Surface Dressing & Microsurfacing

A Technical Library

HRA Patching

5 Year Guarantee

A Failed Surface Dressing

Intermittent Website Access

Motto of the Month

Introduction

Good morning to you all, I say good morning because I am beginning to write this newsletter early in the morning, with my study (spare bedroom) window open wide and the local blackbird singing his head off, everything is right with the world.
So let me begin and start to discuss the world of highways maintenance. 
Because it is this time of the year, early Summer, in my opinion the best time of the year, this newsletter may be short, but sometimes they "develop".
For those of you who are not aware of my policy on newsletter writing, I feel entitled to add to any current newsletter until a subsequent newsletter is written, from that time there will be no alteration to a past newsletter unless it is to correct some spelling or grammatical error, so past newsletters will be as they were originally produced. 
This means it is quite interesting to browse through back copies of the publications from time to time to see how things have "progressed".
It is just as interesting to browse through back copies of highways maintenance journals and publications, even technical reports. 
I am sure their are those in the highways maintenance fraternity who wished they could retract some of the comments they have made, and articles they have written, but they seem to survive remarkably well in the elite positions they occupy, just like some politicians.
I cannot think of any comments that I would like to retract. I still recommend hot rolled asphalt and precoats as my premium road surfacing. I still like and recommend surface dressing designed and performed by experienced "crews". This process not only provides cost effective highway maintenance but I really I appreciate the rugous texture of this surface on the rural roads I travel in the winter, when not all of them receive salting as a priority.
And, for a surface course on a rural road/light urban highway network you cannot go far wrong with a good 10mm. or 14mm. close graded macadam, or asphaltic concrete if you want to use its new name, it is still the same material, and the recipe, yes recipe, specification you will find in Table B.14 of PD 6691 is very similar to those proven specifications (recipes) found in BS 4987. 
But I do recognise and appreciate the full diversity of excellent materials and processes available, and the craft of the gangs able to provide them. 
But, you the Engineer and Engineering Technician must have the knowledge and experience to select and use them appropriately, and I am afraid that these skills are not present in many of the younger Engineers and Engineering Technicians.
Do not be "sold" materials and processes that, at best, are not value for money, and often not able to cope with the site conditions that prevail. So be cautious, there is an increasing amount of "hype" out there, offering you materials and processes that are just not able to "deliver", if something appears to be too good to be true, it is most likely to be just that, too good to be true. 
Unfortunately it often takes a little time for this to become apparent, and by then it is often too late to seek redress.

So, moving on with regard to this theme, and the first of a couple of items on new developments in the real world of highways maintenance, let's talk surface dressing, again, do not groan, it really is interesting, well I think so.
Also slurry surfacing and microsurfacing, these being materials and processes you may be less familiar with, especially under their new names, but still worthy of study, and use on appropriate sites. 

PD 6689:2009:Surface Treatments (Surface Dressing and Microsurfacing)

The full title of this recent publication, which came into effect on the 31st. of May 2009, being,
Published Document, PD 6689 : 2009: Surface treatments - Guidance on the use of BS EN 12271 AND BS EN 12273
and to help clarify the nature of this important document let me straight away give the full title of the two British European Standards that it refers to, 
BS EN 12271 : 2006 : Surface dressing : Requirements
and
BS EN 12273 : Slurry surfacing : Requirements

PD 6689 is in essence a document to give guidance to those on the client/purchaser side of the highways maintenance industry who are purchasing surface dressing or slurry seal products on a performance basis.
Meaning they will enter into a contract with their contractor/producer/supplier to supply a product that conforms to defined "specified" characteristics.

I cannot improve on the descriptions of the nature of BS EN 12271 and BS EN 12273 than to include the introduction to PD 6689 here, and I acknowledge the copyright of BSI on the following extracts.

"Introduction 
BS EN 12271 - Surface dressing
BS EN 12271 specifies a range of categories for the properties of surface dressing to enable users to select appropriate limiting values for a wide range of uses within Europe.
The specifier needs to define BS EN 12271 categories for the properties relevant to the particular end-use of the surface dressing. Some example specifications for different end-uses are given in Annex A.
BS EN 12271 covers surface dressing specified by performance of the finished product. It does not cover surface dressing works carried out to the purchaser's design, commonly called a recipe specification.
This type of specification can continue to be used, but purchasers are responsible for the performance of the surface dressing provided that the works have been executed correctly.
Performance categories set out in BS EN 12271 should not be included as part of a recipe specification as this might result in the recipe being correctly placed, but the performance categories not being met.
NOTE  The body responsible for the design is responsible for the performance of the surface dressing (provided that the works have been correctly executed).

BS EN 12273 - Slurry surfacing and microsurfacing
BS EN 12273 specifies a range of categories for properties of slurry surfacing and microsurfacing to enable users to select appropriate limiting values for a wide range of uses in Europe.
Specifiers need to define BS EN 12273 categories for properties relevant to the particular end use of the slurry surfacing and microsurfacing. Some example specifications for different end-uses are given in Annex B."
"Scope (a further extract)
This Published Document gives guidance on the performance requirements and control procedures for the installation of both surface treatments as products for the maintenance of roads and other trafficked."

I am a person who took my role seriously, and when I need to appraise a new document/specification I still take the same approach. So when presented with a new publication such as this I read it from cover to cover, put it down, come back and read it again cover to cover, every little nuance, and I can often see the hand of one or other of the authors supplying snippets of very useful information.  
It is my opinion that this Published Document does everything "that it says on the can", and some.
The level of information included in this document with reference to any product/process that involves the use of aggregate and bitumen/bitumen emulsion is excellent, and the associated cross referencing to other technical specifications/documents is extremely good, inviting the reader to gain further useful information/knowledge. 
This aspect of the document will be a significant help to any Engineer or Engineering technician who wishes to increase his understanding of these products/processes by accessing/studying the many cross referenced source documents.
My concern, if I have a concern, is that "specifiers" will just "poach" the sample specifications from the annex to the specification without any study as to what they actually mean.
I do not believe this is the intention of the document and I feel the significant contribution it could make to the understanding of these particular surface treatments will be lost if this occurs, and the reader will not have enjoyed the opportunity to learn from the many "snippets" of helpful information included in the text.
To give one small example of a helpful snippet, 
"Aggregates used in surface dressing should conform to BS EN 13043 . Recommendations for the grading of surface dressing chippings are given in PD 6682-2:2009:Table 4. In order to ensure the absence of any potentially damaging oversize, the guidance in PD 6682-2:2009:Table 4, footnote (A), should be followed."
Now I know what it means, and I think it is important, and at least some members, if not all, of the committee preparing this document know what it means and thought it was important to include it, but do you know what it means, perhaps you need to ask your Materials Engineer.

To briefly recap, if you the client/purchaser are procuring your surface dressing or microsurfacing as a product, i.e something that is likely to carry a brand name, and this is the way the commercial side of the industry is trying to move, these are the documents for you to purchase and study.
If you still use more traditional methods for letting your highways maintenance contracts, and still have an Engineering Team capable of designing the work and instructing the contractor on what work he is to perform, these documents are not aimed at you.
The latter situation is most likely in county and large metropolitan authorities that still retain a Direct Labour Force, with past knowledge and experience of surface dressing and slurry seal for footways.
However, I would still strongly recommend the above documents as a useful addition to your Technical Library because of the information and references that they contain, I regard them just as much as a learning/instructional reference as specifying documents.
As a young lab technician I learnt most of what I know from comprehensive (and I think more user friendly) British Standards, the Specification for Highway Works, TRL Reports, and other related technical documents, and because I worked in the practical side of highways maintenance and highway construction for most of my career I could see the importance of their application.
PD 6689 is a Published Document and is not to be regarded as a specification, its purpose is to give guidance on the use of BS EN 12271 and BS EN 12273, it is my opinion that it does it rather well.

Reference to most of the current BS EN Standards that are relevant to current Surface Dressing and Slurry Surfacing practice can be found on the web page,
Guide to some of the BS EN (European) Specifications, relevant to Highways Maintenance and Construction
and/or the web page,
Carriageway Slurry Macadam / Micro Asphalt 

A Technical Library

It is my opinion that all purchasers of materials for use in highway maintenance and/or construction should possess a Technical Library of all relevant British Standards, copies of the Specification for Highway Works, particular TRL Design Guides and other technical documents pertinent to the products and processes they are purchasing. 
This includes any contractor or consultant who is the "agent" for the purchasing organisation. 
I also firmly believe purchasers should have at least one competent member of staff who is familiar with the content of the technical documents in the library, and who is able to access the necessary information as and when it is required.
I would hope that this is a qualified and experienced Materials Engineer, (this used to be one of my responsibilities).
I really cannot comprehend the amounts of money that are spent on materials and materials processes without having access to the information that controls the quality of the materials, and the nature of their use.
These documents are also a great store of knowledge on the many items they cover, and accessed correctly are an extremely beneficial source of instruction for young Engineers and Engineering Technicians.
It used to be surprising to me the number of young graduates that would be employed into the Highways Department where I was employed who had very little experience, if any, of the "materials" side of highways maintenance and construction.
I used to liken these young people to top of the range PC's with an operating system, and maybe a few basic programmes, but without any "data" on the hard drive.
A technical library provides a good source of "data", and newcomers to the profession who are interested, with a little direction from their peers will find this "data", and then it remains for the Engineers and Engineering Technicians of the future to build up their experience of implementing the various standards.
The argument is that British Standards are too expensive for the, in many cases, small number of pages that make up a standard or part of a standard, and I have to admit their are a few extreme examples of this that perhaps BSI could deal with. 
But in general when you consider the importance of what is covered in the text I believe they are extremely good value, especially when you consider the time and effort that has gone into producing them.
Even a single site of work, such as slurry surfacing, may cost several thousand pounds. A contract of a number of sites of such work may cost tens of thousands or even hundreds of thousands of pounds. 
And a surface dressing contract for a large rural county is likely to cost into the millions of pounds. 
The cost of total bituminous mixtures purchased and associated laying in a year, could cost into the tens of millions for a large authority.
So the cost of "standards" in reality are of little consequence, in my opinion, and to work without access to them is foolhardy.
I really would like to hear the argument why, more often than not, it is not the policy of our "Strategic Managers" to ensure that the organisations they control have appropriate Technical Libraries and the Engineers or Engineering Technicians who understand how to maintain and use them.

Hot Rolled Asphalt Patching - A5 Trunk Road

This is a far more interesting, and far reaching, item than most readers will realise.

Do you recall the image to the left, from the Winter 08/09 Newsletter, showing breakout/potholing of proprietary thin surfacing in a highly stressed area around an island on the length of the A5, close to the town of Hinckley, between the A5/A47 island and the A5/M69 interchange.

Perhaps you would now like to look at the image below of the same site showing patching work on the failed area of the road surface.

I would like to think that it is unnecessary for me to explain what is shown in this image, but just for clarification I will give some minimal information, leaving you the reader to verify what I indicate.
Yes, it is hot rolled asphalt and 20mm. precoats.
It is my opinion that that the patching has been completed to a high standard, perhaps the precoats could have been spread a little better but I am being fussy,
More importantly the joints appear to have been well cut with a minimum of disturbance in the existing surface, and the overbanding has been kept within the allowed tolerance.
The really interesting point regarding this patching is not so much that it is HRA and precoats, but that as far as I am aware this goes against all Highways Agency "directives", unless there has been some drastic and surprising recent changes.


I am assuming that the HRA is a generic mixture produced to a proven "regular" recipe/design with a 50pen. binder, possibly from PD 6691.
( However I cannot rule out the possibility that the industry have recently started to produce proprietary HRA and precoats, as it would easily fit in to the "Thin Surfacing" thickness/thinness requirements, usually being laid as a 40mm. layer, and I certainly hope that nobody is going to have the nerve to brand it  "Aspho-Chip".)

If it is any comfort to the Managing Agent for this area of Motorways and Trunk Roads I believe that HRA is the most appropriate bituminous mixture to use in this situation, but I would say this for the reasons I mentioned in the introduction to this newsletter.

It remains to see the Pandora's Box of comments this small action will produce, I have a feeling that there is going to be a considerable response from the "industry" to this action.
I would give my support the Engineer/Contractor who sanctioned this work on this particular site, but this may only cause  him/her more problems.
This simple operation will be hotly "discussed", even if it is behind closed doors.

5 Year Guarantee

Following on from the above item, and what I perceive as definite changes in policy to the supply and use of proprietary bituminous mixtures produced to Thin Surface Course System guidelines supervised by the BBA, you may like to read Para 15 (08/08) of Clause 942:Thin Surface Course Systems of the Series 900 - Road Pavements - Bituminous Bound Materials, the August 2008 amendment.
There has been a major revision from the previous version of Clause 942, i.e. in the Amendment 2004 of the Series 900, please check out the differences for yourself, do not just take my word for it.
Clause 942 now states, "On the trunk road including motorway network the Contractor shall guarantee the integrity of the surfacing and the workmanship for a period of five years from the date of opening to traffic, unless otherwise specified in Appendix 7/1.
Para 16 (08/08) states, "The five-year guarantee shall include for defects such as fretting, ravelling, stripping and loss of chippings. The guarantee shall exclude defects arising from accidental damage or damage caused by settlement, subsidence or failure of the underlying carriageway on which the surfacing material has been laid."
Whether this will bring about a change to the "guarantee period" stated on BBA certificates for the Thin Surface Course Systems that have gained approval I am not sure, it may be just as Para 15 (08/08) states and be site/contract specific. 
What I would suggest is that this extended guarantee period may indicate that the Highways Agency (Government) are not happy with the performance of some proprietary bituminous mixtures that have been supplied under the Thin Surface Course System approval scheme.
Please do not blame the failure of these materials just on workmanship. I knew, still know, many of the men in the laying gangs, they do their best with what they are supplied, they really do.

I am not going to elaborate any further, my views on this subject are well known, perhaps somebody somewhere is beginning to take note. 
Five years still seems a relatively short period for a surface course to survive, to me, but it is a hell of a lot better than a two year guarantee. 
If we are going to be satisfied with a five year surfacing life I can foresee the eighty year backlog on whole network resurfacing extending to eight hundred years. It is a poor joke, but I am sure that you get my meaning. 
I know that my views are shared by many others, but they are not for various reasons and commitments, able to be as vocal as I am.
But do not even believe me, get out of your office and look at the roads surfaces laid from 1998 onwards and the road surfaces (bituminous mixtures) still existing from before that time.

A Failed Surface Dressing (and possible consequences)

This is a brief story of the consequences of a surface dressing failure, should it happen, they are rare occurrences, certainly around where I live.
Should a major surface dressing failure happen soon after dressing, i.e. loss of chippings, areas of exposed bitumen, fatting up in wheel tracks, etc. etc. the initial response must be to get fresh, usually smaller, chippings down to stabilise the situation to give you some time to think and to protect the road users, and of course keep the 20mph. signs up, somebody might take some notice of them.
When the situation has stabilised, and you have had time to think, you do not want to be rushed into a decision, you may decide to overlay the failed area with a modern "Thin Surfacing / Negative Textured" type material, possibly of an SMA "type".
Nothing wrong with this decision, if you have thought it through, and the consequences, and costs, that will result, at least in the initial years, possibly for the life of the surface if it is porous.
A successful surface dressing provides a rugous and impervious surface, with a "normal" PSV chipping its surface texture and skid resistance will be good, with a high PSV chipping it will be very good.
These are benefits that you will acquire all through the year, especially beneficial in wet weather when skid resistance of a road surface is truly judged.
However we must not forget that during winter, and winter maintenance treatments, a good surface dressing will require only "normal" precautionary salting treatment, if it is on a primary salting route, whereas "Thin Surfacing / Negative Textured" bituminous mixtures will require an increased rate of spread of salt/grit.
This requirement is now well documented, if little talked about, do not believe me, check out the information and links that can be found on the page, Road Salt for Winter Maintenance .
Before you know it the "Cold Comfort" conference will be with us, perhaps somebody, possibly from a large rural authority would like to raise such issues. These are real issues that will place an increased demand on budgets, which in turn may impact on the maintained safe condition of our highway networks during the winter period.
In my opinion it is the rural networks that will feel the cuts, and their effects, before the motorways and trunk roads.
I have said many times, and I will say it again, there is a great deal to think about when maintaining a highway network, and you need "real" engineers and technicians, with experience, to be able to do the thinking, "suits" just do "deals", mostly with other "suits".

"Keep thinking Butch, it is what you are good at", sorry to squeeze in another quote, but I think that is my favourite film of all time, but he did get cut down in a hail of bullets at the end when up against the might of an established army, or did he?

Intermittent Website Access

I am sorry if you are experiencing poor access to my website, this is entirely beyond my control and rests with my Web Hosting Provider.
I have contacted them on a number of occasions, but they say, I think, that they do not experience the problem when they access my website.
But I did have difficulty understanding the gentleman in the call centre who had to continually put me on hold to consult the "engineer", about the problem I had described.
It is likely that the situation will be rectified, eventually, by somebody who actually knows what he/she is doing, possibly "an engineer", until then I hope that you will be patient.

Motto of the Month

"Knowledge is of two kinds. We know a subject ourselves or we know where we can find information upon it."

I find I cannot resist adding an item to "Motto of the Month" based on what I heard recently on the Radio 4 "Today" programme. The item was in response to the news that the London underground rail system were going to be introducing well documented little anecdotes of a philosophical nature amongst their various other platform and onboard train announcements.
The "Today" programmed had invited the stand-up comedian and writer (and "grumpy old man") Arthur Smith into the programme for his comments. 
As part of his response he voiced a number of his own anecdotes which he thought worthy of consideration for the current world situation.
The one I particularly liked and wrote down while I remembered it, is,
"Everything has been said before, but because nobody listens it has to be said again."