Mix design for improved strength and freeze-thaw durability of pervious concrete fill in Pearl-Chain Bridges

Pearl-Chain Bridges are an innovative precast arch bridge technology which can utilize pervious concrete as fill material. The present study investigates how the mix design of the pervious concrete fill can be influenced by use of an air-entraining admixture, a high-range water reducing admixture, fibers, and by internal curing using lightweight aggregate to best possibly meet the requirements for a fill material in Pearl-Chain Bridges. The 28-day compressive strength, splitting tensile strength, shear strength, permeability, and freeze-thaw durability were determined and compared for eight different mixture proportions using two different sizes of granite coarse aggregate and at two different water-to-cement ratios. The specimens had an average void content of 24-28 %. Specimens containing air entraining and high-range water reducing admixtures were most workable, as determined by fresh density, and thus the easiest to place. The addition of a high-range water reducing admixture and lightweight sand (expanded shale) for internal curing improved the 28-day compressive strength and splitting tensile strength. The coarse aggregate gradation had a large influence on permeability; however, all tested permeabilities were high enough to drain the rain from a 100-year rain event in Denmark. The air entraining agent dosage used was not sufficiently high to create the necessary protective air content in the cement paste, and the freeze-thaw durability of the specimens were generally poor for the utilized test procedure; however, the mix design containing lightweight sand showed improved freeze-thaw durability compared to the other mix designs.