Crumb Rubber Content Research Articles

The Effect of Aging on the Molecular Distribution of Crumb Rubber Modified Asphalt Based on the Gel Permeation Chromatography Test

Asphalt aging is one of the main causes of asphalt pavement cracking, loosening and other issues. On a macro level, the asphalt hardens and becomes more brittle, while on a micro level, the chemical composition and molecular weight distribution change. This is a very complicated physicochemical process. Gel permeation chromatography (GPC) is a powerful technical tool for understanding the mechanism of asphalt aging and expressing the asphalt aging process. GPC can be used to measure the distribution and content of each component in the asphalt aging process. The mechanism of action of crumb rubber modified asphalt has not been fully elucidated due to its complex composition. This study investigated the molecular weight of crumb rubber modified asphalt before and after aging, and filtered asphalt based on gel permeation chromatography. The results indicated that crumb rubber itself experiences severe degradation following PAV aging and that a significant number of macromolecular materials are incorporated into the asphalt phase, causing changes in key parameters. The average molecular weight (Mw) and dispersion (D) of crumb rubber modified asphalt are directly related. At the same time, the Mw of crumb rubber modified asphalt has a positive correlation with LMS content, while SMS content has a negative correlation with Mw. The increase in crumb rubber content has a positive impact on the material interaction, and the molecular weight distribution of crumb rubber modified asphalt is affected by the reaction degree of the crumb rubber in asphalt. The complex physical and chemical reaction of crumb rubber in asphalt has a direct impact on the external macro rheological properties of asphalt.

Rubber particle bridging effect on crack width control of low carbon Engineered Cementitious Composites (ECC)

Engineered Cementitious Composites (ECC) exhibit high tensile ductility and multiple cracking behaviors. The weak bonding between hydrophobic fiber and matrix tends to enlarge the crack width of ECC. This paper investigated recycled crumb rubber (CR) to tailor the crack width control of ECC as an artificial flaw. The experimental results show that CR can enhance the multiple cracking and reduce the crack width of ECC, which can be attributed to the CR weakened matrix and particle bridging effect. Micro-CT scanning revealed how CR influences the initiation and propagation of microcracks qualitatively. A constitutive model of CR particle bridging was developed to evaluate the quantitative contribution of CR particle bridging to the crack width reduction of ECC. Although the effect of bridging on crack width reduction is not as strong as that of the weakened matrix, the combined effect is consistent with the experimental magnitude of crack width reduction. Further parametric analysis indicates that small particle size, higher content, and narrower size distribution range of CR are preferred for better crack width control of ECC. The insights gained provide guidance on ECC composite design for a tight crack width with better durability properties.

Cement mortar containing crumb rubber coated with geopolymer: From microstructural properties to compressive strength

Coating rubber particles with cement paste has been widely adopted as an effective method to improve the mechanical strengths of rubberised concrete. However, this method introduces an additional amount of cement into the mixture system, thus unnecessarily further increasing the overall cement usage. This study introduced a new method of coating rubber surfaces with cement-free geopolymer paste. The geopolymer-coated crumb rubber was incorporated into cast cement mortar at three different replacement levels of river sand, including 7.5%, 15% and 22.5% by weight. The 28-day compressive strengths of different mixtures with geopolymer-coated (GP series) or untreated crumb rubber (U series) were measured, and the strength recovery was evaluated. Although the compressive strengths of GP series were constantly higher than those of U series, the effectiveness of strength recovery due to geopolymer coating on the rubber surface became less prominent with the increase in the crumb rubber content. Microstructural investigations included nanoindentation and scanning electron microscopy (SEM). The interfacial transitional zone (ITZ) between the cement matrix and geopolymer paste was observed to have porous microstructures with relatively low indentation modulus. Meanwhile, X-ray micro-computed tomography (μCT) analysis in coated rubber particles showed air voids existed within large rubber particles due to the agglomeration of crumb rubber. The microstructure in the ITZ region and internal voids in large rubber particles, together with the increased stiffness of rubber particles due to coating, jointly affected the effectiveness of strength recovery in cement mortar containing different proportions of crumb rubber.

Predicting Rubberized Concrete Compressive Strength Using Machine Learning: A Feature Importance and Partial Dependence Analysis

Rubberized concrete is a material that is both ecologically friendly and sustainable, and it has been finding more and more usage in building applications recently. In this study, a machine learning model, namely LightGBM, is developed to predict the compressive strength (CS) of rubberized concrete using 11 input parameters. The performance of the model is measured using a number of different statistical criteria after it has been trained on a dataset containing 275 samples. In order to evaluate the impact that each input parameter has on the CS, feature importance and partial dependency plots (PDP) are used as analytical tools. According to the findings, the superplasticizer, chipped rubber, crumb rubber, coarse aggregate, fine aggregate, and water content all have a significant impact on the CS of rubberized concrete. On the other hand, the results indicate that the cement content, slag/fly ash content, and type of CS have a relatively minor effect. In addition to this, the PDP offers insights into the manner in which the input parameters have an effect on the CS of rubberized concrete. Overall, the developed model and analytic techniques may be used as a helpful tool in forecasting the CS of rubberized concrete and improving its mix design for a variety of construction applications.

Raveling performance of conventional and rubberized chip seal under field and laboratory traffic loading

Raveling, or the loss of surface aggregate, is a major concern in chip seal pavement. Previous studies have used the Standard Sweep, Vialit, and Pennsylvania tests to evaluate raveling, but these tests do not replicate the stresses of rolling vehicle tires on chip seal and have produced inconsistent results. Additionally, these tests mainly evaluate early-stage raveling due to their short curing time. In this study, a small-wheel traffic simulation device (SWTS) was used to apply similar stresses as rolling vehicle tires and produce comparable raveling results. This was confirmed through a 13-month field observation of chip seal, where the laboratory and field data were compared and correlated. Both conventional (mineral aggregate) and eco-friendly rubberized chip seal with 25%, 50%, and 100% crumb rubber as aggregate were tested in the laboratory and field. The effects of different aggregate types, binder application rates, and crumb rubber contents were studied. The results showed that each wheel application by SWTS is equivalent to 2.5 to 3 passenger car passes in the field. It was also found that the majority of macrotexture loss occurred in the first 50,000 passenger car equivalent load. Up to 50% replacement of mineral aggregate with crumb rubber did not significantly affect the raveling resistance but using more than 50% rubber impaired the raveling resistance. Using crumb rubber instead of mineral aggregate also significantly reduced tire wear and microplastic emissions from vehicle tires. Moreover, it was found that Pennsylvania and Vialit tests may not be suitable for assessing aggregate retention under traffic load.

Experimental study and molecular simulation on regeneration feasibility of high-content waste tire crumb rubber modified asphalt

The application of crumb rubber modified asphalt (CRMA) in road engineering can not only improve pavement performance, but also solves the environmental pollution problems caused by the accumulation of waste tires, producing economic and environmental benefits. This study aims to investigate feasible methods of regenerating CRMA with 35% content of waste tire crumb rubber (CR) through molecular dynamics and experimental methods. Three regeneration approaches were studied and compared, including using a rejuvenator, virgin binder and CR, and a mixture of the above two. Results show that the regeneration of short-term aged CRMA is the converse process of aging, while the regeneration of long-term aged CRMA is the process of repairing internal structural damage and improving its integrity and thermal stability. Although the traditional rejuvenator only restores the asphalt properties in CRMA, it can improve the compatibility of long-term aged CRMA and other components in the regeneration system. The self-aggregation of asphaltene in the aged CRMA is alleviated after regeneration. Besides, the light components are closely attracted by the asphaltene for better lubricating the asphaltene micellar. The colloidal structure of aged CRMA is more ordered after regeneration.

Effect of particle size of the coated and un-coated crumb rubber on the mechanical properties and water absorption of rubberized concrete

To diminish the environmental impact of enormous waste tires and reduce the concrete cost, crumb rubber (CR) was utilized to replace concrete aggregates. The CR and sand sizes were sieved and separated. Moreover, the CR was pre-coated with silica fume slurry, having a water-to-cement ratio of 0.55. The coated and uncoated CR was used as a partial replacement of sand by five percentages (0, 5, 10, 20, and 25% by volume). Cubes and cylinders were cast and then cured in water tanks until the date of testing. The compressive strength of the control and rubberized concrete (RuC) samples was measured at 7, 28, and 56 days, the tensile strength was obtained at 28 days, and the water absorption was measured at 56 days. Replacing sand with a 2.36 mm particle size with the same CR size showed lower effects on the concrete compressive strength than replacing sand with 1.18 mm CR. Moreover, replacing sand with 5% pre-coated CR (particle size 1.18 mm) enhanced the compressive strength (fcu) by 104.88, 100.44 and 101.9% at 7, 28, and 56 days, respectively, compared to the subsequent mixes with uncoated CR while at 10% pre-coated CR content, the fcu enhancement was 118.3, 108.53, and 104.80%, respectively.

Nonlinear rheological performance characterization of styrene-butadiene-styrene and crumb rubber composite modified bitumen using large amplitude oscillatory shear tests

The crumb rubber (CR) recycled from waste tires can improve the mechanical properties of bitumen effectively. For the widely used modified bitumen today, it could work in nonlinear regime in many occasions. This study focuses on the nonlinear properties of styrene-butadiene-styrene (SBS) and CR composite modified bitumen (CMB) by analyzing the results of stress-controlled large amplitude oscillatory shear (LAOS) tests. The results show that the nonlinearity of SBS/CR CMB was significant under low load frequency, high temperature and high stress level. Lissajous curves at these conditions are distorted obviously due to the presence of higher-order harmonics. By analyzing the geometry parameters of Lissajous curves, it can be concluded that the incorporation of CR has a positive influence on the nonlinear properties of bitumen, which effectively improve the stress bearing capacity of bitumen. However, the high-order harmonic analysis indicates that improving the CR content simply does not always improve the performance of bitumen. Besides, the nonlinearity of SBS/CR CMB with lower CR content is similar to that of SBS modified bitumen through the value of I3/I1 and intrinsic nonlinear parameter Q, thus there are two critical CR contents for the prospect of modifying the nonlinearity of bitumen.

Influence of multi-scale fiber on residual compressive properties of a novel rubberized concrete subjected to elevated temperatures

Green and environment-friendly rubberized concrete has attracted extensive attention from scholars worldwide. However, the incorporation of crumb rubber can weaken the mechanical properties of concrete, particularly when it is subjected to elevated temperatures. To improve the residual compressive performance of rubberized concrete, a novel multi-scale fiber reinforced rubberized concrete (MSFRRC) is developed by adding calcium carbonate whiskers, polyvinyl alcohol (PVA) fibers, and steel fibers. In this study, 10%, 20%, and 30% of the sands are substituted by the same volume of crumb rubber with sizes between 0.4 mm and 0.8 mm. The impacts of the crumb rubber content and multi-scale fiber on the residual Young's modulus, axial compressive strength, peak strain, stress-strain curve, and compressive toughness of MSFRRC after being heated up to various temperature levels (25 °C, 200 °C, 400 °C, 600 °C, and 800 °C) are discussed. Also, the failure mode combined with the acoustic emission technology and the thermal effect on the microstructure of rubberized concrete specimens, are investigated. Results reveal that incorporating multi-scale fiber can effectively restrain the development of cracks and explosive spalling under high temperatures. Besides, it can cover the strength loss caused by crumb rubber and impose a positive effect on resisting thermal damage. The compressive strength of MSFRRC can be enhanced by about 5.4%–19% with the incorporation of different fibers. The results show that specimens without fibers suddenly fail once the peak stress is reached and exhibit brittle fracture. However, the brittleness can be improved by adding multi-scale fibers. It can be observed that, after exposure to 800 °C, the damage of MSFRRC can develop at the early loading stage and develop in the whole loading process, showing a relatively ductile fracture. Meanwhile, the pore structure can be refined by adding CaCO3 whiskers and the addition of multi-scale fibers can slightly increase the porosity and cannot restrain the heating-induced pore coarsening. Furthermore, the empirical formulas to predict the residual stress-strain relation of MSFRRC under uniaxial compression are proposed by considering crumb rubber, multi-scale fibers, and high temperature.

Sustainable crumb rubber modified asphalt mixtures based on low-temperature crack propagation characteristics using the response surface methodology

Fracture regime of asphalt concrete is of utmost importance in the sustainable design of optimized mixtures against low-temperature cracking. The energy dissipated in blunting the crack tip, stable crack growth, as well as post-peak resistance of the mixtures to the propagating crack comprise the overall fracture performance of the mixtures. In this research, employing the fracture resistance curve (R-curve) concept, three energy parameters: cohesive energy, fracture energy, and energy rate, are extracted to quantify the crack propagation regime of the mixtures incorporating ground recycled waste tire. A temperature range of 0 °C to −20 °C with 0 %, 10 %, and 20 % crumb rubber contents (CRC) were considered and the experiments were carried out in Single Edge notched Beam (SE(B)) fracture testing protocol. An environmental index comprising CO2 and CH4 emissions, as well as the energy consumption, was developed and the production cost of AC samples were also determined. A design of experiments based on the Central Composite Design (CCD) is applied. The Response Surface Methodology (RSM) is used to develop the best model between the fracture response, environmental factor, cost, and the input mixture properties. Multi-objective optimization scenarios were assessed by the RSM and a 4.74 % binder content with 19.5 % crumb rubber incorporation was resulted as the optimal mix design for maximum fracture response and minimized cost and environmental concerns in low temperatures. The environmental effects and costs were by average reduced by 15 % and 1 %, respectively and fracture responses have been improved compared to the reference optimum mix design (CRC = 0).

Effect of Normal and Rubberized Concrete Properties on the Behavior of RC Columns Strengthened with EB CFRP Laminates and Welded Wire Mesh under Static Axial Loading.

The huge amounts of old and damaged tires spread worldwide has caused many complex environmental risks. The old tires have been converted to crumb rubber (CR) and tire recycled steel fiber (RSF) to facilitate their use. This study used CR to partially replace natural sand in reinforced (RC) columns. Externally bonded (EB) carbon-fiber-reinforced polymer (CFRP) laminates, welded wire mesh (WWM), and RSF were used to enhance the axial behavior of the tested columns to overcome the concrete deficiencies resulting from the inclusion of the CR instead of natural sand. Eighteen columns were prepared and tested to discuss the effects of strengthening type, CR content, RSF, and strengthening area on the axial behavior of the RC columns. Certain columns were internally reinforced with WWM, while others were externally strengthened with EB CFRP laminates. Partially or fully EB CFRP laminates were used to strengthen the columns. Moreover, one column was cast with NC and 0.2% RSF to investigate the role of RSF in confining the column. The results demonstrated a concrete strength reduction for the rubberized concrete (CRC) as the CR content increased. Conversely, the strengthened columns experienced higher load capacities than the corresponding un-strengthened ones cast with the same concrete mix. Moreover, adding 2% RSF to the NC mix could enhance the column capacity, although it decreased the concrete strength. Furthermore, using two CFRP layers increased the load capacity and ductility of the strengthened columns. The strengthened column cast with 50% CR showed the highest load efficiency (334.3% compared to the un-strengthened one).

3D printed rubber modified asphalt as sustainable material in pavement maintenance

• Rubber modified 3DPA has good viscosity, elasticity, compatibility, high temperature and printability with 80 mesh and 18% of crumb rubber, and 4% of C 9 petroleum resin; • Only physical blending is occurred and C 9 petroleum resin play an effective compatibilization role in R−3DPA; • Recommended printing temperature and the speed of R−3DPA is 150 ∼ 160 °C and 1 cm/s. The application of 3D asphalt printing technology can be used to effectively improve the automation level and reduce the construction risk in pavement maintenance. In order to prepare and optimize 3D printed asphalt with good high-temperature performance and printability by sustainable utilization of waste rubber powder, the conventional properties and printability of rubber modified 3D printed asphalt (R-3DPA) were analyzed according to the basic properties and printing tests. The results were used to determine the optimal mesh and content of crumb rubber and additive content of C 9 petroleum resin. Then, the thermal storability and high temperature rheological property of R-3DPA were studied by phase separation test and dynamic shear rheological test. Fourier transform infrared spectroscopy and fluorescence microscopy were used to analyze the modification mechanism of R-3DPA. The printing temperature and speed were determined by a 3D printing test. The results show that R-3DPA has good viscosity, elasticity, compatibility, high-temperature rutting resistance, and printability with 80 mesh and 18 % of crumb rubber and 4 % of C 9 petroleum resin. Physical blending occurred, and C 9 petroleum resin can play an effective compatibilization role in R-3DPA. The recommended printing temperature and speed R-3DPA are 150–160 °C and 1 cm/s.

The optimal use of crumb rubber in hot-mix asphalt by dry process: A laboratory investigation using Marshall mix design

This paper aims to use the Marshall method to design and evaluate crumb-rubber modified (CRM) and conventional dense-graded (DG) hot mix asphalt (HMA), as there were limited previous experimental investigations that compared their properties by varying crumb rubber (CR) sizes, CR contents and aggregate types. Two types of crushed aggregate – diorite and granite – were mixed with 5.0% to 7.0% bitumen contents and 0%, 1%, 2% and 4% CR contents sized at 0.71 mm, 2 mm and 2.36 mm by dry process. The laboratory test results showed that the optimum bitumen content (OBC) and CR content that commonly satisfied international standards of CRM-DG-HMA by dry process and conventional DG-HMA were 5.5% and 1% respectively. CR content significantly contributed to the swelling of the CRM-DG-HMA, followed by the aggregate type and CR size. CRM-DG-HMA using granite aggregate was slightly more prone to swelling than that with diorite aggregate. Diorite-based CRM-DG-HMA with 2 mm CR size was more durable than conventional DG-HMA, granite-based CRM-DG-HMA and diorite-based CRM-DG-HMA with 0.71 mm CR size, with the last two being less durable than conventional DG-HMA. Granite-based CRM-DG-HMA was more stable and stiffer than conventional DG-HMA, while diorite-based CRM-DG-HMA was less stable but stiffer than conventional DG-HMA. Moreover, granite-based CRM-DG-HMA was more stable and stiffer than diorite-based CRM-DG-HMA with 0.71 mm CR size, with the latter being more stable and stiffer than diorite-based CRM-DG-HMA with 2 mm CR size. The findings from this paper have shown that partial replacement of mineral aggregate with CR in DG-HMA is a sustainable option, which could yield comparable or improved properties over conventional DG-HMA, provided that the CR size, CR content and aggregate type have been determined and selected in the mix design.

Experimental investigation on the behaviour of crumb rubber concrete columns exposed to chloride–sulphate attack

This research presents an experimental study to investigate the structural behaviour of crumb rubber concrete (CRC) short columns subjected to different exposure conditions. Thus, three different concrete mixtures were designed with varying replacement ratios of crumb rubber (CR) (0 %, 10 %, and 20 %) to the total volume of fine aggregate. The experimental program of this study includes the testing of 27 short columns characterised by three different environmental conditions, that is, laboratory, chloride, and sulphate. Nine columns were kept in a neutral laboratory environment condition. Nine columns were immersed in a sodium chloride solution, and the remaining nine columns were immersed in a magnesium sulphate solution for 90, 180 or 365 days. Experimental results illustrate that the addition of CR to concrete adversely affects the mechanical properties and durability of the CRC. The column strength, stiffness, and toughness continuously degrade with the increase in the CR content and immersion time. The column’s strength, stiffness, and toughness decrease as the level of corrosion damage increases. Specifically, the reduction levels in the strength of the columns immersed in 10 % magnesium sulphate solution are more noticeable than those immersed in 10 % sodium chloride solution.

Rheological Behaviour of WMA-Modified Asphalt Binders with Crumb Rubber.

Crumb rubber (CR) is one of the materials most widely used in the road infrastructure industry due to its mechanical and environmental benefits as an asphalt binder modifier. Nonetheless, CR decreases the workability of mixes by increasing the viscosity of the binder, leading to an increase in the production temperatures of asphalt mixes. However, warm mix technologies can reduce the temperature demand associated with these processes. The preceding explains the growing interest in producing rubberised asphalt binders incorporating warm mix asphalt (WMA) additives. In this research, the mechanical and rheological properties of a 60/70 penetration grade asphalt binder modified with CR (at a dosage of 15, 18 and 21% by the wet process) and WMA chemical additives (Evotherm M1 and Iterlow T) were investigated. Laboratory tests included penetration, softening point, rotational viscosity, frequency sweep through dynamic shear rheometer (DSR), and multiple stress creep recovery (MSCR) tests. The results indicate that CR increases the stiffness of the asphalt binder, which is reflected in a lower penetration grade and improved softening point. It also improves its rutting resistance but decreases fatigue performance. Furthermore, it has been shown that under the conditions studied, the higher the CR content, the more elevated the degree of stiffness and performance of the asphalt binder. On the other hand, WMA technology decreases asphalt stiffness and performance at high temperatures.

Enhancing the asphalt binder's performance against oxidative ageing and solar radiations by incorporating rubber from waste tyres

• Comparisons were made between PAV and UV ageing of neat and rubber modified bitumen. • 1× PAV ageing cycle is compared with 1-year of Melbourne’s UV ageing. • Compared to neat bitumen, crumb rubber reduced the PAV ageing by 2.35 times. • Compared to neat bitumen, crumb rubber reduced the UV ageing by 1.30 times. This study investigates the ageing of neat and crumb rubber modified bitumen (CRMB) under various conditions. Bitumen was modified with a high content of crumb rubber (CR) (22.5% by weight of base bitumen) and subjected to the equivalent amount of UV radiation occurring in one year in Melbourne, Australia. Long-term ageing via pressure ageing vessel was also used to age CRMB. Fourier transform infrared spectroscopy (FTIR) was used to capture the mechanism and evaluate the ageing effect that UV radiation and PAV ageing had on both types of binders. It was found that PAV ageing, due to its high temperature and pressure, mainly involves the evaporation of volatiles, oxidation of bitumen, and the conversion of aromatics to asphaltenes, while UV radiations, on the other hand, destroy the molecular structure of bitumen in addition to providing oxidation. The effect of ageing on rheological performance parameters such as crossover modulus, J nr , and %R was also found in line with the findings from the FTIR spectroscopy. The ageing index developed from the crossover modulus showed that applying a 1-year equivalent of UV radiations in Melbourne (Australia) provides 1.51 times increase in ageing to the neat bitumen while ageing is up to 2.64 times after 20-hour PAV. When the same neat bitumen was modified with CR, the ageing resistance against both PAV and UV radiations was enhanced by limiting the level of ageing to 1.16 and 1.12 times, respectively. Kruskal-Wallis test showed that there is no significant difference between the unaged and aged samples of CRMB in terms of I com . That showed 20-h PAV ageing and 1-year UV ageing did not significantly affect the CRMB, which is evidence of the ageing resistance of CRMBs.

Mechanical properties and shear strength of rubberized fibrous reinforced concrete beams without stirrups

• Presenting the experimental shear strength results of sixteen rubberized RC beams with/without fibers. • Investigating the impact of crumb rubber on mechanical properties and shear strength of concrete beams. • Investigating the effect of fiber types and ratios on the shear strength of rubberized reinforced concrete beams. • Investigating the effect of shear span to depth ratio on the shear strength of rubberized RC beams with/without fibers. This study investigates the mechanical properties and shear strength of rubberized reinforced concrete (RC) beams with/without fibers with no web reinforcement. A total of 16 RC beams were cast and tested under four points bending to fail in shear. The study parameters are; replacement ratio by volume of fine aggregate by crumb rubber (CR) (0, 15, 30, and 40%), types of fibers (hooked long steel fiber, smooth short steel fiber, and polypropylene fiber), fiber volume fraction (0, 0.4, and 0.8%) and shear span to depth ratio a/d (2.5, 3.5, and 4.5). The results show that the mechanical properties of rubberized concrete and its weight are reduced with increasing the CR content due to the low strength, stiffness, and elastic modulus of CR, while the addition of different types of fibers, particularly hooked large steel fiber, significantly improves the mechanical properties of rubberized concrete. Using lightweight CR contributes to increasing the deformability of the tested beams and reducing their self-weight. However, increasing the CR content decreased their ultimate shear force, post-diagonal crack shear resistance, and energy absorption capacity. The inclusion of CR and fibers in concrete production can be considered as a potential technique to develop new types of eco-friendly concrete with decreased self-weight and exhibits higher shear strength than that of the control beam. Moreover, the comparison of experimental results with the predicted results of five codes and six equations from the literature showed that most of them overestimate the shear capacity of rubberized RC beams; therefore, a new predicted equation is required to predict the combined effect of rubberized fibrous RC beams.

Study on the Properties of Waste Oil-Activated Crumb Rubber-Modified Asphalt Based on Molecular Dynamics Simulation and Rheology

To investigate the effect of activated crumb rubber content on the molecular interactions and the properties of crumb rubber-modified asphalt (CRMA) with waste oil, six models of asphalt with various rubber dosages were developed using Materials Studio software, and the molecular dynamics performance of the system was further examined. Then, the fatigue and high- and low-temperature performances of the CRMA binders were characterized by dynamic mechanical experiments in the laboratory. The mean square displacement and diffusion coefficient were used to quantify the migration of molecules. The aggregation state of the components was evaluated using a radial distribution function. The bulk modulus of the CRMA models was calculated to study the mechanical properties. Dynamic shear and bending beam rheometer tests were implemented to evaluate the road performances of the CRMA binders. The results show that increasing the amount of powder could improve the mechanical properties of the asphalt, that is, the modulus of 70% of the asphalt was improved by 57.5%. The rubber and waste oil were evenly dispersed in the system, and the distribution of asphalt components was in accordance with the colloid theory. The temperature-sensitive properties of the rubber led to the improvement of road properties of the CRMA binders with the increase of the admixture. Combined with the distribution of molecules in the asphalt model, the results of rheological indexes show that the waste oil could improve the rheology and stability of binders. This will provide theoretical support for upgrading the content of crumb rubber in CRMA binders.

Mechanical and thermal properties of fibrous rubberized geopolymer mortar

Nowadays, geopolymers play an important role in developing eco-friendly construction materials to avoid the pollution that comes from the Portland cement industry. Geopolymers show enhanced mechanical properties while ductility tends to be relatively low. Moreover, the thermal properties of construction materials are important in terms of energy-saving and sustainability. On the other hand, by increasing the used rubber tires and with low recycling processes, these wastes become a serious environmental problem. So, this work is directed to develop and investigate enhanced rubberized geopolymer composites regarding ductility as well as thermal properties. To achieve these targets, reusing Crumb Rubber (CR) from used rubber tires as a partial replacement of sand by volume was investigated with (10 %, 20 %, and 30 %) replacement ratios and different CR particle sizes (0–1 mm, 1–3 mm, 4 mm, and 0–4 mm). Parallel with using CR, polypropylene fibers with different volume fractions of (0.5 %, 1.0 %, and 1.5 %) were implemented. The effect of CR content and size on the Physical, mechanical, and thermal properties have been investigated. Additionally, the effect of incorporating polypropylene fibers in rubberized geopolymer mortar has been studied. The results indicated that despite the mechanical properties of rubberized geopolymer mortars tend to be lower, the mode of failure, toughness, and performance under flexural due to the synergistic influence of rubber and fibers have been improved remarkably. Additionally, the results of the transient plane source method indicated that thermal conductivity, thermal diffusivity, and heat capacity have been significantly enhanced in terms of heat insulation. Incorporating 20 % CR with 1 % fibers increases the flexural toughness by 27.5 % more than the mix containing 1 % fiber only. Incorporating 30 % CR decreased the thermal conductivity by about 39.7 %. Furthermore, the regression analysis by developing numerous relationships was proposed. The results of the regression model revealed that the models developed were adequate in explaining the effect of the independent parameters on the responses. It will be helpful to the engineers in deciding the levels of the fibrous rubberized geopolymer composites parameters for desired performance properties serving some environmentally friendly construction applications.

Experimental probe on machining attributes of Al 7075-T6/SiC/crumb rubber/MoS2-based green hybrid composite using artificial neural network model

Machinability of hybrid metal matrix composite is quite difficult because of an anisotropic nature, abrasive effect, and nonhomogeneous arrangement of two (or more) hard reinforcements, which are infused in an unreinforced base alloy. Therefore, this paper proposes an experimental probe on machining attributes of the novel green hybrid metal matrix composite which is prepared by an advanced vacuum-sealed bottom pouring stir casting technique with Al7075-T6 as a base matrix and SiC/crumb rubber/MoS2 as three distinct reinforcements. The variable input parameters such as SiC content (3.5 and 4.5 wt.%), crumb rubber content (0.3, 0.6, and 0.9 wt.%), MoS2 content (3.5, 4.5, and 5.5 wt.%), stirring speed (580, 600 and 620 rpm), stirring time (2, 5 and 8 minutes), and pouring temperature (670, 700, and 730°C) are selected for the fabrication of hybrid composites via Taguchi L18 mixed-level orthogonal array. For the machinability of fabricated composites in terms of material removing rate and surface roughness under dry conditions, a conventional turning operation on a lathe machine was opted for fixed input parameters such as spindle speed (200 rpm), depth of cut (1.0 mm), feed rate (0.25 mm/rev), and machining time (30 seconds). In contrast to an unreinforced base alloy, the material removing rate of the proposed green hybrid composite is slightly increased by 1.47%, whereas surface roughness is significantly decreased by 12.14%. Further, these experimental outcomes are validated with the model created using an artificial neural network, which is based on Levenberg–Marquardt algorithm. Besides, the predicted values obtained from the artificial neural network model lie in the close vicinity of the experimental outcomes, which in turn ensure the authentication of the developed artificial neural network model for the machined aluminum-based green hybrid composites.