A total of 25 papers are included in this Symposium Publication on HPC. The general topics include HPC bridges, HPC structural lightweight concrete, material science of HPC, and structural safety of HPC. Note: The individual papers are also available as .pdf downloads.. Please click on the following link to view the papers available, or call 248.848.3800 to order. SP189

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.

The fracture process of cement-based material cause by compressive loading is a complex, three-dimensional phenomenon that occurs as a result of material heterogeneity and complicated mixed-mode cracking mechanisms. However, obtaining three-dimensional information describing this process requires equipment-and time-intensive techniques. One such technique is X-ray Microtomography, which provides high resolution data, but is limited to small specimens. A more straightforward technique, Digital Image Correlation (DIC), can be used to characterize the fracture pattern of a wider range of specimens, but only in two dimensions on the surface. In order to determine the relationship between surface and internal cracking mortar specimens were tested in compression and examined using both DIC and X-ray Microtomography. Microtomography is an X-ray technique that can be used to produce three-dimensional images which reveal the full internal structure of the specimen, including cracks and pores. DIC is a Computer Vision technique that compares successive images to measure two-dimensional deformation on the surface of the specimen, providing information on the location and opening of surface cracks. Rectangular mortar specimens (25.4 mm by 12.7 mm by 12.7 mm) were loaded to certain levels past the peak stress to induce significant cracking and then unloaded. Deformations of the unloaded specimen were measured with DIC and used to determine crack shape, size and location. This surface phenomena was compared to the shape and size of internal cracks seen in tomographic reconstructions of the same specimen. It was observed that these techniques give complementary information about crack geometry and development.

This paper describes the measured behavior of a bridge made with precast, prestressed, high-performance concrete (HPC) girders. The concrete was considered high-performance, because it was specified to have a compressive strength of 51 MPa (7400 psi) at release and 69 MPa (10,000 psi) at 56 days. By using HPC instead of normal-strength concrete, the bridge designer was able to reduce the number of girder lines from seven to five. These girders were the first to be constructed in Washington State using HPC. To monitor the girders, vibrating-wire strain gages with thermistors were installed in five girders, and camber was monitored by various means, including a stretched-wire system that could be monitored by the data-aquisition system. Temperatures measured during fabrication indicate the presence of a large and unexpected temperature gradient over the height of the girder. As a result the concrete strength at release may have been lower at the bottom of the girder than at the top. The long-span girders were stressed to an initial bottom stress of approximately 28 MPa (4000 psi). The strength of the concrete was higher than usual and permitted the high initial stress. However elastic modulus rises only with the square root of strength, so elastic shortening strains, and creep strains that are assumed to depend on them, are higher for high-strength concrete. In these girders, elastic shortening and creep dominated the loses. The measured losses were compared with the predicted losses form two standard methods, but neither method was able to provide a universally superior match. In general, the measured losses exceeded the calculated losses initially, but with time, the discrepancies decreased.

Concrete structures that are expected to last a long time in a severe environment must be built with proper attention to design, materials selection and proportioning, and construction practices. This paper addresses the construction issues, including placement and curing of concrete. In placement, the importance of cover depth, effects of pumping on air content, need for properly functioning vibrators and screed, and the consequences of improper consolidation are described. The necessity of proper curing is addressed by explaining cracking that result from loss of moisture. The variation in strength between that of the test samples and that of the member is described for concrete subjected to steam curing.