13th International Conference on Fracture June16–21, 2013, Beijing, China -4Table 2. Chemical composition and physical properties of silica fume Chemical composition (%) Physical properties SiO2 Al2O3 K2O CaO MgO L.O.I Blaine SG 97.2 0.32 0.29 0.05 0.1 2.12 % 25.69 m2/g 2.25 SG: Specific Gravity Table 3. Mix design of UHPC concretes (kg/m3) Mix Cement Silica sand Silica fume Quartz Steel fiber SP Water UHPC0 720 900 256 252 0 7.1 133.7 UHPC0.5 720 860 256 252 40 7.1 133.7 UHPC1.0 720 820 256 252 80 7.1 133.7 UHPC1.5 720 780 256 252 120 7.1 133.7 UHPC2.0 720 740 256 252 160 7.1 133.7 UHPC2.5 720 700 256 252 200 7.1 133.7 UHPC3.0 720 660 256 252 240 7.1 133.7 UHPC3.5 720 620 256 252 280 7.1 133.7 Note: SP means Super-plasticizer. 2.2. Test Specimens The UHPC precast specimens had dimensions of 600 mm × 350 mm ×40 mm with eight opening holes as shown in Figure 1. The fibers included in the UHPC were always Dramix steel fibers that were 13 mm long and had two 0.2-mm and 0.25-mm diameter. These fibers were included in the mix at a specific concentration of 0, 0.5, 1.0, 1.5, 2.0, 2.5, 3.0, and 3.5 percent by volume. The demolding of the UHPC precast specimens occurred approximately 48 hours after casting. The normal curing and heat curing treatments were used in this study. The heat curing treatment used heat water to cure the UHPC at 90 ºC for three days. In practice, this procedure included 2 hours of increasing temperature and 2 hours of decreasing temperature, leaving 68 total hours of constant heat water at 90 ºC. This treatment was initiated within 4 hours after demolding. This curing condition will henceforth be referred to as heat water treatment. 2.3. Freeze-thaw Tests One accelerated deterioration environment, namely the freeze-thaw cycle test, was selected for the evaluation of UHPC precast products. Freeze-thaw cycling of all specimens was conducted using the cold climate testing facilities at Chaoyang University of Technology in Taiwan. Freeze-thaw cycles were applied to the blocks at a rate of one cycle/185 min, in accordance with ASTM C 666-97, Test Method for Resistance of Concrete to Rapid Freeze and Thawing, with 1.5 hours of freezing in cold air at –18°C followed by 1.5 hours of thawing in cool air at + 4.4°C. Specimens that were not subjected to freeze-thaw cycling were stored in the material testing laboratory by immersing in saturated lime water for 24 hours prior to testing, for more detail see Lee et al [11]. The specimens were divided into groups of three, with groups subjected to 0, 200, 400, and 600 freeze-thaw cycles. Before and after freeze-thaw cycling, the samples were tested for their drop-off
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