Abstract
This paper discusses the use of self-consolidating concrete (SCC), in a large-scale placement during new nuclear plant construction. SCC has provided cost and labor savings and construction process improvements. Use of SCC has been effective in schedule acceleration by reducing placement durations and early curing termination with rapid strength gain. Self-consolidating properties were particularly of value at placements of poor access as internal vibrators were not effective and large surface area made form vibrators ineffective beyond the perimeter. This paper provides a discussion of technical challenges encountered in development of a properly functioning SCC mixture, and testing performed to overcome these challenges. The paper discusses the engineering considerations and laboratory and field trials preparing for a 3950 m3 placement for the base of a nuclear plant. The placement was anticipated to take 35 h at 110 m3/h batch plant output. Overview of mix design specifications and mix development is provided. The mixture satisfied the laboratory test parameters including SCC tests; stability and column segregation. However, the mixture had to undergo rounds of constructability testing beyond laboratory development prior to the large placement. Among the constructability properties was the distance SCC will move with the stone before stopping. A long trough was filled as a mockup for and subsequently cored. The number of pumps and pump nozzle placement spacing was determined as a result. Slump flow retention as the polycarboxylate loses effectiveness and foaming of the mixture when pumped were also investigated. Foaming was attributed to viscosity, air entrainer, and pump pressures or rate of pumping. Laboratory trials with various admixtures and pumping studies in the field were conducted to achieve a mixture that retains slump flow and can be pumped at the desired rates without instability or excessive foaming. The placement was completed successfully in 35 h over multiple shifts.
