COMPARISON OF THE METHODS OF DETERMINING SIF AND ERR AND THEIR APPLICATION TO RECYCLED MATERIALS

This paper provides recommendations for performance-related tests to select recycled materials to be used in pavement foundations (base/sub-base layers). The test protocol presented in this paper will help transportation agencies, pavement design engineers and construction industry professionals to mechanistically evaluate and select sources of recycled hot-mix asphalt and portland cement concrete materials and identify factors that contribute most to the longevity of layers using recycled pavement materials. Extensive literature review was conducted on the aggregate specifications in the United States and other countries to identify the protocols used to evaluate the suitability of virgin and recycled aggregates in base and sub-base layers. The test procedures, typically designed for virgin aggregates, were modified to account for the recycled materials in the aggregate mix. The test procedures were further evaluated on the basis of mechanical performance, accuracy, practicality, complexity, precision, and test cost. The performance of the developed aggregate evaluation systems was determined through testing and analysis of 12 aggregates with different lithology and known field performance history. These samples were selected from seven states with different seasonal frost cycles. The performance tests were conducted and modifications were made to the tests procedures to better understand the mechanical behavior of aggregate systems with recycled materials. This study revealed that shear strength, toughness, abrasion, durability, and frost susceptibility influence the performance of the unbound aggregate layers. Statistical analysis of the data showed that shear strength of the aggregate systems has the most impact on the performance of the unbound systems consisted of recycled materials.

Three-dimensional concrete printing (3DCP), an innovative fabrication technique, has emerged as an environmentally friendly digital manufacturing process for using recycled waste materials in the construction industry. The aim of this review paper is to critically evaluate the current state of research on the use of recycled materials such as aggregates and powders in 3DCP, correlating the environmental, economic, and performance parameter effects. This review comprehensively evaluates the potential benefits of incorporating recycled waste materials in 3D printing by critically reviewing the existing peer-reviewed articles through a scientometric review. The resulting bibliometric analysis identified 73 relevant papers published between 2018 and 2024. Through the critical review, five main research categories were identified: recycled materials in 3DCP arising mainly from construction demolition in powder and aggregate forms, which investigates the types of recycled materials used, their extraction methods, morphology and physical and chemical properties. The morphology properties of the materials used displayed high irregularities in terms of shape and percentage of adhered mortar. In the second category, printability and performance, the buildability, rheological properties and the mechanical performance of 3DCP with recycled materials were investigated. Category 3 assessed the latest developments in terms of 3D-printed techniques, including Neural Networks, in predicting performance. Category 4 analysed the environmental and economic impact of 3DCP. The results indicated anisotropic behaviour for the printed samples influencing mechanical performance, with the parallel printing direction showing improved performance. The environmental performance findings indicated higher global warming potential when comparing 3DCP to cast-in situ methods. This impact was reduced by 2.47% when recycled aggregates and binder replacements other than cement were used (fly ash, ground slag, etc.). The photochemical pollution impact of 3DPC was found to be less than that of cast-in situ, 0.16 to 0.18 C2H4-eq. This environmental impact category was further reduced up to 0.10 C2H4-eq following 100% replacement. Lastly, category 5 explored some of the challenges and barriers for the implementation of 3DCP with recycled materials. The findings highlighted the main issues, namely inconsistency in material properties, which can lead to a lack of regulation in the industry.

This article investigates the fracture toughness in self-compacting concrete containing different percentages of recycled concrete materials using edge-notched disc bend (ENDB) samples. For this reason, 0, 25, 50, 75 and 100 percent of recycled aggregate were used instead of natural aggregate in the mixing designs. To obtain the fracture toughness, ENDB samples were used under loading of mixed mode I/III and pure modes I and III. Cubic samples were also used to obtain compressive strength. The results show that the compressive strength of the samples has a direct relationship with the fracture toughness and the reverse ratio with the percentage of recycled concrete materials. Also, samples containing 25% recycled materials have the highest compressive strength and fracture toughness. Furthermore, as the recycled percentage of the samples increases, the performance of samples against shear forces and compressive strength is reduced. Keywords: Fracture toughness, Mixed mode I/III, Recycled materials, Self-compacting concrete, ENDB sample

With the widely equipped Lithium-ion batteries (LIBs) in electronics and electric vehicles, proper handle spent LIBs has been the subject of increasing concern. Significantly raised concerns about resource constraints and environmental issues are brought by spent LIBs. Therefore, properly handling spent LIBs is urgent and necessary.[1] However, until now, getting manufacturers to recruit recycled materials has been a hard sell because recycled materials are deemed as inferior to commercial materials, which limits the development of recycling. Although previous publications stated that their recovered materials had a comparable performance as commercial materials, the results, based on coin cells and low electrode loading, cannot convince manufacturers to employ recycled materials in the new LIBs.[2] Here, we demonstrate that recycled cathode materials with optimized microstructure have the best industrial relevant testing results (up to 11Ah cells) so far and compare them with state-of-the-art commercial equivalent. Interestingly, the recycled materials not only pass all the aggressive industrial plug-in hybrid electric vehicle (PHEV) battery tests, but also outperform control counterparts in some tests. Specifically, 1 Ah cells with the recycled LiNi1/3Mn1/3Co1/3O2 have the best cycle life result reported for recycled materials and enable 4,200 cycles and 11,600 cycles at 80% and 70% capacity retention, which is 33% and 53% better than the state-of-the-art, commercial LiNi1/3Mn1/3Co1/3O2. Meanwhile, its rate performance is 88.6% better than commercial powders at 5C. Through detailed experimental and modeling analysis of pristine and cycled materials, we discover that the unique porous and larger inside void microstructure enables the superior rate and cycle performance and less phase transformation. Compared with the control sample, the surface area of the recycled LiNi1/3Mn1/3Co1/3O2 is 82.14% larger and the cumulative pore volume is 61.25% larger. Even some recycled particles have an outer diameter of the void space equal to 40% to 60% of the particle diameter. The unique microstructure can reduce 16% hoop stress during the discharge/charge process compared to control materials, and improve the lithium chemical diffusion coefficient, enabling the superior performance of cycle life and rate performance and less phase transformation. The results pave the way to re-introduce recycled materials into new batteries.[3] [1] M. Chen, X. Ma, B. Chen, R. Arsenault, P. Karlson, N. Simon, Y. Wang, Recycling End-of-Life Electric Vehicle Lithium-Ion Batteries, Joule 2019, 3, 2622.10.1016/j.joule.2019.09.014[2] X. Ma, L. Azhari, Y. Wang, Li-ion battery recycling challenges, Chem 2021.10.1016/j.chempr.2021.09.013[3] X. Ma, M. Chen, Z. Zheng, D. Bullen, J. Wang, C. Harrison, E. Gratz, Y. Lin, Z. Yang, Y. Zhang, F. Wang, D. Robertson, S.-B. Son, I. Bloom, J. Wen, M. Ge, X. Xiao, W.-K. Lee, M. Tang, Q. Wang, J. Fu, Y. Zhang, B. C. Sousa, R. Arsenault, P. Karlson, N. Simon, Y. Wang, Recycled cathode materials enabled superior performance for lithium-ion batteries, Joule 2021.10.1016/j.joule.2021.09.005

The trade of recycled raw materials is an essential part of the circular economy model of economic development, which contributes to resource efficiency, keeps goods in circulation, and reduces society’s negative environmental impact. Recycling raw materials is particularly relevant for countries with a limited number of natural resources, where the recycling of raw materials significantly impacts the reduction of raw material imports and raw material prices. Recycled raw materials provide significant conservation of primary raw materials. In this paper, the authors used a multistage research methodology to review key variables, identified relationships between trade in recycled raw materials and private investment into recycling, and links between construction and demolition waste recovery and circularity. The authors described the evolution of different types of waste, the volume they generate, and their influence on the trade of recycled raw materials. After applying the Robust least squares method, the authors formed a regression equation and reflected the result in a graph to forecast the trade volume in recycled raw materials in the 27 European Union (EU) countries for 12 years. The paper concludes that the study of the volume of trade in recycled raw materials is a relatively new topic that focuses on recycled raw materials, promotes sustainability and circularity, and conserves natural primary resources. The results of this study show that trade in secondary raw materials (i.e., recycled materials) is an important element of the circular economy and an important environmental and economic policy instrument. This study bridges the gap between sustainability ambitions and practical implementation mechanisms within circular economic systems. The proposed regression model not only enables forecasting of trade volumes but also serves as a strategic tool for policymakers and stakeholders aiming to promote investment and optimize waste recovery systems.

The binder properties were determined in accordance with Chinese standard such as ductility test, which allowed to measure the distance in centimeters that a standard briquette of asphalt had been stretched before breaking. Then, penetration test was carried out in order to know some properties of the asphalt, which are the hardness and the softness. Finally, softening point test was carried out in order to determine the temperature at which the bitumen attains a particular degree of softening under the specification of the test. According to Chinese standard for performance tests, firstly, Marshall test was carried out in order to measure the theoretical density, air voids, voids filled with asphalt, stability, flow, and voids in mineral aggregate of asphalt specimens. Secondly, Freeze-thaw splitting test was carried out in order to determine Splitting strength ratio. Finally, dynamic stability (rutting) test was carried out to determine average dynamic stability. Beside the tests carried out, the gradation of the extracted aggregate in accordance with American Association of State Highway and Transportation Officials was carried out to determine the dimensions of the particles weight distribution. Furthermore, both the percentage of recycled asphalt pavement materials and binder in mixture were determined to know how much of the new material during the mixture was needed. However, two specimens were used to evaluate the performance of recycled asphalt pavement materials. One specimen of recycled asphalt pavement materials was ten years old, and another one of recycled asphalt pavement materials was five years old. The results show that the conditions of the environment such as moisture, temperature, and age, decrease the ductility and penetration properties of binder when increase the softening point property of binder. Then the gradation of recycled asphalt pavement aggregate is of the required values to reuse in the mixture, while the flow ratio, the splitting strength ratio, and the dynamic stability ratio, are less than the required value test. With regard to the properties of mixture of recycled asphalt pavement material binder with rejuvenator, the results show that when the penetration and ductility versus percentage of rejuvenator increase, softening point versus percentage of rejuvenator decreases. Also, when the bitumen and rejuvenator percentage increase, the air voids decrease. Consequently, voids filled with asphalt and voids in the mineral aggregate increase. Moreover, the theoretical density and stability values decrease in a mixture containing four-point fifty percent to six percent of bitumen and rejuvenator, whereas the flow values increase. More interestingly, with four percent to four-point fifty percent mixture ratio of bitumen and rejuvenator, density, stability, and flow values increase. The splitting strength ratio values of mixtures and the dynamic stability test (rutting test) values of mixtures with forty percent of specimen one and specimen two respectively are greater than the required value of the standard test. In addition, the high percentage of rejuvenator increases the rut of pavement, in the same manner, the low percentage of rejuvenator induces low rut. In conclusion, the binder content from recycled materials without rejuvenator seems not be sufficient to be reused on the new pavement while the aged recycled material seems to be performed better than no aged recycled material with rejuvenator into bitumen. Then, the rejuvenator can influence the bitumen properties and performance of the pavement. Finally, the pavement made by only recycled pavement materials as a base layer appears to be more economical but cannot be more effective than the pavement made by mixture of new and recycled pavement materials as a base layer.

The utilization of recycled materials has emerged as a pivotal strategy for mitigating resource depletion and reducing carbon emissions in the construction industry. However, existing reviews predominantly focus on specific technical aspects, often overlooking the interdisciplinary complexities associated with recycled materials as a systems engineering challenge. This study systematically reviews 1533 documents from the Web of Science Core Collection, integrating quantitative and qualitative analytical approaches to assess the current state and future trajectory of the field, thereby addressing existing research gaps. The findings highlight the substantial evolution of recycled building materials from waste recovery to a multifaceted domain encompassing value assessment, circular economy principles, advanced technologies, interdisciplinary collaboration, and long-term societal benefits. This study identifies six key research themes in recycled building materials: life cycle assessment, biological and natural materials, recycled concrete, recycled asphalt and building infrastructure, construction and demolition waste, and environmental impacts with composite factors. Furthermore, current research is categorized into two primary dimensions: value strategies and technological tools. The analysis of future research directions underscores the potential of AI-driven innovations and their role in enhancing human living environments. However, developing countries continue to face critical challenges, necessitating further interdisciplinary integration and knowledge exchange. Finally, this study proposes a comprehensive and systematic disciplinary framework that offers valuable insights for future strategic planning and technological advancements in the field.

The complexity of plastic polymers and even more so of additives has increased enormously in recent years. This makes the material recycling of plastic waste considerably more difficult, especially in the case of mixed plastic waste. Some additives have now been strictly regulated or even completely banned for good reasons (‘legacy additives’). Material or mechanical recycling generally uses old plastics that still contain these substances. Consequently, products that are manufactured using such recyclates are contaminated with these harmful substances. This poses a major challenge for sustainability, as there is a conflict of objectives between protecting the health of consumers, especially vulnerable groups, conserving resources and recycling, keeping material cycles ‘clean’ and destroying pollutants, and transporting them to a safe final sink. With regard to the first objective, we recommend avoiding the use of contaminated recyclates for products with intensive contact with consumers (‘contact-sensitive products’) until further notice. We also show that the climate policy challenges for the plastics (and chemical) industry necessitate defossilization (‘feedstock change’). This turnaround can only succeed if solely closed-loop recycling takes place in the future; recyclates should primarily replace virgin plastics. For material or mechanical recycling, this means that this can only work if used plastics with a high degree of homogeneity and known formulation are collected separately, as is already the case today with PET bottles. The objective of this article is to illustrate the increasing complexity of plastic polymers and additives, especially legacy additives, which will force a legislative readjustment of todays’ material recycling.

18 - Recycling of materials containing inorganic and carbonaceous nanomaterials

11 - Recycling of materials in automotive engineering

The use of recycled granular materials for road construction should be a necessity in current times; both for economic and environmental reasons. By the use of such materials, the road construction industry helps to protect natural resources and reduce its carbon footprint, while lowering the cost of pavement construction. However, the use of recycled materials can often raise concerns, viz. design compliance, low homogeneity, perceived lower quality and an onerous production process when compared to the use of virgin materials. It may be common practice for the variability in the engineering parameters of these materials to influence designers to specify thicker pavement layers in order to ensure that the required bearing capacity and/or design life of the road is achieved. The use of hexagonal stabilisation geogrids may provide a method of mitigating against the loss of homogeneity and improve the engineering parameters of recycled granular materials. The case-studies presented herein demonstrate that the mechanical stabilisation of recycled granular materials with a hexagonal geogrid, results in an increased stiffness of the layer and significantly aids compaction. When aggregate is placed and compacted on a stiff hexagonal geogrid, aggregate particles interlock within the geogrid apertures and are confined by its stiff ribs. A composite mechanically stabilised layer (MSL) is created, in which the geogrid and aggregate act in unison. Lateral restraint, provided by the geogrid, reduces strain within the aggregate skeleton and thereby increases the stiffness of the layer. The result is that the required performance parameters, be it a bearing capacity of a layer and/or life of the pavement, can be successfully achieved with the use of, and possible reduction in the required layer thickness of, recycled granular materials. The concept of mechanical stabilisation of aggregate layers by the use of geogrids is detailed in this paper. Furthermore, several case studies are presented which demonstrate the use of hexagonal stabilisation geogrids to improve the bearing capacity of various recycled materials such as recycled asphalt, recycled concrete, and coal mine shales.

Use of recycled materials as mid layer in three layered structures-new possibility in design for recycling

Recycled materials, such as recovered materials from the transportation sector or secondary or by-product materials from the industrial, municipal, or mining sectors can be used as substitutes for natural materials in the construction of highway infrastructure. Trace metals in these recycled materials may leach out and contaminate the groundwater and soil posing a long-term environmental problem. Environmental risk assessments are necessary to evaluate which recycled material applications are acceptable. The first step for determining the environmental risk of using recycled materials is to characterize the source term. Estimates of contaminant release fluxes can then be used in a comparative risk assessment. This paper will give an example of a comparative, probabilistic approach for exposure assessment. Existing deterministic models for estimating contaminant release will be presented and incorporation of variability in these models will be discussed.KeywordsAsphalt ConcreteRecycle MaterialMunicipal Solid Waste IncineratorConcrete PavementPortland Cement ConcreteThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

Recycling spent lithium-ion batteries can play a significant role in alleviating the shortage of raw materials and environmental problems. However, recycled materials are usually deemed inferior to commercial materials in terms of electrochemical performance, preventing the industry from adopting recycled materials in their batteries. Here, we demonstrate that the recycled LiNi1/3Mn1/3Co1/3O2 has a superior rate and cycle performance, verified by various industry-level tests. Specifically, 1 Ah cells with the recycled LiNi1/3Mn1/3Co1/3O2 have the best cycle life result reported for recycled materials and enable 4,200 cycles and 11,600 cycles at 80% and 70% capacity retention, which is 33% and 53% better than the state-of-the-art, commercial LiNi1/3Mn1/3Co1/3O2. Meanwhile, the recycled LiNi1/3Mn1/3Co1/3O2also shows an 88.6% better rate performance than the commercial powder at 5C. From both experimental and modeling results, the optimized microstructure of recycled materials enables the superior electrochemical performance. The recycled cathode material outperforms commercially available equivalent, providing a green and sustainable solution for spent lithium-ion batteries.

Industrialization and continuous increase in population growth have contributed immensely to various kinds of solid waste generation which most times are indiscriminately dumped. These activities have negative effects resulting in environmental pollution which could be a menace to the environment. Moreover, to preserve the environment, many researchers have made efforts to ensure that some of these wastes are recycled and utilized in the production of various alternative materials as a means of sustainable technology. Among several alternative materials for construction, some of these wastes are considered to be very useful.This study examines the various recycled waste materials that can be adopted for construction, including their prospects and challenges. Some of the recycled waste materials examined are plastic waste, mill tailings, geopolymers, waste glass, rubber tyre waste, shingles, construction and demolition wastes (C&D) and slag. These recycled materials have been accepted globally due to their characteristic properties which made the materials suitable in the construction industry. This review also examines some limitations relating to the adoption of these materials as alternative construction materials for highway/pavement construction. However, it is generally accepted that reuse of waste materials in construction industry has minimal environmental impact and their exploration would have huge economic impact.