The Effectiveness of Self-Consolidating Concrete (SCC) for Drilled Shaft Construction
Type of DegreeThesis
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Due to increasing design requirements and the advancement in technology, deep foundations have become larger and more congested over the years. Reinforcement congestion required to resist high lateral forces, has lead to an increased interest in alternative solutions to minimize problems associated with congested reinforcing cages. Self-consolidating concrete (SCC) is a highly flowable concrete that is not completely recognized by the U.S. construction industry, outside of the precast/prestressed industry. This thesis presents research supported by the Alabama Department of Transportation (ALDOT) to study the effectiveness of SCC for drilled shaft applications. The study determines and presents an SCC mixture to be used for the construction of the middle two piers of the B.B. Comer Bridge in Scottsboro, Alabama. The experimental program consists of a series of SCC mixtures that vary in water-to-cementitious (w/cm) ratio from 0.42, 0.40, and 0.38 and sand-to-aggregate (S/Agg) ratio varying from 0.45, 0.50, and 0.55. Nine mixtures are developed by pairing each of the w/cm with each of the S/Agg, and the fresh and hardened properties are tested and compared to a mixture representing the conventional drilled shaft concrete currently used in construction. One of the 9 SCC mixtures is chosen for an experimental field test where 3 drilled shafts will be constructed; two of the shafts will be constructed using the conventional concrete and the SCC mixture chosen. The third shaft will be constructed with a mixture similar to that of the SCC mixture, except that 10% of the cementitious material will be replaced with a non-cementing limestone powder in order to study its effectiveness for reducing excess bleed water. The fresh properties tested in the laboratory consisted of the slump flow, including the T50 and VSI, slump flow retention, air content, unit weight, a Modified J-Ring, and the segregation column. The hardened properties tested were the compressive strength, modulus of elasticity, drying shrinkage, and the permeability. The tests revealed that SCC provided a more workable concrete without any signs of segregation. The material also provided workability over a longer period of time compared to the conventional mixture. The SCC provided a sound and durable concrete with low permeability and compressive strengths well beyond the required minimum. The SCC also showed less drying shrinkage compared to the conventional concrete. One of the SCC mixtures tested will be used in the construction of the B.B. Comer Bridge.