New TRL Reports

There are number of TRL reports that have been published during the last year that I believe the engineers and technicians whose area of work deals with bituminous materials and road pavement design should be aware of, and consider obtaining copies for study.

They are :-

TRL Report 456 : Development of a high performance-based surfacing specification for high performance asphalt pavements

TRL Report 494 : The behavior of asphalt in adverse hot weather conditions

TRL Report 497 : The design of porous asphalt mixtures to performance-related criteria

TRL Report 499 : Material performance of Porous Asphalt, including when laid over concrete

I regard all these reports as worthy of study if your area of work is road pavements.

I particularly found TRL Report 456 of interest as it included a great deal of information relevant to "super single" tyres and the increased rate of damage they cause to road pavements, a topic I have mentioned previously in the June newsletter.  
It is mentioned in this report that there is a new development of the "super single", that will be more economic in use for hauliers, that will be even more damaging to road pavements. 
The development and use of these types of tyres will have a significant effect on the life, or reduced life, of road pavements and must not be ignored in future road pavement design and the materials we use in such designs. 
It is my belief that we must look beyond the single factor of stiffness in road pavement materials, thinking it is the answer to increased wheel loading, and pay more importance to the durability of a material so that it may be able to resist the other damaging factors of tyre to road contact such as impact loading due to uneven ride quality.
It is my belief and observation that if there is not sufficient binder holding the aggregate particles tightly in the matrix, impact loading and vibration may cause them to separate from a firm bond, and the stiffer the bitumen we use the more brittle it will be in the winter increasing the risk of brittle failure.
We keep talking of failure due to occasional hot summers, we must not ignore the possibility with the "new" stiffer materials being used that brittle failure in occasional cold winters is also a distinct possibility, and it is likely to be far more dramatic than rutting.

SMA / Thin Surfacing Reports

I would draw your attention to a report in the technical journal "Surveyor" of Friday the 14th. of December regarding early life properties of Stone Mastic Asphalt. 
The article raises some interesting issues which I hope you will explore with an open mind in conjunction with your Materials Engineer or engineer with responsibility for road pavement design.
I am not going to make any comment other than to say there are many factors that could have a bearing on the possible problems indicated that have not even been mentioned, so do not jump to conclusions too quickly as this is a fairly rudimentary press report.
I understand a more comprehensive industry initiated report may be published in the fullness of time revealing results of appropriate surveys conducted on SMA surfaces.

If, while you have the "Surveyor" to hand you may wish to also read (on page six) the small reference to the early failure of the surface of the M5 Avonmouth bridge. 
Although there were few specific details I would surmise this must have been a failure of a proprietary Thin Surfacing as the road in question was part of the motorway/trunk road network.
Perhaps a little more "investigative journalism" is called for so that engineers and technicians reading the articles  will gain useful information that will assist them in avoiding similar problems.
But in view of the fact mention is made of water getting "underneath the asphalt" perhaps you might like to read the page on road pavement drainage.

Motto of the Month

"A march of a thousand miles begins with a single step"