Evaluation of cracking of the US 331 bridge deck.
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2010-08-01
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Abstract:The focus of this report is a three-span, continuous, skewed bridge that was constructed in the
summer of 2003 as the northbound roadway bridge on US 331 in Montgomery County,
Alabama. This bridge deck exhibited extensive transverse and horizontal cracking and was
replaced in 2005 before being opened to traffic. The primary objective of this study was to
evaluate the mechanisms that may have contributed to horizontal cracking in this bridge deck.
The concrete satisfied all standard slump, total air content, and compressive strength
requirements. Core results revealed adequate in-place compressive and splitting tensile
strengths. Finite-element analyses were used to rule out excessive skew and differential
support settlement as causes of the cracking. Horizontal cracking in this deck was most likely
caused by excessive early-age temperature gradients combined with drying shrinkage
gradients that produced large shear and normal stresses at the top reinforcement mat location
in a concrete with a high coefficient of thermal expansion and high modulus of elasticity. The
effect of supplementary cementing materials, water-cement ratio, and placement temperature
conditions on the early-age cracking tendency of bridge deck concrete was evaluated by rigid
cracking frame testing techniques. Use of either fly ash or ground-granulated blast-furnace
slag was found to significantly reduce thermal stresses at early ages. Coefficient of thermal
expansion values were determined for concretes made with aggregates found in Alabama.
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