Compacted Mixtures Research Articles

Towards a use of waste polyethylene in asphalt mixture as a compaction aid

As one of the most common plastic wastes in the world, polyethylene (PE) has been recycled and utilized to improve the performance of asphalt pavement, enabling it to withstand these conditions. Previous studies on the use of waste plastics as part of mix design have shown mixed results. On the other hand, adequate compaction has been essential to asphalt pavement performance and agencies/contractors strive to improve compactability of asphalt mixture. This study investigated the incorporation of waste PE with different sizes into asphalt mixtures in accordance with modified dry process as a compaction aid to facilitate compaction. The results show that the asphalt mixture modified by waste PE improves compactability and reduces the rut depth, with cracking performance being dependent on the size and type of the waste PE. The use of shredded waste PE flakes was observed to enhance the cracking performance of asphalt mixtures at intermediate temperatures, as evidenced by an increased CT-index. This improvement indicates that the use of PE flakes could potentially serve as a promising solution for achieving good compaction of asphalt mixture and thus extending pavement life, as well as enabling large-quantity use of waste plastics.

Research on void characteristics during compaction of asphalt mixtures

Void is an important manifestation of the strength of asphalt mixture, but few studies have focused on the change of voids during the compaction of asphalt mixtures. The voids of SMA-13 and OGFC-13 were selected as the research objects, and the compaction process of the asphalt mixture was analyzed based on different compaction degree specimens in lab through gyratory compactor. Firstly, CT scanning was used to extract the void structure of the asphalt mixture at different degrees. Secondly, based on the 26-connectivity algorithm, the connected voids and closed voids of asphalt mixture were extracted, and the volume and particle size distribution were analyzed. Thirdly, the gradation of voids was analyzed by the two-parameter Weibull function, and the morphological characteristics of voids were analyzed by roundness, sphericity, and abundance. The results showed that the distribution of cross-section voids ratio and the number of voids of the SMA-13 was more uniform than that of OGFC-13. The characteristic parameters of two-parameter Weibull function showed that with the increase of specimen density, the three-dimensional void size became smaller and smaller, and the void size distribution became more and more uniform. The sphericity and roundness of the voids of SMA-13 and OGFC-13 were less affected by the compaction degree, and the void abundance of the OGFC-13 gradation asphalt mixture was greatly affected. For the connectivity of voids, the closed void volume of OGFC-13 increased with the increase of compaction degree, but the maximum proportion of closed voids in the total void volume does not exceed 10% during the compaction process. For the gradation SMA-13, the compaction degree of 90%∼93% was the boundary interval of connected voids from existence to nonexistence, which may be a critical interval for forming skeleton strength during the compaction process.

ОТХОДЫ ОБОГАЩЕНИЯ ЖЕЛЕЗИСТЫХ КВАРЦИТОВ КАК СТРУКТУРНЫЙ КОМПОНЕНТ МЕЛКОЗЕРНИСТОГО БЕТОНА

The article describes problematic situation with waste accumulation from iron ore concentrate production (beneficiation tailings) from ferruginous quartzite at JSC Olkon (Murmansk Region). The task is to utilize beneficiation tailings as a fine-grained concrete component. The paper presents results of beneficiation tailings diagnostics and their testing as a part in the processes of fine-grained concrete structure formation in comparison with quartz sand from the Olenegorsk quarry. According to the research, the replacement of natural sand with beneficiation tailings in their original form leads to a decrease in strength due to insufficient compaction of mixture under adopted vibration compaction modes. At the same time, the use of ground beneficiation tailings in binder composition ensures increase in strength of concrete compared to concrete on "pure" cement and increase of efficiency by using clinker part of binder in formation of concrete strength by 57-58%. The study recommends the use of fine-grained concrete composition of class B40 for production of vibration-pressed urban land improvement products (paving slabs, curbstones, etc.). It reveals prospects for further research in construction and technological utilization of ferruginous quartzite enrichment tailings as a factor in the formation of biosphere-compatible living environment in the region.

OVERVIEW OF THE DESIGNS OF HINGED VIBRATION EXCITERS AND RESEARCH OF THEIR PARAMETERS AND THE FEASIBILITY OF THEIR USE ON VIBRATION PLATFORMS TO IMPROVE THE COMPACTING OF REINFORCED CONCRETE PRODUCTS

Construction of buildings using prefabricated technology is increasingly used in Ukraine. In parallel with this, the list of ready-made reinforced concrete products, which are used in monolithic-frame and monolithic-prefabricated technologies, is expanding. Because of this, it becomes necessary to increase the number of lines for the production of ready-made reinforced concrete products and to use equipment that will allow to quickly adjust the production process depending on the change in the type and size of the final products. At the same time, the most responsible process is the compaction and formation of the concrete mixture using volumetric compaction technology on vibrating platforms of block or frame construction. Such installations are designed for the compaction of concrete mixtures in forms standardized by size and which do not fully meet the requirements of universality when changing the production program, ensuring high quality of finished products, and are characterized by significant energy consumption. One of the directions for solving the mentioned shortcomings is the creation of a vibration installation with attached vibration exciters and a variable mode of operation. Such an idea is ensured by the use of a vibrating installation in which the frame with a plate welded on top is directly the pallet on which the compaction process takes place. The dimensions of the future product are limited by the installation of sides and partitions on the pallet, which are fixed using magnetic fasteners, thanks to which it is possible to easily rearrange the installation for other standard sizes of panels. The use of attached vibration exciters, which are evenly spaced over the area of the forming plate, aims to improve the distribution of amplitudes in the volume of the concrete mixture, improve quality and reduce the time for compaction of the product. The work includes an overview of the existing designs of mounted vibration exciters, an analysis of their disadvantages and advantages, as well as technical parameters. Ac-cording to the obtained results, it was determined that planetary pneumatic vibrators have advantages in the amount of disturbing force that they are able to generate per unit of their own mass, higher indicators of dyna-mism criteria compared to electric and hydraulic centrifugal analogues. Pneumoplanetary vibration exciters are simple in design, reliable and allow adjusting the frequency of oscillations within certain limits without the use of additional devices.

Crumb Rubber in Alkaline Activated Clay Roof Tiles at Low Temperature

The continuous increase in vehicle uptake escalates the number of rubber tyre waste to avoid landfilling and stockpiling. The present research focused on the sustainable use of crumb rubber in clay roof tiles. Tile samples were fabricated by heating the compacted mixtures at 50°C for 72 h, followed by increasing the temperature to 200°C for 24 h. Clay, crumb rubber, NaOH, and Na2SiO3 with a 10% alkaline activator were adopted. The weight of the crumb rubber was 0.5%, 1%, 1.5%, 2%, and 2.5%. X-ray diffraction (XRD) and scanning electron microscopy (SEM) analyses to study the phases and microstructures of the samples. The present study found that the optimum crumb rubber concentration was 0.5%, and 1% satisfied the standard requirement for the roof tiles.

Drainage Performance of Long Longitudinal Slope and High Safety Permeable Asphalt Pavement

Permeable asphalt pavement refers to an asphalt mixture layer with an air void content of more than 18% and internal water permeability and drainage capabilities that can quickly drain away water on the road surface, improve rainy day travel safety, and improve ride comfort. This paper aims to explore the optimal asphalt mixture design for long longitudinal slope pavement (referred to as the FAM mixture). By using CT scanning technology to analyze the air void content of different rotated and compacted asphalt mixture specimens and extensively testing and evaluating the performance of permeable pavement mixtures, the following conclusions are drawn: Based on the research philosophy of functional integration, a new asphalt mixture gradation suitable for long longitudinal slope roads is proposed, with the optimal key factor composition being: 0.075 mm passing rate of 7%, 2.36 mm passing rate of 20%, 9.5 mm passing rate of 55%, and an oil-stone ratio of 4.8%. The FAM mixture was divided into three parts for air void analysis, with the upper part having a slightly higher air void content than the lower part. The air void distribution diagram of the FAM mixture is concave, with higher air void rate curves on both sides and a lower middle curve. Through dynamic modulus testing, the strength requirement for the road asphalt mixture in the pavement structure design was evaluated. It was found that at high temperature conditions (50 °C), the minimum dynamic modulus value of the FAM mixture was 323 MPa, with a peak value of 22,746 MPa at a temperature of −10 °C and a frequency of 25 HZ. The dynamic modulus value at high temperature conditions is lower than at low temperature conditions, while the dynamic modulus value at high frequency conditions is higher than at low frequency conditions. This study provides useful information and experimental data for the design of new asphalt mixtures for long longitudinal slope roads and has conducted in-depth research on the air void distribution and performance of the mixture, providing strong support for related research fields and practical applications.

Type series of resonant vibration equipment for concrete mixtures compaction and its main parameters calculation method

Introduction. Increasing the energy efficiency of vibration technology poses a number of challenges for its developers. A promising direction for reducing energy costs for driving vibration machines is the use of the resonance phenomenon. Due to the dynamic properties of the oscillatory system, it is possible to significantly reduce the power consumption of resonant vibration equipment, and in some cases, improve the quality of the products. The purpose of this article is to develop a standard range of resonant vibration equipment for compacting concrete mixtures and a methodology for calculating its main parameters.The object of research is the oscillatory system of a vibrating machine, consisting of two masses connected by the elastic and dissipative elements. In addition, the first mass is connected to a fixed base through elastic and dissipative elements.Materials and methods. The basic principles of theoretical mechanics, mathematical modelling and statistical processing of results were used in the research.Results. According to the research results, it was established that with an increase in the mass ratio of the oscillatory system, the dynamic coefficient decreases, and the width of the resonant zone increases. The regression equations are given. It has been established that with increasing rigidity of the working body, the dynamic coefficient decreases, and the horizontal section on the frequency response, the width of which does not change significantly, shifts to the region of higher frequencies. With an increase in the damping coefficient, the dynamic coefficient decreases, and the width of the resonant zone and the frequency range practically do not change. A wide range of nomenclature and masses of precast reinforced concrete justifies the development of a standard-size range of resonant vibration equipment. A standard range of light (up to 2 tons), medium (2-6 tons) and heavy (6-10 tons) types has been developed. Based on the analysis and generalization of research results, a method for calculating resonant vibration equipment for compacting concrete mixtures has been developed, which makes possible to increase its energy efficiency.

Neuro-fuzzy system of continuous control of density asphalt concrete mixtures

Improving the quality and increasing the service life of asphalt concrete pavements of roads is a national economic problem, which is solved through measures related to improving the regulatory framework, improving the properties of road materials, automating its control and management of the compaction process. Existing automated systems for monitoring and controlling the density of road rollers are based on artificial intelligence methods. A feature of the construction of the upper layers of asphalt concrete road surfaces in the Russian Federation is a significant impact on their quality of the results of the work of asphalt pavers, which provide several technological operations - acceptance, laying and compaction of asphalt concrete mixtures. The use of an automatic density control system for asphalt concrete mixtures in the process of laying them will eliminate many defects in road surfaces during their operation. The aim of the work is to build a system of continuous density control in the process of laying and compacting asphalt concrete mixtures by pavers based on artificial intelligence methods. The article presents the results of the development of a new system for intelligent control of the density of the asphalt concrete mixture by pavers. It is proposed to use the structure of a neuro-fuzzy network of the ANFIS type. Training of a neuro-fuzzy system of the ANFIS type was performed on the basis of a combination of methods of least squares and a decreasing gradient on an array of variables obtained on the basis of the results of experimental studies performed by VNIIStroydormash, SoyuzDorNII, MADI. Automation of density control is aimed at improving the quality of asphalt concrete pavements of roads.

The influence of recycled asphalt pavement materials on low and intermediate fracture behavior of asphalt concrete (AC) after exposing to different thawing and freezing periods

The effects of compaction process, mixture type and environmental conditions on mode I cracking resistance of asphalt concrete (AC) materials was investigated experimentally. To do that, a large number of edge notched disc bend specimens containing 0, 25 and 50% recycled asphalt mixture (RAP) material and exposed to different numbers of thawing and freezing cycles (0 to 10 cycles) were fractured. The critical values of stress intensity factor and fracture energy indexes were obtained for the AC mixtures at three test temperatures of −25, 0 and + 25 °C. Based on the results, the fracture resistance capacity of the AC mixture was decreased by increasing the RAP content, number of thawing/freezing cycles and decreasing the test temperature. The effect of thawing/freezing cycles on decreasing the cracking resistance was more pronounced for the first cycles and the variations of fracture toughness and fracture energy values with the numbers of thawing/freezing cycles showed a plateau form for higher numbers of cycles. The fracture curves of the tested samples manufactured using the Gyratory compaction method was upper than the related curves of samples made by Marshall compaction method. The sensitivity of fracture results (i.e., gradient of reduction in the fracture resistance versus freeze/thaw cycles) became low by increasing the test temperature.

Studying water infiltration on bentonite/sand blocks with MRI and X-Ray μCT techniques

Radioactive waste management agencies all around the world are focusing their efforts to provide a reliable technical solution to the Deep Geological Disposal (DGD) concept, in order to store high level (HLW) and intermediate level long lived (IL-LLW) radioactive waste. The protection and isolation of radionucleides is guaranteed by a set of barriers. Bentonite/sand blocks -in proportion of 40/60 on dry mass of the mixture- constitute the main core of the sealing barrier in the French concept run by the French National Radioactive Waste Management Agency (Andra). Its high swelling potential (>2MPa) during hydration, its low hydraulic permeability (<10-11 m/s) and its gas entry pressure (<2MPa) make it ideal to seal the DGD galleries excavated inside the host rock used as geological barrier. Bentonite/sand blocks are placed at unsaturated state during construction. Afterwards, water migration –in both liquid and vapour states- from the saturated host rock to the blocks will induce the humidification of the blocks until hydraulic equilibrium is reached, hypothetically reaching the saturation state. As this natural process will take hundreds of years, a multitude of experimental devices have been reported at laboratory [3, 5] and real scale [4] to understand the evolution of water transfer in bentonite mixtures and support the predictions of numerical models [1]. In laboratory experiments, samples made of a compacted bentonite mixture are usually placed inside a rigid cell connected to a water source. The infiltration of water is not measured directly but deduced by relative humidity gradients measured along the specimen height.
 Numerical models and experimental results have not yet reached accurate predictions of how long it takes for bentonite mixtures to hydrate until complete saturation or how the unsaturated hydraulic permeability evolves. In this context, there is a motivation to study this phenomena by advanced techniques able to capture, image and quantify water transfer through porous media. Thus, an experimental campaign based on Magnetic Resonance Imaging (MRI) and 3D X-Ray micro computed tomography (µCT) is proposed to analyze water infiltration in bentonite/sand blocks. MRI is extensively used in health sciences to create images where the contrast is given by the water’s hydrogen proton content in the different tissues of the body. For geological media, where water content is much smaller than in biological tissues and relaxation times of the porewater are shorter -from 0.1 to 2 ms for compacted bentonite/sand [2]- the experimental requirements are different and less documented. On the other hand, µCT scanning provides high spatial resolution images based on the contrast between the X-Ray absorption properties of the constitutive phases observed. Its temporal variations, in a bentonite/sand mixture, might be the result of concurrent phenomena, namely, porosity and saturation changes together with heterogenous motions induced by hydromechanical couplings -the swelling of bentonite solids when they absorb water-.
 On going MRI and µCT experimental campaigns on a PEEK cell aim at proving the suitability of these techniques to track the evolution of water infiltration in compacted bentonite/sand mixtures, characterizing the water front and the water content along the specimen in function of time. At this stage, preliminary MRI tests have shown the potential of Single Point Imaging (SPI) sequence to quantify, with one-dimensional images, the water content along the bentonite/sand specimen based on a linear correlation with its signal intensity. Preliminary X-Ray radiography tests (Figure 1) run on a cylindric cell of PMMA filled with small blocks of 12 mm in diameter and 10 mm high, prove that X-Ray radiography image analysis gives access to observable and quantifiable increase of absorption associated to the measured decrease in grey level at different transversal sections of the sample. This evolution is linked to the increase of apparent density of the solids -that indeed are absorbing the water-, as described by the Beer-Lambert equation. Even though apparent density increase is goverened by the augmentation of water content, changes in porosity due to the hydromechanical coupling along the sample cannot be neglected. Thus, observing the liquid phase evolution (hydraulics) by MRI, as well as the evolution of the solid/liquid phase (hydromechanics) by 3D-µCT imaging, will potentially provide complementary insight into the mechanisms governing water infiltration in bentonite/sand mixtures.

The temperature-time dependence of the amount and type of niobium beryllides formed during the synthesis of the binary intermetallic compound NbBe3

Intermetallic compounds of beryllium with refractory materials (niobium, tantalum, zirconium, etc.) possess exceptional characteristics, such as high-temperature strength, excellent corrosion resistance, and high hardness. However, despite the impressive physical and mechanical properties of beryllides, the current manufacturing methods for producing components from these materials have not yet reached industrial maturity.The main producers of beryllides in the global market are Brush Wellman Inc. (USA) and Ulba Metallurgical Plant (UMP) JSC (Kazakhstan). In this study, niobium beryllides manufactured by UMP JSC were chosen as the object of research. Specifically, this work focuses on studying the synthesis process of the binary intermetallic compound of niobium beryllide NbBe3. The current study presents the results of determining the type and quantity of intermetallic pairs of niobium beryllides during the synthesis of the binary intermetallic compound NbBe3 from a compacted mixture of beryllium and niobium powders in the temperature range of 800 °C–1300 °C.

Study on Compaction Properties and Skeleton Structural Characteristics of Porous Asphalt Mixture

Porous asphalt pavements have a skeletal structure with a large number of interconnecting pores, which can improve drainage, ensure traffic safety, and reduce tire noise. However, it can weaken the mechanical properties of the pavement. One of the key factors affecting the performance of porous asphalt pavements is the quality of compaction, the assessment of which is difficult to accurately quantify. Therefore, Superpave gyratory compaction (SGC) and skeleton penetration tests of porous asphalt mixtures were carried out using three engineering-differentiated gradations in this paper to investigate the gyratory compaction characteristics and the skeleton contact state during penetration. The results show that obvious stages with the increase in number of cycles can be observed during the compaction process. All gradations can achieve the maximum porosity requirements within a reasonable number of compaction cycles, while only the medium and fine gradations can approximately meet the minimum porosity requirements. The coarse gradation takes too long to finish compaction and is almost impossible to meet the minimum porosity. The optimum match between the void ratio of the design gradation and the skeleton contact state can be verified using the VCA ratio and void ratio curves. This is a new method to determine the corresponding target compaction number that can ensure better accuracy and ease of engineering application. Moreover, medium-graded mixtures with better skeletal embedding exhibit greater skeletal strength than coarse-graded aggregates, which provide theoretical support for the establishment of material grade optimization methods.

THE USE OF MECHANICAL FILTER MODELS IN THE ANALYSIS OF FORMING AND COMPACTION PROCESSES OF FORMATION AND COMPACTION OF BUILDING/CONCRETE MIXTURES BY VIBRATING FIELD

The paper describes the use of various types of mechanical filter models, which are used for the analysis of the processes of formation and compaction of the construction/concrete mixtures of building/concrete mixtures by means of vibrating fields. The values of resonant frequencies and equivalent masses for different resonators modeling the propagation in the latter of vibrating-wave formations have been established. The analysis of the influence of a vibrating field on the processes of formation and compaction of concrete/concrete mixtures in this study is based on the methods of mathematical physics, classical variation calculus, physics of oscillations and waves and methodology of solution of ordinary differential equations and partial differential equations. The conditions and main integral characteristics of resonance phenomena, the possibility of occurrence of which is conditioned by: 1) the geometry of the initial boundary-edge problem (it is The so-called "geometric resonances" of the considered system with distributed parameters simulating the mixture to be processed); 2) the working rheological model of the mixture involved in the study (these are the so-called "rheological resonances"). The approach developed and scientifically substantiated in this work allows us to establish the main parameters and opportunities for the use of energy-saving modes of operation of vibration systems intended for the formation and vibration compaction of the above mixtures. The results obtained in the work The results obtained can be further used to clarify and Improvement of existing engineering methods of calculation of vibration systems for the formation and compaction of concrete/concrete mixtures in order to optimize the operating modes of their functioning both at the design stage and in the modes of real operation.

Micro-structural characterization of the lubrication behavior of asphalt binder during the compaction of asphalt mixture

This study aims to investigate the lubrication behavior of asphalt binder on the basis of Stribeck tribology theory, employing viscosity test, gyratory compaction test, and image processing techniques. The quantification of the lubrication regimes and their transformation was performed by an image processing algorithm that measures the thickness of the mortar film based on the minimum distance. The hydrodynamic regime transforms into the elasto-hydrodynamic regime by 23.2% below 60 gyrations. 11.6% of the elasto-hydrodynamic regime transforms into the mixed regime above 60 gyrations, causing an increase in friction. The slope of the compaction curve follows the variation rule of the Stribeck friction coefficient. Asphalt viscosity in the range of 380–460 mPa·s is recommended for optimum compaction.

Regulations of the Influence of External Thermal Influences on Speed and Explosive Safe Combustion Modes of Pyrotechnic Nitrate-Metallized Mixtures with Metal Fluoride

A study was made of the regularities of the influence of the main parameters of external thermal effects (elevated heating temperatures and external pressures) on the rate and explosive modes of combustion development of compacted mixtures of magnesium, aluminum and sodium nitrate with fluoride additives metals for different values of technological parameters (excess ratio of the oxidizing agent, nature and content of the additive, dispersion of the components). The effect of technological parameters (ratio and dispersion of components, compaction coefficient, charge diameter, shell material, etc.) on the dependence of the burning rate of mixtures on elevated heating temperatures and external pressures was established; critical ranges of changes in these parameters are determined, the excess of which leads to premature explosive development of combustion of mixtures and fire hazardous destruction of products. On the basis of the research, methods were developed to prevent these destructions of products by regulating technological parameters at the stage of preparation of charge mixtures, which increases the stability of the combustion process of mixtures to external thermal influences. A database has been obtained on the burning rates of compacted mixtures of metal powders (Mg, Al), nitrate-containing oxidizer (NaNO3 ) and additives of inorganic substances (metal fluorides (LiF, NaF, BaF2 , SiF2 , SrF2 , AlF3 )) under conditions elevated heating temperatures and external pressures for various values of technological parameters, which makes it possible to determine the explosive modes of their combustion.

Research on microscopic contact characteristics of aggregates during compaction of asphalt mixtures

The compaction process is the stage when the skeleton structure and strength of asphalt mixture are developed. In order to explore the strength development mechanism of asphalt mixture skeleton, the microscopic contact characteristics of aggregates during asphalt mixture compaction process were evaluated. Firstly, the CT scanning and image processing techniques were employed to obtain digital images of the asphalt mixture during the compaction process. Then, the processed digital images were reconstructed in three dimensions to achieve dynamic simulation of the asphalt mixture compaction process. A novel index of contact chains was proposed to characterize the different state of aggregate contact within the asphalt mixture, and then, the characteristic parameters of contact chains during compaction, such as the number of contact chains, contact chain length, and contact chain angle, were analyzed. The results showed that for the typical used SMA-13 asphalt mixture, the primary role of 13.2–16 mm grade aggregates in the asphalt mixture was to form the main skeletal structure, and 4.75–9.5 mm and 9.5–13.2 mm grade aggregates provided more than 90% of the contact points for the asphalt mixture. The contact chains formed by the aggregates of 4.75–9.5 mm and 9.5–13.2 mm were the main source of strength of the asphalt mixture. The aggregate was dominated by migrating movements in the early and middle stages of compaction, and rotating movements in the later stages of compaction dominated the aggregate.

Performance Evaluation of Open-Graded Bituminous Concrete Modified with Natural Fibers

Open-graded bituminous concrete (OGBC), also known as open-graded friction course or permeable asphalt layer, is a skid-resistant surface applied to pavements with high bitumen content. This mixture contains more coarse aggregates than fine aggregates, which improves subsurface drainage and indirectly reduces hydroplaning potential during wet weather conditions. The objective of the present study was to enhance the properties of the OGBC mix with fibers. Hence, four distinct natural biofibers, namely, sisal fiber, jute fiber, coir fiber, and bamboo fiber, were considered during experimental investigation at different dosages like 0.15%, 0.3% & 0.45% by weight of mix. Binder content levels ranged from 5 to 6% with an increment of 0.25% between the values in the range. Fiber-reinforced OGBC mixes were tested for air voids (%), draindown, resistance to moisture susceptibility, Cantabro loss, and indirect tensile strength of the compacted mixtures. The experimental findings demonstrate that fibers enhance the performance of OGBC mixes. Fiber incorporation reduced binder draindown and the percentage of air voids in OGBC mixes while maintaining the desired characteristics. The optimal fiber content was determined to be 0.30% for sisal, bamboo, and coir fibers and 0.45% for jute fibers. With the addition of sisal fibers at a dosage rate of 0.30%, the tensile strength of the OGBC mixture increased along with resistance to susceptibility to moisture.

Reuse of plastic waste in asphalt mixtures with residual porous aggregates

The reuse of plastic and poor-quality residual aggregates in the manufacture of bituminous mixtures for paving could contribute to reclaim significant quantities in the pavement construction industry since certain polymers can enhance the mixture properties. This study investigates the potential use of waste from recycled polyethylene terephthalate (PET) in asphalt mixtures with extremely-vesiculated residual aggregates, which are also rejected in quarry production. In this research, the physical, compaction, and mechanical properties of asphalt mixtures with these marginal aggregates, different binder consistencies and PET contents replacing part of the aggregate are studied. The results indicate that limited proportions of waste PET (up to 1 %) are compatible with extremely porous aggregates and can improve certain mixture engineering properties, such as the resistance to water action and to rutting. These mixtures meet specifications for base courses and even for pavement surfaces under limited heavy-truck traffic, while contributing to the sustainability of asphalt pavements by reducing the extractive demand of natural resources and replacing them with waste materials.

Investigation of 6PPD-Quinone in Rubberized Asphalt Concrete Mixtures.

N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine (6PPD)-quinone (6PPD-Q), a transformation byproduct of 6PPD used in tires as an antiozonant and antioxidant, was recently discovered as the chemical primarily responsible for the acute lethal toxicity of urban storm runoff to coho salmon. The asphalt concrete (AC) surface layer is the primary medium to contact 6PPD-Q immediately upon its release from tires, and the addition of recycled tire rubber (RTR) to the asphalt binder and mixture is a widely accepted practice in asphalt production. Therefore, it is urgent to understand the fate of 6PPD-Q at the asphalt concrete surface layer-water interface. This study analyzed the sorption and desorption of 6PPD-Q by compacted and crushed loose (loose particles, ∼5 mm) rubberized asphalt mixtures and their mobilization from compacted asphalt mixtures during simulated rainfall events. It should be noted that the crushed loose asphalt mixtures demonstrated the physicochemical properties of the asphalt materials, while the compacted asphalt mixtures represent in-service AC layers. Sorption of 6PPD-Q by crushed loose and compacted asphalt mixtures reached equilibrium within 12 days, with a sorption coefficient of 151.57-257.51 L/kg for compacted asphalt mixtures. Within 12 days, desorption of 6PPD-Q from crushed loose and compacted rubberized asphalt mixtures (20 g particles/L) to the double deionized (DDI) water and synthetic stormwater was 0.01-0.09 and 0.025-0.05 μg/L, respectively. Through the rainfall simulation experiments, 0.0015-0.0049 μg/L 6PPD-Q was detected in the runoff water, much lower than the lethal concentration (LC50) of 6PPD-Q of 0.095 μg/L and 308.67 μg/L for coho salmon and zebrafish larvae. Our results indicate that, while the release of 6PPD-Q from compacted rubberized asphalt mixtures is minor, the mixtures can serve as sorbents for tire-derived 6PPD-Q and retain this emerging contaminant.

Strength, Stiffness, and Microstructure of Stabilized Marine Clay-Crushed Limestone Waste Blends: Insight on Characterization through Porosity-to-Cement Index.

The porosity-to-cement index (η/Civ) has been extensively applied to study the evolution of different types of soil stabilization. However, this index has still not been used to characterize soils cemented with crushed limestone waste (CLW). In this sense, this paper sought to analyze the applicability of the porosity-to-cement index over the unconfined compressive strength (qu) and initial stiffness at small deformations (Go) of clayey soil improved with CLW and Portland cement. In addition, a microstructural analysis (SEM and EDX tests) was also conducted. CLW addition increased soil strength and stiffness over time. Moreover, qu and Go compacted mixtures containing CLW have established a distinctive correlation. Chemical microanalyses have uncovered a complex interfacial interaction between the soil, cement, and fine CLW particles, leading to a notable reduction in porosity.