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Home > Publications > International Concrete Abstracts Portal
Showing 1-5 of 26 Abstracts search results
Document:
SP189-01
Date:
January 1, 2000
Author(s):
M. W. Beacham
Publication:
Symposium Papers
Volume:
189
Abstract:
The AASHTO “Task Force on Strategic Highway Research Program (SHRP) Implementation” developed and instituted the Lead State Program in 1996. The mission of the Task Force was to optimize ways in which SHRP technologies could be implemented at the state level. The Task Force understood the benefits of mutual cooperation in sharing resources, working as teams, and collectively implementing the technologies. In order to achieve their mission the Task Force developed the concept of “Lead States Teams”. A “Lead States Team” is a group of states that are willing to take the lead and assist in the implementation of specific, targeted SHRP technologies in which they have interest and have gained some practical experience.
DOI:
10.14359/5842
SP189-02
M. K. Tadros, X. Huo, Z. (John) Ma, and M. Baishya
Based on four strength parameters testing of three high-performance concrete (HPC) design mixes and parametric studies, the following conclusions have been made. Creep and shrinkage strains of HPC are lower than those in conventional concrete. Amount and type of coarse aggregates affect the value of modulus of elasticity. The modulus of elasticity of HPC should be determined through experiments with local materials. Beam sections that have large bottom flange are efficient for HPC application. The most significant property of HPC prestressed beam is compressive strength at release. Allowable compression at release has the most impact on span capacity, while allowable tension at service has minor impact. Prestress loss can be reasonably predicted by either the proposed method or AASHTO LRFD Lump Sum method. PCI deflection multipliers at final time are not accurate. The proposed multipliers which are the functions of creep coefficient can be used for conventional and HPC members.
10.14359/5843
SP189-03
J. J. Myers and R. L. Carrasquillo
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.
10.14359/5844
SP189-04
C. Ozyildirim
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.
10.14359/5845
SP189-05
J. F. Stanton, P. Barr, and M. O. Eberhard
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.
10.14359/5846
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