Tire Crumb Rubber Research Articles

Mechanical and Durability Properties of Rubberized Sulfur Concrete Using Waste Tire Crumb Rubber.

The use of rubber crumbs provides a viable solution for alleviating the disposal problem of waste tires. In this study, rubberized sulfur concrete (RSC) was researched to investigate the optimal mixture proportion and to improve the mixing process in terms of compressive strength and durability performance. For the mixture of the RSC, sand, rubber particles, and micro-filler were adopted as aggregates and sulfur was used for the binding material. Moreover, two mixing processes were applied: the dry mixing process and the wet mixing process. Based on the test results, the increment of rubber particles in the mixture led to a decrease in the compressive strength for both the dry and wet mixing processes. To minimize the voids between the sand and rubber particles, the micro-filler was used at 5% of the total volume. The amount of sulfur varied slightly depending on the mixing process: 30% sulfur for the dry mixing process and 34% sulfur for the wet mixing process, respectively. Consequently, compared to the dry mixing process, the wet mixing process increased the bonding force between sulfur and rubber powder due to the simultaneous heating and combining. In toughness, the wet mixing process demonstrates a 40% higher energy absorption capability compared to the dry mixing process. For the durability performance of the RSC, the mixture with 20% rubber particles produced using the wet mixing process exhibited better corrosion and freeze-thaw resistance.

Compressive stress-strain response of freshly compressed rubberized concrete: An experimental and theoretical study

Although using crumb tire rubber concrete (CTRC) in constructing structural elements is accompanied by various environmental and economic advantages, it always comes with challenges due to a significant loss in some mechanical properties of this concrete type. To tackle this challenge, a novel technique of compressing fresh concrete was used, and its impacts on improving the mechanical features of CTRC were investigated. For this purpose, concrete specimens containing crumb tire rubber (CTR), as the fine aggregate substitute, were constructed considering the variables of the water-to-cement ratio (w/c), volume percentage of CTR, and the fresh concrete pressure level as a fraction of steel tube (mold) yielding stress. After the application of a specified short-term pressure to the fresh mix inside the steel molds and the time required for the concrete setting, the steel tubes were removed after curing, and the concrete core alone was exposed to an axial compressive load. According to the test results, the mechanical properties, weight loss resulting from compressing the fresh concrete, energy absorption, failure pattern, the concrete microstructure, water absorption, and porosity were evaluated. By applying an initial axial pressure of 25–80 MPa on the mixes containing 0 %, 15 %, and 30 % CTR replacing the fine aggregate, the compressive strength, the ultimate strain, the toughness, and the initial modulus of elasticity experienced 100–140 % increase, 130–420 % increase, 120–1140 % increase, and 66–70 % decrease, respectively, compared with the uncompressed specimen. Finally, a regression analysis was employed to propose prediction models for the compressive capacity, modulus of elasticity, peak strain, ultimate strain, and relative toughness of freshly compressed concrete containing CTR particles; these models show proper agreement with the experimental results.

In vitro human oral bioaccessibility assessment of hazardous chemicals, including N, N′-substituted-p-phenylenediamines, coming from recycled tire crumb rubber

Tires, apart from being formed by rubber and filling materials, contain organic compounds added to make them resistant and durable. The widely use of recycled tire crumb rubber (RTCR), main product of the shredding process of end-of-life tires, can cause human exposure to these chemicals due to its use in synthetic football fields and kid's playgrounds. In 2023, the European Commission banned the use of recycled tire crumb rubber in synthetic fields, giving eight years to replace the used material. This study intends to assess the oral bioaccessibility of antiozonants, crosslinking and vulcanizer agents present in RTCR. With this purpose, the Unified Bioaccessibility Method (BARGE) was used to simulate the material ingestion. RTCR is put into contact with the four simulated biological fluids including saliva, gastric and duodenal juice and bile, attempting to simulate human digestion. Afterwards, the organic compounds present in the fluid need to be extracted and Solid-phase extraction (SPE) was the technique selected after being optimized to obtain the best extraction conditions. Ultrasound assisted extraction was performed to evaluate the total concentration of the target compounds in the crumb rubber matrixes. Liquid chromatography coupled to tandem mass spectrometry (LC-MS/MS) was employed to identify and quantify the target compounds. The results showed the bioaccessibility of all the studied analytes, with values ranging from 0.1 % up to 70 %. Benzothiazole was the compound with the highest bioaccessibility with a mean value of 40 % and concentrations reaching 32000 ng g−1 in the bioaccessible fraction. N-(1,3-dimethylbutyl)-N′-phenyl-p-phenylenediamine and its transformation product ((4-Methylpentan-2-yl)amino)-5-(phenylamino)cyclohexa-2,5-diene-1,4-dione) showed an average bioaccessibility of 0.1 % and 1.8 %, respectively, the latter being present in all the analysed samples.

Characterization of light components in rubber-oil mixtures reclaimed asphalt and their effect on the self-healing performance of asphalt

The aging process of asphalt pavement results in the loss of light components (saturates and aromatics) in asphalt, necessitating the use of regenerators for restoration. The study examined the variation pattern of light components in reclaimed asphalt and their effect on the self-healing performance of asphalt after regeneration. Two types of aged asphalt were analyzed using low-temperature co-pyrolysis products of waste tire crumb rubber (WTCR) and waste cooking oil (WCO). The reclaimed asphalt was fractionated into light components using the SARA (saturates, aromatics, resins, and asphaltenes) method. The regenerator containing the highest concentration of light components was identified through the Soxhlet extraction test. The compound compositions and functional groups of the light components in reclaimed asphalt were characterized using gas chromatography-mass spectrometry (GC-MS) and Fourier transform infrared spectroscopy (FTIR). Moreover, the self-healing performance of the reclaimed asphalt was evaluated using a dynamic shear rheometer (DSR). The results indicate that the 260-1-WROM regenerator produced an optimal content of light components under pyrolysis conditions at 260 °C for 1 h. Incorporating the 260-1-WROM regenerator in RTFO resulted in an increase in hopanoids, oxygenates, heterocyclics, and aromas. Similarly, the PAV regeneration process exhibited elevated levels of paraffins, hopanoids, oxygenates, alkanes, heterocyclics, and aromatic compounds. However, the presence of 260-1-WROM failed to increase the contents of steroids. Both types of reclaimed asphalts exhibited superior self-healing capabilities compared to 70#A, RTFO, and PAV. This suggests that 260-1-WROM effectively restored the light components in the aged asphalt, thereby optimizing the flowability of the reclaimed asphalt and enhancing its self-healing properties. Given the above findings, the recommended dosage for 260-1-WROM is 8 % for RTFO and 10 % for PAV.

Rheological behaviour of modified binders for different loading conditions and temperatures: A case of using pig tallow and crumb rubber from end–of–life tyres

This study investigates alternatives to Styrene-Butadiene-Styrene (SBS) polymer in asphalt mixtures by evaluating End-Of-Life tire (ELT) crumb rubber (CR) and fatty acid amide wax (FAA) derived from pig tallow. The research focuses on triple modification of binders with SBS, ELT and FAA to improve performance and reuse waste and industrial by-products in an economical and environmentally responsible manner. The results show that the incorporation of ELT and FAA significantly reduces the SBS content, achieving a 73 % improvement in elastic performance according to Multiple Stress Creep Recovery (MSCR) tests. In addition, this combination improves peak stress and fatigue life in Linear Amplitude Sweep (LAS) tests, demonstrating potential benefits in asphalt mixtures. The study concludes that the combination of pig tallow and end-of-life tire materials doubles the yield energy (Yield Energy of Asphalt Binders, BYET) compared to samples with higher SBS content. In particular, a modification with 6 % CR, 3 % SBS and 2 % FAA doubles the toughness (Er) of a binder with 5 % SBS. This contributes to higher tensile strength in asphalt mixtures, promoting sustainability and efficiency in the road construction industry. This study provides a deeper understanding of how the combination of ELT, FAA and SBS can optimize the properties of asphalt mixtures, highlighting the potential of these additives to improve performance, reduce costs and minimize environmental impact.

Experimental study on freeze-thaw failure of concrete incorporating waste tire crumb rubber and analytical evaluation of frost resistance

The incorporation of waste tire crumb rubber into concrete in appropriate size and content not only facilitates the recycling and safe disposal of waste tires but also enhances concrete frost resistance. The exploration of the frost resistance of rubberized concrete is necessary to fill the major gap of standard evaluation guidelines for rubberized concrete. Through rigorous testing and analysis of parameters such as Wn, Pn, and XEdtn of the rubberized concrete incorporating waste tire crumb rubber ranged from 1.0 % to 5.0 % during rapid freeze-thaw cycles, the study clarified the mechanisms by which crumb rubber affects concrete frost resistance. An increase in durability life was noted as rubber content increased, but a decline occurred when rubber content exceeded 3.0 %. Additionally, pretreating crumb rubber further enhanced frost resistance. The durability life of concrete samples with 3.0 % rubber content reached 275 freeze-thaw cycles. Rubberized concrete containing 2.0–4.0 % crumb rubber saw at least a 25-cycle increase by pretreating crumb rubber, and 5.9–17.9 % increase for Pn compared to that of the concrete with untreated crumb rubber reaching the failure state. The inclusion of crumb rubber altered concrete mesoscopic pore structure and the bonding performance of concrete matrix interface, thereby affecting its frost resistance and failure state. A new set of evaluation equations was developed to quantify the frost resistance of rubberized concrete, providing a robust method for assessing the freeze-thaw response of concrete integrated with waste tire crumb rubber. The DFM proposed in this study proves to be more advanced and effective than existing methods for evaluating frost resistance of rubberized concrete.

Effect of Scrap Tyre Crumb Rubber (STCR) and Lime on the California Bearing Ratio (CBR) of Non-Lateritic Soil

Nigeria is one of the countries generating many used tyres with only small quantity utilized for different local use and the remaining large quantity dumped in different areas as waste. In this study non – laterite soil was stabilized with 3 % Scrap Tyre Crumb Rubber (STCR) and 5.0, 7.5, 10.0, 12.5 and 15.0 % lime for use as road construction material. Atterberg limit tests, compaction (using West African Standard energy) and California Bearing Ratio (CBR) tests were carried out using standard methods, on the natural non-lateritic soil and the treated soil specimens. Preliminary test on the soil was carried out which classified the soil as A-6 (9) and CL in accordance with ASHTO and USCS classification systems respectively. Compaction and California Bearing Ratio (CBR) parameters of the treated non-lateritic showed a great improvement as the MDD increased from 1.68 Mg/m3 to 1.88 Mg/m3 while the OMC reduced from 17.1 % to 14 %. Both soaked and unsoaked CBR values equally increased to 109 % and 103 % respectively with the addition of lime up to 15% plus 3% STCR waste. Based on results obtained from the study, the use of a mixture of 15% lime and 3% STCR waste, are recommended for the treatment of non-lateritic soil for road construction purposes.

Analytical evaluation of stress–strain behavior of rubberized concrete incorporating waste tire crumb rubber

The advancement of rubberized concrete technology and its application in engineering can significantly promote the complete recycling and safe disposal of waste tire rubber. Integrating crumb rubber into concrete alters its compressive stress–strain behavior. This study investigated the stress–strain characteristics of rubberized concrete containing waste tire crumb rubber, addressing the absence of standard guidelines for the design of rubberized concrete. By examining the complete stress–strain curves of rubberized concrete, key parameters such as peak stress, initial elastic modulus, peak strain and secant modulus were meticulously evaluated. The study delved into the mechanisms through which crumb rubber influences the stress–strain behavior of concrete, considering factors including variations in rubber content and pretreatment methods. The experimental data were analyzed using conventional concrete constitutive theories to quantify the impact of crumb rubber on rubberized concrete's stress–strain relationship. Significant variations were observed, including a notable decline in strength with increasing rubber content. For instance, increasing the rubber content from 0.0% to 5.0% led to reductions of 44.2% in peak stress and 47.0% in secant modulus compared to the reference concrete. In addition, pretreating the crumb rubber markedly improved rubberized concrete strength, and the peak stress of concrete with 1.0%–5.0% pretreated crumb rubber increased by an average of 7.0% compared to that with untreated crumb rubber. The study identified that crumb rubber's inclusion significantly altered the coordination of stress and strain in concrete, thereby affecting its stress–strain behavior. A set of evaluation equations for the stress–strain relationship of rubberized concrete was developed, offering a reliable method for predicting its behavior. This research fills a critical gap in the analytical assessment of rubberized concrete and marks a significant stride towards its broader use in sustainable construction practices.

Enhancing Concrete Performance with Crumb Rubber and Waste Materials: A Study on Mechanical and Durability Properties

In addressing the dual challenges of sustainable waste management and environmental conservation in the construction industry, particularly the disposal of waste tire crumb rubber (CR) and the demand for eco-friendly building materials, this study explores a novel solution. It examines the sustainable incorporation of waste tire crumb rubber and mineral additions—namely silica fume (SF), marble slurry powder (MSP), and fly ash (FA)—as partial substitutes for natural fine aggregates and cement in concrete. Through comprehensive testing of seventeen concrete samples, the study reveals that the specific mix of R10S5M10F15 that contained 10% crumb rubber as replacement of fine aggregates, and 5% silica fume, 10% marble slurry powder and 15% fly ash as replacements of cement, not only achieves compressive and split tensile strength comparable to the control mix, while the 90 days flexural strength was improved by 4.48%; credited to SF’s pozzolanic action and the filler effects of MSP and FA, but also that the inclusion of CR, while reducing compressive strength due to material variations, enhances ductility and improves resistance to sulfate and acid attacks, despite increasing water absorption. The primary goal of this research is to investigate the feasibility and effectiveness of using waste materials in concrete to foster more sustainable construction practices. The objectives include a detailed assessment of the mechanical properties and durability of concrete incorporating these waste materials, aiming to determine the optimal mix proportions for their effective utilization. This study’s novelty lies in its detailed analysis of the synergistic effects of combining CR, SF, MSP, and FA in concrete, contributing to the field by offering a sustainable alternative approach to traditional concrete formulations and highlighting the delicate balance required for optimized concrete performance.

Experimental study and predictive modelling of damping ratio in hybrid polymer concrete

The improved damping capacity of concrete materials is crucial for many applications, especially the ones exposed to dynamic external forces. This study explores the optimal circumstances of copolymer composite binder, ratio of fine to coarse aggregate, curing time, size and content of tyre crumb rubber on enhancing damping ratio of hybrid polymer concrete. Owing to the limitation of conventional models and experimental methods in effectively handling the multiple and complicated relationship between the input parameters of the hybrid polymer concrete and its damping capacity, two robust machine leaning models including extreme gradient boosting (XGB), and artificial neural network (ANN) algorithms were developed to predict the values of damping ratio from an experimental database of 196 samples. Multiple linear regression (MLR) was employed in this study as a benchmark for comparing with the ANN and XGB methods. The results indicate that the considered algorithms yield accurate models for predicting the damping ratio of HPC composites. However, ANN and XGB outperform MLR with an impressive R-square of 0.985 and 0.981, respectively versus 0.875. Analysing the importance of input features using the XGB algorithm also reveals that the curing time has the highest impact on predicting the damping ratio. The volume fractions of resin matrix and crumb rubber are the next most important features. The crumb rubber size, within the studied range, appears to be the least impactful one.

Physical, strength and acoustic properties of lightweight cement composite with preplaced chemically-treated crumb rubber

The valorisation of waste tyre crumb rubber (CR) as a sustainable construction material can alleviate environmental pollution and save natural aggregate consumption. However, its use in cement composite can result in a significant loss of strength due to weak adhesion and the non-uniform dispersion of CR. To compensate this strength loss, this research aims to investigate the innovative incorporation of chemically treated CR via the preplaced aggregate mixing (PM) method in producing a lightweight cement composite. The CR was treated with different chemicals, namely soaking in potassium permanganate and sulphuric acid solutions. The findings reveal a significant improvement in compressive strength (up to 160%) and water absorption reduction (from 20% to 175%) using the chemically treated CR and PM mixing methods, producing a lightweight cement composite with a density of about 1535 kg/m3. The SEM observation demonstrates the improvement in the CR–paste interface due to the treatment of the CR and the PM mixing methods, and due to the chemical treatment, which improved the wettability of the CR. On the other hand, the sound absorption and noise reduction coefficient of the chemically treated CR lightweight cement composite was almost similar for both the normal mixing (NM) and the PM methods. Overall, the results demonstrate that the CR treatment with sulphuric acid is promising for the PM method to produce a lightweight cement composite.

Emission reduction agents: A solution to inhibit the emission of harmful volatile organic compounds from crumb rubber modified bitumen

Volatile organic compounds (VOCs) in bitumen fumes pose health risks to workers. Adding end-of-life tire crumb rubber (CR) to bitumen increases VOC emissions. To promote cleaner asphalt production, recycled materials like cementitious materials, activated carbon, zeolite, and geopolymers were incorporated into crumb rubber modified bitumen and explored as emission reduction agents (ERAs). Proton-transfer-reaction time-of-flight mass spectrometry was used to compare VOC emissions across blends. ERAs reduced emissions by at least 33%, with Portland cement, activated carbon, and geopolymer-based fly ash achieving up to 58%, 49%, and 48% reduction, respectively. Multivariable regression analyses showed that the BET surface area, BJH adsorption cumulative surface area, BJH desorption cumulative surface area, and average pore diameter of the ERAs were the predominant factors contributing to the reduction of VOC emissions.

Assessment of a Non-Destructive Testing Method Using Ultrasonic Pulse Velocity to Determine the Compressive Strength of Rubberized Bricks Produced with Lime Kiln Dust Waste

This paper presents a comprehensive study in which non-destructive testing utilizing ultrasonic pulse velocity (UPV), considering both pressure (P) waves and shear (S) waves, was used to assess the compressive strength (CS) of rubberized bricks. These innovative bricks were manufactured by blending lime kiln dust (LKD) waste with ground granulated blast furnace slag (GGBFS), sand, and fine waste tire crumb rubber (WTCR). This study introduces mathematical models to explain the relationships between the results of destructive tests (DTs), specifically compression strength (CS) tests, and non-destructive tests (NDTs) employing UPV. These models were subsequently used to conduct validation exercises to accurately predict the strength of the rubberized bricks produced. The outcomes of the validation tests underscore the effectiveness of the UPV method in predicting the CS of rubberized eco-friendly bricks produced using an LKD-GGBFS blend. Importantly, the prediction using the power model exhibited minimal errors, confirming the utility of the UPV method as a reliable tool for assessing the compressive strength of such sustainable construction materials. This research contributes to advancing the field of eco-friendly construction materials and highlights the practical applicability of non-destructive ultrasonic testing in assessing their structural properties.

Synergetic Effects of Waste Engine Oil and Crumb Tyre Rubber on Bitumen Modification

Bitumen is a widely used road infrastructure material exhibiting black color and sticky consistency and is known for its versatile use and thermoplastic nature. In recent years, predicting road life has been arduous due to increasing traffic, global warming, and ever-changing stresses on pavements. Meanwhile, a large amount of waste engine oil (WEO) and vehicle tyres from various automobiles is disposed of into the atmosphere as hazardous waste. Relatedly, heavy metals and the huge capital involved in the sustainable treatment of these materials have been challenging. Therefore, this study aims to analyze modified bitumen using (WEO) in combination with waste crumb tyre rubber (CTR), thus reducing virgin bitumen (VB) use and making bitumen a sustainable material. During the characterization of modified bitumen, the following WEO concentrations were utilized: 3%, 5%, 7%, and 9%, and the following CTR concentrations: 5%, 7%, 9%, 12%, and 15%. The properties of modified and virgin bitumen were compared. It has been found that the blend of 5% CTR and 9% WEO exhibit the highest penetration value and the lowest softening temperature of all the samples examined. As a result, this mixture can be used to reduce the excessive brittleness of bitumen to a greater extent. Moreover, the flash and fire point values have increased after modification, while the ductility and specific gravity values have decreased. In summary, the modified bitumen has shown promising results regarding physical changes in bitumen.

Anti-deformation performance of asphalt modified by carbon black extracted from waste cooking oil pyrolysis waste tires rubber

As a promising renewable resource, waste tire rubber powder has been utilized to enhance asphalt performance but it has compatibility concerns with matrix asphalt. To solve the phase separation between crumb tire rubber (CTR) and asphalt, waste cooking oil (WCO) has been successfully employed as the solvent to desulfurize crumb rubber. However, about 30 % of carbon black is wrapped in crumb rubber, which has a high recycling value. The cross-linking network structure of the crumb rubber can be loosened by waste cooking oil, and the carbon black will gradually peel off. This study desulfurizes crumb rubber with waste cooking oil at 180 ℃, and the carbon black produced by the evolution of rubber structure was separated by Soxhlet extraction. The rubber-cracked carbon black (RCCB) and the industrial carbon black N330 were added to asphalt, and the impact of the two different carbon black on the anti-deformation of asphalt was analyzed by dynamic shear rheometer (DSR). The results indicated that at the same dosage of 5 %, the carbon black separated from rubber will weaken the deformation resistance of asphalt at high temperatures, rather than improving it like N330 produced in the industry.

Evaluation of sorbent amendments used with stormwater management practices to remove contaminants: Impacts of rainfall intensity and antecedent dry periods

For a comprehensive evaluation of the suitability and efficiency of soil amendments in bioretention systems, it is crucial to investigate the capability of amendments for simultaneously serving three important functions under intermittent and variable flow conditions: removing a wide range of contaminants, supporting plant health, and maintaining media infiltration rate. However, most studies have not considered these important factors and conditions simultaneously, which may overestimate or underestimate the bioretention performance. In this study, a long-term vegetated column study was conducted to investigate the ability of various sorbent amendments– coconut coir fiber (CCF), blast furnace slag (BFS), and waste tire crumb rubber (WTCR) –for removal of metals, nutrients, and polycyclic aromatic hydrocarbons (PAHs) from stormwater. The experiments were performed under intermittent flow conditions considering different runoff intensities and antecedent dry periods (ADP). The long-term effect of bioretention usage on plant health and media infiltration rate was also investigated.All amended and unamended columns were able to remove >99 % of influent metals, except Cu, over the 7-month experiment period with different rain intensities and dry periods; modest effluent Cu concentrations occurred with higher rainfall. The performance of different media for removing PAHs such as naphthalene and acenaphthylene varied with the rain intensity. The BFS-amended media had high phosphate removal capacity (>90 %) under tested conditions. In all columns, nitrate removal was notably affected by changes in stormwater intensity and ADP, with high nitrate removal during heavy rainfall. Over the entire experiment, all media had good infiltration rate within the locally acceptable range (1–25 cm/h). The high iron and aluminum contents of BFS adversely affected the plant health in BFS-amended media. Overall, this study identifies the opportunities and challenges associated with the usage of bioretention amendments, and improves awareness among bioretention designers to consider seasonal effect on the performance of bioretention systems.

Ingestion of car tire crumb rubber and uptake of associated chemicals by lumpfish (Cyclopterus lumpus)

Car tire rubber constitutes one of the largest fractions of microplastics emissions to the environment. The two main emission sources are tire wear particles (TWPs) formed through abrasion during driving and runoff of crumb rubber (CR) granulate produced from end-of-life tires that is used as infill on artificial sports fields. Both tire wear particles and crumb rubber contain a complex mixture of metal and organic chemical additives, and exposure to both the particulate forms and their leachates can cause adverse effects in aquatic species. An understanding of the exposure pathways and mechanisms of toxicity are, however, scarce. While the most abundant metals and organic chemicals in car tire rubber have multiple other applications, para-phenylenediamines (PDs) are primarily used as rubber antioxidants and were recently shown to cause negative effects in aquatic organisms. The present study investigated the responses of the marine lumpfish (Cyclopterus lumpus) to crumb rubber exposure in a controlled feeding experiment. Juvenile fish were offered crumb rubber particles with their feed for 1 week, followed by 2 weeks of depuration. Crumb rubber particle ingestion occurred in >75% of exposed individuals, with a maximum of 84 particles observed in one specimen. Gastrointestinal tract retention times varied, with some organisms having no crumb rubber particles and others still containing up to 33 crumb rubber particles at the end of the experiment. Blood samples were analyzed for metals and organic chemicals, with ICP-MS analysis revealing there was no uptake of metals by the exposed fish. Interestingly, high resolution GC-MS analysis indicated that uptake of PDs into lumpfish blood was proportionate to the number of ingested CR particles. Three of the PDs found in blood were the same as those identified in the additive mixture Vulkanox3100. N-(1,3-dimethylbutyl)-N′-phenyl-p-phenylenediamine (6PPD) was the most concentrated PD in both the crumb rubber and lumpfish blood. The transformation product 6PPD-quinone was detected in the rubber material, but not in the blood. This study demonstrates that PDs are specific and bioavailable chemicals in car tire rubber that have the potential to serve as biomarkers of recent exposure to tire chemicals, where simple blood samples could be used to assess recent tire chemical exposure in vertebrates, including humans.

Effects of Tire Crumb Rubber and Steel Fiber on Punching Shear Behavior of Two-way Alkali-activated Concrete Flat Slabs

As a result of the rapid increase in the demand for transportation vehicles recently, the accumulation of waste tires causes environmental problems. One of the methods that can contribute to the reduction of this environmental problem is the recycling of waste tires as a construction material in aggregate form. This research investigated the impacts of waste tire crumb rubber with/out steel fiber (SF) on the two-way punching-shear behavior alkali-activated concrete (AAC) flat slabs and performed center point load tests. In the study, one-type of SF and two kinds of scrap tire waste i.e., crumb rubber (CR) and tire particles, were used on the producing of rubberized AAC slabs obtained by 100% as binder made of ground-granulated blast furnace slag (GGBFS). Also, while both fine crumb rubber (FCR) and coarse crumb rubber (CCR) were used together in the AAC slabs, tire crumb rubber (TCR) was used alone at the same proportion. Additionally, the fine aggregate was substituted with 10% and 15% FCR and CCR, and coarse aggregate was substituted with TCR in the same proportions. Additionally, AAC slabs with recycled tire rubber (RTR) were produced as fibrous and non-fibrous using 1% by volume hook-end SF. In total, nine AAC slabs with sizes of 50 x 50 x 6 cm3 were manufactured for the study. Experimental data showed that the inclusion of RTR only slightly reduced the punching shear strength of AAC slabs and the punching shear strength of the slabs increased when SF was added to the mixtures containing RTR.

Properties of sustainable self-compacted concrete with recycled concrete and waste tire crumb rubber aggregates

The concrete building industry has to adhere to stringent sustainability standards. In previous investigations, the utilization of recycled concrete aggregates (RCA) from construction and demolition waste (CDW) or crumb rubber (CR) from waste tires in producing sustainable self-compacted concrete (SCC) was well studied; however, the combined effect of RCA and CR on the performance of SCC is scarce. Therefore, the main purpose of this study is to evaluate the feasibility of developing SCC mixtures containing both RCA and CR and their influence on the performance of SCC. Three distinct series of SCC mixes were designed so that the water-to-binder ratio and total binder content were kept at 0.32 and 505 kg/m3. In the first series, the effect of RCA content (0%, 50%, and 100%) in place of natural coarse aggregate (NCA) on the performance of SCC mixtures was studied. Moreover, the effect of various CR contents (0%, 10%, 20%, 30%, and 40%) as a sand substitution and 50% RCA was investigated in the second series. In the third series, the influence of CR inclusion and 100% RCA was utilized to promote the sustainability of SCC. The fresh behavior of the mixtures was assessed by measuring followability, viscosity, and segregation resistance. Density, water absorption, and apparent porosity for all mixes were also examined. The mechanical properties were assessed for compressive, splitting tensile, and flexural strengths. The findings show that the inclusion of RCA and CR has an adverse impact on the fresh, physical, and mechanical properties of SCC, excluding segregation resistance. However, it is possible to produce a SCC using 100% RCA and 40% CR with a slump flow diameter of 605 (SF1 class) and a compressive strength of greater than 31 MPa, which is applicable for structural applications. Moreover, the ACI and Euro code CEB-FIP proposed models can predict the mechanical properties of the developed SCC made with recycled materials. This research could contribute to a more sustainable SCC by substituting recycled materials for natural aggregates.

Assessing children’s potential exposures to harmful metals in tire crumb rubber by accelerated photodegradation weathering

Whether a tire crumb rubber (TCR) playground would expose children to potentially harmful chemicals such as heavy metals is an open question. The released metals available for pickup on the surface of TCR tiles was studied by accelerated 2-year aging of the TCRs in the NIST-SPHERE (National Institute of Standards and Technology Simulated Photodegradation via High Energy Radiant Exposure). The dermal contact was mimicked by a method of composite surface wiping from US Environmental Protection Agency throughout the weathering process. The surface release of ten most concerned harmful metals (Be, Cr, Cu, As, Se, Cd, Sb, Ba, Tl, Pb) was monitored through the course of aging. The cumulative release of Cu, As, Tl, and Sb reached potentially harmful levels at various times within 3 years, although only Cr was found at a harmful level on the surface of the tiles. Taking the cleansing effect of precipitation or periodic cleansing with rain into account, TCR playgrounds may still be safe for use.