Juan Gallego

Risk Sharing in the New Public Works Concession Law in Spain

Budgetary constraints are forcing transport infrastructure authorities to raise private funds to finance the construction of new projects and the maintenance of existing ones by using concession contracts. One of the key elements in correctly defining a concession scheme is to establish an adequate risk-sharing mechanism among the stakeholders that take part in the process. This paper describes and analyzes the effect of the new Spanish Concession Law on risk sharing, in particular, the effect of the so-called progress clause on the calculation of risk held by the concessionaire. This law was designed both to reinforce private financing of public facilities and to improve the legal framework by defining a new risk-sharing approach, particularly in relation to the risks involved in estimating traffic demand. The paper finishes with an analysis of a specific application of the traffic risk-sharing approach for highway concessions in Spain.

Thermal Sensitivity and Fatigue Life of Gap-Graded Asphalt Mixes Incorporating Crumb Rubber from Tire Waste:

The most usual asphalt mix applied for thin overlays on Spanish roads is produced with a gap-graded combination of aggregates and a polymer-modified binder. Nevertheless, reflective cracking usually affects the overlay so that the surface of the pavement soon begins to reveal a network of cracks. The brittleness and aging of asphalt mixes at low temperatures encourage the appearance and progress of these cracks. Asphalt mixes incorporating rubber from discarded tires are believed to control reflective cracking well. This paper presents a study performed on five gap-graded asphalt mixes, three containing rubber from tire waste. Every mix was tested at two stages of aging in accordance with the laboratory-accelerated aging processes proposed by SHRP. Dynamic moduli at several temperatures, ranging from −15°C to 40°C, and the fatigue life of each mix at 20°C were measured. The results are provided to help researchers build realistic models for studying reflective cracking as a function of the actual characteristics of the materials. The results show that the tire rubber, especially when incorporated by the wet process, enhances the fatigue life of the mixes. The thermal sensitivity of the mix decreases as the content of rubber arises, regardless of whether the rubber has been incorporated by the wet or the dry process. In addition, the paper reports the difficulties with the SHRP accelerated aging processes and raises some doubts about these aging processes when applied to rubberized asphalt mixes.

New Laboratory Equipment for Study of Reflective Cracking in Asphalt Overlays

One of the current road maintenance problems continues to be the appearance of reflective cracks in asphalt overlays. It would be of real benefit if laboratory equipment were available during the design stage to allow the best solution to be selected for site laying. A new piece of laboratory equipment is reported on for the process known as the wheel reflective cracking (WRC) test based on the traditional wheel-tracking device. The WRC apparatus allows the chief failure mechanisms leading to the phenomenon of reflective cracks to be simulated in the laboratory. Initial results obtained with it on several overlay sections are consistent with the current Spanish experience in full-scale test sections. The WRC test can also be of help to researchers in this field since it enables test parameters to be varied for the purpose of carrying out sensitivity studies. In addition, it allows the loss of structural capacity and the shape of the cracks to be monitored beyond the mere comparison between different overlay sections.

Master curves of crumb rubber modified binders containing Montan waxes as warm mix asphalt additives

Energy consumption and the corresponding greenhouse gas (GHG) emissions can be reduced with technology recently developed in the field of road pavement materials: warm mix asphalt (WMA). This technology is being incorporated to improve workability and, consequently, production and compaction temperatures of asphalt mixtures can be lowered without significantly affecting their mechanical properties. However, since this technology is relatively new, the influence of WMA additives on the properties of crumb rubber modified (CRM) binders has not yet been investigated in depth and clearly identified. The main objective of this study is to investigate the effect of different types and quantities of WMA additives on the high and intermediate temperature properties of a 20%CRM binder. For this purpose, binder ́s properties are determined using a dynamic shear rheometer (DSR) which allows elastic, viscoelastic and viscous properties of bitumen to be defined over a wide range of temperatures and frequencies. The results of this study indicate that there are significant improvements produced by the additives concerning the mechanical behaviour and the elasticity for the whole temperature range; the complex modulus (stiffness) is increased at the high temperatures avoiding permanent deformation and the phase angle curve is shifted on lower values over a wide range of frequencies. However, the increased content of additives slightly shifted the complex modulus master curves in high frequency regions, increasing the stiffness at low temperatures.

Proyecto LCweb. Respaldo documental para prácticas de laboratorio - [LCweb Project. Documental support for laboratory practices]

Laboratory practices in the university education are being replaced for virtual laboratories or web-based applications which allow the students to work offsite. Nevertheless, it appears that the best model for this purpose is a combination of traditional hands-up laboratory work and virtual or web-based applications. This technical communication presents the LCweb Project. It is a web-based application which does not replace the hands-up work in the laboratory but complements it for the students of Pavements in the Universidad Politécnica de Madrid. The web site offers several road materials standard trials, practical examples, self-evaluation tests and the in force specifications for materials, useful to solve the practical examples. Although it has been implemented during 2016/2017 it appears that the students make use of this resource as a complement of the hands-up laboratory work rather than a substitute. This kind of projects demands a strong initial effort by the professor but when it is ongoing a small effort is required even though it gives an important support to the student.

Fatigue Behavior of Reinforced Concrete Haunched Beams without Stirrups

In this paper, results of fatigue tests on reinforced concrete haunched beams without stirrups are presented for the first time. Two types of failure modes have been obtained, either due to fatigue of the reinforcement or due to shear fatigue. In addition, progressive increase of deflections with load cycles was measured. An analysis of tests is carried out in terms of the consequences of fatigue loading on ultimate strength and serviceability of reinforced concrete. Regarding fatigue strength, the limitations of existing models are shown and discussed. Regarding serviceability, it is shown that deflections are even higher than those theoretically obtained by the fully cracked member. This is due to development of shear deformations, cyclic creep, and negative tension stiffening during unloading stages.