International Concrete Abstracts Portal

When insulated concrete sandwich panels are used in the envelope of a building, the experior and interior are subjected to two different environments. The exterior concrete wythe is subjected to outside weather swings in the temperature and humidity causing thermal expansion and contraction, whereas the interior is exposed to a controlled steady room temperature environment. Dimensional change in the panel depends primarily on the height of the panel and the relative change in temperature. The severity increases when the outside concrete wythe of a tall panel is supported (and hence constrained) on the foundation dlowing vertical movements only at the top. If these weather cyclic movements are restricted, the panels may experience cracking and eventually may experience a premature failure. Therefore, the tie system used in the panels should be flexible enough to accommodate these differential movements. This often is the most critical issue in the service life of the building when sandwich panels are used. There is no standard test method available to evaluate the thermal non-uniform cyclic behavior of insulated panel systems. The authors have followed a sci- entific approach to evaluate these stresses by subjecting the ties to real life cycles occurring over a period of time. The system used in this study includes a low-conductivity polymer connector with extruded polystyrene rigid foam insulation. The testing was continued until the failure of the system or to more than 100 years of equivalent cycling (the expected service life of the building), whichever is less. This paper focuses on the methodology developed and parameters considered in developing the criteria for testing weather cycles. The procedure may be followed to evaluate any given insulated panel system to predict its long-term durability.

The performance of beam-to-column connections subjected to reversed cyclic loading depends on several variables. In this investigation, the effects of eccentric spandrel beams, wide normal beams, column section aspect ratio, loading in two principal directions, and slab participation on the inelastic behavior of beam-to-column connections are studied. The experimental program features three 3/4-scale exterior reinforced concrete beam-column-slab subassemblies. The major design variables for the specimens are the eccentricity of the spandrel beam with respect to column, beam and column section aspect ratios, and joint shear stress level. Results of the experimental program, including load-displacement response, beam plastic hinge rotation, joint distortion, and bond deterioration are presented in this paper.

The objective of this paper is $to introduce an innovative sandwich wrapping confining system (SWCS) for upgrading and repairing rectangular columns. The system described here replaces the conventional fiber reinforced polymer (FRP) wrapping, which has only axial stiffness, by a sandwich wrapping confining system that has both axial and flexural stiffness. The new system is made up of two FRP faces separated by a light incompressible core. Experimental and numerical analyses are performed on rectangular columns upgraded and repaired using the SWCS. Thuty rectangular columns with different dimensions are upgraded and repaired using the SWCS and tested to failure. A numerical study based on nonlinear finite-element analysis (material nonlinearity) is used to investigate the behavior of the columns repaired using the SWCS and to predict the experimental failure loads. Finally, the experimental and the analytical results are compared. Unlilce conventional FRP jackets, the SWCS can be used to improve the strength, stiffness, and ductility of rectangular columns.

Recent European and UK policies, for example the Landfill Duecave and the UK landfill tax, have set an agenda to promote reuse and recycling by con-trolling and minimising the landlilling of secondary materials. The UK Govern- ment and it’s agencies are actively pursuing policies of sustainable and environ- mentally responsible construction. The changing attitute towards secondary materials has encouraged investigation into the use of ferro-silicate slag from the Imperial Smelting Furnace (ISF) production of zinc in construction processes. The UK Ten Year Transport Plan, including the development of the highway infrastructure, offers opportunities to successfully demonstrate the consumption of small volume streams of secondary materials, including ISF slag, within the local area. Pavement construction offers several opportunities for consumption, the most credible of these being the replacement of the sand fractions by the slag in bound mixtures, cement and bituminous. This paper focuses upon cementitious mixtures alone. The presence of zinc and lead ions in the ISF slag are proven to have an impact on the setting characteristics of concrete mixtures, although there is little difference in the compressive strengths after 28 days. The leaching, characteristics of the slag suggest that the retardation is not linearly related to the quantities of zinc or lead leached. Additiwuilly, leaching tests in combination with pulverised fuel ash (fly ash) and ground granulated blastfurnace slag indicate that it may be possible to minimise retardation of set in by including these materials in the concrete mixture.

During concrete construction, form oil, bond breaker, concrete splatter and other types of contaminants often contaminate reinforcement. Current specifications and quality control measures require the removal and clean up of these contaminants before the placement of concrete due to a concern of a reduction in bonding capacity. This is costly, labor intensive, and may not be necessary. Currently, there is limited research on the effect of reinforcing bar contami- nation on the bond between the deformed steel reinforcing bar and concrete. Because of this lack of data, specifications are conservative and require the removal of the contaminant. Inspectors often cite ACI 301-96, Standard Specifications for Structural Concrete, which states, When concrete is placed, all reinforcement shall be free of materials deleterious to bond. If it could be conclusively proven that this level of care is unnecessary, the construction industry would benefit greatly. To address the effects of contaminants on bond characteristics of deformed steel reinforcing bars, a preliminary study was completed at the University of Missouri-Rolla. The research program focused on three contaminants often seen during construction: form oil, bond breaker and concrete splatter. Other variables included size of reinforcing bar, strength of concrete and epoxy versus uncoated reinforcing bar. This paper will provide the experimental program and test procedures as well as the test results and observations. The results weal that in the majority of situations tested, the ultimate bond stress was not significantly affected by the three contaminants tested. In some cases, the bond breaker and form oil affected the smaller epoxy coated bars, while the effect of concrete splatter was insignificant.