Construction and Building Materials 96 (2015) 172–180

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Construction and Building Materials

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Effects of copper slag and recycled concrete aggregate on the propertiesof CIR mixes with bitumen emulsion, rice husk ash, Portland cement andfly ash

http://dx.doi.org/10.1016/j.conbuildmat.2015.08.0210950-0618/� 2015 Elsevier Ltd. All rights reserved.

⇑ Corresponding author.E-mail addresses: abehnood@purdue.edu (A. Behnood), mmodirig@purdue.edu

(M. Modiri Gharehveran), f.gozali@taraddodrah.ir (F. Gozali Asl), ameri@iust.ac.ir(M. Ameri).

Ali Behnood a,⇑, Mahsa Modiri Gharehveran a, Farhad Gozali Asl b, Mahmoud Ameri b

a Lyles School of Civil Engineering, Purdue University, 550 Stadium Mall Dr., West Lafayette, IN 47907-2051, USAb School of Civil Engineering, Iran University of Science and Technology, P.O. Box 16489, Narmak, Tehran, Iran

h i g h l i g h t s

� The feasibility of the use of copper slag and recycled concrete aggregate as substitutes for virgin aggregates in CIR mixes was investigated.� Effects of different additives such as Portland cement, FA, and RHA were studied.� Copper slag and different additives improved the durability and mechanical properties of CIR mixes.� Recycled concrete aggregate was found to be acceptable type of aggregate as a substitute for virgin aggregate in CIR mixtures.� Hazardous environmental effects were not observed.

a r t i c l e i n f o

Article history:Received 1 April 2015Received in revised form 21 July 2015Accepted 5 August 2015Available online 9 August 2015

Keywords:Cold in place recyclingCopper slagRecycled concrete aggregateRice husk ashFly ashAsphalt emulsion

a b s t r a c t

Construction and maintenance of roads require a large volume of aggregates for use in base, sub-base andsurface layers. At the same time, the expansion of asphalt roadways results in the production of a largeamount of asphalt road waste, known as reclaimed asphalt pavement (RAP). This paper aims to investi-gate the feasibility of the use of copper slag and recycled concrete aggregate (RCA) as substitutes for vir-gin aggregates in modifying the gradation of cold recycled mixes made with RAP material. In addition, theeffects of three types of additives including Portland cement, fly ash, and rice husk ash on the propertiesof recycled mixtures were investigated. Marshall, Indirect tensile strength, resilient modulus, moisturesusceptibility, and dynamic creep tests were conducted to evaluate the mechanical properties of themixes. Toxicity characteristic leaching procedure was used to assess the environmental impacts of copperslag. The use of copper slag had better results than limestone and RCA probably due to better interlockingand superior physical and mechanical properties. With regard to the effects of additives, Portland cementwas found to be the most effective additive. The difference between fly ash and rice husk ash was foundto be statistically insignificant.

� 2015 Elsevier Ltd. All rights reserved.

1. Introduction

Construction and maintenance of roads require a large volumeof aggregates for use in base, sub-base and surface layers of pave-ments. At the same time, the expansion of asphalt roadways resultsin the production of a large amount of asphalt road waste materialknown as reclaimed asphalt pavement (RAP). Knowing that recy-cling of asphalt pavements is very advantageous from technicaland environmental perspectives, transportation organizations

and material scientists encourage beneficial use of RAP [1–5].RAP material can remain on site for a long period of time, be dis-charged at a waste landfill or be used in a number of highwayapplications. Some of these applications include its usage as anaggregate substitute and asphalt cement supplement in recycledasphalt paving (hot mix or cold mix). It can also be used as a gran-ular base or sub-base, stabilized base aggregate, embankment orfill material.

Cold in-place recycling (CIR) is defined as a rehabilitation tech-nique in which the RAP materials are used in place without theapplication of heat [6]. Some of the advantages associated withCIR technique as a pavement rehabilitation approach are reductionin traffic disruption, virgin aggregates and bitumen consumption in

Table 1Physical properties of copper slag [15].

Property Value

Appearance Black, glassy, more vesicular when granulatedParticle shape IrregularDensity (g/cm3) 3.16–3.87Water absorption 0.15–0.55Hardness 6–7Abrasion loss (%) 24.1Aggregate impact value (%) 8.2–16Aggregate crushing value (%) 10–21Soundness 0.8–0.9Water soluble chloride

(ppm)<50

Conductivity (ls/cm) 500

A. Behnood et al. / Construction and Building Materials 96 (2015) 172–180 173

asphalt mixes, environmental concerns, cost and energy. Since CIRtechnique does not require heating, there is no negative change inthe structure of the asphalt binder due to aging [7]. Moreover, CIRneeds lower construction time than conventional rehabilitationprocedures [4]. The CIR technique can be applied to eliminatetransverse, reflective, and longitudinal cracks. It is also a robustapproach to restore old pavement to the desired profile, eliminateexisting wheel ruts, restore the crown and cross slope, and elimi-nate pothole, irregularities and rough areas [8].

The RAP material is obtained by milling or crushing the existingpavement. The obtained material is then laid and compacted afteradding recycling agent and/or virgin aggregate. In many applica-tions, virgin aggregate is added when the gradation of RAP materialis not within the blending chart limits [2,9]. However, other typesof waste and by-product materials could also be used to improvethe gradation of RAP material. For example, steel slag has been suc-cessfully used as a substitute for virgin aggregates to satisfy thegradation requirements of the CIR mixes [2].

Type of additives that is used in CIR mixtures has also beenfound as a factor that improves the mechanical properties and per-formance of these mixtures [10,11]. Various types of additives suchas Portland cement, fly ash, and lime have been successfully usedin CIR mixtures [2,10–13].

This study aims to investigate the feasibility of using of copperslag (CS) and recycled concrete aggregate (RCA) as substitutes forvirgin aggregate in modifying the gradation of cold recycled mixesmade with RAP material. Nine different types of mixtures contain-ing three types of aggregates (limestone (LS), CS, and RCA) andthree types of additives (cement, fly ash, rice husk ash) as well asthree types of mixtures without additive were used to study theeffects of different aggregates and additives on the mechanicalproperties of CIR mixes. Marshall stability and flow, Indirect tensilestrength (ITS), resistance to moisture damage, resilient modulus,and dynamic creep tests were conducted to study the mechanicalproperties of the mixes. Environmental impacts of the use of differ-ent aggregates in CIR mixes were evaluated by the toxicity charac-teristic leaching procedure (TCLP) test.

2. Background

2.1. Copper slag (CS)

Copper slag (CS) is a by-product from matte smelting and refin-ing of copper [14]. Production of one ton of copper approximatelygenerates 2.2–3 tons of CS. Consequently, annually about 24.6 mil-lion tons of CS is produced worldwide. CS has been widely used asrailroad ballast abrasive tools, roofing granules, cement and con-crete industries. It can also be used in broad areas of road construc-tion including surface layers and in unbound bases or sub-bases.

Due to its significant amount of free iron, CS has high densityand hardness [15]. The average specific gravity of CS is about3.5 g/cm3, which indicates that CS is denser than ordinary naturalaggregate [15]. Therefore, CS can be considered as a suitable artifi-cial source of aggregate in pavement industry. Many attempts havebeen done to investigate the feasibility of the use of CS as fine andcoarse aggregates in concrete industry [15,16]. However, a com-prehensive literature review did not reveal widely use of CS inbituminous mixtures. Based on the physical, chemical, andmechanical properties of it, there is not any reason why CS wouldnot make durable asphalt mixes. Table 1 shows the typical physicalproperties of CS.

Pundhir et al. reported that the use of CS as fine aggregate invarious bituminous mixes provides good interlocking andimproves mechanical properties of the mixes [17]. Havanagiet al. investigated the feasibility of the use of CS as fine aggregate

in bituminous mixtures [18]. They performed Marshall stabilitytest, indirect tensile strength, dynamic modulus, and moisture sen-sitivity. It was found that CS could replace fine aggregate in therange of 17–32%. In another study, Hassan and Al-Jabri [19] evalu-ated the effects of granulated CS as a fine aggregate in hot-mixasphalt concrete. In their study, stripping potential was evaluatedby the indirect tensile strength. A reduction in strength wasobserved due to the use of CS; however, the tensile-strength ratiowas superior to that of the control mix. Higher copper contentresults in an increase in the voids in the mineral aggregates inthe asphalt mixtures [19]. This, in turn, results in higher asphaltbinder content percentage to satisfy the air-voids criteria.Consequently, it is plausible to expect higher potential for ruttingfor mixes with a higher slag content [19].

2.2. Recycled concrete aggregate (RCA)

Concrete aggregate collected from demolition sites has beenwidely used in hot-mix asphalt mixtures in recent years [20–22].However, after a review of the technical literature, we could notfind any use of RCA in cold mixtures. The properties of RCA are dif-ferent from those of natural aggregate because of the attachedmortar to the surface of RCA particles [23,24]. The type and theamount of the impurities also affect the properties of RCA [23].

The properties of RCA can vary from source to source. Therefore,a wide disparity of opinions exists in terms of the properties of themixtures prepared with these aggregates. Some researchers haveaffirmed that HMA containing RCA are stiffer than conventionalmixes [25,26], while others suggest the opposite [22,27]. Withregard to the permanent deformation, some authors have reportedsimilar or better performance of HMA made with RCA [21,26,27].However, some other researchers have reported that the resistanceto permanent deformation decreases as the percentage of RCA inthe mix increases [22]. Turning to the water resistance of HMAmade with RCA, some investigators have reported an adequatewater resistance [28,29], while others suggest the use of a certainamount of RCA in HMA in order to get acceptable results.

2.3. Application of additives in CIR mixtures

Previous studies have shown that additives can improve theperformance of asphalt mixtures mixes [11,30,31]. Various addi-tives such as bitumen emulsion, cement, quick lime, coal waste(ash), silica fume or fly ash have been used during the compactionof the recycled mixtures [2,10,11,13,30,32]. Different factors suchas cost, performance, and climate condition should be consideredwhen choosing the appropriate type of additive [30].

Portland cement and fly ash (FA) are among the most widelyused additives in CIR mixtures. Previous studies have shown thatcement can improve the durability of CIR mixtures [11,33]. The

Table 2Properties of asphalt emulsion.

Property CSS-1

Sabolt furol viscosity @ 25 �C (s) 55Storage stability test (%) 0.5Residue by distillation 65Penetration on residue @ 25 �C 150Portland cement mixing test 2

Table 3Physical and chemical analysis of cement, fly ash and rice husk ash.

Item Portland cement Fly ash Rice husk ash

174 A. Behnood et al. / Construction and Building Materials 96 (2015) 172–180

use of cement increases the initial stiffness, indirect tensilestrength, resilient modulus, and moisture resistance and decreasespermanent deformation [11,33–35]. Similar to cement, FA canimprove the mechanical properties and durability of the recycledmixtures [12].

Rice husk ash (RHA) is a by-product from the burning of ricehusk. The utilization of RHA as a pozzolanic material in cementand concrete industry provides several advantageous such as bet-ter durability properties and improved strength. Although RHAhas been widely used in many work area, there are only few stud-ies about the use of RHA in the asphalt concrete mixtures. In arecent study, Sargın et al. [36] investigated the usability of RHAin HMA concrete as mineral filler. They found that 50% RHA and50% LS of filler rate mixtures had the best Marshall stability.

Physical propertiesSpecific gravity 3.10 2.3 2.05

Chemical composition (%)SiO2 23.1 59.10 92.00Al2O3 4.78 21.00 0.34Fe2O3 3.59 3.72 0.37MgO 2.55 1.38 0.78SO3 1.98 1.05 1.24P2O5 0.05 – 0.95Na2O 0.40 2.52 0.11K2O 0.70 0.90 3.29Loss on ignition (%) 0.49 4.6 6.7

3. Materials

Characterization and properties of the materials should be identified in order toobtain an accurate explanation and analysis of the experimental results. The prop-erties of the binders, additives, and aggregates are presented in the followingsections.

3.1. Aggregates

The reclaimed asphalt pavement (RAP) material in this study was taken from ademolition/reconstruction road site project. Since most project demand theremoval of oversize material, the material larger than 25 mm in size was removedbefore gradation. Gradation of the RAP material was determined according to ASTMC136.117 Test Method. The bitumen content of the RAP material was determinedbased on ASTM D2172 and obtained as 3.5%. The gradation of the RAP materialdid not meet the required specification of Road and Transportation of Iran forCold Mix Recycling [37]. Therefore, it was modified by adding new sources of aggre-gates (18% by the weight of total aggregate). The gradation of specification limits,RAP material, and mix blend are shown in Fig. 1.

In this study, three types of new aggregates were used to modify the gradationof RAP materials and satisfy the specification requirements. These aggregates wereLS, CS, and RCA.

3.2. Binder and additives

Choosing the appropriate binder is a vital task from the compatibility perspec-tive with aggregate and its gradation [2]. Due to the presence of positive or negativeelectric charges on the surface of particles, bitumen emulsions can show differentcharacteristics while being blended with different aggregates [2]. In this study, acationic slow setting (CSS-1) was used. The properties of asphalt emulsion thatare used in the current study are given in Table 2.

In this study, three types of additives including Portland cement, fly ash, andrice husk ash were used. In addition, mixtures without additives were preparedto study the effects of each of the additives. The chemical and physical propertiesof the utilized additives in this study are given in Table 3.

4. Mix design procedure

CIR mixes were designed based on modified Marshall method(ASTM D1559), which is accepted by AASHTO [37]. Following this

0

20

40

60

80

100

120

0.01 0.1 1 10 100

Perc

ent p

assi

ng

Sieve size (mm)

Lower limit

Upper limit

RAP

Mix blend

Fig. 1. Gradation of RAP material, mix blend and specification limits.

method, the mixtures were prepared in such a way to contain 3%water. This water consists of emulsion water, RAP water and thewater added to the mixture. Bitumen emulsion was added to themixtures at the percentages ranging from 2.5% to 4.5% by weightof total mixture at 0.5% increments. Marshall hammer was usedto apply 50 blows per side of each mixture. The samples were thenoven cured for 24 h at a temperature of 60 �C. After oven curing,the samples were kept for 24 h at room temperature in the moldsand then were extruded and air cured for 5 days at room temper-ature. Optimum emulsion content was determined using the max-imum specific gravity and Marshall stability. Air void content wasused as the only design criterion, which should be between 9% and14% [2]. To determine the optimum emulsion content, three repli-cate samples were prepared for each of the emulsion content-aggregate type combination (i.e. a total of 45 specimens).Optimum additive content was determined for the samples pre-pared with optimum emulsion content and optimum water con-tent using the maximum Marshall stability. To determine theoptimum additive content, three replicate samples were preparedfor each of the additive content-mixture type (i.e. a total of 153specimens). The amount of cement was changed from 1.0% to3.0% at 0.5% increments. With Regard to FA and RHA, the amountof additives was changed from 1.0% to 6.0% at 1.0% increments. Itshould be noted that all the additives were utilized in powder formand were added to the mixed aggregates before adding water andasphalt emulsion. Asphalt mixtures were prepared for mixing afteradding water and asphalt emulsion to the blend of aggregate andadditive. Mixing was continued for about two minutes in orderto achieve a homogenous blend. Table 4 shows the optimum emul-sion, water, and additive contents for 12 types of mixtures. In orderto identify the mixes, they were labeled with two letters. In theselabels, the first and the second letters indicated the type of blendedaggregate and the type of additive, respectively.

5. Testing program

The laboratory tests used in this study to analyze the mechan-ical properties and durability of cold recycled mixtures are dis-cussed in this section.

Table 4Optimum emulsion and additive contents of mixes.

SampleID

Blendedaggregate

Additive Optimumbitumen (%)

Optimumadditive (%)

LW LS None 3.4 0.0LP LS Cement 3.3 2.0LF LS FA 3.4 5.0LH LS RHA 3.4 3.0SW CS None 3.5 0.0SP CS Cement 3.5 2.5SF CS FA 3.6 5.0SH CS RHA 3.6 3.0RW RCA None 4.0 0.0RP RCA Cement 4.2 2.5RF RCA FA 4.1 6.0RH RCA RHA 4.1 4.0

A. Behnood et al. / Construction and Building Materials 96 (2015) 172–180 175

5.1. Marshall stability, flow and Marshall Quotient

Stability is one of the most important properties of asphalt mix-tures. Marshall stability which is a measure of the maximum loadsustained by the bituminous material at a constant loading ratewas measured based on ASTM D1559. Flow, as an indispensablepart of Marshall Test, measures the specimen’s plastic flow owingto the applied load. The flow value refers to the vertical deforma-tion when the maximum load is reached.

The ratio of Marshall stability (kN) to Marshall flow (mm) isdefined as the Marshall Quotient (MQ) and can be used as a mea-sure of the bituminous mixture’s resistance to rutting [2,38]. A stif-fer and more resistant mixture to permanent deformation has ahigher value of MQ [39].

5.2. Indirect tensile strength (ITS) test

Tensile properties of the compacted bituminous mixtures,which are related to the cracking properties of the pavement, canbe determined by the indirect tensile strength (ITS) test (ASTMD6931). Higher tensile strength is an indication of higher resis-tance to fatigue and thermal cracking. The ITS test involves loadinga cylindrical specimen with compressive loads; which develops arelatively uniform tensile stress perpendicular to the direction ofthe applied load and along the vertical diametrical plane. The loadis applied at a deformation rate of 50 mm/min and at a tempera-ture of 25 �C. Failure usually occurs by splitting or rupturing alongthe vertical diameter [38,40]. The tensile strength of the specimenswas determined as:

ITS ¼ 2Pmax

ptdð1Þ

where ITS is the indirect tensile strength (kN/m2); Pmax, is the peakload (kN); t is the thickness of the specimens (mm); and d is thediameter of the specimens (mm).

In order to conduct ITS test, five specimens with optimumdesign contents were prepared for each type of mixtures (i.e. atotal number of 60 specimens).

5.3. Resistance to moisture damage

Moisture damage in flexible pavements occurs due to the loss ofadhesion and or cohesion and results in the separation andremoval of asphalt binder from the aggregate surface in the pres-ence of water. This phenomenon leads to the reduced strength orstiffness of the asphalt mixture. The moisture susceptibility ofasphalt mixtures was evaluated by performing the AASHTO T283test and Marshall conditioning (immersion of the asphalt mixturesin a water bath for 24 h at a temperature of 60 �C).

AASHTO T283 test is used to determine the effect of saturationand accelerated water conditioning on the indirect tensile strengthof cylindrical specimens. To conduct the AASHTO T283 test, sixsamples from each mixture (i.e. a total number of 72 specimens)were prepared and grouped equally into conditioned and uncondi-tioned samples. Conditioning was done by vacuum saturation ofthe specimens at 55–80% saturation level followed by a freezecycle for 16 h at a temperature of �18 �C and subsequently soakingthe specimens in warm water (60 �C) for 24 h. The indirect tensilestrength ratio (TSR) was then computed as:

TSR ¼ 100� ðScon=SunconÞ ð2Þwhere Scon is the average tensile strength of the conditioned speci-mens (kN/m2), and Suncon is the average tensile strength of theunconditioned specimens (kN/m2). A minimum ratio of 0.8 has beentypically used as a minimum acceptable TSR value for hot mixasphalt. Mixtures with ratios greater than 0.8 are considered as rel-atively resistant to water damage. For cold recycled mixtures, a uni-versally minimum acceptable value for TSR has not been reported.However, it can be considered that mixtures with high TSR values(above 0.8) are relatively resistant to moisture damage and mix-tures with low TSR values (less than 0.8) are susceptible to moisturedamage [2,38].

For Marshall conditioning test, six samples from each mixture(i.e. a total number of 72) were immersed in a warm water bath(60 �C). Three specimens (unconditioned) from each mixture weretested at a loading rate of 50 mm/min after 40 min immersion inwater bath. The remaining specimens (conditioned) were keptfor 24 h in the water bath and subsequently loaded under similarcondition. The Marshall Stability Ratio (MSR) was then computedas:

MSR ¼ 100� ðMScon=MSunconÞ ð3Þwhere MScon is the average Marshall stability for conditioned sam-ples, and MSuncon is the average Marshall stability for unconditionedsamples.

5.4. Resilient modulus

Resilient modulus of asphalt mixtures, measured in the indirecttensile mode (ASTM D4123), is the most important parameter usedin the mechanistic design of asphalt pavements. The test is also themost popular form of stress–strain measurements used to evaluatethe elastic properties of asphalt mixtures [41]. In elastic theoriesmodel, resilient modulus along with some other information isused as input to generate an optimum thickness design. For eachtype of asphalt mixture, five cylindrical specimens (i.e. a totalnumber of 60 specimens) were prepared at optimum emulsionand additive content using a gyratory compactor.

5.5. Dynamic creep test

Different test methods are available to evaluate the permanentdeformation of asphalt mixtures such as wheel tracking test anddynamic creep test [42,43]. In this study, dynamic creep test wasemployed to assess the resistance of mixes to rutting since it hasbeen reported as one of the best test procedure to assess the per-manent deformation of asphalt mixtures [43]. The dynamic creeptest applies a repeated pulsed uniaxial load on asphalt specimensand measures the resulting deformations in the same directionusing linear variable differential transducers (LVDTs). For each typeof asphalt mixture, five cylindrical specimens (i.e. a total number of60 specimens) were prepared at optimum emulsion and additivecontent using a gyratory compactor. To perform the dynamic creeptest, a conditioning stress of 10 kPa was applied for 600 s. Then the

Table 5Summary of Marshall test results and volumetric parameters (asterisk shows themixture with optimum emulsion and optimum water contents).

SampleID

Additivecontent(%)

Airvoid

Bulk specificgravity (g/cm3)

Marshallstability(kN)

Flow(mm)

MQ

LW 0.0 12.4 2.321 9.87 2.65 3.72LP 1.0 13.2 2.191 10.89 2.71 4.02LP 1.5 13.2 2.236 11.34 2.88 3.94LP* 2.0 13.1 2.214 12.89 2.94 4.38LP 2.5 13.1 2.148 12.37 3.01 4.11LP 3.0 13.1 2.126 12.00 2.98 4.03LF 1.0 12.7 2.271 10.59 2.67 3.97LF 2.0 12.5 2.285 10.53 2.97 3.55LF 3.0 12.6 2.340 10.76 2.78 3.87LF 40 12.6 2.294 10.65 2.81 3.79LF* 5.0 12.4 2.317 11.45 2.73 4.19LF 6.0 12.4 2.336 11.22 2.71 4.14LH 1.0 12.9 2.295 10.04 2.70 3.72LH 2.0 12.9 2.272 10.60 2.73 3.88LH* 3.0 12.6 2.318 11.16 2.65 4.21LH 4.0 12.6 2.330 11.49 2.78 4.13LH 5.0 12.6 2.225 10.71 2.63 4.07LH 6.0 12.7 2.270 10.77 2.68 4.02SW 0.0 12.6 2.355 10.86 2.71 4.01SP 1.0 12.4 2.371 11.40 2.88 3.96SP 1.5 12.5 2.325 12.71 2.95 4.31SP 2.0 12.6 2.348 12.49 2.90 4.31SP* 2.5 12.4 2.372 13.15 2.71 4.85SP 3.0 12.5 2.315 13.11 2.68 4.89SF 1.0 12.9 2.300 11.78 2.92 4.03SF 2.0 12.7 2.276 11.65 2.77 4.21SF 3.0 12.4 2.293 12.20 2.87 4.25SF 4.0 12.4 2.324 12.27 2.91 4.22SF* 5.0 12.6 2.371 12.33 2.73 4.52

176 A. Behnood et al. / Construction and Building Materials 96 (2015) 172–180

conditioning load was removed and a stress of 50 kPa for 1800cycles with 1 s loading and 1 s unloading.

5.6. Toxicity characteristic leaching procedure (TCLP) test

Potential environmental impact of RAP on soil and groundwateris of a great concern, because some of RAP materials may containtoxic substances such as heavy metals and hydrocarbons. Thus,an assessment of environmental characteristics of RAP is impera-tive before use of this material in road construction especiallywhen this material is combined with another material such as CSor RCA which are suspicious of being hazardous.

There are various procedures to conduct a batch test. These pro-cedures typically involve mixing size-reduced waste with extrac-tion solution and then agitating the mixture. The main differencesamong these procedures are leaching solution, liquid to solid (L/S)ratio, and number and duration of extraction [44]. In this study,the Toxicity Characteristic Leaching Procedure (TCLP) developedby the US Environmental Protection Agency [45] was employed tostudy the leaching of contaminants from the RAPmaterials and theircold and hot mixtures. For each specimen, a sample of 100 g,crushed to a grain size of <9.5 mm, was extracted for 20 h. The liq-uid/solid ratio was selected as 20:1 in accordance with TCLP. Atthe end of 20 h tumbling period, the extracts are separated fromthe solids using a 0.7 lm glass fiber filter. Heavy metals were thenanalyzed by atomic absorption spectrophotometry. Polyaromatichydrocarbons (PAHs) concentrations were measured in leachatesby applying gas chromatography ion trap mass spectrometrydetection.

SF 6.0 12.6 2.359 12.33 2.74 4.50SH 1.0 12.7 2.318 10.78 3.22 3.35SH 2.0 12.6 2.389 11.95 3.15 3.79SH* 3.0 12.6 2.365 12.38 2.74 4.52SH 4.0 12.5 2.393 12.25 2.87 4.27SH 5.0 12.6 2.425 12.30 2.77 4.44SH 6.0 12.6 2.341 12.03 2.77 4.34RW 0.0 12.9 2.197 8.10 2.85 2.84RP 1.0 13.0 2.275 9.88 3.15 3.14RP 1.5 12.9 2.300 10.32 3.02 3.42RP 2.0 13.0 2.312 10.44 3.20 3.26RP* 2.5 12.5 2.289 10.63 2.90 3.67RP 3.0 12.8 2.259 10.49 2.91 3.60RF 1.0 12.2 2.255 8.32 3.05 2.73RF 2.0 12.3 2.253 8.67 2.99 2.90RF 3.0 12.3 2.260 8.65 3.22 2.69RF 4.0 12.4 2.258 9.04 3.15 2.87RF 5.0 12.2 2.264 8.98 3.27 2.75RF* 6.0 12.3 2.269 9.12 3.12 2.92RH 1.0 12.5 2.262 8.87 2.98 2.98RH 2.0 12.6 2.257 9.12 3.27 2.79RH 3.0 12.3 2.266 9.94 3.07 3.24RH* 4.0 12.3 2.273 10.39 3.15 3.30RH 5.0 12.3 2.287 10.22 3.12 3.28RH 6.0 12.3 2.303 9.97 3.04 3.28

Table 6Summary of ANOVA results for Marshall stability.

Source DF Sum of square Mean square F value Pr > F

Aggregate 2 14.32 7.16 45.51 0.0002Additive 3 10.57 3.52 22.39 0.0012Error 6 0.94 0.16Total 11 25.84R2 0.93

6. Results and discussion

Results of performed laboratory tests have been presented inthis section.

6.1. Marshall stability, flow and Marshall Quotient

The results of the Marshall test and the volumetric parametersof the mixtures are given in Table 5. It should be mentioned thatthe values presented herein are the average of three measure-ments. It can also be seen that air void contents for all mixes werein the acceptable range. CIR mixture containing CS and Portlandcement has the highest Marshall stability and MQ values. The low-est Marshall stability and MQ values were obtained for the mixturecontaining RCA and without additive. The low Marshall stabilityand MQ values obtained for this mixture could be due to the com-bination effects of the inferior properties of RCA and higher emul-sion content in these mixtures.

Analysis of variance (ANOVA) was conducted on the results thatwere obtained from the mixtures with optimum emulsion andoptimum additive contents to analyze the effect of aggregate typeand additive type on Marshall stability and MQ values. In theANOVA, mean comparisons of Marshall stabilities or MQs for eachpair of aggregates or additives were tested using Tukey’s multiplecomparison method. The multiple comparisons test is a statisticalapproach to distinguish the difference between test results.Table 6 shows the summary of ANOVA results for the Marshall sta-bility values. Tables 7 and 8 show the multiple comparison resultsfor the effects of aggregates and additives, respectively.

The test results indicated that the Marshall stability and MQvalues are statistically different between RCA and two other aggre-gates, where a = 0.05. In other words, Marshall stability and MQvalues for the mixtures containing LS or CS are higher comparedto the mixtures containing RCA. However, it should be noted thatthe Marshall stability of all mixes was more than 8 kN which is

the minimum acceptable value for heavy loading conditions [46].With regard to the difference between the mean of the Marshallstability and MQ values of CS and LS, it was found that they arenot statistically different where a = 0.05. However, Marshall

Table 7Tukey’s comparison results for the effect of aggregates – Pr > |t| for H0: least squaremean (i) = least square mean (j).

i/j LS CS RAC

LS 0.0554 0.0017CS 0.0054 0.0002RAC 0.0017 0.0002

Table 8Tukey’s comparison results for the effect of additives – Pr > |t| for H0: least squaremean (i) = least square mean (j).

i/j Without additive PC FA RHA

Without additive 0.0008 0.0223 0.0077PC 0.0008 0.0312 0.1068FA 0.0223 0.0312 0.7239RHA 0.0077 0.1068 0.7239

A. Behnood et al. / Construction and Building Materials 96 (2015) 172–180 177

stability and MQ values of the mixtures containing CS and LS arestatistically different where a = 0.1. It can be seen that theMarshall stability and MQ values of the mixtures containing CSare higher compared to those containing LS. This might be due tothe improved aggregate interlocking and better compatibility ofCS with anionic asphalt emulsion.

Turning to the effects of the additives, Tukey’s multiple compar-ison test indicated that the utilized additives affect significantly(a = 0.05) on the Marshall stability test results. In addition, it wasfound that the Marshall stability of the mixtures containingPortland cement is higher than the Marshall stability of the mix-tures that contain FA and RHA. However, the difference betweenPortland cement and RHA is statistically different where a = 0.1.In addition, the difference between FA and RHA is not statisticallysignificant.

6.2. Indirect tensile strength (ITS) test

The results of the indirect tensile strength tests are shown inFig. 2. It can be seen that the use of additives in CIR mixturesincreased the tensile strength of these mixtures. The maximumtensile strength was obtained for the mixtures containing CS andPortland cement. CS and Portland cement were found to be themost effective aggregate and additive, respectively. Among theadditives that were used in this study, Portland cement was foundto be the most effective additive in increasing the tensile strengthof the CIR mixtures. Portland cement increased the tensile strengthup to 56% in the mixtures containing LS. In the mixtures made withCS and RCA, the use of Portland cement resulted in an increase of50% and 32%, respectively, in ITS of the mixtures as compared tothe corresponding samples without additives. Interestingly,

050

100150200250300350400450500

LW LP LF LH SW SP SF SH RW RP RF RH

Ten

sile

stre

ngth

(kPa

)

Type of mixture

Fig. 2. Effects of the types of additives and aggregates on ITS of CIR mixes.

regardless of type of the blended aggregate, the use of FA resultedin an increase in ITS of 24%. RHS was found to increase the tensilestrength in the range from 20% to 33%. Tukey’s multiple compar-ison test showed that the effects of FA and RHA were not signifi-cantly different, where a = 0.05.

It should be noted that the effects of different additives werenot found to be significantly different in the mixtures containingRCA. However, the use of additives in these mixtures significantlyincreased the tensile strength.

Turning to the effects of aggregates, CS was found to increasethe tensile strength while RCA was found to decrease it as com-pared to the mixtures made with LS. In the mixtures made withoutadditives, CS resulted in an increase in the tensile strength of 18%and RCA resulted in a reduction in the tensile strength of 7%. It canbe seen that the reduction in the ITS of CIR mixtures due to the useof RCA is not statistically significant. In addition, the use of addi-tives in these mixtures could be a helpful approach to improvethe ITS results.

6.3. Resistance to moisture damage

Marshall stability and indirect tensile strength values for bothconditioned and unconditioned specimens are shown in Figs. 3and 4, respectively. MSR and TSR values for different mixturesare shown in Figs. 5 and 6, respectively.

It is evident that the use of Portland cement increased theretained Marshall stability (MSR) of the CIR mixtures. With regardto the effects of other additives (i.e. FA and RHA), they did notimprove the moisture resistance of the mixtures significantly.Moreover, a negligible reduction in the MSR values of the mixturescontaining RCA can be seen where FA or RHA were used as addi-tives. The reason could be due to the poor compatibility and poz-zolanic reaction of these additives with RCA. The maximum MSRvalue was observed for the mixtures containing LS and Portlandcement. The minimum MSR value was observed for the mixturescontaining RCA and FA.

Similar to the Marshall conditioning tests, the TSR values indi-cated that Portland cement was the most effective additive inimproving the moisture resistance of the CIR mixtures. In the mix-tures containing, LS and CS, the use of FA and RHA resulted in anincrease in the TSR values. However, in the mixtures containingRCA, the effects of FA and RHA were not found to be significant.

Comparing the mixtures containing LS and CS, Tukey’s compar-ison test results indicated that the difference in MSR and TSR val-ues were not significant.

6.4. Resilient modulus

Fig. 7 shows the average resilient modulus for each mix. It isclearly evident that the use of additives increases the resilient

0

2

4

6

8

10

12

14

16

LW LP LF LH SW SP SF SH RW RP RF RH

Mar

shal

l Sta

bilit

y (k

N)

Type of mixture

Fig. 3. Marshall stability values for unconditioned and conditioned specimens(shown as unconditioned/conditioned).

0

50

100

150

200

250

300

350

400

450

LW LP LF LH SW SP SF SH RW RP RF RH

Ten

sile

stre

ngth

(kPa

)

Type of mixture

Fig. 4. Tensile strength values for conditioned and unconditioned specimens(shown as unconditioned/conditioned).

00.10.20.30.40.50.60.70.80.9

1

LW LP LF LH SW SP SF SH RW RP RF RH

MSR

Type of mixture

Fig. 5. MSR values for different CIR mixtures.

00.10.20.30.40.50.60.70.80.9

1

LW LP LF LH SW SP SF SH RW RP RF RH

TSR

Type of mixture

Fig. 6. TSR values for different CIR mixtures.

0

500

1000

1500

2000

2500

3000

3500

LW LP LF LH SW SP SF SH RW RP RF RH

Res

ilien

t Mod

ulus

(kPa

)

Type of mixture

Fig. 7. Effects of the types of additives and aggregates on resilient modulus of CIRmixes.

0

0.5

1

1.5

2

2.5

0 500 1000 1500 2000 2500

Def

orm

atio

n (m

m)

Number of cycles

LW LP LF LH SW SP

SF SH RW RP RF RH

Fig. 8. Dynamic creep test results.

Table 9WHO and EPA’s drinking water standard regulations for heavy metals and PAHs.

Element/substance(lm/L)

WHO’s drinking waterstandards [47]

EPA’s drinking waterstandard [48]

Pb 10 15Cu 2000 1300Cr 50 100Zn 3000 –Ni 20 –Cd 3 5Hg 1 2PAHs 0.7 0.2

178 A. Behnood et al. / Construction and Building Materials 96 (2015) 172–180

modulus of the CIR mixtures. Portland cement was found to be themost effective additive. The reason could be due to the role ofwater in the hydration of Portland cement and strong pozzolanic

reaction. The use of Portland cement in the mixtures containingLS, CS, and RCA resulted in an increase in resilient modulus of36%, 14%, and 41%, respectively. It should be noted that in the mix-tures containing CS, the effects of different additives were notfound to be significantly different. In addition, in all the mixes,the difference between the effects of FA and RHA was not foundto be statistically significant.

Turning to the effects of aggregates, compared to the samplescontaining LS (virgin aggregate) CS resulted in an increase in theresilient modulus while RCA resulted in a reduction of it.However, the amount of reduction was found to be statisticallyinsignificant.

6.5. Dynamic creep test

The results of dynamic creep tests for different CIR mixtures aregiven in Fig. 8. It can be seen that the use of CS along with Portlandcement resulted in the minimum rut depth.

The results of dynamic creep test show that the use of Portlandcement, FA and RHA resulted in decreased rut depth. In the mix-tures containing LS, the use of Portland cement, FA and RHAresulted in a reduction in rut depth of 20%, 10% and 7%. Withregard to the mixtures containing CS, the use of Portland cement,FA and RHA resulted in a reduction in rut depth of 13%, 5% and 11%.

Turning to the effects of aggregates, the results of dynamiccreep test show that the use of CS as a substitute for virgin aggre-gate (LS) resulted in a decreased rut depth. RCA was found toincrease the rut depth of CIR mixtures.

6.6. Toxicity characteristic leaching procedure (TCLP) test

TCLP test was conducted to assess the environmental impacts ofthe use of CS and RCA in CIR mixes during the service life. To con-trol the amount of concentrations, World Health Organization’s(WHO) drinking water standard and Environmental ProtectionAgency’s regulations for drinking water were used. These

A. Behnood et al. / Construction and Building Materials 96 (2015) 172–180 179

standards are presented in Table 9. It should be mentioned thatthese levels are reference point for standard setting anddrinking-water safety. It was found that the concentration of allheavy metals and PAH’s are below the regulatory levels. That is,the use of CS in CIR mixes does not have harmful effects toenvironment.

7. Conclusion

This study was conducted to investigate the feasibility of theuse of CS and RCA as substitutes for virgin aggregate (LS) in mod-ifying the gradation of CIR mixes. Furthermore, the effects of differ-ent additives such as Portland cement, FA, and RHA on themechanical properties of CIR mixtures were investigated. On thebases of the results obtained in this research, the following conclu-sions are made:

1. RHA has very high water absorption characteristic and RHAmust be used at low ratios and under control. High waterabsorption will contribute to stripping of asphalt from aggre-gate and other problems.

2. The results of Marshall and indirect tensile strength test showthat the use of copper slag enhances the Marshall stability, bulkspecific gravity, and tensile strength. The addition of additivessuch as Portland cement, FA and RHA further improves theMarshall stability and ITS of the CIR mixtures. Portland cementwas found to be the most effective additive. The differencebetween FA and RHA was not found to be significantly different.The use of RCA as a substitute for virgin aggregate decreasesMarshall stability and ITS of the CIR mixtures. However, theMarshall stability of these mixtures was more than 8 kN whichis the minimum acceptable value for heavy loading conditions

3. The results of the resilient modulus tests show that the use ofCS in CIR mixes improves the resilient modules of the mixes.The use of additives also resulted in an increase in the resilientmodulus of the mixes.

4. The results of the dynamic creep test show that the addition ofPortland cement, FA and RHA can reduce the permanent defor-mation of recycled mixtures. The best additive for reducing per-manent deformation proved to be Portland cement. CS can beused as a substitution for virgin aggregate to further reducethe permanent deformation. The use of RCA resulted inincreased permanent deformation.

5. The maximum MSR and TSR values were obtained for the mix-tures containing CS and Portland cement. CS can be used in CIRmixes to enhance the resistance of the mixes to moisturesusceptibility.

6. The heavy metal and PAHs concentrations obtained in all mixeswere below than the conventional drinking water standards’regulations. Therefore, the use of CS and RCA along with addi-tives did not result in harmful environmental impacts.

7. Use of Portland cement had better results compared to FA andRHA. With regard to the effects of aggregates, CS found to bean appropriate substitute for LS. Although RCA did not improvethe durability and mechanical properties of CIR mixtures signif-icantly, it can be used as a substitute for LS since it resulted inacceptable mechanical properties.

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