Browsing by Subject "concrete"
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Item Air-Coupled Surface Wave Transmission Measurement Across A Partially Closed Surface-Breaking Crack In Concrete(2011-06) Kee, S. H.; Zhu, J. Y.; Kee, S. H.; Zhu, J. Y.Previous researchers have demonstrated that the transmission of surface waves is effective to estimate the depth of a surface-breaking crack in solids. However, most of the results were obtained using a well-defined crack (or notch) in laboratory. In fact, there is a critical gap to apply the theory to surface-breaking cracks in concrete structures subjected to external loadings where the cracks are generally ill-defined, and partially closed. In this study, the authors investigated transmission coefficients of surface waves across a partially closed surface-breaking crack in concrete subjected to monotonically increasing compressive loadings. First, a concrete beam (0.5 X 0.154 X 2.1 m(3)) having two surface-breaking cracks with various crack widths was prepared in laboratory. Second, transmission coefficients of impact-induced surface waves were measured across a surface-breaking crack in the concrete beam with increasing compressive loadings from 0 to 140kN (10% of the ultimate compressive strength of the concrete beam). External post-tensioning was used to apply the compression. For comparison purpose, sensitivity of surface wave velocity to compressive loading was also investigated. As a result, observations in this study reveal that transmission coefficient is a more sensitive acoustic parameter than phase velocity to evaluate a surface-breaking cracking in concrete subjected to compressive loadings.Item Bursting and spalling in pretensioned U-beams(2009-12) Dunkman, David Andrew; Bayrak, Oguzhan, 1969-; Jirsa, James O.An experimental program was conducted at the Ferguson Structural Engineering Laboratory of The University of Texas at Austin, under the auspices of Texas Department of Transportation (TxDOT) Research Project 5831, to investigate the tensile stresses that develop in the end regions of pretensioned concrete U-beams at transfer of prestress. Understanding the effect of these “bursting” and “spalling” stresses is essential in order to design standard details that might lead to reliably-serviceable end regions. Two full-scale beam specimens, designed to be worst-case scenarios for bursting and spalling, were fabricated. Each beam had one square and one highly skewed end. Extensive instrumentation, including strain gages on transverse and lateral reinforcing bars, was employed in the end regions of these U-beams. Experimentally determined bursting and spalling stresses in these bars were compared to results of past projects (from the literature) investigating I-beams and inverted T-beams. Preliminary recommendations are made for changes in the standard reinforcing details for U-beam end regions. Such recommended details will be tested in the upcoming phase of Research Project 5831.Item Effect of Physical Properties of Stone Used as Coarse Aggregate on the Wear and Compressive Strength of Concrete(University of Texas at Austin, 1928-04-08) University of Texas at AustinItem Progress Report of the Engineering Research Division of the Bureau of Economic Geology and Technology(University of Texas at Austin, 1922-03-15) University of Texas at AustinItem Role of relative humidity in concrete expansion due to alkali-silica reaction and delayed ettringite formation: relative humidity thresholds, measurement methods, and coatings to mitigate expansion(2009-05) Rust, Charles Karissa; Folliard, Kevin J.; Juenger, Maria C. G.Premature concrete deterioration due to alkali-silica reaction (ASR) and delayed ettringite formation (DEF) is a significant problem all over the world. In cases where these mechanisms were not initially prevented, mitigation is critical to halt expansion and cracking. The main objectives of the research presented herein were to study the effect of ambient relative humidity (RH) on rates of concrete expansion, to determine RH thresholds below which expansion due to ASR and/or DEF may be suppressed, and to evaluate coatings intended to lower the internal RH of concrete and thus minimize future potential for damage. Results from testing showed that the RH threshold for ASR was below 82%, the RH threshold for DEF was below 92%, and the RH threshold for combined ASR and DEF could be about 83% for the materials tested. Furthermore, it was shown that some coatings are effective in reducing ASR- and DEF-related expansion by lowering the internal RH of concrete.Item The Strength of Fine-Aggregate Concrete(University of Texas at Austin, 1918-10-01) University of Texas at AustinItem Structural Implication of Post-Tensioned Ducts in Prestressed Concrete Girders(2012) Massey, Joshua; Bayrak, OguzhanPrestressed concrete girders are used extensively to support bridge decks in highway bridges. The maximum length of a typical prestressed concrete girder is generally limited to what can be transported safely by trucks to the construction site – approximately 160 feet. With the use of post‐tensioned strands placed in ducts cast into the girders, multiple pretensioned concrete girders can be spliced together to form a continuous member along the length of a bridge, allowing greater structural continuity and more efficient use of materials. However, due to the location of the ducts in the relatively thin web regions of the girders, new failure modes can control the shear strength of the members. The structural implications of corrugated steel and plastic ducts cast in the web regions of spliced Tx‐Girders under the effects of compressive loading are studied in this report.Item Using Air-Coupled Sensors To Measure Depth Of A Surface-Breaking Crack In Concrete(2009-03) Kee, S. H.; Zhu, J. Y.; Kee, S. H.; Zhu, J. Y.Previous studies show that surface wave transmission ratio across a surface breaking crack in concrete can be used as an indicator of the crack depth. However, due to inconsistent sensor coupling condition on rough concrete surface, reliable measurement of the transmission ratio is still a challenging task. In this study, the air-coupled sensing method is proposed as a solution to this problem. Without direct contact between sensors and the testing surface, the air-coupled sensing not only allows rapid testing speed, but also enables more consistent signal measurement owing to removal of sensor coupling variation. The latter feature is especially valuable to wave transmission measurement. This paper first presents results from a numerical analysis (FEM model). Based on the results, a simplified algorithm is proposed for surface wave transmission ratio calculation. A calibration curve between the transmission ratio and normalized crack depth (actual crack depth/wavelength) is obtained. Experimental study using the air-coupled sensing method verifies the validity of the curve.