US 34

The State Highway 34 project entailed reconstruction of 2.5 miles of existing 4 lane asphalt highway near Greeley, Colorado. The project was 76,151 SY of 9 “dowelled concrete paving which had to be constructed in 2 phases. The existing asphalt road had to be ground up and mixed with 10” of existing base to form the new sub base. This sub base had water mixed with it and rolled to achieve and stable platform for the new concrete paving. This sub base was then trimmed for grade control of the 9” Portland Cement Concrete Paving.

Traditional on rural roadways, Colorado has used a FDR (Full Depth Reclamation) and then covered with an asphalt overlay with the budget for these projects coming from the maintenance division. CDOT and Industry determined with a little ingenuity these projects could be accomplished efficiently with concrete pavement. The Project on US 34 in Greeley, Colorado was the one of the first project to use concrete paving rather than asphalt.

Castle Rock Construction designed an optimized concrete mix for this project. The mix design was a flexural strength mix with four aggregates, #4 coarse aggregate, #57/67 coarse aggregate, #9 aggregate, and concrete sand. The goal of this mix was to produce a consistent mix which could maintain a Coarseness Factor (CF) of 60 and a Workability Factor (WF) of 35 in a modified Shilstone Graph. This was accomplished with the use of a four bin feeder and pug mill being added to the concrete batch plant. The four bin feeder was used to provide the proper proportions of the four aggregates to the pug mill which mixed the aggregate into a single aggregate which was then fed to the batch plant. The purpose of this proportioning and mixing was to aid in the production of a more consistent concrete batch and a better platform for the concrete paver with the ultimate goal of producing a smoother ride on the concrete paving.

The paving crew came up with a plan to monitor and achieve a smooth concrete pavement. The measures included the use of wire stringline which was checked daily to make sure there was less than .2’” deflection when a 3 pound weight was hung on the stringline. The team used a spreader to help control surge at the paver to consistently maintain head pressure, grout box pressure and the roll size at the OCB. Behind the paver a “V Float” was used to eliminate chatter. A real time profiler was utilized behind the paver to monitor slab smoothness and to monitor the effects of changes to the paving process on smoothness.

The end result was a very consistent concrete being produced and very good rides on this project. Some of the incentives were attained on this project for strength, depth and ride. The paving team produced a concrete project with HRI numbers in the mid 50’s. CDOT was very happy with the concrete mix design and the ride numbers.