Page 53

2016SpringShotcreteEMag

Nozzleman Knowledge crete has developed sufficient strength to withstand induced thermal stresses. Rapid cooling of concrete surfaces or large temperature differences between the exterior and interior (20°F 11°C minimum change) of the patches can cause cracking and be detrimental to strength and durability. To protect the patch, or new work, the cold weather protection needs to be removed slowly once the curing and protection period has been met, allowing the concrete temperature to change gradually in a 24-hour period as long as the desired strength has been reached. This will help to prevent rapid temperature change in the new shotcrete material. Figures 1 through 3 show some of the approaches needed for cold weather protection and heat needed to perform shotcrete work during the cold weather months. Concrete construction in cold weather must meet these objectives: • Prevent damage to concrete due to early-age freezing; • Ensure that the concrete develops the required strength for safe removal of forms, shores, reshores, and safe loading of structure during and after construction; • Maintain curing conditions that further normal-strength development without using excessive heat and without causing critical saturation of the concrete at the end of the protection period; Fig. 1: Cold weather protection Lake Placid bobsled and luge track, which had a fast-track build from 1998-1999 through the winter. The track needed one season to operate before the Goodwill games in 2000 Fig. 2: High-low thermometers for monitoring the 50°F (10°C) heating within the tenting of the pool structures. The 50°F (10°C) was maintained during the shotcrete placement and curing Shotcrete • Spring 2016 51


2016SpringShotcreteEMag
To see the actual publication please follow the link above