Title:
Formwork Pressures for Self Consolidating Concrete
Author(s):
N. J. Gardner,
Publication:
CRC
Volume:
Issue:
Appears on pages(s):
Keywords:
Rheology, Self Consolodating Concrete, SCC,
DOI:
Date:
10/1/2007
Abstract:
The major, labor intensive and expensive part of the project involved measuring form pressures at 4 sites operated by Ellis-Don Construction in Charleston, London Ontario, Peterborough Ontario and Toronto. Obviously industry is most interested in the maximum form pressures for formwork design; which are determined by the rate of concrete placement versus the rate/development of concrete stiffness/strength. Unfortunately the term “Self Consolidating Concrete” is a non-unique, generic description. Identifying and characterizing the flow/stiffening properties of the concrete relevant to the magnitude of the lateral pressure envelope would be very useful. Material characterization evolved over the course of the project. Effectively this project has been on hold since 2008. The project depended upon access to construction projects of the co-investigators (Ellis-Don Construction) using Self Consolidating Concrete. Unfortunately the current construction situation has not resulted in any suitable projects.
The following lessons were learned thus far: Discontinuous placement, by bucket or programmed interruptions of pumping, allows the concrete to gain shear strength, reducing the maximum form pressures. For formwork pressure purposes, the ideal admixture combination would produce a concrete that flows under agitation and immediately stiffens when agitation ceases. The SCC mixture design has to be done with care and admixtures cannot be changed or substituted without diligent consideration. In addition changes to the water content of the aggregates can significantly affect the stability of the mixture and strict control for moisture compensation needs to be instituted at the ready-mix plant. Testing for production, mixture selection/qualification and formwork selection must be done in concert and concrete control parameters must be established to ensure compliance.