Runway Success
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he recent contract for Highland and Islands Airports Ltd (HIAL) to extend and upgrade the Trunway at Sumburgh Airport in the Shetland Islands, the UK’s most northerly gateway, was a notable project for a number of reasons. Not least was that Colas Ltd became the first contractors to successfully utilize European airport surfacing materials within the UK’s airfields industry, coupled with the logistical problems posed by Sumburgh’s remote location, some 150 miles from the Scottish mainland. Working as specialist Runway Success subcontractors to Balfour Beatty Sumburgh Airport in the Shetlands becomes the first UK airfield to benefit Civil Engineering Ltd, as part of an overall £9.75m redevelopment from Colas’s European airport surfacing materials project, Colas undertook the £1.8m resurfacing and grooving of By Carl Fergusson, business manager – Airfields Division, Colas Ltd, and Steve Cant, the existing runway and newly technical manger, Colas Ltd constructed runway extensions. To ensure an efficient, cost-effective programme of physical and mechanical mechanical performance targets works, Colas worked closely with properties of the mix of the Sumburgh laboratory Balfour Beatty and HIAL and, by constituents had to meet French mixture are shown in table 1. drawing on the airport expertise standards. Betoflex provides numerous of their parent company, Colas Unlike typical UK standards, benefits compared with more SA, were able to offer various NF P98-131 does not provide expensive traditional airfield innovative solutions during initial grading or binder content paving materials, not least in project investigations. These specification envelopes. Instead, terms of whole-life cost, and can included sourcing the required mechanical performance targets be manufactured and laid more aggregate from a temporary for laboratory mixtures are quickly, which meant some 200 quarry (Wilsness Hill) inside the linear metres of runway could be defined and end-product airfield perimeter and using their laid each night at Sumburgh. performance characteristics own on-site high-output mobile Installation is not constrained by specified, which the producer is asphalt plant. the grooving process and, at most required to meet. In this way, European airports, due to its three classes of mixture are Specification enhanced texture and higher defined by the standard. The class Designed and project-managed by friction value, it is used without the Capital Programme Service of required for a particular contract being grooved. However, by Shetland Islands Council, the is determined from a pavement grooving runway 09/27 at project introduced into the UK design process that brings into Sumburgh, aircraft are able to play the type and mass of aircraft, for the first time an advanced, stop over shorter distances in ® high-performance airfield frequency of use, and aircraft tyre surfacing material, developed by pressure. Once a satisfactory Table 1 Colas SA in France. Known as design has been produced the Betoflex, it meets the French appropriate class of BBA may be Mixture Characteristics selected together with an Beton Bitumeux Aeronautique Richness Modulus 3.4 minimum (BBA) standard NF P98-131 and appropriate aggregate size and has been widely used on airfields grading (continuous or at 10 revolutions > 9% across Europe. The Airfields gap-graded) and appropriate Percentage voids under Division of Colas Ltd was the aggregate requirements (related gyratory compaction at 40 revolutions between first contractor to use it in the to the layer and type of airfield). 5–9% UK. Uniquely in the UK, the Thus, for Sumburgh Airport the Duriez 0.80 minimum French material standard was design produced required a Class adopted as the job specification 2 BBA 0/10D with aggregate of Rutting 10% maximum for the asphalt element of the Class BIIIa laid to a depth of works and, correspondingly, all 45mm. Requirements for the Modulus 5,000MPa minimum QM January 2007 www.quarrymanagement.com 29 Asphalt Technology Table 2 Aggregate characteristics required by NF P98-131 mechanical performance properties of Class 2. The choice Test LA MDE PSV MS AAV of binder in this instance was also influenced by the logistics of Class Bllla getting the binder to the island. LA MDE PSV MS AAV requirement 20 15 50 NR NR Production and Test ARD FI WA MB MBF control Colas’s mobile asphalt plant, Class Bllla which had been transported to –– FI 25 WA 24 1 MB 2 MB F10 requirement the Shetlands from Birmingham, was sited a short distance from the wet, allowing the runway was composed of Old Red the entrance to the terminal extension to be significantly Sandstone, to ensure this shape building. One of the few truly shorter than it would otherwise requirement was met, as well as a mobile asphalt plants in the UK, have been, saving the client a more stringent test regime. and certainly one of the largest considerable amount of time and Aggregate characteristics with a production capacity of 225 money. In addition, when required by NF P98-131 are tonnes/h, the plant was central to compared with Marshall Asphalt, summarized in table 2. The use of the efficient handling of the Betoflex has been shown to have local material and on-site contract. The Ermont TSM 225 greater load-spreading ability, production meant greater control plant, which requires no reduced temperature over quality and supplies. It also foundations, was erected and susceptibility, increased resistance minimized airport disruption and commissioned within 10 days of to age hardening, increased was environmentally and socially its arrival on site. The surface resistance to permanent beneficial as it avoided the impact course was laid by two Vogele deformation, comparable levels of of some 1,100 lorry movements pavers laying in echelon and fatigue resistance and no on local roads. compacted by two Bomag 161 susceptibility to moisture damage, rollers, with a Hamm HW90 providing significant whole-life Mix design deadweight following each paver. cost benefits. The mix design process follows a With no reliance on external staged approach. Provided the asphalt supplies, work on the Pre-works testing mix meets each stage of the 100,000m 2 resurfacing project, and mix design process, it proceeds to the next including 43,000m 2 of runway Aggregates stage or level of test. If not, extension, could be closely Clearly, transporting the required adjustments are made and the monitored and controlled. The 22,200 tonnes of aggregates from process repeated until a presence of Colas’s fully equipped the mainland would have been satisfactory mixture is achieved. mobile site laboratory and extremely expensive, therefore For the Sumburgh contract three experienced staff allowed quality Colas identified Wilsness Hill, levels of test were deemed control to be established in within the airport perimeter, as a necessary, each building upon the accordance with the suitable source of aggregate for previous level (NF P98-131 has requirements of Sector Scheme all asphalt production. Thus both four levels of test available). The 14, and the plant was accredited time and costs were reduced by first level is mandatory and to ISO 9001 while on this using local aggregate and involves designing the target PSD contract as a result of this. In manufacturing the asphalt on site. to achieve the desired air voids addition, a 50-tonne capacity A comprehensive study of the under compaction in the PCG weighbridge was shipped from aggregate source was undertaken, (Gyratory Compactor NF P98- the mainland to the site. starting with an examination of 252). Once this is satisfactory, the A comprehensive quality plan for the geology by Colas’s in-house Duriez Test is performed (NF sampling and testing was geologist. There followed a series P98-251-1) to assess the water established, which included the of tests looking at the mechanical sensitivity of the mixture. The usual minimum compositional and physical properties of mixture then proceeds to analysis test rates required by aggregates produced from level-two testing where resistance Sector Scheme 14, based on Q Wilsness Hill, conducted both by to rutting is assessed (NF P98- level. At the outset these were independent test houses in the 253-1) and then to level three for onerous because the plant was UK and by Colas’s own Campus assessment of complex modulus operating at Qx until 30 results for Science and Techniques facility (NF P98-260-2). were available to establish a Q at Magny-les-Hameaux, near Paris. The choice of binder is left to level, and production at the The work in France focused on the producer who must decide beginning of the contract was in the relationship between LA, which type and grade to use to excess of 1,400 tonnes per shift. MDE and FI and resulted in a achieve the required mixture Basecourse and binder course more stringent shape characteristics and mechanical compaction was monitored by requirement for aggregate for use performance at the design binder NDM and confirmed by PRD on in the BBA 0/10 D surface content. The design team at Colas cores taken every 500 lane course. This in turn required SA suggested penetration grade metres. During installation of the additional processing of the 40/60 bitumen would be sufficient surface course, compaction was Wilsness Hill aggregate, which to achieve the required monitored by an NDM suitable 30 www.quarrymanagement.com QM January 2007 for use with thin layers, and Table 3 in-situ air voids were confirmed on extracted cores taken every Type/Quantity Source 1,000m 2 installed. Production was carefully Asphalt plant Ermont TSM 225 Colas Ltd co-ordinated with the supply of 1,080 tonnes of bitumen, which Aggregate 22,200 tonnes Wilsness Hill, Sumburgh was shipped by Colas from the 525 tonnes mainland in 54 loads along with Bitumen Shell the bond coat (Colbond 65) to 70/100 pen meet site demands.