International Concrete Abstracts Portal

SP-228CD This CD-ROM of Special Publication 228 contains the papers presented at the Seventh International Symposium on the Utilization of High-Strength/High- Performance Concrete that was held in Washington, D.C., USA, June 20-24, 2005. The symposium continued the success of previous symposia held in Stavanger, Norway, (1987); Berkeley, California (1990); Lillehammer, Norway, (1993); Paris, France, (1996); Sandefjord, Norway, (1999); and Leipzig, Germany, (2002). The symposium brought together engineers and material scientists from around the world to discuss topics ranging from the latest applications to the most recent research on high-strength and high-performance concrete. In the years since the first symposium was held in Stavanger, there has been worldwide growth in the use of both high-strength and high-performance concrete. In addition to more research and applications of traditional types of high-performance concrete, the use of self-consolidating concrete and ultra-high-performance concrete has moved from the laboratory to practical applications. This publication offers the opportunity to learn the latest about these developments.

This study discusses the possible ways in which the characteristics of a testing machine can influence the strength of a HSC specimen. Particular attention is given to the platen rotation, which is caused fundamentally by the eccentricity of the reaction force from the specimen, and results in non-uniform straining over the loaded area of the specimen. The strain gradient is measured by a parameter denoted “strain-ratio,” while the apparent strength is expressed by a parameter referred to “strength efficiency.” An empirical method for establishing the relationship between strength efficiency and strain ratio is described. This is done using batches of similar HSC specimens deliberately subjected to different degrees of non-uniform straining and compared to predictions using simple theory. It is found that the test results confirm the validity of the theoretical assumptions. Strain measurement between the loading platens during a regular compression strength test is suggested as a practical proposition due to its economic benefit.

The Brazilian standard states limit to the ordinary strength concrete. Some foreign standards regulate the use of the high strength concrete, which may not be adopted nationally without consideration of the differences that can exist among the materials. An experimental program consisting of the pull out test and the most traditional test in Brazilian standard in the concrete strength levels (60, 80 and 100 MPa) and three different steel diameters (16.0, 20.0 and 25.0 mm) was carried out. The experimental results were compared with specifications of foreign standards. It occurred a statical analysis of the experimental results trying to identify the influence of the several parameters that affect the behavior of the bond. In the end proposing mathematical models for assessing bond stress of high strength concrete.

Numerous pull-out tests, tests on the transfer of prestressing forces, and load bearing tests on pretensioned beams made of High Performance Concrete (HPC) have been conducted. Using these tests the bond properties of 7-wire strands (dp = 0.5 in. = 12.5 mm) and ribbed wires Ø 12 mm are investigated. The lateral strain-dependent bond behavior in different types of concrete as well as the general transfer of prestressing forces are determined. Hereby, missing bases for code specifications, regulations and standards are derived for the use of bond anchorages of pretensioned tendons. The corresponding test results are presented and compared with current code specifications from Europe and the US. Furthermore, initial test results are presented concerning the influence of lateral tension and longitudinal cracks in the surrounding concrete on the anchorage of pretensioned strands.

Ultra high strength concrete (UHSC) is undoubtedly an engineered high-tech material, which can be seen as the latest step in the concrete technology development. Because this concrete type is relatively new, the structural behavior in the ultimate limit states as well as in the serviceability limit states is not fully investigated and understood, so is the bond behavior of reinforcement. An experimental program was set up to investigate the bond behavior of conventional reinforcement and of reinforcement with a new deep-ripped surface pattern in ultra high strength concrete. The assessment of the bond behavior at concrete ages of 3, 7, 28 and 56 days using pull-out specimens was the subject of the investigation. Varying parameters in this research program were rebar diameter, type of reinforcement, surface geometry of the rebar, size of the concrete cover and the loading rate. The concrete compressive and splitting tensile strength were measured at the same test ages. In general, the bond of reinforcement in UHSC is characterized by very high maximum bond stresses as well as high bond stiffnesses, even at early ages. The reinforcing mesh bars with the “deepribbed” surface showed a remarkable ductility. This paper presents the details of the investigation and discusses the results obtained.