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

Construction and Building Materials 96 (2015) 172–180

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Effects of copper slag and recycled concrete aggregate on the properties of CIR mixes with bitumen emulsion, rice husk ash, Portland cement and fly ash Ali Behnood a,⇑, Mahsa Modiri Gharehveran a, Farhad Gozali Asl b, Mahmoud Ameri b a b

Lyles School of Civil Engineering, Purdue University, 550 Stadium Mall Dr., West Lafayette, IN 47907-2051, USA 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 2015 Received in revised form 21 July 2015 Accepted 5 August 2015

Keywords: Cold in place recycling Copper slag Recycled concrete aggregate Rice husk ash Fly ash Asphalt 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 and surface layers. At the same time, the expansion of asphalt roadways results in the production of a large amount of asphalt road waste, known as reclaimed asphalt pavement (RAP). This paper aims to investigate the feasibility of the use of copper slag and recycled concrete aggregate (RCA) as substitutes for virgin aggregates in modifying the gradation of cold recycled mixes made with RAP material. In addition, the effects of three types of additives including Portland cement, fly ash, and rice husk ash on the properties of recycled mixtures were investigated. Marshall, Indirect tensile strength, resilient modulus, moisture susceptibility, and dynamic creep tests were conducted to evaluate the mechanical properties of the mixes. Toxicity characteristic leaching procedure was used to assess the environmental impacts of copper slag. The use of copper slag had better results than limestone and RCA probably due to better interlocking and superior physical and mechanical properties. With regard to the effects of additives, Portland cement was found to be the most effective additive. The difference between fly ash and rice husk ash was found to be statistically insignificant. Ó 2015 Elsevier Ltd. All rights reserved.

1. Introduction Construction and maintenance of roads require a large volume of aggregates for use in base, sub-base and surface layers of pavements. At the same time, the expansion of asphalt roadways results in the production of a large amount of asphalt road waste material known as reclaimed asphalt pavement (RAP). Knowing that recycling of asphalt pavements is very advantageous from technical and environmental perspectives, transportation organizations ⇑ Corresponding author. E-mail addresses: [email protected] (A. Behnood), [email protected] (M. Modiri Gharehveran), [email protected] (F. Gozali Asl), [email protected] (M. Ameri). http://dx.doi.org/10.1016/j.conbuildmat.2015.08.021 0950-0618/Ó 2015 Elsevier Ltd. All rights reserved.

and material scientists encourage beneficial use of RAP [1–5]. RAP material can remain on site for a long period of time, be discharged at a waste landfill or be used in a number of highway applications. Some of these applications include its usage as an aggregate substitute and asphalt cement supplement in recycled asphalt paving (hot mix or cold mix). It can also be used as a granular base or sub-base, stabilized base aggregate, embankment or fill material. Cold in-place recycling (CIR) is defined as a rehabilitation technique in which the RAP materials are used in place without the application of heat [6]. Some of the advantages associated with CIR technique as a pavement rehabilitation approach are reduction in traffic disruption, virgin aggregates and bitumen consumption in

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asphalt mixes, environmental concerns, cost and energy. Since CIR technique does not require heating, there is no negative change in the structure of the asphalt binder due to aging [7]. Moreover, CIR needs lower construction time than conventional rehabilitation procedures [4]. The CIR technique can be applied to eliminate transverse, reflective, and longitudinal cracks. It is also a robust approach to restore old pavement to the desired profile, eliminate existing wheel ruts, restore the crown and cross slope, and eliminate pothole, irregularities and rough areas [8]. The RAP material is obtained by milling or crushing the existing pavement. The obtained material is then laid and compacted after adding recycling agent and/or virgin aggregate. In many applications, virgin aggregate is added when the gradation of RAP material is not within the blending chart limits [2,9]. However, other types of waste and by-product materials could also be used to improve the gradation of RAP material. For example, steel slag has been successfully used as a substitute for virgin aggregates to satisfy the gradation requirements of the CIR mixes [2]. Type of additives that is used in CIR mixtures has also been found as a factor that improves the mechanical properties and performance of these mixtures [10,11]. Various types of additives such as Portland cement, fly ash, and lime have been successfully used in CIR mixtures [2,10–13]. This study aims to investigate the feasibility of using of copper slag (CS) and recycled concrete aggregate (RCA) as substitutes for virgin aggregate in modifying the gradation of cold recycled mixes made with RAP material. Nine different types of mixtures containing three types of aggregates (limestone (LS), CS, and RCA) and three types of additives (cement, fly ash, rice husk ash) as well as three types of mixtures without additive were used to study the effects of different aggregates and additives on the mechanical properties of CIR mixes. Marshall stability and flow, Indirect tensile strength (ITS), resistance to moisture damage, resilient modulus, and dynamic creep tests were conducted to study the mechanical properties of the mixes. Environmental impacts of the use of different aggregates in CIR mixes were evaluated by the toxicity characteristic leaching procedure (TCLP) test.

2. Background 2.1. Copper slag (CS) Copper slag (CS) is a by-product from matte smelting and refining of copper [14]. Production of one ton of copper approximately generates 2.2–3 tons of CS. Consequently, annually about 24.6 million tons of CS is produced worldwide. CS has been widely used as railroad ballast abrasive tools, roofing granules, cement and concrete industries. It can also be used in broad areas of road construction including surface layers and in unbound bases or sub-bases. Due to its significant amount of free iron, CS has high density and hardness [15]. The average specific gravity of CS is about 3.5 g/cm3, which indicates that CS is denser than ordinary natural aggregate [15]. Therefore, CS can be considered as a suitable artificial source of aggregate in pavement industry. Many attempts have been done to investigate the feasibility of the use of CS as fine and coarse aggregates in concrete industry [15,16]. However, a comprehensive literature review did not reveal widely use of CS in bituminous mixtures. Based on the physical, chemical, and mechanical properties of it, there is not any reason why CS would not make durable asphalt mixes. Table 1 shows the typical physical properties of CS. Pundhir et al. reported that the use of CS as fine aggregate in various bituminous mixes provides good interlocking and improves mechanical properties of the mixes [17]. Havanagi et al. investigated the feasibility of the use of CS as fine aggregate

Table 1 Physical properties of copper slag [15]. Property

Value

Appearance Particle shape Density (g/cm3) Water absorption Hardness Abrasion loss (%) Aggregate impact value (%) Aggregate crushing value (%) Soundness Water soluble chloride (ppm) Conductivity (ls/cm)

Black, glassy, more vesicular when granulated Irregular 3.16–3.87 0.15–0.55 6–7 24.1 8.2–16 10–21 0.8–0.9 <50 500

in bituminous mixtures [18]. They performed Marshall stability test, indirect tensile strength, dynamic modulus, and moisture sensitivity. It was found that CS could replace fine aggregate in the range of 17–32%. In another study, Hassan and Al-Jabri [19] evaluated the effects of granulated CS as a fine aggregate in hot-mix asphalt concrete. In their study, stripping potential was evaluated by the indirect tensile strength. A reduction in strength was observed due to the use of CS; however, the tensile-strength ratio was superior to that of the control mix. Higher copper content results in an increase in the voids in the mineral aggregates in the asphalt mixtures [19]. This, in turn, results in higher asphalt binder content percentage to satisfy the air-voids criteria. Consequently, it is plausible to expect higher potential for rutting for mixes with a higher slag content [19]. 2.2. Recycled concrete aggregate (RCA) Concrete aggregate collected from demolition sites has been widely used in hot-mix asphalt mixtures in recent years [20–22]. However, after a review of the technical literature, we could not find any use of RCA in cold mixtures. The properties of RCA are different from those of natural aggregate because of the attached mortar to the surface of RCA particles [23,24]. The type and the amount 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 the mixtures prepared with these aggregates. Some researchers have affirmed that HMA containing RCA are stiffer than conventional mixes [25,26], while others suggest the opposite [22,27]. With regard to the permanent deformation, some authors have reported similar or better performance of HMA made with RCA [21,26,27]. However, some other researchers have reported that the resistance to permanent deformation decreases as the percentage of RCA in the mix increases [22]. Turning to the water resistance of HMA made with RCA, some investigators have reported an adequate water resistance [28,29], while others suggest the use of a certain amount 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 the performance of asphalt mixtures mixes [11,30,31]. Various additives such as bitumen emulsion, cement, quick lime, coal waste (ash), silica fume or fly ash have been used during the compaction of the recycled mixtures [2,10,11,13,30,32]. Different factors such as cost, performance, and climate condition should be considered when choosing the appropriate type of additive [30]. Portland cement and fly ash (FA) are among the most widely used additives in CIR mixtures. Previous studies have shown that cement can improve the durability of CIR mixtures [11,33]. The

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use of cement increases the initial stiffness, indirect tensile strength, resilient modulus, and moisture resistance and decreases permanent deformation [11,33–35]. Similar to cement, FA can improve the mechanical properties and durability of the recycled mixtures [12]. Rice husk ash (RHA) is a by-product from the burning of rice husk. The utilization of RHA as a pozzolanic material in cement and concrete industry provides several advantageous such as better durability properties and improved strength. Although RHA has been widely used in many work area, there are only few studies about the use of RHA in the asphalt concrete mixtures. In a recent study, Sargın et al. [36] investigated the usability of RHA in HMA concrete as mineral filler. They found that 50% RHA and 50% LS of filler rate mixtures had the best Marshall stability. 3. Materials Characterization and properties of the materials should be identified in order to obtain an accurate explanation and analysis of the experimental results. The properties of the binders, additives, and aggregates are presented in the following sections. 3.1. Aggregates The reclaimed asphalt pavement (RAP) material in this study was taken from a demolition/reconstruction road site project. Since most project demand the removal of oversize material, the material larger than 25 mm in size was removed before gradation. Gradation of the RAP material was determined according to ASTM C136.117 Test Method. The bitumen content of the RAP material was determined based on ASTM D2172 and obtained as 3.5%. The gradation of the RAP material did not meet the required specification of Road and Transportation of Iran for Cold Mix Recycling [37]. Therefore, it was modified by adding new sources of aggregates (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 gradation of RAP materials and satisfy the specification requirements. These aggregates were LS, CS, and RCA. 3.2. Binder and additives Choosing the appropriate binder is a vital task from the compatibility perspective with aggregate and its gradation [2]. Due to the presence of positive or negative electric charges on the surface of particles, bitumen emulsions can show different characteristics while being blended with different aggregates [2]. In this study, a cationic slow setting (CSS-1) was used. The properties of asphalt emulsion that are used in the current study are given in Table 2. In this study, three types of additives including Portland cement, fly ash, and rice husk ash were used. In addition, mixtures without additives were prepared to study the effects of each of the additives. The chemical and physical properties of 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

120

Percent passing

100 80

Lower limit 60

Upper limit

40

RAP

20

Mix blend

0 0.01

Table 2 Properties of asphalt emulsion. Property

CSS-1

Sabolt furol viscosity @ 25 °C (s) Storage stability test (%) Residue by distillation Penetration on residue @ 25 °C Portland cement mixing test

55 0.5 65 150 2

Table 3 Physical and chemical analysis of cement, fly ash and rice husk ash. Item Physical properties Specific gravity Chemical composition (%) SiO2 Al2O3 Fe2O3 MgO SO3 P2O5 Na2O K2O Loss on ignition (%)

Portland cement

Fly ash

Rice husk ash

3.10

2.3

2.05

23.1 4.78 3.59 2.55 1.98 0.05 0.40 0.70 0.49

59.10 21.00 3.72 1.38 1.05 – 2.52 0.90 4.6

92.00 0.34 0.37 0.78 1.24 0.95 0.11 3.29 6.7

method, the mixtures were prepared in such a way to contain 3% water. This water consists of emulsion water, RAP water and the water added to the mixture. Bitumen emulsion was added to the mixtures at the percentages ranging from 2.5% to 4.5% by weight of total mixture at 0.5% increments. Marshall hammer was used to apply 50 blows per side of each mixture. The samples were then oven 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 molds and then were extruded and air cured for 5 days at room temperature. Optimum emulsion content was determined using the maximum specific gravity and Marshall stability. Air void content was used as the only design criterion, which should be between 9% and 14% [2]. To determine the optimum emulsion content, three replicate samples were prepared for each of the emulsion contentaggregate type combination (i.e. a total of 45 specimens). Optimum additive content was determined for the samples prepared with optimum emulsion content and optimum water content using the maximum Marshall stability. To determine the optimum additive content, three replicate samples were prepared for each of the additive content-mixture type (i.e. a total of 153 specimens). The amount of cement was changed from 1.0% to 3.0% at 0.5% increments. With Regard to FA and RHA, the amount of additives was changed from 1.0% to 6.0% at 1.0% increments. It should be noted that all the additives were utilized in powder form and were added to the mixed aggregates before adding water and asphalt emulsion. Asphalt mixtures were prepared for mixing after adding water and asphalt emulsion to the blend of aggregate and additive. Mixing was continued for about two minutes in order to achieve a homogenous blend. Table 4 shows the optimum emulsion, water, and additive contents for 12 types of mixtures. In order to identify the mixes, they were labeled with two letters. In these labels, the first and the second letters indicated the type of blended aggregate and the type of additive, respectively. 5. Testing program

0.1

1

10

100

Sieve size (mm) Fig. 1. Gradation of RAP material, mix blend and specification limits.

The laboratory tests used in this study to analyze the mechanical properties and durability of cold recycled mixtures are discussed in this section.

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

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

Table 4 Optimum emulsion and additive contents of mixes. Sample ID

Blended aggregate

Additive

Optimum bitumen (%)

Optimum additive (%)

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

LS LS LS LS CS CS CS CS RCA RCA RCA RCA

None Cement FA RHA None Cement FA RHA None Cement FA RHA

3.4 3.3 3.4 3.4 3.5 3.5 3.6 3.6 4.0 4.2 4.1 4.1

0.0 2.0 5.0 3.0 0.0 2.5 5.0 3.0 0.0 2.5 6.0 4.0

175

TSR ¼ 100  ðScon =Suncon Þ

5.1. Marshall stability, flow and Marshall Quotient Stability is one of the most important properties of asphalt mixtures. Marshall stability which is a measure of the maximum load sustained by the bituminous material at a constant loading rate was measured based on ASTM D1559. Flow, as an indispensable part of Marshall Test, measures the specimen’s plastic flow owing to the applied load. The flow value refers to the vertical deformation when the maximum load is reached. The ratio of Marshall stability (kN) to Marshall flow (mm) is defined as the Marshall Quotient (MQ) and can be used as a measure of the bituminous mixture’s resistance to rutting [2,38]. A stiffer and more resistant mixture to permanent deformation has a higher value of MQ [39].

ð2Þ

where Scon is the average tensile strength of the conditioned specimens (kN/m2), and Suncon is the average tensile strength of the unconditioned specimens (kN/m2). A minimum ratio of 0.8 has been typically used as a minimum acceptable TSR value for hot mix asphalt. Mixtures with ratios greater than 0.8 are considered as relatively resistant to water damage. For cold recycled mixtures, a universally 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 mixtures with low TSR values (less than 0.8) are susceptible to moisture damage [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 were tested at a loading rate of 50 mm/min after 40 min immersion in water bath. The remaining specimens (conditioned) were kept for 24 h in the water bath and subsequently loaded under similar condition. The Marshall Stability Ratio (MSR) was then computed as:

5.2. Indirect tensile strength (ITS) test

MSR ¼ 100  ðMScon =MSuncon Þ

Tensile properties of the compacted bituminous mixtures, which are related to the cracking properties of the pavement, can be determined by the indirect tensile strength (ITS) test (ASTM D6931). Higher tensile strength is an indication of higher resistance to fatigue and thermal cracking. The ITS test involves loading a cylindrical specimen with compressive loads; which develops a relatively uniform tensile stress perpendicular to the direction of the applied load and along the vertical diametrical plane. The load is applied at a deformation rate of 50 mm/min and at a temperature of 25 °C. Failure usually occurs by splitting or rupturing along the vertical diameter [38,40]. The tensile strength of the specimens was determined as:

where MScon is the average Marshall stability for conditioned samples, and MSuncon is the average Marshall stability for unconditioned samples.

ITS ¼

2Pmax ptd

ð1Þ

where ITS is the indirect tensile strength (kN/m2); Pmax, is the peak load (kN); t is the thickness of the specimens (mm); and d is the diameter of the specimens (mm). In order to conduct ITS test, five specimens with optimum design contents were prepared for each type of mixtures (i.e. a total number of 60 specimens). 5.3. Resistance to moisture damage Moisture damage in flexible pavements occurs due to the loss of adhesion and or cohesion and results in the separation and removal of asphalt binder from the aggregate surface in the presence of water. This phenomenon leads to the reduced strength or stiffness of the asphalt mixture. The moisture susceptibility of asphalt mixtures was evaluated by performing the AASHTO T283 test and Marshall conditioning (immersion of the asphalt mixtures in a water bath for 24 h at a temperature of 60 °C).

ð3Þ

5.4. Resilient modulus Resilient modulus of asphalt mixtures, measured in the indirect tensile mode (ASTM D4123), is the most important parameter used in the mechanistic design of asphalt pavements. The test is also the most popular form of stress–strain measurements used to evaluate the elastic properties of asphalt mixtures [41]. In elastic theories model, resilient modulus along with some other information is used as input to generate an optimum thickness design. For each type of asphalt mixture, five cylindrical specimens (i.e. a total number of 60 specimens) were prepared at optimum emulsion and additive content using a gyratory compactor. 5.5. Dynamic creep test Different test methods are available to evaluate the permanent deformation of asphalt mixtures such as wheel tracking test and dynamic creep test [42,43]. In this study, dynamic creep test was employed to assess the resistance of mixes to rutting since it has been reported as one of the best test procedure to assess the permanent deformation of asphalt mixtures [43]. The dynamic creep test applies a repeated pulsed uniaxial load on asphalt specimens and measures the resulting deformations in the same direction using linear variable differential transducers (LVDTs). For each type of asphalt mixture, five cylindrical specimens (i.e. a total number of 60 specimens) were prepared at optimum emulsion and additive content using a gyratory compactor. To perform the dynamic creep test, a conditioning stress of 10 kPa was applied for 600 s. Then the

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conditioning load was removed and a stress of 50 kPa for 1800 cycles with 1 s loading and 1 s unloading. 5.6. Toxicity characteristic leaching procedure (TCLP) test Potential environmental impact of RAP on soil and groundwater is of a great concern, because some of RAP materials may contain toxic substances such as heavy metals and hydrocarbons. Thus, an assessment of environmental characteristics of RAP is imperative before use of this material in road construction especially when this material is combined with another material such as CS or RCA which are suspicious of being hazardous. There are various procedures to conduct a batch test. These procedures typically involve mixing size-reduced waste with extraction solution and then agitating the mixture. The main differences among 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) developed by the US Environmental Protection Agency [45] was employed to study the leaching of contaminants from the RAP materials and their cold 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 liquid/solid ratio was selected as 20:1 in accordance with TCLP. At the end of 20 h tumbling period, the extracts are separated from the solids using a 0.7 lm glass fiber filter. Heavy metals were then analyzed by atomic absorption spectrophotometry. Polyaromatic hydrocarbons (PAHs) concentrations were measured in leachates by applying gas chromatography ion trap mass spectrometry detection. 6. Results and discussion Results of performed laboratory tests have been presented in this section. 6.1. Marshall stability, flow and Marshall Quotient The results of the Marshall test and the volumetric parameters of the mixtures are given in Table 5. It should be mentioned that the values presented herein are the average of three measurements. It can also be seen that air void contents for all mixes were in the acceptable range. CIR mixture containing CS and Portland cement has the highest Marshall stability and MQ values. The lowest Marshall stability and MQ values were obtained for the mixture containing RCA and without additive. The low Marshall stability and MQ values obtained for this mixture could be due to the combination effects of the inferior properties of RCA and higher emulsion content in these mixtures. Analysis of variance (ANOVA) was conducted on the results that were obtained from the mixtures with optimum emulsion and optimum additive contents to analyze the effect of aggregate type and additive type on Marshall stability and MQ values. In the ANOVA, mean comparisons of Marshall stabilities or MQs for each pair of aggregates or additives were tested using Tukey’s multiple comparison method. The multiple comparisons test is a statistical approach to distinguish the difference between test results. Table 6 shows the summary of ANOVA results for the Marshall stability values. Tables 7 and 8 show the multiple comparison results for the effects of aggregates and additives, respectively. The test results indicated that the Marshall stability and MQ values are statistically different between RCA and two other aggregates, where a = 0.05. In other words, Marshall stability and MQ values for the mixtures containing LS or CS are higher compared to the mixtures containing RCA. However, it should be noted that the Marshall stability of all mixes was more than 8 kN which is

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

Additive content (%)

Air void

Bulk specific gravity (g/cm3)

Marshall stability (kN)

Flow (mm)

MQ

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

0.0 1.0 1.5 2.0 2.5 3.0 1.0 2.0 3.0 40 5.0 6.0 1.0 2.0 3.0 4.0 5.0 6.0 0.0 1.0 1.5 2.0 2.5 3.0 1.0 2.0 3.0 4.0 5.0 6.0 1.0 2.0 3.0 4.0 5.0 6.0 0.0 1.0 1.5 2.0 2.5 3.0 1.0 2.0 3.0 4.0 5.0 6.0 1.0 2.0 3.0 4.0 5.0 6.0

12.4 13.2 13.2 13.1 13.1 13.1 12.7 12.5 12.6 12.6 12.4 12.4 12.9 12.9 12.6 12.6 12.6 12.7 12.6 12.4 12.5 12.6 12.4 12.5 12.9 12.7 12.4 12.4 12.6 12.6 12.7 12.6 12.6 12.5 12.6 12.6 12.9 13.0 12.9 13.0 12.5 12.8 12.2 12.3 12.3 12.4 12.2 12.3 12.5 12.6 12.3 12.3 12.3 12.3

2.321 2.191 2.236 2.214 2.148 2.126 2.271 2.285 2.340 2.294 2.317 2.336 2.295 2.272 2.318 2.330 2.225 2.270 2.355 2.371 2.325 2.348 2.372 2.315 2.300 2.276 2.293 2.324 2.371 2.359 2.318 2.389 2.365 2.393 2.425 2.341 2.197 2.275 2.300 2.312 2.289 2.259 2.255 2.253 2.260 2.258 2.264 2.269 2.262 2.257 2.266 2.273 2.287 2.303

9.87 10.89 11.34 12.89 12.37 12.00 10.59 10.53 10.76 10.65 11.45 11.22 10.04 10.60 11.16 11.49 10.71 10.77 10.86 11.40 12.71 12.49 13.15 13.11 11.78 11.65 12.20 12.27 12.33 12.33 10.78 11.95 12.38 12.25 12.30 12.03 8.10 9.88 10.32 10.44 10.63 10.49 8.32 8.67 8.65 9.04 8.98 9.12 8.87 9.12 9.94 10.39 10.22 9.97

2.65 2.71 2.88 2.94 3.01 2.98 2.67 2.97 2.78 2.81 2.73 2.71 2.70 2.73 2.65 2.78 2.63 2.68 2.71 2.88 2.95 2.90 2.71 2.68 2.92 2.77 2.87 2.91 2.73 2.74 3.22 3.15 2.74 2.87 2.77 2.77 2.85 3.15 3.02 3.20 2.90 2.91 3.05 2.99 3.22 3.15 3.27 3.12 2.98 3.27 3.07 3.15 3.12 3.04

3.72 4.02 3.94 4.38 4.11 4.03 3.97 3.55 3.87 3.79 4.19 4.14 3.72 3.88 4.21 4.13 4.07 4.02 4.01 3.96 4.31 4.31 4.85 4.89 4.03 4.21 4.25 4.22 4.52 4.50 3.35 3.79 4.52 4.27 4.44 4.34 2.84 3.14 3.42 3.26 3.67 3.60 2.73 2.90 2.69 2.87 2.75 2.92 2.98 2.79 3.24 3.30 3.28 3.28

Table 6 Summary of ANOVA results for Marshall stability. Source

DF

Sum of square

Mean square

F value

Pr > F

Aggregate Additive Error Total R2

2 3 6 11 0.93

14.32 10.57 0.94 25.84

7.16 3.52 0.16

45.51 22.39

0.0002 0.0012

the minimum acceptable value for heavy loading conditions [46]. With regard to the difference between the mean of the Marshall stability and MQ values of CS and LS, it was found that they are not statistically different where a = 0.05. However, Marshall

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A. Behnood et al. / Construction and Building Materials 96 (2015) 172–180 Table 7 Tukey’s comparison results for the effect of aggregates – Pr > |t| for H0: least square mean (i) = least square mean (j). i/j

LS

LS CS RAC

0.0054 0.0017

CS

RAC

0.0554

0.0017 0.0002

0.0002

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

Without additive

Without additive PC FA RHA

0.0008 0.0223 0.0077

PC

FA

RHA

0.0008

0.0223 0.0312

0.0077 0.1068 0.7239

0.0312 0.1068

0.7239

stability and MQ values of the mixtures containing CS and LS are statistically different where a = 0.1. It can be seen that the Marshall stability and MQ values of the mixtures containing CS are higher compared to those containing LS. This might be due to the improved aggregate interlocking and better compatibility of CS with anionic asphalt emulsion. Turning to the effects of the additives, Tukey’s multiple comparison test indicated that the utilized additives affect significantly (a = 0.05) on the Marshall stability test results. In addition, it was found that the Marshall stability of the mixtures containing Portland cement is higher than the Marshall stability of the mixtures that contain FA and RHA. However, the difference between Portland cement and RHA is statistically different where a = 0.1. In addition, the difference between FA and RHA is not statistically significant.

6.2. Indirect tensile strength (ITS) test The results of the indirect tensile strength tests are shown in Fig. 2. It can be seen that the use of additives in CIR mixtures increased the tensile strength of these mixtures. The maximum tensile strength was obtained for the mixtures containing CS and Portland cement. CS and Portland cement were found to be the most effective aggregate and additive, respectively. Among the additives that were used in this study, Portland cement was found to be the most effective additive in increasing the tensile strength of the CIR mixtures. Portland cement increased the tensile strength up to 56% in the mixtures containing LS. In the mixtures made with CS and RCA, the use of Portland cement resulted in an increase of 50% and 32%, respectively, in ITS of the mixtures as compared to the corresponding samples without additives. Interestingly,

regardless of type of the blended aggregate, the use of FA resulted in an increase in ITS of 24%. RHS was found to increase the tensile strength in the range from 20% to 33%. Tukey’s multiple comparison test showed that the effects of FA and RHA were not significantly different, where a = 0.05. It should be noted that the effects of different additives were not found to be significantly different in the mixtures containing RCA. However, the use of additives in these mixtures significantly increased the tensile strength. Turning to the effects of aggregates, CS was found to increase the tensile strength while RCA was found to decrease it as compared to the mixtures made with LS. In the mixtures made without additives, CS resulted in an increase in the tensile strength of 18% and RCA resulted in a reduction in the tensile strength of 7%. It can be seen that the reduction in the ITS of CIR mixtures due to the use of RCA is not statistically significant. In addition, the use of additives in these mixtures could be a helpful approach to improve the ITS results. 6.3. Resistance to moisture damage Marshall stability and indirect tensile strength values for both conditioned and unconditioned specimens are shown in Figs. 3 and 4, respectively. MSR and TSR values for different mixtures are shown in Figs. 5 and 6, respectively. It is evident that the use of Portland cement increased the retained Marshall stability (MSR) of the CIR mixtures. With regard to the effects of other additives (i.e. FA and RHA), they did not improve the moisture resistance of the mixtures significantly. Moreover, a negligible reduction in the MSR values of the mixtures containing RCA can be seen where FA or RHA were used as additives. The reason could be due to the poor compatibility and pozzolanic reaction of these additives with RCA. The maximum MSR value was observed for the mixtures containing LS and Portland cement. The minimum MSR value was observed for the mixtures containing RCA and FA. Similar to the Marshall conditioning tests, the TSR values indicated that Portland cement was the most effective additive in improving the moisture resistance of the CIR mixtures. In the mixtures containing, LS and CS, the use of FA and RHA resulted in an increase in the TSR values. However, in the mixtures containing RCA, the effects of FA and RHA were not found to be significant. Comparing the mixtures containing LS and CS, Tukey’s comparison test results indicated that the difference in MSR and TSR values were not significant. 6.4. Resilient modulus Fig. 7 shows the average resilient modulus for each mix. It is clearly evident that the use of additives increases the resilient

Marshall Stability (kN)

Tensile strength (kPa)

16 500 450 400 350 300 250 200 150 100 50 0

14 12 10 8 6 4 2 0 LW LP LF LH SW SP

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

SF SH RW RP RF RH

Type of mixture

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

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

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

450 400 350 300 250 200 150 100 50 0

LW

LP

LF

LH

SW

SP

SF

SH

RW

RP

RF

RH

2.5

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

Deformation (mm)

Tensile strength (kPa)

178

2 1.5 1 0.5 0 0

Type of mixture

MSR

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

Type of mixture

TSR

Fig. 5. MSR values for different CIR mixtures.

1 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0 LW LP LF LH SW SP SF SH RW RP RF RH

Type of mixture

1000

1500

2000

2500

Number of cycles

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

1 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0

500

Fig. 8. Dynamic creep test results.

reaction. The use of Portland cement in the mixtures containing LS, CS, and RCA resulted in an increase in resilient modulus of 36%, 14%, and 41%, respectively. It should be noted that in the mixtures containing CS, the effects of different additives were not found to be significantly different. In addition, in all the mixes, the difference between the effects of FA and RHA was not found to be statistically significant. Turning to the effects of aggregates, compared to the samples containing LS (virgin aggregate) CS resulted in an increase in the resilient modulus while RCA resulted in a reduction of it. However, the amount of reduction was found to be statistically insignificant. 6.5. Dynamic creep test The results of dynamic creep tests for different CIR mixtures are given in Fig. 8. It can be seen that the use of CS along with Portland cement resulted in the minimum rut depth. The results of dynamic creep test show that the use of Portland cement, FA and RHA resulted in decreased rut depth. In the mixtures containing LS, the use of Portland cement, FA and RHA resulted in a reduction in rut depth of 20%, 10% and 7%. With regard 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 dynamic creep test show that the use of CS as a substitute for virgin aggregate (LS) resulted in a decreased rut depth. RCA was found to increase the rut depth of CIR mixtures.

Fig. 6. TSR values for different CIR mixtures.

6.6. Toxicity characteristic leaching procedure (TCLP) test Resilient Modulus (kPa)

3500

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

3000 2500 2000 1500 1000

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

500 0 LW LP LF LH SW SP SF SH RW RP RF RH

Type of mixture Fig. 7. Effects of the types of additives and aggregates on resilient modulus of CIR mixes.

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

Element/substance (lm/L)

WHO’s drinking water standards [47]

EPA’s drinking water standard [48]

Pb Cu Cr Zn Ni Cd Hg PAHs

10 2000 50 3000 20 3 1 0.7

15 1300 100 – – 5 2 0.2

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

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

[3]

[4]

[5]

7. Conclusion This study was conducted to investigate the feasibility of the use of CS and RCA as substitutes for virgin aggregate (LS) in modifying the gradation of CIR mixes. Furthermore, the effects of different additives such as Portland cement, FA, and RHA on the mechanical properties of CIR mixtures were investigated. On the bases of the results obtained in this research, the following conclusions are made: 1. RHA has very high water absorption characteristic and RHA must be used at low ratios and under control. High water absorption will contribute to stripping of asphalt from aggregate and other problems. 2. The results of Marshall and indirect tensile strength test show that the use of copper slag enhances the Marshall stability, bulk specific gravity, and tensile strength. The addition of additives such as Portland cement, FA and RHA further improves the Marshall stability and ITS of the CIR mixtures. Portland cement was found to be the most effective additive. The difference between FA and RHA was not found to be significantly different. The use of RCA as a substitute for virgin aggregate decreases Marshall stability and ITS of the CIR mixtures. However, the Marshall stability of these mixtures was more than 8 kN which is the minimum acceptable value for heavy loading conditions 3. The results of the resilient modulus tests show that the use of CS in CIR mixes improves the resilient modules of the mixes. The use of additives also resulted in an increase in the resilient modulus of the mixes. 4. The results of the dynamic creep test show that the addition of Portland cement, FA and RHA can reduce the permanent deformation of recycled mixtures. The best additive for reducing permanent deformation proved to be Portland cement. CS can be used as a substitution for virgin aggregate to further reduce the permanent deformation. The use of RCA resulted in increased permanent deformation. 5. The maximum MSR and TSR values were obtained for the mixtures containing CS and Portland cement. CS can be used in CIR mixes to enhance the resistance of the mixes to moisture susceptibility. 6. The heavy metal and PAHs concentrations obtained in all mixes were below than the conventional drinking water standards’ regulations. Therefore, the use of CS and RCA along with additives did not result in harmful environmental impacts. 7. Use of Portland cement had better results compared to FA and RHA. With regard to the effects of aggregates, CS found to be an appropriate substitute for LS. Although RCA did not improve the durability and mechanical properties of CIR mixtures significantly, it can be used as a substitute for LS since it resulted in acceptable mechanical properties.

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