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OCR for page 27
27 of coarse aggregate that reduces aggregate interlock and gation potential and in-situ properties of the hardened results in lower energy absorption capability on the sliding concrete. shear failure plane. ­ Evaluation of the effect of concrete workability, place- ment techniques, casting rate, and form release material on surface finish of SCC. 4.6 Recommendations for ­ Evaluation of the effect of rheological properties of SCC, Future Research delivery period, and delay between successive place- The following recommendations are made for future ment on cold joint formation and surface defects. research related to SCC used in precast, prestressed applications. Test Methods Constructability · Short term · Short term ­ Development of a reliable test method to determine ­ Validation of the recommended workability character- bond-strength and modification factor to prestressing istics proposed in Table 13 using full-scale prestressed strands. girders. · Medium term ­ Evaluation of the effect of horizontal flow distance and ­ Development of a QC test method to evaluate plastic free-fall distance of concrete in the formwork on segre- viscosity of SCC. Table 13. Workability values of SCC used in precast/prestressed applications. Slump flow J-Ring L-box Caisson (ASTM (Slump flow­ blocking filling C 1611/C 1611 J-Ring flow) ratio (h2/h1) capacity M-05 ) (ASTM C 1621) 23.5-25 in. 25-27.5 in. 27.5-29 in. 70%-75% 75%-90% 3- 4 in. 0.5-0.6 0.6-0.7 90% 2-3 in. 2 in. 0.7 Relative values Low Reinforce- Medium ment density High Small Shape Moderate intricacy Element characteristics Congested Shallow Moderate Depth Deep Short Moderate Length Long Thin Moderate Thickness Thick Low Coarse Medium aggregate content High 1 in. = 25.4 mm Shaded zones indicate suggested workability characteristics. All SCC mixtures must meet requirements for static stability.

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28 ­ Development of a QC test method to determine struc- on workability, mechanical properties, and visco-elastic tural build-up and evaluate its effect on consolidation properties of SCC. level, surface quality, and cold joint formation. ­ Investigation of the effect of finely ground limestone ­ Development of a dynamic stability test to assess segre- fillers on fresh and hardened concrete properties of gation resistance of SCC subjected to horizontal flow SCC, in particular stability, temperature rise, strength and free-fall into the formwork. development, and visco-elastic properties. Material Selection and Mix Design Structural Performance · Short term · Short term ­ Evaluation of the effect of shrinkage-reducing admix- ­ Determination of modification factor (top-bar effect) of tures on shrinkage and creep of SCC used in precast, reinforcing bars in structural elements cast with SCC of prestressed applications (relevant because of the higher different workability characteristics (especially static drying shrinkage and creep of SCC). stability) and element depth. ­ Investigation of the compatibility issues between chemi- ­ Evaluation of the effect of SCC on transfer length with cal admixtures (in particular HRWRA, VMA, shrinkage- simple transfer length specimens. reducing admixtures, and air-entraining admixtures) on ­ Evaluation of the influence of coarse aggregate content flow properties and strength development of SCC. and MSA on aggregate interlock (direct shear "push-off" ­ Determination of key factors affecting robustness of specimens) and companion tests to investigate the shear SCC and ways to enhance it in order to ensure consis- behavior of simple SCC elements (non-prestressed rec- tent concrete quality and productivity. tangular beam specimens). · Medium term · Medium term ­ Extension of the modeled region of the factorial design ­ Evaluation of key engineering properties, durability beyond the range of -1 to +1 as well as incorporating characteristics, and structural performance of SCC other parameters in order to take into consideration the with high-release strength [e.g., 7,000 psi (48 MPa)] quadratic effect of various parameters in the derived and design compressive strength greater than 12,000 psi models, in particular those of the visco-elastic proper- (83 MPa). ties and formwork pressure. ­ Evaluation of the use of steel and synthetic fibers in SCC ­ Investigation of the influence of mixture proportioning mixtures. and material characteristics that were not considered in ­ Extensive testing and evaluation of full-scale specimens this research {e.g., MSA [3/8 and 1/2 in. (9.5 and 12.5 mm)], to provide definitive information on structural per- combined sand and coarse aggregation content and gra- formance, including the contribution of the presence of dation, sand type [crushed vs. natural], and paste volume} top and bottom flanges to the shear resistance.