Title:
Putting the Pressure on Formwork
Author(s):
M.K. Hurd
Publication:
Concrete International
Volume:
24
Issue:
10
Appears on pages(s):
48-55
Keywords:
DOI:
Date:
10/1/2002
Abstract:
For most of my professional life I’ve been aware of controversy over the amount of pressure that freshly placed concrete puts on vertical form surfaces. Uncertainty comes in part from the (theoretical) approach of comparing unhardened concrete to a fluid that exerts pressure equally in all directions, at whatever point the measurement is made—in effect assuming a hydrostatic pressure effect. In 1958, as a group concerned with the contractor’s need for economy as well as safety, ACI Committee 347 developed a formula for maximum pressure that could be expected under placement conditions like those from the work where pressure measurements were made. By 1988, recognizing that many changes had taken place in concrete mixture formulations, admixtures, and rate and method of placing, ACI Committee 347 decided that formulas based on the old conditions could not be universally applied, and created in a new committee document. ACI 347-01 still presents the liquid head formula p = wh, but the conditions under which its use is required are greatly reduced through application of the new chemistry and unit weight coefficients that cover a variety of mixtures.