Estimating carbon dioxide emissions for aggregate use

Proceedings of the Institution of

Civil Engineers

Engineering Sustainability 162September 2009 Issue ES3

Pages 135–144

doi: 10.1680/ensu.2009.162 .3.135

Paper 800013Received 13/07/2008

Accepted 21/04/2009

Keywords:environment/recycling & reuse of

materials/urban regeneration

Andrew ThomasResearch Fellow,

School of Engineering,

University of

Birmingham,

Edgbaston, UK

D. Rachel LombardiSenior Research Fellow,


University of

Birmingham,

Edgbaston, UK

Dexter HuntResearch Fellow,


University of

Birmingham,

Edgbaston, UK

Mark GaterellSenior Lecturer, School

of Engineering,

University of

Birmingham,

Edgbaston, UK

Estimating carbon dioxide emissions for aggregate use

A. Thomas MICE, MSc, D. R. Lombardi PhD, D. Hunt MICE, PhD and M. Gaterell MCIWEM, CEnv, PhD

Tools such as the carbon dioxide estimator tool from the

UK Waste and Resources Action Programme (WRAP)

and Aggregain have been developed to allow engineers to

quantify and optimise carbon dioxide emissions asso-

ciated with aggregate use. An extended WRAP tool

methodology has been developed and is illustrated

through assessing the relative carbon dioxide perfor-

mance of different aggregate sourcing options for the

large redevelopment project known as Masshouse, in the

centre of Birmingham, UK. Previously unconsidered

factors such as aggregate quality and highway congestion

have been included. It is shown that significant reductions

in carbon dioxide emissions can be achieved where site-

derived demolition waste is reprocessed for use on site as

a recycled aggregate and that relative haulage distances

are of particular importance to overall carbon dioxide

emissions. As these outcomes depend upon the distances

to materials sources and sinks in Birmingham, it is

concluded that the carbon dioxide emissions associated

with aggregate sourcing are not just a function of material

type but also of local conditions. Therefore, the devel-

oped methodology provides a useful decision-making

framework for assessing aggregate sourcing that accounts

for factors such as distribution of materials sources and

sinks, aggregate grade, and the effects of road speed and

congestion.

1. INTRODUCTION AND BACKGROUND

1.1. Introduction

This paper provides an insight into the sustainability-related

consequences of decision-making scenarios associated with

redevelopment projects involving both demolition and use of

high-quality unbound aggregates (a term used to denote an

aggregate not mixed with other materials such as cement or

bitumen). This is achieved through development of an appraisal

methodology and illustration of its use in the analysis of a

redevelopment in the heart of Birmingham, UK, known as

Masshouse, which is considered to have optimised aggregate

sustainability in its construction. For Birmingham, the sustain-

ability of Masshouse is important as it reflects the interest being

shown in the sustainability of the surrounding Eastside area.1

The appraisal methodology is based on embodied energy and

emissions data (using reduced carbon dioxide emissions as a

proxy for improved sustainability) from the carbon dioxide

emissions estimator tool2 produced by the UK Waste and

Resources Action Programme (WRAP)3 and Aggregain4 and

from a data source upon which it relied.5 This tool, referred to

here as the WRAP tool, has provided a significant step forward

in the ability of engineers to quantify carbon dioxide emissions

associated with aggregate sourcing. For the purposes of this

study, the calculation was extended to include estimated

emissions as a result of haulage vehicle speeds (which are in

turn a function of highway congestion) and variations in

emissions associated with the production of different aggregate

grades. This provided a means to determine the extent to which

these context-specific factors impact on emissions arising from

aggregate use.

As well as the actual scenario of in situ recycling adopted for the

Masshouse project, a number of other scenarios were analysed in

order that their relative impact on carbon dioxide emissions could

be considered on a like-for-like basis. In this manner, not only

was the relative sustainability of aggregate use in the Masshouse

project critically examined but the examination was also

extended to potentially less sustainable decision-making sce-

narios. Furthermore, through detailing specific activities within

each scenario – that is, material production and transportation –

the resulting emissions summaries provide an insight into how

sustainable aggregate sourcing can currently be. The methodol-

ogy presented thus allows developers to assess the carbon dioxide

emissions associated with their designs, essentially using the

design as a functional unit embodying a certain tonnage of

aggregates, and to compare it with a range of alternative

scenarios in order to develop the lowest emissions option.

1.2. A brief history of Birmingham ring road and

Masshouse Circus

The Masshouse area was most likely named during the 17th

century following the construction of a local Catholic mass-

house.6 During Victorian times the area was well populated with

residents and thriving local industries (e.g. tanneries); this was

due in no small part to its connectivity with Birmingham’s city

centre and the canal and railway infrastructure, including Moor

Street and Curzon Street Stations (the latter being Birmingham’s

first railway station). In 1864, Curzon Street Station was

replaced by a new railway station. New Street Station, as it was

named, was situated almost 1 km to the western side of the two

main roads that served the Masshouse area, Masshouse Lane and

Jennens Road (aptly named after a local landowner). Curzon

Street was left empty and the popularity of the area and its

industry began to decline in part due to the declining use of

Engineering Sustainability 162 Issue ES3 Estimating carbon dioxide emissions for aggregate use Thomas et al. 135

canal transport of goods (although some canal transport did

remain in use until the late 1950s).

In the first decades of the 20th century, the presence of motor cars

on the inner city roads was increasing; subsequently, pressures for

upgrading began to mount on the public works committee. This

continued in the periods between the world wars as traffic on the

roads became increasingly heavy and congested. By the 1950s,

Birmingham had become well established as a motor city and the

city council realised that a significant upgrading programme was

unavoidable. With two clear objectives in mind – enlarge business

and shopping areas of the city centre and provide a solution to

traffic problems – pockets of land were bought and cleared. In

1967, construction began on an inner ring road, which included

7?7 km of dual carriageway, two flyovers (Masshouse Circus and

Holloway Circus), five bridges, four footbridges, four underpasses,

one twin tunnel, 52 pedestrian subways, 1067 m of elevated

carriageway, two mains tunnels (one almost 17 m deep), 20 public

conveniences, 45 shops and four car parks.7 It was completed in

1971, and five years later the ring road was hailed as a success

story having completed its objectives satisfactorily.8 The sup-

porting structure for the Masshouse Circus flyover included

single- and double-span portal frames below the carriageways and

cantilevered walkways; the 7?6 m height allowed for provision of

car parking and pedestrian underpasses below.

By reducing congestion and improving public transport net-

works in the city centre, it could be argued that construction of

Masshouse Circus provided some sustainability benefits at the

time. Cowles and Piggott8 described Birmingham as a progres-

sive city that was getting on with the job of redevelopment:

construction of the inner ring road sparked off a decade (1965–

1975) of rebuilding work within many parts of the city centre.

However, the length of time required to implement such huge

projects is often accompanied by changes in society; road

systems then become outmoded, which in turn leads to knock-

on effects, as with Masshouse Circus. This section of road

quickly became known as the ‘concrete collar’ because it in fact

restricted expansion of the city centre. This caused the cost of

office space within the inner city centre to rise substantially – to

levels that deterred potential occupiers. In addition, the areas

outside the collar became isolated and impoverished. The

pedestrian underpasses in the form of tunnels often became

occupied by homeless people or were used for illegal or illicit

activities. Importantly, the appearance of the elevated concrete

roadways began to lose favour with local workers and residents.

In 1999, Birmingham City Council launched a new regeneration

project, commonly referred to as Eastside. At this time, the

Masshouse Circus roadway ran along the north-west boundary

of the 170 ha development area and the ‘breaking of this

concrete collar’ was seen as the necessary first step in opening

up a new gateway to Eastside. In the early days of strategic

thinking about the future of Eastside, sustainability was neither

a central, nor ancillary, feature.9 However, the costs for

removing the concrete collar and refashioning the inner ring

road were covered through funding gained from the objective 2

programme of the 2000–2006 European Regional

Redevelopment Fund (ERDF).10 This funding required that

certain sustainability objectives be met (e.g. land remediation,

promotion of energy- and water-efficient design, energy

consumption strategy, carbon-free development, use of waste

materials, waste reduction and recycling schemes.10 For

Masshouse, this required that concrete rubble from demolition

of the flyover be recycled (i.e. crushed and reused) within the

new construction works.

In March 2002, the £24?2 million demolition of Masshouse

Circus began. Large pockets of land were cleared, allowing for a

new ground-level transport system (including bus routes and

pedestrian crossings). During the demolition 20 000 m3 of

concrete were recycled and used within the refashioned inner

ring road that now connects the newly regenerated Bullring

shopping centre with Jennens Road. Opened in August 2003,

this 18-month project was completed on time and within

budget. A view of the area during redevelopment is shown in

Figure 1. Two development sites were created from what once

formed Masshouse Circus and these were subsequently pur-

chased by David McLean Developments in 2003. By 2010, some

35 years after the ring road was hailed a success, Masshouse

Circus will have been replaced with new apartments, offices and

areas of retail. The longevity of this new development can only

be assessed when looking back in future years. It could be

argued that a constant cycle of redevelopment is unavoidable

for a city like Birmingham. However, by recycling materials,

some of the harmful environmental effects of regeneration can

be reduced. How far this reduction can go is the topic of this

paper.

2. METHODOLOGY

2.1. System boundary

Figure 2 depicts the sequence of events leading to the

redevelopment of Masshouse, starting with its original con-

struction in 1967. The system boundary of this analysis is shown

by the dashed box: events prior to and including the demolition

are not included. The analysis focuses on the recycling (labelled

(R) in Figure 2), landfill (L) and primary aggregate (P) materials

streams relevant to the construction process; thus neither the

embodied carbon dioxide associated with the original con-

struction of the Masshouse site nor the emissions associated

with demolition are included in the system boundary. Lack of

consideration of these emissions can be justified on the basis

that the construction and later demolition of the obsolete

structure is not a variable in the current redevelopment – it will

not change from scenario to scenario.

It should also be noted that only the relevant technical systems

Figure 1. The Masshouse area during demolition (looking west)

136 Engineering Sustainability 162 Issue ES3 Estimating carbon dioxide emissions for aggregate use Thomas et al.

for aggregate production and haulage were considered; placing

and compaction were considered external constants for all

aggregate types and so were not included in the analysis (for

further details of these emissions see the WRAP tool2 and

Stripple5). Also, it should be acknowledged that other factors,

including noise nuisance, the health effects of emissions other

than carbon dioxide and impacts on road users, may impact on

sustainability. These factors were considered to be outside the

scope of this study, as was the use of bound aggregates (e.g.

bitumen and cement bound) even though they can be analysed

using the WRAP tool.

2.2. Background data on demolition, waste disposal and

aggregate sourcing

Based on the total volume of demolition arisings from

Masshouse (20 000 m3), at an average density of 2?4 t/m3,

48 000 t of primarily concrete waste was generated to be either

landfilled or recycled. Based on 30 t loads per haulage vehicle,

haulage off site would therefore require 1600 vehicle journeys

(or 2400 journeys for 20 t vehicles). As the flyover was

predominantly reinforced concrete, the recycled aggregate was

taken as being 100% of the demolition waste.

A number of materials sources and sinks are available to

redevelopment projects in the Masshouse area, the relevant

parameters being as shown in Figure 3. The haulage distance to

the nearest waste disposal point or landfill (HL) was found to be

6?1 km. As large procurement projects require competitive

procurement and tendering, distances to aggregate supply

sources were based on the average of the nearest three sources.

Recycled sources identified through use of the Aggregain

supplier directory4 provided an average haulage distance for

recycled aggregate (HR) of 2?0 km, the nearest source being at a

distance of 1?2 km. For primary aggregates, using sources taken

from the British Geological Survey database,11 the average

haulage distance (HP) was found to be 13?2 km, the closest

source being at a distance of 9?3 km.

2.3. Data requirements

Analysis of carbon dioxide emissions based on diesel and

electricity consumption can be divided between aggregate

production/processing and haulage, haulage also being sub-

divisible between aggregate sources and waste sinks (as

summarised in Figure 3). Data requirements are the emissions

relating to landfilling (L) and production of both primary (P) and

recycled (R) aggregates, together with haulage associated with

each (HL56?1 km, HP513?2 km and HR52?0 km for ex situ

recycling, HR50 km for in situ recycling). For the purposes of

this analysis, it is assumed that there is no haulage between the

landfilled waste, primary aggregate and recycled aggregate

locations.

The basic factors for calculating carbon dioxide emissions from

these fuels are provided in Table 1. Data for electricity use are

based on the UK values used in the WRAP tool. It should be

noted that UK electricity emissions values may vary signifi-

cantly between electricity providers and can be expected to

improve in the future as more renewable energy sources are

phased in. However, as this study aimed to extend the WRAP

tool methodology, it was considered pertinent to use its

electricity base data to ensure consistency.

2.4. Emissions due to aggregate production

Three types of aggregate were considered to investigate

Figure 2. System boundary of the study described in this paper

Figure 3. Haulage inputs for calculating fuel use associated withthe various scenarios

Energy Emissions

Fuel type Unit MJ/unit gCO2/MJElectricity kWh 3?6 119?0{Diesel oil l 35?1* 73?0{

*Stripple5

{Aggregain2

Table 1. Fuel carbon dioxide emissions factors


differences in carbon dioxide emissions that would result from

decisions involving reduced aggregate grades: low-grade

aggregates for fill purposes; and medium- and high-grade

aggregates (denoted eng 1 and eng 2) suitable for engineering

uses such as sub-bases. Low-grade aggregates require less

crushing and screening than well-graded high-quality aggre-

gates and so it is important to recognise that decisions relating

to grade also have impacts in terms of emissions. However, as

has been noted by others,12 information on the embodied energy

and carbon dioxide emissions associated with different aggre-

gate grades is scarce. Therefore, published data on embodied

energy values for a road aggregate5 were taken as being

representative of the eng 2 grade as primary and recycled

aggregates both involve the same manufacturing processes,

emissions being calculated using the data of Table 1. Values

were then calculated for the fill and eng 1 aggregates based on a

pro rata using data from a study of recycled aggregates that

considered energy requirements for equipment used in the

production of comparable grades.13 Aggregate emissions were

calculated in this way because, as mentioned earlier, very

limited emissions data relating to different grades are available

and the data available13 are not based on a full life-cycle

analysis (being financial data covering only the most significant

items of plant used). Therefore, while it is acknowledged that

further research is required in this area, the method used allowed

the WRAP tool to be extended, in the absence of exact data, to

consider how aggregate grade impacts on emissions. The results

are summarised in Table 2, excluding haulage to the final-use

destination.

In considering carbon dioxide emissions associated with

aggregate production, it should be noted that the crushing of

concrete to produce recycled aggregate can be expected to

increase its surface area and so increase the potential for carbon

dioxide to be reabsorbed in the process of carbonation. The

degree to which this will occur is a complex function of the

remaining carbonation potential after the concrete’s original

service, the size of the aggregate particles produced and the

underground highway environment within which it is buried.14

While carbonation could be considered to offset the carbon

dioxide associated with recycled aggregate production, com-

plications arise in this regard as these savings could be

considered more related to the sustainability of the original

Masshouse construction. Therefore, its sustainability credentials

would be increased due to the potential for the concrete used

eventually to approach carbon neutral. Also, because the exact

type of concrete used in Masshouse, the extent to which it was

carbonated at demolition and the resulting aggregate grading

are unknown, it is difficult to assess the significance of

carbonation. For these reasons, adjustments have not been made

to the emissions calculations in this study.

A further consideration in assessing emissions due to aggregates

is that, particularly for the case of Masshouse, waste concrete

often contains significant amounts of steel in the form of

reinforcement. In order to produce crushed concrete it is

necessary to remove this reinforcement, using magnetic

separation for example. This causes significant difficulties in

analysing emissions, as waste concrete can essentially be

considered to be a raw material for the production of two

recycled materials (steel and aggregate) whereas quarry rock

would only be used to produce aggregates. For the purposes of

this study, magnetic separation (which in the USA is associated

with around 4% of the recycling cost and yields around

US$100/t of scrap metal15) and haulage of steel for recycling

were therefore not considered part of the system boundary (as

shown in Figure 2). However, it should also be noted that the

difficulty inherent in trying to separate these two recycling

processes and the lack of data on which to assess emissions

implications means that there may be hidden emissions benefits

in recycled aggregate production that cannot be incorporated

into the methodology described here without further research.

2.5. Emissions due to haulage vehicles

Carbon dioxide emissions associated with waste and aggregates

haulage were considered solely in terms of those associated with

fuel use. Calculation of fuel use per kilometre was based on the

UK Highways Agency Design Manual for Roads and Bridges.16

Although a number of vehicle types can be modelled using this

method, this study considered OGV2, which comprises all goods

vehicles with four axles or more, including articulated vehicles.

Fuel consumption was calculated from16

1 L~azbvzcv2zdv

3

where L is fuel consumption (l/km), v is average speed (km/h)

and a (1?0244315577), b (–0?0302181229), c (0?0004428547)

and d (–0?0000020059) are vehicle-specific parameters, the

values in parentheses being those appropriate for OGV2.

Due to the significant quantities of waste and aggregates

involved in the Masshouse project, haulage vehicles were

assumed to carry 30 t for the purposes of this study. This is

considered appropriate as haulage fleet operators can be

expected to favour the greater efficiency of larger vehicles

where possible.17 However, for smaller projects, or where gross

vehicle weight restrictions on available highways prevent the

use of larger haulage vehicles, smaller vehicles may be

employed and the calculations in this paper will require

appropriate adjustment.

From Equation 1 and Table 1, speed–emissions relationships for

haulage vehicles can be plotted. Figure 4 shows the greater

Grade Energy: MJ (diesel/electricity) Baseline, a: gCO2/t Factor, b a6b: gCO2/t

Eng 2 16?99*/21?19* 3762 1?00{ 3762Eng 1 – 3762 0?64{ 2408Fill – 3762 0?36{ 1354

*Stripple5

{Based on Gaterell13

Table 2. Derivation of carbon dioxide emissions for recycled and primary aggregate production


emissions efficiency achievable at an optimum speed of

approximately 50 km/h (31 mph). However, in congested urban

environments, goods vehicles can be limited to lower speeds, or

even stop–start conditions, resulting in much reduced fuel

efficiency. For instance, at 10 km/h (6 mph) the fuel use is

approximately twice that for the optimum driving speed. In this

circumstance, the carbon dioxide emissions associated with

haulage can also be expected to approximately double, solely

due to the effects of congestion. It is clearly evident that road

speed is an important aspect of assessing sustainability where

haulage is required.

2.6. Road speeds and congestion in urban areas

Due to the city centre location of the Masshouse redevelopment,

consideration of variations in traffic speed was achieved

through use of the 2006 UK Transport Statistics Bulletin,18

which tracks road usage for three road types (rural, urban and

motorways) as a function of time of day for every day in the

period 2000–2006 inclusive. This allowed estimation of the

impact of road speed and congestion on fuel use and, therefore,

carbon dioxide emissions. While traffic on motorways and rural

roads is shown to exhibit significant seasonal trends centred

around a summer peak, urban road traffic on average shows less

variation.18 Only minor reductions in average daily traffic flows

around Christmas and mid-summer holiday periods were

identified. Average traffic flows for goods vehicles, for all three

road types, appear to follow the urban road trend, with only

relatively minor variations associated with reduced numbers of

working days during major holidays.

The day of the week was also cited as a significant variable in

traffic flows. Weekday flows (i.e. Monday to Friday) are shown

on average to be largely constant, with a slight peak on Fridays.

Weekend traffic was found to be considerably less than on

weekdays, particularly for goods vehicles. However, the most

significant variation in traffic flows that impact on aggregate

haulage in urban areas is that due to time of day on weekdays.

There are two distinct peaks in traffic flow associated with rush

hour traffic which, for the purposes of this study, were taken as

being 08:00 to 10:00 and 16:00 to 18:00. Short-distance waste

and aggregate haulage was assumed to occur mostly between

08:00 and 18:00. Taking average peak and off-peak speeds from

the bulletin18 can therefore provide average journey speeds for

haulage vehicles, based on 4 hours’ travel in peak conditions

and 6 hours in off-peak conditions. Applying this approach to

various English urban areas for which data were available18

resulted in Figure 5, which shows significant geographical

variation in average speed; the majority of urban areas,

including the West Midlands (which includes Birmingham), are

unable to support average speeds close to the optimum 50 km/h.

In order to include variations in average haulage vehicle road

speeds, three journey speed classes were considered for this

study (Table 3)

(a) the ‘optimum’ speed of 50 km/h

(b) based on 10 h day ‘average’ speeds for the West Midlands

(but excluding data for the 2006 reporting due to

significantly reduced average speeds during that period

associated with major improvement works on the M5 and

M6 motorways)

(c) ‘congested’ class, developed using the same rationale as for

average speeds; the data used were those only for 2006 to

give an indication of speeds that may apply during periods

of greater-than-average congestion.

2.7. Potential scenarios for redevelopment at Masshouse

Recycling of wastes is, of course, not entirely a recent

development. Even before the landfill tax and aggregates levy

(introduced in the UK in 1996 and 2002 respectively), up to two-

thirds of UK construction/demolition wastes were known to be

38.1

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Figure 5. Ten-hour average speeds in various UK urban areas 2000–2006 (based on DfT data18)

Figure 4. The effect of road speed on haulage carbondioxide emissions


recycled, although only 4% was used for recycled aggregate

production, the remainder being split equally between low-

grade use close to site and for landfill engineering.19 Use of low-

grade waste close to its source may indicate that the cost

advantages of limiting waste haulage were equally as effective

as financial drivers a decade ago as they are at present. The

limited demand for recycled aggregates at that time can be

considered, at least partly, to have originated in the need for

caution in using materials with potentially unknown prove-

nance. In 1995, Sherwood19 explained there was a perceived

need to ‘play safe’ and, referring to primary aggregates, stated

‘… even if such materials do cost more; criticism of needless

expenditure is muted compared with the criticism that occurs if

a costly failure should arise through the use of a material that

subsequently proves to be unsuitable’.

For these reasons, potential scenarios for analysis are mostly

limited to those associated with materials sources and sinks and

attempts to minimise haulage (such as through recycling in situ

where space and materials quantity permits). Therefore, as well

as the actual scenario used in the redevelopment of Masshouse,

four alternative scenarios were considered for comparison.

These scenarios are intended to reflect real decisions that could

have been made during implementation of the project (had the

ERDF guidelines not been in place) and, while other scenarios

could have been considered, those selected were chosen to

reflect a wide range of potential carbon dioxide emissions. The

rationale behind the decision-making system the scenarios

reflect is illustrated in Figure 6.

(a) Scenario 1: Dispose to landfill and import primary

aggregate. The option of disposing of concrete waste to

landfill and importing primary aggregates for engineering

construction was chosen for analysis as a non-recycling

option. While the waste, being inert, would not be expected

to produce significant carbon dioxide equivalence in landfill

gas emissions, it would require haulage and aggregate

import with associated emissions.

(b) Scenario 2: In situ recycling for fill applications. The need to

improve sustainability through durable construction is as

important today as it was over a decade ago.19 It was

therefore considered appropriate to quantify the carbon

dioxide emissions that could result from the use of primary

aggregates, together with in situ use of concrete waste as a

low-grade fill aggregate, for example in landscaping

features. This scenario therefore investigates the impact of

considering recycled aggregates as materials of unknown, or

variable, provenance that should be avoided for high-grade

engineering use.

(c) Scenario 3: In situ recycling for engineering applications.

This option was chosen for the Masshouse redevelopment

and could have been expected to reduce carbon dioxide

emissions from aggregate production while allowing

absolute minimisation of haulage vehicle use. For sites other

than Masshouse, this scenario allows investigation of

carbon dioxide emissions improvements associated with the

use of recycled aggregates and minimised haulage require-

ments.

(d) Scenario 4: Ex situ recycling for engineering applications

excluding back-haulage. This option represents a means of

producing recycled aggregate where site constraints prevent

in situ recycling. As this option does not include back-

haulage, it is assumed that the imported aggregate is not

derived from the exported waste, but that the facility

receiving the concrete waste for recycling and the source of

recycled aggregates are the same. Also, it is assumed that

each haulage vehicle travels a two-way route between the

site and recycling facility, carrying waste or aggregates on

one leg and nothing on the other leg due to there being no

space available for stockpiling of imported aggregates until

demolition rubble is removed.

(e) Scenario 5: Ex situ recycling for engineering applications

including back-haulage. This option was chosen for analysis

because it allows quantification of the potential advantages

of optimised phasing of the exportation of concrete waste

and importation of resultant high-grade aggregates.

However, as for scenario 4, there is no requirement that the

imported aggregate be derived from the exported waste. It is

assumed only that each haulage vehicle travels a two-way

route carrying waste on one leg and aggregate on the other.

The relevant landfill tonnages, primary and recycled materials

requirements and haulage distances (calculated based on the

Journey class

Optimum Average Congested

Average speed: km/h 50?0 40?0 34?2Fuel use: l/km 0?3699 0?3959 0?4287Emissions: gCO2/km 947?8 1014?4 1098?5Emissions for 30 t load:gCO2/t per km

31?59 33?81 36?62

Table 3. Summary of the three haulage journey speedclasses adopted

Demolition and

construction

Use the'traditional'approach?

Yes

Yes

No

No

No

Is the quality ofrecycled

aggregate ofsignificantconcern?

Is there room onsite to allow insitu recycling?

Ex situ recyclefor a valid

engineeringapplication on

site

Can import andexport be carried

out together?

Scenario 5:Back-haul

Scenario 4:Don't back-haul

Scenario 3:In situ recycle for

a validengineering

application on site

Scenario 2:Find a use within

the site andimport primary

Scenario 1:Dispose tolandfill and

import primary

Can a use befound on site?

No

Yes

No Yes

Yes

Figure 6. The decision-making system behind the fivepotential scenarios


data of Sections 2.2 and 2.3) for each of the above Masshouse

scenarios are summarised in Table 4.

3. RESULTS AND DISCUSSION

Based on Table 4, the carbon dioxide emissions associated with

the production and haulage of aggregates, using eng 1 and eng 2

for non-fill applications, are shown in Table 5; it is apparent

that greater emissions are related to production, even if lower

grade eng 1 aggregate is used. Table 5 also indicates that use of

primary aggregates at the Masshouse site involves significantly

greater haulage in comparison to the scenarios in which

recycled aggregates are used. Furthermore, there is an increase

in haulage emissions due to the effects of congestion.

The total carbon dioxide emissions for each scenario were

calculated (Table 6); the data for average road conditions and

eng 2 aggregate are illustrated in Figure 7. It is evident from

these data that the option chosen for Masshouse (i.e. scenario 3)

provided the minimum level of carbon dioxide emissions, being

approximately three-quarters of the total emissions of scenario

1. However, the two ex situ recycling options (scenarios 4 and 5)

would have involved emissions only slightly greater than the

chosen option of in situ recycling. As can be seen from Figure 6,

the rationale behind these two scenarios is based on available

site space for establishment of recycling plant and stockpiling of

raw and recycled materials. Therefore, for other Birmingham

city centre sites where space is more limited than it was at

Masshouse and recycling facilities are available within a short

distance, it can be seen that ex situ recycling is still more

sustainable, in carbon dioxide terms, than primary aggregate

use, particularly if back-haulage is undertaken.

For the materials quantities associated with Masshouse, use of

30 t vehicles would be expected as a minimum. However, from a

transport management perspective, it cannot be guaranteed that

such vehicles will always be available in sufficient numbers.

Therefore, total emissions resulting from each haulage vehicle

carrying a reduced load of 20 t (as a simple example based on

haulage distances and emissions increasing by 50%) are also

shown in Figure 7; there is an increase in overall emissions due

to the additional haulage distances, which is proportional to the

reliance of each scenario on road transport. Figure 7 also shows

the results of using the WRAP tool (also included in Table 6) in

an unmodified form to calculate carbon dioxide emissions for

each scenario. It can be seen that under average road conditions

the only significant difference between the WRAP tool data and

data from the modified version used in this study occurs for

scenario 2. This is because the unmodified WRAP tool uses a

single value for all aggregate production emissions, whereas this

study ascribes fewer emissions to aggregates produced for low-

grade fill applications.

It is also evident from Table 6 that both primary aggregate

scenarios involve significantly greater reliance on haulage,

which is of particular concern in a congested city centre

environment (total haulage distances for each scenario are

Landfill and aggregate requirements: kt

Landfill Primary Recycled Total

Scenario 1 48 48* 0 96Scenario 2 0 48* 48{ 96Scenario 3 0 0 48* 48Scenario 4 0 0 48* 48Scenario 5 0 0 48* 48

Haulage distances: km

Landfill Primary Recycled Total

Scenario 1 19 520 42 240 0 61 760Scenario 2 0 42 240 0 42 240Scenario 3 0 0 0 0Scenario 4 0 0 6 400 6 400Scenario 5 0 0 3 200 3 200

*Engineering-grade aggregate{Fill-grade aggregate

Table 4. Summary of landfill quantities, aggregate requirements and haulage distance data for the five considered scenarios

Carbon dioxide emissions: t

Aggregate production Haulage of wastes and aggregates

Eng 1 Eng 2 Optimum Average Congested

Scenario 1 115?6 180?6 58?5 62?6 67?8Scenario 2 180?6 245?6 40?0 42?8 46?4Scenario 3 115?6 180?6 0?0 0?0 0?0Scenario 4 115?6 180?6 6?1 6?5 7?1Scenario 5 115?6 180?6 3?0 3?2 3?5

Table 5. Summary of carbon dioxide emissions for production and haulage of aggregates


illustrated in Figure 8). However, it should be noted that this is

due to the closer proximity of recycling facilities in comparison

to quarries. Therefore, this outcome can be considered

geographically variant – redevelopment sites outside

Birmingham city centre may be closer to quarries and further

from recycling facilities. As a simple example, if the total

haulage distances associated with scenarios 1 and 4 were

swapped, the total carbon dioxide emissions would be,

respectively, 186?7 and 239?1 t, assuming optimum road

conditions and eng 2 aggregate grade. Therefore, under such

circumstances, carbon dioxide emissions for the primary

aggregate scenario would be less than for the recycled aggregate

scenario, which illustrates that haulage requirements can have a

significant impact on the relative sustainability of recycled

aggregates.

The importance of back-haulage as a mitigation of environ-

mental impacts can be illustrated for scenario 1 as, even though

it would still be less sustainable than the other scenarios, back-

haulage on 100% of journeys could allow a reduction in

emissions of approximately 18?5 t if the most efficient haulage

strategy were achieved. For compatibility with Figure 7,

Figure 8 also illustrates the increased haulage distances for each

scenario due to each vehicle carrying a reduced load of 20 t. Of

further note is the large decrease in emissions shown in Tables 5

and 6 associated with use of eng 1 aggregates in place of eng 2;

this is further illustrated in Figure 9. Aggregate quality is an

important decision requiring careful consideration on the part of

decision makers and in itself has the potential to degrade

sustainability if reduced grade adversely affects the lifetime of

the construction. This is largely outside the scope of this paper,

but it can be inferred that specifying a higher grade of aggregate

than is truly required for the desired performance, whether

primary or recycled, can have a significant impact on carbon

dioxide emissions, even if the volume of aggregate used has to

be increased slightly in compensation for differences in the

material grade.

Finally, it is apparent that the effects of congestion on haulage

vehicle speeds impact carbon dioxide emissions. This is

particularly the case for scenarios where haulage distances are

longer, in this case those based on primary aggregates. For

example, the increase in carbon dioxide emissions between

optimum and congested conditions for scenario 1 is greater than

the total haulage emissions for scenarios 4 and 5. Therefore, the

planning of haulage to optimise speeds can be considered an

important aspect of ensuring the sustainability of aggregate

sourcing. This is illustrated in Figure 10, which shows, for

scenarios 1 and 4, emissions for optimum, average and

congested journey classes. The magnitude of variations in

emissions due to road speed can be seen to be of greater

significance for longer total haulage distances.

4. CONCLUSIONS

There is great complexity inherent in assessing carbon dioxide

Total carbon dioxide emissions: t

Optimum Average Congested Wrap tool

Scenario 1 239?1 (174?1) 243?2 (178?2) 248?4 (183?4) 237?4Scenario 2 285?6 (220?6) 288?4 (223?4) 292?0 (227?0) 395?7Scenario 3 180?6 (115?6) 180?6 (115?6) 180?6 (115?6) 177?3Scenario 4 186?7 (121?7) 187?1 (122?1) 187?7 (122?7) 183?5Scenario 5 183?6 (118?6) 183?8 (118?8) 184?1 (119?1) 180?4

Proportion of emissions associated with haulage: %

Optimum Average Congested Wrap tool

Scenario 1 24?5 (33?6) 25?7 (35?1) 27?3 (37?0) 25?3Scenario 2 14?0 (18?1) 14?8 (19?2) 15?9 (20?4) 10?4Scenario 3 0?0 (0?0) 0?0 (0?0) 0?0 (0?0) 0?0Scenario 4 3?3 (5?0) 3?5 (5?3) 3?8 (5?8) 3?4Scenario 5 1?6 (2?5) 1?7 (2?7) 1?9 (2?9) 1?7

Table 6. Summary of carbon dioxide emissions for each scenario for different road conditions, assuming use of eng 2 aggregates(figures for eng 1 use in parentheses)

Scenario 1

0

50

100

150

200

250

300

350

400

450

Tota

l C

O2 e

mis

sio

ns: t

Scenario 2 Scenario 3 Scenario 4 Scenario 5

30 t vehicle 20 t vehicle Wrap tool (32 t vehicle)

Figure 7. Total carbon dioxide emissions under averageroad conditions

Scenario 1

100 000

90 000

80 000

70 000

60 000

50 000

40 000

30 000

20 000

10 000

0

Tota

l haula

ge: km


20 t vehicle30 t vehicle

Figure 8. Total haulage distances for each scenario


emissions associated with aggregate use in redevelopment

projects and the WRAP tool provides a very valuable first step in

such estimations. However, it can be concluded that parameters

not hitherto incorporated into the WRAP tool, such as highway

congestion and aggregate grade, are an important part of an

emissions assessment and should not be ignored. The following,

more detailed, conclusions can be drawn from this study.

(a) The sustainable use of aggregates (as measured using the

proxy of reduced carbon dioxide emissions) can be

improved through consideration of geographical location,

aggregate grade, haulage management, vehicle selection,

highway congestion and distances.

(b) The ‘traditional’ option of disposing of waste to landfill and

importing primary aggregate (scenario 1) was shown to

involve carbon dioxide emissions approximately one-third

greater than the chosen Masshouse option (in situ recy-

cling).

(c) Avoidance of landfilling (scenario 2) significantly increased

carbon dioxide production relative to scenario 1 due to the

need for crushing of waste to be used as fill material and the

relative proximity of landfill facilities.

(d) The in situ recycling option chosen for Masshouse (scenario

3) was the lowest emissions option, but cannot be held up as

a model for all redevelopments as not all sites will have

sufficient ground area available to stockpile and process

demolition waste and store the resulting aggregate.

(e) Scenarios 4 and 5 were characterised by only marginally

higher emissions than the chosen Masshouse option,

particularly due to the close proximity of a number of

recycling facilities.

(f) In the Birmingham case considered in this paper, use of

recycled aggregate produced substantially less carbon

dioxide emissions than primary aggregate use. However,

under other circumstances, it may potentially cause greater

carbon dioxide emissions.

(g) Significant differences were noted in carbon dioxide

emissions between eng 1 and eng 2 aggregates due to

different production energy requirements.

(h) The relationship between quality, durability and emissions

associated with aggregate production requires further

research and relevant system boundaries should be further

defined.

ACKNOWLEDGEMENT

The authors gratefully acknowledge financial and other support

from the UK Engineering and Physical Sciences Research

Council (EPSRC) under grant reference EP/E021603/1.

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Scenario 1

0

50

100

150

200

250

300

Pro

duction C

O2 e

mis

sio

ns: t


Eng 1 Eng 2

Figure 9. Carbon dioxide emissions from aggregate production

Optimum Average Congested

0

10

20

30

40

50

60

70

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Haula

ge C

O2 e

mis

sio

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Scenario 1 Scenario 4

Figure 10. Effect of journey class on haulage emissions


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