Road Recycling 11

8/13/2019 Road Recycling 11

1/3

Department of the Environment, Transport and the Regions Research Contract MP0623 Digest no. 060 (2:1/99)

Symonds 1

This digest is one of a series produced by the Aggregates Advisory Service to provideinformation on aggregates efficiency issues.

The aim of this service, funded by the Department of the Environment, Transport and theRegions, is to assist the Government to achieve its objective of reducing the constructionindustrys dependence on landwon primary aggregates and increasing the contribution fromsecondary and recycled materials.

Further information on aggregates efficiency issues, whether relating to primary, secondaryor recycled materials, can be obtained from the Aggregates Advisory Service on Freephoneno. 0800 374 279 or visit the website at http://www.planning.detr.gov.uk/aas/index.htm.

ROAD RECYCLING

Ex-situ Road RecyclingWhy Recycle a Road?

Road reconstruction conventionally consists of the

excavation of existing material and its replacement

by new. This process results in the requirement for

significant quantities of new materials usually from

primary sources. It is coupled with the need to

dispose of the existing material and the

environmental impacts from the associated

transport operation.

The recycling of existing materials can result in

both cost savings and reduced environmentalimpacts.

Ex-situ Road Recycling

Recycling can be undertaken either in-situ or ex-

situ. This digest relates to ex-situ recycling.

Ex-situ recycling consists of the excavation and

removal of existing road construction material to a

stockpile. From here it is processed by grading

and mixing with appropriate binders prior to being

recompacted to form a road.

In-situ recycling is covered in Digest 056.

This digest briefly describes one of the methods

of road recycling. This digest covers ex-siturecycling. Digest 056 covers in-situ recycling.

Two example projects are included.

Contact Details

Walsall Example

Address:

Roadstone Recycling LtdGatherley Road Industrial Estate

Brompton on SwaleRichmondNorth Yorkshire DL10 7JQ

Telephone: 01748 811232Fax: 01748 812005

Contact: Mr G Cook

A52 Example

Address:

Staffordshire County CouncilDevelopment Services DepartmentHighways Northern Area OfficeLadder EdgeLeekStaffordshire ST13 7AB

Telephone: 01538 483012

Contact: Mr P Pytlik


2/3


Symonds 2

Ex-situ recycling has the following characteristics:

The recycling plant is easily transported and can

be established on site in a few hours

The plant is smokeless, odourless and is quiet

in operation

Recycling plant can be located in surroundings

appropriate to the nature of the operation where

environmental impacts can be mitigated

Environmental impacts at the reconstruction site

are reduced

A wide range of materials can be processed

including road planings, crushed concrete and

masonry

The materials can be crushed and screened to

fit a predetermined grading envelope, before

being mixed with a binder

All materials are processed in a controllable

environment resulting in the production of a

quality controlled product

The graded material can be stockpiled for the

later incorporation of a binder

Bound material, if correctly stored, can be used

for up to four weeks after production

The excavation of the road and its replacement

can be undertaken using conventional plant and

equipment

Example Project:Estate Roads in Walsall

In a recent operation, Roadstone Recycling Ltd (a

joint venture company formed by a partnership

between Tarmac and Bruce Cook Road Planing)

reconstructed sections of estate roads in central

Walsall.

The roads consisted typically of 60-80mm of

asphalt covering an unbound stone base consisting

of well graded granular slag. Locally concrete was

also present within the base materials.

Planing operation to remove existing road surface

Excavation of existing material in preparation forresurfacing


3/3


Symonds 3

The recycling process incorporated a Foamix

binder. Foamix has been widely used for a number

of years in Canada and has been particularly

successful in areas where indigenous aggregates

are of poor quality. The binder was added atapproximately 2.2% by weight and the moisture

content was adjusted to achieve adequate in-situ

density figures. The in-situ density was determined

using a nuclear density meter.

Paving using Foamix macadam

The grading of the feedstock material was checked

on a daily basis. This was undertaken by

thoroughly mixing the stock material prior to wash

grading it through a series of sieves. Density

checks were undertaken each day and cores were

cured and subsequently tested in a laboratory.

In isolated areas of the site, soft clay was found to

exist below the road base level. As this method of

repaving is equally as liable to settlement as any

other, a number of soft spots were excavated and

backfilled with granular material reinforced with a

geotextile.

A wearing course consisting of Masterpave (a

Tarmac product) was used as a surfacing layer.

Example Project: A52, Staffordshire

In the summer of 1997, a 0.9km stretch of the A52,

which is a heavily trafficked trunk road, was

reconstructed using ex-situ recycling techniques.

In this instance, the existing road was planed out to

full depth and stockpiled. The resulting material

was then graded and, where necessary, crushed to

provide material of suitable particle sizes. This was

then mixed with 3% lime and 12% pulverised fly

ash (PFA). The mixture was recompacted in two

150mm layers as subbase and base course. It

was topped with new wearing course. Where

necessary, small quantities of primary aggregates

were brought in to make up volumes.

It is believed that this is the first project where a

lime/PFA binder has been used in conjunction with

recycling of existing road materials.

Further Potential

These examples illustrate how recycling techniques

can compete successfully with conventional road

construction methods.

The ex-situ approach provides a consistent

construction material and eliminates some of the

variables which could occur with direct in-situ

recycling and allows more engineering control

during the construction operation. It is anticipated

that the performance monitoring can thus be more

objective.

An increased use of recycling techniques such as

these would reduce demand for primary aggregate,

assisting the Government to achieve its aim of

sustainable development.

Road Recycling 11

Documents

Transcript of Road Recycling 11