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Investigation Of The Lower Bound Compressive And Flexural Strengths Of Conventional Concrete And Clay Masonry

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Investigation Of The Lower Bound Compressive And Flexural Strengths Of Conventional Concrete And Clay Masonry

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Title: Investigation Of The Lower Bound Compressive And Flexural Strengths Of Conventional Concrete And Clay Masonry
Author: Harris, Benchmark Henry
Abstract: Conventional masonry is a handcrafted product in which units are placed by hand in a mortar bedding that is prepared during construction. TMS 402 Building Code Requirements for Masonry Structures (also referred to by the industry as the Masonry Standards Joint Committee or MSJC) and referenced standards consequently permit a range of various field conditions so as to allow practical construction (1). The primary objective of the testing program was to measure a statistically significant number of test results to investigate the lower bound compressive and flexural strengths of conventional concrete and clay masonry under simulated field conditions.96 compression tests and 144 flexural tests were performed on unreinforced, ungrouted masonry prisms. Half of these prisms consisted of hollow concrete masonry units (CMU) that were nominally 8 in. wide, 8 in. tall, and 16 in. long. The other half consisted of hollow brick units with standard modular brick dimensions. Masonry prisms were constructed for this research with both Type S and Type N Portland Cement-Lime Mortars and both Type S and Type N Masonry Cement Mortars with the maximum permitted sand to cement ratio and the maximum permitted lime to cement ratio where applicable. This research investigated the combined effects of constructing masonry with the maximum permitted mortar age, maximum permitted low and high curing temperatures which do not require special measures, minimum and maximum conventional initial rates of absorption (IRA), minimum and maximum conventional mortar water contents as determined by professional masons, and minimum and maximum conventional unit water contents. For each of the 32 variations of mortar, the following mortar properties were recorded: mortar cube compressive strength, mortar flow, cone penetrometer resistance, and air content. Half of each set of prisms was constructed with an "A" series of materials; and the other half was constructed with a "B" series of materials. All materials in the two series were mutually exclusive, obtained from different sources; and, two different professional masons were each assigned to a different series. The "B" sand was typical of common masonry sand used in North Texas and many other areas of the United States, having a much smaller average particle size and not complying with the gradation requirements of ASTM C 144 Sections 4.1 and 4.2. The primary relevance of this investigation with regard to compressive strengths is to generate data for simulated field conditions that are unfavorable but currently permitted, to assist the design community in evaluating the common expectation among designers that field mortar cube compression strengths exceed the values of ASTM C 270 Table 2, though this practice is currently prohibited (2, 3, 4). The primary relevance of this investigation with regard to flexural strengths is to assist TMS 402 in evaluating current permitted design strength assumptions considering current limitations on construction conditions. These provisions are the product of much debate and research over the last century. The research primarily focused on laboratory conditions with wide recognition that flexural strength of unreinforced, ungrouted masonry is a highly variable property; however, failures of unreinforced, ungrouted masonry structures have been observed in the field during extreme load events and these provisions warrant further investigation (5, 6, 7, 8).
URI: http://hdl.handle.net/10106/4884
Date: 2010-07-19
External Link: https://www.uta.edu/ra/real/editprofile.php?onlyview=1&pid=967

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