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2015SpringShotcreteEMag

Nozzleman Knowledge Fig. 1: Cylinder tests information necessary to calculate how much water can be added to the mixture to stay within the specified water­cementitious material ratio (w/cm) (Fig. 2). Most jobs will require third-party testing and any reputable testing firm is going to Fig. 2: Batch recordings require batch weights. We can not stress enough how important batch records are. They are a critical piece of information that is very often overlooked. Quality and cleanliness of the trucks is a much bigger factor than most would think. We are not concerned by the outward appearance of the truck. We are only concerned about the inside of the drum—mainly the fins—and if they have exces- sive buildup on them (Fig. 3(a) and (b)). A dirty barrel with excessive buildup on the fins is not effective at properly mixing the concrete. Proper mixing is much more critical in very low w/cm shotcrete mixtures than it is with standard con- Fig. 3(a): Clean truck crete mixtures. Trucks with excessive buildup on the fins will produce inconsistent concrete throughout the discharge cycle that leads to poor- quality, inconsistent in-place concrete. The con- sistency of a mixture is crucial when doing vertical and overhead work. We have rejected trucks and banned trucks from returning to jobs due to them not being clean enough to properly mix the concrete. How do you determine if a supplier has clean or dirty trucks? Take a look at some of their trucks and you will be able to get a feel pretty quickly about how clean their fleet of trucks is kept. We have found that suppliers who require the drivers to chip their trucks have much Fig. 3(b): Dirty barrel Shotcrete • Spring 2015 45


2015SpringShotcreteEMag
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