Imagine you’re in your car sipping coffee and hoping for a smooth commute when you’re greeted by those big, orange signs. Construction. Still? This has been going on for weeks and the traffic is now the source of your daily headache. What is worse is it looks finished. Why can’t they just open the road?
That’s the problem being looked at in Project R27-154, “Effect of Early-Age Concrete Elastic Properties on Fatigue Damage in PCC Pavements Containing Fibers.” It’s a problem that is magnified by an increase in traffic throughout the state. The project was conducted by Illinois Center for Transportation (ICT) researchers and the Illinois Department of Transportation (IDOT) under the direction of a Technical Review Panel chaired by James Krstulovich, Concrete Technology Engineer at IDOT’s Central Bureau of Materials. Professor Mohsen Issa was the project’s principal investigator (PI).
Researchers have been searching for a way to keep road closure times down while also not compromising the life-span of new concrete pavements. Keeping road closure times down will not only help reduce traffic but save money too.
Currently, the earliest pavement will be opened to traffic is when test specimens have attained a flexural strength of 650 pounds per square inch (psi) or a compressive strength of 3,500 psi. Similar criteria applies to concrete patches. In order to open a patch as quickly as possible, an accelerating chemical admixture could be added to the concrete mix, or the mix could be designed to have a larger volume of cement. However, such methods could ultimately compromise the long-term durability of the concrete.
“Thinking outside the box, industry approached IDOT suggesting that at early ages, concrete is a more elastic material with a relatively low modulus compared with its rigid properties at later ages; thus, the implication being that stresses may be considerably lower in “green” concrete than generally assumed, possibly allowing earlier loading without imparting damage that would reduce the patch’s or pavement’s serviceability,” Krstulovich said.
A thorough experimental program was conducted at the University of Illinois at Chicago to evaluate the elastic properties of Portland Cement Concrete (PCC) pavement, or rigid pavement, and patch mixes at early ages. The research included testing “green” concrete samples and then subjecting those samples to various environmental changes.
Krstulovich says there were two main questions researchers were looking to answer; “Can ordinary PCC pavements or patches be opened earlier than currently specified? And does including fibers help?”
Researchers evaluated the potential long-term effects of opening up new concrete roads earlier to traffic by subjecting concrete beams to fatigue loading at early ages and then subjecting the fatigued beam to rapid freezing and thawing cycles to measure deterioration. They determined that adding fibers improved the toughness and structural performance of pavement and patch mixes.
According to PI Issa, the findings of the research can greatly help in determining the plausibility of opening up newly paved sections early to traffic.
“IDOT engineers are provided with a practical tool that can be employed in critical construction situations such as high-traffic volume intersections and during challenging climatic conditions,” Issa said. “IDOT can benefit from the substantial decrease of closure times, which can be potentially reduced to the first three days after paving.”
The research team noted that this decrease in closure time can assist construction budgets by choosing a suitable design thickness of PCC pavements with either fibrous or plain concrete solutions without detrimentally affecting highway serviceability.
The implementation of this new procedure is being recommended for future roadway-construction projects in the State of Illinois.
The complete findings of this research study are available on ICT’s website and can be accessed here.