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.

This paper presents a rational approach used for the evaluation of inplace concrete pavement with flexural strength requirements. During the construction of a concrete paving project at McCarran International Airport in Las Vegas, Nevada, data was developed from the testing of over 450 specimens of concrete beams, cylinders, and cores representing samples from nearly 170 locations. Hexural, compressive, and splitting tensile strength testing was performed on these samples obtained from locations where comparison between the different types of strength tests was possible. Relationships between this data were evaluated and a rational approach to the evaluation of in-place concrete for compliance with flexural strength requirements was developed. This approach that begins with trial batch data and includes cast and cored specimen, could be applied to other concrete paving projects with similar concerns.

An optical fiber monitoring system was designed and built into a three-span high performance concrete highway bridge. The Rio Puerco Bridge, locgted 15 miles west of Albuquerque, is the first bridge to be built using HPC in New Mexico. The bridge has 3 spans with length of 29 to 30 m. It is designed to be simply supported for dead load and continuous for live load. HPC was used for the cast-in-place concrete deck and the prestressed concrete beams. A total of 40 long-gage (2-m long) deformation sensors, along with thermocouples were installed in parallel pairs at the top and bottom flange of the girders. The embedded seams measured temperature and deformations at the supports, at quarter spans and at mid-span. Measurements were collected during: Beam Fabrication (Casting of the beams, Steam curing, Strand release, Storage), Bridge Constructio~ and Service. The data collected was analyzed to calculate the prestress losses in the girders, compare the losses to the predicted losses using available code methods, and get a better understanding of the properties and behavior of high performance concrete. The project is funded by the Federal Highway Administration, the New Mexico State Highway and Transportation Department, and the National Science Foundation.

Recently in Mexico and other Latin-American Countries, reinforced concrete (RC) buildings with precast floor systems have been widely used, although such structural types are not yet included in the design codes. In order to understand the behavior of this type of building, the response of a RC building model to seismic loads was investigated by testing two full scale structural models. The building models were subjected to lateral aud torsional displacements. The models simulated the first story of a four-story building, and consisted of three dimensional one-story moment resisting single-span frames. The model was designed to assess the seismic performance of ductile frame structures following the Mexico City Building Code. The variable in the tests was the type of floor structural system: (a) the first model (CR model) was cast in-situ beam-slabs structure; and, (b) the second model (PCR model) had the same structural system, but with precast elements composing the floor structure. Both models were subjected to the same loading history and had similar instrumentation. This paper presents the results and conclusions obtained from the comparative study of the behavior of both models. One of the main conclbsions is that the presence of precast elements at the floor system was found to be an important parameter for the torsional stiffness of the whole structure.

The effect of varying cement source fresh and hardened concrete properties is studied under hot weather conditions. For the seven ASTM Type 11 cements studied here, the same mix proportioning was adopted at a mixing temperature of 95 F (35 C) with a constant dosage of water reductiag and air entraining admixtures. Properties of fresh concrete including slump loss over an extended mixing period (EMP) of 90 minutes, air content, and setting times are reported. Also, hardened properties including compressive strength development and rapid chloride permeability test data are reported. Results indicate that the rate of slump loss and setting times are affected by the cement compound composition, calcium sulfate content aad calcium sulfate type. The compressive strength, under hot mixing conditions, is found to be dependent on composition, fineness and morphology of cement compunds.