Most of the worlds paved roads are surfaced with. Reclaimed Asphalt in Airport Pavement. Asphalt Recycling

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1 Reclaimed Asphalt in Airport Pavement Sonjoy Deb, B.Tech, Civil Associtate Editor Most of the worlds paved roads are surfaced with asphalt, which gives good performance and durability under the most heavily trafficked conditions. Asphalt mixes are also widely used in the construction of hard standing and parking areas for both light and heavy vehicles. They are therefore eminently suitable for use in the construction and surfacing of access roads, perimeter roads and vehicle parking areas on airfields. Asphalt is also widely used in airport construction, although this usage is not always recognised. In airports, there are different areas such as runways, taxiways, aprons and parking areas. For each, the required specifications could be different particularly for surface courses. For parking and aprons, good resistance is needed to puncturing, to fuel and to chemical agents. For other surfaces, a good skid resistance is necessary. Asphalt mixes provide the answer to these various requirements. In addition to these uses, asphalt mixes are widely employed in the surfacing of runways and aircraft handling areas on a wide range of airfields, from international airports regularly used by the heaviest airliners, through military airfields carrying high performance jet aircraft and the smaller domestic airfields regularly used by light or medium-sized aircraft to the smallest private airfield used by light single or twin-seat aircraft. The volume of aircraft in an airport is multiplying year by year. This has led to various distresses in the pavement. The ageing of bitumen binder is yet another problem causing deterioration of pavements. The method commonly preferred to protect the pavement system is overlaying the distressed pavements with virgin courses. But this leads to thickening of pavement layers, depletion of natural ingredients, and use of non- renewable resources and emissions of harmful gases. Reclaimed asphalt pavement (RAP) technology is one 204 The Masterbuilder - November

2 Asphalt Recycling of the rehabilitation methods used in many of the developed countries. In developing countries like India, this method is in its initial stages. Depletion of natural resources and increase in road elevation due to continuous overlaying, necessitate the adoption of reclaimed asphalt pavement technology. This technique is a promising and cost effective technology for rehabilitating distressed and aged pavements. Reclaimed Asphalt Aggregate Recycling in place of overlaying of asphalt pavements contributes to various ecological and economic advantages. The use of RAP in asphalt mixes is a mean to recycle the existing roadway and use that material in a limited amount in the construction of new pavements. This report discusses about various methods of recycling. The advantages of Reclaimed asphalt pavement technology over conventional method are discussed. An integrated mix design approach for hot recycled mix from RAP samples was also studied. Refer Figure 1 for RAP pavement, Figure 2 for Recycled Asphalt aggregate. Figure 1: Recycling of Asphalt pavement and making new Reclaimed Asphalt Pavement Concept behind RAP Recycling, in place of conventional method of overlaying of asphalt pavements has made a rapid advancement in the developed countries. The availability of proven and efficient recycling technology favoured the adoption of Reclaimed Asphalt Pavement (RAP) Technology in many countries. This Figure 2 : Recycled Asphalt aggregate method of strengthening and repairing roads was based on their durability rather than their initial cost. The concept of RAP lies in restoring the physico-chemical properties of the aged bitumen to its original and the same time to enhance the mechanical properties and strength of the aged binder. The various ecological and economic advantages which contributed to enhancement of recycling processes throughout the world are conservation of aggregates and binders, reduced cost of transportation, preservation of existing pavement geometrics, preservation of environment, conservation of energy and labour, decrease in pavement thickness/height. With the development of RAP technology, asphalt pavement rehabilitation costs would significantly decrease. The effective use of RAP solves a larger societal problem because it does not occupy landfill space. In addition to the economic benefits of using RAP, rehabilitation options that create RAP may have substantial engineering benefits. For example, the ability to mill and remove old, distressed pavements allows for more effective rehabilitation techniques. Severely cracked or rutted layers can be removed so that their damage is not reflected through a new surface layer. The Masterbuilder - November

3 Figure 3 : Airport pavement resurfacing and use of RAP The Need of RAP in Airport Pavement Airports maintenance and rehabilitation have taken over from new construction as the major focus of airport work. More frequent repair of airport pavements has become necessary in recent years due to substantial increases in both traffic volume and aircraft weight. At the same time, with today s higher construction costs (especially the cost of raw materials like asphalt and aggregates) and rising awareness of environmental protection and the need to save resources, the use of reclaimed asphalt aggregate (RAA) with a particle size adjusted to suit the specifications has become more and more important. Refer Figure 3 for airport pavement resurfacing and use of RAP. General considerations for Airport Pavement Without hard paving, access may be difficult to the airfield, flying may be restricted in inclement weather or the facilities may not come up to the minimum standards required by the regulatory authorities for passenger carrying. The following areas on a typical airfield are likely to require hard paving: Runways & taxi-ways providing access to runways Runways and taxi-ways both need to be constructed with sufficient strength to carry the moving aircraft but from the surfacing point of view the difference between the two is that runways require a higher degree of resistance to skidding and aquaplaning in view of the higher speeds involved. One means of achieving the latter, employed on many runways in Europe, is to use a porous open-graded surface course known as porous asphalt or friction course as the running surfacing. This acts as a drainage layer to prevent surface water adversely affecting aircraft tyre grip on the surfacing in wet weather. Beneath friction course a strong impervious binder course of, for example, asphaltic concrete or an impervious existing surfacing is required, laid to adequate falls. When resurfacing work is being undertaken on runways, it is essential that the existing surfacing is of good regularity and laid to adequate falls or is made so by applying a regulating layer if a porous surface course is to be applied. This is to ensure that water is not retained in the new surfacing to lead to heavy ice formation in winter. Hanger Floors: Hanger floors can be subjected to extreme severity of use in the form of heavy point loadings and regular spillage of grease and oil. This can give rise to serious damage to normal asphalt surfacings and these are therefore not recommended for this type of flooring. Special proprietary materials, e.g., epoxy asphalt or sand/cement/polymer grouted asphalts, or alternative forms of construction such as concrete, will be more appropriate in such circumstances. Aircraft parking, re-fuelling and maintenance areas: Where re-fuelling or maintenance operations are to be undertaken, the same considerations apply as for hanger floors. However, where areas are simply intended for aircraft parking, highstrength design asphalt mixtures, particularly high-stone content asphalts have been used for the purpose and should prove Vehicle parking areas: The thicknesses and types of asphalt used in the various layers of the construction of vehicle parking areas need to be carefully designed with due consideration to the high loadings from large numbers of parked vehicles, higher axle loadings from buses etc. serving those parking areas, and the likelihood of high stresses from tightly turning and manoeuvring vehicles. Access roads: The type of construction to be adopted for 206 The Masterbuilder - November

4 access roads on airfields will depend on the severity of their use. For roads carrying heavy traffic, the designs specified by national highways agencies in their Pavement Design Standards will be appropriate. Where relatively light use is to be encountered, the design guidelines used by local highway authorities for housing estate roads etc. might well be appropriate. Methodology of RAP in Airport Pavement A. General Reclaimed Asphalt Pavement is formed by cold milling, heating/softening and removal of the existing aged asphalt pavement, full depth removal, or plant waste Hot Mix Asphalt (HMA) materials. The escalating increases in crude oil prices as well as cost of energy are expected to result in increased prices of asphalt binders and a resulting interest in the use of RAP in pavements. Methods of Recycling Pavements The common types of recycling operations include hot mix recycling, Hot In-place Recycling (HIR), Cold In-place Recycling (CIR), and Full Depth Reclamation (FDR). Among this, hot mix recycling is very commonly used for producing hot mix asphalt, which can be used as overlays in preventive maintenance operations where as thick layers in rehabilitation. Hot in- place and Cold in-place recycling are commonly used for preventive maintenance operations, where as full depth reclamation is generally used for rehabilitation work. Hot In -Place Recycling Hot in place recycling has been described as an onsite, in-place method that rehabilitates deteriorated asphalt pavements and thereby minimizes the use of new materials. Basically, this process consists of four steps: (1) Softening of the asphalt pavement surface with heat (2) Scarification and/or mechanical removal of the surface material (3) Mixing of the material with recycling agent, asphalt binder, or new mix and (4) Lay down and paving of the recycled mix on the pavement surface. Figure 4 : Hot In Place Asphalt recycler a specified grade and slope, free of bumps, ruts and other imperfection. The modern cold milling equipment has tungsten carbide teeth on drums, with variable cutting width for a variety of pavements and excellent maneuverability for different milling situations. (ii) Cold In-place Recycling (CIR) It is defined as a rehabilitation technique in which the existing pavement materials are reused in place. The materials are mixed in place without the application of heat. The reclaimed asphalt pavement material is obtained by milling or crushing the existing pavement. Virgin aggregate or recycling agent or both are added to the RAP material, which is then laid and compacted. The use of cold in place recycling can restore old pavement to their desired profile, eliminate existing wheel ruts, restore the crown and cross slopes and eliminate potholes and rough areas. Some of the major reasons for the increased use of this method are the increase scarcity of materials, particularly gravel and crushed rock, minimum traffic disruption, the ability to Refer Figure 4 below for such machine. Cold Recycling Cold recycling can be divided into two main parts-cold inplace recycling and cold milling. Cold milling is used for obtaining materials for hot mix recycling. (i) Cold Milling It is a method of automatically controlling the removal of pavement to a desired depth with specially designed equipment and restoration of the surface to Refer Figure 5 for Cold in Place Asphalt recycling 208 The Masterbuilder - November

5 airport research centre of Port and Airport research Institute of Japan in which a fiber material was introduced into recycled asphalt concrete (RAC) to improve it and allow a recycling rate greater than the currently specified 40%. The performance of this RAC was examined in a series of laboratory tests. The results give an encouraging indication that RAC containing 70% RAA can be considered acceptable when the fiber is used and modified asphalt binder is adopted, which has comparable performances with new asphalt concrete consisting of entirely new materials (NAC). Conclusion Figurue 6 : Full Depth Asphalt Reclamation retain the original profile, the reduction of environmental concerns and a growing concern for depleting petroleum reserves. Refer Figure 5 for Cold in Place Asphalt recycling Full Depth Reclamation (FDR) It has been defined as a recycling method where all of the asphalt pavement section and the pre-determined amount of underlying materials are treated to produce a stabilized base course. Different types of additives, such as asphalt emulsions and chemical agents such as calcium chloride, Portland cement fly ash, and lime are added to obtain an improved base. Refer Figurue 6. Hot Mix Recycling It is a method in which RAP is combined with new aggregates and an asphalt cement or recycling agent to produce HMA. The RAP may be obtained by paving milling with a rotary drum cold milling machine or from a ripping or crushing operation. RAP from different sources and containing different asphalt contents and aggregates with different gradations should be stockpiled separately. The RAP cannot be processed in normal drum mix plant since excessive blue smoke is produced when the RAP comes in contact with the burner flame. Most of the smoke problem is caused by the light oils in soft grades of asphalt binder used to rejuvenate the aged asphalt in the RAP. Technological Innovation for maximizing use of RAP in Airport pavement The amount of Reclaimed Asphalt Aggregate (RAA) is limited to 40% or less in most of the available design manuals. This hinders the extensive use of RAA. Based on the situation that rehabilitations gradually increasing in the coming years, the need for the use of RAA beyond the currently specified limit of 40% is a challenge for the engineers and researchers. With this aim of more fully utilizing RAA, a research carried out in the The cost of construction using recycled mix is economical compared to virgin mix. Percentage saving in the material cost is found to be varying in different mixes due to the variation in the thickness and constituent proportions of different airport pavements. The economic benefits of using RAP, rehabilitation options that create RAP have substantial engineering benefits. The ability to mill and remove old, distressed pavements allows for more effective rehabilitation techniques. Severely cracked or rutted layers can be removed so that their damage is not reflected through a new surface layer multiple studies that the structural performance of recycled mixes is equal and in some instances better than that of the conventional mixes. A sustainable development is a development that meets the needs of the present without compromising the ability of future generations to meet their own needs. Recycling of pavements by re-using the existing materials will protect natural resources for future generation. Thus RAP is a sustainable pavement construction for the environment. However care needs to be taken so that it does not effect the performance the important pavement areas like runway and taxiways and all the necessary checks to be done to doubly ensure the performance. Reference - Aravind, K. and Animesh Das, Pavement design with central plant hot-mix recycled asphalt mixes, ASCE Journal of Transportation Engineering, Vol. 21, 2007, pp Elie, Y. Hajj, Peter, E. Sebaaly and Pratheepan Kandiah, Evaluation of the use of reclaimed asphalt pavement in airfields HMA, ASCE Journal of Transportation Engineering, Vol. 35, 2009, pp Rajib B. Mallick and Tahar El-Korchi, Pavement engineeringprinciples and practice, CRC Press, London, 2009, pp Examination of Fiber - Added Recycled Asphalt Concretes for Surface Course in Airport Pavements, Kai SU and Yoshitaka HACHIYA, Airport research Center, Independent Administration Institutions, Port and Airport research Institute - Reclaimed Asphalt Pavement (RAP) Technology for a Sustainable Pavement, Dr. R. Sathikumar and Nivedya M. K, National Technological Congress, Kerala 2011, College of Engineering Trivandrum, January 28-29, The Masterbuilder - November