Hot bituminous mixtures are becoming widely used in modern railway tracks in the sub-ballast layer. The reason is that these materials allow for both an increase in bearing capacity and greater ...protection of the substructure respect the traditional granular sub-ballast. Despite these advantages, the fact that these materials are manufactured at a temperature of 160°C means that their application can lead to an important increase in construction costs, pollution and energy consumption. This paper aims to study the possibility of using WMA manufactured at lower temperatures, as bituminous sub-ballast, in order to save energy and reduce emissions throughout the production process, as well as diminish the global costs of this layer. To this end, this study focuses on a comparison of the mechanical behaviour of warm and hot bituminous mixtures as sub-ballast under various loading conditions. The results indicate that WMA offers mechanical behaviour that is comparable to conventional HMA.
AbstractAsphalt pavement properties (strength, durability, bearing capacity, etc.) are considerably affected by environmental conditions. Because of this fact, regions with severe climates (high ...thermal gradients, abundant precipitation, presence of freeze-thaw cycles, solar radiation, etc.) have serious problems in maintaining the functional integrity of these infrastructures. Thus, it is necessary to develop new materials that could extend the service life of these pavements without increasing the construction costs. Accordingly, the present paper studies the improvement of the mechanical performance of high-modulus asphalt mixtures through the addition of acrylic fibers, for their use under severe environmental conditions. For this purpose, different tests were carried out thermal stress restrained specimen test, immersed wheel-tracking test, freeze-thaw sensitivity test, and UGR-FACT (University of Granada-Fatigue Asphalt Cracking Test) under variable conditions (simulating cold and hot scenarios). The results show that the use of acrylic fibers improves the mechanical behavior of high-modulus asphalt mixtures (at high and low temperatures, as well as under the presence of water and ice), and could thus be considered an interesting alternative for extending the service life of asphalt pavements in severe climates.
Crumb rubber modified binders are environmental-friendly alternatives to polymer modified bitumens in asphalt mixtures. This paper compares the performance of both types of binders with different ...modifier contents. Six binders were characterised by conventional tests and analysed using the UCL method. This method evaluates different properties of binders regarding their role in asphalt mixtures (cohesion, water and thermal sensitivity and resistance to ageing). Results showed that i) crumb rubber concentration has to be higher than that of SBS-polymers in order to obtain a similar performance to that of SBS-polymer modified bitumen; ii) crumb rubber modified binders are more stable than SBS-polymer modified binders in terms of modifier concentration; iii) crumb rubber modified binders exhibited less water sensitivity and similar thermal and ageing susceptibility to SBS-polymer modified binders; iv) linear relationships have been found between modifier concentration and the properties studied for both kind of binders.
The modulus value of bituminous materials is a key factor in the design of road pavements and the estimation of their life service. This parameter can be measured in laboratory but, unfortunately, ...this requires the deterioration of the pavement so as the consumption of time and resources. Therefore, this study analyses the feasibility of using impact resonance frequency tests as an alternative to traditional methods for determining the dynamic modulus of bituminous mixtures. The sensitivity of this technique has been studied by analyzing its repeatability and reproducibility, studying the variations in the values measured by modifying the dimensions of the specimens, test temperatures and types of mixture tested. In addition, this non-destructive technique has been compared with other traditional tests used to determine the elastic properties of bituminous materials. The results show that this test could be an interesting tool to characterize the properties and damage state of asphalt layers.
•An alternative solution to improve ballast performance in railway.•Viability of using crumb rubber as elastic aggregates mixed with ballast particles.•Laboratory study of the ballast performance ...with diverse percentages of rubber.•An optimal quantity of rubber is defined to be used in ballasted tracks.
Ballasted track is the most common form of construction used in railway transportation due to a number of benefits in comparison with other solutions such as slab track. However, the degradation of the ballast particles and the layer settlement lead to important maintenance costs. Thus, diverse research has been carried out to develop new materials with the aim of increasing the service life of the track. To this end, the present paper focuses on the use of crumb rubber (from end-of-life tires) as elastic aggregates mixed with ballast particles, which could reduce ballast degradation and consumption of natural aggregates. At the same time, an abundant waste source is reused and the use of raw binders (proposed technique employed to bond elastic particles to ballast particles) is not necessary, which potentially reduces costs and consumption of raw materials. For this reason, the influence of different percentages of crumb rubber was studied in the laboratory using a ballast box. In addition, once the optimal quantity of rubber had been determined, its effect on ballast behaviour under high stress level was analysed. Results show that the use of 10% of crumb rubber (by volume) could reduce ballast degradation and at the same time as the capacity of the ballast layer to dissipate energy is increased and its stiffness is reduced. Additionally, based on the present laboratory study, the track settlement could be reduced with 10% rubber particles used as elastic aggregates.
To cite this article: Gámez C, Sánchez‐García S, Ibáñez MD, López R, Aguado E, López E, Sastre B, Sastre J, del Pozo V. Tropomyosin IgE‐positive results are a good predictor of shrimp allergy. ...Allergy 2011; 66: 1375–1383.
Background: Shrimp is a common cause of food allergy. Our aims were to determine the value of IgE antibodies in the diagnosis of shrimp allergy and to study red shrimp (Solenocera melantho) tropomyosin both as a new allergen and as a cross‐reactive IgE‐binding protein.
Methods: We have studied 45 subjects. Skin prick test (SPT) was carried out in all subjects, and specific IgE (sIgE) to shrimp, recombinant and natural shrimp tropomyosins rPen a 1 and nPen m 1, recombinant Der p 10, and Dermatophagoides pteronyssinus was assessed by fluoroimmunoassay and/or immunoblotting. Double‐blind, placebo‐controlled food challenges were carried out to confirm diagnosis of shrimp allergy. Also, in vitro inhibition tests were performed to evaluate cross‐reactivity.
Results: Shrimp allergy was confirmed in 18 shrimp‐allergic patients. Skin prick test and IgE antibodies to shrimp were positive in all shrimp‐allergic patients; sIgE to rPen a 1 was detected in 98% of these patients. Of the 18 shrimp‐tolerant patients, 61% had positive SPT to shrimp, 55% were IgE‐positive to shrimp, and 33% showed IgE antibodies to rPen a 1. Determination of IgE to rPen a 1 yielded a positive predictive value of 0.72 and a negative predictive value of 0.91.
Conclusion: IgE levels to rPen a 1 provided additional value to the diagnosis of shrimp allergy. Some allergens in mite extract are recognized by patients who are allergic to shrimp, though their clinical relevance remains unknown.
•Testing temperature is a key factor in analyzing the resistance to fatigue cracking of WMA.•WMA could slow down the initiation of micro-damage at low temperatures in comparison with HMA.•Similar ...resistance to fatigue cracking of WMA manufactured by different techniques to reduce the production temperature.
In recent decades, warm mix asphalts have been proven to provide a series of benefits in the field of asphalt mixture production. However, to exploit these advantages it is essential that these materials present a mechanical performance and durability that is at least equivalent to traditional hot mix asphalts. The short-term mechanical behavior of warm mix asphalt has been widely studied and compared to that offered by hot mix asphalts, however few analysis have been made in the long-term. Among the various failure modes, fatigue cracking is regarded as one of the main concerns that can arise during the long-term service life of asphalt pavements. Based on these considerations, the present paper conducts a comparative analysis of the fatigue cracking life of hot and warm mix asphalts produced through the three main technologies currently used to reduce the manufacturing temperature (chemical additives, organic additives, and the foaming process). The results reveal that warm mix asphalts present similar resistance to micro and macro-cracking development to that measured for hot mix asphalts under the different testing conditions, whilst there are no significant differences between the various types of technologies evaluated.
Very Thin Asphalt Overlay (VTAO) has been introduced as an alternative to traditional thick overlays, seal coats, and micro-surfacings. Nonetheless, there are some challenges that still remain ...regarding the application of VTAOs (such as mixture type, cohesiveness, wear resistance, cracking and durability), particularly in heavy traffic urban areas. Therefore, this paper presents an extensive comparative evaluation of the mechanical performance, durability and safety issues (cohesiveness, adhesiveness, ageing, cracking, plastic deformation, permeability, macrotexture, skid and wear resistance, and fuel resistance) of a VTAO (20 mm thick) and a high performance BBTM 11B (35 mm thick), commonly used as an open-graded mixture for pavement overlays. The results demonstrated that VTAO is an appropriate material for urban pavements as it provides good durability and resistance to the propagation of defects. Nonetheless, further studies are required to improve its behavior under distresses related to plastic deformations and safety properties.
•HMAM with optimal fatigue resistance behavior avoiding cracking propagation were obtained.•HMAM with fibers and crumb rubber increase the resistance to plastic deformation.•The use of crumb rubber ...increases the stiffness, bearing and stress distribution capacity.•HMAM with crumb rubber or fiber is more economical than HMAM with polymer modified binders.
The high stiffness provided by high modulus asphalt mixes significantly decreases the loads transmitted by the traffic to the road foundation whilst at the same time increases their resistance against plastic deformations. Thus, the use of these types of mixtures can be an effective solution in road construction, due to the fact that they can reduce the thickness of the pavement, saving economic and material resources. Nevertheless, in some cases this high stiffness constitutes a drawback because it could reduce the fatigue resistance offered by these materials, leading to a premature appearance of cracks in the pavement, which decreases its service life. Due to this fact, the use of high modulus asphalt mixes is limited, especially in cold climates. In order to solve this problem, this research has been focused on the improvement of the mechanical performance of high modulus asphalt mixtures through the use of additives (crumb rubber and acrylic fibers), which could increase their fatigue resistance by maintaining the stiffness required. Different tests have been carried out under different temperatures for the mixtures assessment. The results obtained have shown that the incorporation of these additives could lead to a better mechanical behavior of high modulus asphalt mixes, and thus it could improve their performance.
The adaptation of pavements to autonomous vehicles has become one of the main challenges in the field of road engineering. These infrastructures must provide a safer and comfortable circulation ...whilst helping to guide the vehicles and provide information about the status of the road. In spite of the significant advances that have been made in autonomous vehicles in recent years, the development of new pavements adapted to their use has been left behind. This paper presents some of the results obtained in a project aimed at developing an innovative asphalt material, which has been codified using magnetic particles in order facilitate the driving of autonomous vehicles. The results have demonstrated that these encoded materials are sufficiently sensitive to provide information to autonomous vehicles, and can be developed by using less invasive construction procedures.
•Asphalt codified with magnetic particles permits for the driving of autonomous vehicles.•Encoded materials are sufficiently sensitive to provide information to autonomous vehicles.•Encoded materials can be developed by using less invasive construction procedures.•Asphalt materials can be codified by using metallic particles.•Dosages of metallic particles lower than 5% showed the best results in terms of performance and costs.
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