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As an advanced technology for pavement crack maintenance with high automation level, high precision and high efficiency, 3D asphalt printing technology can effectively improve worker safety and ensure the stability of maintenance quality. In order to optimize the printing parameters of rubber modified 3D printed asphalt (R-3DPA), a three-axis asphalt 3D printer was developed in this study through the design and selection of each component, and it was used for the 3D printing of R-3DPA strips, layers, and structures. Based on the comparison of continuity, uniformity, and width of R-3DPA strips, the recommended extrusion nozzle diameter, printing temperature, and printing speed parameter combinations were superiorly selected. According to the analysis of filling degree, width error and thickness of R-3DPA layers, the optimal printing strip width was recommended. Through the evaluation of integrity, surface characteristics and accuracy of R-3DPA structures, the suitable printing layer thickness was determined. The test results showed that the three-axis asphalt 3D printer can be used to measure the parameters of R-3DPA, and the printing accuracy and scale meet the requirements. The recommended parameters for R-3DPA are an extrusion nozzle diameter of 2 mm, a printing temperature of 180 °C, a printing speed of 20 mm/s, a printing strip width of 2.25 mm and a printing layer thickness of 0.4 mm, resulting in structures with good integrity and precision. • Optimize the printing parameters of R-3DPA. • Develop a three-axis asphalt 3D printer. • Recommend equipment parameters combinations of 3D printer. • Obtain the printing parameters of R-3DPA in pavement maintenance. [ABSTRACT FROM AUTHOR]

Highlights • Investigate dependence of overlay field cracking performance on overlay thickness. • Investigate dependence of overlay field cracking performance on fracture energy. • Propose a new performance parameter for reflective cracking performance evaluation. • Propose thresholds for selection of overlay thicknesses and material types. Abstract This study investigates the dependence of overlay field cracking performance on overlay thickness and fracture energy of asphalt mixture. A total of 15 pavement sections in Minnesota for which Disk-shape Compact Tension (DCT) testing was performed on field cores from overlays were used for the study. Due to the difference in the overlay lives, different cracking performance measures such as average transverse cracking rate (ATCR), maximum transverse cracking rate (MTCR) and transverse cracking performance index (TCTotal) were calculated. These cracking performance measures were compared with asphalt overlay thicknesses and DCT fracture energies. The analysis indicated the dependence of TCTotal on both overlay thickness and fracture energy. The observed relationship was assessed for reliability using a statistical analysis and a new performance parameter that combines overlay thickness with fracture energy is proposed to provide measure of total fracture resistance of the overlay. Preliminary thresholds are also proposed for selection of overlay thicknesses and material types in new overlays. [ABSTRACT FROM AUTHOR]

This work shows the self-healing results of surface cracks on bituminous mixtures after microwave heating. Different mixtures (semi-dense AC, BBTM and PA) with diverse types, sizes and proportions of metallic additions were tested (steel wool, steel filing and metallic powder). 3 aspects were evaluated: a) influence of the mass and type of addition on the heating speed; b) temperature increase ratio with the specific energy; c) monitoring of the healing process using ultrasounds. It was found that metallic filler replacing the mineral powder was the most efficient and practical addition. This method allows complete closure of the cracks, using an industrial waste, and offers certain improvements compared to induction heating. The results validate the microwaves healing capacity, as well as the use of ultrasounds for tracking the crack depth. [ABSTRACT FROM AUTHOR]

• 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. [ABSTRACT FROM AUTHOR]

Abstracts Environmental sustainability in transportation infrastructures can be achieved by using recycled materials. Commonly, road and airport pavement construction is identified as a greatly polluting factor for greenhouse gas and odor emissions. This paper presents a case study concerning two rehabilitation methods adopted in a reconstruction project of two taxiway pavements in a major Italian airport. The paper describes the entire process of rehabilitation works starting from the preliminary investigations to the final quality controls. It includes the pavements design phase and the materials optimization and environmental assessment, which is the core of the research. The findings show that recycling does not necessarily result in lower performance. In fact, up to 65% of CO 2 e emissions were saved by constructing the recycled pavements. Performance was instead comparable to a standard asphalt pavement. Finally, the paper shows the eco-efficiency of including low-energy treatments and sustainable strategies into pavement construction to enhance environmental savings and cost effectiveness in airport construction practices. [ABSTRACT FROM AUTHOR]

• An overview of pothole formation, classification and maintenance was reported. • A comprehensive comparison between different kinds of patching materials was made. • Repair methods, cost and durability of cold mix patching materials were studied. • Cold patching materials components and their impact on the patch were inspected. • Methods of evaluating cold mix patching materials performance were investigated. Cold Mix Patching Materials (CMPMs) are usually used instead of Hot Mix Asphalt (HMA) to repair potholes and localized distresses. Although these materials provide immediate serviceability, they have a relatively short life. However, worldwide interest in these solutions, which started as fragmented industrial initiatives, is growing. This article provides a critical comparison between several aspects regarding using CMPMs and HMA in repairing potholes. Specifically, repair techniques, productivity and costs were investigated in detail. Plus, the impact of the main crucial factors, i.e., workability, bonding, water susceptibility, stability, and storageability, on the performance of CMPMs was investigated through an overview. [ABSTRACT FROM AUTHOR]

• Database of MSRL test results of large amount of field cores was developed. • GEP model outperformed MLR model with the same database. • Uncertainty analysis was conducted through the Monte Carlo simulation. • Binder property dominates rutting resistance of in-service middle asphalt layer. For a multilayered asphalt pavement, rutting resistance of the mixture in the middle asphalt layer underneath the surface course plays a significant role in the high-tempearture stability of the whole pavement structure. Thus, evaluation of the rutting resistance of the middle asphalt layer using field cores is often necessary for project-level pavement maintenance decision-making. However, the extrusion and tests of field cores are time-consuming and destructive to pavement. To address this problem, developing an empirical model to predict the rutting resistance of the middle asphalt layer at a certain service time from historical test results may be a potential alternative. This study aims to address this challenge by using the gene expression programming (GEP) method and a database composed of a large number of multiple-stress repeated load (MSRL) test results of field cores. By correlating the compound creep rate (CCR) of the middle asphalt layer from the MSRL tests to material properties, environmental and traffic parameters, field rutting depth, and middle layer age, the optimal GEP model was developed, and then compared with the conventional multiple linear regression (MLR) model built on the same database. Uncertainty analysis was also conducted through the Monte Carlo simulation (MCs). It was found that the GEP model outperformed the MLR model, with a 6%-7% higher R-square. The uncertainty analysis allows the transport agencies to estimate the reliability of their prediction and make maintenance and rehabilitation (M&R) plans according to the specified reliability target. [ABSTRACT FROM AUTHOR]

• Parameters, RRDD and IAR, are proposed to evaluate the treatment effectiveness. • Multiple regression analysis is employed to investigate the effect of initial RD and AADT on effectiveness. • LCCA is performed to evaluate the treatment cost-effectiveness over a 50-year analysis period. • HIR outperforms other treatments in restoring pavement rutting resistance. • Establishment of the rutting-based maintenance decision-making system is recommended. The present study compared the effectiveness and cost-effectiveness of four pavement treatments, including hot in-place recycling, milling and filling, thin HMA overlay and microsurfacing. The multiple regression analysis was employed to investigate the effectiveness of treatments and the effect of pretreatment rutting severity and traffic conditions on maintenance effectiveness. The rutting depth (RD) was selected as a performance indicator. The reduction of RD degradation rate and increase in average RD over monitoring period were used as measures of treatment effectiveness. Life-cycle cost analysis was performed to evaluate the treatment cost-effectiveness over a 50-year analysis period. Results indicate that the hot in-place recycling possesses the highest effectiveness and cost-effectiveness. Using reclaimed asphalt pavement (RAP) at appropriate maintenance timing substantially benefits for restoring the rutting resistance of asphalt pavement. These findings provide project agencies with quantitative evidence to support the establishment of the rutting-based maintenance decision-making system and the utilization of RAP in the sustainable pavement management strategies. [ABSTRACT FROM AUTHOR]

• 8 highway segments, in total 491.74 km, were investigated in field. • Treatment effectiveness was quantitatively compared by PJ, DRR and ADRR with RD. • Rutting tests by cylindrical samples was proposed and successfully performed. • Applicability of proposed effectiveness analyses was assessed by rutting tests. • High-quality RAP are recommended for timely maintenance activities. To evaluate the effectiveness of maintenance treatments for asphalt pavement, four types of treatments, including the hot in-place recycling (HIR), milling and resurfacing (M&F), thin HMA overlay (THO) and microsurfacing (MS), were analyzed. 8 highway segments, in total 491.74 km, in Jiangsu Province in China, were investigated and the data of rutting depth (RD) in their maintenance history was collected. Based on the data of RD, the effectiveness of four treatments was quantitatively compared by three indicators, namely, performance jump (PJ), deterioration rate reduction (DRR) and average deterioration reduction rate (ADRR). Moreover, the applicability of the proposed effectiveness analyses was assessed by laboratory rutting tests with field cylindrical samples. Results indicate that the HIR is the most effective treatment, followed by M&F and THO. While the MS is the least effective treatment, whose service life is only three or four years. The findings highlight the significance of the proper traffic opening time after maintenance to avoid the weakened rutting resistance caused by high-temperature mixtures, the effect of the RD before maintenance on maintenance decision-making, and the application of high-quality RAP in the timely maintenance activities. Therefore, the performance-based maintenance strategy should be establish to improve pavement performance and extend pavement service life. Further research on the pavement performance after RAP application is necessary. [ABSTRACT FROM AUTHOR]