FAILED THIN 6MM. BITUMINOUS WEARING COURSE ON A SECOND SITE,
9 YEARS AFTER LAYING

Although with this second site that is discussed, here it may be fairer to say that it has just come to the end of the projected life for this type of material, i.e. 20mm. nominal thickness of a rubberised 6mm. medium textured surface course laid on an existing surface.
This page cannot be read in isolation, you must read the previous two connected pages, and possibly the other pages, that are provided on this website, that relate to bituminous mixtures that can be laid thinly, and proprietary bituminous mixtures described as "Thin Surface Course Systems" and "Negative Textured Surface Course".

The first site discussed, at the time of laying the surface course
The first site discussed, four years after laying
The first site, after six years, and this adjacent second site eight years later, summary

FOREWORD - This page contains many images and I have heavily compressed them to allow for speedy downloading.
This does mean that image quality has been sacrificed but I hope that it does not compromise the information that I am trying to present.

I have also taken the opportunity in writing this page to bring to the attention of readers a number of associated aspects that an Engineer or Technician should be aware of in highways maintenance, especially road surfacing.
There is a lot of discussion within this page on "real" aspects of highways maintenance. 
This very important aspect of ensuring the flow of modern living is not achieved by "networking" at "meetings" in your posh suit. 
The bottom line is that somebody has got to know what they are doing and be encouraged, not discouraged, from exercising that knowledge.
And, the knowledge required is how to cost effectively maintain a highway network. This ability being especially important when highways maintenance budgets are reduced, as always, to fund other areas of local and national authority responsibility in times of financial difficulty.
All I see in my "area" is the premature loss of more and more "knowledge", which will ultimately result in the decline of the standard of the highway network.
An increasing number of examples of this failure in performance becoming quite obvious to me, if not to others.
It is hard to see it from an office, but our "customers" the road users, of all types, can see it, and these people vote, locally and nationally.
Perhaps the driving public have other matters on their minds at the moment, but every time they drop in a pot-hole or are stuck in traffic queues caused by road works to a highway that was only constructed or resurfaced a few years before, the item foremost in their minds is probably, "what is happening to all the money 'they' keep taking of road users", perhaps the road user should take more time in finding out.
It is also hard to determine from an office what surfacing materials are performing best, perhaps the "suits" should take the time to go out on site with a real Engineer and see for themselves, rather than be persuaded what is best from office "presentations".

	To recap, the picture to the left shows the nature of the surface at the time of laying. It is a 6mm. medium textured surface course as specified in the now superseded BS 4987, with rubber added as latex at the time of mixing to modify and enhance, the qualities of the bitumen. This is subject to correct procedure for the addition  of the rubber latex, the correct method of mixing at the correct temperature.  Also the time in storage after mixing is critical,  including time in hot storage bins and the time held in the lorry body, as the beneficial properties of the added rubber will, for practical purposes, be lost after 4/5 hours depending upon temperature at storage, it could be less at the higher temperatures. (NOTE This same degradation of modified binder properties related to heat and time will occur to a greater or lesser degree with other forms of polymer binder modification.)
	This picture shows material supplied to the same 6mm. medium textured specification after eight years of trafficking on the non turning, non stressed part of the junction. I regard the material in this area of surface course  to still be in good condition.  However it would not be an appropriate course of action, or cost effective in the long term, to leave this small area of sound surfacing in place, when individual areas have deeper failure in the road pavement in these same areas. A total response is needed to the total needs of this extended junction including deeper repair to the road pavement in some locations. This need for deeper repair, in places, being entirely unconnected to the failure of the surface course, but is related to utility work, however old.

	It is this type vehicle, with this type of axle configuration and "super single" tyres that does the real damage to a road surface, especially where tight turning movements are involved, as with areas of this junction. In my opinion, the relatively small but significant percentage of this type of vehicle using this junction would have been the cause of the major part of the failure on this particular site. I feel the actual bituminous mixture supplied to this site has faired well before the onset of failure in the highly stressed areas.
	The image to the left shows the site immediately before resurfacing in June 2008. The image shows that the bulk of the road surface failure has occurred on the right turning lane into the side road, and the left turning lane on the main road after exiting from the side road, i.e. the areas of greatest stress from vehicle wheels. Note that this junction is access to a "natural" route avoiding the town centre and carries a great deal of traffic with significant number of commercial vehicles. You will note other white road markings, not completely removed, from when this route through the town was used as a diversion route taking traffic off the A5 trunk road during lengthy improvements to that road. This surfacing material, on this junction, has not had "an easy life".
	This image shows the considerable amounts of failure of the surface course material, on the lane on the main road that is receiving traffic turning left from the side road. This damage has increased dramatically over the last 12 months, to the point where the whole junction is being resurfaced, including extensions to the original road surface either side of the thinly laid rubberised 6mm. surface course section. There does appear to be one conclusion on the use of bituminous mixtures that are laid thinly, that seems to be in common from all commentators. This is, that once the surfacing material begins to fail, the failure of the majority of the surface experiencing similar trafficking is swift and irreversible. Meaning that preventative highways maintenance measures such as surface dressing or slurry macadam must be performed at the earliest signs of failure or they will have little or no effect. These preventative maintenance processes not being available/allowed for trunk roads or motorways, although it could be claimed that proprietary micro asphalt (slurry macadam by another name) is a Thin Surfacing, read the appropriate HA Design Manual. I have been involved in the use of surface dressing to significantly extend the life of "porous" SMA's, where the treatment was applied before significant failure had occurred. I have also seen poorly/inappropriately  designed low binder content "porous" SMA's almost "disappear" under traffic because the opportunity to apply treatment was lost.
Of course these materials should not have needed treatment so early in their lives, I am talking of periods of just three or four years, and on occasions less. But if you can cost effectively increase the life of a poor surface course a responsible highways maintenance engineer should do so. But please do not take these comments to mean that you can/should surface dress highly trafficked junctions, you should not, it will result in a "mess" as turning traffic, some of it heavy. will "scrub" it to pieces, with a lot of "raw" bitumen becoming exposed, being picked up by tyres, getting on to vehicles, and picking up and removing good surface dressing further down the site. That is why the decision was made nine years ago to lay a thin layer of a suitable surfacing material on these junctions while the rest of the road was surface dressed.
	A view of the junction showing the "non stressed" lane of the junction still in an acceptable/good condition. With the damage that there is to the surface course attributable to the underlying weakness of utility works. These being trench reinstatement works that were in satisfactory condition prior to the surfacing. This indicates that utility reinstatement works are, and the immediate area around them, with a few exceptions, always going to be weaker than the existing road pavement. But poor reinstatement of Utility trench work, especially poor compaction is a subject all on its own.

	This image shows damage to the surface course that is not failure of the actual surfacing material. This is reflective cracking from widening of the road from a junction improvement prior to current surface course being laid. It has taken many years but the haunching/widening has settled in relation to the main carriageway with a resulting crack in the surface course. But I will point out that their has been no fretting of the material around the cracking, indicating to me that the surfacing material has retained its integrity, having not received the stress of a "turning" manoeuvre.
	Again an image of an area of loss of surface course due to underlying weakness of the road pavement. But note the surface course material either side of the quite old trench is still sound, indicating that the loss of the surface course is due to underlying weakness. If you enlarge the image you will see a close up of the situation showing the nature of the failure of the HRA surface course below. Again not, in my opinion, a failure of the actual bituminous mixture, but a failure induced by underlying weakness. For the record the HRA surface course of the trench reinstatement was in good condition at the time of laying the rubberised 6mm. medium textured macadam. It was from this area of the sound surface course that the second picture on this page was obtained.

	This junction has been resurfaced, this being the area of the surfacing laid eight years ago, and extensions either side of that length that were in poor condition, mainly due to settlement in old trench reinstatements eventually reflecting through to cause failure in the road surface. The planing was of 40mm. depth with the weak areas being removed to 100mm. allowing for a 60mm. binder course beneath the new HRA surface course. I believe the binder course was a 50/20 HRA, or whatever its new title is, but it is a high binder content material with a 50pen binder with a 50% stone content of a nominal 20mm. single size aggregate. This material, which has been around as a generic HRA base/binder course bituminous mixture for as long as I have have been in the industry,
is very similar to what a good EME should be, except the EME is likely to have a stiffer binder, which I would still argue you do not need on local roads with correctly designed mixtures. I will point out that the only planing performed prior to laying of the previous thinly laid surface course was extremely short lengths at the tie-ins to allow an even ride into the new surfacing. The thinly laid surfacing being applied to the existing, HRA and precoats surface.
	Not a lot to say, other than on walking the planed surface it could be seen that this evolved road pavement was in a strong condition with the exception of the small areas of weakness attributable to utility works. I wish I had taken the opportunity to take photographs of some recent utility work in this area of the highway to show you the nature of the evolved construction of this particular road pavement. I think that Engineers and Technicians unfamiliar with the nature of evolved roads would have found it interesting, especially the layer of large granite "pitchings" at the base of the construction.
And as an aside if you are ever tasked with the  reconstruction an evolved road pavement, never remove the "pitching" layer unless you have a very good reason to do so. These layers are an excellent load spreading layer and are rarely a part of any weakness in the road construction. However the pitchings are of necessity removed when utility work takes place, usually causing major disturbance to the integrity of the road pavement.
An aside, the man in the green safety hat below is Ray, an Engineer and gentleman of a similar age to myself who has just retired, early. I believe that this was his last "larger" job before he retired, his engineering ability, experience, and especially the local knowledge he has of his "patch" will be sorely missed.  Happy Retirement Ray, but expect the telephone calls.
	The 40mm.of hot rolled asphalt surface course being laid, closely followed by the chipping spreader applying the 20mm. high PSV bitumen precoated chippings. This process being, by far, the most economical use of dwindling resources of high PSV aggregate. Gangs with the skills to lay this material are becoming scarce, and are usually older operatives who have been taught their skills by those who have gone before them. This was a typical "older" gang who produced a good piece of HRA surfacing. The extra dedication required to produce a good HRA surface course will repay you admirably in the life that you will obtain from this surfacing material.
I will continue to support the use of HRA wherever it can be laid without causing significant traffic disruption. In my opinion on higher class local authority (you are prevented from using it on motorways and trunk sites) roads or particularly stressed highway situations, and certainly when a road closure is going to be needed HRA and precoats should be the preferred surface course bituminous mixture. Note, you can always use a 14mm. precoated chipping if you feel a 20mm. chipping is likely to produce an unacceptable level of tyre noise generation. But again, in my experience tyre generated noise, and total vehicle generated noise, is largely dependent upon traffic speed not road surface texture depth.
	The chipping spreader. This needs to be kept in good working condition, as often the finished quality of a HRA and precoats surface course is a result of a poor performing spreader and not attributable to a poor quality HRA bituminous mixture. And, as with all hot bituminous mixtures rolling / compaction is critical, this being largely related to temperature. Roll an HRA and precoats surface course while it is two hot and you could lose most of the precoated chipping layer in to the mat of the HRA. Do not roll soon enough and you could have chippings "standing proud" causing an extremely rough surface where the bitumen coating of the  chipping is not melted thus enabling the chipping to
physically fuse with the asphalt layer making it impossible for the chipping to be dislodged by traffic.  The gang on this job was extremely competent in laying this type of surface, which I have to say I am finding unusual these days for the larger contracting companies. I am finding that over recent years it appears that it is the "local gangs" that have retained their skills to lay HRA and precoats, mainly because they have had the continued practice from obtaining/winning the more difficult "local" site surfacing work in these materials. While the large company gangs have been working on the larger more profitable schemes laying vast areas of proprietary Thin Surfacing on sites that from a surfacing point of view are much easier to lay. How long these "new" materials perform is not likely to be down to the laying gang, even though the "suits" would have you believe this, and it seems to be the standard form of defense from "management" when these materials fail prematurely. Personally I have never known surfacing contractors, whether large or small, let their gangs do their "own thing", so who is responsible. However I have known a number of competent surfacing gangs, with good Supervisors, get their employers out of the "proverbial" when poor, perhaps "cool", material has been delivered to site.
	After the surface course has more or less received full compaction, but while the material is still plastic a vertical joint will be cut by the "cutting wheel" on the roller. This compacted vertical joint will be coated with a bitumen binder to ensure a complete bond with the following mat of material. The new hot material being laid causing the applied bitumen to melt, this resulting in the complete bond between both mats. If the joint has not been correctly cut, i.e. not sufficiently back into the fully compacted mat, and if the coating of bitumen to that vertical joint has not been complete, then it is highly likely that at some time in the future the centre joint will fail prematurely and need expensive, traffic disrupting, remedial treatment.

	The finished work, and a very nice piece of work, credit it where credit is due. Credit to the gang who laid the hot rolled asphalt and precoats, and a big credit to the Engineers who supported the use of generic HRA and precoats to be laid on this site, allegedly against against strong pressure for a more "fashionable" proprietary mixture to be used. The Engineers, or should I say their customers and ultimate providers of funds, will reap the benefit from the durability that this material provides especially in situations such as this.
	I hope the contents of this page will inform Engineers and Technicians, who are no longer familiar with HRA and precoats as a surface course, especially younger people that this material is still very much available and in my opinion should still be the preferred option in highly trafficked, and highly stressed sites. If you have seen wheel tracking in this material it is because the design is incorrect not the material.  And, I am going to keep repeating myself until you are sick of hearing it, you need engineers and technicians who understand materials to assist you in selecting/designing materials suitable for particular sites.
The latest sales presentation is unlikely to be the best way of selecting the correct bituminous mixture for a particular site.  And let me again point out that one bituminous mixture will not be the best, most cost effective, bituminous mixture for all situations.  It is necessary to consider every aspect of the site from available funds, to traffic control, to what time you can start making a noise in the mornings, it all has to be considered. But primarily select the most appropriate bituminous mixture for the site, and sort the other items out later.
	The approach to the traffic crossing received an antiskid surface a few weeks after the surfacing.
	A nice day, and a road closure, every opportunity for good road markings to be applied. I hope that you can see there has been ample application of glass beads to the surface of the newly applied, molten, road marking thermoplastic. I wonder if the presence of a supervising Engineer on site has had an influence. Looking for sufficient application of glass beads on road markings on sites out in the countryside can be quite a different situation. That is if you actually knew that the gang were on site carrying out road marking, they can be an elusive lot, bless 'em.

SUMMARY This particular thin (20mm.) overlay surfacing, on the second site, has currently achieved eight years life, a life expectancy which I believe is fair for this material at this more highly stressed site, and at the thickness it was laid.  It also needs pointing out that the failure of the surfacing material has only occurred on the more highly stressed sections of the site. I hope that this simple case study is sufficient to make engineers, technicians  and "management" realise that the real world of highways maintenance is a lot more "interesting" than most of them are aware. To provide a little background to the work on this particular site. I was present on site at the time of laying. The Materials Engineer for the material supplier was also on site. It was a good laying gang and good weather for laying bituminous material. The material had been produced, transported and laid with little delay. There had been a good application of tack coat. So there was every reason if a site was to be successful it would be this one, and I repeat I think this site has been successful for the "minimal" treatment that it received. Now I could compare this site to a site, that was part of the same contract, that was laid with the same material in the middle of the night, after being told the material would not be used, because the rubberised material had been in the lorries, on site, since mid afternoon, with all of us standing around in the pouring rain waiting for it to stop.  The Engineer and myself leaving the site at about 9:30pm. after being told the material would not be laid.  Imagine our surprise next morning when an excellent piece of workmanship presented itself. Everybody must have worked extremely hard to to achieve the result after a very long day.  However the "guts" of the material, i.e. the quality of the modified binder, had been lost from the prolonged storage at high temperatures and the surface course failed, by just fretting away, after about four years.   This a true anecdote and there are many still around who are aware of it, but I am not going to pursue it, other than to say the guidance provided in specifications and design manuals is there for a reason, but I am just pointing out how "interesting" real highways maintenance can be. Organisations and authorities need engineers with good experience in "materials observation" if appropriate decisions are to be made in the choice of materials for future highways maintenance.  This means observing the performance of known materials, i.e. the composition/specification, having seen them laid, and have sampled and tested them to know that the material complied with the design/specification. It also needs every aspect of the site, such as, road pavement requirements, material design, production, storage, transportation and laying to have been performed correctly as described in more detail in the text above. Without this thorough engineering approach engineers are not going to know what is really happening. To my knowledge Engineers and Technicians are not being, trained, employed and supported in this role, and I personally cannot see how the maintenance of the highway network of this country can be professionally undertaken without such Engineers and Technicians. It is my opinion that the role of the Materials Engineer and his Materials Laboratory need to be supported and reintroduced in many areas if the term "intelligent client" is to have any meaning at all, and be able to cost effectively maintain the standard of the highway network. It is also my opinion that large organisations should not make very important, and expensive decisions, without such support, and be seen to demonstrate how this support is instrumental in their decision making. In the area I live and travel, mainly on trunk roads and motorways, I observe too many examples of surface course failure where a full engineering approach has not been applied to resurfacing and reconstruction of road pavements resulting in a the relatively short life of the work. There have been a number of reports on these problems culminating in the publishing of two new TRL Road Notes, TRL RN 41 & TRL RN42, which I recommend that you obtain and read. However you must still have Engineers and Technicians with the appropriate knowledge and experience to put the guidance in these documents into practice, and suppliers and contractors who comply with instruction.  In my opinion there are too many "engineers" and "technicians" being influenced into buying what they are sold, rather than purchasing the material that is the best engineered bituminous mixture for the site, and the most cost effective. And, finally, finally, for those who are not practically involved in highways maintenance perhaps you ought to have a bit more respect for those who are, because maintaining a highway network in good condition, in a cost effective manner is an extremely complex occupation. Everybody in the Industry would like to see more money spent on the highways network, including me, it is needed.  Perhaps I am wrong, but I would like to think that those who hold the purse strings are more likely to continue funding those who spend the money well, rather than those that spend it badly. If this is not the case I would suggest the credibility of the "funders" needs scrutiny, and remember "they" are not spending their money "they" are spending yours and mine, and just about everybody else's.

For more information on British Standard bituminous mixtures that can be laid thinly, press ----------------> HERE

For more information on proprietary "Thin Surfacings", press ----------------------------------------------------------------> HERE

For access to a table comparing and contrasting many bituminous surfacing materials, press --------------> HERE 

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