Internal Curing Case Study: State Highway 121 (Collin County, TX)

by TXI - Texas Industries, Inc.

Location: State Highway 121, north of Dallas, Texas

State Highway 121 Owner: State of Texas

Architect / Designer: Texas Department of Transportation

Engineer: Texas Department of Transportation

Sub Contractor: Balfour Beatty

Material Suppliers: TXI ESC / TXI NTRM

General Facts: 1300 cy of concrete paving with expanded shale added to provide
a test for internal curing

On November 16, 2006, approximately 1300 cubic yards of Class P concrete was placed into continuously reinforced concrete paving using slip-form paving machinery.

A portion of the normal weight limestone coarse aggregate and the fine aggregate were replaced by an intermediate grade of rotary kiln structural lightweight aggregate. This aggregate had been soaked in a stockpile under a sprinkler system in order to provide a nearly saturated aggregate to both optimize the combined gradation of the aggregates and provide additional water for hydration of the cement and reduce autogenous shrinkage. Compressive test cylinders and a crack survey confirmed the improved performance of the pilot section compared to the standard concrete.

Construction of SH 121 represents the next logical step following research, taking the laboratory to the field in the form of this major highway project. TxDOT had recently defined new optimized gradations for concrete aggregate that were more uniform. Existing specifications are gap graded with no intermediate sized rock. There are advantages to the new gradations, such as reduced paste content, which will lead to less drying shrinkage cracking, and less susceptibility to freeze thaw damage. TxDOT anticipates higher strengths, leading to a potential reduction in cement, thereby reducing concrete cost.

The total cost of the 5.049-mile SH 121 project was $84,322,926.90. Work began in late October 2004 and was completed in 2007.

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