The paper presents a comprehensive analysis on reclaimed asphalt pavement (RAP) milling material collected from a single source, namely from a secondary road in Romania, county road DJ109. The following characteristics are investigated: particle size, binder content, material variability and uniformity, and the clustering phenomena. Variability is demonstrated using the results of particle size gradation and binder content. The coefficient of uniformity and the coefficient of curvature demonstrate that the RAP used in this research is a well-graded material. However, the visual analyses conducted on RAP highlight the presence of RAP particle agglomeration and the need for further testing. The study presents three different experimental phases: (i) RAP-milling old asphalt pavement, RAP; (ii) RAP milling after binder extraction, RAPabe; and (iii) RAP after Los Angeles crushing, RAPac. After processing, the coarse part (C) had a great influence on the fine part (F), and F/C ratio increased, respectively, from 0.4 to 1.5 and 1.61. Material variability on the extended site, the difference between the design values and particle size, as well as the existing clustering process indicated that RAP material collected from secondary roads must be pre-processed prior to its storage and reuse in the recycling process. Considering that secondary roads represent 71% of the overall network of asphalt course roads in Romania, and around 24,000 km of roads are in need of at least extensive maintenance (wearing asphalt courses) or rehabilitation, RAP is a highly recyclable material. Therefore, this study provides advice and guidance for re-using RAP in new pavement mixtures.

This work aims to show the advantages of using GGBS (Ground Granulated Blast Furnace Slag) and ACBFS aggregate (Air-Cooled Blast Furnace Slag) on the tensile strength and durability properties of infrastructure concrete at the reference age of 28 days. Three concrete mixes were prepared: the first one was a control sample; the second one had 15% GGBS (instead of Portland cement) and 25% ACBFS (instead of natural sand); and the third had 15% GGBS (instead of Portland cement) and 50% ACBFS (instead of natural sand). The studies on mortars focused on the ratio of compressive strength (CS) in correlation with the specific surface area (obtained by the Blain method). The microstructure of the prepared mortars was examined at the age of 28 days by X-ray diffraction, SEM electron microscopy with an energy-dispersive EDX spectrometer, and NMR nuclear magnetic resonance relaxometry. The results of the tests carried out afterwards on the concretes containing slag (15% GGBS and 25% or 50% ACBFS) showed values that met high-quality criteria for exfoliation (S₅₆ < 0.1 kg/m²), carbonation, and gelling G100 (with a loss of resistance to compression η < 25%). The slag concretes showed a degree of gelation of G100 (with a loss of compressive strength below 25%), low volume losses below 18,000 mm³/5000 mm² (corresponding to wear class 4, grade I), and moderate penetration of chlorine ions (according to the RCPT test). All of these allow the concrete with slag (GGBS/ACBFS) to be recommended as an ecological road concrete. Our study proved that a high-class road concrete of BcR 5.0 can be obtained, with tensile strengths of a minimum 5 MPa at 28 days (the higher road concrete class in Romania, according to national standards).

Incorporating blast furnace slag into the composition of paving concrete can be one of the cost-effective ways to completely eliminate by-products from the pig iron production process (approximately 70% granulated slag and 30% air-cooled slag). The possibility to reintroduce blast furnace slag back into the life cycle will provide significant support to current environmental concerns and the clearance of tailings landfills. Especially in recent years, granulated and ground blast furnace slag (GGBS) as a substitute for cement and air-cooled blast furnace slag (ACBFS) aggregates as a substitute for natural aggregates in the composition of concretes have been studied by many researchers. But concrete compositions with large amounts of incorporated blast furnace slag affect the mechanical and durability properties through the interaction between the slag, cement and water depending on the curing times. This study focuses on identifying the optimal proportions of GGBS as a supplementary cementitious material (SCM) and ACBFS aggregates as a substitute to natural sand such that the performance at 90 days of curing the concrete is similar to that of the control concrete. In addition, to minimize the costs associated with grinding GGBS, the hydration activity index (HAI) of the GGBS, the surface morphology, and the mineral components were analyzed via X-ray diffraction, scanning electron microscopy (SEM), energy dispersive spectrometry (EDX), and nuclear magnetic resonance relaxometry (NMR). The flexural strength, the basic mechanical property of road concretes, increased from 28 to 90 days by 20.72% and 20.26% for the slag concrete but by 18.58% for the reference concrete. The composite with 15% GGBS and 25% ACBFS achieved results similar to the reference concrete at 90 days; therefore, they are considered optimal percentages to replace cement and natural sand in ecological pavement concretes. The HAI of the slag powder with a specific surface area equivalent to that of Portland cement fell into strength class 80 at the age of 28 days, but at the age of 90 days, the strength class was 100. The results of this research present three important benefits: the first is the protection of the environment through the recycling of two steel industry wastes that complies with European circular economy regulations, and the second is linked to the consequent savings in the disposal costs associated with wastefully occupied warehouses and the savings in slag grinding.

The results presented in this paper on the appropriateness of using of blast furnace slag (BFS) in the composition of roads make an original contribution to the development of sustainable materials with the aim to reduce the carbon footprint and the consumption of natural resources. The novelty of this work consists of determining the optimal percentage of BSF in road concrete, in order to: increase mechanical resistances, reduce contractions in the hardening process, and ensure increased corrosion resistances, even superior to classic cement-based mixtures. Thus, the physical-mechanical characteristics and the microstructure of some road concretes were studied in the laboratory for three different recipes. We kept the same amount of ground granulated blast furnace slag (GGBS) as a substitute for Portland cement, respectively three percentages of 20%, 40%, 60% air-cooled blast furnace slag (ACBFS) and crushed as sand substitute from now on called S54/20, S54/40, S54/60. Drying shrinkage, mechanical resistances, carbonation-induced corrosion, microstructure characterization of hardened concretes, and degree of crystallinity by SEM and XRD measurements were analyzed after a longer curing period of 150/480 days. The obtained results on the three BSF mixtures indicated a reduction of drying shrinkage and implicitly increased the tensile resistance by bending to 150 days well above the level of the blank composition. The degree of crystallinity and the content of the majority phases of the mineralogical compounds, albites, quartz, and tobermorite out of the three BSF samples justifies the increase in the compressive strengths at the age of 480 days in comparison with the test samples. Scanning electron microscope (SEM) and X-ray diffraction measurements showed the highest compactness and lowest portlandite crystal content for the S54/20 slag composite. Future research concerns are the realization of experimental sections in situ, the study of the influence of BFS on the elasticity module of road concrete, and the opportunity to use other green materials that can contribute to the reduction of the carbon footprint, keeping the physical and mechanical properties of road concrete at a high level.

The network arch bridge (NAB) is a new structural form of arch bridge that was devised 60 years ago by the Norwegian engineer Per Tveit, who is now prof. dr. docent emeritus at the University of Agder, Norway. The network arch is a tied-arch (also known as a bowstring-arch) bridge that combines the benefits of tied-arch bridges and trusses in a single system. While in a classical tied arch, the hangers are vertical, in a network arch, the suspension of the deck to the arch is ensured through a network of inclined hangers that intersect each other at least twice. Thus, the core of the NAB is the hanger arrangement that minimizes the bending moment in the arch to very small values, leading to compression in the arch. Compression with only small bending leads to very slender cross-sections for the elements of the bridge, and deep reductions in terms of materials used and economic and environmental costs. This paper reviews the research into the structural form proposed by Per Tveit and extended by researchers and engineers worldwide. The research methodology included bibliometric literature research, obtained by interrogating the ISI Web of Science (WoS) database and the cited references from the articles on WoS. While the first structural form of a network arch is still in use today and it has proven to be a good idea for spans around 100–120 m, engineers worldwide devised new bridge cross-sections. A brief view of the types of bridge cross-section in use today is given, with details about the bridges chosen as representative. Using analysis of Prof. Tveit’s map, Structurae database and literature review, a database of the network arches around the world was created, emphasizing the development of network arches from the perspectives of continental distribution, opening year, number of structures in different structural forms, and bridge purposes. The structural form was assessed from the perspective of materials used for the arch and the tie, span, purpose and number of lanes, the presence/absence of upper wind-bracings and arch disposition in the vertical plane. In the last part of this review, the newest research into the development of the network arch is discussed. In the past 15 years we have seen an acceleration in network arch development from multiple perspectives: new materials used, such as glulam for the arch or carbon fiber-reinforced plastic for the hangers; span lengths of 250 m and 380 m for large bridge widths; architectural constraints that lead to the outward inclination of the arch, that is pleasing to the eye, but difficult to address from an engineering perspective; the most slender arch bridge in the world, with very slender cross-sections for the arch and the tie.

This paper’s aim is to assess the rail wear evolution of railway tracks under mixed traffic conditions for sharp curves. Field investigations were conducted over a period of five years, at 800 points on a rail track, for two curves that underwent maintenance interventions: sleeper and rail replacements during measurements. Lateral and vertical wear measurements were monitored with mechanical instruments, and Prokon and Sap simulations were performed in order to determine the bearing capacity of the rail at different stages of wear. The results obtained after five years of investigation show wear speed propagation on the outer rail of small-radius curves as well as the bending moments and admissible stress variation. At more than 18% of the studied points, lateral wear exceeded the maximum admissible limit, showing a faster propagation speed on the outer rail compared to the vertical wear rate.