Wes Heald, Executive Director, Texas Department of Transportation
The Texas Department of Transportation (TxDOT) is promoting the use of high performance concrete (HPC) through research, construction, and technology transfer. Our first two federally funded HPC bridge research projects, which resulted in the construction of the Louetta Road overpass in Houston and the San Angelo U.S. 67 bridge, have increased our knowledge of how to use HPC.
We have modified our statewide specifications to make use of higher strength HPC beams, and we are evaluating specification requirements for improved durability of conventional strength, cast-in-place HPC in current projects. With HPC, we anticipate being able to build bridges faster, thus, reducing traffic disruption.
Quality Control and Quality Assurance
Quality control and quality assurance (QC/QA) were important aspects of the first two HPC bridge projects. The initial steps were implemented through job specifications and partnering. Researchers from The University of Texas at Austin’s Center for Transportation Research performed structural and materials testing, and assisted TxDOT and the contractor as needed in solving HPC mix design, fabrication, and construction problems. This help was extremely useful and kept construction on schedule. The FHWA sent trained personnel and its mobile concrete laboratory to aid in the onsite testing. Implementation of the QC/QA program was a dynamic process with continuous updating of the program to accommodate test results and findings during construction.
Partnering
Partnering was another element in the successful production of HPC at reasonable costs. Partnership and teamwork were not accidental; they were clearly laid out as objectives of the contract and partnering agreements. Prebid, prefabrication, and preconstruction meetings were all held. These meetings allowed concerns to be expressed and options to be considered while plans could still be changed relatively easily and inexpensively. The meetings assured contractors that construction would not be hampered by the use of innovative techniques and materials, and that local materials and conventional methods would be used to the maximum possible extent. The meetings also promoted discussion and fair resolution of problems of precasting bed requirements, special HPC construction requirements, and curing concerns associated with HPC mixes.
Several notable benefits came from the collaborative process. One was TxDOT’s acceptance of the precaster’s redesign of the San Angelo HPC beam stressing sequence. The contract drawings required that all the strands be pretensioned. The fabricator proposed a mix of pretensioned and post-tensioned strands. The arrangement allowed the fabricator to use the company’s existing precasting beds. This saved both time and money. Another benefit was the special lifting frame that the fabricator designed to help in transporting the beams safely. Working together on the hauling system and routing resulted in the successful transportation of beams with lengths up to 153 feet (46.6 m) from the fabrication site to the job sites — a journey of over 300 miles (480 km) for the San Angelo project.
Concrete Durability
In addition to allowing longer spans with fewer beams, a very attractive feature of HPC is its durability. Durable, impermeable concrete should mean lower maintenance over the life of a structure and longer life expectancy. An environmental benefit is that the researchers recommend the use of fly ash – a waste material—as 25 to 35 percent of the cementitious material in HPC to decrease permeability.
Summary
Based on what we have learned, the future looks bright for HPC. Through its use, we expect durable, reasonably priced bridges that can be built faster, last longer, and require less maintenance.