How to Make Capsules Containing Rejuvenators for Their Use in Asphalt Concrete

Rejuvenators are products designed to restore original properties to oxidized asphalt binders by restoring the original ratio of asphaltenes to maltenes. But,for a rejuvenator to be successful,it must penetrate the pavement surface. Besides,application of a rejuvenator will also reduce the skid resistance of the pavement. To solve this,these rejuvenators can be encapsulated and mixed in asphalt concrete. Once the stress in the capsules reaches a certain threshold,the particles break and the rejuvenator is released,giving back the original properties of the pavement. The objective of this paper is to show how these capsules behave and define the most appropriate testing methods to find their effect on asphalt concrete. For this,two different types of rejuvenators will be encapsulated and their effect on the properties of the capsules investigated. Besides,the release mechanisms of the capsules will be unravelled.

Environmental Concern of Using Coal Tar in Road Engineering and Its Possible Alternatives

Coal tar,a by-product from the destructive distillation of coal in coking oven,is widely used in road engineering for its excellent adhesion and fuel resistance properties,especially for pavement surface treatments in gas stations and airports. However,coal tar has a high Polycyclic Aromatic Hydrocarbons (or PAHs) content,which makes it toxic. In 1985,the International Agency for Research on Cancer (IARC) has proved that coal tar is carcinogenic to humans. Research showed that Coal Tar-based Sealers (CTS) contribute to the majority of PAHs pollution in the water environment.Because of this environmental concern,CTS are not allowed in many developed countries in the USA and Europe. In contrast,coal tar is still used for road engineering in China and is even used increasingly.This paper gives a literature review on the general information and research about environmental concern of using coal tar in road engineering. Based on the review,some possible alternatives to replace coal tar are described. These alternatives include nano-clay/epoxy modified bitumen/bitumen emulsion and waterborne polyurethane/epoxy resin,which are environmental friendly. They have the potential to perform as well as CTS,and even better in some special applications.

Durable Asphalt Pavements Are Self Healing

The traffic volume and the number of heavy vehicles are growing continuously. Considering the continuous traffic flow and the limited time available for road maintenance,it is very important to design a durable pavement system. Asphalt pavements with a healing capability are believed to be very useful since they can extend the pavement service life thanks to rest periods and hot summers. In order to design durable asphalt pavements,research in understanding and upgrading the self-healing capability of bituminous materials in time is of major importance. The self healing capability of bituminous mastic was evaluated in this research with a direct tension healing test. In the test program,different healing times,crack status and modifications were applied. The results indicate that elastic recovery and flow capacity are important factors for the self healing capability of bituminous materials at different crack phases as simulated with the direct tension test.

Waste Materials to Replace Natural Resources

A number of waste materials were studied on their application into asphalt mixtures. Materials tested were plastic waste as (soft) granular material,ceramic waste from electrical insulators,foundry sand and sintered granulate from burned household waste. Both plastic waste,crushed ceramics and large fractions of sintered household waste could be used as partial replacement for coarse aggregates. Foundry sand could partially replace natural sand in asphalt mixtures. The first step of the study was to find out if the waste materials could satisfy basic requirements and for some if their leaching behavior was acceptable. In the next phase mixtures were designed and mechanical tests were done on several mixtures with waste components to determine indirect tensile strength,stiffness,fatigue. In order to estimate the water sensitivity of some mixtures,retained indirect tension tests were done. The properties are reported and compared with each other and reference mixtures. From the research it becomes clear that it takes a lot of work to replace virgin materials in asphalt mixtures with waste materials.