Ductile Lightweight Concrete For Lightweight Structural Application

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Ductile Lightweight Concrete For Lightweight Structural Application

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Title: Ductile Lightweight Concrete For Lightweight Structural Application
Author: Piyamaikongdech, Ake
Abstract: This study developed a ductile concrete for precast wall systems which are capable of resisting high wind in excess of 500 mph. The developed concrete mix design consists of sand, cement, glass fiber, and a foaming agent to produce lightweight concrete in the range of 87 pcf (1392 kg/m3) to 90 pcf (1440 kg/m3). A comprehensive testing program for evaluation of the developed concrete material was undertaken. The mix designs were prepared both in the laboratory and in the mix truck with drum capacity of 27 ft3 (0.77 m3), and 177.6 ft3 (5 m3), respectively. The large concrete batches using trucks were prepared at the Hanson plants in Grand Prairie, Texas and News Orleans, Louisiana. The material test included: 188 compressive strength tests (ASTM C39); 166 Modulus of rupture tests (ASTM C78); and 310 Pull-out test (ASTM C234-86) for both sites. From each mix design, three specimens for 1, 3, 7, 14, 28, 56, and 90 day(s) were prepared and tested on the designated test day. The relationships between the concrete unit weight and each of the a aforementioned properties were obtained and recorded. Two types of pull out test (ASTM C234-86) were conducted: (1) the steel bar (#4) was embedded at 4 in. (10.16 cm.) in the 6 in.(152.4 mm.) x 12 in.(304.8 mm.) cylinders and (2) the steel bar was embedded at 12 in.(304.8 mm.) in the 6 in.(152.4 mm.) x 12 in.(304.8 mm.) cylinders. This was done to document both the pull-out and fracture mode of the failure during the pull-out test. Full-scale beam tests with specimen sizes of 8 in.(20.32 cm.)x 20 in.(50.8 cm.) x 96 in.(243.8 cm.) were conducted with and without reinforcements. A total of 124 beams (95 without reinforcement and 29 with reinforcement) were tested in four-point bending. The crack patterns and failure loads were identified and recorded. Also, the behavior of the non-reinforced full-size test beams were compared with the ASTM C78 beams. The full-scale testing was continued by testing lightweight precast wall panel with two types of opening configurations: (1) window opening and (2) door opening. Four full-scale walls were tested by being subjected to a single concentrated load at the center of the panel and being loaded to failure. These wall panels were cast at the Hanson's News Orleans's site (Site2) and were transported for testing to the University of Texas at Arlington structural field laboratory at the Hanson's Grand Prairie plant (site1). The wall panels were loaded to failure in an incremental manner and the crack initiation and propagations were identified and recorded. Also the load-deformation plots were obtained. Finally, a three dimensional nonlinear finite element model (FEM) of the wall panels were developed which included elements for the lightweight ductile concrete and the reinforcements. The material geometric and contact algorithms were coupled with the smeared crack model was incorporated in the analysis. The developed FEM is capable of predicting crack initiation and propagation which verified against the experimental tests. Also, the load-deformation plots from the experimental results were compared with those obtained from the FEM analysis, which showed very close correlations.
Date: 2008-08-08
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