Sand-rubber Mixtures Research Articles

Experimental study on cyclic shear characteristics of geogrid and rubber–sand mixture interface

Rubber–sand mixtures are an excellent alternative backfill material in geotechnical engineering. To study the dynamic shear characteristics of the geogrid and rubber–sand mixture interface, cyclic direct shear tests were conducted to analyse the effects of rubber content, particle size ratio (r), normal stress, and shear displacement amplitude (A). The variation law of shear stiffness and damping ratio was also analysed. The results revealed that, as the rubber content increased, the shape of the hysteresis loop evolved from a full fusiform to a flat state; as r decreased, the hysteresis loop became flatter. The peak shear stress was the largest (increased by 5.4%–15.7%) when the rubber content was 10%. When the rubber contents were 10% and 30%, as r increased, the interface peak shear stress increased. The geogrid and rubber–sand mixture interface exhibited shear hardening when A = 3 mm and shear softening when A = 12 mm. When A = 6 mm, the interface with rubber contents of 10%, 30% and 50% tended to transition from shear softening to shear hardening. The damping ratio was the largest (increased by 9.3%) when the rubber content was 10%. Additionally, as r increased, the shear stiffness and damping ratio increased.

Stress-dilatancy relationship of sand-rubber mixtures

The results of drained triaxial compression tests and DEM simulations of sand-rubber mixtures presented in the literature were analysed using of frictional state concept. The stress-plastic dilatancy relationship at different shear stages can be approximated by straight lines determined by critical state angle and two parameters of the frictional state concept. The points representing failure state lie on the frictional state line as for pure sand without rubber. The frictional state concept can be used to simply describe the stress-dilatancy relationship of various sand-rubber mixtures.

Towards more realistic modelling of sand–rubber mixtures considering shape, deformability, and micro-mechanics

This paper presents realistic discrete element method (DEM) simulations of mixtures of sand and rubber grains. The shape of the grains and the deformability of the rubber are accounted for in the model. A set of 1D compression tests and triaxial compression tests are performed on samples with different rubber contents. It is shown that the model can accurately predict the mixture behaviour at macro-scale. The insights from a micro-mechanical analysis of force chain network, coordination number, and side-wall friction indicate that deformability plays a key role in exhibiting realistic behaviour. Finally, a new criterion is presented to determine the limits of sand-like and rubber-like behaviour.

Stress–Deformation Response of Rigid–Soft Particulate Mixtures under Repetitive Ko Loading Conditions

Sand–rubber mixtures used in transportation infrastructure experience repetitive loading. Hence, in this study, the mixtures of rigid sand particles and soft tire chip particles with two different size ratios at varying tire chip fractions (TF) by weight were prepared, and repetitive loading tests were performed for 10,000 cycles at 100 kPa stress amplitude (Δσ). The results of this study demonstrate that significant volume contraction occurs for the tested rigid-soft mixtures during repetitive loading due to the continuous accumulation of plastic strain. Most notably, this study reveals that the magnitude of elastic strain recovery of the tested mixtures decreases with increasing cyclic loading number, reflecting the transition of the structural skeleton from the contacts between sand-to-rubber and/or rubber-to-rubber to those between sand-to-sand and/or rubber-to-sand under repetitive loading conditions with constant Δσ. The effects of TF and size ratio on the compressibility of the tested mixtures are also evaluated in this study.

Shear modulus and damping characteristics of uniform and layered sand-rubber grain mixtures

Large numbers of vehicles manufactured annually result in massive traffic and in turn creates huge numbers of waste tires entering into the environment and causing problems. Therefore, it is necessary to find reasonable applications for waste tires. They may be used to reduce seismic effects on structures due to their damping characteristics and energy absorption. Although comprehensive research studies have been carried out on static and dynamic properties of soil mixed with waste rubber, dynamic tests on layered mixtures of sand and rubber are highly demanding due to their easy to perform for practical applications. In this study, dynamic properties of sand mixed with different percentages of waste tire grains in uniform and layered forms were studied using a series of consolidated drained cyclic triaxial tests. The results show that for a given rubber percentage, layered mixtures have less shear modulus and more damping ratio than rubber-sand mixtures with uniform distribution. It has also been observed that for 50% tire content in layered sand-rubber mixtures, the Sand-Tire-Sand (STS) configuration offers lower shear modulus and a greater damping ratio than the Tire-Sand-Tire (TST) arrangement.

Effects of Crumb Rubber on the Shear Strength of Sand: An Experimental Study

The application of waste rubber tires for ground improvement helps to improve the environment by recycling and reusing it as admixtures. This research aims to investigate the shear strength parameters of rubber-sand mixtures. By using crumb rubber with a constant size (425μm), the sand is replaced by different percentages (0, 2.5, 5.0, 7.5, and 10%) of crumb rubber by weight. A direct shear box test is used to determine the shear strength parameters of rubber-sand mixtures with two different controlled densities. The samples were loaded with normal stresses of 20, 40 and 80kPa and were sheared at a rate of 1mm/min. Although, this experiment discovered that crumb rubbers improve the shear strength parameters in loose sand, however, a reduction in shear strength parameters was found in dense sand. Moreover, it was observed that the inclusion of crumb rubbers into sand greatly improve the strain energy of both loose and dense sand. Likewise, rubber has a low unit weight which makes it suitable for lightweight backfill materials. The surface properties of rubber should be further studied to understand the contribution of shear strength in the rubber-sand mixture.

Micromechanical investigation of the shear behaviors of sand‒rubber mixtures using a multibody meshfree method

Micromechanical investigation of the shear behaviors of sand‒rubber mixtures using a multibody meshfree method

Evaluation of open and filled (TDA and RSM) trenches efficacy on vibration screening caused by transient loads

Forging hammer machine foundation is subjected to multiple consecutive transient or impact loads during operation which results in a powerful dynamic effect that transmits to the surroundings in the form of unwanted vibration thus affecting workers, other sensitive equipment, and/or adjacent residential areas. Previous studies incorporated open and filled trenches to mitigate the ground vibrations caused by harmonic loads. However, studies pertaining to precisely evaluate the vibration isolation performance of trenches in presence of transient loads are limited, and no attempt has been made to evaluate the use of tire-derived aggregates (TDA) and rubber-sand mixtures (RSM) as filling materials. This paper aims at investigating the potential of using the TDA and RSM barriers to reduce vibration caused by transient or pulse loads. Abaqus software was used to perform two-dimensional (2D) finite element modelling for checking the efficiency of open and filled trenches. The model was first calibrated by comparing the results under harmonic loading conditions with the previous literature. The calibrated model was further employed to evaluate different trench parameters, such as depth, width and distance from source to the barrier, upon shielding vibrations. Additionally, a multi-trench isolation system was simulated, and its performance was evaluated by comparing it with a single barrier. The results showed that the TDA and RSM barriers effectively reduces the vibration induced by pulse loading. The difference in vibration screening efficiency between open and filled TDA trenches was recorded as 10%. Moreover, the results indicated that the multiple trenches are preferred alternative owing to their capability of attenuating vibration more effectively in comparison to the single barrier.

Experimental Study on Dynamic Modulus and Damping Ratio of Rubber–Sand Mixtures Over a Wide Strain Range

This paper systematically investigates the dynamic behavior of sandy soils mixed with recycled tire rubber over a wide strain range in the order of 10[Formula: see text]–10[Formula: see text], using combined resonant column and cyclic triaxial tests for measurement of the shear modulus and damping ratio. The experiment integrates small-strain tests using a resonant column apparatus and large-strain tests using a cyclic triaxial apparatus. The results demonstrated that the addition of rubber particles significantly enhances the linear elastic properties of the host sandy soils and improves the critical shear strain from which the rubber–sand mixtures change from linear to nonlinear stress–strain behavior. The critical shear strain is therefore introduced as the function of rubber content (RC), to identify the influence of RC on the strain-dependent dynamic properties of the host sandy soils. Then, a well-calibrated prediction formula is applied in conjunction with the concept of binary packing material to describe the behavior of the host sandy soils with various RC. Remarkably, the obtained normalized shear modulus and damping ratio vs. shear strain relationships address the limitations of existing testing methods to simultaneously capture the soil dynamic properties at low-strain (stiffness) and the large-strain (energy dissipation) regimes. The model constants can be simply determined through a unique set of explicit expressions which incorporate some basic index properties of the host sand and recycled tire rubber. In this regard, the proposed procedure provides a significant advantage in the evaluation of strain-dependent dynamic properties of rubber–sand mixtures in practice.

Experimental Investigations on the State-Dependent Thermal Conductivity of Sand-Rubber Mixtures

Soil-rubber mixtures are potential construction materials for use in civil engineering applications such as the thermal insulation layer for buried pipelines in the permafrost zone and underground energy storage systems. Currently, however, the thermal conductivity of soil-rubber mixtures in various stress, saturation, and void ratio conditions is not fully understood. In this study, a stress-controlled apparatus based on the thermal needle probe technique was developed. It was employed to study the influence of the aforementioned factors on the thermal conductivity of sand-rubber mixtures. Thirty-four tests were completed with a wide range of net stresses (0–600 kPa), initial degrees of saturation (0%–100%), void ratios (0.45–0.95), and rubber contents (0%, 10%, and 20%). Three replicates were used in each condition. The results showed that the thermal conductivity was strongly dependent not only on void ratio, rubber content, and degree of saturation but also on net stress. For instance, the thermal conductivity of a dry sand-rubber mixture increased by 30% when the stress increased from 0 to 600 kPa. This increase in thermal conductivity can mainly be attributed to an increase in interparticle contact area, accounting for about 25% of the 30% increase; the reduction in void ratio played a minor role. A semiempirical equation was proposed to calculate the thermal conductivity of sand-rubber mixtures at different stress levels.

Compressibility Behavior of Soft–Rigid Granular Mixtures Bound with Polyurethane Binder

Mixtures of recycled tires and granular material have been used for a variety of applications in geotechnical engineering over the years. The characteristics and mechanical properties of sand–rubber mixtures as unbound soft–rigid mixtures have been extensively studied over the years. Research on bound soft–rigid mixtures, however, has been mainly focused on using a brittle binding agent, for example, Portland cement. A very limited number of studies over the last years have examined the behavior of soft–rigid mixtures bound with a nonbrittle binder. This study aims to provide a better understanding of the deformation mechanism of the soft–rigid mixtures bound with a polyurethane binder. Sixteen one-dimensional compression tests were conducted on bound and unbound samples to study the impact of the binding agent on the behavior of the soft–rigid mixture. In addition, computed tomography scan images of samples were used to visualize the deformation mechanism. A multiphased behavior, as opposed to single-phased behavior for unbound mixtures, was observed and each phase was explained in detail. The observed multiphased behavior is divided into up to four phases, that is, initial compression, normal compression, bond degradation, and secondary compression, with boundaries defined based on constrained modulus curve.

Mechanical Behavior of Sand Mixed with Rubber Aggregates

The main objective of this study is to compare the mechanical behavior of two sands (Hostun or Dune sands) mixed with crushed rubber obtained from used tires. However, it is essential to ensure that his geotechnical application do not result in long-term negative impacts on the environment. The chemical properties of these two sands are given by energy dispersive analysis X-ray fluorescence spectrometry. The mineral composition of these two sands is performed by X-ray diffractometry. The morphological characteristics of the sand grains are given by the analysis of the images of the two sands given by the scanning electron microscope. This study is based on 120 direct shear tests performed on sand-rubber aggregate mixtures. The results show that the rubber content of the aggregates has a significant effect on the shear strength of sand-rubber mixtures in both cases of sand. In fact, the shear strength of the sand-rubber mixture increases with increasing crushed rubber up to 20% for different normal stresses. The analysis of the test results also shows the effect of the angular shape of the sand grains on the interparticle friction. The contribution of the structure effect in the mobilized friction is analyzed by comparing the shear test results of Hostun and dune sand mixtures.

The Experimental Investigation of the Repeated-Loading Behaviour of the Sand-Rubber-Mixture (SRM)

Nowadays the waste rubber problems are concerned due to the environmental issues, storage, and recycling difficulty. However, the rubber base equipment has been widely used to protect structures for vibrations - that has been generated by the structure or induced from the vicinity area or the bedrock into the structure - due to the notable capability of absorbing energy. In this study, the repeated-loading behaviour of the Sand Rubber Mixture (SRM) has been investigated and the remarkable energy absorption properties of the mixture have been illustrated. The test soil material that has been used in this study was a well-graded sand (SW) with a mean grain size of 2 mm. The test martial rubber that has been used was grain particles with a uniform size of 4.76 mm. The sand rubber mixture (SRM) was prepared by using 7.5% rubber inclusion because it was found as the optimum rubber content. A series of force control repeated-loading CBR tests have been arranged. The effect of mixing rubber particles with the well-graded sand (SW test material) has been investigated. This shows the remarkable energy absorption capability of Sand Rubber Mixture (SRM) to protect the bed of a machine’s footing that is generating repeated loads. The SRM usage could be extended to be employed as a part of an energy absorption unit and dampers facilities beneath a machine footing or structures that are sensitive to the vibration to prevent destructive deformation and resonance phenomenon.

Using Granular Waste Tire as a Factor to Increase Shear Strength of Cohesionless Soils

Soils are called problematic soils when they do not have sufficient bearing strength to provide a founda-tion for the structures to be built on them and these types of soils need to be improved with appropriate methods depending on their properties. Improvement methods applied to strengthen soils often cause financial burden. Recently, there are studies about the use of waste rubber tires, which pose an environ-mental risk during storage, as a reinforcement material for soils. The main purpose of this study is to examine the effect of poorly graded sand (SP) mixed with granular waste tires in different proportions (10%, 20%, 30%, 40% and 50%) on the shear strength of the sand. For this purpose, the physical (water content, specific weight, unit weight) and mechanical (shear strength) parameters of the mixtures were determined. According to the results of the research, the material with 100% sand content contributes to the shear strength by a certain proportion when compared to the mixed materials containing granular-sized waste rubber. According to the results of this research, the highest slip resistance value was observed in material with 20% tire content in waste rubber sand mixtures, while higher rates of tire addition provided lower results than 100% sand material. In addition, considering the issue in terms of environmental im-pact, a column test was carried out on the mixture containing 20% rubber-80% sand and no adverse ef-fects of the pollutants were observed.

Dynamic shear modulus and damping ratio of rubber-sand mixtures with a wide range of rubber content

The binary mixture of rubber and clean sand has been used as a synthetic porous material characterized by such advantages as light density, strong compressibility and good durability compared to the natural sandy soil. Previous research researches mainly focused on the static properties of this binary mixture. In this paper, the dynamic properties of the binary mixture including dynamic shear modulus and damping ratio, were investigated through a series of resonant column tests. The results indicated that the addition of rubber particles into clean sand significantly improves the dynamic performance of the host sandy soil. A unified model was proposed to describe the dynamic shear modulus and damping ratio of the rubber-sand mixtures with a wide range of rubber content. The synthetic mixture showed a great potential in the applications of the seismic isolation and reduction technique.

Influence of creep on the small-strain stiffness of sand–rubber mixtures

A series of bender element tests was carried out to investigate the variation of small-strain stiffness (Gmax) of sand–granulated rubber mixtures under long-term loading. Comparisons were made using two different host sands: a non-crushable material called Sydney sand and a crushable material composed of completely decomposed volcanic rock (CDV). The test results suggested that, at the selected stress states in the study (mean effective confining stress ranged from 250 to 333 kPa), the influence of creep on the stiffness of the pure sand specimens was more pronounced for CDV compared with Sydney sand and the presence of rubber amplified creep effects on both types of mixtures. The influence of creep on Gmax was therefore associated with two major mechanisms: the increased compressibility of specimens predominantly because of grain crushing (contribution of sand fraction), and the increased compressibility because of the presence of soft rubber grains (contribution of the rubber fraction). The significant influence of grain breakage on the relationship between stiffness and creep was confirmed by post-test examination of the grain-size distribution curves of pure CDV samples. For rubber–CDV mixtures, the inclusion of soft and viscoelastic rubber grains prevented breakage, in this way reducing the creep mechanism due to grain crushing, but increased the overall influence of creep on stiffness. These conclusions were drawn based on 20% of rubber by mixture weight, and very similar behaviour was observed for 10% rubber. It was therefore understood that the aggravation of creep induced by the increased deformations due to the presence of rubber, for the given contents of rubber included in the study, was more dominant compared with the adverse influence of rubber on samples’ creep by preventing sand grain breakage.

Applicability of Waste Rubber Particles as Buried Pipe Backfill Material

The primary purpose of this work is to evaluate the viability of using waste rubber particles as buried pipe backfill. By applying confined compression test and model test, this research studied the compressibility of sand and rubber-sand mixtures (RSM) and also, investigated the behavior of pipe surrounded by sand and RSM subjected to impact loading. The findings are as follows: 1) The vertical elastic strain and plastic strain of compression test samples increase with rubber content, and the elastic strain and plastic strain of saturated samples are greater than those of dry samples. 2) The settlement of RSM model soil is greater than that of pure sand model soil subjected to impact loading. The addition of rubber particles to pure sand reduces the earth pressure increment. The cumulative strain of pipe surrounded by dry RSM is less than that surrounded by dry pure sand. However, the cumulative strain of pipe surrounded by saturated RSM is greater than that surrounded by saturated pure sand. This investigation provides an environmentally friendly approach for recycling waste tire particles in geotechnical engineering.

Shear strength characteristics of geosynthetic reinforced rubber-sand mixtures

Shear strength characteristics of the geosynthetic-reinforced rubber-sand mixture (RSM) has been investigated by conducting Unconsolidated Undrained (UU) triaxial test. In the first part, a series of UU triaxial tests have been carried out to know the size effect of granulated rubber/tyre chips from seven different rubber sizes. RSM sample that provides higher strength, energy absorption capacity and stiffness is considered as the optimal size and has been used in the investigation on geosynthetic-reinforced RSM. In the second part, shear strength characteristics of geosynthetic-reinforced RSM has been investigated by varying proportions of rubber content (50% and 75% rubber by volume), type of geosynthetic (geotextile, geogrid and geonets), number of geosynthetics (1–4) layers, geosynthetic arrangement and confining pressure. The results demonstrate that RSM reinforced with geosynthetic has enhanced peak strength, failure strength and corresponding axial strain at failure. Fifty percent RSM reinforced by geotextile and 75% RSM reinforced by geonets with 4 layers of reinforcement, led to a maximum increase in shear strength. The strength and energy absorption capacity are doubled for the reinforced RSM's, and reduced the brittleness index values as close to zero, which depends on the type, number of layers and arrangement of geosynthetic.

Exploring the micromechanical behaviour of sand-rubber mixtures using X-ray micro-tomography

The micromechanical behaviour of sand-rubber mixtures (SRMs) under monotonic triaxial shear were investigated using X-ray micro-tomography. The localisation of sand particle rotations that occurred in a pure sand sample under shear was inhibited in the sand mixed with 30% rubber grains by mass. Meanwhile, the SRMs exhibited an evolution of sand-sand contact coordination number that is not negatively correlated with sample porosity, dramatically different from that was observed in pure sands. Substantially increasing anisotropy degree of sand-rubber contacts compared with minor changes of sandsand contact fabric was observed, implying the increasingly important role of sand-rubber contacts in the transmission of deviatoric loads as the shear of SRMs progressed.

Anti-liquefaction performance of rubber-sand mixture for water treatment

Anti-liquefaction performance of rubber-sand mixture for water treatment