splitting tensile strengthTable 11 shows that the incorporation of CRA and FRA causes a

decrease of the splitting tensile strength. This is due to the increasein the effective w/c of these mixes and the negative effect of thecomposition of some of the RA. Kou et al. (2004) also observed thatthe use of 100% of CRA from CDW caused a 28-day tensile strengthloss of the mixes of around 17%.

Table 11 and Fig.11 show that, similarly to compressive strength,the loss of tensile strength increases as the fine RA's replacementratio goes up. This is due to the great clay content of the FRAEuropontal and Vimajas and the consequent higher w/c ratio of themixes with them. The tensile strength loss is also due to the worstquality of the paste of cement and FRA, which is essential to thisproperty (Neville, 1995).

It is concluded that the composition of the RA used in thesemixes also had great influence on the tensile strength results.

cylinders of RA concrete mixes.

Table 10Compressive strength class of the mixes with 100% of RA.

Compressivestrength class

Characteristic valuespecified in cylinders (MPa)

Characteristic valuespecified in cubes (MPa)

Characteristic valueobtained in cylinders (MPa)

Characteristic valueobtained in cubes (MPa)

RC C35/45 35 45 37.5 53.9C100C-Valnor C25/30 25 30 25.6 35.3C100C-Vimajas C30/37 30 37 30.5 42.0C100C-Ambilei C30/37 30 37 31.1 51.1C100C-Europontal C25/30 25 30 25.7 36.2C100C-Retria C25/30 25 30 29.4 40.1C100F-Vimajas C20/25 20 25 21.8 30.2C100F-Ambilei C30/37 30 37 30.8 38.4C100F-Europontal C20/25 20 25 23.3 29.9

M. Bravo et al. / Journal of Cleaner Production 99 (2015) 59e74 69

Accordingly the mixes with FRA and CRA from Ambilei are the oneswith the best results out of the mixes with full aggregates'replacement. When 100% of CRA from Ambilei are incorporated inthe mix, the splitting tensile strength decreases only from 4.0 MPato 3.6 MPa (�11.1%), while the worst result, from the mix with 100%CRA from Europontal, represents a reduction of 36.1%. This differentperformance as a function of the RA's nature agrees with the ob-servations of Gomes et al. (2014). They found that the splittingtensile strength is little affected by the use of RA from concrete inthe mix but highly reduced by the use of ceramics' RA.

There is no reasonable explanation for the low splitting tensilestrength of the mixes C25C-Valnor and C25C-Ambilei. Therefore, itis considered that these values may result from unidentifiedexperimental errors.

Fig. 10. 28-day compressive strength in cylinders of CRA and

Table 11Splitting tensile strength.

Aggregates' replacement ratio (%)

0 10 25

Splitting tensilestrength (MPa)

Splitting tensilestrength (MPa)

D (%) Splitting tstrength (

RC 4.0 ± 0.0 3.7 ± 0.3 �8.3 3.0 ± 0.1C100C-Valnor 3.9 ± 0.1 �2.2 3.8 ± 0.2C100C-Vimajas 3.7 ± 0.1 �7.2 3.2 ± 0.2C100C-Ambilei 3.4 ± 0.1 �14.9 3.5 ± 0.2C100C-Europontal 3.9 ± 0.2 �2.8 3.7 ± 0.2C100F-Vimajas 4.1 ± 0.3 2.1 3.1 ± 0.2C100F-Ambilei 3.5 ± 0.4 �13.2 3.8 ± 0.1C100F-Europontal 4.0 ± 0.4 �0.4 3.4 ± 0.1

Fig. 12 allows finding out that the splitting tensile strength lossis linearly proportional to the replacement ratio of NA with RA asproved by the relatively high values of the determination coeffi-cient (R2) of the linear regressions tried (0.85 and 0.89, for coarseand fine aggregates).

4.3.4. Modulus of elasticityTable 12 shows the modulus of elasticity results of all mixes

tested. It is clear that the replacement of NA with RA reduces theconcrete's modulus of elasticity.

Fig. 13 shows that the RA's composition is the factor that mostinfluences the modulus of elasticity. The mixes with FRA and CRAfrom Ambilei have the best results. Contrarily, the mixes with RAfrom Valnor have the worst results in terms of this property. This

FRA concrete mixes versus aggregates' replacement ratio.

50 100

ensileMPa)

D (%) Splitting tensilestrength (MPa)

D (%) Splitting tensilestrength (MPa)

D (%)

�26.3 3.2 ± 0.0 �19.5 3.1 ± 0.1 �24.3�5.4 3.7 ± 0.3 �8.5 2.9 ± 0.0 �27.5

�19.5 3.0 ± 0.2 �26.2 2.6 ± 0.0 �34.6�12.4 3.4 ± 0.3 �14.6 3.2 ± 0.1 �20.7�8.9 3.4 ± 0.5 �16.3 2.6 ± 0.1 �34.4

�22.8 3.4 ± 0.1 �16.7 3.6 ± 0.3 �11.1�6.1 3.6 ± 0.2 �10.0 2.6 ± 0.1 �36.1

�15.8 3.2 ± 0.3 �20.6 2.7 ± 0.2 �32.1

Fig. 11. Splitting tensile strength of RA concrete mixes.

Fig. 12. Splitting tensile strength of CRA and FRA concrete mixes versus aggregates' replacement ratio.

M. Bravo et al. / Journal of Cleaner Production 99 (2015) 59e7470

difference is due to the great influence of the stiffness of the RAfrom each source on the modulus of elasticity of concrete. Theseresults are similar to those of Kou et al. (2004). These authorsobserved that full replacement of the coarse NA with CRA from

Table 12Modulus of elasticity.

Aggregates' replacement ratio (%)

0 10 25

Modulus ofelasticity (GPa)

Modulus ofelasticity (GPa)

D (%) Modulus ofelasticity (G

CRA Valnor 40.5 ± 0.2 39.1 ± 0.4 �3.5 34.6 ± 0.0CRA Vimajas 40.8 ± 0.6 0.7 38.4 ± 0.2CRA Ambilei 38.7 ± 0.3 �4.3 39.2 ± 0.5CRA Europontal 39.8 ± 0.4 �1.1 36.9 ± 0.0CRA Retria 37.7 ± 0.0 �6.9 35.5 ± 0.4FRA Vimajas 38.6 ± 0.9 �4.7 34.9 ± 0.5FRA Ambilei 40.3 ± 0.3 �0.5 38.0 ± 0.2FRA Europontal 40.2 ± 0.0 �0.8 37.5 ± 0.3

CDW caused a 28-day modulus of elasticity loss of 40%. Oliveiraet al. (2004) analysed the influence of RA from CDW mostlymade of concrete and found a decrease of around 18% of themodulus of elasticity, lower than the one in our study. This is

50 100

Pa)D (%) Modulus of

elasticity (GPa)D (%) Modulus of

elasticity (GPa)D (%)

�14.6 29.2 ± 0.9 �27.9 21.1 ± 0.5 �47.9�5.2 34.8 ± 0.3 �14.1 26.7 ± 0.4 �34.1�3.2 35.9 ± 0.0 �11.3 29.9 ± 0.1 �26.3�9.0 34.3 ± 0.6 �15.4 25.2 ± 1.3 �37.9

�12.2 31.5 ± 0.2 �22.3 26.3 ± 0.0 �35.1�13.8 31.9 ± 0.2 �21.2 23.3 ± 0.6 �42.5�6.2 37.4 ± 0.4 �7.7 32.5 ± 0.6 �19.8�7.4 35.6 ± 0.2 �12.2 26.0 ± 0.6 �35.8

Fig. 13. Modulus of elasticity at 28 days for RA concrete mixes.

M. Bravo et al. / Journal of Cleaner Production 99 (2015) 59e74 71

justified by the absence of ceramic material in the RA used. Asreferred by Gomes et al. (2014), when the RA contain ceramicmaterial, the loss in modulus of elasticity is greater, because of thelower particles density of that material. These studies confirm thatthe RA's source significantly influences concrete's modulus ofelasticity. The results of our research are additionally explained bythe increase of the effective w/c ratio (i.e. less stiff paste) with theRA's incorporation.

The moduli of elasticity of the mixes with CRA and FRA from thesame source are similar. The maximum difference is of 8.4%, for theRA from Vimajas and it results from high clay content of the FRAfrom this source. Therefore, unlike in the previous properties, theaggregates' size did not influence the influence the modulus ofelasticity of the resulting concrete mixes.

Fig. 14 shows the determination coefficient (R2) values of thelinear regressions between the mixes' modulus of elasticity and theCRA and FRA incorporation ratio (1.00 and 0.99, respectively). Thesevery high values demonstrate the validity of the linear relation-ships. Fig. 14 also confirms that the incorporation of FRA and CRAaffects concrete’ modulus of elasticity in a similar way.

Fig. 14. Modulus of elasticity at 28 days of CRA and FRA

4.3.5. Abrasion resistanceThis test's objective is to define the concrete’ capacity of with-

standing actions that cause disaggregation or section loss. The testwas performed for four of the RA's types only (CRA from Valnor andRetria and FRA from Vimajas and Ambilei).

Table 13 and Fig. 15 present the average wear registered for themixes tested, measured by the mass loss, as well as its variationrelative to the RC. The abrasion resistance increases with the use ofCRA, in agreement with previous researches. De Brito et al. (2005)evaluated the abrasion resistance of various concrete mixes withred-clay ceramic CRA and found that the loss of thickness of thespecimens decreased as the replacement ratio increased. The au-thors explained these results with the better bond between thecement paste and the ceramic RA, because the greater porosity ofthese RA allowed a better penetration of the cementitious pasteinside them. Matias et al. (2013) also performed the wear test byabrasion and found a decrease of the thickness loss between 24%and 28% of the mixes made with CRA from concrete relative to theRC. The authors justified these results with the better bond be-tween the RA and the new cement paste.

concrete mixes versus aggregates' replacement ratio.

Table 13Abrasion resistance (measured as mass loss).

CRA Valnor CRA Retria FRA Vimajas FRA Ambilei

Massloss (%)

D (%) Massloss (%)

D (%) Massloss (%)

D (%) Massloss (%)

D (%)

0% RA 7.6 ± 0.4 e 7.6 ± 0.4 e 7.6 ± 0.4 e 7.6 ± 0.4 e

10% RA 7.2 ± 0.2 �4.6 7.5 ± 0.5 �1.2 7.2 ± 0.4 �4.6 8.0 ± 0.3 6.425% RA 6.7 ± 0.5 �11.8 6.9 ± 0.4 �8.8 8.9 ± 1.2 18.3 8.0 ± 1.2 5.950% RA 6.6 ± 0.1 �12.2 7.1 ± 0.3 �5.6 10.1 ± 0.1 34.2 7.9 ± 0.4 4.7100% RA 6.3 ± 0.5 �16.7 6.4 ± 0.9 �15.5 11.5 ± 1.3 52.4 8.9 ± 0.8 18.0

M. Bravo et al. / Journal of Cleaner Production 99 (2015) 59e7472

Table 13 and Fig. 15 show that the RA's nature strongly in-fluences the abrasion resistance results. For example, in the mixesmadewith 100% of FRA fromAmbilei therewas a reduction of 18.0%of the abrasion resistance but in the mixes made with 100% of FRAfrom Vimajas this reduction reached 52.4%. This results from twofactors. The first one is the greater w/c ratio of the mixes with FRAfrom Vimajas, because they contain clay. The second factor is thedifferent composition of these FRA. Those from Ambilei are mademostly of concrete, natural stone and glass, while those fromVimajas have 75% of concrete, mortar and natural stone, 12% ofceramic materials and 11% of bituminous materials.

Fig. 15. Abrasion resistance at 28 days for RA

Fig. 16. Abrasion resistance at 28 days of CRA and FRA c

However, as seen in Fig. 16, the main influencing factor on theabrasion resistance is the size of the RA used. Full replacement ofthe coarse NA caused an increase of abrasion resistance higher than15%, independently of the CRA's source. Contrarily, full replacementof the fine NA led to an abrasion resistance loss between 18% and53%.

Fig. 16 shows that the abrasion resistance variation dependslinearly on the replacement ratio of NA with RA, as proved by thedetermination coefficient (R2) values of the corresponding linearregressions: 0.73 and 0.98 for CRA and FRA.

5. Conclusions

This research intends to analyse the mechanical performance ofconcrete made with recycled aggregates (RA) from CDW fromvarious Portuguese recycling plants. The objective is to evaluate theinfluence of the collection point of the RA, and consequently oftheir composition on the characteristics of the concrete produced.Five types of coarse CDW RA (from Valnor, Vimajas, Ambilei,Europontal and Retria) and three types of fine CDW RA (fromVimajas, Ambilei and Europontal) were collected. The objective ofcolleting both coarse and fine CDW RA is to also analyse the in-fluence of their size on concrete's performance.

concrete mixes (measured as mass loss).

oncrete mixes versus aggregates' replacement ratio.

Table 14Variation of all concrete mechanical properties with the incorporation of RA.

Tests Quantitative variation of the mixes relative to the RC

C100C-Valnor C100C-Vimajas C100C-Ambilei C100C-Europontal C100C-Retria C100F-Vimajas C100F-Ambilei C100F-Europontal

Compressive strengthin cubes (at 28 days)

�34.5 �22.1 �5.2 �32.9 �25.6 �44.1 �28.8 �44.6

Compressive strengthin cylinders(at 28 days)

�31.6 �18.6 �17.1 �31.4 �21.5 �42.0 �17.8 �38.0

Splitting tensilestrength (at 28 days)

�24.3 �27.5 �11.1 �36.1 �32.1 �34.6 �20.7 �34.4

Modulus ofelasticity (at 28 days)

�47.9 �34.1 �26.3 �37.9 �35.1 �42.5 �19.8 �35.8

Abrasion resistance(mass loss)

þ16.7 e e e þ15.5 �52.4 �18.0 e

M. Bravo et al. / Journal of Cleaner Production 99 (2015) 59e74 73

In order to better understand the experimental results, the RA'scomposition was analysed and several physical and chemical testsof the aggregates were performed. These tests detected a greatvariety in the RA's composition, comprising ceramic materials,concrete, glass, metals, and others.

The results from the fresh-state concrete tests allowedconcluding that the use of RA caused a decrease of concrete'sdensity. This reduction reached values between 4.7% and 7.7% in themixes with 100% RA (fine and coarse). It was also found that, inorder to maintain the slump, it was necessary to increase theeffective w/c ratio of the mixes as the replacement ratio of NAwithRA increased. This situation was more evident with the use of FRAfrom Vimajas and Europontal.

The mechanical tests in hardened concrete showed that in mostcases the use of RA caused a decline of the performance of concrete.Table 14 summarizes the results obtained, allowing the analysis ofthe variations in the mixes with 100% RA, relative to the RC, for allfive properties tested.

There is a wide scatter of results according to the source of theRA. This was predictable since each RA type has a differentcomposition, influenced by the location of the collection point. Thisdifference causes a significant range in the aggregates' character-istics and consequently in the resulting concrete mixes' properties.Table 14 shows that themixes with FRA fromVimajas had theworstresults, partly because of their high clay content. These fine parti-cles coat the RA grains and hinder a correct bond between themand the cement paste, weakening the concrete's structure.Furthermore, clay absorbs the mixing water and that forced anincrease of the effective w/c ratio in order to obtain the same slumpas in the other mixes.

Finally, the abrasion resistance is the property that presentsbetter results in terms of the use of RA in concrete. As seen inTable 14, the abrasion resistance seems to improve when coarseCDW RA are used.

The durability performance of the same concrete mixes hasbeen analysed in Bravo et al. (2015).

Acknowledgements

The authors gratefully acknowledge the support of the ICISTResearch Institute, Instituto Superior T�ecnico from University ofLisbon, and FCT (Foundation for Science and Technology).

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