Development of SCC Placement Methodology for the Monolithic Construction of Slab-to-Wall Members Using Formwork Pressure and Time of Set-Based Modeling

Abstract

This paper discusses the use of Self Consolidating Concrete (SCC) in a unique approach for the construction of combined slabs and wall members commonly encountered in modular construction in new nuclear facilities required to be cast monolithically. Use of vibrators or other tools for surface set determination was not feasible due to lack of access in the 20 m steel-composite module walls. In addition, a material “upwell” in the slab segments during the vertical rise of SCC in the steel-composite module wall was not desired and needed to be managed. Therefore, the rate of rise, time of set, and formwork pressure-related considerations needed to be properly managed for the apparently “fluid” SCC mixture in the combined slab-to-wall placement to prevent upwell and/or high formwork pressures while avoiding cold joint/bond issues. This paper discusses the unique engineering approach to the construction challenges and related testing performed to overcome these challenges and manage the engineering properties in a critical slab-to-wall placement. Engineering considerations and the field trials in preparation for a 71 h, monolithic 1415 m³ placement in critical areas in a new nuclear facility are discussed. Among the testing performed in preparation for the placement was the filling of 3 m, and 6 m tall mock-ups to measure formwork pressures at intended placement rates. Floor-to-wall mock-ups were performed consisting of an exposed horizontal section and a vertical section to observe upwell tendency as well as verify set or cold joint occurrence by subsequent saw cutting. Multiple time of set determination testing of the SCC mixture at different concrete temperatures were performed with the purpose of developing time of set curves to be used in the development of a placement plan.

The engineering evaluation and input was particularly of value in the successful completion of the 1415 m³ placement lasting 71 h.