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Specifications for ready-mixed concrete limit drum revolution and mixing time to 250 drum revolutions and/or 1.5 hours before discharge. These specifications have been in place for many years with the objective of ensuring the qua...
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Specifications for ready-mixed concrete limit drum revolution and mixing time to 250 drum revolutions and/or 1.5 hours before discharge. These specifications have been in place for many years with the objective of ensuring the quality and performance of the finished concrete product; however, these limitations could potentially increase construction costs without additional benefits, especially when longer transport distances are required. Because there have been significant changes in concrete constituent materials (e.g., chemical admixtures) and equipment since these limits were first implemented, research is needed to assess the effects of time to discharge and drum revolution counts on concrete performance. The objective of this research program is to evaluate and verify whether existing specifications for mixing and transporting concrete are applicable for today’s materials and equipment and if not, to identify key variables or tests that can ensure adequate placeability and good mechanical and durability characteristics. This study evaluated the influence of coarse and fine aggregate, supplementary cementitious materials quantity and type, chemical admixtures, temperature and mixing time and drum revolution on the mechanical and durability characteristics of concrete. Results indicate that existing specifications may be appropriate due to loss of workability. However, mixing time and drum revolution counts had no significant effects on the majority of mechanical properties and durability characteristics of ready-mixed concrete and results from this research indicate that existing specification limits are very conservative.
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The first part of the investigation, performed at Oregon State University, assessed the use of high strength reinforcement (HSS) for use in reinforced concrete (RC) columns. HSS is not currently allowed in RC due to lack of inform...
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The first part of the investigation, performed at Oregon State University, assessed the use of high strength reinforcement (HSS) for use in reinforced concrete (RC) columns. HSS is not currently allowed in RC due to lack of information on the material characteristics and lack of performance information when used in columns. But potential benefits in construction, performance, and economics justify the need for research, especially for critical corridors. Results indicate that a column constructed with Grade 80 HSS reinforcement performs similar to column constructed with conventional Grade 60 reinforcement. The second part of the investigation, performed at the University of Washington, focused on a new type of connection between a precast concrete column and a cast-in-place drilled shaft. The column is precast with a roughened outer surface at the bottom of the column which will be embedded in the cast-in-place shaft. The connection can be built rapidly and allows generous construction tolerances. Building on two previous tests, a third quasi-static scaled connection test between a precast bridge column and a drilled shaft was performed to investigate the seismic performance of the new connection. The geometry of the test specimen was based on the minimum practical difference between the diameters of the shaft and the column, and so represented the most critical cases. The performance of the system was investigated up to a drift ratio of 10%. The experimental results showed that, if adequate confining steel is included in the splice zone, the plastic hinging mechanism forms in the column, without incurring damage in the splice zone or shaft. If the confinement is insufficient, the strength of the splice zone deteriorates rapidly with cyclic loading. Recommendations for transverse reinforcement in the transition area are provided to ensure desirable performance. The third part of the investigation, also performed at the University of Washington, focused on the performance of concrete filled steel tubes (CFST), with specific focus on connections to precast concrete piers and piles caps. CFSTs have the potential to improve performance in seismic events and decrease overall costs. CFSTs may be used for bridge piers, shafts, caissons, and columns, but their use is limited because AASHTO design specifications for CFSTs are dated and few validated, constructible connections exist. Part 3 of this report (Part 3) compares current CFST design provisions to experimental results, noting limitations and deficiencies. Improved provisions proposed for the AASHTO specifications and partly based on the AISC provisions are summarized. CFST connections are also addressed. A foundation connection capable of developing the full composite capacity of a CFST was evaluated experimentally and initial study of CFST column-to-cap beam connections was conducted using numerical simulation. Both are effective in developing and transferring the full capacity of the CFST and are summarized.
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Prestressed-precast panels are commonly used at interior beams for bridge decks in Texas. The use of these panels can provide ease of construction, sufficient capacity, and good economy for the construction of bridge decks in Texa...
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Prestressed-precast panels are commonly used at interior beams for bridge decks in Texas. The use of these panels can provide ease of construction, sufficient capacity, and good economy for the construction of bridge decks in Texas. Current practice for the overhang deck sections require that formwork be constructed at the outer edges of the bridge. The cost of constructing the bridge overhang is significantly higher than that of the interior sections where precast panels are used. The development of a precast overhang system has the potential to improve economy and safety in bridge construction. This research investigated the overhang and shear capacity of a precast overhang system for potential use during the construction of bridges with precast overhang panels. The research was performed in three phases: the Phase 1 research including work specifically for the Rock Creek Bridge in Parker County, Texas; the Phase 2 research for general precast overhang panels, and; the Phase 3 research investigating the shear capacity. Grout material characteristics were also assessed for possible use in the haunch; constructability issues were also addressed. Results indicate that the capacity of the precast overhang system is sufficient to carry factored AASHTO loads with no or very limited cracking. Results from the shear study indicate that the shear capacity of threaded rods with couplers is lower than the conventional R-bar system. However, sufficient shear capacity can be achieved if sufficient pockets in the precast overhang panel are provided. A recommendation for the haunch form system for use on the bridge is also provided. The use of the precast overhang system evaluated can be implemented in bridge construction. However, further testing is needed to determine the number of pockets on the overhang panelan issue critical to the constructability and economy of the system. This will be further addressed in report 0-6100-3.
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The implementation of full-depth, precast overhang panel systems has the potential to improve constructability, productivity, and make bridges more economical. Initial testing and analyses reported in the 0-6100-2 report resulted ...
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The implementation of full-depth, precast overhang panel systems has the potential to improve constructability, productivity, and make bridges more economical. Initial testing and analyses reported in the 0-6100-2 report resulted in a design that required a large number of shear pockets in the overhang panels. The general design methodology used in this report was to determine the number of connectors based on the shear capacity of a girder with conventional R-bars (not necessarily based on the required demand). The large number of shear pockets reduced the constructability and economy of the precast overhang system. Report 0-6100-1 (produced after 0-6100-2) used the American Association of State Highway Officials Load and Resistance Factor Design (AASHTO LRFD (2008)) demand requirements to design the number of shear pockets for a precast overhang panel system and reported that the number of pockets per panel could be reduced from the numbers reported in report 0-6100-2. However, this report only included an analysis for one beam type and one span length. In addition, the demand load used did not include all factors typically used by designers. Additional testing was required to assess different connector systems and further analyses were needed for the new Texas Department of Transportation (TxDOT) girders. The testing and analyses documented in this report (0-6100-3) provides a new equation for determining the number of shear pockets required for the various shear connector/coupler systems evaluated in this research. This equation was used to determine the number of shear pockets required for the newer TxDOT girders. Results from this research indicate that the roughened surface provides strong adhesion between the top girder surface and a precast panel. Steel reinforcing hoops placed in the shear pocket and shear reinforcing hoops placed in the overhang panel around the opening of the shear pocket provided limited or no improvement in capacity of the shear connector/coupler system. Hollow structural section (HSS) steel tubes placed around the perimeter of the shear pocket during fabrication did result in samples with higher shear capacities and could result in overhang panels with fewer shear pockets. This system could make constructing bridges with precast overhang systems more constructible, economical, and could reduce the construction time.
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The existing test method used to assess the corrosion performance of reinforcing steel embedded in concrete, mainly ASTM G 109, is labor intensive, time consuming, slow to provide comparative results, and can be expensive. However...
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The existing test method used to assess the corrosion performance of reinforcing steel embedded in concrete, mainly ASTM G 109, is labor intensive, time consuming, slow to provide comparative results, and can be expensive. However, with corrosion of reinforcement a major challenge to the durability of infrastructure systems, improvements in the corrosion performance of materials could add significant value. With limited resources, new procedures and test methods are needed to assess corrosion performance of potentially value-adding materials. This research evaluated four accelerated test procedures (rapid macrocell (a.k.a. mini-macrocell), ACT test, CCIA test, and a modified ASTM G109 test) and compared these tests with the standard ASTM G 109 tests. The reasonableness of the test results, test simplicity, test cost, and test duration were all assessed. Results indicate that the rapid macrocell, ACT, and CCIA tests can reduce the time required to perform the tests by approximately 90 percent compared to standard ASTM G 109 test. Not considering the one-time equipment cost, the rapid macrocell, ACT, and CCIA decrease the cost by approximately 75, 58, and 67 percent compared to the standard ASTM G 109 test, respectively. The rapid macrocell test was determined to be relatively simple while the CCIA and ACT tests were considered to be more complex to perform. Based on the research findings, it is proposed that TxDOT use the rapid macrocell test to evaluate the corrosion performance of most materials. To evaluate the performance of dielectric coatings on reinforcement, it is recommended that the MG 109 test be used to evaluate these system types. For specific testing needs, other tests may be appropriate.
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The existing test method to assess the corrosion performance of reinforcing steel embedded in concrete, mainly ASTM G109, is labor intensive, time consuming, slow to provide comparative results, and often expensive. However, corro...
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The existing test method to assess the corrosion performance of reinforcing steel embedded in concrete, mainly ASTM G109, is labor intensive, time consuming, slow to provide comparative results, and often expensive. However, corrosion of reinforcement is a major challenge to the performance and long-term durability of infrastructure systems. Improvements in the corrosion performance of materials could add significant value to the infrastructure. New procedures and test methods are needed to assess the corrosion performance of potentially value-adding materials. This study evaluated four accelerated test procedures: the mini-macrocell (MM) test, the concrete chloride ion assessment (CCIA) test (also referred to as the concrete corrosion inhibitor association test), the accelerated chloride threshold (ACT) test, and the modified G109 test. Results from the accelerated tests were compared with results from the standard ASTM G109 results. The rapid MM test proved to be relatively simple, and researchers recommend that it be used to assess the relative performance of several material systems. The CCIA and ACT tests are recommended only when the critical chloride threshold of a reinforced system is needed. These tests are more complex and expensive to perform than the MM test. This product provides the procedures for performing these tests. The modified G109 test can continue to be used, but test durations are still relatively long.
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Segmental, post-tensioned (PT) bridges are major structures that carry significant traffic. These bridges are designed and constructed because they are economical for spanning long distances. In Texas, there are several signature ...
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Segmental, post-tensioned (PT) bridges are major structures that carry significant traffic. These bridges are designed and constructed because they are economical for spanning long distances. In Texas, there are several signature PT bridges. In the late 1990s and early 2000s, several state highway agencies identified challenges with the PT structures, mainly corrosion of the PT strands. The Texas Department of Transportation (TxDOT) performed some comprehensive inspections of their PT bridges. A consultants report recommended that all ducts be re-grouted. However, the environment in Texas is very different than the environments in which the corrosion of the PT strands was observed in the other bridges. Report 0-4588-1 summarized the research findings from a comprehensive study on the corrosion characteristics, reliability, materials, and repair for PT bridges. This document, an inspection and repair manual, was developed from information from this research program. This document provides an efficient approach to inspect and repair PT bridges. However, it should be noted that in this manual, repair does not include filling the voids in the tendons with grout. A recent failure of a tendon in a bridge in Virginia was suspected of being caused by repair grouting of the tendon, possibly due to the formation of a galvanic couple between the new repair grout and the original grout. Although a procedure for pressure-vacuum grouting of tendons is provided in Appendix A of this manual, this method should not be used until the potential issue associated with galvanic corrosion of the strands after repair is resolved.
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Research objectives: 1. Assess environmental conditions at Post-tensioned (PT) bridge locations in Texas; 2. Identify critical environmental, void, and stress parameters affecting corrosion and tension capacity of PT strands; 3. D...
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Research objectives: 1. Assess environmental conditions at Post-tensioned (PT) bridge locations in Texas; 2. Identify critical environmental, void, and stress parameters affecting corrosion and tension capacity of PT strands; 3. Develop methods to detect and assess the void, water, and corrosion conditions in PT systems; 4. Assess the structural reliability of PT bridges during their service life and when exposed to various environmental and tendon conditions; 5. Identify critical material parameters affecting void fillability of PT grouts and, if needed, recommend modifications to PT grout specifications; and 6. Develop a repair grouting procedure.
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Post-tensioned (PT) bridges are major structures that carry significant traffic. PT bridges are economical for spanning long distances. In Texas, there are several signature PT bridges. In the late 1990s and early 2000s, several s...
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Post-tensioned (PT) bridges are major structures that carry significant traffic. PT bridges are economical for spanning long distances. In Texas, there are several signature PT bridges. In the late 1990s and early 2000s, several state highway agencies ide
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