The Situation
To the best of anyone’s knowledge, Nazareth became the first city in Pennsylvania to incorporate Roller Compacted Concrete (RCC) into a public street project. Could it be the start of something bigger? Time will tell but our Industry continues working with PennDOT to develop a specification.
How did this transpire? That question, and others were put to Sean Dooley, Ph.D., P.E. (Keystone Consulting Engineers) who spearheaded the project.
The Solution
What led you to specify RCC for this project?
“This segment of Sycamore Street had completely failed due to inadequate pavement strength. The road was so cracked it looked like a dried creek bed. We assessed various repair methods, including: cold-in-place recycling (CIP); full-depth reclamation (FDR); and full-depth reconstruction using conventional asphalt pavement. CIP was found to be technically infeasible because there was inadequate existing asphalt pavement thickness to work with. FDR was eliminated because it was found to be economically infeasible for the relatively short length of road that needed to be reconstructed – FDR requires a substantial amount of process equipment that is costly to mobilize. This left us choice to go with conventional asphalt pavement or look at alternatives. The fact of the matter is that asphalt construction costs have steadily and substantially risen with higher oil prices over the last five years or so. With severely limited construction budgets, we need alternatives.
Our research led us to roller compacted concrete (RCC) because it has been in the various national trade publications. We found that RCC has been used in the Lehigh Valley by private owners for warehouse facilities and service yards subject to heavy loads. Further research led us to conclude that we could save at least 15% to 20% on the initial cost using RCC over asphalt. The location and functional characteristics of Sycamore Street made it a prime location to introduce this material. We had confidence in the project’s outcome because RCC pavement has been around since the 1970’s when it was developed by the Canadian logging industry. It has been used over the last decade on local roads in Ohio, including the City of Columbus, as well as other northern locations in the US and Canada where pavements are subject to freeze-thaw.
Because it is a rigid material, the RCC allowed for a thinner pavement cross section. What was the final design?
“On our project we used a six (6”) inch pavement base of RCC founded over three (3”) inches of stone subbase. The subbase is not in fact necessary for structural purposes. We decided to use the stone to facilitate fine grading prior to paving and to create a layer between the RCC and soil subgrade for drainage. The six inches of RCC has the equivalent strength of an asphalt road comprised of 8” of stone subbase, 7” of asphalt base and 1.5” of asphalt wearing. “
What advantages did the use of RCC rather than asphalt provide for the project?
The key advantages to us using RCC are as follows:
1.Our overall pavement section is 10.5” using RCC as opposed to 16.5” using asphalt. This substantially reduces the amount of excavation, the number of truck trips to remove and dispose of waste material, and the amount of new material and corresponding trucks that would have to be moved back in.
2.Concrete is currently around $40/ton as compared to $60/ton for asphalt.
3.For our project, the installed cost is $39/SY for RCC as compared to between $55 and $64 per square yard for the equivalent asphalt pavement. The overall cost is about $70,000 as opposed to $99,000 to $116,000 for 1,728 square yards.
Even with the stone and overlay, our cost using RCC came in at an estimated 30% below the cost of using asphalt. This is a rather atypical savings (15%-20% is typical), but it does demonstrate that there are great cost advantages to considering RCC.
What are your thoughts about the viability of RCC for future projects?
RCC holds the real potential to save municipalities substantial money (which will free up money to do additional projects). I know from our own perspective serving as municipal engineers to 27 municipalities that their road programs are severely underfunded. The condition of their infrastructure is degrading because there is not enough money to keep up. In Upper Nazareth Township we should be doing four (4) miles of road surface treatments a year but we can only afford to do just over one (1) mile.
We should note that our project was bid in accordance with Liquid Fuels requirements and was approved by PennDOT with the caveat that they would pay for anything that is PennDOT approved (excavation, stone subbase, tack coat, asphalt overlay, etc.). So, on the $70,000, Upper Nazareth Township paid $28,000 out of their General Fund to pay for the RCC base. Liquid fuels funding covered the remainder of the project.
Concrete, It Just Makes Cents!
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