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2015SummerShotcreteEMag

Sustainability turned out, the loader operator had dug into the ballast rock below the sand with his bucket and contaminated the entire sand pile. Thus, the concrete was delivered to the site with the large ballast rocks that caught on the wet-mix pump grate. The smaller rocks that made it through the grate hung up in Coastal’s 2 in. (50 mm) shotcrete line. Other cast-in-place concrete projects going on down the street were using concrete buckets and didn’t notice the problem. The batch plant concrete was quickly adjusted and a test load of concrete was batched for Coastal to shoot on the wall. When the con- Fig. 4: Large ballast rock caught on the grate. The smaller pieces that crete went through the system with no additional managed to slip through the grate caught in the reducer pumping issues, it was decided to bring the concrete from another plant for better QC of the concrete and safety of the shotcrete crew. (a) This now posed an issue of the 90-minute placement window. The plant with the contam- inated sand pile was only 10 minutes away while the other plant was 30 to 45 minutes away with- out traffic. Master Builders (now BASF) was consulted to provide admixtures that could extend the truck delivery time and give Coastal the 90 minutes to shoot the shotcrete on-site without rejecting the truck. Master Builders sup- plied Delvo ESC pucks (hydration control addi- tive) to delay hydration of the concrete to gain the extra concrete delivery time without jeopar- dizing the quality of the concrete. The Delvo ESC pucks made it easy to field-mix in the truck (one puck equates 1 hour for 1 yd3 0.76 m3 of Fig. 5(a) and 5(b): Congestion in front of the next wall sections to be shot hydration control in the truck). This would cover the delivery time and give Coastal at least (b) 90 minutes to empty the truck. The next challenge on the project was to tie and anchor the reinforcing bars more securely. The first wall section Coastal shot broke the minimal anchors and ties, and the section bulged out 4 in. (100 mm) from the weight of the shot- crete. Fortunately, that wall section was at the stairwell and did not interfere with the building structure. By adjusting the grade wires, Coastal and Hensel Phelps were able to reshoot the sec- tion to take the bulge out of the wall. This is something that cast-in-place concrete could not do. It was apparent from the bulging problem that the reinforcing bars had to be tied at a much closer spacing as well as increasing the number of wall anchors and ties before the shotcrete operation could proceed (refer to Fig. 2(b)). Once the shotcrete operation began in earnest, the crew planned to start in one area and work their way around the foundation so that the other trades could follow. Hensel Phelps moved 38 Shotcrete • Summer 2015


2015SummerShotcreteEMag
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