1. HOW LOCAL AGENCIES DECIDE
TO USE PCC OVERLAYS
NCPA Concrete Paving Conference
January 16, 2018
2. Who am I, and how would I know the answer to this
question?
Today, 37 years out of Iowa State in 1980 with a BSCE
Registered PE in CO, and Iowa (PLS too), Previously in OK,
though about it in several other states, but not really
wanting to collect registrations … , but ….
17 years in Consulting (Land Development, City and IDOT
type projects)
20th year in County Engineering.
That said, …
3. Specific PCC Overlay Experience?
Hired as Dallas County Engineer in 1989, after less than two years in
Montgomery County
Within a month of arrival, before I turned 30, Contractors started on 18 miles
of PCC Overlays that had been let before my arrival. All over old HMA.
It was kind of a “throw the baby in the pool and see if it swims” approach, but
the contracts were in place and the paving plant was being moved in.
I didn’t make the call, but I learned why it was decided and lived with it ever
since.
Since then, I have managed another ten miles or so of PCC Overlays, 16 lane-
miles of widening, plenty of full depth highways and City streets - overall
more than sixty miles of PCC Pavements
I’ve also done about thirty miles of HMA Overlays over HMA or Seal Coat –
because it was the right thing to do for the situation at hand
4. So first, decide if an overlay is appropriate, then we will get to what type.
Existing pavement (PCC or HMA) not too bad, but not enough.
Can the existing hold up during hauling of the mix?
Good enough structure present that you don’t need to start from
scratch?
Future traffic can be accurately estimated.
Adjacent access and road-top width can accommodate the additional
thickness?
Funding is available to do something more than routine surface
maintenance.
Is a recycled in place pavement covered with a new slab really “just
another type of overlay”?
5. Also, need to know what you want out of an overlay, if a reasonable choice.
Add structure?
Correct grades? If so, isolated or wide spread?
Generate smoothness?
Good enough condition for an HMA Overlay? PCC Overlay can
accommodate more underlying problems – long term. Less need for prep
patching with PCC onto HMA
Minor wheel tracks? Problem to be addressed for HMA, beneficial for
PCC.
You can use a little black stuff to buy time.
Or, go for an enduring pavement with a true addition of structure
6. HOW MUCH FUNDING IS AVAILABLE WHEN THE WORK IS NEEDED
$$$$$$$$$$$$$$$$
?
7. Bottom line is Overlays are not the cookbook solution we tend to
get into with standard pavement replacement or new
development.
Nice to use some engineering judgement once in a while, with
or without punching a bunch of numbers.
Seldom a toss-up based upon pavement condition, but PCC
and HMA industry, as well as ASHTTO and others have
structural number calcs that you can use to compare
outcomes. Please be aware each formula tends to favor their
sponsor!***
8. HMA Pluses:
1. Shallow “T” potential because strength isn’t an issue
a. Maybe in a residential subdivision
b. Facelift on an already substantial section
2. A Band-aid will do … for now. . Ease of maintenance in ensuing years (but
always doing maintenance?)
3. Maybe save $ short term with a thin overlay – budget pinch with a pending
disaster (avoid “losing a pavement”), but you’ll be back again sooner than
you want.
4. Fewer adjacent grade adjustments, if a couple inches matters?
5. If over a Seal Coat, creates an actual maintainable pavement, as a product
of several Overlays
9. PCC Pluses:
1. Minimal thickness (<4”) might work in those residential subdivisions or
in a “bonded” situation
2. Longer life cycle which normally means better life cycle costs (totally
market dependent)
3. Less maintenance over the life of slab
4. Annualized cost is almost always less if using honest future maintenance
projections
5. Project access usually much better than on a fresh grade
6. An extra inch will buy years more performance – geometric
improvement on performance
7. Doubtful you need to go back during your career to repave – not so
much with HMA
10. Ultimately, HMA is a placeholder, short term, or Band-aid – sorry to my friends
that sell the black stuff. Or it can be a way of life, a default process, seldom the
engineered solution. PCC, on the other hand, can only perform well if it has a
proper foundation.
Another point, HMA makes a great base to place PCC on!
If you can afford it, and it fits geometrically, PCC overlays have been a good life-
cycle cost choice (where an improvement is needed) throughout my thirty some
year career, and I don’t see that changing.
