final report carbon impacts and cost benefit analysis of trench … trench... · 2019-05-09 ·...

Final Report

Carbon impacts and cost benefit analysis of trench reinstatement options

WRAP’s vision is a world without waste, where resources are used sustainably. We work with businesses and individuals to help them reap the benefits of reducing waste, develop sustainable products and use resources in an efficient way. Find out more at www.wrap.org.uk

Written by: Joanne Edwards, Roxane Fisher, David Hann and Sue Hornby.

Front cover photography: Trench reinstatement using recycled trench arisings, photography courtesy of Scott Wilson. WRAP and Scott Wilson believe the content of this report to be correct as at the date of writing. However, factors such as prices, levels of recycled content and regulatory requirements are subject to change and users of the report should check with their suppliers to confirm the current situation. In addition, care should be taken in using any of the cost information provided as it is based upon numerous project-specific assumptions (such as scale, location, tender context, etc.). The report does not claim to be exhaustive, nor does it claim to cover all relevant products and specifications available on the market. While steps have been taken to ensure accuracy, WRAP cannot accept responsibility or be held liable to any person for any loss or damage arising out of or in connection with this information being inaccurate, incomplete or misleading. It is the responsibility of the potential user of a material or product to consult with the supplier or manufacturer and ascertain whether a particular product will satisfy their specific requirements. The listing or featuring of a particular product or company does not constitute an endorsement by WRAP and WRAP cannot guarantee the performance of individual products or materials. This material is copyrighted. It may be reproduced free of charge subject to the material being accurate and not used in a misleading context. The source of the material must be identified and the copyright status acknowledged. This material must not be used to endorse or used to suggest WRAP’s endorsement of a commercial product or service. For more detail, please refer to WRAP’s Terms & Conditions on its web site: www.wrap.org.uk

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Carbon and cost benefit analysis of trench reinstatement 3

Contents 1.0 Introduction ............................................................................................................................. 4

44

556899

101112121314

2.0 Excavation types ...................................................................................................................... 2.1 Trenchless technologies .........................................................................................................

3.0 Reinstatement methods........................................................................................................... 5 4.0 Reinstatement materials..........................................................................................................

4.1 Bituminous bound mixtures (asphalt)...................................................................................... 4.2 Structural materials for reinstatement (SMR)........................................................................... 4.3 Unbound mixtures ................................................................................................................. 4.4 Stabilised material for fill (SMF) ..............................................................................................

5.0 Supplier/recycling facility availability ..................................................................................... 6.0 Carbon comparison ................................................................................................................

6.1 Results................................................................................................................................ 7.0 Cost analysis ..........................................................................................................................

7.1 Findings.............................................................................................................................. 8.0 Conclusions ............................................................................................................................ References .........................................................................................................................................

Acknowledgements The project has also been supported by:

1.0 Introduction In 2005, water and gas maintenance trench works were estimated to generate around 4.8 million tonnes of trench arisings across Great Britain, equivalent to 4.5% of the total national construction, demolition and excavation wastei generated. A substantial amount of work has been carried out in recent years to reduce waste, increase recycled content in various reinstatement materials and increase the use of utility trench arisings within hydraulically bound mixtures (HBMs) for use in trench reinstatement. Carbon impact modelling of various trench reinstatement scenarios and a comparison of the indicative costs of the different reinstatement methods was undertaken to provide an evidence-base, to aid the utilities sector in making informed choices and demonstrate their contribution to reductions in carbon emissions in relation to delivery of National Indicator 186ii. 2.0 Excavation types

iiiThe ‘Specification for the Reinstatement of Openings in Highways’, second edition , herein referred to as the SROH defines four categories of excavation based on the surface area, these are:

Small excavations – all openings with a surface area <2 m2 (Test holes <150 mm diameter are not included).

Narrow trenches – all trenches with a surface area >2 m2 and surface width <300 mm.

Deep openings – all excavations and trenches in which the depth of cover over the asset is >1.5 m.

Other openings – all excavations and trenches with a surface area >2 m2.

However, these categories do not relate the size of excavation to the size of the asset. Therefore, a further three categories are also used by industry, these are; ‘open-cut’, ‘low-dig’, and ‘no-dig’. Both low-dig and no-dig are made possible through the use of trenchless technologies, and require minimal or no reinstatement. Open-cut excavation comprises a full-sized trench to allow access to the asset for maintenance, or installation, for which the whole length of the asset may require excavating. This means that there is full access to the asset but it requires the most digging and disruption to the surface, and considerable reinstatement. Low-dig methods need a smaller trench volume to be excavated, relative to the asset maintenance or installation required. For example, keyhole methods may be employed instead of a trench to access an asset reducing the size of the excavation, or open-cut trenches may be excavated as access and egress points for directional drilling. In certain cases a seemingly large volume of excavation is required for directional drilling, for example a three metre trench at each end of the run, but if it allows a 140 m stretch of pipe to be laid which otherwise would have required a full length excavation, it is still relatively low-dig. Although there may be reduced disruption at the surface, utility arisings are still generated and trench reinstatement required. No-dig methods generally employ manholes to access the asset, negating the requirement for excavation. Other no-dig methods include the development of alternative technology negating the requirement to excavate and replace assets. For example Yorkshire Water has developed rubber platelets that can be introduced to the water supply at source and block leaks in the system. These cause minimum disruption and surface damage and so can be very useful for areas of work in environmentally protected areas. 2.1 Trenchless technologies Trenchless technologies provide an alternative to traditional ‘open-cut’ reinstatement methods, and can be extremely useful in situations where the ground is crowded by utilities and large open works are not feasible. The term is used to encompass both ‘low-dig’ and ‘no-dig’ reinstatements. These methods involve minimum excavation as openings are only required for access at either end, rather than a full length open-cut trench causing less disruption; and the reinstatement requires a relatively smaller amount of material. There are, however, some potential drawbacks to trenchless technologies; unexpected underground obstacles can make the installation impossible or may cause damage to existing utilities, particularly where no maps or drawings of the underground utility layout are available. The methods often have a high initial cost as they require specialist equipment and training, but for high volumes of work it may be cheaper in comparison with full lengths of open-cut trench due to savings in materials and labour costs; and also reduce disruption.


3.0 Reinstatement methods First time permanent reinstatement: The excavation is reinstated to a permanent standard at the first visit, in accordance with the SROH. Second time permanent reinstatement: A combination of pavement layers are reinstated to a permanent standard at the first visit and temporary reinstatement is also used. A second visit is required to reinstate the temporary layers to a permanent standard in accordance with the SROH. 4.0 Reinstatement materials Table 1 summarises material groups included in the SROH. The surfacing material varies between asphalt, modular blocks and concrete. However, the surfacing should be reinstated as existing; therefore, the surfacing is considered a constant for the purposes of this cost benefit analysis and so is not covered in detail. This study has focussed on reinstatement of the trench below the surfacing layer. Further guidance is given in Recycled materials in trench reinstatement: Guidance document.

Table 1: Summary of reinstatement materials

SROH requirement for A9 trial

Potential for recycled content

Covered by BS EN

Application Material/Mixture

Concrete Low/medium Yes No Rigid pavements

Flexible pavements

Bituminous Bound Mixture (Asphalt) Medium Yes No

Foamed Bitumen Medium No No

Foamed concrete Medium No No

4.1 Bituminous bound mixtures (asphalt) Bituminous bound mixtures generally comprise bitumen, aggregate, filler and additive(s). There are many mixtures that are suitable for trench reinstatement, the choice of which will provide the road with different characteristics. These include mixtures which utilise various techniques to avoid the requirement of dry aggregates and/or lower the temperature of mixing (ranging through hot, half warm, warm and cold mixtures). The bituminous bound mixtures used for permanent or temporary reinstatement are given in HAUC(UK) Advice Note No. 2008/03iv and summarised in Table 2. Foamed bitumen mixtures compliant with clause 948 of the Manual of Contract Documents for Highways Worksv (MCHW) are permitted for use as a BBA HAPASvi approved material.

Flowable (FSMR) Medium No Yes

BS EN HBM

High Yes No

Structural Material for

Reinstatement (SMR)

Non-Flowable (NFSMR) Proprietar

y NFSMR High No Yes

Up to base and subbase in road

Types 1 to 4

Unbound Mixtures (GSB1/Type1) High Yes No

Class S SMF (will not exist in the third edition of the

SROH) High No Yes

Backfill and subbase

Stabilised Materials for Fill

(SMF) Class A to D SMF High No Yes Backfill

Bedding and surround

Aggregates for bedding and surround materials High Yes No



Figure 1: Compaction of an Appendix 9 SMR

Table 2: Bituminous bound mixtures Table 2: Bituminous bound mixtures

4.2 Structural materials for reinstatement (SMR) The SROH defines Structural Materials for Reinstatements (SMRs) as a “group intended to include proprietary or alternative bound reinstatement materials that include a cementicious, chemical or hydraulic binder, or are inherently self cementing.”

According to the SROH, SMRs may be used at any position within the surround to apparatus, backfill or as the whole layer, or in combination with othpermitted materials within any reinstatement. They can be used as a combined subbase and binder course within reinstatement in footways, footpaths and cycle tracks, surfaced with asphalt.

er

d below.

They can also be used as a subbase in any reinstatement, or a combined subbase and base in road Types 1 to 4, or as a base in road Types 3 and 4, as shown in Table 3. Road Types are defined in the SROH (Table S1.1), and liste There are two compressive strength criteria specified in the SROH:

2 to 10 N/mm2 at 90 days for subbase in road Types 0 to 4 and all layers below the binder course in road

Types 3 and 4

4 to 10 N/mm2 at 90 days for base and subbase in road Types 1 and 2.

Reference in SROH (2002) PD 6691 Reference*vii

6 mm Dense Surface Course (DSC) macadam AC 6 dense surf

10 mm Close Graded Surface Course (CGSC) macadam AC 10 close surf

15/10 Hot Rolled Asphalt (HRA) surface course (SC) HRA 15/10 F surf

30/14 Hot Rolled Asphalt (HRA) Type F surface course (SC)* 30/14 Hot Rolled Asphalt (HRA) Type C surface course (SC)*

HRA 30/14 F surf HRA 30/14 C surf

“des” suffix where a design mix is required

6 mm Stone Mastic Asphalt (SMA) surface course (SC) SMA 6 surf



10 mm Porous Asphalt No reference

20 mm Porous Asphalt No reference

50/20 HRA Binder Course (BC) HRA 50/20 bin

14 mm Stone Mastic Asphalt (SMA) binder course (BC) SMA 14 bin

20 mm Stone Mastic Asphalt (SMA) binder course (BC) SMA 20 bin

20 mm Dense binder course macadam (DBC) AC 20 dense bin


SMRs must not be used either as a substitute for permanent surface course materials or within 100 mm of the finished reinstatement surface for carriageways. SMRs can be delivered to site as ready-made materials or be prepared partly or wholly on site. SMRs include:

foamed concretes for reinstatements (FCRs);

BS EN Hydraulically bound mixtures (HBMs);

flowable structural materials for reinstatement (FSMR); and

non-flowable structural materials for reinstatement (NFSMR).

Foamed concretes and BS EN HBMs are considered approved for use without an A9 approval trial (SROH and HAUC Advice Note 2009/01viii, respectively), whereas FSMRs and NFSMRs require an A9 trial.

Table 3: Requirements for SMRs

Foamed concretes for reinstatements (FCR) are commonly used Alternative Reinstatement Materials (ARMs) and are detailed in the Practical Guide to Street Worksix. They generally comprise aggregate, filler, cement and foaming agent. FCRs are normally prepared off site, as a “prescribed” mix, following quality controlled procedures. FCRs may be obtained from a ready-mix supplier or be produced using the contractor’s own materials, equipment and plant. The mixtures that conform to MCHW Clause 1043x are considered approved for use as ARMs, and therefore, do not require an A9 trial. FCR may contain up to 50% air and, as a result, has a low density but high workability. The air bubbles can be introduced into the foamed concrete by adding pre-formed foam or an air-entraining agent either at the batching plant or on site. The flowable properties of foamed concrete yield advantages such as; it may be pumped, it is self levelling and should not require compaction. FCRs that are designed for road trench reinstatement have no settlement, which allows for full resurfacing in a single operation, once the foamed concrete has gained strength. BS EN hydraulically bound mixtures (HBM) are materials which set and harden through a hydraulic reaction and are produced in accordance with the relevant standard (BS EN 14227 Parts 1 to 3 and 5, and Parts 10 to 14) under a factory production control system, a summary of HBM designation and corresponding BS EN is given in Table 4. These materials are compliant with the MCHW Series 800xi and, as such, these materials are considered approved for use without an A9 trial in accordance with the HAUC Advice Note 2009/01 . viii

This material group includes both fast-setting materials based on the hardening characteristics of cement, and slow-setting mixtures with binders made from industrial by-products such as pulverised fuel ash (PFA) and granulated or ground granulated blast-furnace slag (GBS and GGBS, respectively). Several advantages of using HBMs have been highlighted on the WRAP Aggregain website. Plant and material supply are both widely available because HBMs are becoming well known and the plant is similar to that required for the laying and compaction of other paving materials, such as unbound or bituminous bound mixtures.

Road Type (msa – million standard axles per annum)

Layer 0 over 30 to 125

msa

1 over 10 to 30

msa

2 over 2.5 to 10

msa

3 over 0.5 to 2.5

msa

4 Up to 0.5

msa

Footway, Footpath or Cycle Track

Combined Binder Course and Subbase

Not to be used Not to be used Not to be used Not to be used Not to be used >150 mm thick 2 to 10 N/mm2

Base Not to be used Not to be used Not to be used>300 mm thick2 to 10 N/mm2

>200 mm thick 2 to 10 N/mm2

Base and Subbase

Not to be used >450 mm thick4 to 10 N/mm2




Subbase and/or below








Flowable structural materials for reinstatement (FSMR) do not normally need compaction and can reach the strength requirements given in Table 3. These materials are proprietary products, and therefore, may only be used on a trial basis, following the approval procedure which is detailed in A9.5 of the SROH, and after prior agreement with the highway authority (Table 1). The balance between flowability and achieving comparable mechanical performance to mixtures which do not have such a high water content (non flowable mixtures), may require higher binder content. Therefore, the costs are relatively high; however, this additional cost can be offset by speed and ease of placement, as such FSMRs are suited to larger scale projects where efficiency gains can be made. Non flowable structural materials for reinstatement (NFSMR) generally utilise a proprietary product for the binder, and will require compaction. They may not comply with the quality or specification requirement of a BS EN HBM, and therefore, require an Appendix A9 trial to demonstrate fitness for purpose (Table 3).

Table 4: Types and designation of HBM covered by BS EN 14227 Parts 1 to 3 and 5

Part 1 Part 2 Part 3 Part 5

Type of mixture Cement bound granular mixtures

Slag bound mixtures

Fly ash bound mixtures

Hydraulic road binder bound

mixtures Graded slag mixtures without specified binder

requirements SBM A1 – A5

31.5 mm wide graded mixture (includes sand mixtures)

CBGM A

31.5 mm well graded mixtures CBGM B SBM B1 FABM 1 HRBBM 1

0/20, 0/14 and 0/10 mm well graded mixtures with compacity requirement

CBGM C 0/20, 0/14, 0/10

SBM B2 0/20, 0/14, 0/10

FABM 2 0/20, 0/14, 0/10

HRBBM 2 0/20, 0/14, 0/10

Sand mixtures with Immediate Bearing Index (IBI) requirement

SBM B3 FABM 3 HRBBM 3

Mixtures with declared grading and other properties if appropriate

SBM B4 FABM 4 HRBBM 4

Treated fly ash mixture FABM 5

For the mixtures above, the quality of the aggregate used is at the discretion of the specifier / user / producer. Since grading is specified in the relevant mixture clause, the main aggregate properties for consideration include particle shape and hardness. These, together with grading are relevant properties for immediate traffickability. These properties and their classes are found in the aggregate standard BS EN 13242. In addition, fines quality and chemical and physical impurities may need consideration

in relation to volumetric stability and durability (although these are better considered by examining the HBM). Note that soil mixtures are specified in BS EN 14227 Parts 10 to 14.

4.3 Unbound mixtures Recycled, secondary or virgin (primary) materials, or any combination thereof, are permitted for use in the SROH, providing they meet the performance and compositional requirements for the relevant material layer. The MCHW Series 700xii permits the use of Recycled Coarse Aggregates and Recycled Concrete Aggregates as subbase in pavement construction, providing that the materials are compliant with the WRAP Quality Protocolxiii, and Clause 801.5 MCHW Series 800 . In addition, the MCHW requires that an unbound mixture (irrespective of source) must comply with BS EN 13285

xi

xiii

xi

xiv. The WRAP Quality Protocol was developed to ensure that recycled aggregates are processed in a quality controlled manner, resulting in a quality product. While, Clause 801.5 MCHW Series 800 provides an upper limit on the amount of recycled asphalt, glass and impurities permitted in recycled aggregate. Unbound applications have a high potential for using recycled aggregates (Table 1), which may come from trench arisings that are suitable for reuse; processed or treated arisings which are made suitable for reuse; or aggregate from the processing of inert material previously used in construction. These materials could all be suitable for use as backfill or subbase depending on the material class and type of road.


Figure 2: Aggregate processing

Figure 3: UK coverage of suppliers on the AggRegain Directory

either:

raded granular mixtures (Type 1

ixtures; or

Class D – Cohesive mixtures.

ble hydraulic binder and used as an SMF or SMR.

s permitted for use in the MCHW Series 800 are equivalent to GSB1 (granular subbase) as ecified in the SROH.

essed, re-graded, or include a cementitious, hemical or hydraulic binder”. They are not necessarily bound.

re

be used on a trial basis by prior agreement with the authority following the approval procedure in e SROH.

fill, either as the whole layer or combined with , or as a combined surround to

pparatus, backfill or subbase.

th or

ed in

tes ot be used as a permanent binder course or

rface course.

of aterial suppliers across the UK, as illustrated in Figure 3.

The SROH classifies unbound materials as

Class A – G

and Type 2);

Class B – Granular mixtures;

Class C – Cohesive/granular m

Class E is unacceptable material, although sometimes it can be improved by drying, re-grading or adding a suita

The recycled aggregatesp 4.4 Stabilised material for fill (SMF) The SROH definition of this group is “materials which are derived from excavated spoil, primary, or recycled materials, or any combination of these, which have been re-procc The materials in this category are generally non-flowable and so need to be compacted. Source and process anot specific to SMFs and so they are defined by a set of compositional and performance requirements. These materials canth To replace materials with SMFs, they should be trialled in layers which are dependant upon their strength classification within Appendix 9 of the SROH (table A9.2), but not dependent on the type of materials used above or below. This may be at any position within the surround to backother materials in any proportiona Materials which are defined as SMF Class A in the SROH can be used in the subbase layer within any road, footway, footpacycle track. SMFs are split into classes which are deemed equivalent to the backfill classes defined in the SROH. The classes of the SMFs are based on the soaked CBR; determinaccordance with BS1377. Backfill layer thicknesses for the different road structures are given in the SROH. The SROH stathat SMFs shall nsu 5.0 Supplier/recycling facility availability The WRAP AggRegain Suppliers Directoryxv provides detailsm

6.0 Carbon comparison The WRAP Carbon Dioxide Emissions Estimator Tool was used to quantify and compare the CO2 emissions associated with different trench reinstatement methods, using a ‘standard trench’ to maintain parity for comparison. The tool includes consideration of CO2 embodied in reinstatement materials, and transport of materials to and from the site. The tool does not include the embodied CO2 of landfilled materials and additional calculations were carried out to account for this. A revised version of the tool, available from May 2010, will include the embodied CO2 of landfilled materials; therefore, additional calculations will no longer be necessary. The tool does not include any provision for flowable SMRs, so an approximation to a flowable SMR scenario was devised by increasing the percentage of cement in the flowable cement bound material scenario; this should be taken only as a rough approximation. Insufficient data were available to enable modelling of foamed concrete. 18 scenarios were analysed for an ‘average’ trench location, derived from a series of theoretical trench locations across the UK. Site visits were carried out to observe trench reinstatement work and verify the design and modelling assumptions. Surfacing material varies between asphalt, modular blocks and concrete. However, the surfacing should be reinstated as existing; therefore, the surfacing is considered a constant for the purposes of this cost benefit analysis and so is not covered in detail. This study has focussed on reinstatement of the trench below the surfacing layer. The modelled scenarios included various combinations of excavation material destination (landfill, recycled at trench, recycled at hub) and reinstatement materials (primary and secondary aggregates, HBMs and flowable materials). For comparison purposes, analysis was based on a trench which was assumed to be 10 m long, 0.5 m wide, and 1.2 m deep (Figure 4), with the individual layers as appropriate to the reinstatement scenarios. The ‘standard’ trench used a reinstatement design for a Type 1 road, which has a combined base, binder and surface thickness of 350 mm, this is typically 285 mm for Type 2, 190 mm for Type 3 and 150 mm for Type 4. The subbase construction for a flexible pavement should be in accordance with Appendix A3.5 of the SROH for all five road types. Therefore, the 200 mm difference in thickness of the asphalt layers between road Type 1 and Type 4 will be made up in the backfill, resulting in a 900 mm layer of backfill in a Type 4 road compared to 700 mm in a Type 1 road (Figure 4). The increased thickness of backfill allowed in road Types 2, 3 and 4 compared to a Type 1 road will increase the opportunity to reduce carbon. This is because more material can be reused in the backfill application and less material will be sent to landfill.

Figure 4: Standard trench (assumed 10 m long)

10 m0.7 m

0.35 m

0.15 m

0.5 m

Base, binder and surface course

asphalt

Subbase

Backfill

0.9 m

0.15 m

0.15 m

‘Standard’ Trench (Type 1 road with flexible pavement) Type 4 road with flexible pavement


6.1 Results Figure 5 presents a comparison of the CO2 emissions for the various scenarios. In Scenarios 1 and 2a, where arisings are sent to landfill, CO2 emissions were approximately 390 kg for the standard trench. The modelled CO2 emissions were not reduced by the use of unbound recycled aggregate instead of primary aggregates in these scenarios, as the embodied CO2 and transport distances were similar for both materials. Recycling arisings reduced modelled CO2 emissions by over 40% compared to the landfill scenarios; a reduction of around 160 kg carbon for the 10 m standard trench. Modelled CO2 emissions for scenarios using by products (PFA and GGBS) as hydraulic binders were comparable to the baseline scenario. The modelled CO2 emissions were similar for the mix at trench and recycling hub scenarios for the two binders. The embodied energy value associated with cement production results in a substantial increase in modelled CO2 emissions for the materials containing cement. Where superior performance of cement bound mixtures is not utilised within a pavement design, or permitted in the specification, then the benefits from a CO2 perspective may be realised by partial replacement of cement or the use of an alternative hydraulic binder. This is already common practise for the production of HBMs for trench reinstatement. There is an added benefit that slow-setting hydraulic binders tend to produce reinstatement materials with a longer shelf life (workability period). ‘Low-dig’ method results are estimated to have 15% of the carbon emissions of a standard trench; hence, substantial carbon savings can result from the reduced excavation and reinstatement. Based on even the ‘best case’ emissions of approximately 200 kg for a 10 m trench (recycling arisings and using recycled aggregates), for example, in comparison to using primary aggregates, trenchless technologies could reduce modelled carbon emissions of 1 km of trench works from approximately 20 tonnes to 3 tonnes

Figure 5: Modelled carbon dioxide emissions

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7.0 Cost analysis A comparison of indicative costs of the various trench reinstatement methods was carried out, including material, transport and labour costs for the scenarios modelled in the carbon analysis. The cost analysis was based largely on the values published in Spon’s Civil Engineering and Highway Works Price Book 2010, supplemented by information from material suppliers, site visits, the WRAP Net Waste Tool and utilities contractors. 7.1 Findings The results suggest that using recycled materials for the backfill and subbase, and sending the excavated materials to a recycling hub is the most cost effective method (Figure 6); followed by the use of foamed concrete, which does not incur the labour cost associated with compaction. Recycling at the trench has a cost advantage over the other methods. The hub recycling methods have a cost advantage over landfill scenarios, but are marginally higher than the other recycling scenarios. However, hub recycling has a greater degree of quality control associated with production than recycling at the trench. Therefore, there is less potential to revisit a trench to repair defects when using a quality controlled product, and may in the long term have a cost advantage over recycling at the trench. For hub recycling HBM production, the materials transport distance is a key factor; hence, the cost effectiveness of HBMs produced at a recycling hub will be heavily dependent on the hub locations, which vary across the UK. Scenarios involving landfill of materials are the most costly, due to the addition of landfill tax and tipping charges. As expected, the use of primary materials combined with the arisings being landfilled is the most expensive scenario, combining a higher cost of transport with the addition of landfill costs. Material costs were highest in the South and lowest in Scotland/North Wales. For the backfill materials included in the cost analysis (graded granular and reclaimed), regional differences were small; for example, £1 per tonne for reclaimed fill. However, the variation in asphalt costs was almost £6 per tonne, which could result in considerable differences in overall costs. Minimal variation was apparent in subbase costs between the Midlands/South West and South General regions; however, subbase costs in Scotland and North Wales were approximately £2.50 per tonne lower. It was not possible to assess regional variation of HBM costs due to a lack of available cost data.

Figure 6: Cost comparison (All results are based on a 10 m trench, consistent with the carbon analysis)

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Ind

icat

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co

st £

Material cost £ Asphalt Material cost £ Subbase Material cost £ Fill

Landfill cost (excavated material) £ Transport cost (median distances) £ Subbase compaction labour £

Asphalt compaction labour £



8.0 Conclusions The study demonstrated that scenarios in which trench arisings are sent to landfill have high carbon and financial costs compared to recycling the material. CO2 emissions were estimated to be more than 40% higher than most other methods, and costs up to 35% higher. The embodied energy value associated with cement production results in a substantial increase in modelled CO2 emissions for the materials containing cement. Where superior performance of cement bound mixtures is not utilised within a pavement design, or permitted in the specification; for example where there is no reduction in the overlying asphalt thickness. Then the benefits from a CO2 perspective may be realised by partial replacement of cement or the use of an alternative hydraulic binder. This is already common practise for the production of HBMs for trench reinstatement. There is an added benefit that slow-setting hydraulic binders tend to produce reinstatement materials with a longer shelf life (workability period). Substantial CO2 savings were shown when arisings were recycled and recycled aggregates used instead of primary aggregate, reducing estimated CO2 emissions by over 40% (an estimated 16,000 tonnes of CO2 per 1,000 km of trench reinstatement), in addition to diverting 1.3 million tonnes of waste from landfill. This was also shown to be the most cost effective method Low-dig’ methods have a high potential for reducing waste to landfill. Although these methods often have higher initial costs than full length open-cut methods, as they require specialist equipment and training, they can be cost-effective for high volumes of due to savings in materials, labour and disposal costs. They can be extremely useful in situations where large open works are not feasible; and reinstatement can generally be completed faster, causing less disruption. ‘Realisation of the potential cost and CO2 savings of the various methods will depend on the local availability of materials and recycling hubs, in addition to regional and local variability in the cost of material and labour. These factors will, therefore, affect the feasibility of the various methods and materials for individual situations.

Figure 7: Indication of typical impacts of using different methods of trench reinstatement

Trench reinstatement option Cost CO2 Savings

Waste diverted

Highway occupancy

Trenchless / Low dig* Recycled aggregates fill & subbase / arisings recycled HBM fill & subbase (PFA) / arisings recycled** Foamed concrete / arisings recycled*** Primary aggregates fill & subbase / arisings recycled Primary aggregates fill & subbase / arisings sent to landfill

* Trenchless technologies may have a high initial cost, but this will be offset when used for an appropriate

application. ** HBMs facilitate diversion of material from landfill by recycling arisings that may otherwise be considered

unsuitable for use. *** Using foamed concrete will not be using recycled aggregate, but the arisings can still be sent for

recycling.

References i WRAP, 2005. Identifying opportunities for recycling of excavated spoil from utility works within local authority areas, and promoting the use of recycled materials through good practice in procurement. WRAP, Banbury. ii DEFRA, National indicator 186: Reducing CO2 emissions in local authority area, Available online - www.defra.gov.uk iii HAUC, 2002. Specification for the Reinstatement of Openings in Highways. The Stationary Office, London. iv Highway Authorities & Utilities Committee Advice Note. 2008/03. Guidance Note on the European Asphalt Standards. v HA, 2009. The Manual of Contract Documents for Highways Works Volume 1. Specification for Highways Works. Series 900. Road Pavements - Bituminous Bound Materials. The Stationery Office, London. vi Highways Authorities Product Approval Scheme (HAPAS) (2001). Guideline for the Approval and Certification of Permanent Cold-Lay Surfacing Materials (PCSMs). British Board of Agrement (BBA). vii PD 6691:2007, Guidance on the use of BS EN 13108 Bituminous mixtures. Material specifications. British Standards Institute. viii Highway Authorities & Utilities Committee Advice Note. 2009/01. The Use of Alternative Reinstatement Materials. ix Highway Authorities & Utilities Committee. (2006). Practical Guide to Street Works. Dft London TSO. x HA, 2009. Manual of Contract Documents for Highways Works. Volume 1. Specification for Highways Works. Series 1000. Road Pavements – Concrete Materials. The Stationery Office, London. xi HA, 2009. Manual of contract documents for highways works. Volume 1. Specification for highways works. Series 800. Road pavements - unbound, cement and other hydraulically bound mixtures. The stationery office, London. xii HA, 2009. Manual of Contract Documents for Highways Works. Volume 1. Specification for highways works. Series 700. Road pavements - General. The stationery office, London. xiii WRAP, 2005. The Quality Protocol for the production of aggregates from inert waste. WRAP, Banbury xiv BSI, 2003. BS EN 13285:2003 Unbound mixtures. Specifications xv WRAP Suppliers Directory, available online at aggregain.wrap.org.uk/supplier_directory/index.html

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