Title: Mixture Proportioning for High-Strength High-Performance Concrete Bridge Beams
Author(s): J. J. Myers and R. L. Carrasquillo
Publication: Symposium Paper
Appears on pages(s): 37-56
Keywords: aggregates; compressive strength; elastic modulus; flexural strength; fly ash; high-performance concrete; high-strength
High performance concrete (HPC) with its improved service under load and improved resistance to environmental conditions represents a promising material to assist with the rehabilitation of the crumbling infrastructure. Although HPC has found widespread application within the building industry in certain pockets of the country, its incorporation into transportation structures has been very recent. To demonstrate the suitability of transportation structures has been very recent. To demonstrate the suitability of transportation structures has been very recent. To demonstrate the suitability of HPC for use in highway structures, the Federal Highway Administration (FHWA) initiated a series of projects that included the complete incorporation of HPC from design to long-term monitoring of the bridges in service. The design and construction of Louetta Road Overpass in Houston, Texas and the North Concho River US 87 & S.O. RR Overpass in San Angelo, Texas were conducted as a joint effort by The University of Texas at Austin and the Texas Department of Transportation (TxDOT). The Louetta Road Overpass project incorporated the use of a newly developed pretensioned precast U-Beam. The high initial prestressing forces required high early release strengths of 63.4 MPa (9,200 psi) and design strengths of 91.0 Mpa (13,000 psi) at 56 days. The designers (TxDOT) also required a high initial modulus of elasticity of 41.3 kPa (6,000 ksi) at release and long-term to satisfy the serviceability requirements for the beams. The North Concho River US 87 & S.O. RR Overpass project incorporated the use of pretensioned AASHTO Type IV beams. This is the most widely used bridge system in the state of Texas. These members also required high initial release strengths of 74.5 MPa (14,700 psi) at 56 days. In order to satisfy these design requirements, but also result in an economical mix design. The following paper discusses the evolution and optimization of the mix design and it's subsequent use in the field. In addition, the selection process of the aggregate determined to be most suitable for the production of high performance concrete beams is discussed. A brief description of each project is also presented.