PLC Plus Fly Ash Equals Greener Iowa Pavements
U.S. Route 30 was originally constructed as a part of the Lincoln Highway, the first transcontinental highway in the United States which spanned from New York to San Francisco. A route through Iowa was chosen because of the important link between Omaha, Nebraska, and Chicago, Illinois. It is maintained by the Iowa DOT, and over the years, long sections have been upgraded to a four-lane expressway to meet the needs of increasing traffic.
As part of the route’s improvements, four miles east of Ames were repaved in 2013 with a 10 ½ in. doweled PLC concrete pavement, covering two eastbound lanes with turn lanes.
In 2012, after testing was completed for sulfate resistance on the Type IL cement, the Iowa DOT approved it for use in all concrete mixtures for any of their paving applications. Of note, this concrete mixture is a ternary blend, meaning it has three cementitious components. The PLC accounts for two of them (clinker with 10% limestone), and an additional 20% Class C fly ash. Compared to a portland cement-only mix, this mix is estimated to further reduce CO2 emissions by 25-30%. The contractor didn’t notice any difference in placement or performance over the usual Type I/II plus fly ash mix they use.
Immediately following the highway improvement, the PLC/fly ash mixture was also used for a 6 in. plain pavement at the Central Iowa Expo Center in Boone, IA.
Near Boone, IA to the west, the ternary concrete mixture used by the Iowa DOT contained 20% Class C Fly Ash. The full project used approximately 21,806 cubic yards of concrete requiring 4,823 tons of Type IL (10) cement. This concrete mixture with PLC and the addition of fly ash allowed the paving contractor to haul the concrete 19 miles to the second pavement project near the Central Iowa Expo Center without the need to relocate the paving concrete plant. Both pavements were complete within the span of a month and will serve the surrounding communities for decades to come.