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Internal curing of high-performance concrete for bridge decks.
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    High performance concrete (HPC) provides a long lasting, durable concrete that is typically used in bridge decks due to its low permeability, high abrasion resistance, freeze-thaw resistance and strength. However, this type of concrete is highly susceptible to the deleterious effects of both autogenous and drying shrinkage. Both types of shrinkage occur when water leaves small pores (< 50 nm) in the paste matrix to aid in hydration or is lost to the surrounding environment. Autogenous deformation (self-desiccation) occurs as the internal relative humidity decreases due to hydration of the cementitious material. Drying (and subsequent shrinkage) occurs when water is lost to the environment and continues until the internal relative humidity is equivalent to the ambient relative humidity. Typically, the magnitude of autogenous shrinkage is significantly less than that of drying shrinkage. These two types of shrinkage do not act independently, and the total shrinkage is the aggregation of the two shrinkage mechanisms, among other types of deformation. It is thus imperative to minimize the amount of shrinkage in restrained members, such as bridge decks, to reduce subsequent cracking potential. Various methods have been investigated to minimize both types of shrinkage. Two methods to date that have been reported to reduce shrinkage were selected for further research; internal curing using pre-soaked fine lightweight aggregate (FLWA) and a shrinkage reducing admixture (SRA).The purpose of this study was to determine the long-term drying shrinkage performance of these two methods while reducing the current external curing duration of 14 days for new bridge deck construction as specified by the Oregon Department of Transportation. In addition to monitoring drying shrinkage, durability testing was performed on concrete specimens to ensure these shrinkage mitigation methods performed at levels similar, or superior, to concrete with the current mixture design. Freeze-thaw testing, permeability testing and restrained drying shrinkage testing were conducted. It was concluded that the pre-soaked FLWA and the SRA were effective at reducing the long-term drying shrinkage, but the combination of SRAs and pre-soaked FLWA was the most effective method to reduce long-term drying shrinkage for all curing durations (1, 7, and 14 day). Additionally, for durability testing, it was found that the use of SRAs performed the best in freeze-thaw testing, chloride permeability and restrained shrinkage when compared to the control.

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