Asphalt pavement, recycled, using

Two of the more recent innovations for using sulfur modified binders are in conjunction with recycling old asphalt pavements and the construction of open graded friction courses (OGFC). 

Table 2. Properties of Recycled Asphalt Pavement Using Sulfur/ Asphalt Emulsion Binder.

Recycling rubber from tires for use in asphalt pavements is a promising technology. Asphalt pavements incorporating tire rubber are claimed to have twice the lifetime of ordinary asphalt, but they can cost twice as much. Pavements with crumb rubber additives consume over one million tires per year now, and both asphalt-rubber and rubber modified asphalt concrete have considerable potential for expansion. If Federal, state, and local governments promote much broader use and demonstration of this technology, perhaps the technical issues will be resolved and usage will expand. 

An additional approach which will result in the conservation of asphalt, which is under investigation by both the Bureau of Mines and Til, involves using sulfur in recycling old bituminous pavements (2,14). Sulfur can reduce the viscosity and hence improve the workability of age-hardened asphalt pavement material and can increase the stiffness of the recycled mix when it cools. 

This chapter discusses current research on the use of sulfur in recycled asphaltic concrete pavements. In addition, it describes the results of laboratory tests and theoretical predictions using the latest linear viscoelastic layered pavement analysis methods (15,16) to compare the performance of various sulfur-asphalt concrete pavements with conventional asphalt concrete pavements in a variety of climates. The relationship between pavement distress and performance used in the computer program was established at the AASHTO road test (17). Finally, the results of domestic field tests of sulfur-asphalt pavements are presented along with a discussion of future trends for the utilization of sulfur in the construction of highway pavement materials. 

The use of plant-recycled hot-mixed asphalt (HMA) for public road pavement in Japan first began in 1975. The Japan Road Association promoted the technology for plant-recycled HMA pavement in Japan with its 1984 publication of The Plant-Recycled HMA Pavement Technical Guideline, and since 1985, positive efforts have been made to reuse more reclaimed asphalt pavement (RAP). 

Grzybowski KF (1993) Recycled asphalt roofing materials - a multi-functional, low cost hot-mix asphalt pavement additive. In Use of waste materials in hot-mix asphalt (Special Technical Publication 1193). American Society for Testing and Materials, Philadelphia, PA, p 723... 

Recycled AC is allowed to be used in all pavement layers except runway surface course. The recycled AC, consisting of reclaimed asphalt pavement (RAP), coarse aggregate, fine aggregate, mineral filler and asphalt cement, should meet the requirements set for an AC (see Tables 5.16 and 5.17). However, the amount of RAP to be incorporated in the mix is limited to 30%. 

The decision to choose the most suitable asphalt plant is quite complicated. It is influenced by the market conditions related to demand and selling price of the asphalt, the typical hourly output capacity, the cost of purchasing the plant, the types of asphalt usually required to be produced, the capability of the plant to produce recycled asphalt, the amount of reclaimed asphalt (or reclaimed asphalt pavement [RAP]) to be used, the land space availability and the environmental restrictions (mainly emissions and noise). 

The material removed from the asphalt layers to be re-used, hence recycled, containing bitumen and aggregates, is called reclaimed asphalt (RA), under European Union terminology, or reclaimed asphalt pavement (RAP), under US terminology. 

The repave process offers perhaps the ultimate rehabilitation/hot recycling results compared to the other two hot recycling in situ processes. In particular, its advantages over the other two in situ processes are as follows (a) complete restoration of surface skid resistance since new asphalt material is used, (b) strengthening of the pavement to a certain extent and (c) minimisation of smoke emission. 

Pavement design using hot or cold recycled asphalts may be carried out by the same methodologies as the ones used for pavements with virgin hot or cold asphalt layers, provided the mechanical properties of the recycled materials are considered. 

Stroup-Gardiner M. 2011. Recycling and Reclamation of Asphalt Pavements Using In-Place Methods A Synthesis of Highway Practice. NCHRP Synthesis 421. Washington, DC Transport Research Board. 

Many existing roads fail because the asphalt becomes stiff and brittle. If the materials are too stiff, additives that lower the viscosity must be used. The feasibihty of usiag sulfur to soften or reduce the viscosity of the oxidized biader ia recycled pavements has been successfully demonstrated by the U.S. Bureau of Mines and others (55—57). 

The surface courses for the selected pavements were assumed to consist of either conventional asphaltic concrete with limestone aggregate, sulfur-asphalt concrete with beach sand aggregate, or recycled Boulder asphaltic concrete with sulfur. Material properties used as VESYS IIM input data for these four surface layers are listed in Table IV. 

This report contains the results of one study of long-term performance of recycled HMA pavement. The study in question is a 15 year follow-up survey of one of Japan s earlier (1978) full-scale applications of recycled pavement using recycled HMA to pave municipal roads in Nagoya City. In this pavement test, new HMA was applied at the same time so as to compare it with to the recycled pavement. Both the new and recycled pavements are in good condition even to date, and serve as a source of valuable information about pavement durability. We will also report on the results of our investigation of recycled and re-recycled HMA using asphalt concrete lumps collected at a study site. 

Pulverised pavement materials are also known as recycled asphalt plannings. They are produced by crushed and screening old asphalt materials during reconstruction projects. They can be used as an aggregate replacement in new asphalt materials. 

A major contribution to the above concerns is re-using or recycling the materials of old pavements, such as asphalt mixtures (asphalts), concrete or base/sub-base material. 

Cold milling (or planning) is the removal of the existing asphalt layer to a desired depth determined by the surface/pavement deficiency to be corrected, using special machinery called milling machines or planners. The generated reclaimed material is removed from the site and stockpiled for future use (production of recycled asphalt or other usage). 

Cold recycling in a central plant is the process in which asphalt removed from the surface of an existing pavement is transported to a central cold mix plant where it may be stockpiled for future use or processed immediately. 

Other studies on the use of polypropylene fibers from carpet waste in concrete [81], used tire cords in concrete [82, 83], and using recycled nylon fibers to reduce plastic shrinkage cracking in concrete [84] have also been reported and reviewed [85]. Gordon et al. [86] used the waste nylon fibers and ground carpet to stabilize asphalt concrete. Increase of asphalt content in asphalt concrete is favorable because it leads to more durable roads. But it is limited by the resultant flushing and bleeding of pavements and possible permanent deformation of the pavement. Addition of 0.3 wt% waste fibers increased the allowed asphalt content by 0.3-0.4 wt%. 

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