Comparison of Field-Oriented Test Methods to Assess Dynamic Stability of Self-Consolidating Concrete

摘要

The successful casting of self-consolidating concrete (SCC) necessitates that the concrete achieves a high level of deformability to flow into place and fill the formwork without consolidation. Such concrete should exhibit adequate stability to ensure flow among closely spaced obstacles with minimum risk of segregation. The selection of effective test methods to assess stability is critical for the successful design and placement of SCC. A two-pan experimental program was undertaken to compare a number of test methods that can be used to evaluate both the dynamic and static stability of SCC. Methods pertaining to dynamic stability are discussed in this paper and include visual observation of spread out concrete, flow testing of concrete using various test apparatus (JRing, L-box, U-box, and V-funnel), and the pressure bleed test. In total, 16 SCC mixtures proportioned with or without viscosity-modifying admixture, with slump flow consistencies of 615 +- 15 mm and 715 +- 15 mm, were investigated. Test results show that some of the dynamic stability parameters influencing the passing ability of SCC can be related to rheological properties of the concrete. Mixtures with an apparent yield value g of 0.3 to 1.7 N.m and a torque plastic viscosity h of 17 to 27 N.m.s are found to ensure high passing ability determined using the L-box flow test. The L-box flow time of these mixtures can range between 4 and 8 s. Good correlations are established between h and the T_(50)flow time, corresponding to the duration to attain 500 mm slump flow spread. Similar correlations are established with flow time determined with the V-funnel, L-box, and U-box test apparatus. The L-box test can enable simultaneously the evaluation of deformability and narrow-opening passing ability characteristics and is recommended along with the slump flow test for field-oriented quality control of SCC. The pressure bleed test is suitable to evaluate the ability of the paste to retain free water in suspension and may be used to quantitatively evaluate the stability of SCC in the field.