The project presents a dually unique aspects in Illinois: it represents the

1) 1st use of AAASHTO M240 Type IL portland-limestone cement concrete and
2) 1st extensive use of two-lift paving, with the more wear-resistant course cast for the top 3-in. of the 11¼-in.-thick pavement.

The Illinois Tollway is a revenue bond-financed administrative agency of the State of Illinois that is solely funded by user-fee and concession revenue. As part of a 15-year, $12 billion capital program—Move Illinois: The Illinois Tollway Driving the Future—for construction in 2014 the Illinois Tollway commissioned about sixty eastbound lineal miles of three-lane-wide highway upgrades along the Jane Addams Memorial Tollway (I-90) between Rockford, Illinois and Elgin, Illinois. In this, I-90 was rebuilt and widened into a state-of-the-art 21st century corridor.

There were seven contracts for the combined westbound-mainline work, and these were awarded to four contractors. All told, approximately 325,000 cubic yards of concrete were needed. Of this, a significant portion used concrete containing Type IL portland cement—the first time this new AASHTO M 240 (ASTM C595) material had been used on a major project in Illinois.

The Illinois Tollway’s use of the Type 1L cement adds onto the innovation that the Tollway has brought to Illinois pavements. The Tollway’s research into the use of “black rock” (the coarse portion of fractionated reclaimed asphalt pavement – FRAP) allowed them to incorporate recycled aggregate into the Rockford-to-Elgin portion of the I-90 reconstruction. The “black rock” mix was incorporated into the pavement using two-lift concrete construction: two lifts of concrete were placed “wet-on-wet,” with the black-rock mix covered by a typical paving mix containing no recycled aggregate.

For the concrete containing Type IL(10) cement, there were two nominal eight-mile-long contracts and one nominal four-mile long-contract, summing to 20.6 lineal miles of three-lane-wide mainline paving. All of the Type IL(10) cement concrete pavement was 11¼-in. thick. FH Paschen/SN Nielsen paved two contracts; K-Five Construction paved one contract. K-Five Construction paved 52,500 cubic yards of the concrete, and FH Paschen/SN Nielsen paved 105,000 cubic yards of the concrete. Also, all three Type IL(10)-cement contracts, 21,000 cubic yards were cast in barrier-wall base concrete, and 30,000 cubic yards were cast in the barrier walls.

Of additional interest, the 11.25-in.-thick mainline pavement transitioned to 12 in. and then to 13 in. toward the east end of the work.

Concrete mix designs: for the Ozinga-supplied contracts, two mixes were used in the 20.6-lineal mile-long two-lift composite pavement:

1) For the bottom/base lift: The lower lift (8.25 inches) was a “black-rock” mix containing coarse fractionated RAP (recycled asphalt pavement) as 15% of the coarse aggregate. The mix also contained 40% of slag cement as part of the cementitious materials;
2) For the top lift (3-in. thick): The design was for an IDOT PV mix 75% Type Type IL(10) portland-limestone cement with 25% slag cement.

The concretes followed Illinois Tollway requirements regarding extensive laboratory evaluation. The specific portland-limestone cement material was a Type IL(10), with the (10) meaning it contained 10% finely-divided limestone, per AASHTO M240/ASTM C595 nomenclature; and the specific product was manufactured to match the performance of the Type I/II low-alkali portland cement that was used in some other portions of the work.