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23 CHAPTER 4 Conclusions and Suggested Research This chapter presents the major conclusions of the research bility (typical w/cm for precast, prestressed applications effort and provides suggestions for future research. can range between 0.34 and 0.40). Low S/A values (e.g., 0.46 to 0.50) should be used to obtain adequate workability. 4.1 Test Methods and Coarse aggregate with 1/2 in. (12.5 mm) MSA is recom- Material Requirements mended to achieve adequate workability and mechanical The use of proven combinations of test methods is neces- properties. sary to reduce time and effort required for quality control of Use of thickening-type VMA is required for SCC made SCC used in precast, prestressed bridge elements. These with moderate and relatively high w/cm and low binder methods include the components required for evaluating the content to enhance stability and obtain homogenous in- deformability, passing ability, and resistance to segregation of situ properties. The use of thickening-type VMA at a low the concrete. The most promising SCC test methods for these level can enhance static stability (lower column segregation evaluations are: index). VMA can also be used in highly stable SCC (e.g., with low w/cm) to enhance robustness. Filling ability (slump flow and T-50); Use of air entrainment is required for frost durability (use Passing ability (J-Ring and L-box); of air-entraining admixture will help stabilize small air Filling capacity [caisson test (filling vessel)]; and bubbles). Segregation resistance (VSI, surface settlement and rate of SCC made with Type III cement and 20% Class F fly ash settlement, and column segregation). can exhibit better slump flow retention, higher passing ability, and higher filling capacity than SCC made with Recommended acceptance values for these tests are summa- Type I/II cement. rized in Table 10. These tests are appropriate for material selec- The HRWRA demand decreases with the increase in w/cm tion and mix design as well as for quality control (QC) testing. and binder content. The use of Type III cement and 20% Class F fly ash necessitates higher HRWRA demand than that required for SCC prepared with Type I/II cement 4.2 Material Constituents (thus resulting in lower early-age compressive strength). and Mix Design Better slump flow retention can be obtained with SCC made Based on the results derived from the factorial design, the with low w/cm because of the higher HRWRA demand relative influence of various mixture parameters on the mod- required to achieve 26.0 to 27.5 in. (660 to 700 mm) slump eled properties of SCC are summarized in Table 11. Table 12 flow. gives recommendations for proportioning of SCC mixtures Surface settlement of SCC increases with the increase in for use in precast, prestressed applications. binder content and w/cm. Regarding the fresh SCC properties, the following recom- Plastic viscosity decreases with the increase in binder mendations and observations are made: content and w/cm but increases slightly with the increase in S/A. A w/cm should be selected to obtain the targeted stability, Thixotropy or structural build-up at rest of the SCC mechanical properties, visco-elastic properties, and dura- decreases with the increase in binder content and w/cm.

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24 Table 10. Recommended test methods and target values. Design QC Property Test method Target value Filling Slump flow 23.529 in. (600735 mm) ability T-50 (ASTM C 1611) 1.56 sec (upright cone position) J-Ring flow (ASTM C 21.526 in. (545660 mm) Passing 1621) 03 in. (075 mm) ability Slump flow J-Ring flow L-box blocking ratio (h2/h1) 0.51.0 Filling capacity 70%100% Filling capacity Slump flow and J-Ring flow Slump flow and L-box tests Rate of settlement, 2530 min (value can decrease to 1015 min) MSA of 3 8 and in. Surface settlement (9.5 and 12.5 mm) 0.27%/h (Max. settlement 0.5%) Static MSA of in. (19 mm) 0.12%/h stability (Max. settlement of 0.3%) Column segregation Column segregation index (C.O.V.) 5% (ASTM C 1610) Percent static segregation (S) 15% VSI (ASTM C 1611) 01 (0 for deep elements) 4%7% depending on exposure Air conditions, MSA, and type of HRWRA. volume AASHTO T 152 Ensure stable and uniform distribution of small air voids. Table 11. Relative significance of modeled SCC parameters. Binder VMA Binder w/cm S/A content content type Medium Medium Medium Medium Medium High High High High High Low Low Low Low HRWRA demand Low Slump flow retention J-Ring Slump flow J-Ring flow L-box blocking ratio (h2/h1) Caisson filling capacity Maximum surface settlement Column segregation index Plastic viscosity Thixotropy (Ab) Form pressure 18-hour f c ' 56-day f c ' 18-hour MOE 56-day MOE 7-day flexural strength 56-day flexural strength Autogenous shrinkage at 7 days Autogenous shrinkage at 56 days Drying shrinkage after 28 days of exposure Drying shrinkage after 112 days of exposure Creep after 28 days of loading Creep after 112 days of loading Darkened areas indicate high degree of influence for the modeled mixture parameter.

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25 Table 12. Recommendations for proportioning SCC mixtures. Binder w/cm Binder type S/A VMA content (440 kg/m) (500 kg/m) 742 lb/yd 843 lb/yd III + 20% Moderate fly ash 0.34 0.40 0.46 0.54 I/II 0 Filling ability retention Passing ability Filling capacity Static stability ' 18-hour f c ' 56-day f c 18-hour MOE 56-day MOE Flexural strength Autogenous shrinkage Drying shrinkage Creep Darkened areas indicate better performance for each property. Higher thixotropy can be detrimental to surface finish and Regarding the visco-elastic properties, the following rec- advantageous to formwork pressure. ommendations and observations are made: Initial relative form pressure at 3.3 ft (1 m) in height cast at 13.1 to 16.4 ft/h (4 to 5 m/h) varies between 0.80 and 1.00 of The increase in binder content increases drying shrinkage hydrostatic pressure; it increases with the increase in binder and creep. content and w/cm but decreases with the increase in S/A. Although for a given binder content drying shrinkage is Incorporation of thickening-type VMA in the mixture expected to increase with increased w/cm, for the derived could delay setting and increase the time to attain peak tem- statistical models an opposite trend appears because the perature, thus leading to some delay in early-age strength drying shrinkage also includes autogenous shrinkage that development. In that case, steam curing could be used to decreases with the increase in w/cm. accelerate the strength development. SCC mixtures made with Type I/II cement develop less creep and shrinkage than those prepared with Type III cement and Regarding the mechanical properties, the following rec- 20% Class F fly ash. However, the latter concrete has better ommendations and observations are made: workability and higher mechanical properties than the for- mer SCC. Therefore, use of Type III cement and 20% Class F Mechanical properties increase with the decrease in w/cm. fly ash will require reduction of binder content to ensure Increase in binder content can lead to higher 56-day com- better overall performance. pressive strength but to lower 18-hour MOE and 7-day Concrete mixtures containing high binder content and low flexural strength. w/cm can exhibit high autogenous shrinkage; the majority The increase in S/A results in lower MOE at 18 hours (85% to 95%) of which occurs in the first 28 days (values (steam curing) and 56 days (moist curing) and higher flex- after 56 days can vary between 100 and 350 strain depend- ural strength. ing on mixture composition). SCC made with Type III cement and 20% Class F fly Autogenous shrinkage is mostly affected by binder type and ash exhibits lower early-age compressive strength than paste volume. SCC made with Type III cement and 20% that made with Type I/II cement (due to higher HRWRA Class F fly ash can develop higher autogenous shrinkage and demand). creep than SCC made with Type I/II cement. SCC made with Type III cement and 20% Class F fly ash For a given w/cm, increasing binder content can result in can develop higher compressive strength and MOE at higher drying shrinkage (500 and 1000 strain after 300 days 56 days but lower mechanical properties at 18 hours than is possible). for concrete made with Type I/II cement (mainly because SCC exhibits up to 30% higher drying shrinkage at 300 days of delayed setting resulting from greater HRWRA demand). than HPC made with similar w/cm but different paste