Case Study 4 Recycling in BAA maintenance and construction projects Construction Project: Pavements - airports

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1 Case Study 4 Recycling in BAA maintenance and construction projects Construction Project: Pavements - airports Application: Product: Material: Region: Title: Date: Client: Client advisor: Hydraulically bound sub-base Bitumen bound base Unbound sub-base Capping BS EN aggregates Grade 0/4 (MP) Type 1 Granular sub-base material Type 4 Granular sub-base material Aggregates for bituminous materials (roadbase) Class 6F2 Selected granular material (coarse grading) Class 6F3 Selected granular material Recycled concrete aggregate Recycled asphalt Incinerator bottom ash South East Recycling in BAA maintenance and construction projects 1995 to present; on-going practice Heathrow Airport Limited Gatwick Airport Limited Stansted Airport Limited BAA Pavement and Infrastructure Team Contractor: AMEC / Laing O Rourke (until January 2003) Subcontractors: Designer: Tarmac Topmix Associated Asphalt Browns (Gatwick) Tarmac Recycling (Heathrow) Priors (Stansted) BAA Pavement and Infrastructure Team TPS consult Scott Wilson Jacobs Recycled aggregates Internal arisings (Heathrow and Gatwick) Suppliers: Local suppliers (Stansted) Specifications: BAA in-house specification based on the Specification for Highway Works (airside) Specification for Highways Works (landside) 1

2 Conditions of contract: National Engineering Council Option C (Cost reimbursed basis) Summary The Pavement and Infrastructure Team (PIT) in BAA is responsible for construction and maintenance of airside and landside infrastructures for airport operations inside and around the seven airports under BAA management. The team acts as in-house specifier, client advisor, designer and contractor, as the different players of the supply chain have formed a partnership continuously improving and innovating. The atmosphere of trust and the continuity of the partnership have enabled the team to implement innovative sustainable construction practices thus allowing optimisation of resource use through an holistic approach. Concrete pavements and Marshall asphalt surfacing are seen as a source of recycled aggregates, and the management and infrastructure is in place for stockpiling, specifying, supplying and using those materials in various applications. The economic, technical and environmental benefits of such practices act as drivers for continuous improvement and innovation. Background The PIT has been recently formed by the union of the former Pavement team, responsible for construction and maintenance of airside pavements (e.g.: taxiways, aprons, runways ) and the Infrastructure team, who were in charge of landside structures such as access roads and car parks. The teams work only on and for the seven British airports owned by BAA and each managed by a subsidiary of BAA (e.g.: Heathrow Airport Limited, Gatwick Airport Limited, etc.). They manage and undertake a programme of maintenance and construction estimated in the region of 40m per annum. It is now common practice during maintenance and reconstruction of airside infrastructures to make sure that pavement quality concrete and asphalt arisings are not wasted. Concrete rubble is stored in designated areas at the airport locations or at the materials subcontractor s premises for subsequent use. When needed, the subcontractor partnered to the main contractor in each airport location, processes the concrete to meet the specification for unbound sub-base or aggregates for lean concrete. Asphalt arisings have been used as 10% virgin aggregates substitute in new asphalt layers, as capping or as sub base material in airport pavements shoulder widening. The team includes specifiers, designers and contractors from BAA, consultancies and contractors working together in a partnership, under a framework agreement. The framework, which was established in 1995, allows for all parties of the supply chain to discuss at design/commissioning stage the projects requirements, the materials specification and their supply, thus enabling an efficient management of the available resources, in particular recyclable concrete and asphalt arisings which are stored from one project to another and reused whenever opportune. The framework agreement and the supply chain Both Pavement and Infrastructure teams had been partnered through a 5 years framework agreement with the design consultant TPS consult and a contractor party, namely AMEC for airside operations and Laing (now Laing O Rourke) for landside. The teams shared very often supply chain, administration and even resources. The framework contract was recently renewed for both teams with AMEC being awarded in January 2003, through an open tender competition, both contracts for ten years and beyond, providing continuous improvement is shown throughout. The framework agreement with a contractor has been instrumental to the successful application of traditional recycling techniques and innovative sustainable construction practices in various construction and maintenance projects throughout the years. The continuity of and trust in the partnership enabled the team to have an holistic approach to their construction and maintenance 2

3 program, and so to foster innovation and continuous improvement and overcome barriers to the use of alternative construction practices. The establishment of such a partnership has improved aggregates recycling performance. Even though the in-house BAA specification for pavement construction did not exclude the use of Recycled Concrete Aggregate (RCA), it had been rarely used before the framework was established, i.e. while each project was tendered for and awarded to different contractors. The main issue was the difficulty of controlling size and quality of any stockpile of recyclable concrete rubble that may arise: single contracts did not enable the establishment of a supply chain whereby proper storage and management of the recyclable material could be carried out. Understandably, the contractors that in turn were awarded any single contract would be wary of using unknown batches of material without costly testing. The situation improved radically with the establishment of the partnership (see Fig.1): specifier, designer and contractors now working together in a team could provide for the establishment of controlled and well managed stockpiles of arisings, either in compounds areas at the airports (e.g.: Gatwick, Southampton, Heathrow up to T5 construction started) or at subcontractors sites (for Heathrow, Tarmac Recycling site in Shepperton, where the crushing was also carried out). Whenever possible, e.g. when available in sufficient quantities, the team would specify the recycled concrete, initially only as sub-base material, then in the lean concrete base. The clients, e.g. the seven airports subsidiaries, have trust in the team, supported also by the BAA Sustainability policy. The team has contributed to the implementation of this policy by initiating best practice in the use of aggregates, which is now under review for formalisation into an overarching policy. Materials and specifications The PIT has full ownership of most of the adopted specifications and it is very much geared towards introduction of innovation and continuous improvement to ensure that the best solution is adopted for each case. Therefore, novel or unusual practices such as crack and seat or cold in situ recycling are trialled and if necessary adapted to the needs of the construction. The team of designers and specifiers are also looking at pushing the use of recycled concrete aggregate (RCA) and recycled asphalt planings (RAP) up the value chain, so as to further improve resource efficiency. Airside construction Airside pavements are mainly built in pavement quality concrete, using slipform paving. (Marshall) Asphalt, a more expensive option, is mainly used for runways construction or for resurfacing when corrective maintenance on concrete is needed. Marshall asphalt is a very dense material whose mix design is based on a Marshall compactor test. It is used, grooved, as friction course. Both types of constructions are based on an in-house BAA specification, which was originally based on the Highways Agency s Specification for Highways Works (SHW) for the pavement quality concrete. With regard to recycled aggregates, the in-house specification did not forbid their use, but in reality alternative materials were rarely used before the partnership between BAA in house specialists and designer and contractor consultancies enabled the establishment of the appropriate supply chain. Landside construction Landside maintenance and construction work includes construction of car parks and access roads around the airports. The former Infrastructure team was partnered with Laing O Rourke, who adopted the SHW as standard. The newly formed PIT may now reconsider which specification to 3

4 adopt for those constructions with the potential for an in-house standard to be developed as for airside projects. This approach may enable the supply chain to gain further cost and environmental savings through avoiding any over-specification. Car park construction, particularly around Stansted, was undertaken on green land. Wherever possible, recycled aggregates such as recycled concrete to Type 1 or asphalt planings to Type 4 specification have been used, sourced from time to time from local construction projects undertaken by the same contractor. Sub grade stabilisation has also been used wherever possible. Technical benefits The ownership of the specifications enable the team to continuously explore new practices and materials and amend its own standard to introduce the most technically, economically and environmentally beneficial solutions. Innovative practices have lead to improved resource efficiency, with consequent economic and environmental savings. Development of a high flexural strength concrete mix design. A typical example is the latest mix design for a high flexural strength (7 MN/m 2 ) concrete for Heathrow T5 pavements, developed with the same cement content as the 5.3 MN/m 2 concrete mix. Increased traffic loads on airport pavements meant that thicker concrete structures of the highest flexural strength specified needed to be built. The Pavement team, aware of the increased economical and environmental costs, initiated the development of a new specification which would allow for thickness reduction and no cost increase. The work led to the definition of a mix design for a 7 MN/m 2 concrete, with the same cement content as the lower strength mix. The new pavements resulted in 25% thinner constructions than with the old design. The mix also included PFA as substitute for 30% of the original cement content. Crack and Seat. The Pavement team has carried out an extensive R&D program aiming at introducing this practice into the UK for airport pavement reconstruction. The technique allows for the old pavement to be kept on site and used as a very strong base for the new construction. This means that there is no need for importing aggregates for the sub-base layer. The pavement to be maintained is broken up in suitably sized slab-like lumps which are then compacted into the substrate and overlaid with the new pavement. This technique can be used wherever raising the levels of the concrete pavement is not an issue. Temporary car parks, adjusted design. Car parks around the airports are designed to a 5-years design life. The team is currently reviewing the specification (based on the SHW) with the aim of reducing the thickness and frost susceptibility requirements, and, as a consequence, quantity of aggregates required. Lime and cement stabilisation of sub-grade. Lime/cement stabilisation of clay sub-grade is currently used to provide sub base for car park construction, thus avoiding imports of aggregates. At Heathrow T5, the gravel sub-grade, after levelling, is stabilised with cement to provide the sub-base for the airfield concrete pavement. Cold in situ recycling. The team is currently considering introducing this technique for car parks maintenance. 4

5 Please refer to Table 1 for a brief summary of some of the projects and locations and Fig.2 and following for a schematic representation of the material flows in and out of Gatwick, Heathrow and Stansted. Cost benefits Cost savings have been and are one of the major drivers to the partnership for the adoption of new construction practices, including use of recycled aggregates or alternative techniques such as crack and seat and sub grade stabilisation. The teams have always understood the value of their own concrete and asphalt arisings and found in this long term partnership the right contractual environment for avoiding wastage and maximising savings in disposal costs and aggregates supply. Instead of importing primary aggregate from other regions, the use of in-house arising is maximised. Direct cost savings are therefore obtained as the recycled aggregate is virtually free except for the cost of processing it. Indirect savings come from avoidance of landfill tax and charges for disposal of the material to landfill. The team is aware of how recycled aggregates are a winning choice also from the economics point of view. Use of processed municipal waste Incinerator Bottom Ash (IBA) in bitumen bound base. Stansted is a relatively new airport which does not generate as yet recyclable arisings. However, the PIT has been exploring the use of IBA, which is conveniently available from two incinerators around London, namely Edmonton in North London and the SELCHP in South London. These two sources are closer to the airport than for any primary aggregates. IBA was used in the construction of over 7,000 car parking spaces at Stansted. The Infrastructure team saved up to 6% of the contract value, compared to traditional car park construction, by specifying and using over 30,000 tonnes of ASH-phalt, a bituminous mix containing 30% IBA. Economic benefits resulted mainly from savings in primary aggregates costs and fuel use, as the ash was delivered using a back haul system, on the return leg of a trip to deliver waste to the incinerator. Environmental benefits BAA has a corporate sustainability policy and the PIT and predecessors are and have been champions for originating and implementing the BAA approach towards sustainable construction and resource efficiency. The Pavement team has drafted a best practice document on use of aggregates which is now underway to become a BAA policy. It also set itself the target of recycling at least 95% of the concrete pavement taken up. This target is fully met, and only contaminated concrete is going to waste. Improved resource efficiency is one of the many environmental benefits obtained from the teams innovative approach to construction. Here are some examples of savings of natural aggregates: The use of ASH-phalt for the car parks construction in Stansted saved 9,300 tonnes of primary aggregates. Stabilisation with lime/cement of the clay subgrade saves about 11 tonnes of aggregates per parking space in temporary car parks. Each year, the use of internal concrete arisings saves a considerable amount of virgin aggregates, depending on the construction and maintenance programme for the year. From July 2003 to October 2004 inclusive, for example, the Team recycled about 100,000 tonnes of concrete at Heathrow. As a consequence of avoiding extraction and transport of natural materials, a significant amount of lorry movements, and fuel and CO 2 emissions, can be saved. The use of 18,000 tonnes of ASH- 5

6 phalt, for example, saved at least 460 lorry movements to and from the primary aggregates railhead deposit and the asphalt plant (18 miles per leg), and 34 from the plant to Stansted (23 miles). Conclusions The PIT is organised so that client advisor, specifier, designer and main contractor are all part of a team sharing knowledge and resources and collaborating to find the best available solutions for maintenance and construction projects. The atmosphere of trust and cooperation fosters innovation: early involvement of all parties means that the team can consider and possibly carry any risk deriving from adopting unusual practices. Contractual arrangements do not constitute an obstacle but at the same time the partnership needs to demonstrate continuous improvement to ensure its continuation in the long term. Resource efficiency is one of the drivers for continuously introducing new materials and techniques. However, the economics play a relevant part, so that use of alternative materials and techniques are adopted as and when they prove cost effective. So for example, redundant concrete pavements are taken up only if due for reconstruction, and the concrete rubble kept if not immediately used. Conversely, demolition costs would be too high to justify sourcing recycled aggregates from an unused pavement. Availability and locations of materials are also key issues to their use: recycled and secondary aggregates are used if available locally in sufficient quantity, like IBA for Stansted or imported asphalt planings arising from local construction projects. The PIT is therefore a good example of how collaborative partnership and consequent early involvement of the major players in the supply chain enable the implementation of sustainable construction principles. BAA s attitude towards sustainability is also fostering this approach and its targets are in turn been pushed further and expanded: the PIT internal target of 95% recycling of the concrete rubble generated is amply met and good practices on aggregates use adopted by the PIT are now evolving into a BAA policy. 6

7 Client: 7 BAA subsidiaries (airports) Specifier: BAA Specifiers Pavement and Infrastructure Team (PIT): Designers: BAA designers TPS Consult Scott Wilson Jacobs Principle Contractor AMEC Subcontractors: Heathrow Tarmac Recycling: Storing and crushing of recycled concrete Gatwick P J Brown: Earthmoving and concrete crushing Tarmac Topmix: Readymix Stansted C J Pryor: Earthmoving Project/practice Figure 1: current supply chain for BAA, Pavement and Infrastructure Team Recycling of internal concrete aggregate arising in airfield pavements Recycling of asphalt arisings (RAP) in airfield surfacing and shoulder widening Reduction of cement content in high strength pavement quality concrete specification Locations Gatwick, Heathrow Gatwick, Heathrow New specification first adopted at Heathrow RSA used and product / sustainable practice Recycled concrete in cement bound sub-base layer (lean concrete) RAP in base course (10% virgin aggregate substitution), as Type 4 sub-base and (capping) PFA as 30% cement substitute and reduction of cement use Crack and seat Gatwick Avoided use of aggregates in bound sub-base Use of RAP in capping layers and RCA in Stansted (RAP), sub-base layers in car park construction Gatwick, Heathrow RAP as capping and RCA as Type1 Lime/cement stabilisation of clay sub grade for car parks Stansted, Gatwick, Heathrow Avoided use of aggregates in subbase Reduction of thickness and frost heave New specification to specification for car parks be introduced As above Cement stabilisation of gravel sub-grade Avoided use of aggregates in bound Heathrow for airfield pavements sub-base (lean concrete) Use of ASH-phalt in car park construction Stansted IBA as 15% primary aggregates substitute Cold in situ recycling for car parks reconstruction New practice to be introduced Avoided use of aggregates for asphalt Table 1. Summary of relevant projects and/or practices with locations 7

8 PFA in concrete mix (30% OPC substitute) Airside Airfield pavements construction: Concrete rubble and asphalt planings* Storage and crushing Gatwick: compound area Crushing: (Browns) High strength concrete mix Gravel sub-grade stabilisation (LHW) (Marshall asphalt friction course) Pavement quality concrete Bound sub-base (lean concrete) 1) RAP in base course (10% subst.) for bound sub-base 2) RCA for bound sub-base Heathrow: Shepperton (Tarmac Recycling premises) Crushing: Tarmac recycling Cold in situ recycling Landside Car parks and access roads construction: RCA for sub-base and capping Clay sub-grade stabilisation (lime/opc) Asphalt surface course Stansted: Imported RAP in capping layer Local arisings Reduced thickness frost-heave layer Sub-base Stansted: Use of ASH-phalt (IBA) IBA sourced in London *Stansted pavements have not needed structural maintenance and therefore this does not apply to Stansted until maintenance is required. Fig.2: Materials flow and resource-efficient construction techniques used by BAA Pavement and Infrastructure Team(s) 8

9 Contact details Designer: Contact BAA Pavement and Infrastructure Team Andy Delchar Head of Performance Improvement Pavement & Infrastructure Team First Point, 3rd Floor Buckingham Gate South Terminal, Gatwick Airport West Sussex RH6 0NT Tel: (01293)