The shrinkage of mixtures containing replacements of total aggregate with prewetted lightweight aggregate (LWA) (0, 8, and 10% by volume) and replacements of cement with Grade 100 slag cement (0 and 30% by volume) and silica fume (0, 3, and 6% by volume) is evaluated. The results show that internal curing provided by prewetted LWA reduces the tendency of the mixtures to develop shrinkage strains. Further reductions are observed as slag is added in conjunction with prewetted LWA and as silica fume is added in conjunction with the prewetted LWA and slag.

The compatibility of two shrinkage-reducing admixtures (SRAs) with two air-entraining admixtures (AEAs)-one surfactant-based and one foaming polymer-based-was examined based on freezing-and-thawing durability, scaling resistance, and air-void characteristics of hardened concrete. SR4 dosages of 0, 0.5, 1.0, and 2.0% by weight of cement were used. Test results show that interactions between admixtures can reduce air-void stability contributing to lowered freezing-and-thawing durability and scaling resistance. Without an SRA, concrete mixtures containing either AEA exhibited good freezing-and-thawing durability and scaling resistance. With an SRA, mixtures containing the surfactant-based AEA performed well, while those containing the polymer-based AEA did not. Mixtures containing higher dosages of SRA, regardless of AEA, experienced a greater loss in air content in concrete between the plastic and hardened conditions. Mixtures with an increased air-void spacing factor experienced decreased durability with the greatest decrease observed in those with air-void spacing factors greater than 0.008 in. (0.20 mm).

Bridge deck crack surveys were performed on twelve bridges on US-59 south of Lawrence, Kansas, to determine the effects of mixture proportions, concrete properties, deck type, and girder type on the crack density of reinforced concrete bridge decks. Of the twelve decks surveyed, eight are supported by prestressed concrete girders and four are supported by steel girders. Four of the decks supported by prestressed girders are cast on partial-depth precast deck panels, two are monolithic with synthetic fibers, and two have overlays. Of the four decks supported by steel girders, two have silica fume overlays (SFO) and two are monolithic. One of two decks with a silica fume overlay contains synthetic fibers in the overlay. Following the surveys, crack maps were plotted and analyzed and cracking trends were observed. The results for the US-59 bridge decks are compared with crack densities obtained in a study of low-cracking high-performance concrete (LC-HPC) bridge decks. The monolithic concrete bridge decks supported by prestressed concrete girders within this study exhibit less cracking than decks supported by steel girders. At an age of approximately three and a half years, the US-59 monolithic decks supported by prestressed girders with deck panels are not displaying significant cracking; most of the cracks are short transverse cracks aligned with the joints between the deck panels. The US-59 decks supported by prestressed girders with overlays exhibit significantly more cracking than the decks on prestressed girders without overlays. Bridge decks supported by steel girders without overlays have slightly higher crack densities than the decks with overlays. No benefits of using fibers in either the overlay or deck have been observed in this study, the sample size, however, is small. An increase in crack density was observed with an increase in average concrete slump for decks supported by both prestressed and steel girders. Decks with deck panels supported by prestressed girders exhibited an increased crack density with an increase in paste content. .

Drying shrinkage is a principal cause of cracking in concrete structures. The cracking can be accommodated or modified so that the performance of the overall structure is not affected. This is not true for bridge decks where drying shrinkage cracking combines with plastic shrinkage, settlement, and thermal cracking to lower the durability of the deck by allowing water and deicing chemicals to penetrate the concrete and increase the susceptibility of the reinforcing steel to corrosion. Work is underway at the University of Kansas to develop concrete mixtures that will minimize concrete shrinkage to minimize cracking in bridge decks. It has been well established that the lower restraint provided by lightweight aggregates (LWAs) can lead to increased drying shrinkage compared with mixtures containing normal aggregates, and if not adequately prewettted, the unsatured pores lead to greater water demand during construction and result in inadequate water for hydration. Due to the absorption and desorption properties of the aggregate, vacuum-saturated LWAs can readily provide an internal source of water to increase hydration and lessen the drying effects on a concrete mixture. The effectiveness of prewetted, vacuum saturated (PVS) light-weight aggregates as an internal curing agent to reduce concrete shrinkage is evaluated for curing periods of 7 and 14 days in this paper.

Funding for this research was provided by the Kansas Department of Transportation serving as the lead agency for the “Construction of Crack-Free Bridge Decks” Transportation Pooled Fund Study, Project No. TPF-5(174). The Federal Highway Administration (FHWA) of the U.S. Department of Transportation (DOT), Colorado DOT, Idaho Transportation Department, Indiana DOT, Michigan DOT, Minnesota DOT, Mississippi DOT, New Hampshire DOT, New York DOT, North Dakota DOT, Ohio DOT, Oklahoma DOT, Texas DOT, Wisconsin DOT, and the University of Kansas Transportation Research Institute provided funding for the project. Representatives from each sponsor served on a Technical Advisory Committee that provided advice and oversight for the project. On-site support and data on the bridge decks was provided by the Minnesota Department of Transportation.