ABSTRACT Compression testing is often used as a quality control measure in
concrete masonry production and construction. Caps are used on masonry prisms to
eliminate surface imperfections and provide uniform load distribution. Currently
bonded caps, specifically gypsum and sulfur, are the only accepted method for
Concrete Masonry Unit (CMU) prism capping. Preparing bonded caps is time
consuming and labor intensive. The use of reusable or unbonded caps could
dramatically reduce specimen preparation time and labor while still providing
accurate results. This project researches the viability of several unbonded caps
as suitable for compressive strength testing. Selection of cap material was
based on multiple criteria, including compressive strength, surface bonding,
thickness, Poisson’s ratio and hardness. Hydrocal Gypsum cement was chosen as
the control method and was compared against recycled rubber, neoprene,
fiberboard and laminated foam. The rubber and neoprene pads were restrained
against lateral expansion using a steel confining apparatus to avoid development
of lateral tensile forces at the prism-cap interface. Results indicate that the
rubber caps provide nearly identical strengths compared to the control, with a
3% reduction in observed strength. The fiberboard caps also produced comparable
strengths to the control with a 5% increase in observed strength. The
repeatability of these methods is evident from the calculated coefficient of
variation. The neoprene cap results had a small coefficient of variation (3.18),
but strengths were 13% greater than the control’s. The significant increase in
strength was likely a product of high confining stresses at the prism ends. The
laminated foam exhibited the lowest strength with a 27% reduction compared to
the gypsum. Based on results, rubber caps of a durometer hardness of 65 with
proper confinement could be adopted as a suitable alternative to hard capping.
Keywords: Jacob Ballard, gypsum capping, soft capping, unbounded capping,
neoprene cap, board cap, reusable cap, masonry compression test, masonry prisms,
rubber cap. More
http://ceen.et.byu.edu/sites/default/files/snrprojects/644-jacob_richard_ballard-2012-fsf.pdf
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