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5 CHAPTER 1 Findings The major findings of the research study are described in this (600 to 735 mm), L-box blocking ratio (h2/h1) greater than chapter. Further details of the experimental work, analyses of 0.5, J-Ring flow of 21.5 to 26.0 in. (545 to 660 mm), filling the data, and conclusions are presented in Attachment D. capacity greater than 70%, and a difference in slump flow and J-Ring flow values lower than 4 in. (100 mm). Regardless of the MSA, stable SCC should develop a col- 1.1 Test Methods and umn segregation index (C.O.V.) less than 5% and percent Mixture Requirements static segregation lower than 15. The recommended limits for Various test methods are used to assess the workability surface settlement depend on the MSA. SCC proportioned characteristics of SCC. The most promising test methods that with 3/4 in. (19 mm) and 1/2 or 3/8 in. (12.5 or 9.5 mm) MSA are relevant for the fabrication of precast, prestressed concrete should have maximum rates of settlement at 30 minutes of bridge elements (details of test are given in Attachment D) are: 0.12%/h and 0.27%/h, respectively. SCC mixtures investigated in this study developed yield · Filling ability: slump flow and T-50 (ASTM C 1611); stress values varying between 0.00145 and 0.01885 psi (10 and · Passing ability: J-Ring (ASTM C 1621) and L-box; 130 Pa). SCC made with crushed aggregate should develop plas- · Filling capacity: caisson test (filling vessel); and tic viscosity of 100 to 225 Pas at the time of casting to ensure · Segregation resistance: column segregation (ASTM C 1610), adequate passing ability and static stability. This range can be visual stability index (VSI), surface settlement, and rate of 0.0145 to 0.0326 psis (100 to 400 Pas) for SCC made with settlement. gravel having 1/2 in. (12.5 mm) MSA. The lower limit of plastic The use of a combination of test methods is necessary to viscosity is necessary to secure a maximum rate of settlement reduce the time and effort required for quality control in the of 0.27%/h at 30 minutes of testing and a maximum C.O.V. of precasting plant. The caisson filling capacity test (modified 5%. The upper limit of plastic viscosity of 250 and 400 Pas is from initial value) is found to be promising to evaluate both necessary for the SCC with slump flow consistency of 26.0 to the filling ability and passing ability of SCC. This test can be 27.5 in. (660 to 700 mm) to achieve adequate passing ability especially useful for SCC cast in densely reinforced sections. A (minimum L-box blocking ratio of 0.5). Based on the proper- ties of SCC made with different viscosity levels cast in experi- mean caisson filling capacity value of 80% (75% to 90%) is mental wall elements, plastic viscosity higher than 500 Pas considered as a lower limit for precast, prestressed concrete should be avoided to ensure proper self-consolidating proper- applications. A lower limit of 70% can be tolerated for rela- ties and homogeneity distribution of in-situ properties. tively simple elements. Values greater than 90% can be secured for highly flowable and stable mixtures. The L-box blocking ratio (h2/h1) index, J-Ring flow, or the 1.2 Selection of difference between slump flow and J-Ring flow can be com- Concrete Constituents bined with slump flow testing to evaluate the filling capacity Effect of Binder Type of SCC. The recommended combined test methods for evalu- ating the filling capacity of SCC are (1) slump flow and L-box The binder content and composition were shown to have blocking ratio (h2/h1) and (2) slump flow and J-Ring flow. direct influence on high-range water-reducing admixture SCC mixtures suitable for use in precast, prestressed (HRWRA) demand, fluidity retention, temperature rise, early- concrete girders should exhibit slump flow of 23.5 to 29 in. age strength development, and mechanical properties at 28 and
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6 56 days. Among three binder types used in the parametric flow and J-Ring flow diameters less than 2 in. (50 mm)] and study, SCC mixtures made with Type III cement and 20% high filling capacity (caisson filling capacity greater than Class F fly ash exhibited better workability than that for simi- 90%). Both SCC types exhibited similar segregation resist- lar mixtures prepared with Type I/II cement or Type III cement ance (column segregation index of 2% to 5%). However, and 30% slag. SCC containing 20% Class F fly ash developed mixtures made with gravel developed lower compressive high fluidity retention, high passing ability and filling capacity, strength and modulus of elasticity (e.g., up to 25% and 16% as well as a high level of static stability. The concrete propor- lower, respectively, under moist curing conditions at 56 days) tioned with Type III cement and 30% slag exhibited relatively than those for mixtures made with crushed aggregate of the low passing ability [difference between slump flow and J-Ring same MSA. In terms of hardened concrete properties, mix- flow diameters larger than 4 in. (100 mm)]. tures made with crushed aggregate exhibited better overall The evaluated mixtures developed similar compressive performance than those made with gravel. strengths after 18 hours of steam curing regardless of binder type. However, concrete made with Type III cement and Effect of w/cm and Air Entrainment 20% Class F fly ash developed slightly higher 56-day moist- cured compressive strength than that of concrete made with In general, SCC mixtures with 0.38 w/cm exhibited better Type I/II cement. workability than those with 0.33 w/cm in terms of passing abil- Based on this evaluation, a mixture of Type III cement and ity, filling capacity, and fluidity retention. However, SCC mix- 20% Class F fly ash was selected for the experimental evalua- tures made with 0.33 w/cm developed greater static stability tion that was performed to model the performance of SCC and higher 18-hour and 56-day compressive strengths under for precast and prestressed girder elements. steam-cured and moist-cured conditions. Also, air-cured SCC mixtures made with 0.33 w/cm exhibited lower 18-hour com- pressive strength than the latter concrete under the same cur- Effect of Type and Maximum ing regime, possibly due to the relatively higher dosage of Size of Coarse Aggregate HRWRA necessary to achieve the target slump flow. No sig- The maximum size of coarse aggregate and coarse aggre- nificant difference was found in the 18-hour modulus of elas- gate type had a marked effect on passing ability, filling capac- ticity between the 0.33 and 0.38 w/cm mixtures. ity, and static stability of SCC. The MSA should be selected SCC with 0.38 w/cm will attain a minimum release compres- with consideration of the minimum clear spacing between sive strength of 5,000 psi (34.5 MPa) and ultimate compressive the reinforcing steel bars and prestressing strands, the cover strength of 8,000 psi (55.2 MPa). Such concrete can be used for over the reinforcement, and the geometry of the elements casting highly reinforced and restricted sections because of its to be cast. The reduction in MSA is required to enhance sta- good filling capacity. Higher strength may require the use of bility. From a workability point of view, SCC mixture made mixtures with lower w/cm (e.g., 0.32 to 0.35). with crushed aggregate of 3/8 in. (9.5 mm) MSA exhibited In general, air-entrained SCC exhibited superior passing greater passing ability [difference between slump flow and ability and filling capacity than SCC without air entrainment J-Ring flow diameters lower than 2 in. (50 mm)] and higher because of its lower viscosity and greater paste content. How- filling capacity (caisson filling capacity higher than 90%). ever, air-entrained concrete developed lower static stability In particular, mixtures containing 3/4 in. (19 mm) MSA exhib- and lower compressive strength and modulus of elasticity, ited a relatively low level of filling capacity (caisson filling both under steam-curing and moist-curing conditions. capacity less than 70%) and relatively low resistance to seg- regation (column segregation index higher than 5%). The SCC Effect of Fluidity of SCC mixtures made with 3/8 in. (9.5 mm) MSA exhibited surface settlement and column segregation index values similar to Workability responses and mechanical properties of SCC those for mixtures made with larger MSA. designed for relatively high, medium, and low slump flow As in the case of fresh properties, SCC mixtures made with values of 28 to 30 in. (710 to 760 mm), 25 to 28 in. (640 to crushed aggregate of 3/8 in. (9.5 mm) MSA developed similar 710 mm), and 23.5 to 25 in. (600 to 640 mm), respectively, are or higher compressive strengths after 18 hours of steam cur- compared. SCC mixtures with low and medium slump flow ing and 56 days of moist curing than those for mixtures made had similar levels of passing ability (medium), filling capac- with 1/2 or 3/4 in. (12.5 and 19 mm) MSA. SCC proportioned ity (medium), and resistance to surface settlement (high). with gravel developed better passing ability and filling capac- Mixtures with high fluidity (slump flow) exhibited high pass- ity than similar concrete made with crushed aggregate of the ing ability and filling capacity, but relatively medium to low same MSA [1/2 in. (12.5 mm)]. The former had high passing static stability. As expected, SCC with high fluidity developed ability [h2/h1 greater than 0.7 and difference between slump lower compressive strengths at 18 hours of steam curing and