The 18th NZ Transport Agency & NZIHT conference at Trinity Wharf Tauranga was another rich discussion for our roading engineers. Alan Titchall was there.
Up until about the mid 18th century it was a ‘highway robbery’ demand, before being replaced with the less subtle ‘money or your life’, prompting Spike Milligan to quip – “take my life please, I am saving for my birthday”.
Anyway, I digress. The themed NZTA/NZIHT roading conference at Tauranga was aimed, of course, at doing the opposite of ripping the public off and was delivered with the mantra, ‘Making the customer the centre of thinking for the operation of New Zealand roads’.
This event is the ‘thinking’ roading engineer’s annual feast of roading technology and systems discussions, acronyms and corporate jargon. The term ‘customer’ has replaced what we used to call the ‘client’ and before that the ‘road user’. It has also become synonymous with the terms ‘journey’ (which replaced ‘road use’) and ‘safe’ as in – ‘safer journeys for our customers’.
Blame a lack of policing, road design, or the nut holding the wheel, but ‘safe’ and ‘roads’ have not been a successful marriage over the past year, if the fatality and injury rate on our roads is any guide.
It was for this reason that a highlight of the conference were the two keynote presentations by industry outsiders who directly represent most of the NZTA’s roading ‘customers’. They were Simon Douglas, the national manager of policy and research at the NZ Automobile Association, and Ken Shirley, the CEO of the Road Transport Forum.
There was also lots of good juicy technical presentations that we intend to publish in this magazine in the new year.
Meantime, in this issue we bring you the highlights of Ken’s presentation from the view of trucking customers and another on a new (in this country) French asphalt product from Road Science that was delivered by Darcy Rogers, the company’s technical development manager.
Darcy Rogers, technical development manager for Road Science, made a presentation to the NZTA/NZHIT conference on an asphalt product that drew enormous interest. Highlights by Alan Titchall.
WE THINK EME is a real game changer for structural asphalts in New Zealand and it is really just a very, very, high modulus, very stiff asphalt and we believe it’s going to offer a lot more value to our customers and that structural asphalts base.
EME was developed 30 years ago in France and is an acronym for ‘High Modulus Asphalt’ in French. So we’re not renewing the build here we are just taking technology that was developed a long time ago and slowly made its way around the world, ending up in Australia. We’ve jumped on the band wagon there and helped introduce it into New Zealand.
Because it’s so hard and stiff, and very high modulus, it has a much longer life than conventional structural asphalt and we can actually apply a lot thinner application than with a conventional mix.
This allows less disruption and, in a lot of cases we’re not having to work with granular material.
We certainly think it offers more for less to our customers.
EME is a structural layer so it sits in between your base-course and the surfacing layers and uses a very, very hard grade binder that we’re actually able to manufacture in New Zealand through some of our capabilities down in New Plymouth.
That’s one part of the product. The second part is about performance based mix designs and with EME the grade doesn’t matter, you can make whatever you want.
With grading it is about maximising the performance of the grade binder you put in there. If you’re talking mix for a conventional asphalt, you are trying to get really good aggregate interlocks. The strength of the asphalt directly relies on the aggregate getting really good interlock with those particles. With EME you’re more reliant on the strength of the binders.
In the case of EME we’re normally getting about three times higher modulus than what you can achieve with a conventional mix so in some cases you’re getting up to 14,000/18,000 mega pascals. So, if you’re a pavement engineer you might get excited when you hear these kinds of numbers.
In practice what that means is we’ve made it a lot stiffer so if you put the same truck loading it’s bending half as much as conventional mix and normally that translates to about 10 times the fatigue time. So, you can take 10 times more traffic loadings before it’s going to fail the same way as a conventional mix.
Or, say, we can reduce the pavement thickness by 30 percent and get the same fatigue life as the conventional mix but get savings in terms of mix quantity and construction time.
We’ve actually been using this stuff for over a year now and introducing it over a period time on a number of sites.
And the first site we targeted was the State Highway 2/58 project in Wellington. We didn’t just jump straight into this project, we did background work. The proposed design for this project was originally 210mm of asphalt over granular which involved a 160mm base layer with 50mm surfacing.
When we put it through our design process looking at what we do with EME, we managed to reduce that asphalt depth down to 150mm, or 30 percent thinner – 100mm of EME with 50mm of surfacing.
The first area we tackled was in Aotea Quay and the road that runs parallel to the waterfront.
What we’ve got there is the main freight depot, so out of here we’ve got a lot of slow moving, heavy vehicles both coming in and out of this intersection and the structural asphalt had erupted after five years. So not the best outcome for the customer.
It was due to be replaced and so we thought this was a good opportunity to trial the design we proposed for State Highway 2/58, and make sure we could construct it and also make it through our asphalts plant and confirm the properties we had developed in the lab.
We did exactly the same as we proposed for the State Highway 2/58 out of the lab and that material has been down for over a year, and we haven’t seen any sign of distress.
We also did another job at Wellington International Airport where asphalt was actually rutting six months after being applied under very slow taxiing aircraft loadings.
Normally we only use EME as a structural layer but in this case we were able to use it as a wearing course as well. EME is quite rich in bitumen so you don’t get much texture but if that’s not a functional requirement at the airport. So we did full depth EME application here. So far its lasted over 10 months and is already out performing the conventional mix that was used in the past.
So, through those two projects we were able to gather enough evidence to prove that we could construct the EME and also make it through our plant.
Since then we’ve gone ahead and done State Highway 2/58 using the design we spoke of earlier and that’s been a real success for us.
So now we consider this material as just kind of business as usual for us, as we’re well past the trial phase, it’s got a lot of proven history, and it’s part of our standard tool box of treatment selection.
Paving crews don’t need to invest in any special equipment to use it and they love using it because it is rich in bitumen and very easy for them to handle and use.