1 Introduction

A significant volume and variety of solid waste materials have been produced by industrial, mining, domestic and agricultural activities as a result of urbanization, industrialization, and technical advancements in various fields [1]. According to projections, By 2050, 70% of the world's population will reside in cities, making autos necessary since urban areas have greater mobility needs [2]. As a result, waste rubber tires (WRT) are produced in ever-increasing quantities across the world. According to [3] and [4], An estimated 1.5 billion tires are produced annually in the world. The rate of waste tire generation in developed countries is estimated to be one passenger tire per person, with an estimated 1 billion waste tires produced annually [1]. The number of tires wasted each year was projected to be between 200 and 300 million in the United States [5], more than 10 million in Turkey [6], and 3.4 million tons in the European Union [7].

It is predicted that by 2030, there will be 1.2 billion waste tires produced, and there will be a total of about 4 billion tires deposited in landfills around the world. Aside from The European Association of Tire and Rubber Producers, 3.2 million tons of used tires were discarded in 2009. 96% of the materials were recovered, and of those, 18% were reprocessed or reused, 38% were recycled, and 40% were utilized to produce energy [8].

If the waste tire is not disposed of environmentally, several issues may erupt such as health problems and fire hazards. WRT is almost non-biodegradable, making it a significant cause of environmental pollution. Since the majority of used rubber tire debris is stacked up or dumped in landfills, the hazards connected with scrap tires can negatively impact both human health and the environment. According to [9] and [1], a huge tire fire can smoulder for several weeks or even months and can have a dramatic impact on the ecosystem. Through air, water, and soil contamination, stockpiled tires can provide a variety of health, environmental, and financial hazards [3, 10]. Moreover, tire rubber contains styrene which is very toxic to human health [11]. Therefore, dumping waste tires would be very dangerous. One of the environmentally friendly options for the waste tire is recycling and reusing it for different applications. The strategy of use of end-of-life tires is presented in Fig. 1.

Fig. 1
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End-of-life tires management strategies [109]

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Waste tire rubber can be used in a wide range of civil and non-civil engineering applications, including road construction, geotechnical work, agriculture's sealing of silos, retaining walls, offshore and onshore breakwaters, in harbors and estuaries to cushion the impact of ships, artificial reefs to improve fishing, incineration for electricity production, as a fuel in cement kilns, or as an aggregate in cement-based products [8, 12, 13].

Furthermore, the aggregate, which makes up the highest volume percentage of concrete and is produced in billions of tons annually due to the construction industries' rapid growth and development, is running out quickly and many nations are concerned about a potential shortage [14,15,16]. To meet the challenge of incorporating sustainability into production processes, the construction industry for the last number of years has been looking for more environmentally friendly raw materials or using solid waste as aggregates in concrete. The waste tire can be used as a replacement for concrete components owing to its strain control property, ductility, and good strength. Concrete can be used as a replacement for fine or coarse aggregate. This effort may be environmentally better because it helps to reduce environmental contamination and dispose of used tires [17,18,19,20,21,22,23,24]. Avoiding tire burning, additionally contributes to a decrease in carbon dioxide emissions. This method is also financially feasible because it allows for the preservation of some of the expensive natural aggregates [17,18,19, 25,26,27].

The literature shows that waste rubber tires are a harmful effect on the environment. However, it can be utilized in concrete to up certain extent. Although a lot of research focuses on the utilization of waste rubber tires in concrete. However, an updated review is required to explore its impacts on different properties of concrete. The successful review provides a quick review for the reader to judge its impact on concrete properties without conducting any test which is safe time as well cost.

In this review paper, the use of waste tire rubber on different properties of concrete was discussed. In the fresh state, the workability, air content, and unit weight were evaluated. Moreover, mechanical properties such as compressive strength, flexural strength, splitting tensile strength, and modulus of elasticity were also discussed. In addition to these properties, different durability characteristics such as water absorption and porosity, freeze–thaw resistance, corrosion resistance, and chloride penetration are summarized. Furthermore, the influence of rubber on the rubber concrete for roadside barriers such as impact resistance, energy absorption, toughness, and ductility are also reviewed. Figure 2 shows the different sections of the review.

Fig. 2
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Section of review

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2 Fresh properties of concrete with waste tire rubber

One of the possible solutions for waste tire rubber is to include it in cement concrete as a fine or coarse natural aggregate. Since rubbercrete can be cast and molded into any desired shape when it is in a fresh state, its workability, air content, and unit weight are crucial factors to consider because they may have a negative impact on the rubbercrete's hardened properties.

2.1 Workability

Figures 3 show the workability of concrete containing crumb rubber and chipped rubber respectively, studied by different researchers. A maximum of authors noted that the workability of concrete containing fine rubber or coarse rubber particles has reduced with an increase in rubber content as shown in Fig. 3. The cause for the decrease in workability of rubberized concrete is reduced inter-particle friction between the rubber and other constituents, reduced flowability of the larger rubber particles [28], the surface roughness of fine rubber aggregates [8], low density of rubber particles [29]. The workability of crumb rubbercrete is adversely affected due to the smaller size and surface roughness of crumb rubber. The increased friction caused by the crumb rubber's rougher surface could reduce the flowability of the fresh rubbercrete mixture [30, 31].

Fig. 3
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Workability of concrete containing CR [8, 20, 25, 28, 29, 31, 32, 35, 53, 88, 110,111,112]

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However, fewer of them showed that workability has improved with an increase in rubber content as shown in Fig. 3 [32] proved that the slump value of fresh concrete increased with partial substitution of fine and coarse aggregate with waste rubber. This also signifies that rubberized concrete can be easily mixed, cast, and vibrated like normal concrete.

2.2 Air content

Figures 4 and 5 show the air content of concrete containing crumb rubber and chipped rubber respectively. These Figures show that the air content of rubberized concretes improved with an increase in rubber content as compared to control concrete. However, the air content of crumb rubber concrete is higher than compared of chipped rubber concrete. Most of the authors have reported an increase in the air content of rubberized concrete an increase in rubber content. The main factors contributing to increasing air content are the non-polar nature and hydrophobic properties of rubber, the large specific area of the fine rubber, the size of rubber, and the amount of rubber in concrete.

Fig. 4
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Air content of crumb rubbercrete [29, 31, 35, 112]

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Fig. 5
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Air content of chipped rubbercrete [35, 113]

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Due to the non-polar nature and hydrophobic properties of rubber, crumb rubber acts as an air-entraining agent by repelling water and trapping air on its surface. As a result, crumb rubber is being utilized to add more air to rubbercrete, improving its resilience to freeze and thaw [33, 34]. According to [34], because fine crumb rubber has a large specific area, the air content of fresh concrete increases as the crumb rubber content increases and consequently adding more crumb rubber (CR) will result in more air becoming trapped in the concrete. According to studies by [35], the size of the tire particles affects the air content of rubberized concrete. As the size of rubber particles increases, the air content of rubberized concrete drops. This statement is also supported by the authors' data given in Figs. 4 and 5. The amount of rubber has a clear effect on air content [36]. Data plotted in Figs. 4 and 5 has depicted an improvement in air content with an increase in rubber content.

2.3 Unit weight

Figures 6 and 7 show a past study on the unit weight of concrete containing crumb rubber and chipped rubber respectively. These Figures show that the unit weight of rubberized concretes decreased with an increase in rubber content as compared to control concrete. The reasons for the reduction in the unit weight of rubberized concrete are the non-polar and hydrophobic nature of rubber particles, the higher air content of rubberized concrete, the number of rubber particles, and the low density and specific gravity of rubber particles.

Fig. 6
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Unit weight of crumb rubber concrete [8, 19, 25, 28, 28, 29, 31, 32, 32, 53, 65, 67, 95, 97, 110,111,112, 114]

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Fig. 7
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Unit weight of chipped rubbercrete [8, 20, 25, 28, 32, 35, 56, 112,113,114]

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A study [34] explained that because of the non-polar and hydrophobic nature of crumb rubber, it acts as an air-entraining agent by trapping air on its surface thus reducing the unit weight of rubbercrete. According to [4] the unit weight of mixes containing rubber falls as the amount of rubber content increases due to the low specific gravity of rubber particles. In addition, when rubber content rises, air content rises as well, consequently lowering the unit weight of rubberized concrete. Studies [37] and [19] added that another factor that contributes to the reduced unit weight of rubbercrete is the lower density of rubber particles, the density of fine rubber particles (Crumb rubber) is 192% lower than natural fine sand. The amount of rubber has also the main impact on the reduction of the unit weight of rubbercrete. Figures 6 and 7 show that all authors have reported a decrease in unit weight as compared to control concrete with an increase in rubber content of concrete mixes containing crumb rubber and chipped rubber respectively.

3 Hardened properties of concrete with waste tire rubber

3.1 Mechanical properties

3.1.1 Compressive strength

The effect of fine (CR) and coarse rubber (chipped rubber) on the compressive strength of rubbercrete (rubberized concrete) with different replacement levels are shown in Tables 1 and 2. The compressive strength of concrete containing fine rubber or coarse rubber decreases as illustrated by Tables 1 and 2 respectively. These Tables have experimental data of the number of researchers who used fine or coarse rubber aggregates in concrete as partial replacement of sand or crush (coarse aggregate) respectively with different sizes and percentages by volume. Not a single paper showed an increase in the compressive strength of rubberized concrete but showed a gradual decrease in the compressive strength of rubbercrete.

Table 1 Compressive strength (MPa) of CR concrete
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Table 2 Compressive strength (MPa) of chipped (coarse) rubbercrete
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The causes of the loss in compressive strength of the rubberized concrete have been discussed by [38] (i) The aggregates would be encircled by a cement paste that contained rubber particles. With the rubber particles, this cement paste would be considerably softer as compared to the control cement paste. Due to this, fast formation of cracks occurs around the rubber particles during loading and hence specimens fail quite quickly. (ii) As opposed to cement paste and natural aggregates, rubber particles and cement paste would not adhere well to one another. consequently, cracks occur when non-uniform stresses are applied. (iii) The compressive strength of concrete is influenced by the material's mechanical and physical properties. If rubber completely or partially substitutes any of the materials, it will weaken those materials. (iv) Due to its low specific gravity and lack of adhesion with concrete components, rubber tends to rise during vibration, which causes a higher concentration of rubber at the top layer, causing so non-homogeneous concrete mix and thus compressive strength to be reduced.

Similarly, the cause of the decrease in compressive strength of rubberized concrete was explained by [19]. Due to the porous nature of rubber particles and their shaped surface, they were said to have reduced adhesion between the rubber and cement matrix. According to [39,40,41] and [24] the physical characteristics of CR and its compatibility with fine aggregate were the primary causes of the loss in compressive strength of rubbercrete as indicated in Tables 1 and 2. Due to the hydrophobic nature of CR, increased air content in the fresh rubbercrete mix results in increased void content in the hardened rubbercrete, allowing stresses to concentrate across the pore and resulting in the formation of micro cracks and a corresponding decrease in compressive strength. Also entrapped air on the CR surface thickens the interfacial transition zone (ITZ), which is a porous zone between cement paste and aggregate. The ITZ's poor bonding with the hardened matrix results in the production of micro cracks, which reduces strength and causes premature failure. [35, 42,43,44,45] attributed compressive strength reduction to two factors. First, upon loading, fractures are promptly begun around the rubber particles in the mixture because they are significantly softer (elastically malleable) than the surrounding cement paste, this accelerates the rubber-cement matrix's failure. Second, because they don't adhere to the paste, soft rubber particles may act like voids in the concrete matrix. However, the performance can be improved with the chemicals which it's surface rough. Also, the performance can be improved with the help of filler materials which fills the voids cause due to rubber particle and lead to more compact concrete.

Furthermore, different scholars have made several attempts to either strengthen the bond between hardened cement paste and CR or to speed up the chemical reaction in cement to densify the hardened rubbercrete microstructure to reduce the strength loss in rubbercrete. For instance, CR has been pre-coated with limestone to densify the ITZ and so increase bonding. In another case, cement mortar has been used to pre-coat rubber aggregates [22, 46,47,48,49]. To improve the bond between rubber particles and cement paste, some researchers [50, 51] have made the surface of CR rougher by sodium hydroxide treatment. Similar to this, CR has been treated with UV utilizing water retention to modify its surface energy, preventing it from entrapping air and repelling water and therefore enhancing its bonding [52]. In addition, cement alternatives such as fly ash, metakaolin, ground-granulated blast furnace slag, and silica have been employed to densify the hardened rubbercrete microstructure [50, 53,54,55].

3.1.2 Flexural strength

The flexural strength of rubberized concrete can be assessed by using the three-point loading method on beams (Figs. 8 and 9) [32]. Tables 3 and 4 show, respectively, how crumb and chipped rubber affect rubbercrete's flexural strength, where the maximum authors' data shown indicates a decrease in flexural strength of both CR and chipped rubber concrete. As the percentage of rubber increased as a partial replacement of sand and crush for CR and chipped rubber respectively, flexural strength got decreased.

Fig. 8
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Three-point loading test on concrete containing coarse rubber

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Fig. 9
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Crack behavior of concrete beam after flexural test

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Table 3 Flexural strength (MPa) of crumb rubber concrete
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Table 4 Flexural strength (MPa) of chipped rubbercrete
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A study [31] noted a decrease in the modulus of rupture (MOR) of rubbercrete as CR content increased. This was expected because MOR is the function of compressive strength of concrete which always showed lose. As shown in Fig. 10, when a load is applied to a concrete specimen a ductile failure was observed and the beam was able to hold one-quarter of the ultimate load for a significant time as compared to the control concrete beam which showed sudden failure after reaching its ultimate strength capacity. This phenomenon occurred as a result of the CR acting like fiber reinforcement and upon deformation bridging the fracture. This could be advantageous where crack-widening prevention is desired. [56] and [57] also supported the higher ductility and crack resistance behavior of rubberized concrete and mortars.

Fig. 10
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Flexural failure behaviour of rubberized concrete [31]

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The same factors can be identified as the cause of the reduction in flexural strength as that for compressive strength because flexural strength or modulus of rupture (MOR) is the function of compressive strength and to decrease this lose in flexural strength, the same measures could be taken as that for compressive strength.

3.1.3 Splitting tensile strength

Splitting tensile strength is the indirect method of determination of the tensile strength of concrete. Same to compressive strength, similarly splitting tensile strength decreases. In general, the decrease in indirect (splitting) tensile strength is proportional to the decrease in compressive strength. This could be attributed to the same causes as the decline in compressive strength, namely the creation of air voids [58]. Figures 11 and 12 is showing the past work of some of the researchers on splitting tensile strength of concrete containing CR and chipped rubber respectively. From these figures, it is clear that the splitting tensile strength of both crumbs and chipped rubbercerete decreases as compared to control concrete. In the case of CR content, the splitting tensile strength values are higher as compared to chipped rubber content which signifies that rubber particle size also affects splitting tensile strength [59].

Fig. 11
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Surface treatment of rubber particles in two stages

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Fig. 12
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Split tensile test of specimens after 28 days

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According to [60] and Najim et al., the crumb rubber particles' lower elastic modulus compared to the sand particles may be the cause of the reduction in tensile splitting strength caused by the substitution of sand with crumb rubber. The low density of concrete manufactured with crumb rubber, which results in reduced tensile strength of concrete, may also be a factor [61].

Su et al. explained that to control the loss of rubberized concrete tensile splitting strength, well-graded rubber particles must be used. Additionally [29] suggested that by developing a cementitious coating of silane coupling agent around rubber particles Fig. 13, the splitting tensile strength will not reduce significantly. It was noted that concrete specimens containing coated rubber particles did not disintegrate after failure. Figure 14 displays the breakage surfaces of concrete specimens following the split tensile strength test. Cement hydration products covered the surface of coated rubber particles, whereas nothing remained on the surface of uncoated rubber, demonstrating that the weakest part of the specimen was not the rubber-concrete interface. Thus, the interfacial characteristics between rubber particles and the cement matrix were significantly improved by the chemical bonding that was produced.

Fig. 13
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Crumb Rubbercrete split tensile strength. *[29], ^[38], ^^^^^[137, **[110], ^^[112], ***[20], ^^^[9], ****[31], ^^^^[114]

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Fig. 14
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Chipped Rubbercrete Split Tensile Strength. *[56], ***[115], ^, ^^ and ^^^[114], **[38], ****[116]

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3.1.4 Modulus of elasticity (Ec)

The "modulus of elasticity" (MOE) (Ec) of the concrete is the ratio of the applied stress to the corresponding strain". It shows the concrete's stiffness and resistance to deformation due to applied stress. In other words, it demonstrates the concrete's elastic deflection feature. Although adding rubber to concrete lowers its compressive strength and elastic modulus, it also benefits the seismic safety of structures by preventing the stiffness of structures from being too large based on structural safety [62, 63]. Since the use of CR and chipped rubber decreased the compressive strength of rubberized concrete, thus MOE would also decrease.

Figure 15 depicts a reduction in the MOE of concrete incorporating crumb rubber as a volumetric partial replacement for sand. With an increase in the particle content of recycled waste tires, it was expected that the MOE of rubbercrete would drop. This is because the more elastic material (recycled waste tire rubber) was incorporated into a more rigid material (concrete) [31]. The MOE of rubber is only 0.0007 to 0.004 GPa while that of rock often ranges from 20 to 100 GPa [64].

Fig. 15
figure 15

MOE of crumb rubber concrete at 28 days [31, 67, 114]

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According to [65] The particle size and quantity of rubber affected the MOE of rubberized concrete. The subsequent decrease in the paste amount of rubberized concrete led to a statistically significant decrease in MOE. The addition of very very low modulus crumb rubber in concrete as a partial replacement of fine aggregate is one of the critical factors that affects the MOE of rubbercrete [24]. In line with these researchers [66] also declared that the fine size and increase of rubber content in concrete caused the reduction in MOE of rubberized concrete.

3.2 Durability properties

3.2.1 Water absorption and porosity

Water absorption of rubbercrete is more as compared to ordinary concrete. It is due to different reasons which are explored by different researchers by experimentally investigating concrete containing different types of waste rubbers with different percentages by volume or by weight. According to [67] water absorption of concrete containing CR is increased due to an increase in w/c and content of rubber. Rubber content and w/c increase porosity which subsequently increases the water absorption capacity of concrete. For rubberized concrete, it is difficult to achieve proper compaction as compared to control concrete therefore the density of rubberized concrete is lower than control concrete. This ultimately causes concrete to absorb more water. The trend in water absorption increase with rubber content is also shown in Fig. 16. The reason for the increase in water absorption is the formation of the porous internal structure of rubbercrete, the rubber's capacity to trap air bubbles on its surface due to its non-polar nature. As a result of this phenomenon the interface formed between rubber aggregates and cement is highly porous and absorptive [68]. Sukontasukkul and Tiamlom [69] reported that concrete containing rubber of size passing sieve no. 26 experienced a decrease in water absorption, while the increase in water absorption for rubber of size passing from sieve no. 6. With the inclusion of small rubber, the decrease in water absorption for 10%, 20%, and 30% rubber content was 30.77%, 15.38%, and 11.54% respectively. While for the same percentage replacement levels the increase in water absorption for coarse-size rubber aggregates was 11.54%, 21.15%, and 34.62% respectively. The summary of the above discussion is presented in Fig. 16 and Table 5.

Fig. 16
figure 16

Water absorption of concrete containing rubber (*28 days curing, ** 7 days, ***21 days, ****90 days, ***** 56 days) [19, 71, 78, 102, 111, 117]

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Table 5 Effect of waste recycled tire rubber on water absorption and Porosity of concrete
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3.2.2 Freeze–thaw resistance

According to [34, 64, 68, 70,71,72,73] freezing and thawing resistance of rubbercrete increases with an increase in rubber sand percentage in concrete which is also shown in Table 6.

Table 6 Effect of waste recycled tire rubber on freezing and thawing resistance of concrete
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Rubbercrete has better resistance to freeze/thaw cycles as compared to control concrete, this is brought on by the rubbercrete's increased void ratio. These voids comparatively provide larger space which accommodates the frozen volume of water in rubbercrete [74]. Due to this relaxation internal pressure exerted by freeze water in hardened rubbercrete is relieved and no cracks occur in the rubbercrete [41].CR is a non-polar and hydrophobic substance that repels water and traps air on its surface [34, 66, 68, 70]. Figures 17 and 18 show the shape of CR as seen using the Leica S6D scanning electron microscope (SEM), which demonstrates that during the production of CR, the rubber is broken down and transformed into angular shapes with a rough surface [70]. According to Benazzouk et al. (2008), this irregular shape of CR is responsible for air entrainment on its surface in rubbercrete. Another study conducted by [75] investigated that there is a gap in the interfacial zone between the CR and the concrete/cement paste. This zone's presence in hardened concrete will also help to provide a pressure release system that enables freeze/thaw protection. Finally, it is advantageous to utilize waste tire rubbers in concrete where freeze/thaw cycles occur.

Fig. 17
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80 × magnification of crumb rubber [70]

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Fig. 18
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2000 × magnification of crumb rubber [70]

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3.2.3 Corrosion resistance and chloride penetration

A study [76] replaced the sand with fine rubber with percentages of 0, 5, 10, 15, and 20% by volume and size 0.6 or 0.3 mm. It was concluded that with a 5% replacement level, the best anti-sulfate corrosion resistance can be achieved [77]. Incorporated CR in concrete to check the corrosion resistance of reinforced rubbercrete. It was found that concrete containing 10% CR size 4.75–0.15 mm by volume and concrete without rubber had the same results of reinforcing bar mass loss. From his study, it is clear that when the percentage of CR increased the corrosion resistance decreased and at a 30% replacement level mass loss of reinforcing bars was two times greater than the control concrete. The possible reason for corrosion to steel imbedded rubberized concrete is because raising the CR percentage causes rubbercrete's porosity and void ratio to grow. But from the literature review, it is worth mentioning that the corrosion resistance property of rubberized concrete containing steel needs to be investigated experimentally and very scarce data is available related to the corrosion resistance of steel imbedded rubberized concrete consequently, it will be a crucial subject for further research.

Chloride penetration leads to the steel reinforcement corrosion of cement concrete. Thus, research on chloride permeability is crucial since it has an impact on the durability of rubberized concrete. Some of the past literature is tabulated in Table 7 which describes the effect of CR as a partial replacement of fine aggregate in concrete [24, 67, 73]. Reported an increase in resistance to chloride-ion penetration with the increase in rubber percentage. While [1, 8] and [78] investigated contrary results. From Fig. 19 it is evident that chloride penetration depth increases with increased rubber component which is highest for the 3 and 91 days curing period and lowest for 28 days. The main reason for the increase in chloride ion penetration in rubbercrete is high permeability, interconnected voids, and poor internal packing. CR entraps air on its surface as previously discussed due to which the porosity of rubbercrete increases and this favors higher chloride ion penetration through absorption, permeation, or diffusion [1, 49, 67]. By substituting fly ash (FA) for a portion of the cement in self-compacting rubberized concrete [78] or by substituting 10% of the cement with silica fume (SF), the depth of chloride ion penetration can be lowered in rubberized concrete [22].

Table 7 Effect of waste recycled tire rubber on chloride penetration of concrete
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Fig. 19
figure 19

Chloride ion penetration depth with CR percentage [1, 22]]

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3.2.4 Carbonation resistance

Concrete's capacity to withstand carbonation is a key indicator of its longevity. Concrete will eventually lose its ability to protect steel due to a chemical reaction between atmospheric carbon dioxide and internal alkaline concrete, which will ultimately result in the corrosion phenomenon. The amount of carbon dioxide in the atmosphere rose due to the continued growth of industry, which was aggravated by the greenhouse effect and had a negative impact on the resilience of concrete structures [79,80,81]. Pathak et al. [1] exposed concrete samples (w/c = 0.30) to CO2 curing in a chamber according to CPC 18 RILEM specifications containing CR in 2.5%, 5%, 7.5%, 10%, 12.5%, 15%, 17.5%, and 20% as replacement of sand. Three pieces from each sample were tested after 2, 4, 6, 8, 10, and 12 weeks of CO2 exposure. Thomas et al. concluded that samples containing CR up to 12.5% have decreasing values for carbonation resistance. From 12.5 to 20% substitution samples there is a gradual increase in carbonation depth. A reduction of up to 12.5% CR can be attributed to the lower water-cement ratio which improves pore structures. Also, the size of the CR and replaced sand is the same which results in a closely packed concrete mass and prevents entry of CO2 gas in the rubbercrete. The increase in carbonation depth beyond 10% substitution of rubber results in increased carbonation depth which might be due to the poor internal packing of concrete specimen. This can also be justified by Figs. 20 and 21 [49]. A large cavity is shown in Fig. 21 which acts as a large pore in rubberized concrete and hence allows CO2 gas from the environment to penetrate. Figure 22 also represents a micro crack in the concrete internal structure. These cracks revealed a lack of adequate interfacial adhesion between the rubber fibers and cement paste which provides a favorable environment for CO2 diffusion.

Fig. 20
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SEM image of rubber fiber at 60 × magnification

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Fig. 21
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SEM image of rubber fiber at 600 × magnification

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Fig. 22
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Rubbercrete Specimens showing the depth of carbonation [1]

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A study [8] conducted a test on rubberized concrete (5%, 10%, and 15% coarse natural aggregate replaced by coarse rubber by volume) for carbonation penetration. The depth of carbonation increases with an increase in rubber percentage as shown in Fig. 23. The possible reason for the increase in carbonation depth is more water is needed for concrete containing used tire aggregate to maintain workability and space between cement paste and rubber aggregate. From the data, a 56% increase in carbonation depth was observed at 28 days for a 15% replacement level of coarse aggregate. Bravo et al. also cleared that carbonation depth increases with an increase in the size of rubber.

Fig. 23
figure 23

Carbonation depth (mm) with respect to rubber % volume *[1], **[8]

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4 Rubber concrete for roadside barriers

The barrier is typically made of reinforced concrete and is designed to absorb the impact of a vehicle in the event of a collision, reducing the risk of injury or death to drivers and passengers. The F shape of the barrier as shown in Fig. 24 allows for a gradual redirection of the vehicle in the event of a collision, helping to prevent it from rebounding back into traffic or crossing over into oncoming lanes. Concrete barriers are considered one of the important transportation safety elements on roads to prevent vehicles from leaving the road [82]. Concrete barriers are crucial in preventing vehicles from entering the opposite road lane, falling into the ravines, collision with road side objects or infrastructure, and protecting cyclists and pedestrians from traffic [83, 84].

Fig. 24
figure 24

The F shape concrete barrier [82]

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In case of a vehicle crash on the road or highway may cause serious injuries to passengers which may further cause serious traffic accidents such as rollovers on the road or falling off the cliff. Every year there is a number of crashes occur on roads, in 2009 only in China there were approximately 54,599 crashes occurred on rural highways [85]. As compared to steel barrier vehicles when colliding with concrete barriers a little portion of kinetic energy is transferred into the concrete barrier and a great portion is absorbed by the vehicle, therefore vehicles are badly collapsed, and passengers and vehicle drivers are severely injured [82]. Moreover, concrete barriers are cheaper and require low maintenance as compared to steel non-rigid road safety barriers [86].

Many researchers have tried to reduce the severity of crashes of vehicles with these concrete roadside barriers by increasing their energy absorption capacity, thus minimizing the chances of fatalities. For this purpose [87] intended to use rubberized concrete for the construction of concrete road side barriers. Avcular et al. added that rubberized concrete has the ability of higher impact resistance (energy absorption) as compared to control concrete which results in less damage and injuries during the collision of vehicles with the barrier. [88] tested concrete containing CR and concluded that the mechanical properties (flexural strength, compressive strength, and tangential modulus of elasticity) of rubbercrete reduced as compared to control concrete but impact resistance, ductility, flexibility, and energy absorption are greatly enhanced, thus such type of concrete can be used for structures where strength is not much important. Hence for concrete roadside barriers it would be a best option to utilize end-of-life tire rubber in concrete.

Impact resistance is the ability of concrete to withstand repeated blows by absorbing energy without cracking or spalling. To utilize rubbercrete in concrete roadside barriers impact resistance is much more important because vehicles collide with the high velocity of these barriers. According to [89], the inclusion of CR in concrete improves the impact load behavior of rubbercrete. They also explained that fracture energy also improves with CR sand inclusion in concrete. Fracture energy enhancement was 34.61%, 38.46%, and 46.15% for 5%, 10%, and 20% rubber replacement levels respectively. A researcher [90] reported that crack initiation resistance of concrete containing CR under impact load can be improved. A study [91] added CR sand in concrete by volume with different percentages. They proved that with up to 50% inclusion of CR impact energy improved while beyond 50% replacement level impact energy showed a decrease. A scholar [71] partially added natural sand with shredded rubber in cement mortars. They reported that cement mortar specimens showed improvement in impact behavior. A study [92] prepared concrete beams containing CR. it was concluded that fracture energy, inertial load, impact tup load, and bending load of rubbercrete increased with an increase in rubber aggregate content. Researchers [65] also revealed that the addition of rubber increased the fracture energy of aggregates in concrete. For 10% and 20% rubber inclusion fracture energy increased by 1.38 and 1.33 times greater respectively.

In view of the above literature (Also summarized in Table 8) it can be concluded that impact resistance or impact energy absorption increases with an increase in CR content in concrete as a partial replacement of natural sand. The development of impact resistance can be attributed to some of the properties of rubber-like more elastic behavior, lower stiffness, and higher deformation of CR in comparison to natural sand. Therefore, concrete containing CR as a partial replacement for sand has a better capability of absorbing shocks, and vibrations and consequently having higher impact resistance [53, 93].

Table 8 Effect of CR on the impact resistance of rubbercrete
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The energy absorption capacity can be measured through different methods like peak deflection, peak strain, brittleness index, ultimate strain, load–deflection curve, and peak load [94]. [53] replaced natural sand with CR in percentages of 0, 5, 15, and 25% by volume. The energy absorption improved with an increase in CR percentage. According to Ozbay et al., the reason for the increase in energy absorption is higher rubber content. The more CR aggregates in concrete more will be energy absorption capacity. Researchers [91] conducted fracture and microstructural properties of rubberized concrete that tire particles in rubberized concrete provide crack bridging, compress and twist, and the ability to bend. Tire particles present in concrete absorb a part of energy when an external load is applied. Due to the lower stiffness of rubber particles, the rubberized concrete relatively shows higher flexibility and due to this nature of rubberized concrete, more energy is absorbed as compared to control concrete. Studies [25] and [53] also added that due to the low stiffness property of CR internal friction is reduced and recovering extra strain in the rubberized concrete mass.

[95] replaced natural sand with CR at levels of 0, 20, 40, 60, 80, and 100% by volume. Fine rubber was passed through sieves 10 and 20 (10 and 20 holes per inch respectively). It was concluded that with an increase in rubber percentage energy dissipation increases as shown in Fig. 25. Between the control and 100% rubber specimen, the increment measured was 160.8%.

Fig. 25
figure 25

Energy absorption of concrete containing CR [95, 96]

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A researcher [96] used shredded tire chips (STC) in concrete as a replacement for coarse aggregate with the same replacement level as that of Atahan et al. 2012 also shown in Fig. 26. They concluded that with a replacement level of STC from 0 to 100% the energy absorption capacity is 187% increased. It means that kinetic energy imparted by the vehicle to concrete safety barriers during collision is effectively absorbed which reduces the chances of occupant injury. This discussion clarifies that waste tires can be used with confidence in concrete as a fine and coarse aggregate replacement to increase the energy absorption of rubbercrete.

Fig. 26
figure 26

ECC matrix fracture toughness [101]

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The toughness of rubbercrete is its ability to absorb energy without fracture when an external load is applied. As energy absorption of rubbercrete increases with an increase in rubber content, thus Toughness of rubbercrete will also possibly increase with the increase in rubber content. A past study on the toughness of rubbercrete is listed in Table 9. A study [97] incorporated CR in concrete (See Table 9) and noticed that with sand and coarse aggregate replacements and also with combined replacement the toughness of concrete blocks containing CR increased. A study [98] reported higher toughness of ground waste tire rubber (GWTR) concrete as compared to control concrete. The inclusion of 5% rubber content showed the highest toughness. Researchers [99] partially replaced natural sand with CR in concrete and reported that toughness increased as rubber content increased as shown in Table 9.

Table 9 Toughness of concrete containing CR
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A study [100] added CR in steel fiber reinforced recycled aggregate concrete with 0, 4, 8, 12, and 16% by volume as the sand replacement and noticed that toughness fracture increased up to 8% inclusion of rubber then started to decrease. [101] used rubber (Average size 0.135 mm) in engineered cementitious composites (ECC) as a partial replacement of iron ore tailings (IOTs). It resulted that the fracture toughness of ECC-containing rubber was significantly reduced (almost 50% as compared to control concrete) as shown in Fig. 26. This reduction in fracture toughness may be attributed to the higher porosity of the ECC matrix when rubber is added. The weak interfacial bond between cement paste and rubber particles allows the crack to easily develop around rubber particles [38].

From the above study, it is clear that with rubber particles included in concrete toughness fracture of rubbercrete increases as compared to conventional concrete. This increase in the toughness of rubberized concrete is due to the bending property of rubber, anti-cracking, enhanced strain energy, and compressing and twisting of rubber particles in concrete. The increased toughness of rubberized concrete is one of the advantages to utilize end-of-life tires rubber in concrete for concrete road barriers.

Studies [100] and [102] used CR in concrete as a natural sand replacement with different percentages. They reported an increase in ductility of concrete containing CR as compared to control concrete. [103] utilized waste tire rubber (average size 1.5 mm) in mortar and concrete with different percentages of 0, 10, 15, 20, 30, and 50% by volume as sand replacement. Test results revealed that rubberized cement mortars exhibited significant ductility as compared to control concrete. [104] reported higher ductility of concrete specimens containing CR of size 4–0.5 mm with partial replacement of sand in percentages of 10, 20, and 30% by volume. With these percentages of CR sand in concrete, the increment in ductility index was 25%, 81.25%, and 93.75% respectively. Azevedo et al. [93] reported that when rubber is added to concrete with partial replacement of natural sand the ductility and damping properties of concrete increase. Researchers [105] replaced natural sand with CR (size 4.75 mm) in SCCs at levels of 5, 10, 15, and 20% by volume. They reported a decrease in brittleness index values of SCC containing CR. (Ling 2012) also demonstrated ductile failure rather than a brittle failure of concrete specimens containing fine rubber as partial replacement of natural sand at levels of 10, 20, and 30% by volume. A study [106] partially replaced natural sand with CR in concrete. They concluded that crack propagation in rubbercrete was gradual and not sudden also no major crack was observed as compared to control concrete which showed sudden failure with major cracks as shown in Fig. 27.

Fig. 27
figure 27

Effect of CR on concrete cylinders crack pattern (a) and (d) no rubber, 20% rubber (b) and (e), 40% rubber in c, f, and g. Data obtained from [106]

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5 Circular economy

Tires are converted into the garbage at the end of their useful life and either stored or recycled or repurposed. Aside from retracting or storing tires, good waste management procedures include various options for profiting from reused rubber resources. In a market economy, the potential of recycling is directly tied to the recovery of residual value in proportion to the desire to undertake such efforts. Used tires are remarkable recycling materials since the number of recycling without significant quality is infinite.

End-of-life tire management is a significant environmental concern. Because of the benefits it may provide, recycling discarded rubber tires in civil engineering is regarded as an environmentally friendly and cost-effective alternative. It protects natural resources and creates an environmentally beneficial substance. The use of recycled discarded tires in civil engineering techniques, namely asphalt paving mixes and cement-based products, is gaining popularity across the globe [107].

Every year, about 17 million tonnes of recovered rubber particles are utilized for civil engineering applications including backfilling. The remaining 31% of waste tires are transferred to landfills and stockpiles across the globe. The United States of America (U.S.A.) is a leading tire producer with a moderate to high market share, accounting for around 65 percent of annual industrial sales [108].

Tire recycling is vital not just for trash reduction, but it may also generate valuable materials for other purposes. Rice University, for example, has devised a method for converting used tires into graphene, which may be used to produce stronger and more ecologically friendly concrete.

Other possible uses for recovered tire trash include the recovery of high-value components such as polymeric oils, which may be utilized to manufacture new elastomers. It may also be used to make a very durable multi-use aerogel for applications such as oil spill cleanup, thermal and acoustic insulation, playgrounds, grass, and roadways.

Recycled tire debris may assist to lessen the environmental effect of tire disposal while also providing a valuable resource for the circular economy. It is critical to continue exploring and developing innovative techniques for recycling scrap tires and incorporating them into a wide range of goods and materials.

6 Conclusion

The past research on the characteristics of rubbercrete in both its fresh and hardened states and the application potential of end-of-life tire rubber in roadside concrete barriers have been reviewed in this review study. The fresh properties include workability, air content, and unit weight while hardened properties cover mechanical and durability performances study. Moreover, the potential use of end-of-life tire rubber in roadside concrete barriers was reviewed. Considering an assessment of the prior research undertaken by several researchers listed in this review, the following findings may be drawn:

  1. 1.

    The majority of studies concluded that adding crumb rubber (CR) or chipped rubber to the concrete mixture decreased workability. However, some opposite findings were also observed. In addition, the air content of rubbercrete increased.

  2. 2.

    The unit weight of the concrete mixture was decreased by the addition of CR or chipped rubber.

  3. 3.

    The compressive strength of concrete containing crumb rubber (CR) or chipped rubber decreased substantially as the percentage of replacement of natural aggregate (fine or coarse) with CR or chipped rubber increased. To control and improve rubbercrete compressive strength, incorporating various supplementary cement materials (SCMs) such as fly ash, metakaolin, silica, nano silica, and ground-granulated blast furnace slag are quite successful techniques. Moreover, pre-treatment of rubber aggregates also can be applied to improve the compressive strength such as pre-coating of rubber aggregates with limestone or cement paste, treating rubber surface with NaOH solution, UV utilizing water retention to modify its surface energy, and oxidation of CR with potassium permanganate solution. Moreover, rubber concrete showed lower splitting tensile, flexural strength, and modulus of elasticity (MOE) as compared to normal concrete.

  4. 4.

    Freezing and thawing resistance of concrete increases with an increase in rubber sand percentage. However, the substitution of rubber for concrete makes it porous, permeable, and poor in internal packing, thereby lowering durability because of the increased water absorption, lower corrosion resistance, higher chloride ion penetration, and carbonation depth.

  5. 5.

    Rubber particles have the property of being more elastic, flexible, less stiff, higher deformable, crack bridging, compressible, and twisting, and ability to bend as compared to natural aggregates, therefore the impact resistance, energy absorption, toughness, and ductility increased. Therefore, rubberized concrete is more suitable for roadside barriers.