International Concrete Abstracts Portal

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.

This paper presents strut and tie models that can be used to determine strength and deformation limits for RC members. Conventional strut and tie models have been used for strength design, but they cannot appropriately address the ductility of members that is important to insure safety under severe cyclic loads. This proposed strut and tie model is constituted to address the end region of flexural members, including plastic hinge regions, and will be the basis for the calculation of deformation and corresponding shear strength as well. The behavior of each component of the strut and tie model is evaluated based on the material properties and stress paths. The elongation of the tie element depending on crack spacing and width is obtained from the bond-slip relationship. The contraction of strut element is simply determined from the properties of concrete. The member deformation is obtained by combining the truss deformation determined from components behaviors with joint rotation, The strut and tie model in this paper will provide useful tools for both the design and evaluation of ductility-required RC members.