Assessment of Stability Test Methods for Self-Consolidating Concrete
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Self-consolidating concrete (SCC) is a highly fluid, nonsegregating concrete that can spread through reinforcement and completely fill formwork without the use of mechanical consolidation. Resistance to segregation, also known as stability, is difficult to measure in fresh samples, and few test methods are available to quantify this vital property during production. The objectives of this study were to identify and assess several fresh stability test methods for SCC and recommend the stability testing protocol the Alabama Department of Transportation should implement when using SCC to produce precast, prestressed bridge girders. The following stability test methods were evaluated: Visual Stability Index, Column Segregation Test, Rapid Penetration Test, Sieve Stability Test, Surface Settlement Test, and the Multiple-Probe Penetration Test. These six tests were performed while placing SCC in four walls of heights of 36, 54, 72, and 94 inches, and the fresh concrete stability test results were compared to the results of in-situ uniformity testing conducted on the hardened concrete walls. The wall uniformity testing program included through-wall ultrasonic pulse velocity (UPV) tests that were conducted at multiple heights within each wall. Also, pullout tests were performed on groups of deformed steel bars embedded at the top, middle, and bottom of each wall. The strongest correlations between stability test results and in-situ uniformity were established with the surface settlement test. The results of the sieve stability test and VSI showed reasonable correlations with in-situ uniformity and with each other. The surface settlement test should be the primary stability test used to assess SCC mixture stability during mixture prequalification, and a rate of settlement less than 0.15 percent per hour determined between 10 and 15 minutes should ensure that the tested SCC will exhibit acceptable in-situ uniformity. The sieve stability test should be the primary fresh stability test used to assess SCC mixture stability during production, and a sieved fraction less than 15 percent should ensure that the tested SCC will exhibit acceptable in-situ uniformity. Also, the VSI should be used first to assess SCC mixtures during production, and a VSI less than 2.0 should ensure that the tested SCC will exhibit acceptable in-situ uniformity. If the VSI result is greater than 1.0, though, the sieve stability test result should be used to accept or reject the batch.