1 Associate Professor, Brigham Young University, Dept. of Civil and Environmental Engineering, ffonseca@et.byu.edu
2 Graduate Student, BYU, Dept. of Civil and Environmental Engineering
ABSTRACT
Compression testing is often used as a quality control measure in concrete masonry production and construction. Capping is used on masonry prisms to eliminate surface imperfections, produce a plane surface, and provide uniform load distribution. Currently, bonded capping, specifically gypsum and sulfur, are the only methods allowed by US standards. Preparing bonded capping in masonry prisms is time consuming and labor intensive. The use of reusable or unbonded capping could dramatically reduce specimen preparation time and labor while still providing accurate results. In concrete compression testing, unbonded capping methods are already standardized.
This article presents preliminary results of a study that used several unbonded capping materials for compressive strength testing of masonry prisms. Selection of the materials was based on the compressive strength, thickness, Poisson’s ratio, and hardness of the material. Hydrocal gypsum cement was the control capping material; the other capping materials were fiberboard, laminated foam, and neoprene. The neoprene was restrained against excessive lateral expansion by a steel confining apparatus.
Compressive strength results of the tests with the fiberboard capping were comparable to the results of the tests with the gypsum capping with only a 5 percent increase in average compressive strength. The repeatability of the fiberboard capping procedure was evidenced by the small coefficient of variation of the results. Compressive strength results of the tests with the neoprene capping also had a small coefficient of variation, 3.18, but the average compressive strength was 13 percent greater than that obtained with the gypsum capping. The increase in average compressive strength was most likely due to the combination of the neoprene hardness and additional confining stresses caused by the steel confining apparatus. The average compressive strength of the prisms with laminated foam capping was 27 smaller than that of prisms with gypsum capping. The variability of the laminated foam capping procedure was the highest of all capping procedures.
KEYWORDS: gypsum capping, soft capping, unbounded capping, neoprene, masonry compression test, masonry prisms
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