Use of recycled plastic in self-compacting concrete: A comprehensive review on fresh and mechanical properties

Journal Pre-proof Use of recycled plastic in self-compacting concrete: A comprehensive review on fresh and mechanical properties Rabar H. Faraj, Hunar F. Hama Ali, Aryan Far H. Sherwani, Bedar R. Hassan, Hogr Karim PII:

S2352-7102(19)32754-8

DOI:

https://doi.org/10.1016/j.jobe.2020.101283

Reference:

JOBE 101283

To appear in:

Journal of Building Engineering

Received Date: 5 December 2019 Revised Date:

7 February 2020

Accepted Date: 14 February 2020

Please cite this article as: R.H. Faraj, H.F. Hama Ali, A.F.H. Sherwani, B.R. Hassan, H. Karim, Use of recycled plastic in self-compacting concrete: A comprehensive review on fresh and mechanical properties, Journal of Building Engineering (2020), doi: https://doi.org/10.1016/j.jobe.2020.101283. This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. © 2020 Published by Elsevier Ltd.

Use of recycled plastic in self-compacting concrete: A comprehensive review on fresh and mechanical properties a

Rabar H. Faraj*, a Hunar F. Hama Ali, bAryan Far H. Sherwani, a Bedar R. Hassan, a Hogr Karim a

b

Civil Engineering Department, University of Halabja, Halabja, Kurdistan Region, Iraq

Civil Engineering Department, Faculty of Engineering, Soran University, Soran, Kurdistan Region, Iraq *Corresponding author: Tel: +964-7501125140; [email protected]; [email protected]

Abstract Due to manufacturing processes, municipal solid wastes and service industries, huge amount of waste materials are generated. Recently, a considerable growth in the plastic consumption across the globe can be observed. This has caused enormous quantities of plastic-related waste. Producing new materials such as mortar or concrete from recycling of plastic waste (PW) seems to be one of the best solution for disposing of PW since it is considerded to be environmentally and economically advantageous. In modern constructions, self-compacting concrete (SCC) is employed as a main cementitious material, which functions complex formworks without mechanical vibrations with high segregation resistance and greater deformability. Reuse of recycled plastic (RP) in SCC mixes can provide an environmentally friendly and sustainable construction material. Therefore, it has been an ongoing topic for several researches, and a large number of studies investigating the properties of SCC comprising waste and RP materials have been conducted. In this study, the current and most recent literatures considering plastic recycling method and the influence of plastic materials on the fresh and mechanical properties of SCC are summurized. So that a comprehensive review can be provided in which the reviewed studies are categorized into sub groups based on whether they dealt with SCC containing plastic aggregates (PAs) or plastic fibers (PFs). Furthermore, the effect of RP on the fresh and mechanical properties of various self-compacting composites like self-compacting mortar (SCM), self-compacting high strength concrete (SCHSC) and self-compacting light weight concrete (SCLC) have been reviewed to illustrate the differences with normal SCC.The empirical relationships among various mechanical properties were also developed. Based on the obtained results from previous studies, recycled plastic self-compacting concrete (RPSCC) can be used for structural applications due to its satisfactory fresh and mechanical properties. Moreover, this type of concrete is environmentally friendly and sustainable product due to replacing the natural aggregates (NA) with plastic materials. Keywords: Recycled plastic; Waste plastic; Self-compacting concrete; Recycled plastic Self-compacting concrete; Fresh properties, Mechanical properties. 1

1. Introduction Plastic is one of the most major innovations of 20th century and is an omnipresent material. Recently, the consumption of plastic has remarkabely grown which led to accumulating considerable PW across the globe [1]. Over the last decades, a large amount of non-degradable waste, particularly in the form of PW, have been proven to have serious challenges to the environement; moreover they are regarded as one of the most dangerous sources of pollution [2-7] . In 2017, 348 million tons of plastics were produced in the globe, of which 64.4 million tons were produced in Europe [8]. Fig. 1 shows the treatment of postconsumer plastics in 2017 by EU28+NO/CH. In 2017, mechanically recycled waste was approximately 31.1% of the total PW; 41.6% was recovered for energy; and the rest 27.3% was disposed [8]. However, in 16 out of 30 countries, the rate of the energy recovery was lower than the average value of 41.6%, as can be seen in Fig. 1. In 2006, The UN Environment Programme estimated that for every square mile of ocean, there are 46,000 pieces of floating plastic. Plastic debris can result in the death of approximately 100,000 sea mammals and higher than one million sea birds each year as are ingesting or becoming entangled it. The danger of PW seems to be increasingly serious. For these reason, the use of plastic bags has been restricted by many countries and some are in the process of conducting this [1].

Fig. 1. Post-consumer plastic Treatment in 2017 by EU28+NO/CH [8].

2

Because of the fact that plastic has slow rate of degradation and bulky nature, land-filling of plastic can also be hazardous. The waste bulk might obstruct the ground water flow and it can also restrict the roots movement. It should also be known that PW can pollute soil and water when mixing with the rain water because it contains various toxic elements especially lead and cadmium. Therefore, to reduce the influence of PW on the environment in terms of energy consumption and natural resource, waste disposal, global warming and environmental pollution, the recycling of PW can be one of the best sollutions. There are varieties of recycling methods among which the reuse of RP materials in the construction industry can be regarded as an ideal way for disposing PW. To reduce amount of waste materials, many researches have been conducted to use waste material as an alternative to NA in mortar or concrete mixtures [9-13, 85, 87]. To investigate the implementation of PW in conventional concrete mixture, numerious studies have already been done. There are some examples of PW examined in the studies such as PET bottle [14-20], Polycarbonate PW particles [21], poly vinyl chloride (PVC) pipe [22,23], high density polyethylene (HDPE) [24], thermo- setting plastics [25], polypropylene aggregates [26], shredded and recycled PW [2, 27,28], expanded polystyrene foam (EPS) [29,30], glass reinforced plastic (GRP) [31], polycarbonate [32], polyurethane foam [33, 34], poly-propylene fiber [35] as a fiber or aggregate in the production of concrete. SCC as a type of special concrete, due to its own weight, can easily slide and flow inside different parts of the formwork and generate a remarkable consolidaton within the targeted formwork. It does not need any external and internal vibration and leaves no defects as the result of bleeding and segregation [36-38]. In order to obtain full compaction this concrete should be highly flowable and cohesive [39]. The flowability of the mixture can be achieved by adding superplastisizer admixtures, on the other hand, the cohesiveness and the resistance to segregation can be obtained by adding an appropriate dosage of viscosity modifying admixtures (VMA) [40]. SCC was first developed in Japan in 1980s to improve durability and stability of concrete structures [38, 41-43]. For some congested reinforcement areas where vibrating methods cannot be applied, SCC can be used because it is capable of flowing through these areas. This is considered to be tha main advantage of SCC over the traditional one [10]. The improvement of SCC’s stability and workability can be obtained by mixing fine substances such as silica fume, limestone powder, GGBFS, and fly ash [44, 45]. Due to the constitution of an extremely condensed microstructure of the mixture of these elements, high values of compressive strength and durability enhancements can be obtained, but the failure mode of SCC is still brittle [46]. SCC also provides a better environmental condition because it eliminates the vibration noise, increases productivity rate and gives desingers more flexibility in the design of column-beam intersections [47].

3

Recently, numerous works on the use of RP in SCC and self compacting mortars (SCM) have been done to investigate various engineering properties. Generally, plastics were incorporated in SCC especially in two forms: (1) plastic aggregates (PA), which was an alternative of NAs and (2) plastic fibers (PF), which were implemented in fiber-reinforced self-compacting concrete (FRSCC). Among the RP types used in the SCC in the current literature, it includes: PP plastic particles [12, 48], (PET) plastic bag particles [49], PET waste plastic fibers [50-52], Polyethylene Terephthalate (PET) particles [53, 54], High impact polystyrene (HIPS) granules [55, 56], polypropylene fibers [57-62], plastic waste powder [63], plastic bag waste fibers (PBWF) [64], PVA fibers [65], high toughness poly-propylene (PPHT) fibers [65], shredded and recycled plastic waste [66], Polystyrene lightweight aggregate [67, 68], Expanded polystyrene (EPS) [69, 70]. A comprehensive review of papers regarding the use of RP utilization in cement mortar and concrete preparation are available in the literature [1, 71-74] . However, a review on the incorpotation of different RPs in the production of SCC to produce RPSCC is not available yet. Moreover, an evident representation on the different important properties of SCC containing PAs and PFs in the preparation of SCC has been provided in several works that have been published previously. Therefore, from the author’s standpoint, a comprehensive review might be desirable to focus on the most recent progress on the evaluation of this material as in the production of SCC. Additionally, in this paper, an up-to-date comprehensive review for studies available until 2019 on the use of RP as a partial substitution of aggregates or as fiber addition in SCC preparation is presented. Contrasting normal concrete, due to the variety properties of SCC in its fresh state, this paper focuses on the fresh properties of RPSCC such as Lbox height ratio, V-funnel flow time, J-ring test, segregation resistance, slump flow diameter, T50 slump flow time, density and air content. The different mechanical properties of RPSCC are also reviewed in detail. Moreover, the effect of RP on the properties of dissimilar self compacting composites such as selfcompacting mortar (SCM), self-compacting light weight concrete (SCLC), self-compacting high strength concrete (SCHSC) and recycled aggregate self-compacting concrete (RASCC) is also reviewed to illustrate the differences with normal SCC. In the end, the empirical models among different mechanical properties are proposed. 2. Plastic properties used in SCC 2.1 Preparation of recycled plastics In SCC, two main forms of plastic are generally used; namely, PA and PF. Different studies were performed using PAs. The majority of these PAs were prepared from PW attained from various sources. In the laboratory, plastic bottels were generally grinded by using a grinding machine and then sieved in 4

order to achieve the desired size fraction [53, 54, 66]. Further, PW with proper sizes was collected from PW treatment plants or plastic production plants [49]. In these circumstances, it is only required to sieve into proper size range at the laboratory. In general, the PP plastic particles was firstly prepared by recycling, then grinding it into small possible particles and cleaned. They were finally treated to obtain short columns with different lengths [12, 48]. Kan and Demirbog [29,30] heated the crushed waste EPS in an oven to obtain the modified EPS aggregates; the obtained fine aggregates (FA) and coarse aggregates (CA) had bulk densities of 310–340 kg/m3 and 220–240 kg/m3, respectively. In other studies, for the use of PFs, plastic drinking bottles were cut by hand or by paper shredder or CD's cutter machine to produce the waste fibers (WF) [50-52]. Ghernouti et al. [64] used plastic bag waste to produce PBWF. At a temperature around 250 °C, the plastic bags waste were regenerated, and then finilized as a fibrous pulp that passes through cooling and hardening processes in a tank of water. Then they were cut in fibers. Fig 2 shows some types of recycled plastics which were used in the production of SCC.

a)

b)

c)

d) 5

e)

f)

g)

Fig. 2 Some types of recycled plastics used in the production of SCC (a): PP particles [12, 48]; (b): PET fibers [50]; (c): PET fibers [52]; (d): PET particles [53]; (e): PBWFs [64]; (f): shredded PET particles [66]; (g): Polystyrene lightweight aggregate [67, 68].

2.2 Types and utilization of plastic aggregates and plastic fibers in SCC

In the literature, the addition of PW as fibers in the SCC to improve the properties of the composite have been focused on in several studies. On the other hand, the use of PW to replace the NA in the production of SCC has been conducted in some other investigations. The replacement of both coarse and fine sized natural aggregate by PAs can be reasonable since PAs are generally produced from big sized PW materials. The replacement of cement with PW powder was also reported in the literature [63]. Table 1and 2 highlights the types and utilization of PWs in the preparation of SCC composites.

6

Table 1 Types and utilization of recycled plastic aggregates in the preparation of SCC composites. Refs.

Composite types

Replacement amounts

Type of plastic

Particle size/shape

Properties of plastic aggregates Apparent density (kg/m3) =510

[49]

SCM

FA 10, 20, 30, 40, 50 vol.%

Recycled (PET) plastic bags

0.15-5 mm/ round and smooth

Specific gravity (g/cm3) = 0.96 Water absorption = 0.01% Specific surface (m2/kg) = 1.67

[53]

SCC

FA 5, 10, 15 wt.%

0.15-4.75 mm/ plane shape

SCC

FA 10, 20, 30, 40 vol.%

High impact polystyrene (HIPS) granules

1.18-3mm/ round and smooth

SCC

FA 2.5, 5, 7.5, 10, 12.5 vol.%

shredded and recycled plastic waste

0.15-1mm and 1-4mm/ plane shape

[55] [56]

[66]

Polyethylene Terephthalate (PET) particles

[48]

SCLC

FA 10, 15, 20, 30 vol.%

Polypropylene (PP) plastic particles

1.5-4mm/ round and smooth

[12]

SCHSC

medium size aggregate 10, 20, 30, 40 vol.%

Polypropylene (PP) plastic particles

4-8mm/ round and smooth

Specific gravity (g/cm3) = 1.2 Water absorption = 0.016% Specific gravity (g/cm3) = 1.04

Specific gravity (0.15-1mm plastic waste) (g/cm3) = 0.52 Specific gravity (1-4mm plastic waste) (g/cm3) = 0.68 Apparent density (kg/m3) = 950 bulk density (kg/m3) = 515 Specific gravity (g/cm3) = 0.95

Bulk density (kg/m3) = 417.87 [54]

SCC

FA 2.4, 6, 8.6, 12 wt.%

Polyethylene Terephthalate (PET) particles

4.75 mm< / Flaky or flat particles

Specific gravity (g/cm3) = 1.375 Melting temperature °C = 230-250 Tensile strength (MPa) = 79.3

[68]

Normal and high strength lightweight SCC

FA 20 , 30 vol.%

Polystyrene (BST)

-

-

[67]

SCLC

FA 10, 20 , 30 vol.%

Polystyrene (BST)

-

Specific gravity CA(g/cm3) = 0.018

[69] SCLC

FA and CA 10, 15, 22.5, 30 vol.%

Expanded polystyrene (EPS)

FA (0-4.75 )mm, CA (4.75-9.5)mm/ spherical

[70]

[63]

bulk density CA (kg/m3) = 10.4 Specific gravity FA(g/cm3) = 0.025 bulk density FA (kg/m3) = 13.6

SCC

Cement 5, 10, 15, 20, 25 wt.%

plastic waste (PVC) powder

Mean Diameter = 153 (µmm)/ spherical and smooth

Specific gravity (g/cm3) = 1.53 Water absorption = 0.0 %

[84]

SCC

FA 5, 10, 15, 20, 25, 30, 35, 40 vol.%

Polyethylene boxes waste

4.75 mm< / round particles

Specific gravity (g/cm3) = 0.94

[85]

SCC

FA 0.5, 0.75, 1, 1.25 wt.%

Polyethylene Terephthalate (PET)

1-4mm/ plane shape

-

7

Table 2 Types and utilization of recycled plastic fibers in the preparation of SCC composites Refs.

[50]

Types of composite

Amounts in SCC

Type of plastic

fiber size/shape

Properties of plastic fibers

Polyethylene Terephthalate (PET) waste fibers

Dimensions (length*width*thickness)= 10mm*2mm*0.3mm/ rectangular shape

Specific gravity (g/cm3) = 1.12

SCC

0.25, 0.5, 0.75, 1, 1.25, 1.5, 1.75, 2 vol.%

Density (kg/m3) = 1100 [52]

SCC

0.25, 0.5, 0.75, 1, 1.25, 1.5, 1.75, 2 vol.%

Polyethylene Terephthalate (PET) waste fibers

Dimensions (length*width*thickness)= 35mm*4mm*0.3mm/ rectangular shape

Aspect ratio (l/d) = 28 Tensile strength (MPa) = 101 Modulus of Elasticity (GPa) = 0.19 Density (kg/m3) = 1100

[51]

SCC

0.25, 0.5, 0.75, 1, 1.25, 1.5, 1.75, 2 vol.%

Polyethylene Terephthalate (PET) waste fibers

Dimensions (length*width*thickness)= 30mm*4mm*0.3mm/ rectangular shape

Aspect ratio (l/d) = 28 Tensile strength (MPa) = 101 Modulus of Elasticity (GPa) = 0.19 Specific gravity (g/m3) = 0.93

[58]

self-compacting cement paste

0.75 and 1.5 vol.%

PP fibers

Dimensions (length*width*thickness)= 12mm*150µm *18µm/ rectangular shape

Melting temperature °C = 171 Thermal conductivity (w/m.K) =0.15

Specific gravity (g/m3) = 0.91 [59]

SCC

3, 6, 9 and 12 kg/m3

monofilament PP fibres

Dimensions (length*diameter) = 45mm*1mm/ Wavy shape

Tensile strength (MPa) = 320 Modulus of Elasticity (GPa) = 5.88

[64]

SCC

1, 3, 5 and 7 kg/m3

plastic bag waste fibers (PBWF)

Dimensions/ Length = (2cm,4cm, 6cm), diameter = (1.6-2mm)

poly-vinyl-alcohol (PVA) fibers

Dimensions (length*diameter) = 12mm* 0.2mm

Specific gravity (g/m3) = 0.87 Modulus of Elasticity (GPa) = 0.03 Aspect ratio (l/d) = 62

0.8 and 0.6% by volume

Tensile strength (MPa) = 1000 Modulus of Elasticity (GPa) = 30

[65]

SCC Aspect ratio (l/d) = 51-57 0.8 and 0.6% by volume

high toughness polypropylene (PPHT) fibers

Dimensions (length*diameter) = 35mm* (0.62-0.69)mm

Tensile strength (MPa) = 600-750 Modulus of Elasticity (GPa) = 3.8 Density (kg/m3) = 905

[61]

[62]

SCC

0.1, 0.15, 0.2, 0.25 vol.%

PP fibers

Dimensions (length*diameter) = 65mm*0.85mm/ Crimped

RASCC

Aspect ratio (l/d) = 76.5 Tensile strength (MPa) = 250 Modulus of Elasticity (GPa) = 3 Density (kg/m3) = 900

[86]

SCLC

1.06, 1.08, 1.1, 1.12 kg/m3

PP fibers

Length of fibers = 12 mm

Tensile strength (Mpa) = 350 Melting point °C = 160

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2.3 Mixing procedure and design of SCC containing recycled plastic

To design mixtures of SCC containing RPs, no standarized methodology is available because of the different types and properties of RPs. Generally, the design, production and casting of RPSCC mixtures are similar to the normal SCC mix designs. Several previous studies [12, 50, 54, 63] followed the mixing procedure proposed by Khayat et al. 2000 [75]. However, there is a variety of mixture design methods for normal SCC from which five different classifications are categorized: Empirical design methods, compressive strength methods, close aggregate packing methods, statistical factorial models, and rheological paste models [76]. 2.4. Evaluated properties

The fresh properties of SCC such as flowability, passing ability, filling ability, segregation resistance, density/unit weight and air content and various strength characteristics and elasticity modulus of hardened SCC were generally studied in the literature as shown in Table 3. Further, several durability properties along with other special properties such as fire behaviour, thermal insulation and microstructure behavior were also considered in the past investigations. However, due to the varieties of fresh properties and tests of SCC this study only focused on the fresh and mechanical properties of RPSCC. The applied normal procedures for conventional SCC were conducted to evaluate the fresh and mechanical characteristics. Table 3 Fresh and mechanical properties of RPSCC reported in the literature. Slump

Sulmp

flow

flow

diameter

time

[49]

√(mini slump)

√

[53]

√

√

[55]

√

[54]

√

√

[48]

√

√

[12]

√

√

[66]

√

√

[68]

√

√

Refs.

V-

L-

funnel

box

flow

heigt

time

ratio

√

√

√

√

√

√

JRing test

Density

fresh

√

Air

Compressive

Tensile

Flexural

Elasticity

Fracture

resistance

content

strength

strength

strength

modulus

parameters

√

√ (porosity)

√

√

√

√

√

√

√

dry

√ √

√

√

Segregation

√

√

√

√

√ (Poisson’s ratio)

√

√

√

√

√

√

√(stress/strain)

√

√

√ √

√

√

9

√

√

√

√

√

√

√

√

√

√

√

√

√

√

√

√ √

√

√

√

[69]

√

√

√

√

√

[70]

√

√

√

√

[50]

√

√

√

√

[52]

√

√

√

[51]

√

√

√

[59]

√

[64]

√

[65]

√

[61]

√

√

√

√

√

[62]

√

√

√

√

√

[84]

√

√

√

√

√

√

√

[85]

√

√

√

√

√

√

√

[86]

√

√

√

√

√

√

√

√

√

√

√ (stress/strain)

[67]

√

√ √

√

√

√

√

√

√

√

√

√

√

√

√

√

√ (impact)

√

√

√

√

√ √

√

3. Review of fresh properties of SCC containing PAs and PFs

The research outcomes associated with the influences of PA and PF on the properties of RPSCC are presented, and the sub-categories of SCC containing PA and PF are summarized in this section as shown in Table1 and 2. The fresh properties of SCC were evaluated by carrying out the tests identified under the guidelines published by EFNARC, 2005 [36]. The flowability, passing ability, resistance to segregation and viscosity can be assessed in the experimental tests. Table 4 shows the lower and upper bounds for EFNARC classes. In the next sections, the most significant practical tests to evaluate the aforementioned fresh properties of SCC are reviewed and discussed.

Table 4 passing ability, viscosity and slump flow classes according to EFNARC [36] Class

Slump flow diameter (mm)

Slump flow classes SF1

550-650

SF2

660-750

SF3

760-850

10

√

Class

T50 (s)

V-funnel time (s)

VS1/VF1

≤2

≤8

VS2/VF2

>2

9-25

Viscosity classes

Passing ability classes PA1

≥ 0.8 with two rebar

PA2

≥ 0.8 with three rebar

3.1 Slump flow diameter and slump flow time 3.1.1 Effect of PAs

Slump flow test is considered to be a sensitive test, because it simulates the fluidity of a fresh concrete in unconfined conditions. For checking the consistence of fresh concrete with respect to the specification (EFNARC, 2005) [36], this test can mainly be used. Hence, it can normally be specified for all SCCs. Moreover, from the measurement of T50 time, additional knowledge about segregation resistance can be obtained. T50 time is the measured time for spreading the concrete to a diameter of 500 mm (Fig.3a). The influence of RPs as FA substitution on the fresh properties of SCC has been investigated and reported in several studies. Research outcomes have shown conflicting performances of slump flow diameter and T50 slump flow time under the influence of RP types, as demonstrated in Fig.4. The effect of plastic type, plastic size, plastic replacement level, and replaced material on the slump flow behavior of SCC was evident [12, 48, 53-55, 66, 69]. In most studies, it is claimed that the increment of the percentage of plastic content results in the decrease of the slump flow diameter [12, 53, 54, 66]. Mohammed M.K. et al. [54] substituted FA with recycled PET aggregates at different percentages (2.4, 6, 8.6 and 12% by weight). They noticed that the optimum performance regarding the slump flow diameter of the SCC can be obtained by adding 2.4% of PET aggregates. In the previous studies, it was observed that the flaky and plane particle shape could be the most important factor to reduce the slump flow and behave as restraining material to slow down the flow. On the contrary, in some other studies, different findings were observed. This is mainly because the round and smoother plastic particle as replaced materials was used in the experiments [48, 55, 69]. Madandoust et al. [69] indicated that there was a slight increase in the slump flow diameter of SCC with the increment of EPS content for the same (w/c) ratio. This can be attributed to the fact that replacing natural angular aggregates by EPS granules which are smooth and spherical in shape resulted in decreasing the internal friction [69].

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On the other hand, several studies investigated the T50 slump flow time and different findings were also reported as can be seen in Fig.5 [12, 48, 66, 67, 69]. Madandoust et al. [69] concluded that for the mixture containing higher percentages of EPS, T50 was higher at the same (w/c) ratio. On the other hand, R.H. Faraj, et al. [12] reported slightly lower slump flow time because of increasing PP aggregates content from 0% to 40% by volume replacement with natural medium aggregate. The different properties of plastics such as their surface texture, shape and size can result in the discrepancy of these outcomes. It is worth highlighting that most of the results reported by the researchers presented in Fig.4 and 5 are wellmatched with the limitations provided by EFNARC [36] (Table 4) for different SCC classes.

a: slump flow test

b:V-funnel flow time test

c: L-box test

d: J-Ring test.

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e: Sieve stability test

f: Column segregation test.

Fig. 3. The apparatus used for measuring all the properties of the fresh state of SCC [48, 66, 64]

Fig. 4. Variation of slump flow diameter of SCC with replacement level of PAs (1), (2): PP medium aggregates (SCHSC) [12]; (3): HIPS fine aggregates (SCC) [55]; (4), (5), (6): PET fine aggregates (SCC) [66]; (7): PP fine aggregates (SCLC) [48]; (8): Polystyrene fine aggregates (SCLC) [67]; (9), (10), (11): EPS mixed aggregates (SCLC) [69]; (12), (13),(14): PET fine aggregates (SCC) [53]. [Solid lines: Replacement level by volume; dotted lines: Replacement level by weight].

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Fig. 5. Variation of T50 slump flow time of SCC with replacement level of PAs (1), (2): PP medium aggregates (SCHSC) [12]; (3): PP fine aggregates (SCLC) [48]; (4), (5), (6): PET fine aggregates (SCC) [66]; (7), (8), (9): EPS mixed aggregates (SCLC) [69] (10): Polystyrene fine aggregates (SCLC) [67].

3.1.2 Effect of PFs The slump flow diameter always decreases with growing PF content, irrespective of PF types and content [50, 51, 59, 61, 62, 65]. In some studies, the utilization of PFs to the SCC mixtures was by volume (Fig. 6), whereas in a few other studies it was done by weight (Fig. 7). Al-Hadithi and Hilal [50] studied the use of waste PFs via cutting plastic beverage bottles by hand at different percentages from 0% to 2% by an increment of 0.25%. They concluded that the increase of PF content remarkably lead to the increment of the slump flow diameter. Similar results were found in other studies even though different PF types and percentage contents were used [61, 62]. Gencel et al. [59] studied the workability properties of SCC with four PF contents at 3, 6, 9 and 12 kg /m3. The authors stated that there was a % 22.6 reduction in the slump flow diameter when 12 kg /m3 of PP fiber were utilized to the conventional SCC irrespective of cement content. Entangling fibers together and forming clusters at the center of the flow spread tends to endanger the ability of concrete to flow [50]. Ghernouti et al. [64] used PBWFs with three different lengths (2cm, 4cm and 6cm) and four different percentages contents (1, 3, 5 and 7 kg/m3) in the production of SCC. On the contrary to other findings, they noted that there was a slight increase of the slump flow diameter of SCC with increment of waste PFs content for all three different lengths. It can also be stated that the effect of the aspect ratio (l/d) of PFs on the slump flow was not significant as much as the effect of their content percentage [77].

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The slump flow time increased with growing the PF content as demonstrated in Fig. 8. Aslani F. et al. [62] utilized PP fibers at different volume percentages (0.1, 0.15, 0.2, and 0.25%) into the SCC. They reported that the time (T50) for SCC tends to increase with the increment of the fiber fraction. Al-Hadithi and Hilal [50] also reported that T50 exceeded the limits of EFNARC if the addition of waste PF content was more than 0.75%; this is because of the cumulative adverse effect for polymer fibers and higher fiber factor. Similar results were also found by Gencel et al. [59].

Fig. 6. Variation of slump flow diameter of SCC with PF contents in volume (1), (2): PET fibers (SCC) [50, 51]; (3): PP fibers (SCC) [61]; (4): PP fibers (RASCC) [62]; (5): PVA fibers (SCC) [65].

15

Fig. 7. Variation of slump flow diameter of SCC with PF contents in weight (1), (2): PP fibers (SCC) [59]; (3): PBWF [64]. [LF: Length of fiber].

Fig. 8. Variation of T50 slump flow time of SCC with PF contents (1), (2): PET fibers (SCC) [50, 52]; (3): PET fibers (SCC) [51]; (4): PP fibers (SCC) [61]; (5): PP fibers (RASCC) [62]; (6), (7): PP fibers (SCC) [59]. [Solid lines: Replacement level by volume; dotted lines: Replacement level by weight].

3.2 V-funnel flow time 3.2.1 Effect of PAs The V-Funnel test is usually carried out to assess the flowability and viscosity of SCC mixtures. In a simple procedure, the flow time is determined. The funnel is entirely filled with concrete, and the flow time is measured between two time intervals; time of the opening of the orifice and the complete emptying of the funnel (Fig 3b). Good, stable, and flowable concrete needs a short period to flow out. The viscosities in the EFNARC SCC guide are classified into two classes with respect to the measured Vfunnel and T50 slump flow times. As can be seen in Fig.9 different results were observed in the literature. The V-funnel flow time remarkably increased when FA was replaced by PET plastic particles, because of the plane shape of this type of plastics as they can stick together and this can negatively affect the fresh properties of RPSCC [53, 54, 69]. Hama and Hilal [66] observed that the V-funnel flow time was steadily increased with the increment of PET aggregate content. They also indicated that the reference concrete can be classified as VF1 class, but the substitution of FA with RP shifted the viscosity class from VF1 to VF2. Madandoust et al. [69] reported that for higher EPS volume percentages, the longer V-funnel time 16

was obtained. They found that, the utilization of EPS up to 30% by volume led to the change of a Vfunnel flow time of the reference SCC mixture from 6.2 seconds to 13.6 seconds. On the other hand, the replacement of up to 30% of FA with High Impact Polystyrene (HIPS) grains declines the V-funnel flow time; this can be due to the round shape and smooth surface texture of the particles which can flow easier than natural FA [55]. Based on the literature, most of the obtained results of the RPSCC mixtures can be categorized into VS2/VF2 viscosity classes.

Fig. 9. Variation of V-Funnel flow time of SCC with replacement level of PAs (1): HIPS (SCC) [55]; (2), (3), (4): PET fine aggregates (SCC) [66]; (5), (6), (7) EPS mixed aggregates (SCLC) [69]; (8), (9), 10): PET fine aggregates (SCC) [53]. [Solid lines: Replacement level by volume; dotted lines: Replacement level by weight].

3.2.2 Effect of PFs Utilization of PFs considerably influences the filling ability of SCC. Previous studies have shown that the V-funnel flow time increases remarkably with the increment of PF contents as illustrated in Fig.10 [5052, 59]. Al-Hadithi and Hilal [50] reported the increase of V-funnel flow time from 9 second to 25 seconds by raising the volume of PET fiber content from 0% to 2%. Equivalent results were also obtained by Al-Hadithi et al. 2019 [52]. This increment is reasonable because adding fibers can reduce the fluidity properties of SCC owing to grow internal resistance resulting from the decrement in the thickness of cement paste layer surrounding aggregate particles. Further, both plastic viscosity and friction between aggregate tend to increase. This is also similar for friction between aggregate and fibers [50]. Gencel et al. [59] also examined the effect of PP fibers on the filling ability of SCC by including four different PP fiber contents (3, 6, 9 and 12 kg/m3). They also found that increasing the PP fiber content can adversely affect the filling ability of SCC. The authors applied multiple regression analysis so that the effects of fiber and 17

cement content on the viscosity of the concrete could be quantified and consequently, the following equations were obtained: Vf =13.02-0.00198 S+0.8017 P (R2 = 0.9966)

(1)

Sf = 608.5+0.332 S-14.9833 P (R2 = 0.9882)

(2)

Where Vf is the V funnel flow time (s), P is the PF content (kg /m3), S is the cement content (kg/ m3), and Sf is the slump flow (mm).

Fig. 10. Variation of V-Funnel flow time of SCC with PF contents (1): PET fibers (SCC) [52]; (2): PET fibers (SCC) [50]; (3): PET fibers (SCC) [51]; (4), (5): PP fibers (SCC) [59]. [Solid lines: Replacement level by volume; dotted lines: Replacement level by weight].

3.3 L-box height ratio 3.3.1 Effect of PAs The L-box height ratio by means of H2/H1 ratio can be used to specify the passing ability of the SCC. In the test, the ability of SCC to pass through congested reinforcement can be simulated using two or three bar L-box test (EFNARC, 2005) [36] as shown in Fig. 3c. To ensure and certify the required passing ability of SCC, the L-box height ratio must be equal to or greater than 0.8. L-box height ratio value is 1.0 for perfect fluid behavior of SCCs. The L-box height ratio values considerably decreased with the increment of the replacement level of PET plane shape particles content, as shown in Fig.11. This means that the ability of fresh RPSCC to pass through the congested reinforcement decreased [53, 66]. This

18

might be due to the fact that plane PET particles can stick together preventing passing the fresh RPSCC easily between rebars [53]. Madandoust et al. [69] reported that increasing EPS volume content from 0% to 30% lead to the change of the L-box blocking ratio of SCLC containing EPS from 0.95 to 0.78, as shown in Fig. 11. According to their results SCLC with 10% EPS produced the highest blocking ratio and the lowest was for SCLC with 30% EPS at the same (w/c) ratio. From Fig. 11, it can be observed that the blocking ratio maximizes for 10% substitution of EPS. The incorporation of angular aggregates by EPS with round shape and smooth surface might play a significant role in obtaining such behavior. Nevertheless, if the increment of the replacement of EPS exceeds 10%, the passing ability of the fresh concrete between the steel bars tends to decrease. This can be due to the fact that the influence of the surface characteristic of EPS aggregate is governed by the undesirable influence of its self-weight [69, 70]. However, the utilization of HIPS granules can improve the passing ability of RPSCC, compared to the PET plastic particles. In order to obtain better fresh properties, HIPS replacement level up to 30% with FA can be feasible [55]. The spherical shape of HIPS particles can be the sole reason for the better performance of it in all fresh RPSCC tests, compared to the natural FA [55]. According to Fig. 11, the majority of RPSCC reported results can be at the satisfactory level with the EFNARC limitation for the given L-box height ratio.

Fig. 11 Variation of L-box height ratio of SCC with replacement level of PAs (1): HIPS (SCC) [55]; (2), (3), (4): EPS mixed aggregates (SCLC) [69, 70]; (5), (6), (7): PET aggregates (SCC) [66]; (8), (9), (10): PET fine aggregates (SCC) [53]. [Solid lines: Replacement level by volume; dotted lines: Replacement level by weight].

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3.3.2 Effect of PFs Fig.12 presents the results of the previous studies about the impact of PF quantity on the passing ability of SCC. The results show that there is a systematical decrement of L-box height ratio with increasing the waste PFs [50-52, 64]. Al-Hadithi et al. [52] indicated that the percentage of (H2/H1) decreased because of the addition of waste PFs into the SCC mixes, with low flow velocity. This was as a result of high viscosity of mixtures containing waste PFs as the consequence of impeding the flow by fibers. Thereby, there will be an increment of the internal friction between the particles of aggregates, the friction among the aggregates and with low flow velocity, and the friction between the aggregates and fibers with steel reinforcement. Ghernouti et al. [64] investigated the effect of PBWF lengths (2, 4 and 6 cm) at different percentage contents (1, 3, 5 and 7 kg/m3) on the passing ability of SCC. They reported that there was a significant decrement in the passing ability of SCC among rebars with increasing the length of PBWFs as shown in Fig. 12. They also found that the increase of fiber length of PBWF exceeding 4 cm resulted in immobility of SCC mixes in confined environment. Consequently, EFNARC limitations were not satisfied with the produced SCC mixtures. Reasonably, the spacing between the reinforcement of the Lbox, which is in the order of 3.5 cm, is likely to exceed owing to the length of fibers (4 and 6 cm) [64].

Fig. 12. Variation of L-box height ratio of SCC with PF contents (1), (2): PET fibers (SCC) [50, 52]; (3) PET fibers (SCC) [51]; (4): PBWF fibers (SCC) [64]. [LF: length of fiber].

3.4 J-ring test 3.4.1 Effect of PAs Similar to L-box test, the J-ring test can also be conducted along with the slump flow test to assess the ability of concrete to pass through rebars [78]. The measured difference between the height of concrete 20

outside and inside the ring is denoted as J-Ring height (∆H). In order to obtain appropriate flow through the rebars, the value of ∆H should be smaller than 50 mm for the SCC [78]. The J-ring is steel circular ring and 16 round steel rods with 16 mm in diameter and 100 mm in height are equally circulated, as shown in Fig. 3d. It follows the German SCC guideline [79]. Yang, S., et al. [48] substituted FA with PP plastic particles at various percentages. They stated that, for the SCLC containing 0% plastic, the passing ability is relatively weak. They also observed that the J-Ring height value was (55 mm) for fresh SCLC containing 0% PP particles, as shown in Fig.13, which was slightly larger than the desired value (50 mm) [78]. They found that the passing ability of SCLC can be improved by the utilization of plastic particles and this decreases the J-Ring height values to lower than 50 mm. The replacement level of 10% and 15% provided the lowest value (Fig.13). On the other hand, Law et al. [67] observed that the J-Ring Height value increased from 10 mm to 50 mm by increasing polystyrene aggregates from 0% to 30%. This means that increasing polystyrene aggregates content in the lightweight SCC can result in a considerable increase in J-Ring height value, which indicating poor workability. Opposite Behavior for this type of plastic was reported by Aslani and Ma [68], which they observed that J-Ring height difference values were gradually decreased by incorporating 20% and 30% of polystyrene aggregates into the high-strength lightweight SCC. They also reported that polystyrene aggregates were highly prone to segregation due to their ultra-light weight nature. Therefore, they suggested that a higher dosage of VMA was required to control segregation.

Fig. 13 Variation of J-Ring height difference of SCC with replacement level of PAs (1): PP aggregates (SCLC) [48]; (2): Polystyrene aggregates (SCLC) [67]; (3): Polystyrene aggregates (HSSCC) [68].

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3.4.2 Effect of PFs The inclusion of PFs can influence the passing ability of SCC, as shown in Fig.14. Generally, the J-ring height values also increased with increasing PF contents [59, 61, 62]. As mentioned before, the value of Jring height should be smaller than 50 mm so that the adequate flow through the rebars can be achieved for SCC [78]. Gencel et al. [59] reported that there was a slight increase in the J-ring height value with the addition of PP fibers content for different binder content SCC mixtures. They also observed that fibers can lead to blocking of particles during flow and are relying on fiber quantity in the mix. Aslain F. et al. [62] also noted that there was a fluctuated behavior in the J-ring height value for RASCC. They indicated that the J-ring height value increased from 12.5 mm to 53 mm due to increasing the PP fiber contents from 0% to %0.25. But there was an exception that for the mixture containing 0.2% PP fiber contents its value was fluctuated to 34 mm.

Fig. 14 Variation of J-Ring height difference of SCC with PF contents (1): PP fibers (RASCC) [62]; (2): PP fibers (SCC) [61]; (3), (4): PP fibers (SCC) [59]. [Solid lines: Replacement level by volume; dotted lines: Replacement level by weight].

3.5 Segregation resistance 3.5.1 Effect of PAs Column segregation test can be conducted for SCC to evaluate the PA distribution. This test consists of a steel circular column having four short sections with diameters of 200 mm and heights of 165 mm, as shown in Fig. 3f. The fresh concrete is poured to the column and left to set for 15 minutes. Afterwards, the four samples are successively removed one by one from the top and the mortar is washed out on a 5 22

mm sieve to retain CA [80, 81]. Thus, the mass of CA in each short column can be weighted and the ratio of the CA content in each column to the total mass of CA is determined. The coefficient of variation, symbolized as the aggregate segregation index Iseg [81], can be determined based on the four ratios and used to evaluate the uniformity of the CA distribution. Yang et al. [48] examined the influence of involving PP granules on the uniformity of CA distribution in the SCLC. Their results are demonstrated in Fig. 15. They found that the achievement of uniformity of the lightweight aggregate distribution was available for all substitution levels of SCLC, as illustrated in Fig. 15. They also observed that there was a marginal influence on the CA distribution when plastic was incorporated.

Fig. 15. Variation of Isegvalues of SCC with PAs content (SCLC) [48].

3.5.2 Effect of PFs The stability of SCC can also be assessed by performing sieve stability test. The range of sieve stability values must be in 0-15% [64] (see Fig. 3e). Ghernouti et al. [64] studied the influence PBWFs on the sieve stability of SCC. In the study, three different lengths of fibers (2 cm, 4 cm and 6 cm) were used. They found that there was a segregation rate lower than 15% for all SCC mixtures containing PFs with a length of 2 and 4 cm. This is considered as a good stability, as shown in Fig.16. They also observed that there was a dramatic increase in segregation ratio of RPSCC by increasing the dosage and length of the fibers.

23

Fig. 16. Variation of sieve stability values of SCC with PF contents (SCC) [64] [LF: length of fiber].

3.6 Fresh and/or dry density 3.6.1 Effect of PAs Because of the lightweight nature of plastic particles compared to the natural aggregates, the utilization of plastic particles as NA generally results in the decrease of fresh and dry densities of the resulting SCC, regardless of the type and size of replacements [22, 48, 49, 53, 55, 74, 82, 83]. Some of the results are illustrated in Fig. 17. During concrete casting, the fresh density of SCC mixtures can be measured. Chunchu and Putta [55] reported that the addition of HIPS granules in 10%, 20%, 30% and %40 resulted in a systematic decrease of the fresh densities of SCC by 4.10%, 8.52%, 10.29% and 15.08% respectively. Safi et al. [49] studied the dry density of SCM containing recycled PET plastic as FA. Their results indicated that a concrete containing 50% plastic particles as a replacement of sand, its dry density was likely to decrease by 37.5% below the reference mortar. They also found that the bulk density of 1500 kg/m3 could be obtained for the mortars containing 50% plastic waste, as illustrated in Fig. 17. Chunchu and Putta [55] also found 4.12%, 9.45%, 10.73% and 13.08% lower dry densities of SCC mixtures comprising 10%, 20%, 30% and 40% HIPS plastic granules, respectively. Similarly, Madandoust et al. [69] also indicated that increasing the EPS volume from 0% to 30% significantly decreases the density of SCLC, while aggravating other measured fresh properties of SCLC. They noticed that fresh behavior requirements of SCC can be satisfied for SCLC impregnated EPS with the density greater than 1900

24

kg/m3 (up to 22.5% of EPS by volume), which means that the addition of EPS beyond 22.5% cannot satisfy the SCC behavior but further decreases the density of SCLC [70]. Yang, S. et al. [48] explained that increasing volume of embedded PP particles can reduce the density of SCLC. They also showed that the replacement of the FA with the PP plastic particles by 30% can lead to the reduction in density up to 15%. Thus, there can be further reduction in the dry density of SCLC with the utilization of PP particles as sand replacement. Similar results were also found by Sadmomtazi A et al. [53]. They found that the replacement of natural FA with PET aggregates by 15% reduced the dry density of SCC from 2333 kg/m3 to 2003 kg/m3, from 2333 kg/m3 to 2038 kg/m3 and from 2333 kg/m3 to 2165 kg/m3 for different mixture sequences relying on the amount of fly ash and silica fume used in the mixes.

Fig. 17 Variation of fresh and/or dry density of SCC with replacement level of PAs (1): PP fine aggregates (SCLC) [48]; (2), (3), (4): EPS mixed aggregates (SCLC) [69, 70]; (5): PET fine aggregates (SCM) [49]; (6): HIPS fine aggregates (SCC) [55]; (7): Polystyrene fine aggregates (SCLC) [67]; (8), (9), (10): PET fine aggregates (SCC) [53];. [Solid lines: Replacement level by volume; dotted lines: Replacement level by weight].

3.6.2 Effect of PFs Few studies have focused on the density of RPSCC comprising PFs whether in fresh or dry state. Similar to the PAs, the addition of PFs also decreased the fresh and dry density of SCC as illustrated in Fig.18 [50, 59]. Al-Hadithi and Hilal [50] found that there was a decrement in the fresh density of SCC from 2340 kg/m3 to 2235 kg/m3 with the increase of PF volume content from 0% to 2%. On the other hand, Gencel et al. [59] reported no considerable change in the density of fiber reinforced SCC with the addition 25

of relatively small amounts of PFs. Since the specific gravity of PFs is low; higher fiber content decreases the density of SCC.

Fig. 18 Variation of fresh density of SCC with PF contents (1): PET fibers (SCC) [50]; (2), (3): PP fibers (SCC) [59]. [Solid lines: Replacement level by volume; dotted lines: Replacement level by weight].

3.7 Air content and Porosity 3.7.1 Effect of PAs For the evaluation of air-content of SCC mixes containing RP as aggregate replacement, there was only one study available. Sadmomtazi A et al. [53] reported the air content of SCC comprising PET particles as partial replacement of FA, as shown in Fig.19. They stated that the values of the air content of RPSCC mixes can be increased with the addition of recycled PET aggregates. For reference SCC mix, the value of air content was only 4.2%. With the incorporation of 15% PET particles in substitution of natural FA, this value was increased to 5.8%. Same behavior for RPSCC with silica fume and fly ash blended mixtures was also observed. A perforated concrete structure and reduced congestion between concrete components was obtained by adding the plane shape of PET particles. It also disturbs concrete matrix by high air content values [53]. Safi et al. [49] observed that increasing the replacement percentage of sand by the recycled PET aggregates can reduce the porosity for all SCM mixtures as shown in Fig.20. Compared to other replacement percentages, incorporation of 20% PET plastic instead of natural sand resulted in minimum porosity value [49]. There may be two reasons for this porosity reduction according to Safi et al. [49]; the

26

filling effect of voids in the cementitious matrix, and the PET plastic materials replacing the sand material for mortars which were less porous.

Fig. 19 Variation of air content of SCC with replacement level of PAs (1), (2), (3): PET fine aggregates (SCC) [53].

Fig. 20. Variation of porosity of SCC with replacement level of PAs (1): PET fine aggregates (SCM) [49]

3.7.2 Effect of PFs Similar to the SCC containing PAs, there was only one study found in which the air content of RPSCC was addressed, as demonstrated in Fig.21. Gencel et al. [59] found that there was a remarkable increase in the air content of SCC with the increment of PF content. They indicated that the addition of 12 kg/m3 of

27

PFs resulted in an increase in the air content from 1.77% to 3.07% and from 1.8% to 2.97% for SCC mixtures containing 350 kg/m3 and 450 kg/m3 cement content, respectively.

Fig. 21 Variation of air content of SCC with PF contents (1), (2): PP fiber [59]

4. Review of Mechanical properties of RPSCC containing PAs and PFs In this section, the most important mechanical properties of RPSCC reported in the literature are reviewed and discussed in detail.

4.1 Compressive strength 4.1.1 Effect of PAs The most important mechanical property in concrete industry is compressive strength. Any new concrete mix should satisfy the minimum strength required for structural applications. The results of the 28 day compressive strength reported in literature are presented in Fig.22. RPSCC with compressive strength between 20 to 80 MPa was produced in the past studies [12, 48, 49, 53, 55, 66, 67]. According to the reported compressive strength results, RPSCC can be used for structural applications. The addition of PA to the SCC has an adverse impact on the compressive strength of SCC. The strength of RPSCC decreases with increasing PA content, irrespective of plastic type [12, 49, 53, 55, 66, 67]. The amount of strength reduction depends on the utilization of PA quantity. R.H. Faraj, et al. [12] reported that there was about 24% reduction in compressive strength by incorporating 40% PP plastic granules instead of natural medium aggregates at the same w/c ratio. Sadrmomtazi et al. [53] also stated that the strength of SCC containing 15 wt.% of PET aggregates was reduced by 48.3%. The primary reason behind the reduction of strength with the inclusion of PAs can be attributed to two important factors (i) the bond between 28

plastics and cement paste matrix is easily aggravated due to the addition of PA [53] (ii) the PA is softer than natural aggregates (NA) which means that during loading the PA behaves like voids inside the matrix which results in the crack initiation around the particles [66]. The addition of mineral admixtures such as fly ash and silica fume significantly improves the strength of RPSCC due to improving the microstructure of the matrix [12, 53]. The utilization of 10% silica fume to the RPSCC containing 15 wt.% of PET particles increases the compressive strength by 14% compared to the same mix without silica fume content [53]. R.H. Faraj, et al. [12] also indicated that the compressive strength of RPSCC was increased by 5% with addition of 10% silica fume regardless of PA content.

Fig. 22. Variation of 28 day compressive strength of SCC with replacement level of PAs (1), (2): PP medium aggregates (SCHSC) [12]; (3): PP fine aggregates (SCLC) [48]; (4), (5), (6): PET fine aggregates (SCC) [66]; (7): HIPS fine aggregates (SCC)[55]; (8): PET plastic bags (SCM) [49]; (9): Polystyrene fine aggregates (SCLC) [67]; (10): Plastic waste powder (SCC) [63]; (11), (12), (3): PET fine aggregates (SCC) [53] [Solid lines: Replacement level by volume; dotted lines: Replacement level by weight].

4.1.2 Effect of PFs Fig. 23 presents the 28-day compressive strength results with different PF contents reported in the literature [50-52, 59, 61, 62, 64]. The figure illustrated that opposite findings were reported. Unlike PA, most of the studies showed that the compressive strength of RPSCC increased with the addition of PF. Al-Hadithi and Hilal [50] reported that the addition of 1.5% PF resulted in higher compressive strength comparing to other contents from 0 to 2%. They observed that the strength improvement of RPSCC was 43.4% with the addition of 1.5% PF content. Similar results can also be found in other studies even 29

though different PF was used [51, 52]. Gencel et al. [59] indicated that the PP fiber addition in the range of 3-12 kg/m3 provides similar compressive strength to those of steel fibers at the same binder content without the corrosion risk. They also demonstrated that increasing the cement content from 350 to 450 kg/m3 at the same w/c ratio remarkably increases the compressive strength of RPSCC containing PP fibers. Improvement in the compressive strength can be due to the distribution of PFs inside the microstructure of concrete, which leads to the reduction in the pores inside the concrete matrix [52]. The length of the PFs has a slight influence on the compressive strength of RPSCC [64]. In contrast to the above mentioned results, few studies reported that the compressive strength decreases with the addition of PF [61, 62]. Aslani et al. [61] found that increasing the volume fraction of PP fibers from 0.1 vol% to 0.2 vol%, decreases the compressive strength from 56.58 MPa to 46.76 MPa. Similar findings for RASCC were also observed with the same PF type [62].

Fig. 23. Variation of 28 day Compressive strength of SCC with PF contents (1): PET waste fibers (SCC) [50]; (2): PET waste fibers (SCC) [52]; (3): PET waste fibers (SCC) [51]; (4) PP fibers (SCC) [61]; (5) PP fibers (RASCC) [62]; (6), (7), (8) PBWF (SCC) [64]; (9), (10): PP fibers (SCC) [59]. [Solid lines: Replacement level by volume; dotted lines: Replacement level by weight] [LF: length of fiber].

4.2 Tensile and Flexural strength 4.2.1 Effect of PAs Similar to the compressive strength, the tensile and flexural strength of RPSCC were also decreased with increasing PA content, regardless of plastic type and shape. Fig.24 presented the results of splitting tensile 30

strength obtained in the past studies [12, 48, 53, 55, 67]. R.H. Faraj, et al. [12] studied the influence of PP granules on the splitting tensile strength of concrete. They concluded that the addition of 40% PP granules resulted in the decrease of tensile strength by 41%. They also noticed that the addition of 10% SF tend to increase the tensile strength by an average of 6% irrespective of PA content. Chunchu and Putta [55] also stated that the addition of 10%, 20%, 30% and 40% of HIPS granules caused the reduction of tensile strength by 5.7%, 8.3%, 11.5% and 16.6% respectively at 28 days curing age. Comparable results were also reported for different PA types [53, 67]. Versus to the above mentioned results, Yang et al. [48] reported that the 28-day splitting tensile strength was improved to the maximum when the 15% FA was replaced with PP aggregates. They also found that due to further amplification of PA content, the tensile strength decreases because of the weakened interface between the plastic and cement paste. The flexural Strength of RPSCC follows the same trend as for splitting tensile strength, as can be seen in Fig. 25, which shows the results reported in the past investigations [12, 48, 53, 55, 63, 67]. As the PA content increased the flexural strength of RPSCC decreased remarkably, because of the weak ITZ between PA and cement paste. Sadrmomtazi et al. [53] reported that the flexural strength of SCC, at the age of 28 days, containing PET replacement ratio of 15 wt.% was decreased up to 55%. They also found that the utilization of silica fume and fly ash to the RPSCC significantly improved its flexural strength. Other researchers reported similar results [12, 63].

Fig. 24. Variation of splitting tensile strength of SCC with replacement level of PAs (1), (2): PP medium aggregates (SCHSC) [12]; (3): PP fine aggregates (SCLC) [48]; (4): HIPS fine aggregates (SCC) [55]; (5): Polystyrene fine

31

aggregates (SCLC) [67]; (6): Plastic waste powder (SCC) [63]; (7), (8), (9): PET fine aggregates (SCC) [53]; [Solid lines: Replacement level by volume; dotted lines: Replacement level by weight].

Fig. 25. Variation of flexural strength of SCC with replacement level of PAs (1), (2): PP medium aggregates (SCHSC) [12]; (3): PP fine aggregates (SCLC) [48]; (4): PET plastic bags (SCM) [49]; (5): Plastic waste powder (SCC) [63]; (6), (7), (8): PET fine aggregates (SCC) [53]; [Solid lines: Replacement level by volume; dotted lines: Replacement level by weight].

4.2.2 Effect of PFs Fig. 26 presents the results of existing studies about the effect of PFs on the tensile strength of RPSCC [59, 62, 64]. The majority of studies demonstrated that the tensile strength of RPSCC increased upon the addition of PF. Gencel et al. [59] found that the tensile strength of RPSCC increased from 2.95 MPa to 5.84 MPa by increasing the PP fiber content from 3 kg/m3 to 9 kg/m3 at the same binder content. Ghernouti et al. [64] studied the effect of different fiber length and amounts on the splitting tensile strength of RPSCC. They reported that for RPSCC containing 7 kg/m3 of PBWFs the tensile strength were increased by 67, 74 and by 70% for RPSCC mixtures with fibers length of 2, 4 and 6 cm, respectively, compared to reference mixtures without fibers. This improvement was due to the fact that plastic fibers can prevent the propagation of cracks rapidly [64]. The flexural strength of RPSCC also increased with increasing PF content as shown in Fig. 27 which presents the results of existing studies [50-52, 59, 61, 64]. Al-Hadithi and Hilal [50] reported that flexural strength tended to be increased with the increment of PF content up to 1.75% by volume. Further increase 32

in PF content results in decreasing the strength of RPSCC due to irregular distribution of PFs, but the value was still higher than the control mixture. Comparable results for the same PF types and contents were also reported in other studies [51, 52]. Ghernouti et al. [64] concluded that the utilization of short PFs with 2 cm length in RPSCC does not influence the flexural strength regardless of PF content. They also indicated that for a PBWF amount of 7 kg/m3, the flexural strength was increased about 14% and 11% for concretes with 4 cm and 6 cm PF length, respectively compared to the mixtures with 0% PF.

Fig. 26. Variation of splitting tensile strength of SCC with PF contents (1) PP fibers (SCC) [61]; (2) PP fibers (RASCC) [62]; (3), (4), (5) PBWF (SCC) [64]; (6), (7): PP fibers (SCC) [59]. [Solid lines: Replacement level by volume; dotted lines: Replacement level by weight] [LF: length of fiber].

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Fig. 27. Variation of Flexural strength of SCC with PF contents (1): PET waste fibers (SCC) [50]; (2): PET waste fibers (SCC) [52]; (3): PET waste fibers (SCC) [51]; (4) PP fibers (SCC) [61]; (5), (6): PP fibers (SCC) [59]; (7), (8), (9) PBWF (SCC) [64]. [Solid lines: Replacement level by volume; dotted lines: Replacement level by weight] [LF: length of fiber].

4.3 Modulus of Elasticity 4.3.1 Effect of PAs The modulus of elasticity (Ec) of RPSCC depends on many factors, for example w/c ratio, binder content and PA type. Fig. 28 presents the results obtained from past studies on the influence of PA on the elastic modulus of RPSCC [12, 48, 53, 63]. As can be seen in the Fig. 28 the elastic modulus of RPSCC always decreased with increasing PA content irrespective of plastic type. Yang et al. [48] concluded that the static Ec of SCLC containing 15% PP granules was 10% lower than that of control mixture. R.H. Faraj, et al. [12] also reported that with an increase in the replacement level of PA content from 0% to 40% the static Ec of SCHSC was decreased by an average of 22%. They also found that the addition of silica fume improves the Ec irrespective of PA content. Similar findings on the reduction of Ec with the increase of PA content were also put forward by Sadrmomtazi et al. [53]. Replacing the NAs having high Ec with soft PA which has very low Ec was the main reason behind decreasing the Ec of RPSCC.

Fig. 28. Variation of modulus of elasticity of SCC with replacement level of PAs (1), (2): PP medium aggregates (SCHSC) [12]; (3): PP fine aggregates (SCLC) [48]; (4), (5), (6): PET fine aggregates (SCC) [53]; (7): Plastic waste powder (SCC) [63] [Solid lines: Replacement level by volume; dotted lines: Replacement level by weight].

34

4.3.2 Effect of PFs The effect of PF on the Ec of SCC is comparatively low compared to the PA. Fig. 29 shows the results reported in the literature on the effect of PF content on the Ec of RPSCC [51, 52, 59, 61, 62]. Unlike PA the addition of PF slightly enhanced the Ec of RPSCC compared to the traditional SCC. Al-Hadithi et al. [51] stated that at low to moderate ratios of PET fibers content, (such as 0.25 to 1%), enhancements in the values of the Ec between (3% and 4%) were observed. However, for mixtures with more than 1% PF content, the increments were small. Comparable results for the same PF type were also reported [52]. Gencel et al. [59] reported 5% improvement of RPSCC by increasing PP fiber content from 0 kg/m3 to 12 kg/m3.

Fig. 29. Variation of modulus of elasticity of SCC with PF contents (1): PET waste fibers (SCC) [52]; (2): PET waste fibers (SCC) [51]; (3) PP fibers (SCC) [61]; (4) PP fibers (RASCC) [62] (5), (6): PP fibers (SCC) [59]. [Solid lines: Replacement level by volume; dotted lines: Replacement level by weight] [LF: length of fiber].

4.4 Fracture energy, Load- displacement and/or stress- strain behavior 4.4.1 Effect of PAs In contrast to other mechanical properties, the ductility behavior of RPSCC containing PA is better than that of conventional SCC. Faraj, et al. [12] studied the effect of PP granules on the fracture energy of SCHSC at 90 days curing age. They reported that increasing PA volume from 0 to 40% increased the fracture energy from 89.9 to 98.8 N/m without silica fume and from 80 to 91.9 N/m for mixtures 35

containing 10% silica fume as shown in Fig. 30. They also found that the area under the load displacement curve was significantly increased with increasing PA content, which means that the displacement of the RPSCC increased before total fracture of the beams occurred as shown in Fig. 31. Therefore, the incorporation PA improved the toughness and ductility of the RPSCC [12].

Fig. 30. Variation in the fracture energy of SCC with replacement level of PAs at 90 days (SCHSC) [12].

Fig. 31. Load displacement curves of SCC with replacement level of PAs at 90 days (SCHSC) [12].

4.4.2 Effect of PFs Aslani et al. [61] investigated the effect of PP fibers on the mechanical properties of fiber reinforced selfcompacting concrete (FRSCC). The beam specimens of 100*100*400 mm in size were used to determine

36

the load carrying capacity and deflection. They reported that when the PP fiber volume fraction increased from 0% (CSCC) which was a control mixture to 0.25% (PPFRSCC 25), the ultimate load was significantly increased from 22.5 KN to 28 KN, while critical deflection decreased from 0.99 mm to 0.9 mm, which means that PP fiber had a positive effect on the load carrying capacity but had a negative influence upon critical deflection of the RPSCC as shown in Fig.32. Ghernouti et al. [64] studied the effect of two types of PF namely PBWFs and PP fibers on the stress-strain behavior of RPSCC. They also investigated the effect of different fiber length and contents. As shown in Fig. 33 waste fiber SCC (WFSCC) containing 5 kg/m3 PBWF with 2 cm length had superior stress–strain behavior compared to SCC containing PP fiber (PFSCC) and reference mixture (RSCC) [64]. They also confirmed about 58% gain in strain for WFSCC compared to reference mixture RSCC, which contains zero percent PFs.

Fig. 32. Load-deflection curves of RPSCC containing PP fibers (FRSCC) [61].

37

Fig. 33. Stress–strain curves of RPSCC containing PBWF (WFSCC) (length = 2cm and content = 5 kg/m3), compared to SCC containing PP fibers (PFSCC) and reference SCC mixture (RSCC) [64].

5. Empirical relationships among mechanical properties In this section, the results of the mechanical properties obtained from the underpinned literature for different SCC composites containing various types of PAs and PFs were used to develop empirical equations among the mechanical properties under the effect of PAs and PFs. Moreover, the equations could be helpful to find out whether the strong relationships exist between different mechanical properties for this type of composite or not. It is worth to mention that the below proposed models can be largely affected by the mixture proportions of the different SCC composites. 5.1 Compressive strength vs. splitting tensile strength Fig. 34 shows the relationship between compressive and tensile strength of RPSCC containing PAs. The experimental data obtained from the previous studies show quite linear relation between compressive and tensile strength of RPSCC made with PAs. A simple linear regression can depict the relation with a decent correlation coefficient (R2) of 0.95 as given in equation 3.

0.5

0.07

(3)

Fig. 34. Correlation between compressive and splitting tensile strength of RPSCC containing PAs.

The relation between compressive and splitting tensile strength of past experimental results for RPSCC made with PFs is presented in Fig. 35. It can be noticed from Fig. 35 that a power curve fitting can outcome a reasonably acceptable equation (Equation 4) with R2 of 0.68.

38

0.23

.

(4)

Fig. 35. Correlation between compressive and splitting tensile strength of RPSCC containing PFs.

5.2 Compressive strength vs. flexural strength Based on the previous experimental results for the compressive strength and its corresponding flexural strength for RPSCC, it was found that the relation between the compressive strength and flexural strength is rather parabolic than linear. Therefore, Fig. 36 and Fig. 37 are drawn between compressive strength on the x-axis and the ratio of flexural strength to its corresponding compressive strength in the y-axis for RPSCC made with PAs and RPSCC made with PFs, respectively. Also, Equation 5 and Equation 6 were proposed to predict the flexural strength through the compressive strength for PA and PF concrete, respectively. 0.33

0.0034

(5)

0.25

0.0023

(6)

39

Fig. 36. Correlation between compressive and flexural strength of RPSCC containing PAs.

Fig. 37. Correlation between compressive and flexural strength of RPSCC containing PFs.

5.3 Compressive strength vs. modulus of elasticity The relation between compressive strength and modulus of elasticity of RPSCC containing PAs (Fig. 38) can be described as a linear relation for a large extent. Equation 7 is proposed to predict modulus of elasticity of RPSCC made with PAs from its compressive strength with a convenient value of R2 (R2=0.92). 3.5

0.45

(7)

40

Fig. 38. Correlation between compressive strength and modulus of elasticity of RPSCC containing PAs.

The relationship between modulus of elasticity of RPSCC made with PFs with its compressive strength is presented in Figure 39. Despite some deviations of the data from a linear trend (Figure 39), a linear regression line can be a best fit to link modulus of elasticity of RPSCC containing PFs to its compressive strength with R2 of 0.75 as in equation 8. 7

0.54

(8)

Fig. 39. Correlation between compressive strength and modulus of elasticity of RPSCC containing PFs.

41

6. Critical appraisal Recycled plastic can be used in the SCC composites as the replacement material of NA or as the plastic fiber addition. Different plastic types and shapes can have different influences on the properties of RPSCC. Higher contents of PAs tend to greater decrease in fresh and mechanical properties. The percentages higher than 30% replacement level can have a dramatical decrease in the strength of RPSCC due to the weak bond between the cement paste and PAs, existence of voids and lower strength af PAs compared to NAs. Nevertheless, reducing particles sizes of PAs can decrease the compressive strength loss to a certain extent. Therefore, in order to obtain RPSCC with a satisfactory strenght properties the replacement of PA with FA is better than replacing the PA with CA since the former gives a higher strength. RPSCC has superior toughness and energy absorption compared to plain SCC. The shape and surface texture of PAs were found to influence on the fresh properties of RPSCC. In terms of fresh behavior such as passing ability, fillining ability and segregation resistance, it appears that the use of round and smooth surface PAs would perform better compared to PAs with flaky and rough surface at the same replacement level. The inclusion of PFs into SCC causes the reduction of fresh properties of RPSCC. Nevertheless, the strength properies of RPSCC was slightly increased with increasing the PF content up to 1.75% replacement level by volume. The RP impart unique features in SCC which are not found in normal SCC, especially low unit weight and higher ductility. However, the limitation of its use lies in the reduction of fresh and strength properties. The addition of mineral admixtures such as fly ash and silica fume can compensate the mechanical strength loss by enhancing the bonding between the PAs and cement paste. Thus, the RPSCC with higher compressive strength and improved fresh behavior can be produced. The potential use of RP as aggregate or fiber in SCC not only bring new alternatives to reduce shortage of NA but also improves the environmental concerns associated with its disposal considering the non-degradable nature of PWs. 7. Discussion Recently, substantial works have been done to understand the fresh behavior and mechanical characteristics of SCC containing plastic materials. In this study, a comprehensive review of the previous works on this topic has been presented. Based on the extensive review of research data which reported and analyzed the following discussions can be made: •

The preparation methods for both PAs and PFs can either be the direct mechanical recycling such as grinding plastics by mechanical machines or melting the plastics in the treatment plants and 42

ground them to suitable sizes. The former is economical and effective way to obtain recycled PA and PF. However the latter can yield materials with more uniform size and properties. The PAs can be used in SCC to replace the natural aggregates especially FA either, by volume or weight. On the other hand, PFs can be added as an independent ingredient to the mixture. •

Generally the addition of PA to the SCC has a negative influence on the slump flow properties of RPSCC, although a few authors have claimed the opposite. The utitlization of PAs with smooth textures and round shapes can improve the slump flow diameter and T50 slump flow time especially at lower percentages (smaller than 30% replacement by volume). However, mixtures containing PAs with rough, plane and flat shapes can adversley affect these properties, because they have a tendency towards restraining the flow of the fresh SCC mixture. Moreover, a remarkable reduction in slump flow diameter and a dramatic increase in T50 slump flow time can be observed with the addition of PF irrespective of the mixture composition. Different chemical admixtures such as superplastizers and viscosity modifying agents, also mineral admixtures such as fly ash could be used effectively to improve the slump flow properties of RPSCC.

•

Both plastic shape and replacement level can also affect the filling ability of SCC. The addtion of plane shape PAs can increase the V-funnel time; whereas it is decreased with the addition of spherical shape aggregates. On the other hand, there was a considerable increase in the V-funnel flow time with increasing PF content becuase of the increase in the friction between the aggregates and fibers, which this in turn, can adversely affect the filling ability of SCC.

•

The amount and shape of PA has an influcence on the passing ability of SCC in terms of L-box height ratio. Plane or flat shape aggregates can restrict SCC to pass through the congested reinforcement by decreasing the L-box height ratio. However, spherical shape PAs can improve the passing ability of SCC by increasing L-box height ratio. Furthemore, the addition of PFs remarkably results in reduction in the passing ability of SCC. The length of fibers can also have an fluence on the L-box height ratio of SCC. The passing ability decreases with the increase of PF length. This is due to the blockage of concrete among confined steel bars.

•

The J-ring height value, from which the passing ability of SCC can also be measured, was increased with the addition of EPS aggregates. Moreover, the passing ability of SCC could be improved by the PP aggregates. Regardless of PF content and type, there was a dramatic increase in the J-ring height value with the addition of PFs which in turn, adversely affected the passing ability of SCC.

•

Not much has been reported on the segregation resistance tests of SCC comprising PAs. However, the existing, investigated data illustrated that the incorporation of PA can have a marginal influence on the CA distribution and segregation. Differently, the stability of SCC can 43

considerably be influenced by the PF content and length. Therefore, segregation ratio of RPSCC dramatically increases with increasing the length and the dosage of the fibers. The vicosity of RPSCC mixture can be improved by the addition of silica fume and VMA which improves the behavior of the mixture to resist segregation. •

The utilization of PA can considerably reduce the fresh and dry density of SCC regardless of the type of plastics and amount of substitution. The SCLC can be produced by utilizing EPS aggregates instead of natural aggregates. Nonetheless, there might be a slight reducion in the density of SCC with the incorporation of PFs. Furthermore, it is evident that there is a direct relationship between the density of RPSCC and the substitution level of PAs.

•

The air content of SCC can similarly be influenced by both PAs and PFs as there was a remarkable increase in the air content of the SCC mixtures with the increase of PAs and PFs. However, substantial results were required to have an obvious picture of this property.

•

The addition of PAs has a negative impact on the different mechanical properties of RPSCC. The incorporation of PA as a partial replacement of FA or CA considerably decreases the strength of RPSCC, regardless of replacement level and plastic type. This influence can be explained due to the poor adhesion bond between PAs and cement paste and lower modulus of elasticity of PAs compared to natural aggregates which they decrease the strength and stiffness of the matrix. Diversely, incorporating different types of pozzolanic materials such as silica fume, fly ash, metakaolin and GGBFS can significantly improve the strength and mechanical properties of RPSCC due to increasing the particle packing density and enhancing the microstructure of the matrix. Unlike, PA content the addition of PF slightly enhanced the strength of RPSCC.

•

The incorporation of PA and PF can significantly improve the fracture energy and stress-strain behavior of RPSCC. SCC containing PA or PF is more ductile and has a greater strain capacity compared to conventional SCC. The PAs can behave like voids in the matrix which slows down the propagation of the cracks resulted in higher energy absorption by the RPSCC.

•

The limitations reported by EFNAR for fresh properties of SCC can be satisfied by producing RPSCC. Moreover, structural RPSCC with compressive strength in the range of (20-80 MPa) can be produced. This product can prominently be advantageous from the practical perspective in terms of suitability of the product and its sustainability. As a consequence, the problem associated with plastic waste disposal can partially be solved.

44

8. Conclusion and future research 8.1 Conclusion The major aim of undertaking this reviewing article was to present and analyze a comprehensive literature overview on the use of RP in SCC as NA replacement or PF addition after which the following conclusions became prominent: 1. RP can be used in SCC as the replacement material with NAs or as the addition of PF to improve the FRSCC composite. 2. The majority of investigations reported in the literature replaced the PA with FA. A limited literature was found to replace the PA with CA, mainly because better fresh and mechanical properties were obtained with FA replacement. 3. RP type, the amount of replacement and the shape of the particles significantly influence the fresh and mechanical properties of RPSCC. 4. Mechanical properties of RPSCC were significantly reduced by increasing RP content. irrespective of plastic type. 5. Plastic particles that have smooth texture, can improve the fresh properties of RPSCC. 6. The addition of PF remarkably decreased the fresh properties of RPSCC but slightly improved the mechanical properties. 7. The empirical relationships developed in this paper, illustrated that a relatively strong correlations can be found among different mechanical properties of RPSCC. 8.2 Future research The use of recycled PAs and fibers as a constructiom materials has been an ongoing topic for a substantial number of studies in recent years. The findings of this comprehensive review indicates that the utilization of spherical shape recycled PAs in SCC can improve the fresh properties of SCC. Furthermore, there can still be the produced SCC containing different types and dosages of recycled PAs and PFs to satisfy the desired limitations of SCC fresh properties. This comprehensive review has only focused on the fresh and mechanical properties of SCC containing recycled plastics as it was highlighted before. In order for this composite to be accepted by construction industry some other mechanical properties such as bond strength, abrasion resistance and impact resistance should also be investigated in detail. Currently, SCC is widely used for concreting pile foundations, some durability properties such as sulfate resistance of RPSCC and long term environmental exposure may be of interest to be examined in the future. Moreover, the time dependent properties such as creep and shrinkage needs to be considered. Because of the absence of experimental studies and test results further investigation are still required to be done to determine 45

rheological properties and thixotropy behavior of RPSCC so that a better understanding of the workability properties of this type of SCC can be acquired. Outcomes of this review demonstrate that the use of RP materials in SCC leads to more environmetally friendly products and sustainable construction industry. 9. Abbreviations and definitions CA E

coarse aggregate modulus of elasticity

EFNARC European Federation of National Associations Representing for Concrete EPS

expanded polystyrene

FA

fine aggregate compressive strength splitting tensile strength flexural strength

FRC

fiber-reinforced concrete

FRSCC

fiber-reinforced self-compacting concrete

GGBFS

ground granulated blast furnace slag

GRP

glass reinforced plastic

HDPE

high-density polyethylene

HIPS

high-impact polystyrene

HSSCC

high strength self-compacting concrete

LF

length of fiber

NA

natural aggregate

PA

plastic aggregate

PBWF

plastic bag waste fiber

PET

polyethylene terephthalate

PF

plastic fibers

PP

polypropylene

PPHT

high toughness polypropylene

PVA

poly-vinyl-alcohol

PVC

polyvinyl chloride

PW

plastic waste

RASCC

recycled aggregate self-compacting concrete

RP

recycled plastic

RPSCC

recycled plastic self-compacting concrete

46

SCC

self-compacting concrete

SCHSC

self compacting high strength concrete

SCLC

self compacting light weight concrete

SCM

self compacting mortar

VMA

Viscosity modifying admixture

WF

waste fiber

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Highlights: •

A comprehensive review on the use of recycled plastics in SCC is presented.

•

Recycled plastic can be used in SCC as replacement of NAs or as fiber addition.

•

Influences of properties and types of PWs on RPSCC fresh and mechanical properties are summarized.

•

Spherical and smooth PAs showed better performance than flaky ones.

•

Sustainable SCC containing recycled plastic can be produced and satisfied with requirements for fresh properties of SCC.

•

RPSCC can be used for structural applications due to its appropriate mechanical properties.

•

Empirical models among various mechanical properties were proposed.

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Dear Prof. Editors-in-Chief

We wish to confirm that there are no known conflicts of interest associated with this publication and there has been no significant financial support for this work that could have influenced its outcome. Thank you in advance for your attention Regards Rabar H. Faraj*, Hunar F. Hama Ali, Aryan Far H. Sherwani, Bedar R. Hassan, Hogr Karim

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