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The Defence Infrastructure Organisation requested a pavement evaluation on RAF Waddington and the results indicated that runway rehabilitation and reprofiling was needed in order to meet the physical design requirements set out in the Manual of Aerodrome Design & Safeguarding. The presence of tar in a layer of the old pavement promoted the option of cold recycling this material into the new structure. This paper presents the results from a laboratory investigation into the suitability of cold recycled foamed bitumen asphalt to be used in the structural layers of an airfield pavement.
Laboratory mixture designs with foamed bitumen, incorporating asphalt planings from RAF Waddington runway, were produced in URS Infrastructure and Environment Ltd. laboratory. Specimens were used to assess mix performance and in order to add confidence to the design. The last objective of the research was to demonstrate that asphalt planings from RAF Waddington could be recycled into foamed asphalt for incorporation in the runway rehabilitation works. The optimum binder content was determined from Indirect Tensile Stiffness Modulus tests and Indirect Tensile Strength tests, concluding that the optimum binder content was 3.3% by mass. As a common practice in the UK, up to 1.5% by mass of cement was added to the mixture to improve early life performance. To assess the foamed bitumen samples’ performance with time, specimens were prepared and cured for 28, 180 and 360 days at different temperatures. Post curing, the specimens were tested for a range of performance criteria including fatigue, stiffness and durability.
The study found that asphalt sampled from the runway at RAF Waddington can be recycled into foamed asphalt, meeting the requirements of Defence Infrastructure Organisation Specification 050.
Warm Mix Asphalt (WMA) is a viable alternate to Hot Mix Asphalt (HMA) for airport surfacing in Australia. Limited experience with this technology at Australian airports has prevented its acceptance by airport owners and their designers. WMA does have a significant track record in Europe and the USA, where it has been demonstrated to provide significant environmental, safety, quality and construction flexibility benefits. Differences in available binders and the Australian tendency for thinner asphalt layers and less capable materials makes direct extrapolation of experience from Europe and the USA inappropriate.
The aim of this paper is to demonstrate the comparative performance of WMA (by foamed bitumen technology) to HMA as an airport surface layer. Comparison between HMA and WMA has been made during a number of projects at Australian airports since 2012. A formal trial was performed at a military airfield as part of a broader project in 2013. A combination of production verification, quality assurance and mix performance tests were used to make comparisons. Subject to ongoing monitoring and performance testing of the military airfield WMA trial section, WMA is now verified as a viable alternate surfacing material for Australian airport runways.
A major construction programme is underway in Qatar. A shortage of local aggregate is focusing attention on the use of recycled and secondary aggregates. Site trials using locally available materials in structural concrete and concrete blocks were carried out in three small buildings. By far the largest source of recycled and secondary aggregates in Qatar is construction, demolition and excavation waste, which is generally crudely separated into excavation waste (EW) and construction/demolition waste (CDW). The other material investigated was incinerator bottom ash (IBA). The EW was used to replace 50% of the coarse aggregate in structural C40 concrete, with the CDW replacing 50% and IBA 20% of the coarse aggregate in non-load bearing concrete blocks. The control was 100% imported gabbro coarse aggregate. The trials also incorporated replacement of 60% of the local washed sand with imported crushed rock fines; this was investigated because the reserves of suitable concrete sand in Qatar are limited. Results after one year show the materials giving equivalent or better performance than the primary aggregate controls. The Qatar Construction Specification will be updated to permit greater use of recycled and secondary aggregates (RSA) and further trials are planned in a range of applications, including unbound subbase and pavement concrete. Wider use of these materials will reduce reliance on imported aggregates. The site trials won an award for the most innovative project from the Qatar Contractors Forum 2013.