Search Results (45)

This study aims to investigate the application of nuclear magnetic resonance (NMR) to characterize mortars containing recycled rubber waste as an eco-innovative material for sustainable construction. The primary objective was to analyze the way rubber granules influence hydration kinetics, microstructural development and pore structure. The innovative mortar formulations incorporated rubber granules, casein, natural hydraulic lime (NHL), and latex. NMR analysis revealed distinct T₂ relaxation time distributions correlated with different pore sizes and water states: shorter T₂ values demonstrate strongly bound water in small pores, while longer T₂ values are associated with loosely bound or free water in larger pores. The formulation with 3.5% NHL and 5% rubber granules exhibited optimal microstructural characteristics. These results reveal that NMR is a valuable, non-destructive tool for monitoring cementitious material evolution and supporting the use of tire-derived waste in eco-innovative mortar designs. Full article

The scarcity of natural aggregates and the growing accumulation of waste materials have driven the demand for sustainable and circular economy solutions in transportation infrastructure, and this has led to the utilization of waste materials in transport infrastructure, such as recycled rubber. Although numerous laboratory experiments have been conducted on granular mixtures mixed with rubber, predicting the complex stress–strain behaviour of these mixtures mathematically and capturing the influence of rubber on the geotechnical properties of waste mixtures are imperative. This paper presents a comprehensive review of the constitutive models developed to predict the stress–strain behaviour, dilatancy, and shear strength of rubber-mixed waste materials, including sand–rubber, coal wash–steel furnace slag–rubber crumbs, and coal wash–rubber crumbs in various transport infrastructure applications under static loading. This paper also highlights the innovations and limitations of these existing constitutive models on rubber-mixed materials. It was found that existing constitutive models based on hyperbolic, hypoplastic, critical state, and bounding surface plasticity approaches can capture the behaviour of these materials under static loading conditions. However, further developments are required to incorporate the influence of the type and size of the rubber, particle breakage, and damping properties and also account for train-induced cyclic loading in models developed for railway substructures. This paper contributes to advancing future research aimed at deepening the fundamental understanding of rubber-mixed materials used in transportation infrastructure. Full article

Within the scientific research project ‘RubSuPave’, a large number of laboratory tests were carried out to investigate the addition of waste rubber (WR) to mixtures of a cement-bound base course (CBC) for pavement construction. For mixtures consisting of gravel aggregate, sand, cement (at 3%, 5%, and 7% by mass) and various sand replacements with WR (0%, 10%, 20%, 30% and 40% volume) additions, the compaction characteristics, compressive strength, and resistance to freezing and thawing (F/T) were determined. The results show that compressive strength is negatively affected by the addition of WR, while F/T resistance is improved, with mixtures containing 10–20% WR and 5% cement being optimal. The next step was transferring the knowledge gained into field conditions via the large-scale production of such mixtures in concrete plants and the construction of test fields. The CBC reference and WR mixtures (2% mass) were produced in two different concrete plants; the samples were compacted, and compressive strength and F/T resistance were tested. The CBC mixtures made in the first plant were used for the construction of the test field. The results and problems of mixture production in two different concrete plants are presented, along with the experiences of the construction of a test field with such a rubberised base course. The in-plant production of mixtures with 2% WR also resulted in a reduction in compressive strength and improved resistance to freezing, but these significantly values varied between plants. The main reasons for this are that the addition of WR causes issues due to its dosing and during its incorporation into the second plant, difficulty in achieving a homogenous mixture, and the subsequent maintenance of the concrete plant, implying that the technology should be adapted for large-scale production in future. The test field, with both the reference mixture and the WR mixture from the first plant, will be monitored further to determine its behaviour in real conditions. Full article

The rubber elasticity theory has been lengthily applied to several polymeric hydrogel substances and upgraded from idealistic models to consider imperfections in the polymer network. The theory relies solely on hyperelastic material models in order to provide a description of the elastic polymer network. While this is also applicable to polymer gels, such hydrogels are rather characterized by their water content and visco-elastic mechanical properties. In this work, we applied rubber elasticity constitutive models through hyperelastic parameter identification of hydrogels based on their stress–strain response to compression. We further performed swelling experiments and determined the intrinsic properties, i.e., density, of the specimens and their components. Additionally, we estimated their equilibrium swelling and employed it in the swelling-equilibrium theory in order to determine the polymer–solvent interaction parameter of each hydrogel with regard to cross-linking. Our results show that the average mesh size obtained from the rubber elasticity theory can be regarded as a concentration-dependent characteristic length of the hydrogel’s network and couples the non-linear elastic response to the specimens’ inherent visco-elasticity through hysteresis as a quantifier of energy dissipation under large deformation. Full article

Solution styrene–butadiene rubber (SSBR) is widely used to improve the properties of tire tread compounds. Tire wear particles (TWPs), which are generated on real roads as vehicles traverse, represent one of significant sources of microplastics. In this study, four SSBR compounds were prepared using two SSBRs with high styrene (STY samples) and 1,2-unit (VIN samples) contents, along with dicyclopentadiene resin. The abrasion behaviors were investigated using four different abrasion testers: cut and chip (CC), Lambourn, DIN, and laboratory abrasion tester (LAT100). The abrasion rates observed in the Lambourn and LAT100 abrasion tests were consistent with each other, but the results of CC and DIN abrasion tests differed from them. The addition of the resin improved the abrasion rate and resulted in the generation of large wear particles. The abrasion rates of STY samples in the Lambourn and LAT100 abrasion tests were lower than those of VIN samples, whereas the values in the CC and DIN abrasion tests were higher than those of VIN samples. The wear particles were predominantly larger than 1000 μm, except for the VIN sample in the DIN abrasion test. However, TWPs > 1000 μm are rarely produced on real roads. The size distributions of wear particles > 1000 μm were 74.0–99.5%, 65.9–93.4%, 7.2–95.1%, and 37.5–83.0% in the CC, Lambourn, DIN, and LAT100 abrasion tests, respectively. The size distributions of wear particles in the Lambourn and LAT100 abrasion tests were broader than those in the other tests, whereas the distributions in the CC abrasion test were narrower. The abrasion patterns and the morphologies and size distributions of wear particles generated by the four abrasion tests varied significantly, attributable to differences in the bound rubber contents, crosslink densities, and tensile properties. Full article

With the installation of rubber isolation bearings in the upper and lower ground layers, an isolated step-terrace structure was created. Considering the ultimate bearing capacity of the rubber bearing under tension as the critical condition, a comprehensive framework was established to evaluate the overturning failure mechanisms present in isolated step-terrace structures. The bound of nominal aspect ratio was identified as the principal control index within this framework, which incorporates critical parameters such as height ratio (α), width ratio (β), vertical tensile stiffness to compressive stiffness ratio (γ), seismic coefficient (k), and nominal vertical compressive stress (σ₀) to provide a thorough analysis of the structural responses and potential failure scenarios. In order to further investigate this matter, a scaled model of an isolated step-terrace concrete frame structure featuring two dropped layers and a single span within an 8° seismic fortification zone was meticulously crafted at a 1:10 similarity ratio. Subsequently, a series of shaking table tests were conducted to analyze the structural response under seismic excitation. The findings indicate that: utilizing the bound of nominal aspect ratio as a metric to gauge the anti-overturning capacity of isolated step-terrace structures is a justified approach. In instances where the height ratio remains constant, the bound of nominal aspect ratio for both positive and negative overturning trended upward with an increase in the width ratio. Notably, the bound of nominal aspect ratio for positive overturning consistently registered lower values compared to that of the negative overturning, underscoring the heightened susceptibility of step-terrace structures to positive overturning. Moreover, in scenarios characterized by higher height and width ratios, the structural integrity remained unscathed by any overturning effects arising from insufficient tensile strength in rubber bearings. Furthermore, the bound of nominal aspect ratio exhibited an ascending trend as the seismic coefficient, nominal vertical compressive stress, and vertical tensile stiffness to compressive stiffness ratio decreased. The outcomes derived from the shaking table test not only confirm the impressive seismic performance of the structure, but also, by closely examining the instantaneous stress variations within the upper and lower isolation layers of the model, substantiate the existence of a positive overturning hazard in scenarios marked by higher seismic coefficients (k). This observation aligns seamlessly with the theoretical projections, thereby substantiating the efficacy of the structural overturning failure theory through direct empirical verification. Full article

Permeable pavements are vital in sustainable urban water management, addressing critical challenges while enhancing environmental resilience. This study focuses on the innovative polyurethane-bound Porous Rubber Pavement (PRP), which possesses high permeability and elasticity due to its unique composition of stone and crumb rubber aggregates with polyurethane binders. PRP’s useful benefits, such as noise reduction, efficient snow/ice management, and others, enhance its appeal, emphasizing the necessity for a thorough investigation into its performance and characteristics, especially in North America. To address these gaps, this paper comprehensively analyzes PRP’s durability and performance, including its strength range, failure criteria, and susceptibility to moisture-induced damage. Various testing methods are utilized, such as evaluating the abrasion loss of the stone aggregate, rutting, stripping due to moisture susceptibility, resistance to degradation from impact and abrasion, and permeability tests. This study evaluates five distinct mix compositions with varied proportions of aggregates and binders. Further, it investigates the effects of different binder types on PRP performance, such as aromatic and aliphatic binders obtained from various sources. Upon the analysis of the comprehensive test results, it was found that the mix characterized by increased rubber aggregates and a high binder content demonstrated a superior performance across various tests for PRP applications. This mix exhibited an enhanced resistance to abrasion, raveling, rutting, and permanent deformation, showcasing its durability and functionality. Additionally, when combined with an aliphatic binder, it displayed an optimal performance even in challenging freeze–thaw conditions, making it a recommended choice for long-term pavement solutions. Full article

The optimal mixing conditions for silica-filled NR compounds dictate the need to proceed at a high temperature, i.e., 150 °C, to achieve a sufficient degree of silanization. On the other hand, natural rubber is prone to degradation due to mechanical shear and thermal effects during mixing, particularly at long exposure times. The present work investigates NR rubber degradation during mixing in relation to prolonged silanization times. The Mooney viscosity and stress relaxation rates, bound rubber content, storage modulus (G’), and delta δ were investigated to indicate the changes in the elastic/viscous responses of NR molecules related to rubber degradation, molecular chain modifications, and premature crosslinking/interaction. In Gum NR (unfilled), an increase in the viscous response with increasing mixing times indicates a major chain scission that causes a decreased molecular weight and risen chain mobility. For silica-filled NR, an initial decrease in the Mooney viscosity with increasing silanization time is attributed to the chain scission first, but thereafter the effect of the degradation is counterbalanced by a sufficient silanization/coupling reaction which leads to leveling off of the viscous response. Finally, the higher viscous response due to degradation leads to the deterioration of the mechanical properties and rolling resistance performance of tire treads made from such silica-filled NR, particularly when the silanization time exceeds 495 s. Full article

The high stiffness of cement-bound aggregate (CBA) is recognized as its main drawback. The stiffness is described by the modulus of elasticity, which is difficult to determine precisely in CBA. Incorporating rubber in these mixtures reduces their stiffness, but mathematical models of the influence of rubber on the mechanical characteristics have not previously been defined. The scope of this research was to define a prediction model for the compressive strength (f_c), dynamic modulus of elasticity (E_dyn) and static modulus of elasticity (E_st) based on the measured ultrasonic pulse velocity as a non-destructive test method. The difference between these two modules is based on the measurement method. Within this research, the cement and waste rubber content were varied, and the mechanical properties were determined for three curing periods. The E_dyn was measured using the ultrasonic pulse velocity (UPV), while the E_st was determined using three-dimensional digital image correlation (3D DIC). The influence of the amount of cement and rubber and the curing period on the UPV was determined. The development of prediction models for estimating the f_c and E_st of CBA modified with waste rubber based on the non-destructive test results is highlighted as the most significant contribution of this work. The curing period was statistically significant for the prediction of the E_st, which points to the development of CBA elastic properties through different stages during the cement-hydration process. By contrast, the curing period was not statistically significant when estimating the f_c, resulting in a simplified, practical and usable prediction model. Full article

Natural rubber (cis-1,4-polyisoprene, NR) is an important raw material utilized widely in the manufacturing of medical, agricultural, and industrial products. Rubber tree (Hevea brasiliensis) and several alternative rubber-producing plants (Taraxacum kok-saghyz, Lactuca sativa, and Parthenium argentatum) have the capability to produce high-quality NR. With the progress of genome sequencing, similar rubber biosynthesis pathways have been discovered among different rubber-producing plant species. NR is synthesized and stored in rubber particles, which are specialized organelles comprising a hydrophobic NR core surrounded by a lipid monolayer and membrane-bound proteins. The rubber transferase complex is considered to be the pivotal enzyme involved in catalyzing NR biosynthesis. However, the exact compositions of the RT complex in rubber-producing plants remain elusive and poorly understood. Here, we review the progress of genome sequencing, natural rubber biosynthesis, and the components of the RT complex in rubber-producing plants. We emphasize that identifying the detailed components of the RT complex holds great significance for exploring the mechanism of NR biosynthesis and accelerating molecular breeding in rubber-producing plants. Full article

The seismic response of base-isolated structures is notably influenced by mechanical properties of isolation devices due to their essential role in structural behavior. Consequently, the variability of such properties should be accounted for in the design process. The current seismic codes prescribe a simplified approach based on structural analyses in two extreme situations resulting from the upper and lower bound design properties of bearings (upper and lower bound analyses). In the case that experimental data are not provided by manufacturers, seismic codes provide the so-called “property modification factors” or “λ-factors”, i.e., modification coefficients to be applied to the nominal dynamic properties of bearings to obtain their upper or lower design properties. The aim of this paper is to provide a historical review of values provided for such factors by the main seismic codes by highlighting the limits, as well as some clerical errors, present in some codes. In particular, the European seismic codes are illustrated in detail, i.e., the Eurocode for bridges (EN 1998-2) and product standard on anti-seismic devices (EN 15129). Both these codes account for different sources of variability, such as the bearings production and the environmental and behavioral effects. For all these effects, the same λ-factor values are provided by the two codes, deriving from the second version of the AASHTO guide specifications for seismic isolation of bridges (AASHTO 1999), which are based on limited and/or old data, especially for high damping rubber bearings (HDRBs), and were never updated in the successive versions. More recent standards are also illustrated, providing different perspectives that deserve attention, even though they require further investigations to be applied in the design practice. Full article

In this work, the contribution of different types of carbon blacks (N115, N330, N550, N660) and their primary and secondary thermally cracked recovered carbon blacks to the mechanical properties of NR composites was evaluated. The thermally cracked recovered carbon blacks were prepared by cracking the rubber composites at 500 °C and de-hybridizing them at 900 °C. The characterization of the thermally cracked recovered carbon blacks by scanning electron microscopy, Raman spectroscopy, and X-ray photoelectron spectroscopy showed that carbon blacks after primary and secondary thermal cracking recovery were more prone to aggregation and exhibited a higher degree of carbon defects. The number and type of functional groups on the surface of these carbon blacks were significantly reduced. For NR composites with pristine samples added, the mechanical properties and the bound rubber content tests showed that the mechanical properties of the NR composites became weaker with the increase in carbon black particle size. The bound rubber content also decreased with increased carbon black particle size. The mechanical properties of the NR composites reinforced with carbon black recovered by primary and secondary thermal cracking would therefore decrease. The results of AFM and DSC tests further confirmed the decreasing trend of bound rubber. The present work demonstrates the effect of bound rubber content variation on the mechanical properties of rubber, demonstrates the morphology of bound rubber more visually, and provides new insights into the reinforcement theory of CB. Full article

We investigated the reinforcement behavior of small amounts of chemically unmodified cellulose nanofiber (CNF) in eco-friendly natural rubber (NR) nanocomposites. For this purpose, NR nanocomposites filled with 1, 3, and 5 parts per hundred rubber (phr) of cellulose nanofiber (CNF) were prepared by a latex mixing method. By using TEM, a tensile test, DMA, WAXD, a bound rubber test, and gel content measurements, the effect of CNF concentration on the structure–property relationship and reinforcing mechanism of the CNF/NR nanocomposite was revealed. Increasing the content of CNF resulted in decreased dispersibility of the nanofiber in the NR matrix. It was found that the stress upturn in the stress–strain curves was remarkably enhanced when the NR was combined with 1–3 phr CNF, and a noticeable increase in tensile strength (an approximately 122% increase in tensile strength over that of NR) was observed without sacrificing the flexibility of the NR in the NR filled with 1 phr CNF, though no acceleration in their strain-induced crystallization was observed. Since the NR chains were not inserted in the uniformly dispersed CNF bundles, the reinforcement behavior by the small content of CNF might be attributed to the shear stress transfer at the CNF/NR interface through the interfacial interaction (i.e., physical entanglement) between the nano-dispersed CNFs and the NR chains. However, at a higher CNF filling content (5 phr), the CNFs formed micron-sized aggregates in the NR matrix, which significantly induced the local stress concentration and promoted strain-induced crystallization, causing a substantially increased modulus but reduced the strain at the rupture of the NR. Full article

Porous pavements are designed and used in current construction practices to address environmental and safety issues related to wet weather. Porous rubber pavement (PRP) is a novel porous pavement material consisting of recycled crumb tire rubbers, stone aggregates, and polyurethane binders. The higher permeability (up to 45% of air voids) of PRP and its composition offers excellent benefits to the urban hydrological system and environment. Due to its recent outset in the Canadian climate, its properties and performance are not yet investigated. This research investigates PRP’s properties and performance as pavement material through the construction of two trial sections incorporating three newly developed PRP mixes along with a Control Mix. Samples were obtained from the field and tested in the laboratory to determine the mechanical and durability properties, including indirect tensile strength, moisture-induced damage due to freeze-thaw cycles and permanent deformation. A field evaluation was also performed three times: right after construction, three weeks later and after seven months to determine stiffness, frictional properties, roughness and permeability. The results revealed that all PRP mixes exhibited excellent permeability and retained more than 68% of tensile strength after five freeze-thaw cycles. Although PRP showed significantly lower initial elastic modulus than conventional pavement material, ranging between 28 MPa to 59 MPa, in the springtime none of them went below 23 MPa. Material composition, site geometry and subgrade conditions were found to be the main factors influencing the field performance of PRP pavement. Full article

The paper presents the results of research on a composite mixture intended for use in road construction. The purpose of developing the mixture is to be able to use large amounts of industrial waste to produce building material. The waste used are coal slate from the mining industry, shredded rubber waste from used passenger car tires and fly ash from power plants. The mixture (SRFC) consists of unburnt coal-mining slate (S), shredded rubber waste (R), fly ash (F) and cement(C). A test under cyclic loading conditions was carried out on samples prepared from the SRFC mixture, in which the global deformations and local strains caused on the samples were measured. A measurement system using digital image correlation was used for the research. On the basis of the conducted research, it was found that the content of shredded rubber waste significantly influences the deformability of the tested mixtures and allows for the extension of the scope of elastic deformation in which the tested samples work. Full article