Effect of mix parameters on restrained shrinkage of self consolidating concrete

Self Compacting Concrete (SCC) is a relatively new type of concrete that flows under its own self weight. In order for the concrete to achieve the SCC properties, an increased amount of cementitious material is needed. Increased amount of cementitious content is known to lead to increased amount of shrinkage, which in turn leads to cracking of concrete. The shrinkage of concrete is the main cause of cracking in bridge decks. Bridge decks tend to be restrained from shrinkage, and this restraint along with other factors causes the bridge to crack. The characteristics of SCC under restrained shrinkage are important to understand in order to predict the cracking behavior in actual structures. Mechanical properties testing of compressive strength, tensile strength, and elastic modulus are performed on each concrete mix. Restrained shrinkage testing is done in accordance to AASHTO testing protocol. Cracking patterns are observed due to changes in mixing parameters. The free shrinkage performance and cracking behavior were reported and compared when changing the sand to aggregate ratio and the water to cement ratio. The results showed that the sand to aggregate ratio between the limits of .45 to .55 had little effect on the cracking potential of the SCC mixes. Each of the mixes cracked within a couple days of one another. The water to cement ratio showed that as the water to cement ratio increases, cracking also increases. Free shrinkage specimens were used to correlate the free shrinkage to the cracking behavior of the mixes. Every mix contained 850 lbs of cementitious material (75% Portland type I cement, 20% Fly Ash, and 5% Silica Fume). The results of free shrinkage show that when a mix design has higher free shrinkage, it will crack in restrained shrinkage earlier than a mix with lower free shrinkage.M.S.Includes bibliographical referencesby Carl Fleurimon