Utilization of PET fiber and nanomaterial in concrete: Review of flexural concrete behavior

Concrete may gain maximum flexural strength to a certain percentage with the inclusion of plastic fiber. Because of the weakening bonding concerning the fiber and cement paste, it loses strength under compression at the same rate it gains. The optimal addition ratio must be established to add Polyethylene Terephthalate (PET) fiber to concrete to improve its mechanical and structural qualities. To decide what will change in the microstructure of the concrete and the traction link between the PET fiber’s surface, it is highly advised to use any nanomaterials with PET fibers. Concrete fabric’s characteristics may be enhanced with nanomaterials, thus increasing concrete brittle and proving its activity in case of combination with various fibers as composite materials. The high surface area for fine material can modify concrete texture, one of the properties which leads to increased compressive strength. So, there is a need to create more experimental research and analytical survey. All studies from 2010-2022 It has referenced.


Introduction:
The first use of fiber known to humanity was in 5000 BC when it was used to enhance the composites to create sustainable building materials and has gained fame ever since [1].Another natural fiber called (hay) is used in many construction applications.Nowadays, multiple resources are available from fibers to enhance concrete properties such as steel, Polymer fiber, etc.As a result of the industrial revolution, usage of hay fiber become very rare except in old villages in suburbs.Currently, PET fibers are a kind of high molecular weight (or high viscosity) polyester as demonstrated in figure1[2].Besides that, it is commonly used as a material to manufacture bottles.New technologies enabled the acceleration of the container-blowing process, making the material more competitive in its transformation [3].PET bottle uses have increased significantly as a result of their cheap cost of production and the development of technologies that significantly enhance their physical qualities.They include, among others, the packaging of mineral water, oils, drinks, detergents, personal hygiene items, and pharmaceuticals [4].According to Othman [5] more than a half amount of plastic waste has been collected and recycled then the rest is left as litter.Biodegradations for many years are needed to remove this plastic waste otherwise it will be an accumulative environmental problem .
] 6 [ Expensive ecological damage due to plastic particles is already studied [7].A serious hazard and health threat as a result of the daily using plastic by human beings [8].Some developing and developed countries try to recycle the waste and use it in many industrial environments as an alternative .Moreover, others have already suffered from a deficiency of raw materials; hence, they are still doing several studies to explore the ability of waste as an alternative instead of raw materials or as a primary element.Nanotechnology is known as nanotechnology, which studies, manipulates, and reorganizes matter at a size smaller than 100 nanometers.On the contrary hand, nanomaterials with particles less than 500 nanometers in size are 1232 (2023) 012040 IOP Publishing doi:10.1088/1755-1315/1232/1/012040 2 used to make or include nanomaterials in concrete.Adding nanoparticles (the majority of them) to cementitious mixes enhances the mixture's mechanical and fresh qualities while also significantly increasing its durability [9].The use of nanotechnology in cement composites was explored by Bhuvaneshwari [10] It was shown that incorporating nanoparticles into cement-based materials improved their tensile, flexural, and shear strengths.This paper primarily discusses PET fiber, nanomaterials, and the incorporation of different fibers and nanomaterials in concrete.So, it is encouraging to Combine PET fibers with a new nanomaterial in the concrete mix.

Influence of numerous fibers types on the concrete flexural characteristics:
Several studies have been carried out regarding the usage of PET wastes to develop the engineering features of concrete.These studies highlight the many issues related to the weak bonds between the surface of PET and cement paste, which become very evident when the value fiber addition, shape or size, and type of PET material are neglected.Papong [11] and Beaumont [12] both support that essay.More analytical studies were created by Almeshal [13] which concluded that concrete compressive, flexural, and tensile strengths decrease as the plastic content rises.This propensity is brought on by the deterioration of the connection between the PET's surface and the cement paste.Additionally, concrete with plastic fibers is suggested for quasi-components that do not require a lot of compressive strength.Plastic's low absorption and high permeability allow concrete to be used in various applications, such as well-draining sports courts and pavements.There are still concerns about utilizing recycled plastic as an acceptable aggregate substitute or making concrete despite the much research yet to be done on the topic.A test of concrete reinforced using PET fibers from recyclable bottles, in contrast to the experiments mentioned above.It measured the concrete's fracture toughness, Young's modulus, compressive strength, and flexural strength to evaluate it physically and mechanically.Fibers of 10, 15, and 20 mm lengths and 0.05, 0.18, and 0.30 % of the concrete's total volume were used, respectively.According to table 1, the primary flexural enhancement was with 0.03% of PET fiber at 28 days of curing, while there is a slight improvement for 0.05% of PET with long-term curing, which is 150 days [14].While the added ratio of PET will play an essential role in changing the concrete specification.Also, in the case of using PET as a rectangular fiber shape with a size of 34mm in length,2.5widths, thick 0.35mm, and the aspect ratio was (13.6).AL-Hadithi [15] conducted a more practical study in which they added (0.5, 1, 1.5) percent of PET fiber by volume to concrete with a grade of 50.2 MPa and flexural strength of 8.55 MPa.The perfect PET additive percentage was 1%, but the reduction occurred with compressive strength.Conversely, increasing the PET value from 1% to 1.5 improves the compressive but decreases flexural properties in tables (2) and (3).This case may explain the use of plastic fibers in ideal forms and dimensions.Using the same PET percentage, which is 1%, Al-Hadithi [16] significantly increased compressive strength and toughness by expanding the PET fibers' dimensions from 34 to 40 mm and their breadth from 2.5 to 4 mm.These results are consistent with what the Al-Hadithi [17] study concluded.The reason for the size modification of fibers is to increase their aspect ratio.The same researcher has another experiment, this time by reducing the length of the fiber from 40 to 34 while installing the width (4 mm) of the fiber in the reinforced polymeric concrete mix in different proportions of reinforcement [18].It has been noted that the optimal fiber addition ratio was only 75% for the best resistance to fracture and bending.The interpretation of that low percentage of fiber addition may be due to the addition of polymeric substances making it an enabler for strengthening and adhesion of fiber with cement paste.
Ali [19] used PET fibers in various reinforced concrete beam areas, using 1 and 0.5% PET in each concrete texture of the beam and precise percentages for the compression zone and tension zone, respectively.The highest ductility and toughness were with 0.5% of PET addition, as a result of elonging the PET fibers from 40mm to 50 mm with a fixed width of 4mm. Figure 2 demonstrates how the toughness capacity of 1% PET fiber reinforced concrete in the top half, bottom half, and bottom quarter of multilayer RC beams improved.While other studies investigate the exact PET dosage used by Al-Hadithi [18] in the SSC mix, which needs 1.5% from PET addition to reach an acceptable enhancement.This may explain the weakness of the mechanical properties originally in such a quality of concrete mixtures where it needs more fiber quantities than the ordinary mixture to rely on to resist flexure and compression.
From the above review, plastic fiber adversely impacts the mechanical characteristics of concrete mixture unless the conservation of ideal dimensions of the fiber and perfect addition proportions enhance mechanical and engineering mix properties.The smoothness of the plastic fiber surface, which directly impacts the strength of the bonding between the fiber and its cement dough, is to blame for this user's sensitivity, particularly the direction of keeping the precise value of the improvement to resist compression and fracture.Additionally, these fibers in the concrete fabric cause larger gaps between the fiber and cement paste in the ITZ.It thus increases the proportion of initial micro-cracks at an early age.Some studies in the same field confirmed this and recommended that other additives be used to reduce pores, reduce the interfacial area, and increase the adhesion coefficient Frhaan [20] and Hussein [21].
The assay above is supported by Sharma [22] who recommended that, treating the reduction in compressive strength and other engineering properties by involving another pozzolanic material obtained more traction bond.

Effect of various kinds of nanomaterials on concrete flexural characteristics:
As previously stated, using nanomaterials in concrete mixtures will open new fields for researchers in the intelligent concrete industry with the ability to self-repair and be environmentally friendly.Nanomaterials may also change the composition and textural characteristics of concrete by interfering with rehydration processes, which directly impact the early emergence of desirable compounds.A multiscale modeling framework may link the essential physicochemical characteristics of (C-S-H)FA interactions at the molecular 1 nm, mesoscopic 100 nm, and microscopic 10 microns length scales [23].
In another review paper, Raki [24]inferred that reducing the quantity of cement used in construction can potentially have a considerable positive economic impact, provided that condition is satisfied.Due to the capability of nanoparticle inclusion to quicken the hydration of ordinary Portland cement (OPC) mixtures, there is the potential to significantly decrease the quantity of cement in concrete.The hydration process may be significantly slowed down by high supplemental cementing material (SCM) levels in blended cement; however, the impact can be attributed to involving a nanoparticle as a reaction accelerator.The requirement that the expenditure of the nanoparticles is less than that of the substituted cement is essential for economic feasibility.This circumstance further suggests that significantly lower nanoparticle levels than the amount of cement replaced should be utilized in the mix.Because of the reutilize of waste materials and the drops in greenhouse gas emissions related to OPC production, increasing the potential proportion of SCMs in OPC blends should have a positive environmental impact [24].Also, Singh [25] confirmed that for aiming to improve the concrete's mechanical properties and reduce porosity and permeability-two elements for enhancing durability-nano-silica is being added.To support the essay above, Nazari [26] has investigated how limewater affects the proportion of water absorbed and strength ratings of concrete containing ZnO2 nanoparticles.ZnO2 nanoparticle-containing samples are cured in saturated limewater, which improves permeability and strengthens the gel that surrounds the nanoparticles.After substituting a portion of the Portland cement with ZnO2 nanoparticles with an average particle size of 15 nm and drying the specimens in water, they were immersed in limewater for a predetermined duration.The results indicate that when specimens are cured in saturated limewater, ZnO2 nanoparticles at concentrations as high as 2.0 percent by weight may produce concrete with enhanced strength and water permeability.The percentage for models maintained in tap water was barely 1.0 weight percent.However, when specimens without nanoparticles were cured in limewater, the strength decreased compared to those in water.Additionally, ZnO2 nanoparticles may function as nanofillers and restore the specimens' pore structure by removing unacceptable pores.Additionally, the findings demonstrate that concrete containing ZnO2 nanoparticles performs better in flexural strength than control concrete, particularly when concrete containing a large percentage of nanoparticles is cured in saturated limewater.This might be because more C-S-H gel forms when nanoparticles are present, particularly in specimens cured for 28 days in saturated limewater figure 3. Francioso [27] research has been done on the impact of adding TiO2 nanoparticles to mortar.Other than a lot of research in the same field, where it was at specific temperatures, so used nano TiO2 material in the mortar of the concrete at varying temperatures.At three different curing temperatures-5 °C, 20 °C, and 45 °C-the current study concentrated on the effect of TiO2 nanoparticles.The effects of TiO2 on flexural and compressive strengths after seven days at each curing temperature were tested in a mortar with zero nanomaterial and three mortars with various concentrations of TiO2 (0.25%, 0.5%, and 1%).
The 0.5% replacement rate consistently produced the best results, attaining a maximum curing temperature of 20 °C with a 65% increase in flexural strength and outperforming the reference mortar MC-R (without TiO2) curing strength at 45 °C.The proportion of replacement, TiO2, has beneficial effects on flexural strength appearing at low curing temperatures more than the temperature curing at (45 °C).The impact of many nanoparticle types, including nano-SiO2 (NS), nano-TiO2 (NT), and nano-Fe2O3 (NF), on the initial properties, mechanical characteristics, and microstructure of cement mortar including fly ash as an extra cementitious component are the subject of ongoing research.In powder form, these nanoparticles were added to the mortar at 1%, 3%, and 5% cement weight.The compressive and flexural strengths of mortars built with varied quantities of NS, NT, and NF have consistently included fly ash in mortars that comprise 30% weight of cement.With a larger dose of nanoparticles in the mortar, it can see that both the compressive and flexural strengths rise.Age also enhances strength, as would be anticipated [28].
A more technical study created by Liu [29] described SEM and EDS images of the impact of dosages various of nano-SiO2 with addition (1%,2%,3%, and 4%) in a concrete mortar containing %50 fly ash and 50% cement of weight ratio of the mortar control mix.On average, they employed 15 nm-sized, commercially available nano-SiO2 (NS).These images give a clear perception of changes in the interfacial transition zone (ITZ) area, which seemed rougher and more overlapping.The increased volume of C-S-H gel formed by rapid cement hydration and the enhanced pozzolanic reaction of NS and fly ash are the key drivers of the increase in strength.It was shown that ITZ improved with a compact structure and reduced CH due to a probable NS pozzolanic reaction.The C-S-H gel and the filler effect from unreacted NS reduce porosity and enhance pore structure.These results indicate the need to increase the fly ash in steam-cured precast concrete.
Figure 4 shows how this ITZ improvement affects lifting concrete's mechanical and structural qualities.
According to the data, adding nano-SiO2 (NS) has a similar impact on compressive and flexural strength development: a more considerable amount of NS resulted in more remarkable strength development.This rise is noticeable, as 1.0% NS enhances compressive strength and flexural strength by 22% and 13%, respectively, compared to the standard, whereas 4.0% NS boosts proliferation by 106% and 67% [29].In contrast to the literature by Oltulu [30] and Stefanidou [31], which has an ideal content, the most substantial growth was different.For instance, the optimal content in research by Oltulu [30]was 1.25%, over which the strength began to decline.Studying the mechanism behind this strong growth is so interesting.Early on, power multiplies with steam curing and NS.The finest material used with the concrete mix was graphene oxide (GO) by Lu [32].with the highest particle surface among the numerous nanomaterials ever seen.The effects of additives such as graphene oxide nanosheets (GONS) are shown on cement mortar and ultra-high strength concrete (UHSC).The final GONS-cement composites exhibited good mechanical qualities and were simple to produce.However, when the GONS concentration rose, they became less flexible.The GONSs were used in varying concentrations (0-0.03% by weight of cement) to produce the UHSC specimens.The findings revealed that after 28 days of curing, applying 0.01% by weight of cement GONSs produced a 7.82% rise in compressive strength.Additionally, adding GONSs enhanced the flexural strength and deformation capacity, with the flexural strength increasing more than the compressive strength (table 4) [32].This agrees with the latest review paper on utilizing graphene and graphene oxide in the concrete mix [33].Figure 5 is a summary of Kumar's [34] in-depth examination of the impact of different nanomaterial additions on the flexural strength of concrete 28 days after its placement.Additionally, they recommend additional research to ascertain the shrinkage behavior, microstructure changes, permeability properties, and durability aspects of composites in cementitious systems with nano-incorporated fiber reinforcement.
Figure 5. Impact of different nanoparticles on the concrete's flexural strength [34].

Effect of the combinatof ion nanomaterials and fibers on the concrete flexural characteristics:
Lam [35] describes the main aim as combining fiber with nanomaterials.They abstracted that to create the structure essential to assure the carrying capacity.It is important to research ways to enhance the plasticity of high-strength concrete and nano concrete, including (0.5,1.5, and 3 )% of nano SiO2, which are often brittle.The key benefits of steel fiber concrete are its strong tensile, compressive flexural strength, and great flexibility.The engineering behavior of nano concrete, for example, the tensile bending and the splitting tensile strengths for nano concrete specimens with and without steel fibers, are determined utilizing bending elements such as beams; the tensile area makes it easier for the concrete to develop cracks and causes the structure to deteriorate rapidly.They used an experimental technique in the study.The effects on the mechanical performance and durability of flax fiber reinforced cement (FRC) composites by adding nano clay particles (NC) and finely ground waste glass powder (WG) in place of some of the ordinary Portland cement (OPC) (FRC).The experiment increased the plasticity, tensile bending strength, splitting tensile strength, and other features of the unique steel fiber nano concrete materials, including nano SiO2, by adding steel fibers to the nano concrete.The research also determined the deformation stress condition of nano concrete reinforced with steel fibers and nano concrete.The findings demonstrate that adding WG improves FRC's mechanical characteristics and robustness, mainly when NC is included.Additionally, the composites' longevity as they aged under wetting and drying cycles is shown.In addition, mortars containing WG and mortars containing a hybrid of WG and NC had lower calcium hydroxide (CH) contents, according to the Deferential thermal analyses (DTA) findings and XRD analyses.This demonstrates that mechanical characteristics improved after 28 days of hydration, and the pozzolanic reaction took place.Figure 6 provides the flexure strength data for flax fiber cement composites [36].The specimen with the best mechanical qualities was FRCGN, which had 20 percent WG and 2.5 percent NC.At 28 days of hydration, it also reported gains in flexure strength of 38% above the control specimen.These gains show that the hybrid combination of NC and WG significantly enhances the mechanical performance of the FRC.Additionally, it should be noted that the FRCN (OPC reinforced mortar with 2.5% NC) specimens' mechanical characteristics fall between those of the FRCG (reinforced mortar with a cement replacement by 20 % WG )and FRCGN samples.The addition of nano-silica NS improved the structure of the aggregate contact zone and increased the matrix's C-S-H composition.This resulted in a denser, more uniform system with a stronger binding between the aggregate and cement paste [37].The same experimental design as Zhang [38] work has been used this time, but a constant additive percentage of Nano-SiO2 (NS) was used, which is 3%.A variety of specimens have also been used, including 0.5%, 1%, 1.5%, 2%, and 2.5% from steel fiber (SF).The results showed that the optimal SF percentage of nano-concrete had a 20.0% better flexural strength than non-SF concrete.To further grasp this, consider the following two points: By adding SF to the concrete, its density and stiffness were further boosted, and the growth of microcracks was halted before the concrete reached its maximum strength [39].On the other hand, the NS particles filled the concrete's micropores, made it denser, and accelerated the C-S-H gel's development [40].Several studies supported the debate on the effectiveness of using corrosive materials with fiber in the concrete mixture [41].Analyses examined the flexural strength of NS and nCaCO3-contained cementitious composites reinforced with polyvinyl alcohol (PVA).It found that it may attain the best flexural strength by combining 1-2% of NS with 1-1.5% of PVA.The inclusion of NS increased the bonding strength between the fiber and composite matrix by increasing the mixture's density and reducing its porosity [42].As a result, by adding NS, most PVA fibers broke instead of pulling out under stress.Zhang [43] reveals that the C-H-S gel that develops in the mixture including NS is higher than that which forms in the PVAreinforced compound containing nCaCO3 as shown in figure 7. The C-S-H gel impacts the bond performance and ITZ enhancement in the mixture.As a result, compared to nCaCO3, NS is more wellserved by PVA-reinforced cementitious composites in terms of helping durability.Numerous self-compacting concrete mixes have been produced with a constant water-to-binder ratio of 0.35 and a binder concentration of 490 kg/m 3 .Cement was used as a 25% weight replacement for class F fly ash.A plastic fiber percentage of 0, 0.25, 0.5, 0.75, 1, 1.25, 1.5, 1.75, and 2% was specified for the eighth position.The test findings revealed that plastic fibers harmed self-compacting concrete's initial qualities while improving its hardened properties.It has been found that there is a variation in the amount of improvement between flexural and compressive strength, with compressive strength requiring a 1.5% increase in WPF.On the other hand, 8 MPa flexural needed adding 1.75% of WPF regardless of a combination of fly ash [44].For the same type of concrete, Medher [45] enabled to get a balance in the value of improvement between the flexural strength and compressive.All the results were less than the reference mixture, and the optimal addition ratio of plastic fiber was only 1%. that perfect balance may be due to utilizing silica fume, which considers a nanomaterial.But there will be poor fresh and hardened characteristics because of the large densities of lightweight aggregates and binders.Alfahdawi [46] conducted a thorough investigation.In this study, FA was used to replace 30%, 35%, and 40% of the weight of cement, whereas PET employed PET fiber waste to replace 0.25 percent of the weight of coarse aggregate.To make up for the estimated strength loss after using FA and PET, nano silica (NS) material was replaced for 2.5%, 5%, and 7.5% of the weight of the cement, respectively.The findings showed that adding FA and NS enhanced compressive and flexural strength.The study's fantastic exploration is that the specimen has nevertheless undergone a remarkable improvement.The compressive and flexural values are ideal even without fly ash.It is also important to note that at a curing temperature of 26C, the optimal amount of additive nano-silica was about 5% with a fixed PET additive.Once again, the aim of complaining about the two materials in the concrete mix, fiber, and nanomaterials, is to find the best ways to balance elasticity and plasticity, enhancing the traction bond between cement paste and the fibers [35].

Conclusion:
1 -Concrete gains maximum flexural strength to a certain percentage of the addition of plastic fiber (PET), while concrete suffers from reduction with compressive strength at the same added rate due to the weak interconnectedness that explains this between fiber and cement paste. 2 -Improving concrete's mechanical and structural properties by adding PET fiber needs to determine the ideal addition ratio.So there is a need to create more experimental research and analytical survey.
3 -By enhancing the structure of the concrete and making it more brittle, nanoparticles have been shown via prior research to have a direct impact on those substances.They have also shown their activity when coupled with other fibers to create composite materials.4 -All studies have no specific additive ratio for nanomaterials, especially when combining them with PET fibers.Therefore, more experimental research is recommended to identify this issue.5 -It is strongly encouraged to utilize nanoparticles with PET fibers to identify what will change in the microstructure of the concrete and the traction relationship between the fiber's surface.6-The Nano-material may improve the bridged of PET with the concrete matrix.

Figure 1 .
Figure 1.Structure of "Polyethylene Terephthalate" (PET) [2] As shown by the formation of a new peak, X-ray diffraction (XRD) measurements demonstrate the existence of extra C-S-H during hydration's early phases when nano-silica is involved.The addition of nano-silica to the C3S system caused the CH peak to arrive 30 minutes later, indicating a shift in the supersaturation stage that may be connected to a change in the induction time.According to Fouriertransform infrared spectroscopy FTIR studies, nano silica speeds up polymerization in the silicate chain and accelerates the dissolution of C3S grains.The addition of nano silica induced the production of a denser C-S-H with a low C/S ratio, indicating the material's enhanced reactivity and the existence of extra C-S-H, according to SEM/EDX resulInductivelytive coupled plasma (ICP) measurements also show more C-S-H and a different induction time when nano-silica is present.According to a TG study, nano silica causes a 50% increase in C-S-H formation.
Shakeel M, Khan K, Akbar S and Khan A 2022 A Review on Fiber-Reinforced Foam Concrete Engineering Proceedings 22 13 [2] Nunes C S, Souza P R, Freitas A R, Silva M J V d, Rosa F A and Muniz E C 2017 Poisoning Effects of Water and Dyes on the [Bmim][BF4] Catalysis of Poly (Ethylene Terephthalate)(PET) Depolymerization under Supercritical Ethanol Catalysts 7 43 [3] Ji L N 2013 Study on preparation process and properties of polyethylene terephthalate (PET).In: Applied mechanics and materials: Trans Tech Publ) pp 406-10 [4] Forrest M J 2019 Recycling of Polyethylene Terephthalate: De Gruyter) [5] Othman S N, Noor Z Z, Abba A H, Yusuf R O and Hassan M A A 2013 Review on life cycle assessment of integrated solid waste management in some Asian countries Journal of Cleaner Production 41 251-62 [6] Papong S, Malakul P, Trungkavashirakun R, Wenunun P, Chom-in T, Nithitanakul M, and Sarobol E 2014 Comparative assessment of the environmental profile of PLA and PET drinking water bottles from a life cycle perspective Journal of Cleaner Production 65 539-50 [7] Beaumont N J, Aanesen M, Austen M C, Börger T, Clark J R, Cole M, Hooper T, Lindeque P K, Pascoe C and Wyles K J 2019 Global ecological, social and economic impacts of marine plastic Marine pollution bulletin 142 189-95 [8] Wright S L and Kelly F J 2017 Plastic and human health: a micro issue?Environmental science & technology 51 6634-47 [9] Nazar S, Yang J, Thomas B S, Azim I and Rehman S K U 2020 Rheological properties of cementitious composites with and without nano-materials: A comprehensive review Journal of Cleaner Production 272 122701 [10] Bhuvaneshwari B, Sasmal S and Iyer N R 2011 Nanoscience to nanotechnology for civil engineering: proof of concepts.In: Proceedings of the 4th WSEAS International Conference on Recent Researches in Geography, Geology, Energy, Environment and Biomedicine (GEMESED'11), pp 230-5 [11] Rai B, Rushad S T, Kr B and Duggal S 2012 Study of waste plastic mix concrete with plasticizer International Scholarly Research Notices 2012 [12] Saikia N and Brito J d 2013 Waste polyethylene terephthalate as an aggregate in concrete