| High Performance Concrete (HPC), with its improved resistance to mechanical loads and environmental conditions, has become an increasingly promising material to assist with the deteriorating infrastructure in the U.S.. The Louetta Road Overpass bridge project was initiated to investigate the design, material and constructability aspects of HPC. A new precast, prestressed U-beam was specified for the project. The structural design of the beams required concrete strengths of 8,800 psi in 16 to 24 hours, at transfer of prestress, and 13,100 psi in 28 days, and a minimum elastic modulus of 6 million psi in 24 hours.; The experimental research program consisted of eight phases. In the first two phases, more than eighty trial batches were made using local materials both in the laboratory and at the precast concrete plant. The HPC mix proportions were developed, and the performance of the constituent materials was optimized. In the following three phases, a laboratory research program was conducted to evaluate the effects of accelerated heat curing, partial cement replacement with fly ash, and coarse aggregate characteristics on the mechanical properties of HPC; namely compressive strength, elastic modulus, and flexural strength. Phase VI examined the effect of metakaolin, a new mineral admixture, on the strength development of HPC. In Phase VII, the compressive strength development of portland cement concretes within the initial 24 hour period was monitored. In the final phase, heat evolution of various cement pastes due to hydration of cementitious and/or pozzolanic components was monitored at different isothermal temperatures.; As a result, suggestions were made regarding the effect of inidividual constituent materials on the heat development and mechanical properties of HPC. Empirical equations were also suggested to estimate the elastic modulus and flexural strength of HPC for a wide range of locally available constituent materials, heat treatment, and curing conditions. |
