Implementation of Crack-Reducing Technologies for Concrete in Bridge Decks: Synthetic Fibers, Internal Curing, and Shrinkage-Reducing Admixtures

Abstract

Technologies to reduce cracking in bridge decks, including shrinkage-reducing admixtures (SRAs), shrinkage-compensating admixtures (SCAs), fiber reinforcement, and internal curing (IC), are evaluated based on laboratory tests of concrete mixtures with and without slag cement and silica fume and the cracking performance of in-service bridge decks. Additionally, the influence of construction practices used by contractors is evaluated by field evaluation of bridge decks constructed with and without construction issues. The laboratory portion of this study involves eleven concrete mixtures evaluated based on free shrinkage, scaling resistance, and freeze-thaw durability. The mixtures were cast with or without slag cement and silica fume and contained various quantities of internal curing water; four additional mixtures containing a shrinkage-reducing admixture or one of two shrinkage- compensating admixtures (one of which also contains an SRA) were also evaluated. Results show that the mixtures with slag cement, silica fume, and internal curing exhibited less shrinkage after 20 and 365 days of drying and that shrinkage decreased as the quantity of internal curing water increased from 5.3% to 9.7% by weight of cementitious material. Mixtures with slag cement, silica fume, and 5.3% or 6.5% internal curing water performed well in the freeze-thaw durability test while the mixture with slag cement, silica fume and 9.7% internal curing failed the test. Mixtures with slag cement, silica fume, and internal curing had high mass losses in the scaling resistance test, which was likely due to the harsher test method used in this study or an inadequate air content in the concrete mixture. When a shrinkage-reducing admixture, either by itself or as a part a shrinkage-compensating admixture, is added to the mixture with slag cement, silica fume, and 6.5% internal curing, the freeze-thaw durability and scaling resistance of the mixture was drastically compromised; the mixture with slag cement, silica fume, 6.5% internal curing, and a CaO-based shrinkage-compensating admixture, on the other hand, performed satisfactorily in the freeze-thaw durability and scaling resistance tests. The second portion of this study evaluates the cracking performance of 74 bridge deck placements: 10 cast with fiber-reinforced concrete (FRC), four bridge deck placements containing SRAs, six containing IC, and 54 without crack-reducing technologies. The influence of crack- reducing technologies and poor construction practices are evaluated. Results indicate that using a low paste content in the concrete mixture is the most effective way to reduce bridge deck cracking. Bridge decks with paste contents exceeding 27.3% had higher crack densities than decks with lower paste contents. When used in conjunction with a low paste content, SRAs and IC can further reduce cracking in bridge decks. On the other hand, if the contractors fail to follow proper procedures to consolidate, finish, or cure concrete, bridge decks will exhibit substantially greater cracking, even when low paste contents are used. The use of fiber-reinforced concrete can slightly alleviate, but not overcome, the negative effects of poor construction.