Temperature, stress, and strength development of early-age bridge deck concrete

In bridge deck concrete, early-age cracking can lead to substantial serviceability and structural integrity issues over the lifespan of the bridge. An understanding of the temperature, stress, and strength development of concrete can aid determining the early-age cracking susceptibility. This project, funded by the Texas Department of Transportation, evaluated these properties for various bridge deck materials and mixture proportions.

The research presented in this thesis involved a laboratory testing program that used a combination of semi-adiabatic calorimetry, rigid cracking frame, free shrinkage frame, and match cured cylinder testing program that allowed the research team to simulate the performance of common bridge deck mixture designs under hot and cold weather conditions. In this program, the semi-adiabatic calorimetry was used, with previously generated models, to generate the temperature profile of the mixture. The rigid cracking frame and free shrinkage frame were used to evaluate the restrained stress development and the unrestrained volume changes, respectively, under the simulated temperatures. The match-cure cylinder testing program allowed the research team to generate a strength development profile for the concrete mixtures under the various simulated temperature profiles.
Results from the laboratory program revealed that in hot weather simulations, ground granulated blast furnace slag mixtures developed the lowest stress / strength ratios, and in cold weather simulations, Class F fly ash mixtures developed the lowest stress / strength ratios. In general, use of SCMs and limestone coarse aggregate results in mixtures that generate less heat and lower stress / strength ratios. Isothermal testing showed that shrinkage reducing admixtures were effective in reducing early-age strains from chemical shrinkage.

In addition to the laboratory testing program, a field testing program was completed to measure the temperature development of four bridge decks during the winter and summer months. The recorded concrete temperatures and the effects of the environmental conditions at the time of the pour will aid in the calibration and validation of the temperature prediction component of ConcreteWorks for bridge deck construction. In addition, experience gained through these field pours resulted in an optimized instrumentation procedure that will aid in the successful collection of data in future projects.