Sustainability in Public Works Conference 27 – 29 July 2014

IDM Sustainable Infrastructure Guidelines: Case Study David Conley1, Julius Dowson2 1

Master of Business Administration, Deakin University, Victoria Bachelor of Engineering (Civil), University of Tasmania, Hobart

2

Bachelor of Engineering, University of Tasmania, Hobart

ABSTRACT: The IDM Group is a group of 41 Victorian Councils that have adopted a common infrastructure standard titled the Infrastructure Design Manual (IDM). A supplement to the IDM, the Sustainable Infrastructure Guidelines, was developed by the IDM Group in 2012 with the aim of providing advice on alternative design considerations and materials that will deliver more sustainable infrastructure through  Using recycled materials  Reducing the carbon footprint of infrastructure projects  Reducing maintenance and operating costs  Utilising water in more efficient ways  Utilising materials from sustainable sources This project was funded with the support of the Victorian Government under the Victorian Adaptation and Sustainability Partnership - formerly known as the Victorian Local Sustainability Accord. The IDM Group then selected three demonstration projects that were to be based on the Guidelines and commissioned a case study to:  Develop key performance indicators to assess the effectiveness of the application of the Guidelines  Document the design, construction and delivery of the demonstration projects  Compare the sustainable design and construction approach for each project with a more conventional approach assessing cost, availability of materials, constructability and total carbon emissions Two of the projects were in the City of Greater Geelong and one was in the Colac Otway Shire. The projects included a trafficked laneway redevelopment, the construction of a footpath and streetscape and pavement rehabilitation using Foamed Bitumen Asphalt (Foam Mix). The demonstration projects have recently been completed. The outcomes will be presented at the conference. KEYWORDS: idm, sustainable infrastructure, low carbon concrete, eco-reo, recycled crushed concrete, foammix. .

1.

Introduction

The IDM Group is a group of 41 Victorian Councils that have adopted a common infrastructure standard titled the Infrastructure Design Manual (IDM). A supplement to the IDM, the Sustainable Infrastructure Guidelines, was developed by the IDM Group in 2012 with the aim of providing advice on

alternative design considerations and materials that deliver more sustainable infrastructure through  Using recycled materials  Reducing the carbon footprint of infrastructure projects

 Reducing maintenance and operating costs  Utilising water in more efficient ways  Utilising materials from sustainable sources The IDM Group then selected 3 demonstration projects that were to be based on the Guidelines and commissioned a case study to:  Develop key performance indicators to assess the effectiveness of the application of the Guidelines  Document the design, construction and delivery of the demonstration projects  Compare the sustainable design and construction approach for each project with a more conventional approach assessing cost, availability of materials, constructability and total carbon emissions The three projects were:  Steam Packet Place – a laneway in the City of Greater Geelong  Grant Street Footpath - a footpath and streetscape project in Forrest (Colac Otway Shire)  Pavement rehabilitations using foamed bitumen asphalt (FoamMix) at Grange Park Drive, Waurn Ponds and Townsend Rd, Moolap in the City of Greater Geelong

2.

Steampacket Place

2.1

Background

The site is a laneway near the waterfront of Geelong that caters for service vehicles and pedestrians.

2.2

Description of Works

The works included the removal of existing pavement and the construction of new pavement, drainage infrastructure, street furniture, lighting and landscaping. Sustainable elements have been incorporated throughout the project and are summarised in the following sections.

2.2.1

Pavement

The existing asphalt pavement was demolished and reusable excavated materials were taken to a recycling plant. After excavation works, a new reinforced concrete pavement was constructed. The concrete pavement consists of a low carbon concrete with Eco-reo™ reinforcement. The unbound sub base layer is recycled crushed concrete as opposed to a natural gravel or crushed rock. The low carbon concrete mix design was analysed for embodied carbon content. The concrete mix uses Supplementary Cementitious Materials (fly ash and slag) and alternative aggregates (recycled bricks, waste sand and crushed concrete). In addition to the use of alternative ingredients in the concrete mix, 100% recycled water was used which was collected in the plant from its wash down processes. Eco-reo™ is manufactured by Onesteel and utilises energy reducing Polymer Injection Technology and recycled steel scrap content (typically over 66%). Embodied carbon data has not yet been quantified for this material; however suppliers report a decrease in electricity use and heat requirements which result in a reduction of embodied carbon. It is estimated that CO2 emissions of this steel are reduced by 5% compared to conventional steel reinforcing. Recycled vehicle tyres can be used as an alternative carbon injectant with benefits in reduction in the number of tyres being sent to landfill each year.

2.2.2

Drainage

A mulit-layered biofilter and retention system was constructed in place of a concrete kerb. The layers consist of a vegetated layer, overlying a filter media, transition layer and drainage layer with a perforated collection pipe. The runoff is filtered through the surface vegetation which settles coarse to medium sized sediments, then percolates through the well-graded sand filter media which filters fine sediment and finally into the perforated collection pipe for discharge into existing stormwater infrastructure.

Photo 4: Brachychiton Acerifolius and tufting plants in rain garden Photo 2: Bioretention system during construction A central raingarden pit was also constructed which is positioned to collect storm water runoff and filter it through a multilayered soil system, eventually discharging excess water to existing drainage infrastructure. Irrigation for these gardens is to be sourced from captured runoff water.

2.3

Key Performance Indicators

Key Performance Indicators (KPI) as listed in Table 1 were developed for the projects. Table 1: KPIs Steampacket Place KPI

Evaluation Criteria

Sustainable Infrastructure Checklist

Evaluate the project against the checklist

Carbon footprint

Assess carbon footprint for the project and compare with a conventional approach

Cost

Costs of the project compared with a conventional approach

Constructability

Ease of construction and use of alternative materials and designs

Availability of materials

Were specified alternative materials readily available

Design initiatives

Identify implementation of specific sustainable design initiatives from the Sustainable Infrastructure

Use of sustainable/alternative materials

% use of sustainable/alternative materials

Net flora increase

Identify if there is a net increase in

Drainage

Determine % reduction in runoff and pollutants

Maintenance

Identify any maintenance concerns

Appearance/aesthetics

Determine if the Sustainable Design approach has resulted in enhanced appearance/aesthetics

Photo 3: Completed rain garden

2.2.3

Landscaping

Eight trees (Brachychiton Acerifolius) and 31m2 of tufting plants (Patersonia Occidentalis) were planted. The plants will capture carbon dioxide and therefore contribute to carbon reduction in the atmosphere. They also add aesthetics and the garden area beneath the trees reduce impervious areas with corresponding reduction in stormwater runoff and also aiding groundwater recharge.

2.3.1 Sustainable Infrastructure Checklist

reduces the amount of natural gravels and sands by 44%.

A Sustainable Infrastructure Checklist, which was developed under the Sustainable Infrastructure Guidelines, was completed for this project and a rating of 3 stars out of 5 was achieved.

Concrete Pavement

The bricks are clean rejects that are crushed and screened to 7mm size. The recycled crushed concrete is a 14mm nominal size material produced from clean waste concrete. The manufactured sand is a 2 mm nominal size fine sand and is made by reprocessing waste material generated through the production of coarse aggregates at quarries. The waste material is generally finer than 5mm, and with variable properties. Production of manufactured sand from this waste material generally involves crushing, screening and washing.

The conventional alternative to the low carbon concrete pavement is a GP cement concrete with crushed rock and natural sand aggregate. Table 2 compares the mixes.

The recycled bricks, crushed concrete and manufactured sand are all waste products which would otherwise be sent to landfill and therefore have very low embodied carbon.

Table 2: Concrete Mix Comparison

The low carbon concrete pavement also used Eco-Reo™ which has the same engineering properties as conventional reinforcement and is therefore a 1:1 quantity comparison.

2.3.2

Carbon Footprint

The carbon footprint of the project was compared with a “conventional” design for the two main elements of concrete pavement and drainage system.

Low Carbon Concrete

Conventional Concrete

Quantity (kg/m3)

Quantity (kg/m3)

General Portland Cement

253.75

350

Slag

68.75

0

Fly ash

27.5

0

Coarse and Fine Aggregates

Quantity (kg/m3)

Quantity (kg/m3)

Natural

1030

1840

Recycled

710

0

Waste Sand

100

0

Cementitious Materials

Low carbon concrete has a 27.5% lower GP cement content. Slag and Fly ash are both waste materials which are created during other processes and if not reused will be sent to landfill and accordingly have a very low embodied carbon content. Aggregate for the low carbon concrete contains recycled bricks, recycled crushed concrete and manufactured sand and thereby

The new pavement was placed on a recycled crushed concrete base which reduced the quantity of crushed rock or natural gravel base that would normally be required. Table 3: Concrete Pavement Emission Comparison Low Carbon Concrete

Conventional Concrete

Concrete

Emissions (kgCO2)

Emissions (kgCO2)

Cementitious Material

19060

26290

Natural Aggregates

1980

3538

Recycled Aggregates

1160

0

Reinforcing

2759

2904

TOTAL

24959

32732

Table 4: Sub base Emission Comparison

Bioretention

K&G

Concrete

Emissions (kgCO2)

Emissions (kgCO2)

Cementitious Material

3777

1158

Natural Aggregates

392

156

Recycled Aggregates

230

0

Reinforcement Bar

547

128

Drainage System

TOTAL

4946

1441

The drainage system follows Water Sensitive Urban Design principles and was not specifically designed for the purpose of reducing the carbon footprint of the finished facility. The most important element in this drainage system is the Bioretention system which collects most of the runoff and effectively manages the stormwater by retention and filtering. A conventional approach would utilise kerb and gutter to collect runoff and direct it to a pit rather than the bioretention trench. The kerb and gutter solution can only be compared to the bioretention in terms of moving the water from point A to point B, and does not provide a reduction in the runoff volume during/after rain events or a reduction in pollutant levels.

2.3.3

A standard kerb was compared with the bioretention trench. The kerb has a crosssectional area of 0.12m2 and therefore contains around 4m3 of concrete. The bioretention trench has a larger cross sectional area of 0.54m2 and therefore contains around 17m3 of concrete. The bioretention trench also includes 10.4m3 of drainage materials (natural gravel) and PVC pipes. The bioretention pit option has a higher carbon footprint than the kerb option but provides water quality benefits that cannot be achieved with kerb and gutter.

 The recycled crushed concrete sub base had excellent workability and was readily compacted.

Gravel Subbase

Crushed Concrete Base

Conventional Base

Emissions (kgCO2)

Emissions (kgCO2)

Table 5: Drainage Emission Comparison

Natural Aggregates

2346

Recycled Aggregates

1748

TOTAL

1748

2346

Cost Analysis

For cost comparison purposes the low carbon concrete was replaced with conventional concrete and the bioretention system was replaced with kerb and gutter. The quoted price for the project was $289,035. The conventional design was estimated to cost $261,314.

2.3.4

Constructability

The Contractor highlighted the following points with respect to constructability:  The low carbon concrete and Eco-Reo reinforcement acted identically to conventional Portland cement and reinforcement

 The biofilter was the most difficult and time consuming element to construct but was well within the capabilities of workers using typical equipment and techniques.

2.3.5

Availability of Materials

All required materials were readily available from local suppliers in Geelong. The most difficult material to obtain was the sand filter media for the bioretention trench. The filter had strict grading requirement which could not be met from the supplier’s standard production runs and required additional processing to meet the specification.

2.3.6

Specific initiatives that reduced the carbon footprint were specifying a low carbon concrete pavement and using alternative materials for bedding. Supplementary Cementitious Materials in the concrete mix correlate to a large decrease in overall carbon emissions and the use of alternative aggregates reduces the need for virgin materials. The project also contains a drainage and landscaping solution with environmental and ecological benefits including: reduction in impervious surfaces, reduction in pollution, improvement to water quality and net flora increase.

2.3.7 Use of Sustainable/Alternative Materials The percentage use of sustainable/alternative materials is summarised as follows:  The proportion of slag and fly ash in the concrete reduces the GP cement content by 27.5%  The recycled bricks, recycled crushed concrete and manufactured sand in the concrete reduce the amount of virgin aggregates by 44%  The crushed concrete subbase is entirely a waste material and reduces the amount of virgin aggregates for this element by 100%

2.3.8

Net Flora Increase

Eight trees (Brachychiton Acerifolius) and 31m2 of tufting plants (Patersonia Occidentalis) were planted providing a net flora increase when compared with the previous conditions.

2.3.9

Table 6: Runoff rates and volumes

Design Initiatives

ARI (years)

Rainfall intensity (mm/hr)

Peak runoff (L/s)

Total runoff volume (m3)

10

90.6

19.1

10.3

50

137

28.8

15.6

100

160

33.7

18.2

During a 10 year ARI event the total runoff can be accommodated within the filter media and outflow is limited to 1.2 L/s. During higher return periods, the runoff volume exceeds the available storage and inflow to the stormwater system occurs. The bioretention system also reduces peak runoff considerably as shown in Table 7. Table 7: Reduction of peak outflows ARI (years)

Peak runoff (L/s)

10

19.1

1.2

94

50

28.8

20.4

29

100

33.7

26.5

21

Percentage reduction (%)

Pollutant reduction due to the bioretention was estimated in accordance with WSUD Engineering Procedures (CSIRO 2006 Figure 5.4 to 5.6) and is shown in Table 8. All are within target reduction levels proposed by EPA Victoria. Table 8: Pollutant reduction rates Pollutant

Percentage reduction (%)

Target reduction (%)

Suspended solids (SS)

97

80

Total Phosphorous (TP)

86

45

Total (TN)

47

45

Drainage

The bioretention trench was analysed under 10, 50 and 100 year storm events. The system collects water from an impervious contributing area of about 842m2. The peak runoff rate and total runoff volume during the three different return periods were assessed. Basic parameters and results are given in Table 6.

Estimated peak inflow to stormwater system (L/s)

Nitrogen

2.3.10 Maintenance The most critical maintenance item is the bioretention trench. Vegetation is key to maintaining the porosity of the filter media and a healthy growth of vegetation is critical to its performance. The most intensive period of maintenance is during plant establishment when weed removal and replanting may be required. The bioretention system will also require monitoring in the early stages as deposition of sediments can affect plant growth reduce the infiltration rate of the filter media. Ongoing maintenance will include litter removal which will require removal of the grate. Pruning of plants will also be required at regular intervals.

2.3.11 Appearance/aesthetics The inclusion of planted trees, the bioretention trench and other landscaping elements has improved the general appearance of the laneway by providing lighter neutral tones accompanied by green natural elements and creative lighting. It is a useable space and still serves its primary purpose of pedestrian and vehicular access.

3500kg CO2. The benefit of the drainage works were not carbon reduction but improvement of stormwater quality and runoff volume. The overall cost was increased by $27,721 when the sustainable design was adopted. This is due to the concrete mix and also the landscaping and drainage elements. There were no issues identified regarding constructability or availability of the sustainable design.

3.

Grant Street Forrest Footpath

3.1

Description of Works

Colac Otway Shire carried out construction works for 334m of new 1.5m wide footpath at Grant Street, Forrest and upgraded adjacent carparking. Sustainable materials were incorporated in the footpath and are summarised below.

Photo 6: Grant Street Forrest Footpath

3.1.1

Footpath

The footpath was constructed of 125mm thick Green Star 3 Rated Concrete The concrete contains a high proportion of slag, manufactured sand and recycled water as well as Eco-Reo™ reinforcing.

3.1.2 Photo 5: Near on completion Drainage System

2.4

Findings

The overall carbon emissions were reduced by 4,900kg CO2 when the sustainable design was adopted. The low carbon concrete reduced the total emissions associated with the concrete pavement by 8,400kg CO2, however, the bioretention trench required more concrete than a standard kerb and channel which reduced these savings by

Car Park

The car park has a granular pavement with an asphalt wearing surface. No sustainable elements were applied to this part of the works. An attempt was made to reuse some of the existing granular material however when excavated it proved to be of poor quality and mixed with the clay subgrade and only 5 m3 was able to be reused.

3.2

Key Performance Indicators

The same Key Performance Indicators (KPIs) were applied to this project as for the Steampacket Place Project.

3.3 Sustainable Infrastructure Checklist The Sustainable Infrastructure Checklist was completed and an overall rating of 2 stars out of 5 was achieved. The low rating occurs because some items in the checklist had the potential, in an ideal situation, to be included in the project but were not. From practical and cost considerations there is always going to be a limit on the number of sustainability enhancements that can be considered in a project of this type.

3.3.1

Carbon Footprint

The carbon footprint of the project was compared with a “conventional” design without the sustainable elements. The conventional alternative to the low carbon concrete footpath is a GP cement concrete made up of natural aggregates. The Green Star 3 concrete uses Supplementary Cementitious Materials (slag) and also alternative aggregates (manufactured sand). The mix uses a very high proportion of slag (40%), which, in turn, allows for large reductions in the quantity of GP cement required. A summarised comparison of the alternative and conventional mixes is provided in Table 10. Table 10: Concrete Mix Comparison Green Star

Conventional

Cement

Quantity (kg/m3)

Quantity (kg/m3)

GP Cement

150

310

Slag

100

0

Aggregates

Quantity (kg/m3)

Quantity (kg/m3)

Natural

1620

1904

Waste Sand

284

0

The Green Star Concrete also uses EcoReo® rather than conventional reinforcement. The Eco-Reo® has the same engineering properties as conventional reinforcement and is therefore a 1:1 quantity comparison. Table 11: Concrete Emissions Comparison Low Carbon Concrete

Convention al Concrete

Concrete

Emissions (kgCO2)

Emissions (kgCO2)

Cementitious Material

19060

26290

Natural Aggregates

1980

3538

Recycled Aggregates

1160

0

Reinforcement Bar

2480

2610

TOTAL

24680

32438

3.3.2

Cost Analysis

In assessing the difference in costs, the only change was replacement of the low carbon concrete with conventional concrete. The quoted price for this project was $103,401. The Contractor advised that the rate for the concrete would decrease by $2/m2 for the low carbon concrete, and $4/m 2 for the curing. Therefore the conventional design was estimated to cost $100,395.

3.3.3

Constructability

The low carbon concrete had identical construction methodology in terms of plant and equipment required, however it did require wet curing for 7 days to mitigate against dusting up and cracking. It was the Contractor’s opinion that this amount of curing would not have been required for conventional GP concrete placed under the same conditions

3.3.4

Availability of Materials

The footpath works at Colac were procured through a standard tendering process and a number of tenderers expressed concerns about sourcing the low carbon concrete. The successful Contractor advised that he had no

difficulties sourcing the Green Star 3 Rated Concrete. This suggests that there is some industry resistance to the use of these alternative materials.

3.3.5 Use of Sustainable/Alternative Materials

4.

Foamed Bitumen Asphalt

4.1

Background

Geelong City Council utilised FoamMix Recycled Asphalt technologies in two pavement rehabilitations: Grange Park Drive, Waurn Ponds and Townsend Rd, Moolap.

The percentage use of sustainable/alternative materials in the footpath construction is summarised as follows:  The proportion of Slag in the Green 3 Star concrete reduces the GP cement content by 52%.  The manufactured sand in the Green 3 Star concrete reduces the amount of virgin aggregates in the concrete by 14.9%.

3.3.6

Net Flora Increase

No net Flora increase was achieved for the project.

3.3.7

Maintenance

No additional maintenance requirements are anticipated for this project. The low carbon concrete is expected to perform identically to conventional GP concrete.

3.3.8

Appearance/aesthetics

The final concrete finish was inspected in June 2014 and no cracking or defects were observed. This is a positive outcome for the concrete mix that had a large slag component.

3.3.9 Construction and Maintenance Costs Maintenance costs of the footpath constructed with low carbon concrete are expected to be identical to a conventional concrete.

3.4

Findings

The overall carbon emissions were reduced by 7,800 kgCO2 when the sustainable design was and the overall cost was increased by $3,006. There did appear to be some industry resistance to the use of the Green Star Concrete and a lack of understanding of the objective behind its use.

4.2

Description of Works

Both pavements were in need of rehabilitation due to visible pavement defects caused by a weak subgrade and heavy vehicles. The sustainable treatment that was proposed was pavement reconstruction using FoamMix as a stabilised base layer followed by an asphalt seal. City of Greater Geelong advised that for these particular roads, full reconstruction would be the conventional treatment option and they provided details of a similar project (Pizer Street) for cost comparison purposes. The FoamMix treatment produces a bound pavement with increased stiffness and achieves this by stabilising the existing material rather than increasing the pavement thickness with new material.

4.2.1

Pavement

The FoamMix consists of 95% recycled materials and foamed bitumen which are combined using specialized equipment. The process involves excavating the old pavement to a depth of 200mm, collecting the material and stockpiling it. The material is processed through a recycler which combines the reclaimed material with a foamed bitumen mixture. The FoamMix asphalt is then returned to the site and spread and compacted.

4.3

Key Performance Indicators

The Key Performance Indicators (KPI) used for the previous two projects were also used for this project.

4.3.1 Sustainable Infrastructure Checklist The Sustainable Infrastructure Checklist was completed for this project and an overall rating of 5 stars out of 5 was achieved.

4.3.2

Carbon Footprint

The carbon footprint of the project was compared with a “conventional” design without sustainable elements. The conventional treatment proposed by City of Greater Geelong was to increase the pavement thickness above the subgrade by reconstruction. This option involves excavating 330 mm below the road surface and replacing with two 150 mm of gravel base layers and 30 mm of asphalt wearing course. The gravel base course is a virgin quarried material and transported from elsewhere to the site. The excavated pavement is treated as a waste material and carted offsite. The FoamMix stabilisation treatment option is different to the reconstruction as it reuses the excavated base course. The excavated gravel is mixed with Foamed Bitumen to increase the stiffness of the material. Due to this increase in stiffness, the layer is thinner than the granular pavement proposed in the reconstruction option. Table 13: Comparison

Pavement

Type

Emissions

Foam Mix

Conventional Flexible Pavement

Emissions (kgCO2)

Emissions (kgCO2)

Asphalt

63819

63819

Foamed Bitumen Asphalt

#info from road stone 32130 85092

117222

Cost Analysis

The contractor quoted both jobs at a square metre rate which included the 30 mm of asphalt and FoamMix. For cost comparison purposes City of Greater Geelong provided a square metre rate for a similar job that used the conventional reconstruction option. For both Grange Park Drive and Townsend Rd, the subgrade was found to be of poor quality after excavation of pavement material and not capable of withstanding construction equipment movements and therefore was stabilised with lime to provide a suitable working platform. Even allowing for this additional cost the foam mix option is still cheaper than the granular pavement replacement. The cost comparison summarised in Table 14 below. Table 14: Pavement Type Cost Comparison Rate (/m2) Area

No SG Stab.

SG Stab

Grange Park Drive

2100m2

$73

$120

Townsend Road

1696m2

$63

$120

Pizer St

883m2

$172

n/a

4.3.4

Constructability

The main problem in both projects was insufficient cover over a poor subgrade when the FoamMix was being placed and compacted. After the 200 mm depth of pavement had been excavated there was only 80 mm of gravel overlying the subgrade. The subgrade could not support the truck loads required to place the Foam Mix and may have also become a problem for compaction of the Foam Mix. In both trials the subgrade was stabilised with lime to achieve adequate strength. Following placement the pavement was prepared for asphalt surfacing and could be driven on the same day.

4.3.5

Aggregates TOTAL

4.3.3

Availability of Materials

FoamMix was readily available from a local supplier. The process can be carried out at a fixed plant or by using a mobile recycling plant, provided there is a suitable working

area and stockpile site adjacent to the project..

5.

4.3.6

The case studies were fairly narrow in scope and projects were required to fit in with existing infrastructure. Therefore sustainable opportunities were limited and projects were heavily focussed on material substitution rather than a complete sustainable design. Carbon emission savings of 5 to 22 tonnes were realised across the case studies. In pure carbon accounting terms at the current carbon price of $24/tonne the emission savings do not come close to matching the additional construction costs at Steampacket Place and Grant Street.

Design Initiatives

The FoamMix process maximises the reuse of pavement materials. Pavement re-use is one of the fundamental principles of the Sustainable Infrastructure Guidelines and a key consideration at the design stage when considering pavement rehabilitation.

4.3.7 Use of Sustainable/Alternative Materials FoamMix is essentially a cold mix process and, compared with conventional asphalt, manufacturers claim that carbon emissions are approximately 50% lower. The benefits of using a foamed bitumen process include:  Improved safety due to lower production and handling temperature  Because of lower temperature it has a longer working time and can be taken to more remote sites without compromising its performance  Requires less energy to produce

4.4

Maintenance Costs

Maintenance costs of the pavement are expected to be identical to a full pavement reconstruction

4.5

Findings

The overall carbon emissions were reduced by 22,130 KgCO2 when the sustainable design was adopted. The overall cost was reduced by $52/m2 compared with a conventional reconstruction. Some constructability issues were encountered when soft subgrade material was uncovered during construction which led to additional unplanned subgrade improvement works. Accounting for the subgrade stabilisation the overall cost was still lower than conventional reconstruction. It is also likely that subgrade improvement would have been necessary under a conventional reconstruction approach.

Conclusions

Referring to the aims of the Sustainable Infrastructure Guidelines outlined at the start of the paper we can assess whether adoption of the various initiatives has resulted in those aims being met.  Using recycled materials – achieved for all projects.  Reducing the carbon footprint of infrastructure projects – achieved for all projects.  Reducing maintenance and operating costs – not achieved for any of the projects as maintenance and operating costs largely unchanged  Utilising water in more efficient ways – achieved at Steampacket Place but not achieved at Grant Street or the pavement rehabilitation projects.  Utilising materials from sustainable sources – achieved for all projects.