Copyright © 2000/08, CJ.Summers
A LIST OF ITEMS GIVING GUIDANCE TO RECYCLING IN HIGHWAYS MAINTENANCE & CONSTRUCTION
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BS 6463 : Quicklime, hydrated lime and natural calcium carbonate :
Part 103 : Methods for physical testing
BS 6543 : Guide to the use of industrial by-products and waste materials in building and civil engineering
BS EN 13108-8 : 2005 : Bituminous mixtures. Material specifications - Reclaimed asphalt,
was introduced on the 1st. of January 2008, you need to be aware of its contents when using reclaimed material from existing bituminous mixtures (asphalt).
COLLIERY SHALE - RECYCLING
COLLIERY SHALE can be an excellent general FILL material, used as a CAPPING LAYER or even a TYPE 2 GRANULAR SUB-BASE.
It depends on the quality of the COLLIERY SHALE, and that depends to a large extent on whether the shale has been burnt or not.
Shale that has been burnt will be of a reddish appearance while the shale in its natural state will be black and grey. The shale tips self ignite due to the leaching of sulphates and the build up of sulphuric acid which causes the combustion.
The burnt shale has been rendered relatively inert by the combustion and is the more acceptable material for road making.
All COLLIERY SHALE should be tested for sulphates especially if it is to be used in proximity to concrete.
CSS ENG/1-94 : Use of Recycling for Road Pavement Construction and Maintenance
It is a fairly comprehensive study of materials, processes, specifications and testing that can be used in recycling.
CSS ENG/2-97 : Sustainable road maintenance - Reduce, Reuse, Recycle
This report is a collection of "papers" relating to "Sustainable Road Maintenance" which were presented at the CSS conference held at Leamington Spa on the 18th. of November 1997.
It is very informative and useful reading on the subject.
The report was put together for the CSS by the Soils, Materials, Design and Specification Group.
This European standard is applicable to hydraulic road binders (which are finished products) produced in a factory and supplied ready for use in bsae (roadbase), sub-base and capping layers, also for soil stabilisation
Dft Advice Note HA 74/95 - Design and Construction of Lime Stabilised Capping,
and as its title suggests it contains guidance on the design and construction of lime stabilised capping in highway works.
This Advice Note is contained in :-
Section 1, Earthworks, of Vol.4, Geotechnics and Drainage, of The Design Manual for Roads and Bridges
DfT Advice Note HA 74/00 - Treatment of fill and capping materials using either lime or cement, or both
This report contains advice and guidance on the design and construction of lime stabilised capping in highway works.
The advice note is contained in:-
Section 1, Earthworks, of Volume 4, Geotechnics and Drainage, of the Design Manual for Roads and Bridges
FOAMIX - FOAMED BITUMEN - RECYCLING
I believe the process that "foams" the bitumen is still under patent, but I am not sure whether it is BP or Mobil that own the patent, or they each have a patent for their own process.
A license is needed from the patent holder to use this process, or you can employ a contractor to do the work for you who already has a licence to use the foam bitumen process.
Steam or cold water is injected into hot bitumen that has been treated with appropriate chemicals, as a result the treated bitumen will "foam" to many times its original volume, up to 10/15 times is claimed.
While the bitumen is in this expanded state it will much more readily coat the surface of aggregate.
The process is particularly used in "cold coating" of recycled material.
There are a number of contractors who operate static and mobile operations using foamed bitumen to recycle bituminous road planings as roadbase and basecourse in suitable situations.
FOUNDRY SAND - RECYCLING
This is sand available after it has performed its original function of forming the mould for casting metal objects.
It will sometimes conform to a TYPE 2 GRANULAR SUB-BASE.
It is useful as a general fill, and as a SUB-BASE in lightly trafficked areas/footpaths.
It can be used to blend with other recycled materials to produce more stable gradings.
FURNACE BOTTOM ASH - FBA - RECYCLING
FURNACE BOTTOM ASH is a bye product of the electricity producing industry, i.e. it is the resultant material of coal burning power stations.
ASH is an unfortunate term to use because it does not accurately describe the material.
The term ASH leads you to visualise a soft powdery material, when FBA is more a clinker type of material, and although high in fines, the fines are hard and "glassy".
It is/was considered an "alternative" recycling material but it is becoming scarce with less coal used at power stations.
The material from the Trent power stations usually grades as a Type 2 G.S.B..
It is very free draining, and at the same time is capable of "holding" a great deal of water in its honeycombed structure before it drains, note I say "holding" as opposed to absorbing.
Good quality FBA absorbs little if any moisture, but it can hold/retain a great deal.
The density of material with a good "through" grading and a 10% moisture content :-
loosely compacted ............................... 950kg./cube metre
fully compacted ................................ 1150kg./cube metre
fully compacted and fully saturated ............ 1400kg./cube metre
(It is a good material used correctly.)
N.B. be careful not to buy water, state a maximum moisture content.
GOOD BOOKS ON RECYCLING
These include:-
1) "ALTERNATIVE MATERIALS IN ROAD CONSTRUCTION" published by Thomas Telford.
2) BS 6543
LINEAR QUARRYING - RETREAD - RECYCLING
This is the "new" name for the RETREAD process.
PULVERISED FUEL ASH - PFA - RECYCLING
Pulverised fuel ash, a by product of burning pulverised coal in the electricity generating industry. PFA is a lightweight construction material when compared to general types of fill.
The DRY density range for this material is :- 1.1 to 1.5 tonnes/cu. metre
RECYCLING
RECYCLING means using a material or aggregate that has been previously used, and reclaimed from, existing road construction or another capacity.
The most common recycled materials used (or have been used) in this county are:-
ROAD PLANINGS; BURNT COLLIERY SHALE; FURNACE BOTTOM ASH (FBA); PULVERISED FUEL ASH; CRUSHED SLAG; FOUNDRY SAND; CRUSHED CONCRETE;
BE CAREFUL! when discussing RECYCLING processes, the terms sometimes mean different things to different people, this includes the way contractors describe the processes they offer.
Find out EXACTLY what you are getting.
REMIX - RECYCLING
REMIX is a similar process to REPAVE, i.e. it is a hot insitu carriageway resurfacing process performed by a purpose built machine.
The main difference being that the existing insitu material is completely mixed with the new material not laid on top of a heated and scarified surface.
The new material is designed so that when mixed with the existing material the resultant blend will be suitable for the site conditions and comply with the appropriate specification.
The existing surface is heated to 140-180 degrees C., scarified, and then fed up into the machine where it is mixed with the new material within the machine.
The newly mixed material is laid on a hot, scarified, levelled surface by the machine and PRECOATS are laid onto the surface in the normal way.
N.B. Be careful when discussing RECYCLING processes, the terms sometimes mean different things to different people, this includes contractors descriptions of their "systems".
REPAVE - RECYCLING
The REPAVE PROCESS is a recognised form of in-situ recycling and as such is specified and described in the DfT Specification for Highway Works (WHITE BOOK).
Clause 926 : In Situ Recycling - The Repave Process found in th section Road Pavements - Bituminous Bound Materials.
Information can also be found in DfT. DESIGN MANUAL HD 31/94.
In brief the immediate surface of the carriageway is planed off and removed, the remaining surface material is heated and scarified to a depth of approximately 20mms., it is then reprofiled.
Fresh HRA wearing course material is laid on the top, and this and the scarified material are compacted together, using a highly specialized machine.
The process will provide a new running surface to replace a surface which no longer has the required TEXTURE or ANTI SKID properties required, but the SURFACE COURSE (WEARING COURSE) material is good.
Because of the size of the REPAVE machine the process is only really suitable and economical on fairly long lengths of carriageway with considerable overall width, for smaller areas it is usually more economical to replace all the wearing course.
RETREAD - RECYCLING - LINEAR QUARRYING
This process has been around for 20/30 years, but the process has improved with the availability of better designed machinery with increased power to better carry out the work, more complete pulverisation of existing road pavement to increased depths.
It has somehow acquired the name LINEAR QUARRYING when used on larger projects.
Broadly speaking RETREAD involves assessing the existing road to see if it is suitable for the treatment.
If it is, the road is pulverised to a suitable depth to produce a uniform material, aggregate can be added to modify the insitu grading.
A foamed bitumen or cement is mixed with the pulverised aggregate to act as the binding agent.
After final shaping the material is rolled with a heavy roller.
Also, to produce a better running surface, and to seal the RETREAD material sufficient material can be removed and replaced with a conventional bituminous wearing course.
ROAD PLANINGS - HOT MIX RECYCLING
Up to 30% reclaimed bituminous materials may be used in the production of new base (roadbase) and binder course (basecourse), and up to 10% in wearing course mixtures, providing the end product complies with the appropriate specification.
This is stated in Clause 902 of the Specification for Highway Works, this usually means the reclaimed material is road planings.
It is also usually required that the source of the planings is consistent so that it is possible to formulate a known and constant fresh material.
It is possible to add up to 60% of reclaimed material, with the approval of the supervising engineer, to roadbases and basecourses, subject to the already mentioned points.
( The percentage of reclaimed material allowed in to new mixtures seems to be continually changing so keep up to date by reference to current documents/standards. )
BS EN 13108-8 : 2005:Bituminous mixtures. Material specifications - Reclaimed asphalt,
was introduced on the 1st. of January 2008, you need to be aware of its contents when using reclaimed material from existing bituminous mixtures (asphalt).
ROAD PLANINGS - RECYCLING - FOAMED BITUMEN
This usually refers to bituminous material removed from the surface of roads by COLD PLANING.
If the BINDER in the material is sufficiently stiff it will stay loose and workable, although when laid, and with time it, it binds back together.
This material is ALWAYS used but it is sometimes difficult to know where, it tends to "disappear" to farm drives and private car parks.
There can be a problem stockpiling this material, especially in warm weather, it tends to stick together.
If you are sure of the quality, consistency and grading of the material it can be used in hot mix recycling.
Road planings can also be recycled using foamed bitumen as a binder rejuvenator and bonding agent.
Cold, and in an as planed condition, it can be used in HAUNCHING or CAPPING, but allow for some settlement, it is usually good policy to leave surfacing of the whole road until after haunch settlement has occurred.
TRL PROJECT REPORT PR/CE/178/95 - HAUNCH - RECYCLING
This is an unpublished report, based on work associated with three trials where recycled materials were used in the haunch construction.
There is much useful information in the report with regard to the materials used, and types of testing apparatus and methods of test used.
Also assessment of how successful the various materials have been.
TRL PROJECT REPORT PR/H/40/93 - Use of Alternative Materials in Road Haunches : A Review of Past Practice
The objective of this report is to review the experience of local authorities in re-using conventional road making materials, industrial by-products and other alternative materials for repairing haunches.
TRL REPORT 216 : TRL Report 216 : Road Haunches : A Guide to Re-usable Materials
This is a very comprehensive report, including information on recyclable materials, haunch design and construction practice.
It was derived from information obtained from actual trials using recycled materials in haunch construction, these trials being documented in TRL PROJECT REPORT PR/CE/178/95.
TRL REPORT 386 : Design guide and specification for structural maintenance of highway pavements by cold in-situ recycling
The report refers to this form of cold in situ recycling as "linear quarrying", the existing and more widely recognised term is "retread".
The authors are :- L.J.Milton and M.Earland
Published 1999
Published 1999
This report details work performed by the TRL on secondary aggregates, such as :-
China clay sand
Blastfurnace slag
Steel slags
Pulverised fuel ash
Gypsum
Cement kiln dust
These materials were formulated to a number of blends and the most successful were used in full scale trials at the TRL's Pavement Test Facility (PTF).
A number of secondary aggregate mixtures were found to be successful in producing strong road pavement foundations, and full scale road schemes have been recommended on these materials.
An excellent report covering ALL aspects of undertaking recycling processes in road maintenance and construction.
It includes advice and guidance on all the necessary rules and regulations that must be complied with in any recycling process, as well as practical examples of recycling initiatives already undertaken.
This "state of the art review" is a collection of TRL reports relating to the subject of soil stabilization.
SOIL STABILISATION being a process whereby soils and related materials are made stronger and more durable by mixing with a stabilising agent, usually a hydraulic binder such as lime or cement, or perhaps a bituminous binder like foamed bitumen.
This report is quite comprehensive in discussing all aspects of using lime or cement, or a combination of both as a means of stabilising in situ material to replace an imported granular capping layer.
It incorporates current specifications for use in Britain as well as describing specifications used in the U.S.A..
There is also information on work already undertaken with in-situ stabilisation.
THIS REPORT IS WELL WORTH READING FOR ANYBODY CONTEMPLATING SOIL STABILISATION.
This report describes the investigation of a number of soil types that were stabilised with quicklime, and subjected to a testing methodology aimed at providing data to assess the applicability of the swell test as an indicator to the suitability and acceptability of materials for lime stabilisation.
This has particular relevance to soils/ fills that contain sulphates and sulphides.
This is a fairly comprehensive report on trials performed at the TRL Pavement Test Facility (PTF) on bituminous planings and blends of materials including bituminous planings.
It includes useful information on pavement layer testing devices, including :-
Falling Weight Deflectometer, German Dynamic Plate (GDP) and the Prima 100
The contents of this report forms part of the DTI/WRAP sponsored Aggregates Research Programme to support the development of construction markets for secondary and recycled aggregates.
This is a comprehensive report offering guidance on cold recycled materials that are "bound" using hydraulic (cement, slag, pulverised fuel ash) binder or foamed bitumen, or combinations of these binders.
Although the report places emphasis on performance testing of road pavement materials produced by cold recycling, it also stresses the importance of the initial design, and its documentation.
An outline specification for a number of possible cold recycled materials is included in the Appendix to the report.
This document deals with the idea of increasing the versatility of road pavement design to give the engineer a wider choice of materials and design configurations.
This increased versatility will lead to more economic designs by allowing new materials, recycled materials and a wider range of secondary aggregates and binders to be used.
It offers the potential to enable stronger foundations to be constructed, incorporating hydraulically bound materials, providing the option of reductions in the more expensive surfacing layers.
This report provides information on a number of trials and processes to assess the feasibility of recyling the premium quality aggregate present in failing thin surfaces into new thin surfacings.
A pilot trial has taken place using CKD in the production of both binder course and surface course materials.
There were no exceptional problems to producing a good looking mat. The overall conclusion is that CKD can be successfully used as the added filler in routine asphalt mixtures, but that it varies as a product between sources (the extent of the consistency of properties from a single source has not been investigated).
TRRL Report SR 675 : In-situ recycling of asphalt wearing courses in the U.K.
Author G.D.Goodsall
Published 1981
TRRL RESEARCH REPORT 305 - RECYCLING BITUMEN MACADAMS
This report assesses the performance of off-site recycled bituminous material.
Initial results show that off-site recycling of bituminous materials can be successful when correctly controlled.
Laid sections of recycled material have performed well in trials.
The cost of recycled material may well be more expensive than conventional material.
But the planings MUST be of a consistent analysis for them to be suitable for large scale recycling.
The recent introduction of the Land-Fill Tax has considerably altered the balance in favour of recycling.
TRRL Supplementary Report 20UC : The use of unburnt colliery shale in road construction