Bituminous binders as organic materials are prone to aging mainly by oxidation. Aging changes the viscoelastic behavior of the material over time towards higher stiffness and brittleness. FTIR has been increasingly used lately to investigate impacts of oxidative aging on the chemical structure of bitumen. Especially the carbonyl and sulfoxide bands are affected by aging and commonly used to describe changes due to evolving oxidation of a binder. However, spectra obtained from FTIR can be analyzed in fundamentally different ways and the analysis method applied to a spectrum has an impact on the gathered results and especially on the repeatability and sensitivity with regards to oxidative changes. For the presented study, two bituminous binders, a PG 64-16 and an SBS modified PG 76-22 PM were aged by RTFO and PAV and subsequently measured by FTIR. The obtained spectra (up to 90 individual spectra per aging state) were analyzed employing various methods using either the original or a normalized spectrum, a band maximum or integration based calculation of indices from an absolute or tangential baseline. By analyzing the coefficient of variation of the different analysis methods, it was found that not all analysis methods exhibit the same repeatability and sensitivity. From the findings of the study it can be recommended to work with normalized spectra, use an absolute baseline and work with integration of areas for index production in favor over band maximum based methods.
This study investigated the curing mechanism of foamed asphalt mixes, based on which proposed standard curing procedures that are appropriate for use in project level mix design. Mixes with various asphalt and portland cement contents were subjected to two relatively extreme curing conditions, and multiple types of laboratory tests were performed. It was found that portland cement enhances certain properties of foamed asphalt mixes by strengthening the mineral filler phase, with the curing mechanism similar to that of normal cement treated materials. The curing mechanism of foamed asphalt mastic is primarily related to water evaporation. The bonding between asphalt mastic and aggregate particles cannot fully develop until most of the water retained at the interface evaporates. This bonding, once formed, is only partially damaged by reintroduced water. This mechanism was supported by direct fracture face observations on tested specimens. Two curing methods are proposed as standard procedures for project level mix design. The proposed strategy tests materials under two extreme conditions instead of attempting to precisely replicate field conditions, allowing the engineer to judge whether the tested materials suit the actual range of conditions at a specific project site. Portland cement or other appropriate active filler is recommended to be used in conjunction with foamed asphalt, which has a slow curing rate under most field conditions, to obtain early strength and allow early opening to traffic.
Aspects of dust and dust control have been studied for many years in most countries with unsealed road networks. However, no comprehensive coordinated study to investigate the processes affecting the generation of road dust, road dust measurement, road dust prediction, acceptability criteria for dust, or the performance of dust palliatives has been undertaken. Over the past 6 years, the Council for Scientific and Industrial Research has been engaged in such a study. Although research has been undertaken on behalf of numerous parties, experimental designs have been coordinated in an attempt to develop guidelines for the responsible use of dust palliatives. Unfortunately, many of the experiments that have been undertaken by product manufacturers and road authorities over the years have been uncoordinated and poorly monitored, with minimal information being recorded or published. Many of these experiments have failed, with the product always being blamed, and this, together with poor marketing techniques used by suppliers, has led to skepticism by the roads industry toward the use of the products. Scientific research, following detailed experimental designs, funded by the product suppliers has resulted in the development of guidelines for the use of certain products. Studies have shown that, provided the products are used under appropriate circumstances, they can provide a cost-effective interim measure to improve the quality of life and preserve construction materials until such time as the road can be upgraded to a sealed surface. The holistic approach to dust and dust control research that has been followed is discussed here, a summary of the findings is described, and recommendations toward implementing a dust-control program are made.
The improvement of the street thermal environment for walking and cycling is attracting increased attention as a strategy for increasing livability. This approach has also been proposed as a strategy for mitigating the local heat island effect and reducing energy use for buildings and vehicle air conditioning during hot periods. This research explored a potential pavement design and management strategy for improving the street thermal environment and mitigating the heat island effect. Through field measurements on pavement test sections with both conventional and alternative designs, the thermal behavior and cooling effect of permeable asphalt pavements under dry and wet conditions were investigated. The overall 7-day average cooling effect of wetting once on permeable pavements for near-surface air was approximately 0.2°C to 0.45°C; for the surface, the temperature was approximately 1.2°C to 1.6°C, and it was approximately 1.5°C to 3.4°C for the in-depth layers. On the basis of these findings, permeable asphalt pavements might be a type of cool pavement that produces lower temperatures and thus helps improve the thermal environment and mitigate the heat island effect. However, attention should be given to this type of pavement under dry conditions. As a pavement thermal management strategy, water from rain or irrigation systems might need to be applied to the pavements to produce a better cooling effect for improving the thermal environment and mitigating the heat island effect.
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