United States Department of Transportation
i
Evaluation of concrete bridge mix designs for control of cracking, phase I.
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2014-11-01
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[PDF-2.70 MB]
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Abstract:Cracking of concrete is a common problem with concrete structures such as bridge decks, pavements and bridge
rail. The Agency of Transportation (VTrans) has recently invested in higher performing concrete mixes that are
more impervious and has higher early strength. VTrans has also begun to standardize on bare decks on bridge
rehabilitation projects. Higher strength concrete is more susceptible to cracking. With more decks being
constructed with exposed concrete, the risks of chlorides and other corrosives penetrating to the reinforcing may
lead to early deterioration. Additional moisture within the concrete may compound the deterioration during freeze-thaw periods. These stressors lead to decreased strength, which results in increased maintenance to ensure
safety and durability, a reduction in the overall aesthetics of the structures and a decrease in public confidence and
support. With closer attention made to the concrete mix by the addition of key admixtures, concrete may be able
to perform as desired with fewer resulting problems.
With 22 different concrete mix designs produced and tested for various concrete properties, flexural and
compressive strength, rapid chloride permeability and shrinkage, it is clear that there are seven candidate designs,
given the measured data, which could outperform current VTrans standards. To ensure successful performance of
new mix designs, further testing on each, with additional refining, a second phase of this project has been
approved, with the same testing parameters, to refine the chosen mix designs further. The refining of designs will
entail further optimization of aggregate gradations, as the industry has trended towards reporting benefits of this,
lowering only cement content to achieve design strength within 10% at 28 days while other components remain
unchanged in a mix, and include shrinkage control measures in most if not all mixes.
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