Construction and Building Materials 224 (2019) 173–187

Contents lists available at ScienceDirect

Construction and Building Materials

journal homepage: www.elsevier .com/locate /conbui ldmat

Investigating the effects of recycled PET particles, shredded recycledsteel fibers and Metakaolin powder on the properties of RCCP

https://doi.org/10.1016/j.conbuildmat.2019.07.0120950-0618/� 2019 Elsevier Ltd. All rights reserved.

⇑ Corresponding author.E-mail address: ghshafabakhsh@semnan.ac.ir (G. Shafabakhsh).

Reza Noroozi a, Gholamali Shafabakhsh a,⇑, Ali Kheyroddin a, Abolfazl Mohammadzadeh Moghaddamb

a Faculty of Civil Engineering, Semnan University, Semnan, IranbDepartment of Civil Engineering, Engineering Faculty, Ferdowsi University of Mashhad, Mashhad, Iran

h i g h l i g h t s

� Eco-friendly substitutions of Roller Compacted Concrete Pavements’ (RCCP) components were performed.� The use of recycled PET, Shredded Recycled Steel Fibers and Metakaolin powder was investigated.� Specific gravity, ultrasonic pulse velocity, and 28-day compressive, split tensile, and flexural strengths were tested.� Response surface methodology was employed for modeling and analyzing the results.� Constrained mix design optimization to achieve the optimal mechanical performance was done.

a r t i c l e i n f o

Article history:Received 11 March 2019Received in revised form 1 July 2019Accepted 3 July 2019

Keywords:Roller Compacted Concrete PavementRecycled PET particleMetakaolinShredded recycled steel fiberResponse surface methodology

a b s t r a c t

This study examined the possibility of using PET aggregates as a partial substitute for natural fine-grainedaggregates in RCCP mixtures. To enhance the performance of RCCP, the mixtures were also modified byusing pozzolanic Metakaolin (MK) as a partial substitute for cement and adding steel fibers obtained fromthe recycling of worn vehicle tires. The response surface methodology (RSM), which is capable of predict-ing the variations of a response value in the variations range of independent variables, was used to coverall possible mix compositions. Using this method, 20 mix designs were prepared, which allowed for sig-nificant time and cost saving in experiments without sacrificing thoroughness. The behavior and charac-teristics of RCCP specimens in terms of specific gravity, ultrasonic pulse velocity, compressive strength,split tensile strength, and flexural strength at the age of 28 days were investigated. The obtainedresponses were used to develop statistical models, which were then utilized in the optimization ofmix design with the help of analysis of variance. The results showed that the use of PET aggregatesdecreased the compressive, tensile, and flexural strength as well as specific gravity and ultrasonic pulsevelocity of the RCCP specimens. Partial replacement of cement with MK generally improved the mechan-ical performance of the specimens. The effect of shredded recycled steel fibers (SRSF) was generallydependent on other components of the mixture. The optimal mix design obtained from the statisticalmodels involves replacing 25 vol% of fine aggregate with PET, replacing 20 wt% of cement with MK pow-der, and adding 1.9 wt% SRSF to the mixture. The proposed mix design contributes to clean recycling ofPET and conservation of natural resources and reduces the cost and carbon footprint of RCCP constructionwith considering the standard requirements for pavement structures.

� 2019 Elsevier Ltd. All rights reserved.

1. Introduction

With the worldwide popularity of concrete as a relatively cheapand easy to use construction material, it has become the world’ssecond most widely used substance after water [1]. The environ-mental implications of concrete industry are as massive as the pop-

ularity of concrete in today’s construction business. Research onthe replacement of aggregates, cement, or reinforcements withrecycled materials can yield valuable results in terms of naturalresource conservation, waste handling, and cost saving. The useof recycled materials in construction is indeed gaining popularitybecause of growing attention to the massive amount of waste gen-erated every day as a result of modern lifestyle, exhaustiveexploitation of natural resources, and environmental degradationthat hurts all living organisms. Bottles used in the packaging of

174 R. Noroozi et al. / Construction and Building Materials 224 (2019) 173–187

beverages are mainly made of a polymer known as polyethyleneterephthalate or PET. The past decades have seen an increase inthe use of PET bottles worldwide [2]. In 2010, the total amountof plastic materials produced worldwide was about 265 milliontons. The share of Europe of this amount was 57 million tons, ofwhich 39% was for packaging purposes [3]. Interestingly, boththe manufacturing and recycling of plastic bottles are known tobe environmentally destructive [4–7]. It has been shown that thecradle-to-grave carbon footprint of 1 kg of recycled PET packagingtray containing 85% recycled content can be as high as 1.538 kgCO2 [3].

One way to recycle plastic wastes is to use them as a substitutefor road pavement materials. Roller Compacted Concrete Pavement(RCCP) could be a good choice in this regard, especially given that itis fast and cheap to construct [8] and can be used in a wide varietyof applications (with and without thin asphalt overlay). The exten-sive use of RCCP across the world means that there is a huge poten-tial for the reuse of plastic wastes in this material. For example, in2008, the total area covered by RCCP in the United States exceeded8,000,000 m2 [9]. The most important benefits of using recycledPET in concrete pavements such as RCCP include cleaner manage-ment of waste materials, conservation of natural resources, reduc-tion of carbon footprint [10–12], as well as reasonable cost saving.

Typically, aggregates constitute about 65–80 vol% of the con-crete and are key determinants of concrete properties such asstrength, workability, dimensional stability, and durability [13].The use of recycled PET particles in place of natural aggregates inconcretes has drawn attention to conducting several studies. Abrief summary of notable studies in this area and their results ispresented in Table 1.

Table 1Brief summary of research on the use of recycled PET particles in place of natural aggrega

Author(s) Year Method of replacement

Saikia and Brito [13] 2014 Replacing 5–15 vol% of aggregates with recycledparticles of different types and sizes (<16 mm)

Hannawi et al. [14] 2010 Replacing 3, 10, 20, and 50% of aggregates (sand)particles smaller than 10 mm

Frigione [15] 2010 Replacing 5 vol% of aggregates (sand) with PET pof size 0.1–5 mm

Akçaözoǧlu et al. [16] 2010 Replacing one-third or 100% of fine aggregates wrecycled PET particles of size 0–4 mm

Marzouk et al. [17] 2007 Replacing 2–100 vol% of aggregates (sand) withaggregates smaller than 5 mm

Akçaözoǧlu and Ulu [18] 2014 Replacing 20, 40, 60, 80, and 100% of blast furnaaggregates with recycled PET aggregates with amaximum size of 4 mm

Rahmani et al. [19] 2013 Replacing 5, 10, and 15 vol% of sand with PET pawith a maximum size of 7 mm

Albano et al. [20] 2009 Replacing 10 or 20 vol% of aggregates with PET pwith an average size of 2.6–11.4 mm

Córdoba et al. [21] 2013 Replacing 1.0, 2.5, and 5.0 vol% of aggregates wiparticles of 0.5, 1.5, and 3.0 mm in size

The use of plastic particles in place of natural aggregates canimprove the toughness, flexural strength, and energy absorptionof the concrete; properties that are of significant importance forthe structures exposed to dynamic and impact loadings [14]. Ithas been shown that the replacement of natural aggregates withrecycled PET aggregate can lead to decreased dead load, improvedpermeability, and lower water absorption in comparison to con-ventional concrete [22].

However, it has also been reported that using too much plasticaggregate in concrete leads to reduced bearing capacity and loss ofmechanical performance. For example, research has shown thatreplacing more than 50% of aggregates with recycled plastic mate-rials results in a significant reduction in the mechanical properties[17]. As the replacement ratio increases, so does the negativeimpact on flexural-tensile strength [18]. Such negative impactscan be attributed to the weaker bonds between the cement pasteand PET aggregates, which fail to provide the same adhesion asnatural aggregates normally do [15,23–25]. The most importantreasons for this weaker adhesion is the reduced cement hydration,which can mostly be attributed to the hydrophobic nature of theplastics [26,27].

Cement is the most costly and energy-intensive component ofconcrete. Producing one ton of cement involves releasing 0.5–1ton of carbon dioxide into the atmosphere [28]. For many con-cretes’ applications, cement can be partially replaced with mineraladditives that feature pozzolanic properties. One of these mineralsis Metakaolin (MK). MK is an aluminosilicate produced by the cal-cination of kaolin clay in a temperature range of 600–800 �C [29].MK production is far less energy intensive than cement production[28]. Many researchers have acknowledged the potential of MK as

tes.

Results

PET - Decrease in compressive strength, split tensile strength, elasticmodulus, and flexural strength with the increase in the PETcontent (for all types of PET);

- Improved abrasion resistance of the PET-containing concrete.with PET - Poor adhesion between plastic aggregates and cement paste;

- Decrease in elastic modulus and compressive strength of theconcrete;

- Increase in flexibility and load-bearing capacity after failurewithout fracture.

articles - No change in workability;- Decrease in compressive strength and split tensile strength;- Increase in porosity and in adhesion of PET particles with cement

paste in specimens with higher W/C ratios.ith - Decrease in the specific gravity of the concrete;

- Increase in the shrinkage of the specimens;- Decrease in compressive strength, flexural-tensile strength, and

carbonization depth with the increase in the replacement ratio.PET - Slight decrease in compressive strength and flexural strength in

the replacement ratios of less than 50 vol%.ce slag - Decrease in the specific gravity of the concrete, compressive

strength, flexural-tensile strength, and ultrasonic pulse velocity;- Increase in water absorption and porosity ratio.

rticles - Decrease in workability and density of fresh concrete;- Decrease in elastic modulus and split tensile strength;- Increase in compressive strength and flexural strength at the ini-

tial stages of loading and decrease in these properties after awhile;

- Decrease in ultrasonic pulse velocity.articles - Decrease in compressive strength, split tensile strength, and

elastic modulus;- Decrease in stiffness;- Decrease in slump;- Increase in water absorption;- Decrease in ultrasonic pulse velocity.

th PET - Decrease in compressive strength and Young’s modulus with theincrease in the size of PET particles.

R. Noroozi et al. / Construction and Building Materials 224 (2019) 173–187 175

a substitute for cement in the concretes that are made with naturalaggregates, citing its ability to improve durability and mechanicalproperties [30–33]. MK improves the performance of concretethrough reaction with calcium hydroxide in the secondary C-S-Hformation [34]. The use of MK decreases the water absorption ofthe concrete and the air voids content in its matrix [35,36]. It alsoimproves transport properties such as water penetration, gas pen-etration, water absorption, electrical resistance, and ion diffusion,which result in higher stability of concrete mixtures [37]. Partialreplacement of cement or sand with MK can also lead to improvedcorrosion resistance in reinforcements [38].

Strength and surface friction properties of the concrete can alsobe improved by the use of reinforcing fibers in the mixture. In addi-tion, this method can reduce the pavement thickness and therebycan reduce overall costs [39,40]. The reinforcement fibers are alsoknown to inhibit crack propagation [41–44]. The most importantdrawback of this approach is the cost of steel reinforcementneeded to achieve the desired mechanical properties [45]. Thisproblem can be resolved with the use of shredded recycled steelfibers (SRSF). Various study have shown that concrete structuresreinforced with steel fibers recycled from waste tires perform verysimilarly to those reinforced with primary steel fibers [46–48]. Theflexural behavior of these concretes is also similar to that of con-cretes with conventional steel fibers [47]. The maximum flexuralstrength of the concretes that contain SRSF and industrial steelfibers is independent of the fiber type but depends on the fiberaspect ratio [49]. Nevertheless, the effect of this fiber on the perfor-mance and mechanical properties of RCCPs made with PET aggre-gates and MK powder needs further analysis. The objective of thisstudy was to make an eco-friendlier RCCP by the use ofenvironmentally-friendly recycled materials in the concrete mix-ture. Considering the existing reports on the use of recycled mate-rials in concrete, this objective was pursued by replacing fineaggregates with recycled PET particles and using SRSF as reinforce-ment in order to produce an RCCP that would be cost-effective andmore eco-friendly. MK was also used as a substitute for the cementto stabilize the concrete mixture obtained with the recycled mate-rials. At the end of this paper, the effect of each individual material

Fig. 1. Combined agg

on the mechanical performance of RCCP and the optimal mixdesign for making an RCCP with acceptable mechanical propertieswere illustrated.

To achieve the research objective, a group of RCCP specimens atthe age of 28 days were subjected to standard mechanical tests ofcompressive strength, tensile strength, and flexural strength as wellas non-destructive tests including specific gravity test and ultra-sonic pulse velocity test. Also, the response surface method wasused to estimate a regression model based on the initial test resultsin order to determine the optimal mix ratios that satisfy themechanical requirements. Using this approach, the number of runswas reduced to 20 (with required replications), which resulted insignificant time and cost saving in the experimental process.

2. Experiment procedure

2.1. Material properties

The main materials used in the preparation of laboratory RCCPspecimens were fine-grained and coarse-grained crushed aggre-gates, type-II Portland cement, and tap water. In the specimenscontaining recycled materials, fine aggregates (sand) were partiallyreplaced with PET aggregates and cement was partially replacedwith MK powder. Also, the SRSF were added to these mixtures asreinforcement.

The aggregates with the maximum size of 19 mm were pur-chased from Mousavi & Majidi Crushing companies. Using themethods specified in ASTM C127 and ASTM C128, saturatedsurface-dry absorption of coarse and fine aggregates was measuredto 0.64% and 3.08%, their apparent specific gravity was measured to2720 and 2740, respectively. Using the method of ASTM D854, theapparent specific gravity of the filler material was measured to2720 kg/m3. The resulting aggregate mixtures according toACI211.3R are displayed in Fig. 1.

Binder materials used in the making of RCCP specimens werecement and MK, which was used as a partial substitute for cement(Fig. 2-a). The chemical compositions of type-II Portland cement(Shargh Cement Co.) and MK (made in India) used in this study

regate gradation.

Fig. 2. Eco-friendly materials used in the RCCP specimens (a: MK, b: PET and c: SRSF).

Table 2Chemical compositions of Cement and MK.

SiO2 Al2O3 Fe2O3 CaO MgO SO3 Na2O K2O L.O.I

Cement (%) 21.1 4.65 3.85 62.5 2.9 2.1 0.5 0.45 1.6MK (%) 52.8 36.3 4.21 <0.10 0.81 – <0.10 1.41 3.53

176 R. Noroozi et al. / Construction and Building Materials 224 (2019) 173–187

are presented in Table 2. The specific gravity of cement and MKwas 3100 kg/m3and 2630 kg/m3, respectively. In this study, 0–20 wt% of cement was replaced with MK.

The PET aggregates used in this study (Fig. 2-b) were purchasedfrom a PET flake recycling factory. These aggregates were obtainedfrom the sieves serially installed in the milling unit of this factory.The specific gravity of the obtained PET particles was 1093 Kg/m3.Following the approach of previous studies, the maximum size ofthe PET particles to be used in the mixture was limited to 4 mm.The gradation profile of the PET aggregates obtained from the millis presented in Table 3. In the experimental mixtures, 0–50 vol% ofnatural fine aggregates (between sieves No. 4 and No. 200) wasreplaced with the recycled PET particles.

SRSF produced by mechanical recycling of waste tires was pur-chased from a tire recycling plant. The obtained materials werepassed through sieve No. 8 to eliminate fibers containing rubbercrumb on their surface and separate larger pieces of steel [47].The fibers used in the study had an average diameter of 0.20 mmand a length of 3–50 mm (Fig. 2-c). The maximum tensile strengthof SRSF was considered to be 2000 MPa [47]. SRSF was added to themixture in amounts of 0–2% of the total mixture weight.

2.2. Design of experiments

Experiments were designed using the Response SurfaceMethodology (RSM). This methodology was developed byBox and Wilson in 1951 to help the improvement of productionprocesses in the chemical industry. RSM refers to a set of statisticaland mathematical techniques that can be utilized to formulate andoptimize the factors involved in the production of new products[50]. In the context of experimental research, this method can beused to estimate the final design and to develop the responsemodel with fewer experiments, which results in reduced trial

Table 3Sieve analysis of recycled PET particles.

Sieve Size (mm) 0.075 0.15 0.3 0.6

Recycled PET passed (%) 0.34 0.84 1.47 2.53

and error and therefore reduced spending on materials, specimenpreparation, and testing.

In general, there are two goals in this methodology: (1) to locatea feasible treatment combination of independent variables forwhich the mean response is maximized (or minimized, or equalto a specific target value); and 2) to estimate the response surfacein the vicinity of this good location or region, in order to betterunderstand the ‘‘local” effects of the factors on the mean response[51].

The RSM can provide an approximate relationship (function F)between true response y and several design variables based onthe data observed in the process of research [52,53]. The mostcommon method to derive this relationship with the RSM is theCentral Composite Design method (CCD) [54].

It is typical to use a first-order or second-order polynomialmodel for the approximation function F of the true response y.For better prediction accuracy, one can use the second-order modelobtained from the Taylor series expansion of the function F [50] toestimate the response curves:

y ¼ b0 þXk

i¼1

bixi þXk

i¼1

biix2i þ

X

i

X

j

bijxixj þ e ð1Þ

In this equation, y is the estimated response, xi and xj are thecoded values of the factor studied, i is the linear term, ii is thequadratic term, ij is the coefficient of interactions, b is the regres-sion coefficient, k is the number of independent factors studiedand optimized in the experiments, and e is the random error[54–56].

Using the RSM, the designs for the RCCP mixture were preparedin the following ranges: 0–20 wt% for the replacement of cementwith MK, 0–50 vol% for the replacement of fine aggregates withrecycled PET, and 0–2 wt% for the addition of SRSF to the mixture.

1.18 2.36 4.75 9.5 12.5 19

6.13 56.40 85.70 99.74 99.89 100

R. Noroozi et al. / Construction and Building Materials 224 (2019) 173–187 177

These ranges were decided based on the suggestions of previousworks and the results of initial experiments. The criteria consid-ered in this decision were cost, technical convenience, and real-world applicability. The modeled responses included the specificgravity of fresh concrete, ultrasonic pulse velocity, and compres-sive, tensile, and flexural strengths at the age of 28 days.

For the CCD method, mix designs were classified into threegroups: fractional factorial, center points, and axial points. Thisclassification reveals the manner of changes in independentparameters and the number of mix designs needed for experi-ments. The ID code of designs corresponding to these three groups,the coded values, and the bounds of the variables X1 to X3 are pre-sented in Table 4.

In the present study, the entire process of RSM, including thedesign of experiments, statistical analysis of responses, and opti-mization of models, was performed in the Design Expert software.The interactions between parameters and the effects of each inde-pendent parameter were evaluated with the help of analysis ofvariance (ANOVA).

2.3. Mix proportions

Considering the defined purpose for the design of RCCP speci-mens, among the existing mix design methods (based on consis-tency or soil compaction), the method based on soil compactionwas chosen. This method was used to design specimens for a max-imum aggregate size of 19 mm. Mix ratios were determined basedon the soil compaction method in accordance with ACI211.3R-02R09. The optimum moisture content needed in RCCP specimenswas determined in accordance with ASTM D1557. The percentages

Table 4Limit and coded value of factors.

Factor’s characteristics

Factor Range Coded value

�2

X1 = (MK) 0–20% 0X2 = (PET) 0–50% 0X3 = (SRSF) 0–2% 0

Mixture’s type

CCD Portion Mixture no.Fractional Factorial 1–8Center Point 15–20Axial 9–14

Table 5Mix proportions per one cubic meter of concrete.

Mixture no. Coarse Aggregate Fine Aggregate

1 493.86 878.512 500.45 890.223 498.32 1241.014 497.96 885.805 500.10 1245.446 498.63 886.997 499.41 1243.738 499.20 1243.209 497.97 1417.3110 499.97 1067.2411 500.44 1068.2512 499.98 711.5113 500.33 1068.0114 499.90 1067.1015 493.5 1053.4416 493.5 1053.4417 493.5 1053.4418 493.5 1053.4419 493.5 1053.4420 493.5 1053.44

of additives to be used in the mixture were determined throughthe CCD-based experiment design procedure. The ratios of themain constituents and the replacement materials in the RCCPmix designs are presented in Table 5.

2.4. Preparation of specimens

The mix designs listed in Table 5 were manufactured by a lab-oratory mixer. All mixtures were prepared by first mixing the fineaggregates, the coarse aggregates, and the PET aggregates (whenpresent) together, then adding the binding agent and finally thefiber. The water was added to the mixture in three steps beforeadding fibers.

The most important factor that distinguishes the making ofRCCP specimens from conventional concrete specimens is the needfor proper compaction. Here, this task was performed with avibrating hammer in accordance with ASTM C1435. Compactionwas performed in three steps with the help of the steel platesshown in Fig. 3 and the vibrating hammer. Using this method, con-crete was placed in 20 � 10 cylindrical molds, 10 � 10 � 10 cubemolds, and 10 � 10 � 40 prism molds. Molds were covered withwet cloth and plastic bag and stored for 24 h in a standard environ-ment. Then, specimens were taken out of the molds and kept in awater tub until the age of 28 days.

2.5. Test procedure

At the age of 28 days, specimens were subjected to the com-pressive, tensile and flexural strength, ultrasonic pulse velocity,and fresh concrete specific gravity tests. The destructive tests,

�1 0 +1 +2

5 10 15 2012.5 25 37.5 500.5 1 1.5 2

X1 X2 X3

±1 ±1 ±10 0 00, ±2 0, ±2 0, ±2

Water PET MK SRSF

152.59 225.93 42.74 10.18141.56 228.94 14.44 30.75145.12 75.99 43.12 11.24145.73 227.81 14.36 10.22142.15 76.26 14.43 11.26144.60 228.11 43.15 30.69143.29 76.16 14.41 33.76143.65 76.12 43.20 33.75145.71 0.00 28.73 23.48142.36 152.48 0.00 21.51141.57 152.63 28.87 0.00142.34 304.97 28.85 19.47141.76 152.59 57.73 21.51142.47 152.46 28.84 43.01153.19 150.51 28.47 21.35153.19 150.51 28.47 21.35153.19 150.51 28.47 21.35153.19 150.51 28.47 21.35153.19 150.51 28.47 21.35153.19 150.51 28.47 21.35

Fig. 3. a) Compacted RCCP specimens b) Compacting steel plates.

178 R. Noroozi et al. / Construction and Building Materials 224 (2019) 173–187

which included compressive strength, split tensile strength andthree-point bending tests, were performed respectively on cubic,cylindrical and prism samples in accordance with BS-1881-Part-116, BS-1881-Part-117, and ASTM C293. The non-destructive tests,which included ultrasonic pulse velocity and specific gravity mea-surement, were performed in accordance with ASTM C597 andASTM C642, respectively.

3. Discussion and results

Statistical modeling of the experimental results was carried out.For this purpose, the Design Expert software was used to estimatethe polynomial function with the best fit to the response values ofexperimental specimens. In order to determine the relationshipbetween the responses obtained from the laboratory process andthe independent variables, regression analysis was used to identifythe variables that are statistically significant. For this purpose, thet-statistics were calculated and the terms that are statistically

Table 6Analysis of variance results for concrete responses.

Dependent variable Source of variation Statistical parameters

df Sum of square Mean squ

Fresh unit weight MK 1 92.91 92.91PET 1 1.316E+06 1.316E+0SRSF 1 21145.61 21145.61PET*SRSF 1 6934.00 6934.00(PET)2 1 31262.58 31262.58

Ultrasonic pulse velocity MK 1 39859.15 39859.15PET 1 8.552E+06 8.552E+0SRSF 1 72875.75 72875.75MK*PET 1 4.556E+05 4.556E+0MK*SRSF 1 3.122E+05 3.122E+0(MK)2 1 69901.35 69901.35

Compressive strength MK 1 22.78 22.78PET 1 3507.03 3507.03SRSF 1 8.53 8.53MK*PET 1 162.56 162.56PET*SRSF 1 175.56 175.56

Split tensile strength MK 1 0.2408 0.2408PET 1 37.98 37.98SRSF 1 0.4744 0.4744MK*PET 1 0.8907 0.8907(MK)2 1 1.44 1.44(SRSF)2 1 2.02 2.02

Flexural strength MK 1 1.56 1.56PET 1 130.35 130.35SRSF 1 1.77 1.77PET*SRSF 1 1.39 1.39

insignificant were omitted. This process was continued until theentire terms of the estimated model for each response became sig-nificant. Also, the coefficient of determination (R2), which repre-sents the goodness of fit of the model, was considered to besufficiently close to 1.00. The general information of the modeland the effect of each independent variable on the response valueis presented in Table 6. ANOVA and modeling of the experimentalresults were both performed at the 0.05 significance level. The p-values shown in Table 5 represents the significant variables inthe developed models. The coefficients of regression models areprovided in Table 7. These coefficients are estimated by using mul-tiple regression analysis and assuming normal distribution forresponses.

3.1. Specific gravity of fresh concrete

According to the model presented in Table 6, the specific gravityof the fresh concrete can be estimated with a second-order polyno-

Significant R-Squared Adjusted R-Squared

are F p-value

0.1629 0.6897 No 0.9888 0.98676 2307.29 <0.0001 Yes

37.06 <0.0001 Yes12.15 0.0017 Yes54.80 <0.0001 Yes

2.73 0.1099 No 0.9602 0.95146 586.19 <0.0001 Yes

5.00 0.0339 Yes5 31.23 <0.0001 Yes5 21.40 <0.0001 Yes

4.79 0.0374 Yes

1.04 0.3175 No 0.8673 0.8427159.67 <0.0001 Yes0.3885 0.5383 No7.40 0.0113 Yes7.99 0.0087 Yes

1.31 0.2617 No 0.8953 0.8720207.33 <0.0001 Yes2.59 0.1192 No4.86 0.0361 Yes7.84 0.0093 Yes11.04 0.0026 Yes

5.87 0.0219 Yes 0.9460 0.9386490.60 <0.0001 Yes6.66 0.0152 Yes5.23 0.0298 Yes

Table 7Mathematical formulation of RCCP responses.

Parameters Fresh unit weight Ultrasonic pulse velocity Compressive strength Split tensile strength Flexural strength

Constant +2567.09442 +6738.13354 +45.88913 +22.77181 +8.25552MK +0.347266 �160.38197 �1.10625 +0.253291 +0.044156PET �5.06623 �68.35836 �0.817500 �0.049402 �0.114332SRSF +34.01798 �654.18729 +14.35652 +1.92335 +1.64869MK*PET – +2.70006 +0.051000 �0.003775 –MK*SRSF – +55.87438 – – –PET*SRSF �3.45629 – �0.530000 – �0.047130(MK)2 – +1.49737 – �0.007078 –(PET)2 �0.160228 – – – –(SRSF)2 – – – �0.839919 –

Fig. 4. Effect of PET and SRSF content on the specific gravity of fresh concrete (2D and 3D) for MK = 10%.

Fig. 5. Effect of sand to PET replacement ratio and MK content on ultrasonic pulse velocity at the age of 28 days (2D and 3D) for SRSF = 1%.

R. Noroozi et al. / Construction and Building Materials 224 (2019) 173–187 179

180 R. Noroozi et al. / Construction and Building Materials 224 (2019) 173–187

mial function. The coefficient of determination of the modelreflects its good ability to predict the responses within the limitsof the experiments. The model and the coefficients presented inTable 7 are significant at P-value < 0.0001 level. The introducedresponse function was found to be linearly influenced by theamount of SRSF added to the mixture, nonlinearly (quadratic)affected by the sand to PET replacement ratio, and also the interac-tion of these two variables.

As shown in Fig. 4, the most important factor affecting themodel response was the sand to PET replacement ratio. Accordingto the coefficients of this model, the use of PET and SRSF respec-tively reduced and increased the specific gravity of the fresh con-crete. This effect can be mostly attributed to the differencebetween the specific gravity of these materials and other con-stituents of the concrete. It has been suggested that the low densityof plastic particles compared to conventional aggregates reducesthe density of plastic-containing fresh concrete [13,18]. The PETparticles used in this study had 60% lower specific gravity thanthe sand. Also, given the strip shape of PET particles, using themin place of sand increases the number of pores in the concretematrix. The excess water that remains unused in the cement-

Fig. 6. Ultrasonic pulse velocity variations for sand t

water reaction can also create small ducts and open up more cav-ities [19]. Naturally, the presence of these voids reduces the speci-fic gravity of the concrete.

According to the estimated model, the increase in the specificgravity of the concrete after the addition of SRSF is mainly due tothe high specific gravity of the steel which is in accordance withAlsaif et al.’s study [57]. It should also be noted that the additionof SRSF to the concrete mixture by itself does not significantlychange the air content of the mixture [57].

Kim et al. [58] have reported that using MK in place of cementcan reduce or increase the density of the concrete depending onthe ratio of replacement and the type and size of aggregates.According to the analyses of the present study, the use of MKslightly increases the specific gravity of the concrete; an increasethat can be attributed to further compaction of the mixturebecause of the filler effect and pozzolanic activity of MK [59].The slight increase in the density caused by application of MK,has also been reported in other studies [35,60], which is due to fur-ther hydration products by the pozzolanic activity of this material[61]. The amount of MK used in place of cement was found to be astatistically insignificant variable. This is because of the similarity

o PET replacement ratios of 10, 20, 30 and 40%.

R. Noroozi et al. / Construction and Building Materials 224 (2019) 173–187 181

of cement and MK in terms of specific gravity as well as the smallamount of binder added relative to the mixture volume. Thecement content of RCCP is between 10% and 17%, which is equiva-lent to about 210–360 kg/m3 [62].

3.2. Ultrasonic pulse velocity (UPV)

The UPV prediction model was estimated for the age of 28 dayswith high precision with a coefficient of determination of 0.96.Among the three variables listed in Table 4, the linear form ofthe variable MK was insignificant but variables PET and SRSF werefound to be significant (at 0.05 significance level). Other compo-nents of the model were the second power of MK and its interac-tions with the other two variables. The examination of responsesurfaces showed that the variable with the greatest effect on theresponse is the PET content of the mixture. In Fig. 5, the gradientof change in the horizontal direction (PET) is much higher thanin the other direction (MK), which indicates the response is moreaffected by PET than by MK. Since UPV depends on porosity, cracks,density, homogeneity and elastic properties of the material, theanalysis of this response can provide insight into various character-istics of the specimens tested.

In Fig. 5, it can be seen that with the increase in the PET contentof the mixture, UPV decreased from 4600 to 3600 m/s. The trend ofthe response value for various sand to PET replacement ratios isillustrated in Fig. 6. The reduced UPV can be caused by reducedcompaction and density of the concrete, which result in reducedstrength [63]. The decrease in UPV with the increase in the PETcontent has been observed in various studies [18–20]. There aretwo reasons for this effect. Firstly, using PET in an RCCP mixtureitself creates many voids in the concrete matrix. Secondly because,the elasticity of plastic facilitates the damping of compactionenergy, which leads to imperfect compaction and therefore moreporosity, ultimately resulting in further reduced pulse velocity.

The impact of the quadratic form of the MK variable on themodel implies that it has a decreasing or increasing effect onUPV. According to the graphs plotted in Fig. 6, using MK at lowPET contents (10% and 20%) leads to a decrease in response, butat high PET contents (30% and 40%), it increases the pulse velocity.

Fig. 7. Effect of sand to PET replacement ratio and MK content

This highlights the need for additional activation agents whenusing recycled PET in concrete. This behavior can be attributed tothe role of MK in the absorption of mixture water and its effecton the frequency of voids and pores in the concrete matrix. Whilesome studies [18] have reported that MK increases the UPV of theconcrete, others have reported the opposite [35,64].

As shown in Fig. 6, the use of SRSF when MK content is very lowresults in reduced UPV, but it has the opposite impact when themixture contains high amounts of MK. High friction between thefibers and PET particles, makes fibers balling and allows more airvoids to be trapped in the mixture [65,66]. In the mixtures withhigher SRSF contents, the impact of small size and filler effect ofMK particles is more pronounced; a result that reflects the positiveeffect of simultaneous use of MK and SRSF in the mixtures contain-ing high amounts of PET.

3.3. Compressive strength

The model of the compressive strength of the 28-day RCCPspecimens is presented in Table 6. The results of ANOVA showedthat PET had the most effect on the response among the additives.The linear forms of the other two variables were found to beinsignificant. However, the interactions of PET with the compo-nents of MK and SRSF were found to be significant and substan-tially affect the compressive strength model. As the PET contentof the mixture increased, the compressive strength significantlydecreased; a result that has been reported in several other studies[13–16]. This strength reduction is due to weak joints between PETand texture. PET particles prevent the adhesion of cement paste tonatural aggregates [19]. The weak interaction of PET aggregateswith cement paste leads to the formation of a weak InterfacialTransition Zone (ITZ) [13], which acts as the starting point forthe failure owing to crack initiation and propagation in the speci-men under loading. Also, the presence of PET in the fresh RCCPmixture leads to the loss of a significant portion of compactionenergy, which leads to reduced uniformity of the mixture matrix.

As the plots illustrated in Fig. 7 indicate, the use of MK in themixture had a positive effect on the compressive strength. As theMK content increased, so did the compressive strength, especially

on 28-day compressive strength (2D and 3D) for SRSF = 1%.

182 R. Noroozi et al. / Construction and Building Materials 224 (2019) 173–187

in samples with higher PET contents. This behavior can be attribu-ted to the presence of more voids in the specimen with higher PETcontents, because the presence of voids increases the amount of Ca(OH)2 in the aggregate binder mortar and improves the ITZ perfor-mance, thereby leading to enhanced adhesion in their interface.

The positive effects of MK on compressive strength have beenproved in numerous studies [32,35,67–70]. The observed strengthimprovement is due to three intrinsic properties of this additive:filler effect, pozzolanic reaction with Ca(OH)2, and acceleratedhydration of ordinary Portland cement as a binder after the addi-tion of MK [71,72]. The filler and pozzolanic effects of MK particleshave been proven in the microstructural analyses performed in[73] and [74]. Given the small size of MK particles, as comparedto Portland cement, they are able to bridge the gap between aggre-gates and fill up the voids in the matrix, which leads to better pack-ing of particles in the interface of aggregates with the paste. Thisresults in a more compact ITZ and reduction in micro-cracking.As shown in Fig. 8, the addition of MK to the mixture changesthe composition of ITZ. The pozzolanic reaction then leads to theformation of a more compact C-S-H gel and a decreased Ca(OH)2content [73], thus increasing the strength and reducing the fre-

Fig. 8. Effects of MK admixture on micro

Fig. 9. Effect of sand to PET replacement ratio and MK content

quency of pores in the concrete mixture. Also, the higher surfacearea of smaller MK particles accelerate the hydration of ordinarycement and increases the rate of pozzolan reaction, ultimatelyleading to improved compressive strength [75].

According to the modeling results, at low sand to PET replace-ment ratios, the use of SRSF increases the compressive strength,but at higher replacement ratios, it has the opposite effect.Although a few studies exist on the compressive strength of con-crete containing SRSF, of which, both increase and decrease in thisproperty have been reported. This may be rooted in the preventionof interconnection of the micro cracks in matrix, or trapped airaround the fibers respectively [76].

3.4. Split tensile strength

According to preceding literature review, the tensile strength ofconcrete is mainly affected by the strength of ITZ, strength of bin-der paste and the strength of adhesion between paste and aggre-gates [77,78]. The modeling results presented in Table 6demonstrate the effect of PET variable (linear), MK and SRSF vari-ables (quadratic), and the interaction of MK and PET on the 28-

-morphology of ITZ at 28 days [73].

on 28-day split tensile strength (2D and 3D) for SRSF = 1%.

R. Noroozi et al. / Construction and Building Materials 224 (2019) 173–187 183

day tensile strength of the RCCP specimens. This model showedsuitable goodness of fit with a coefficient of determination of 0.89.

As shown in Fig. 9, using PET in place of sand decreased the ten-sile strength of the concrete and, according to ANOVA, this was the

Fig. 10. Concrete specimens fractured in the split tensile strength test

Fig. 11. Split tensile strength variations for sand to

only linearly significant parameter in this respect. The reduction intensile strength as a result of using PET aggregates in place of sandhas been reported in numerous studies [13,16,19,20]. This resultwas indeed expected, as the literature suggests that the tensile

(a) PET-containing specimens and b) SRSF-containing specimens.

PET replacement ratios of 10, 20, 30 and 40%.

184 R. Noroozi et al. / Construction and Building Materials 224 (2019) 173–187

strength largely depends on the ITZ strength, the strength of thecement paste, and the adhesion between paste and aggregates[78,79]. The smooth surface of PET aggregates and their surfacewater reduce the adhesion of plastic particles to the cement paste,leading to reduced tensile strength. Examination of the specimensdisplayed in Fig. 10-a showed that at the ultimate tensile stress,the PET particles of the concrete matrix do not disintegrate, butrather debond from the cement paste. This points to the weaknessof the bond between cement paste and PET aggregates. As shownin Fig. 11, for each 10% increase in sand to PET replacement ratio,the tensile strength response value decreased by 1 MPa.

The influence of the MK content on the tensile strength was ofsecond-degree (quadratic) and had a maximum value. The varia-tions of tensile strength with the MK value had different gradientsin the upper and lower ranges of the PET content. Fig. 9 shows themaximum tensile strength response obtained for replacing 10 wt%of cement with MK. Because of filler and pozzolanic effects of MK,using this material reduces the frequency of voids in the concretemicrostructure and improves the ITZ strength. This provides theconcrete with a dense microstructure and suitable adhesionbetween aggregates and cement paste, which leads to improvedtensile strength [64]. Several other studies have also reported sim-ilar results for the gradient of variations of tensile strength withthe addition of MK [35,64,69].

In this study, the highest tensile strength was seen in the spec-imen where 1 wt% SRSF was added to the RCCP mixture. The role ofthe fiber in the stability of the specimen is illustrated in Fig. 10-b. Itshould be noted that adding too much fiber can lead to the ballingin the mixture, which could interfere with the even distribution ofother components in the matrix. This can be attributed to ran-domly distributed fibers in RCCP specimens, which, in turn, couldform bundles of fibers, therefore, making discontinuities insidethe concrete matrix [80].

3.5. Flexural strength

The flexural strength model of the RCCP specimens at the age of28 days was estimated based on the data of Table 6 with a coeffi-cient of determination of 0.94. The result showed that all threeparameters had a linear effect on this response. The interaction

Fig. 12. Effect of sand to PET replacement ratio and SRSF conten

of PET and SRSF variables was also found to affect this response.The flexural strength response was most strongly affected by thePET variable, which had a negative impact on this response. Othervariables were found to increase this response.

In Fig. 12, it can be seen that as the PET content increased, theflexural strength decreased; a result that has been reported bymultiple researchers [13,14,16–18]. The basis of the effect of PETaggregates on the flexural strength is similar to what was dis-cussed for compressive and tensile strengths [13]. A notable pointin the performance of PET-containing specimens under flexuralloading is the ductile behavior resulted from the cracks beingbridged by PET particles. In other words, these specimens exhibithigher post-cracking toughness. This property results from theelastic and non-brittle behavior of plastic aggregates under load-ing, which deflects the cracks and distributes them over the matrix.

As shown in Fig. 12, MK content had an impact, although small,on the flexural strength. Research on the details of the effect of MKon flexural strength has been scarce [28]. However, the increase inflexural strength has been observed in several studies [35,81]. Dueto the fineness of MK particles compared with cement [35], theaddition of MK to the mixture improves the adhesion of aggregatesand binder paste, resulting in improved ITZ strength.

The flexural strength model suggests that because of the inter-action of the SRSF variable with the PET variable, its effect dependson the amount of PET. At low PET contents, the use of fibers leadsto an improvement in the flexural strength -as expected[47,49,57]- but at higher PET contents, it has the opposite impact.It should, however, be noted that the latter impact is limited inextremes. Sewing the micro cracks and preventing the propagationof wider cracks could be the probable reasons for the improvementof flexural strength by using SRSF [76,82]. At higher PET contents,because of high friction between steel fibers and plastic particles,fibers tend to agglomerate. This undermines the distribution ofother mixture components, and thereby, negatively influencesthe concrete performance.

3.6. Multi-objective optimization

One of the major uses of statistical models discussed in the pre-vious sections is the determination of the relationship between

t on the 28-day flexural strength (2D and 3D) for MK = 10%.

Table 8Definitions of factors and responses in the optimization process.

Factors & responses Goal Lower limit Upper limit

MK (wt%*) Maximize 0 20PET (vol%*) Maximize 0 50SRSF (wt%) Maximize 0 2Compressive strength (MPa) more than 27.5 49Split tensile strength (MPa) more than 2.5 5.5Flexural strength (MPa) more than 4.2 10

* Wt%: weight by percent, vol%: volume by percent.

Table 9Optimum ratios and related predicted responses.

Factors and responses Optimum ratios &predicted responses

MK (wt%) 19.61PET (vol%) 25.53SRSF (wt%) 1.89Fresh unit weight (kg/m3) 2237.56Ultrasonic pulse velocity (m/s) 4609.79Compressive strength (MPa) 30.41Split tensile strength (MPa) 2.5Flexural strength (MPa) 7.04

R. Noroozi et al. / Construction and Building Materials 224 (2019) 173–187 185

independent variables and responses. It is also possible to define aset of constraints and optimize the dependent variable by indepen-dent variables in the form of an objective function or utility func-tion [55]. This function represents the location of the selectedresponses in a desirability scale ranging from 0 to 1. The searchfor the optimal location of responses begins at a random startingpoint and proceeds through the steepest slope until reaching themaximum value for the function. Here, the optimization was per-formed with the objective of maximizing the use of recycled PETparticles in RCCP mixtures so that the product meets the require-ments of ACI 325.10R [83] for the use of concrete in road’s pave-ment. Accordingly, the minimum acceptable strength valueswere considered as listed in Table 8.

The results of the optimization process are presented in Table 9.According to the results, the admissible RCCP mix design withinthe aforementioned requirements is the design where about20 wt% of cement is replaced with MK, about 25 vol% of fine aggre-gate is replaced with recycled PET aggregate, and 1.9 wt% SRSF isadded to the mixture.

4. Conclusion

This study investigated the behavior of RCCPmodified by partialreplacement of sand and cement with recycled materials and recy-cled steel fibers as an additive. Replacement materials were PETaggregates obtained from the recycling of beverage bottles, MK,and SRSF. For this purpose, a set of destructive and non-destructive tests were performed on standard specimens at theage of 28 days. The response surface methodology was used todetermine the number of designs necessary to investigate thesimultaneous effect of these variables on the physical and mechan-ical properties of the RCCP mixture. Based on the models devel-oped in this study, the analysis carried out for reaching to theoptimal range of the studied variables, and the conducted opti-mization, the following results can be concluded:

� The studied RCCP specimens provided suitable responses(specific gravity, ultrasonic pulse velocity, compressivestrength, tensile strength, and flexural strength) for modelingof their behavior based on independent variables PET, MK,and SRSF.

� The use of recycled PET particles in an RCCP mixture reduces allmechanical properties including compressive strength, splittensile strength, and flexural strength as well as specific gravityand ultrasonic pulse velocity. These effects are mostly caused bythe poor adhesion between the cement paste and the plasticparticles and the higher damping of compaction energy whenplastic is present in this mixture.

� Partial replacement of the cement of the RCCP mixture with MKyielded positive results. MK especially increased the ultrasonicpulse velocity and compressive strength of the RCCP specimenswith higher sand to PET replacement ratios; a result thatreflects the filler effect, pozzolanic property, and enhancedadhesion property of the binder.

� The estimated models suggested that the effect of SRSF on themechanical properties of RCCP specimens generally dependson other components of the mixture. Adding SRSF together withMK increased the ultrasonic pulse velocity of the concrete. Also,the effect of SRSF on the compressive strength and flexuralstrength were found to depend on the amount of PET aggregatesin the mixture. At higher sand to PET replacement ratios, addingSRSF actually decreased the strength. The use of SRSF increasedthe specific gravity and split tensile strength of the RCCPspecimens.

� Using the estimated regression models, the optimal mix designmodification was determined as follows: replacement of about25 vol% of the sand with recycled PET particles, replacementof 20 wt% of cement with MK, and the addition of 1.9 wt% SRSFto the mixture. Experimental results and analyses show thatthis mixture, while being more eco-friendly, can result in suffi-cient capacity to withstand the loads applied to the pavements.

Declaration of Competing Interest

None.

Acknowledgments

The authors would like to express their gratitude to Mr. Hajine-jad at the laboratory of the Ferdowsi University of Mashhad for hishelpful assistance. It is also necessary to thank the director of thePET bottle recycling plant, Mr. Alagheband, and also Mr. Sadeghza-deh at the concrete products laboratory of the Shargh Cement Co.for their cooperation.

References

[1] K. Sakai, Towards environmental revolution in concrete technologies, in: Proc.Int. Fib Symp. Concr. 21st Century Superhero. London, 2009.

[2] Z.N. Kalantar, M.R. Karim, A. Mahrez, A review of using waste and virginpolymer in pavement, Constr. Build. Mater. 33 (2012) 55–62.

[3] A. Dormer, D.P. Finn, P. Ward, J. Cullen, Carbon footprint analysis in plasticsmanufacturing, J. Clean. Prod. 51 (2013) 133–141, https://doi.org/10.1016/j.jclepro.2013.01.014.

[4] A.H. Purcell, F.L. Smith, Energy and environmental impacts of materialsalternatives: an assessment of quantitative understanding, Resour. Recover.Conserv. 2 (1976) 93–102.

[5] S. Kumar, A.K. Panda, R.K. Singh, A review on tertiary recycling of high-densitypolyethylene to fuel, Resour. Conserv. Recycl. 55 (2011) 893–910, https://doi.org/10.1016/j.resconrec.2011.05.005.

[6] A.L. Craighill, J.C. Powell, Lifecycle assessment and economic evaluation ofrecycling: a case study, Resour. Conserv. Recycl. 17 (1996) 75–96.

[7] A.A. Garforth, S. Ali, J. Hernández-Martínez, A. Akah, Feedstock recycling ofpolymer wastes, Curr. Opin. Solid State Mater. Sci. 8 (2004) 419–425.

[8] T.R. Naik, Y.-M. Chun, R.N. Kraus, S.S. Singh, L.-L.C. Pennock, B.W. Ramme,Strength and durability of roller-compacted HVFA concrete pavements, Pract.Period. Struct. Des. Constr. 6 (2001) 154–165.

[9] D.W. Pittman, G.L. Anderton, The use of roller-compacted concrete (RCC)pavements in the United States, in: Sixth Int. Conf. Maint. Rehabil. PavementsTechnol. Control Int. Soc. Maint. Rehabil. Transp. Infrastructure TransportationRes. Board, 2009. https://trid.trb.org/view/899345.

186 R. Noroozi et al. / Construction and Building Materials 224 (2019) 173–187

[10] M. Batayneh, I. Marie, I. Asi, Use of selected waste materials in concrete mixes,Waste Manag. 27 (2007) 1870–1876.

[11] B.-W. Jo, G.-H. Tae, C.-H. Kim, Uniaxial creep behavior and predictionof recycled-PET polymer concrete, Constr. Build. Mater. 21 (2007) 1552–1559.

[12] A. Sadrmomtazi, S. Dolati-Milehsara, O. Lotfi-Omran, A. Sadeghi-Nik, Thecombined effects of waste Polyethylene Terephthalate (PET) particles andpozzolanic materials on the properties of self-compacting concrete, J. Clean.Prod. 112 (2016) 2363–2373.

[13] N. Saikia, J. de Brito, Mechanical properties and abrasion behaviour of concretecontaining shredded PET bottle waste as a partial substitution of naturalaggregate, Constr. Build. Mater. 52 (2014) 236–244.

[14] K. Hannawi, S. Kamali-Bernard, W. Prince, Physical and mechanical propertiesof mortars containing PET and PC waste aggregates, Waste Manag. 30 (2010)2312–2320.

[15] M. Frigione, Recycling of PET bottles as fine aggregate in concrete, WasteManag. 30 (2010) 1101–1106.

[16] S. Akçaözoǧlu, C.D. Atis�, K. Akçaözoǧlu, An investigation on the use of shreddedwaste PET bottles as aggregate in lightweight concrete, Waste Manag. 30(2010) 285–290, https://doi.org/10.1016/j.wasman.2009.09.033.

[17] O.Y. Marzouk, R.M. Dheilly, M. Queneudec, Valorization of post-consumerwaste plastic in cementitious concrete composites, Waste Manag. 27 (2007)310–318.

[18] S. Akçaözoǧlu, C. Ulu, Recycling of waste PET granules as aggregate in alkali-activated blast furnace slag/metakaolin blends, Constr. Build. Mater. 58 (2014)31–37, https://doi.org/10.1016/j.conbuildmat.2014.02.011.

[19] E. Rahmani, M. Dehestani, M.H.A. Beygi, H. Allahyari, I.M. Nikbin, On themechanical properties of concrete containing waste PET particles, Constr.Build. Mater. 47 (2013) 1302–1308.

[20] C. Albano, N. Camacho, M. Hernandez, A. Matheus, A. Gutierrez, Influence ofcontent and particle size of waste pet bottles on concrete behavior at differentw/c ratios, Waste Manag. 29 (2009) 2707–2716.

[21] L. Ávila Córdoba, G. Martínez-barrera, C. Barrera Díaz, F. Ureña Nuñez, A. Loza,Yañez, Effects on mechanical properties of recycled PET in cement-basedcomposites, Int. J. Polym. Sci. 2013 (2013) 1–7, https://doi.org/10.1155/2013/763276.

[22] S.R. Rahimi, I.M. Nikbin, H. Allahyari, T.S. Habibi, Sustainable approach forrecycling waste tire rubber and polyethylene terephthalate (PET) to producegreen concrete with resistance against sulfuric acid attack, J. Clean. Prod. 126(2016) 166–177, https://doi.org/10.1016/j.jclepro.2016.03.074.

[23] S. Gavela, C. Karakosta, C. Nydriotis, V. Kaselouri-Rigopoulou, S. Kolias, P.A.Tarantili, E. Vazquez, C.F. Hendriks, G.M.T. Janssen, A study of concretescontaining thermoplastic wastes as aggregates, in: Proc. Int. RILEM Conf. UseRecycl. Mater. Build. Struct. Barcelona, Spain, 2004: pp. 911–918.

[24] S. Akçaözoǧlu, K. Akçaözoǧlu, C.D. Atis�, Thermal conductivity, compressivestrength and ultrasonic wave velocity of cementitious composite containingwaste PET lightweight aggregate (WPLA), Compos. Part B Eng. 45 (2013) 721–726, https://doi.org/10.1016/j.compositesb.2012.09.012.

[25] S. Akaözolu, C.D. Ati, Effect of Granulated Blast Furnace Slag and fly ashaddition on the strength properties of lightweight mortars containing wastePET aggregates, Constr. Build. Mater. 25 (2011) 4052–4058, https://doi.org/10.1016/j.conbuildmat.2011.04.042.

[26] R. Siddique, J. Khatib, I. Kaur, Use of recycled plastic in concrete: a review,Waste Manag. 28 (2008) 1835–1852, https://doi.org/10.1016/j.wasman.2007.09.011.

[27] N. Saikia, J. De Brito, Use of plastic waste as aggregate in cement mortar andconcrete preparation: a review, Constr. Build. Mater. 34 (2012) 385–401,https://doi.org/10.1016/j.conbuildmat.2012.02.066.

[28] J.M. Khatib, O. Baalbaki, A.A. ElKordi1, Metakaolin, Elsevier Ltd, 2018. doi:https://doi.org/10.1016/B978-0-08-102156-9.00015-8.

[29] B.R. Ilic, A.A. Mitrovic, L.R. Milicic, Thermal treatment of kaolin clay to obtainmetakaolin, Hem. Ind. 64 (2010) 351–356, https://doi.org/10.2298/HEMIND100322014I.

[30] R. Siddique, J. Klaus, Influence of metakaolin on the properties of mortar andconcrete: a review, Appl. Clay Sci. 43 (2009) 392–400, https://doi.org/10.1016/j.clay.2008.11.007.

[31] E. Vejmelková, M. Pavlíková, M. Keppert, Z. Keršner, P. Rovnaníková, M.Ondrácek, M. Sedlmajer, R. Cerny, High performance concrete with Czechmetakaolin: Experimental analysis of strength, toughness and durabilitycharacteristics, Constr. Build. Mater. 24 (2010) 1404–1411, https://doi.org/10.1016/j.conbuildmat.2010.01.017.

[32] P. Nuaklong, V. Sata, P. Chindaprasirt, Properties of metakaolin-high calciumfly ash geopolymer concrete containing recycled aggregate from crushedconcrete specimens, Constr. Build. Mater. 161 (2018) 365–373, https://doi.org/10.1016/j.conbuildmat.2017.11.152.

[33] S. Dadsetan, J. Bai, Mechanical and microstructural properties of self-compacting concrete blended with metakaolin, ground granulated blast-furnace slag and fly ash, Constr. Build. Mater. 146 (2017) 658–667, https://doi.org/10.1016/j.conbuildmat.2017.04.158.

[34] D. Jian Tong, L. Zongjin, Effects of metakaolin and silica fume on properties ofconcrete, ACI Mater. J. 99 (2002) 393–398, https://doi.org/10.14359/12222.

[35] R. Muduli, B.B. Mukharjee, Effect of incorporation of metakaolin and recycledcoarse aggregate on properties of concrete, J. Clean. Prod. 209 (2019) 398–414,https://doi.org/10.1016/j.jclepro.2018.10.221.

[36] B.B. Sabir, S. Wild, J. Bai, Metakaolin and calcined clays as pozzolans forconcrete: a review, Cem. Concr. Compos. 23 (2001) 441–454.

[37] M. Shekarchi, A. Bonakdar, M. Bakhshi, A. Mirdamadi, B. Mobasher, Transportproperties in metakaolin blended concrete, Constr. Build. Mater. 24 (2010)2217–2223, https://doi.org/10.1016/j.conbuildmat.2010.04.035.

[38] G. Batis, P. Pantazopoulou, S. Tsivilis, E. Badogiannis, The effect of metakaolinon the corrosion behavior of cement mortars, Cem. Concr. Compos. 27 (2005)125–130, https://doi.org/10.1016/j.cemconcomp.2004.02.041.

[39] ACI Committee 544, Report on Fiber Reinforced Concrete, 2002. http://indiafiber.com/Files/ACI report.pdf.

[40] K. Neocleous, H. Angelakopoulos, K. Pilakoutas, M. Guadagnini, Fibre-reinforced roller-compacted concrete transport pavements, Proc. ICE-Transport. 164 (2011) 97–109, https://doi.org/10.1258/itt.2010.100803.

[41] V.C. Li, T. Matsumoto, Fatigue crack growth analysis of fiber reinforcedconcrete with effect of interfacial bond degradation, Cem. Concr. Compos. 20(1998) 339–351.

[42] M.K. Lee, B.I.G. Barr, An overview of the fatigue behaviour of plain and fibrereinforced concrete, Cem. Concr. Compos. 26 (2004) 299–305, https://doi.org/10.1016/S0958-9465(02)00139-7.

[43] D.-I. Chang, W.-K. Chai, Flexural fracture and fatigue behavior of steel-fiber-reinforced concrete structures, Nucl. Eng. Des. 156 (1995) 201–207.

[44] P. Rossi, E. Parant, Damage mechanisms analysis of a multi-scale fibrereinforced cement-based composite subjected to impact and fatigue loadingconditions, Cem. Concr. Res. 38 (2008) 413–421.

[45] S.P. Shah, B.V. Rangan, Fiber reinforced concrete properties, in: ACI J. Proc.,1971: pp. 126–137.

[46] K. Pilakoutas, K. Neocleous, H. Tlemat, Reuse of tyre steel fibres as concretereinforcement, Proc. ICE-Eng. Sustain. 157 (2004) 131–138, https://doi.org/10.1258/itt.2010.100803.

[47] H. Tlemat, Steel fibres from waste tyres to concrete: testing, modelling anddesign., University of Sheffield, 2004. https://ethos.bl.uk/OrderDetails.do;jsessionid=B8A9968BF658C1579586EA3836AEF8B9?uin=uk.bl.ethos.506448.

[48] M.A. Aiello, F. Leuzzi, G. Centonze, A. Maffezzoli, Use of steel fibres recoveredfrom waste tyres as reinforcement in concrete: pull-out behaviour,compressive and flexural strength, Waste Manag. 29 (2009) 1960–1970.

[49] K. Neocleous, H. Tlemat, K. Pilakoutas, Design issues for concrete reinforcedwith steel fibers, including fibers recovered from used tires, J. Mater. Civ. Eng.18 (2006) 677–685, https://doi.org/10.1258/itt.2010.100803.

[50] R.H. Myers, D.C. Montgomery, C.M. Anderson-Cook, Response SurfaceMethodology: Process and Product Optimization Using DesignedExperiments, Third, Wiley, New York, 2009.

[51] A. Dean, D. Voss, Design and Analysis of Experiments, Springer, New York, NY,1991. doi: https://doi-org.ezproxy.uwtsd.ac.uk/10.1007/b97673..

[52] D. Lepadatu, R. Hambli, A. Kobi, A. Barreau, Optimisation of springback inbending processes using FEM simulation and response surface method, Int. J.Adv. Manuf. Technol. 27 (2005) 40–47, https://doi.org/10.1007/s00170-004-2146-z.

[53] D. Lepadatu, R. Hambli, A. Kobi, A. Barreau, Statistical investigation of die wearin metal extrusion processes, Int. J. Adv. Manuf. Technol. 28 (2006) 272–278.

[54] M.A.A. Aldahdooh, N.M. Bunnori, M.A.M. Johari, Evaluation of ultra-high-performance-fiber reinforced concrete binder content using the responsesurface method, Mater. Des. 52 (2013) 957–965, https://doi.org/10.1016/j.matdes.2013.06.034.

[55] D.C. Montgomery, Design and Analysis of Experiments, eighth ed., John Wiley& Sons, 2013.

[56] A.I. Khuri, J.A. Cornell, Response Surfaces: Designs and Analyses, CRC Press,1996. https://scholar.google.com/scholar?hl=en&as_sdt=0,5&q=André+I.+Khuri,+John+A.+Cornell,+Response+Surfaces:+Designs+and+Analyses,+CRC+Press,+1996.&btnG=.

[57] A. Alsaif, S.A. Bernal, M. Guadagnini, K. Pilakoutas, Durability of steel fibrereinforced rubberised concrete exposed to chlorides, Constr. Build. Mater. 188(2018) 130–142, https://doi.org/10.1016/j.conbuildmat.2018.08.122.

[58] H.-K.K. Kim, E.A. Hwang, H.-K.K. Lee, Impacts of metakaolin on lightweightconcrete by type of fine aggregate, Constr. Build. Mater. 36 (2012) 719–726,https://doi.org/10.1016/j.conbuildmat.2012.06.020.

[59] O. Rezaifar, M. Hasanzadeh, M. Gholhaki, Concrete made with hybrid blends ofcrumb rubber and metakaolin: optimization using response surface method,Constr. Build. Mater. 123 (2016) 59–68, https://doi.org/10.1016/j.conbuildmat.2016.06.047.

[60] J.M. Khatib, Metakaolin concrete at a low water to binder ratio, Constr. Build.Mater. 22 (2008) 1691–1700, https://doi.org/10.1016/j.conbuildmat.2007.06.003.

[61] M.R. Shatat, Hydration behavior and mechanical properties of blended cementcontaining various amounts of rice husk ash in presence of metakaolin, Arab. J.Chem. 9 (2016) S1869–S1874.

[62] ACI Committee 211, Guide for Selecting Proportions for No – Slump ConcreteReported by ACI Committee 211, 2009.

[63] E.A. Whitehurst, Soniscope tests concrete structures. Research anddevelopment laboratories of the portland cement association, J. Proc. (1951)433–444.

[64] S.C. Kou, C.S. Poon, F. Agrela, Comparisons of natural and recycled aggregateconcretes prepared with the addition of different mineral admixtures, Cem.Concr. Compos. 33 (2011) 788–795, https://doi.org/10.1016/j.cemconcomp.2011.05.009.

[65] A. Alsaif, L. Koutas, S.A. Bernal, M. Guadagnini, K. Pilakoutas, Mechanicalperformance of steel fibre reinforced rubberised concrete for flexible concretepavements, Constr. Build. Mater. 172 (2018) 533–543, https://doi.org/10.1016/j.conbuildmat.2018.04.010.

R. Noroozi et al. / Construction and Building Materials 224 (2019) 173–187 187

[66] R. Siddique, T.R. Naik, Properties of concrete containing scrap-tire rubber–anoverview, Waste Manag. 24 (2004) 563–569.

[67] J.J. Brooks, M.A.M. Johari, Effect of metakaolin on creep and shrinkage ofconcrete, Cem. Concr. Compos. 23 (2001) 495–502.

[68] Z. Li, Z. Ding, Property improvement of Portland cement by incorporating withmetakaolin and slag, Cem. Concr. Res. 33 (2003) 579–584.

[69] R. Madandoust, S.Y. Mousavi, Fresh and hardened properties of self-compacting concrete containing metakaolin, Constr. Build. Mater. 35 (2012)752–760, https://doi.org/10.1016/j.conbuildmat.2012.04.109.

[70] P. Duan, C. Yan, W. Zhou, Influence of partial replacement of fly ash bymetakaolin on mechanical properties and microstructure of fly ashgeopolymer paste exposed to sulfate attack, Ceram. Int. 42 (2016) 3504–3517, https://doi.org/10.1016/j.ceramint.2015.10.154.

[71] S. Wild, J.M. Khatib, A. Jones, Relative strength, pozzolanic activity and cementhydration in superplasticised metakaolin concrete, Cem. Concr. Res. 26 (1996)1537–1544.

[72] M. Said-Mansour, E. Kadri, S. Kenai, M. Ghrici, R. Bennaceur, Influence ofcalcined kaolin on mortar properties, Constr. Build. Mater. 25 (2011) 2275–2282, https://doi.org/10.1016/j.conbuildmat.2010.11.017.

[73] P. Duan, Z. Shui, W. Chen, C. Shen, Effects of metakaolin, silica fume and slag onpore structure, interfacial transition zone and compressive strength ofconcrete, Constr. Build. Mater. 44 (2013) 1–6, https://doi.org/10.1016/j.conbuildmat.2013.02.075.

[74] S. Barbhuiya, P. Chow, S. Memon, Microstructure, hydration andnanomechanical properties of concrete containing metakaolin, Constr. Build.Mater. 95 (2015) 696–702, https://doi.org/10.1016/j.conbuildmat.2015.07.101.

[75] E.-H. Kadri, S. Kenai, K. Ezziane, R. Siddique, G. De Schutter, Influence ofmetakaolin and silica fume on the heat of hydration and compressive strengthdevelopment of mortar, Appl. Clay Sci. 53 (2011) 704–708.

[76] H. Hu, P. Papastergiou, H. Angelakopoulos, M. Guadagnini, K. Pilakoutas,Mechanical properties of SFRC using blended manufactured and recycled tyresteel fibres, Constr. Build. Mater. 163 (2018) 376–389, https://doi.org/10.1016/j.conbuildmat.2017.12.116.

[77] N. Otsuki, S. Miyazato, W. Yodsudjai, Influence of recycled aggregate oninterfacial transition zone, strength, chloride penetration and carbonation ofconcrete, J. Mater. Civ. Eng. 15 (2003) 443–451.

[78] A. Lotfy, M. Al-Fayez, Performance evaluation of structural concrete usingcontrolled quality coarse and fine recycled concrete aggregate, Cem. Concr.Compos. 61 (2015) 36–43.

[79] S. Mindess, J.F. Young, D. Darwin, Concrete (2003) 2003.[80] M. Leone, G. Centonze, D. Colonna, F. Micelli, M.A. Aiello, Fiber-reinforced

concrete with low content of recycled steel fiber: Shear behaviour, Constr.Build. Mater. 161 (2018) 141–155, https://doi.org/10.1016/j.conbuildmat.2017.11.101.

[81] J.M. Khatib, J.J. Hibbert, Selected engineering properties of concreteincorporating slag and metakaolin, Constr. Build. Mater. 19 (2005) 460–472,https://doi.org/10.1016/j.conbuildmat.2004.07.017.

[82] A. Alsaif, L. Koutas, S.A. Bernal, M. Guadagnini, K. Pilakoutas, Mechanicalperformance of steel fibre reinforced rubberised concrete for flexible concretepavements, Constr. Build. Mater. 172 (2018) 533–543.

[83] A.C.I. Committee, 325, Report on Roller-Compacted Concrete, Pavements(2001).