Bridges, Tunnels and other Transportation Structures
Concrete cracking due to restrained drying shrinkage is a widespread problem that could happen to any structural element including bridge decks. One of the main causes of bridge deck cracking is the development of tensile stresses due to restrained drying shrinkage. Cracks allow harmful substances such as water and deicing salts to penetrate the deck and initiate corrosion. This research investigates the use of different concrete mixture to reduce cracking in bridge decks due to restrained drying shrinkage using large-scale experimental decks. Large-scale experimental decks were used in this study in order to provide a better understanding of how strain changes under actual restrained condition in bridge decks. Four large-scale bridge decks of 7 ft x 10 ft were built using four different types of concrete mixtures: (1) a mixture containing 100% Portland cement, (2) a mixture incorporate expansive Type-K cement, (3) a mixture containing internally cured fine lightweight aggregate (LWA) and (4) a combine mixture of Type-K cement and internally cured LWA to promote internal curing. Type-K cement is hydraulic cement which, unlike Portland cement, expands during the early hydration period after setting. Internal curing LWA reduces shrinkage by releasing water from the aggregate into the concrete to maintain the internal relative humidity. The mixture containing combination of Type-K cement and internally cured LWA accumulates both the benefit from expansive cement as well as from extra water supplied by internally cured LWA. The results showed that combined mixture of Type-K cement and internally cured LWA has the highest initial expansion compared to other mixtures during the early-age hydration and produce compressive stress in the concrete; and eventually reduces onset of cracking. Experimental deck poured with combined mixture of Type-K cement and internally cured LWA is less prone to crack prematurely and more durable.