Search

The reduction in consumption of natural resources (fuel, gas, etc.) and contaminant emissions (CO2, CO, NOx, etc.) during the production of asphalt mixtures has become one of the main challenges in road engineering. Warm mix asphalts (WMAs) have been developed in order to achieve this objective while ensuring the mechanical performance and durability of traditional hot mix asphalts (HMAs). However, these materials are commonly manufactured using additives or products whose production could reduce both their environmental benefits and cost effectiveness. This paper presents a research study that aims to analyse the reuse of zeolite wastes derived from petroleum refining in the production of warm mix asphalts. For this purpose, two different types of zeolite wastes were analysed as additives for the manufacture of two warm mix asphalts, whose mechanical performance was compared with conventional WMA and hot mix asphalt. The results indicate that zeolite wastes with a lower particles size presented higher capacity to absorb water, while its dosage at 0.3% allows for producing warm mix asphalts at temperatures around 145°C, with comparable workability and densification to conventional HMA at 165°C without reducing its bearing capacity, fatigue life, and resistance to water action and plastic deformation.

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.

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.

Las capas bituminosas ultra delgadas para rehabilitación superficial de carreteras son una alternativa a las tradicionales capas asfálticas, riegos bituminosos y micro-aglomerados. No obstante, aún son numerosos los aspectos a estudiar para la generalización de su uso, particularmente en zonas urbanas con elevado tráfico. Así, este artículo recoge un análisis comparativo del comportamiento mecánico, durabilidad y factores de seguridad (evaluando parámetros como cohesividad, adhevisvidad, envejecimiento, fisuración, deformaciones, permeabilidad, macrotextura, y resistencia al deslizamiento, al desgaste y a los combustibles) entre una capa delgada de 20 mm de espesor, y una mezcla discontinua de altas prestaciones (BBTM-11B con 35 mm), comúnmente utilizada en capas de rodadura. Los resultados indican que puede ser una adecuada solución para pavimentos urbanos dada su durabilidad y resistencia a la propagación de fallos. No obstante, se requieren futuros estudios centrados en la mejora de parámetros de seguridad y de su resistencia a las deformaciones permanentes.

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 use of crumb rubber modified bitumen (CRMB) in asphalt mixes is a road engineering technology that has become increasingly important in recent years. Given the many economic and environmental benefits of this type of binder, the goal is to give CRMB the same level of performance as conventional polymer-modified bitumen. The appearance and propagation of cracks due to fatigue phenomena is one of the most common distresses affecting road pavements. Since crumb rubber enhances the mechanical properties of asphalt mixes, it can provide a viable solution for fatigue cracking. This paper presents the results of a comparative analysis of the fatigue-cracking behavior of asphalt mixtures manufactured with crumb rubber modified bitumen and polymer-modified bitumen.

Mechanomutable asphalt binders are a new generation of smart materials, which are able to change their mechanical response to the load conditions suffered during their service life. These binders are composed of a bituminous matrix and iron micro-particles that can be activated with an external magnetic field, which induces mechanical changes in the system. However, these particles are expensive and they considerably increase the cost of these materials, reducing their competiveness. Thus, the aim of this work is to study the viability to produce more sustainable and low-cost mechanomutable asphalt mortars using stainless steel slag (SSS). This by-product is obtained from the production of stainless steel and contains a significant quantity of iron that could be used to activate the response of these materials. Different sizes and concentrations of SSS were used to manufacture mechanomutable asphalt mortars, and their mechanical behavior was then examined using several rheological tests. The results show that it is possible to achieve changes in the rheological response of these smart asphalt materials, thereby obtaining mechanomutable mortars from the stainless steel by-products. The efficiency of the slag also appears to be more dependent on its iron content than on its concentration or particle size. [ABSTRACT FROM AUTHOR]