Sustainable Improvements for Mix and Structural Designs for Cold Recycling Technology

The green and low-carbon concept has significantly influenced various industries, including asphalt pavement construction. Cold recycling technology offers notable advantages in reducing carbon emissions during pavement construction. However, traditional cold recycling methods often fail to utilise aged asphalt. They rely heavily on emulsion or foamed asphalt binders, which contradicts the low-carbon principle. Additionally, performance limitations of existing binders prevent these technologies from adequately addressing the deficiencies of RAP. This study introduces a novel approach to cold-recycled asphalt mixtures using cost-effective waterborne epoxy resin to mitigate RAP performance deficiencies. Two diffusion components were incorporated to enhance the utilisation of aged asphalt and improve the overall performance of cold-recycled mixtures. A design method for waterborne epoxy cold recycling asphalt mixtures (WECRM) and suitable evaluation methods for road performance were developed. The results demonstrate that WECRM exhibits excellent high-temperature performance. The inclusion of diffusion components significantly improves low-temperature properties and reduces moisture sensitivity. With a modulus ranging from 12,000 to 13,000 MPa, WECRM is ideal for surface layer applications. Furthermore, the analysis highlights its suitability for lower pavement layers to resist rutting, enabling high-value applications of cold recycling technology while maintaining cost efficiency.

A literature review on cold recycling technology of asphalt pavement

Cold recycling of lime-fly ash stabilized macadam mixtures as pavement bases and subbases

The economic attractiveness of cold recycling technology provides, first of all, the reuse of the existing material on the road for the arrangement of new pavement layers, so there is no need to equip special sites for the storage and disposal of old asphalt concrete. The essence of cold recycling technology which is most commonly used for arranging the subbase in Ukraine is that the defective and destroyed layers of road pavement are reinforced on-site by combined additives of organic and mineral binders. Cold recycling by complexity of works is divided into several types depending on the depth of milling. The choice of a rehabilitation type depends mainly on the general state of the pavement structure state which is determined before the beginning of repair work. In Ukraine, the main focus of R&D in cold recycling technology is the use of new materials such as fiber - basalt or polymer, stabilizing additives, industrial waste - slag of various types of industries or other byproducts. Conducted research has shown that the use of organic and mineral mixtures from an optimal mix design with the introduction of basalt fibers increases the crack resistance and durability of the arranged subbase.

The article represents the results for investigation of a new technology of complex soil consolidation and stabilization and reuse of the material from stripping of the existing roads (cold recycling technology) with portlandcement and enzyme agent Roadzyme (USA), which allows reducing the energy costs significantly and improving ecological situation. Cold recycling has a number of significant advantages before other means of reconstruction. The absence of environmental pollution is due to the complete use of the material of the old pavement. There is no need in disposal sites, and the volume of the new delivered materials is the minimum one and reduces the area of contamination, which is certain during opening of new borrow-pits and rock quarries. Transportation is very small, therefore the consumption of the energy is considerably reduced, as well as devastating impact of vehicles on the road network. Effect of the use of the agent “Roadzyme” is based on the activation of physics and chemical processes, which increase the strength, water resistance and frost resistance of the consolidated soils and materials, reducing material consumption at provision of the required elasticity modulus for pavement structure due to reduction of the thickness for pavement layers, the use of local materials and saving of binders and inert materials. The decrease is noted for the stiffness of the materials, strengthened by complex method (binder with the agent “Roadzyme”), compared to the treatment only with the binder, which allows forecasting the increase of the crack resistance.

A significant influence on stability of the process of filling the CCM mold with liquid metal is exerted by the structural and technological schemes and designs of used devices, modes and parameters of filling the mold with the melt. All this is due to the features of the devices used and the improvement of their design. The high requirements for such devices have determined the need to create new devices designs to reduce the time spent on preparation for work and maintenance and to improve the quality of resulting metal billets. In scientific literature, including patents, more and more articles and materials are devoted to the development of new and improvement of the existing methods of supplying and stirring liquid metal in CCM and devices for their implementation. Experimental studies of liquid metal flow in CCM are a long, complex and laborious process. Therefore, mathematical modeling by numerical methods is increasingly used for this purpose. The authors have proposed a new technology for pouring liquid metal into a mold and a device for its implementation due to the use of effect of a deep-bottom submersible nozzle rotating in the mold with eccentric outlet holes. The purpose of this work is to simulate by proven numerical method a new process of filling a rectangular CCM mold with liquid steel and stirring it. Based on the developed numerical schemes and algorithms, a calculation program was compiled. The article describes an example of calculating the steel casting into a mold of rectangular cross-section and flow diagrams of liquid metal in it.

The most important priority in the field of environmental protection is the implementation of the principle of closed - cycle materials management in construction. This problem also plays an important role in road construction. Due to the increasing traffic load of heavy vehicles and the impact of climatic factors, the road structure is subject to destructive processes that lead to the loss of its durability in time. Therefore, the roads periodically need to be modernized. Very often, it is necessary to carry out critical activities on the foundation to improve the load - bearing capacity of the pavement structure. As part of these works, large amounts of reclaimed asphalt and aggregate are obtained during milling of the lower structural layers of the surface. Applying the principle of closed - cycled material management, the most effective technology for using this material is its re - construction using deep cold recycling technology. This technology uses hydraulic binder and bituminous emulsion, and currently, more and more often, foamed bitumen. Due to the fact that the materials obtained from road structure layers are of very different quality, it is necessary to use a binder that will be dedicated specifically to the materials used (reclaimed asphalt pavement, reclaimed stone). In experiment Portland cement CEM I 32.5, hydrated lime and cement by - pass dust as a by - product obtained from cement plants were used. All components were mixed in various proportions controlled by experiment plan. The influence of a dedicated binder on absorption, dynamic modulus, phase angle in the specific temperature range and rutting resistance of a cold recycled mixture designed with reclaimed asphalt pavement, reclaimed aggregate and foamed asphalt was examined. The obtained test results were subjected to statistical analysis using the ANOVA test in order to determine the significance of the influence of individual components of the dedicated binder on the considered parameter of the cold recycled mixtures. It was determined that the dedicated binder used for the tested recycled asphalt mixture ensures its most favorable parameters when contains: 40% CEM I 35.2, 20% hydrated lime and 40% cement by - pass dust.

A comprehensive review on the plant-mixed cold recycling technology of emulsified asphalt: Raw materials and factors affecting performances

With the application of cold recycling technology in cold seasons or northern regions, suitable low-temperature performance evaluation methods and low-temperature performance improvement measures of a cold recycled mixture (CRM) became very topical. This study attempts to clarify the manufacturing process of low-temperature beam specimens by simulating the secondary thermal compaction of the overlying hot mix asphalt mixture layer. Next, the applicability of indirect tensile tests, low-temperature bend tests, and SCB tests to low-temperature performance evaluation of CRM is evaluated. The low-temperature improvement measures of emulsified asphalt CRM are analyzed, showing that "primary rolling for 24 times + secondary rolling for 12 times" of the low-temperature beam specimens conforms to the field compaction state of the CRM layer. The low-temperature performance of CRM under different design schemes can be characterized by the fracture work in the indirect tensile tests and fracture energy in the SCB tests. Compared with the ordinary emulsified asphalt CRM, the mixture design scheme of "3% latex +5% regenerant" can significantly improve the low-temperature performance of CRM. The lower the temperature, the more pronounced the improvement effect. Considering that the low-temperature performance of CRM meets the road requirements, the design scheme of "3% latex +5% regenerant" is recommended, while the "3% latex" scheme is the most cost-effective.

Asphalt cold recycling technologies allow the use of up to 100 % reclaimed asphalt pavement (RAP) from an existing asphalt pavement to construct new base layers and new subbase layers. Bituminous stabilized materials (BSM), obtained from cold recycling technologies, are susceptible to traffic-induced accumulation of permanent deformation. In the current design methods, BSM pavement layers are typically assumed to have a linear elastic response under traffic loading application, and this does not account for plasticity initiation and accumulation in the material. This research study provides insight on how to integrate plasticity behavior in numerical simulations of rehabilitated pavement structures with BSM. A BSM mixture prepared with 1.5 % cement by weight of total mixture and 1.5 % foamed asphalt binder content by weight of dry aggregates is characterized in the laboratory. Subsequently, a three-dimensional elastic-perfectly plastic finite element model is developed for the simulation of triaxial shear strength tests. Lab measured force-displacement curves are matched with the numerical simulations at different confining pressures. The calibrated mechanical properties are then used as input parameters in multilayer pavement models for pavement evaluation. Different pavement structures with and without BSM layers are compared in terms of a maximum allowable number of loading repetitions before reaching a 20-mm rut depth on the surface of the pavement. The results indicate that structures with BSM and traditional granular base layers yield comparable results in terms of rutting potential. In addition, the study presents a framework for the design and analysis of cold recycled pavement layers and a method to integrate the plasticity behavior of partially-bonded and unbounded layers for pavement evaluation.

The increasing use of bitumen-stabilised materials (BSMs) in the world and especially in Southern Africa necessitates further research into the fundamental properties and behaviour of BSMs. In particular, bitumen stabilisation is increasingly being used to rehabilitate base layers of pavements incorporating thick asphalt layers, resulting in higher percentages of reclaimed asphalt pavement (RAP) in the mixes. There is a significant need for improved understanding of these materials, which is the main objective of the study being undertaken. The extended knowledge gained from this research is intended to improve current mix design and structural design practices. The project's aim is to investigate the feasibility and suitability of producing BSMs that include RAP with relatively high blending ratios of recycled graded crushed stone. In this study, the RAP used in each mix design contains materials with relatively fresh binder. The proportions range from 100:0 to 0:100 of graded crushed stone: RAP. Tri-axial tests at different temperatures are carried out to determine shear properties, resilient modulus and permanent deformation behaviour of the mix. The findings show that the RAP type and percentage influence the rutting resistance, indirect tensile strength (ITS) and moisture susceptibility of the BSMs. A portion of this study is dedicated to the characterisation of the permanent deformation behaviour and to the moisture damage simulation.

Revealing water-biopolymer interactions: Toward advanced water collection from air.

As a kind of paper material, corrugated paper has light weight, good mechanical properties, can be recycled, has good printability, and is not harmful to the environment. Therefore, it is feasible to promote corrugated cardboard furniture. Through the analysis of corrugated paper furniture cases, this thesis proposes sustainable design strategies for cardboard furniture and divides the design process of paper furniture into design stage - use stage - post-use stage, proposes reduction control in the design stage, and provides specific implementation plans, such as in the design stage, using a computer to conduct a corrugated paper furniture model For example, in the design stage, finite element analysis is performed on the corrugated furniture model by computer, which enables a more reasonable structural design that meets the mechanical requirements of the furniture structure while maximizing material savings. In the processing stage, a cutting machine with automatic laser positioning is introduced to accommodate the processing of corrugated paper shaped structures and achieve sustainable design from the perspective of waste reduction. Reuse guidance in the use phase and recyclable technology support in the post-use phase are also proposed, as well as implementation strategies for specific elements of each link.It is hoped that this will bring positive implications for the market, resources, and the environment, and will provide certain valuable references and insights for industry players in the design and production of corrugated furniture.