Page 53

2017WinterShotcreteEMag

Fig. 2: Members of the mockup test and flexural strength testing. For durability assessment, we used rapid chloride ion permeability, freezing and thawing, and surface-scaling resistance tests. Table 1 shows the targeted shotcrete’s basic properties and durability characteristics, including the evaluation methods. The pumpability was improved by incorporating 10 to 15% more air content before shooting. The air content was measured to be 3 to 6% after shooting, thus providing the desired in-place strength and durability. The durability properties were improved by substituting silica fume for 8.7% by weight of the cementitious content. The mixture design also helped to suppress early-age shrinkage cracks by substituting 7% of an expansive admixture by weight of the cementitious content. The concrete mixture was economical because the fine aggregate was set at 75% of the total aggregate weight to reduce the amount of rebound. The mixture proportions are shown in Table 2. SHOTCRETE EQUIPMENT Shotcrete Machine In this project, a Putzmeister TK20 shotcrete pump was used. This delivers the concrete using two hydraulic Fig. 3: Shotcrete pump with a mobile volumetric mixer pistons and it can produce up to 17 yd3/h (13 m3/h) with a maximum concrete pressure of 2000 psi (138 bars). In addition, a Putzmeister TK10 was used at the initial mockup test at Kangwon National University, where a 10 ft3 (280 L) mixer was used. This small mixer is ideal for smallscale projects such as this. Figure 3 shows the shotcrete equipment and mobile volumetric mixer used at the track construction site. Air Compressor An air compressor with a maximum capacity of 390 ft3/min (11 m3/min) was used to provide air pressure at the nozzle. CONSTRUCTION PROCEDURE Bobsleigh Track Support Frame Work First, the support frame, where the bobsleigh track will be installed, had to be placed. The support frame secures the space where the left and right walls of the bobsleigh track are attached and defines the working environment. The support frame was manufactured using steel H-beams and was designed and produced to carry the load applied to the back of the wall. Table 1: Shotcrete Material Properties Targeted Test item Targeted Note Test method Slump test, mm 70 to 130 Fresh KS F 2402 Air content, % 10 to 15 Before shooting KS F 2421 3 to 6 After shooting Compressive strength test, MPa 40 or more Age 7, 28 days KS F 2405 Flexure strength test, MPa 5.0 or more Age 28 days KS F 2408 Rapid chloride ion permeability test, Coulombs >1000 Age 28 days KS F 2711 Surface delamination resistance, rating 1 to 2 Age 28 days ASTM C 672 Freezing-and-thawing test, % 80 or more Age 28 days KS F 2456 Table 2: Mixture Proportion of Shotcrete for the Sliding Track Gmax, mm Slump, mm Air, % w/b, % S/a, % Unit weight, kg/m3 AEA, % SP, % W B S G 10 70 to 130 10 to 15 40 75 184 460 1322 436 0.03 0.3 www.shotcrete.org Winter 2017 | Shotcrete 51


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