Development of a Specification for Low-Cracking Bridge Deck Concrete in Virginia

Abstract

Cracking continues to be the number one concern about bridge deck construction. Rarely is a deck without cracks constructed. Transverse cracking mainly attributable to drying shrinkage is common in bridge decks and has been observed in many bridge decks newly constructed by the Virginia Department of Transportation (DOT). Shrinkage-reducing admixtures (SRAs) in concrete reduce shrinkage and are one of the most effective ways of reducing shrinkage cracking. A low modulus of elasticity and high creep also help minimize cracking. Lightweight concrete (LWC) has a lower modulus of elasticity, higher inelastic strains, a lower coefficient of thermal expansion, a more continuous contact zone between the aggregate and the paste, and more water in the pores of aggregates for continued internal curing than normal weight concrete: all these factors help reduce cracking in LWC. Drying shrinkage can also be counteracted with the use of shrinkage-compensating concrete (SC). When properly restrained by reinforcement, SC can expand an amount equal to or slightly greater than the anticipated drying shrinkage. The research in this paper investigated the effectiveness of SC, LWC, and concrete with SRA in reducing cracks in bridge decks and to develop a low-cracking bridge deck specification for use in future Virginia DOT bridge decks. The study showed that bridges with fewer and narrower cracks could be constructed with SRA, LWC, and SC and that proper construction practices were needed to reduce bridge deck cracking. This study resulted in the Virginia DOT implementing a low-cracking bridge deck specification.

Durable Concrete Overlays in Two Virginia Bridges

“…However, ternary systems are also permitted with reduced amounts of silica fume, which reduces the cracking potential. In the mixtures with lightweight aggregates, a binary system with 7% silica fume is used as lightweight aggregates are expected to reduce the cracking potential ( 10 ). A commercially available air-entraining admixture and a high-range water-reducing admixture were used in varying amounts to achieve the specified air content and workability.…”

“…Lightweight concretes (LWC) are not tested for shrinkage, as in a recent study on reducing cracks in bridge decks, LWC did not crack when shrinkage was above 0.035% and as high as 0.060% ( 10 ). The increased crack resistance in LWC is attributed to their lower elastic modulus, internal curing, and lower coefficient of thermal expansion compared with conventional concretes ( 10 , 11 ). VDOT has been using LWC in decks with very good results for more than 30 years ( 12 ).…”

“…Maggenti et al found that the use of an SRA in the concrete resulted in less shrinkage cracking in bridge decks ( 24 ). The use of prewetted lightweight aggregate can minimize the development of autogenous shrinkage and help to avoid early age-cracking ( 10 ). At the same time, its use has been shown to increase hydration; decrease shrinkage, porosity, and permeability; and increase compressive strength and mitigate shrinkage cracking through internal curing ( 10 ).…”

“…The use of prewetted lightweight aggregate can minimize the development of autogenous shrinkage and help to avoid early age-cracking ( 10 ). At the same time, its use has been shown to increase hydration; decrease shrinkage, porosity, and permeability; and increase compressive strength and mitigate shrinkage cracking through internal curing ( 10 ). Internal curing can also be achieved by replacing a portion of the fine aggregate with prewetted lightweight fine aggregate.…”

Developing Large Slab Airport Runways for the Next Century

“…This allows larger slabs to be placed, that may significantly reduce the demand for joints, which are a primary root cause of airport pavement failures. SCC does come at an increased initial cost; it is typically between $20 and $60 more expensive per cubic yard compared with ordinary PCC ( 18, Chris Ramseyer, personal communication, 2018 ). This cost range is not because of variability in the cost of material; instead, it is often controlled by whether extra equipment such as a separate cement hopper for the expansive cement must be acquired.…”