A Colorado First: PLC & CDOT's Highway 287 Project
U.S. Highway 287 is a major U.S. - Mexico shipping route that experiences a large amount of heavy traffic. When the time came to replace a stretch of this road, the Colorado Department of Transportation saw an opportunity to help meet the state’s Climate Action Plan by lowering the environmental impact of construction.
In 2008, CDOT became the first DOT to approve the use of portland-limestone cement containing up to 10% limestone and to allow blending with fly ash at the ready-mix plant.
For this project, CDOT selected their Class P mixture, which is designed to have a 28-day flexural strength of at least 650 psi; the contractor earned a quality performance incentive by attaining an average of 695 psi. Along with PLC (which replaced the usual Type I/II portland cement), the mix contained 20% Class F fly ash and a carefully selected blend of aggregate to aid in the production of a more consistent concrete batch and a better platform for the concrete paver. And while the fresh mix characteristics were important, perhaps more significantly, the mix design also resulted in a smoother-riding surface for this jointed plain concrete pavement.
This project provided an opportunity to see the effect of hot weather on PLC mixes. Most of the paving work took place during summer months, and the contractor had to deal with placement conditions of 100° Fahrenheit. But site workers noticed no difference in performance or placement with the PLC concrete mix.
The replacement of seven miles of highway pavement and shoulder widening during extreme summer temperatures demonstrated that PLC concrete can satisfy all requirements for batching, mixing, and placing. The CDOT engineer for concrete and physical properties noted that using PLC for more than 10 years has allowed them to reduce the carbon footprint of pavements without compromising quality or long-term performance of mainline paving in the state.