PATCHING WITH BITUMINOUS MATERIALS

CONTENTS

THE PROBLEMS WITH PATCHING
WHAT IS PATCHING
HAND LAY MATERIALS - BITUMINOUS MACADAM & HOT ROLLED ASPHALT PATCHING
CUTBACK BITUMEN - PATCHING
FLUXED BITUMEN - REDUCING THE VISCOSITY (STIFFNESS) OF A PENETRATION GRADE BITUMEN
DEFERRED SET MATERIAL - EMERGENCY PATCHING
DEPOT STOCK - POTHOLE PATCHING WITH BITUMINOUS MATERIALS
EMERGENCY PATCHING WITH BITUMINOUS MATERIAL
BITUMINOUS MIXTURES SUITABLE FOR FOOTWAY PATCHING
HOT STORAGE BOXES FOR MAINTAINING WORKABILITY OF PATCHING MATERIALS
MINI PAVER WORK - PATCHING LARGER AREAS
RECYCLING IN BITUMINOUS ROAD SURFACE PATCHING PROCESSES

THE PROBLEMS WITH PATCHING

The fundamental problem with patching is that, it is a patch, a small area, probably a lot of small areas to be completed during the day.
 It is difficult to keep the workability of hot bituminous materials at/above a level where they are able to receive full compaction, and without full compaction the life of the patched area will be greatly reduced.
The areas patched first in the day may be satisfactory but areas patched late in the day may be poor because the temperature of the material is too low to achieve full compaction.
The temperature of the bituminous material being related to the grade (stiffness) of the bitumen in the mixture, and the grade (stiffness) of the bitumen in the mixture being related to the nature of the traffic passing over that particular road pavement.

I have brought together a number of paragraphs from other sources that will give you some advice and guidance on how to achieve good patching work, but I will make a list of points that need to be considered to obtain satisfactory work.

1) Is the patch a normal maintenance treatment of a failed area, or is it an emergency patch of a temporary nature to make the road / footway safe.
Bituminous material will be chosen appropriate to the work.

2) Where ever possible excavate the patch to sound material both at the edges and beneath.
Remove all loose material.
Tack coat the base, and fully paint with bitumen all vertical joints, when and where this process is possible. 
It is unlikely that tack coating the base and sides of a pothole will be of benefit if you have just brushed water out of the pothole.

3) Choose an appropriate material for the patch. 
It is usually possible to successfully undertake patching with one suitable bituminous mixture. 
I have found that it is usually more successful to use a thicker layer of one material than to lay a thin binder course covered with a thin surface course. Both materials loosing heat rapidly at the time of patching, before compaction.
Of course if it is a large patch, of some area and depth into the road pavement then a binder course and surface course is the correct procedure. 
But in some situations, e.g. rural areas you could lay two layers of the same material, thoroughly compacting the first layer before laying the surface course layer. 
This greatly aids the efficiency of patching with regards to the number, and use, of materials carried on the lorry.

4) Consider the viscosity (stiffness), and the aggregate size.
In patching work it is often wise to choose a material of a slightly smaller stone size than would usually be recommended in that situation in the actual road pavement design, this is because you will obtain better workability, have less segregation and be able to "feather" the material to the edge of the pothole, and you will achieve better compaction.
In my opinion, only use a large material, e.g. a 20mm. dense binder course where potholes are of a deep nature, in access of 50mm., and a good rake-hand should still be able to "feather" the edges by discarding (raking away) the larger aggregate in these areas and use only the fines present in the mixture.

5) Lay, rake and compact the material while it is still hot.
This means having enough operatives on site so that material can be rolled as soon as it has been raked to level.
( This last point can be relaxed if you are using a bituminous mixture with a heavily cutback bitumen binder, but only use this material in temporary patches. )

WHAT IS PATCHING

PATCHING I am afraid is all things to all men !

1) From high quality 14mm./30% HRA SURFACE COURSE with PRECOATS
to low quality DEPOT STOCK used in EMERGENCY PATCHING to make a pothole, or dangerous area of highway, safe.

DfT DESIGN MANUAL FOR ROADS AND BRIDGES : HD 31/94 - Maintenance for Bituminous Roads,
( copies able to be downloaded from www.standardsforhighways.co.uk , gives guidance on this subject. )

What it is necessary to point out is that you require the material, and conditions of laying it, appropriate to the PATCHING in hand.

E.g. 30% HRA in organised patches on major roads already surfaced with this material.

2) Perhaps 10mm.or 14mm. CGM SURFACE COURSE on "shallow" rural and urban road patches where there is not weakness in the road pavement,
and 20mm. dense binder course where the potholes/patching is deeper showing weakness in the road pavement.

3) And highly CUTBACK general purpose 20mm. OPEN GRADED BINDER COURSE as DEPOT STOCK able to be taken cold from the depot at any time for EMERGENCY PATCHING, usually where you have had a dramatic failure of "trench work" to utility work.

Quick curing proprietary "bucket" materials can be used for smallish pot holes, and although material purchased in this way is very expensive, it can be a cost effective procedure for small amounts of emergency work.

N.B. the above are particular examples to highlight the varied nature of patching, and there are many more alternatives that will work equally well in particular situations, especially planned patching work.

In this context, with the modern plant that is available consider a recycling method, such as, "hot patch" treatment or by reclaiming and recycling, on site, the bituminous mixtures in the failed, potholed, areas.
You will find details of, and links to further information, on these processes further down this page.
As well as being a truly "green" option, with the ever increasing cost of bituminous materials, they are also cost effective. 

HAND LAY MATERIALS - BITUMINOUS MACADAM & HOT ROLLED ASPHALT PATCHING

In theory, and in practice, given the good weather and good workmen you can hand lay all coated materials correctly even 14mm. 30% HRA surface course with PRECOATS.

But in reality the term HAND LAY MATERIAL is usually taken to mean bituminous material modified in some way, this modification makes the material easier to work by hand.

This usually means the use of a CUTBACK BITUMEN as the BINDER.
This can be purchased as a ready blended cutback binder for direct mixing on the production plant, or the material can be "cutback" by the addition of a volatile oil at the mixing plant at the time of mixing.
All types of bituminous mixes can be used as HAND LAY MATERIAL, but where CUTBACK BITUMEN is used it is more appropriate to use OPEN GRADED MACADAMS as the volatile cutback oil will evaporate quicker and thus the material will achieve the more favourable base binder properties earlier in its life.
Until the volatile oil evaporates HAND LAY MATERIALS can be susceptible to deformation, as well as be "sticky" to drive or walk on, and can cause problems in frequently used pedestrian areas.

CUTBACK BITUMEN - PATCHING

Cutback bitumens are manufactured by blending a penetration grade bitumen, often 100pen. but more usually 200pen., with a VOLATILE oil usually kerosene or some similar oil based additive, to decrease the viscosity of the binder and improve the workability of the bituminous mixture.
NOTE - The use of creosote as an additive for cutting back bitumen is no longer permitted.

Cutback bitumen mixed with an appropriately graded aggregate will produce materials that are easier to handle at lower temperatures, e.g. HAND LAY MATERIALS and patching materials.

CUTBACK BITUMEN was specified in the easier to understand BS 3690 : Part 1, but this has been superseded
from 1st January 2002, by
BS EN 12591 : 2000 : Bitumen and bituminous binders - Specifications for paving grade bitumens, 

In the course of time the volatile oils will evaporate and the bitumen will assume its original viscosity.
This process can be quite quick or take a considerable time depending upon such factors as :-
(1) the amount and type of VOLATILE oil used.
(2) the thickness of layer, thinner layers quicker volatiles loss
(3) the prevailing weather conditions to aid or hinder evaporation. 
(4) the type of material e.g. close graded or open graded, volatiles will evaporate quicker from open graded

FLUXED BITUMEN - REDUCING THE VISCOSITY (STIFFNESS) OF A PENETRATION GRADE BITUMEN

It is important to know the difference between a "standard" penetration grade bitumen that has been cutback with a volatile oil, that given the correct condition will eventually evaporate, and a standard penetration grade bitumen that has been fluxed to obtain a penetration grade bitumen of reduced viscosity/stiffness.
With a fluxed bitumen the change in viscosity will be permanent, they will not, should not be any evaporation of the flux oil, it has become an integral part of the lower viscosity/stiffness bitumen that you have created.

It is particularly important to be aware of the difference of these processes as they are now both allowed to occur in the mixing plant at the time of production.
The fluxing of stiffer penetration grade bitumen to produce lower viscosity penetration grades of bitumen only being permitted in the last few years. 
Information on these processes can be found in the now superseded later editions of BS 594 and BS 4987, 
and the relevant parts of the family of specifications, BS EN 13108 : 2006 : Bituminous mixtures. Material specifications, that, from the 1st. of January 2008, have taken their place.
I mention this on this particular page because these production processes are more likely to occur when producing small tonnages of bituminous material for patching.
You must also be very careful in the use of "terminology" and "descriptive phrases" related to these processes, not everybody may use the same terminology I have used.
Without any intent to mislead, some sales people, production people, engineers, technicians and contractors just use different terms to describe materials and processes, so just be sure you all know what you actually mean when specifying/ordering a particular bituminous material. 
You can see from the picture to the left when either by an actual error at the production plant or because of the "confused" use of terminology when specifying/ordering the material what may result.

I am assuming that somebody did not deliberately specify/order a "soft" material because it would be easy to lay in the winter, without knowing the consequences of his action when warm summer weather came round. 

DEFERRED SET MATERIAL - EMERGENCY PATCHING

This is the term applied to proprietary bituminous materials designed to stay workable at low temperatures, and with some materials even when cold, hence the name, because the setting of the material is deferred.

This material is used for small areas of emergency patching where a small amount of workable material is needed at any time.

Although you can buy this type of material in bulk, it is more usually bought packed in poly bags or tubs for ease of storage.
It will not start to "set" until it is exposed to the air and the volatile oils that keep it workable are lost.

Some formulations are based on a BITUMEN EMULSION binder and in this case it is usually the evaporation of the water element that causes the setting.
Generally it is not wise to use this material in large areas or under heavy traffic, it has been known to become very lively in hot weather and deform under wheel load, even plucking out on some occasions.

There are some "tubbed" materials that use "white spirit" as the volatile component, this evaporates very quickly and the material reverts to the base binder stiffness quite quickly, these materials are not really a deferred set material, except if you compare them to a conventional hot mixed bituminous material with a penetration grade bitumen.

Because of the many "formulations" involved in the production of "tubbed" materials it is not possible for my comments to relate to all products on the market.
What I would say is, do not commit yourself to purchase large quantities of any product until you have performed trials through the cold of winter and into the heat of summer.
However, it is unlikely that one product will meet all your practical engineering requirements through winter and summer, but some will be better than others, and that is for you to determine and then relate it to cost.

DEPOT STOCK - POTHOLE PATCHING WITH BITUMINOUS MATERIALS

This term usually refers to bituminous material that is highly CUTBACK so that it can be stockpiled in a depot from where it can be collected for several days and still be usable, this material is used only in emergency or temporary work.
You may feel you require two types of material for DEPOT STOCK, a coarser material for larger potholes or the filling of emergency trench work, and a finer material where layer thickness is not great or you need to "feather" the material to nothing.

"Open" materials are chosen to allow the volatile cutback to evaporate more quickly.

The following materials are suitably graded for use with an appropriate cutback bitumen,
20MM. SIZE OPEN GRADED BINDER COURSE (BASECOURSE) MACADAM, ( larger/deeper potholes ) 

6MM. SIZE MEDIUM GRADED SURFACE COURSE (WEARING COURSE), ( smaller/shallower potholes )

MACADAM, 20MM. SIZE OPEN GRADED BINDER COURSE - DEPOT STOCK - TEMPORARY PATCHING

This material is/was specified in BS 4987:PART 1: CLAUSE 6.1,
and it shall be transported / laid / compacted to BS4987:PART 2

However BS 4987:2005 has been superseded, from 01/01/2008, by 
BS EN 13108-1   : 2006:Bituminous mixtures. Material specifications - Asphalt Concrete 
or, easier to understand, 
PD 6691:2007: Guidance on the use of BS EN 13108 Bituminous mixtures - Material specifications

N.B. This is often used as a DEPOT STOCK / EMERGENCY PATCHING material, when it will be heavily cutback with a volatile oil.

Nominal thickness ..................45mm. to 75mm.
Minimum thickness at any point .....40mm.
Rate of coverage at 60mm. ...........9.0 sq.metres/tonne
Viscosity ...............................200pen .......300pen .......200/100secs
Max. delivery temp. .....................125 ..........115 ..........100
Min. delivery temp. ......................95 ...........85 ...........60
Minimum rolling temp. ....................75 ...........65 ...........40
The minimum rolling temperature figures are the minimum temperatures immediately prior to rolling.

EMERGENCY PATCHING WITH BITUMINOUS MATERIAL

The term applied to patching, as the title states of an emergency nature.
If there is a pot-hole or road defect, reported to the authority which requires making safe immediately, DEPOT STOCK material is taken from the depot to fill the hole and make it safe.

This type of PATCHING is of a temporary nature and will require replacing with correctly performed patching with a permanent material when funds and work load permit.

Alternatively DEFERRED SET MATERIAL, i.e. the type that comes in sealed tubs can be used for small areas, these materials are expensive but convenient, and SOME are a lot more effective than others at actually "staying put" in the pothole , know what you are specifying.

BITUMINOUS MIXTURES SUITABLE FOR FOOTWAY PATCHING

There are basically only three SPECIFIED bituminous materials that can be used for footway surfacing and patching.
This is because we usually want to put only a thin layer of material down, so avoiding construction work, i.e. lifting kerbs and ironwork.
These materials are:-
MACADAM, 6MM. SIZE MEDIUM GRADED SURFACE COURSE
MACADAM, 6MM. SIZE DENSE SURFACE COURSE
MACADAM, 3MM. FINE GRADED SURFACE COURSE (this was known as FINE COLD ASPHALT).

These materials  are/were specified in BS 4987, and can now be found in the relevant parts of the superseding British/European standard,  BS EN 13108 : 2006 : Bituminous mixtures. Material specifications

MACADAM, 6MM. SIZE MEDIUM GRADED SURFACE COURSE

This is used for footway surfaces, patching, and minipaver work, it is suitable with cutback binders as volatiles evaporate more readily from the open nature of the material matrix..
Specification information shown is/was BS 4987:CLAUSE 7.6 (And all information in Parts 1 and 2),
However BS 4987:2005 has been superseded, from 01/01/2008, by 
BS EN 13108-1  : 2006:Bituminous mixtures. Material specifications - Asphalt Concrete 
and with finer bituminous mixtures
BS EN 13108-2  : 2006:Bituminous mixtures. Material specifications -  Asphalt Concrete for very thin layers
or, easier to understand, 
PD 6691:2007: Guidance on the use of BS EN 13108 Bituminous mixtures - Material specifications

Nominal thickness .....................20mm. to 25mm.
Minimum thickness at any point ........15mm.
Rate of coverage at 25mm. .............17 sq.metres/tonne
Viscosity .............................200pen ...........300pen ..........100/200secs
Max. delivery temp. ...................125 ..............115 .............100
Min. delivery temp. ....................95 ...............85 ..............60
Minimum rolling temp. ..................75 ...............65 ..............40
(prior to rolling)

MACADAM, 6MM. SIZE DENSE SURFACE COURSE

This material is widely used for footway surfaces often with a 100sec binder for easy working, but 300/200pen would be better.
A straight run 300pen. binder is a good compromise viscosity for hand lay footway work.

Specification is/was BS 4987:CLAUSE 7.5 (And all information in Parts 1 and 2),
A viscosity less viscous (less stiff) than 100secs is NOT specified in BS 4987

However BS 4987:2005 has been superseded, from 01/01/2008, by 
BS EN 13108-1  : 2006:Bituminous mixtures. Material specifications - Asphalt Concrete 
and with finer bituminous mixtures
BS EN 13108-2  : 2006:Bituminous mixtures. Material specifications -  Asphalt Concrete for very thin layers
or, easier to understand, 
PD 6691:2007: Guidance on the use of BS EN 13108 Bituminous mixtures - Material specifications

Nominal thickness ....................20mm. to 25mm.
Minimum thickness at any point .......15mm
Rate of coverage at 25mm. ............17 sq.metres/tonne
Viscosity ............................100pen .....200pen .....300pen .....100/200secs
Max. delivery temp. ..................160 ........150 ........130 ........120
Min. delivery temp. ..................120 ........110 ........100 .........75
Min. rolling temp. ....................95 .........85 .........80 .........50
(prior to rolling)

MACADAM, 3MM. FINE GRADED SURFACE COURSE - FINE COLD ASPHALT

This was previously known as FINE COLD ASPHALT.

This material with the appropriate BINDER is used for footway surfacing (overlays) and patching.
Specification is/was BS 4987:CLAUSE 7.7 (And all information in Parts 1 and 2)

However BS 4987:2005 has been superseded, from 01/01/2008, by 
BS EN 13108-1  : 2006:Bituminous mixtures. Material specifications - Asphalt Concrete 
and with finer bituminous mixtures
BS EN 13108-2  : 2006:Bituminous mixtures. Material specifications -  Asphalt Concrete for very thin layers
or, easier to understand, 
PD 6691:2007: Guidance on the use of BS EN 13108 Bituminous mixtures - Material specifications

Nominal thickness ......................15mm. to 25mm.
Minimum thickness at any point .........10mm.
Rate of coverage at 20mm. ..............21 sq.metres/tonne
Viscosity .........................200pen .........300pen .........100/200secs
Max. delivery temp. ...............150 ............130 ............120
Min. delivery temp. ...............110 ............100 .............75
Minimum rolling temp. ..............85 .............80 .............50
(prior to rolling)

HOT STORAGE BOXES FOR MAINTAINING WORKABILITY OF PATCHING MATERIALS

The "box" can be mounted on a vehicle or be able to be free standing on site or in a depot yard.
It can be just simply insulated or oil jacketed with the circulating oil being heated by a gas burner.
They mobile models usually store a small tonnage, up to 5 tonnes, with depot models able to hold in excess of 20 tonnes.

The purpose is to keep small tonnages of material hot for long periods, thus increasing the workability of the material and the period over which it can be used and is still able to be satisfactorily compacted.
This is especially useful when small amounts of material are being used at a time, e.g. patching.
This allows use of better quality materials with less waste and better results, i.e. better compaction is able to be achieved with hotter material.
But be aware that extended storage, e.g. overnight, of any hot mix bituminous material will affect the quality of the bitumen component of the mixture, and hence the engineering properties of the patching material.
Other factors will influence the storage period, such as, the original viscosity of the bitumen, the original temperature of the mixed material, and the structure of the matrix of the mixture, i.e. "open" materials will lose volatiles more rapidly than dense materials.

MINI PAVER WORK - PATCHING LARGER AREAS

This is a very cost effective way of restoring poor haunches and bad cross section of rural/lightly trafficked roads.
The MINI PAVER has a narrow "bed" for laying purposes, i.e. adjustable but usually 1.5 to 2 metres wide.
For a road which is basically strong but has failed haunches and a convenient high centre crown the bed of the paver is controlled so that a good thickness of material (40/60mm) is laid at the edge and feathered to nothing at the centre.
The road is TACK COATED prior to laying the material to improve bonding.

It is also strongly recommended to use a mini paver to patching work where the patches are large as ride quality will be much better than when materials are hand laid.

The material normally chosen for this process is usually 6mm MEDIUM GRADED MACADAM or 6mm DENSE SURFACE COURSE, this is to allow for the "feathering to nothing" at the road crown to be quite successful, especially if the correct rate of tack coat has been applied.

Even though machine laid, I would recommend a 300PEN binder for increased "stickability", other people prefer a 200pen. binder.

RECYCLING IN BITUMINOUS ROAD SURFACE PATCHING PROCESSES

There are now several processes that can be employed in recycling areas of bituminous road surface that contain cracking or similar types of failure.
The are two main processes, one process is the heating of the road surface in situ by the application of indirect heat to the bituminous mixture that is the road surface, this process is often referred to as "infra red" patching, as in some processes a significant proportion of the applied heat is in the infra red spectrum.
If the nature of the failure is a true crack, because of underlying weakness, in an otherwise sound surface material it may not even be necessary to add any rejuvenating additives.
If there has been localised deterioration of the surface course (wearing course) associated with some loss of material then fresh material can be added along with bitumen based rejuvenating additives.
When the appropriate temperature is reached, in relation to the grade of bitumen in the material, the total material can be reworked and compacted.
A definite bonus to this type of patching is that there are no cut joints at the edge of the area patched, as failed joints from on patch can often be the cause of the next area of failure and need for further patching, or at least joint/crack sealing

The other main process involving recycling in the patching process is still an on site operation but involves the total removal of the failed are placing it in an asphalt remixing machine to reheat the material and to add an appropriate amount of new bitumen to the mixing process to produce a reheated, remixed, rejuvenated bituminous mixture with which to perform the patching operation.
Asphalt mixers are now available to perform small and large amounts of recycling patching work.

The benefits of both these process are similar, in that,

The existing material is reprocessed so a saving on the extraction of new aggregate.
The work is done on site so fewer lorry journeys to tip or off site reprocessing plant, and fewer lorry journeys delivering new material to site.
According to the scale of the operation the cost of extra equipment can be offset by the savings in the cost of new material.
In my opinion, and experience, with larger scale operations there should be a definite saving in costs, especially if this is an "in house" operation.

For access to other useful pages relating the bituminous materials and working procedures  ------------------------------> HERE


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