Page 55

2017WinterShotcreteEMag

Fig. 5: Shotcreting t Fig. 4: Track section ready for shotcreting he sliding track wall rebound had to be constantly removed using an air lance (blow pipe). The upper and lower head parts were shot with lower air pressure, and then the in-place concrete was compacted with a vibrator. The shotcrete process was completed with placement to just above the temporary screed pipes on the primary layer. Figure 5 shows the shotcreting of the inner wall surface. Fabricating Test Specimen For compressive strength and durability test, a 20 x 20 in. (500 x 500 mm) panel was shot and cores from the panel were tested for compressive strength. Flexural strength and a freezing-and-thawing test were performed with samples from 18 x 18 in. (460 x 460 mm) panels. Screed and Surface Finish Using Temporary Screed Pipe After shooting was completed, the freshly placed concrete was screeded to the 1.1 in. (28 mm) plastic tubes installed on the upper reinforcement as a temporary screed pipe. In the straight portions, it was set at a 3.3 to 4.9 ft (1 to 1.5 m) spacing to give the bobsleigh track a smooth surface and uniform thickness, necessary for the cooling pipe to efficiently create ice on the surface. The temporary screed pipes were removed after the surface was screeded and the remaining void was filled with hand-applied concrete. Wet Curing After the final surface finish, the concrete surface was wet-cured with a wetted woven fabric that was continuously watered. No curing membranes were applied. CHALLENGES/CONCLUSIONS Kangwon National University has carried out technical research on shotcrete material and construction methods for many years and is the only specialized shotcrete research institute in Korea that owns shotcrete equipment. To evaluate the best methods for use of shotcrete on this project, university staff conducted an overseas field trip, and encouraged technology and knowhow transfer by inviting foreign experts to help develop the appropriate bobsleigh track construction technology. Fig. 6: A curved track section The advanced research can be broadly divided as material production and construction method development. First, a concrete material appropriate for shotcrete placement with excellent strength, freezing and thawing, and surface-scaling resistance was developed and used because sleigh collisions happen frequently in bobsleigh races. Additionally, the track is continuously exposed to a very cold environment to keep ice frozen on the surface. Second, the overall frame for the bobsleigh track was constructed to place the cooling pipe and reinforcement bars by using a jig support frame with consideration of the required shotcrete placing technique to build the desired shape of bobsleigh track. Because normal formwork or lining cannot be effectively used in creating multiple-curved surface structures, the inner wall stay-form and temporary screed pipe techniques were used. Thus, with these approaches, the multi-curved concrete structure of the track creatively and efficiently used shotcrete placement as the primary construction method. For this project, two initial mockup tests were performed at the university to confirm the materials and placement methods. The final mockup test was successfully performed at the project site in the presence of the FIBT and FIL officials and was accepted with only one trial. This is exceptional compared to other countries’ experience, which www.shotcrete.org Winter 2017 | Shotcrete 53


2017WinterShotcreteEMag
To see the actual publication please follow the link above