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The wall was created with SCC material and filled in one continuous pour lasting about seven hours.It was found that only within the top four feet of placed concrete were pressures approaching full hydrostatic pressures recorded.Their testing apparatus utilizes a short column of concrete, 300 mm, in a steel mold. A loading frame is used to apply a load on the top of the column of concrete to simulate the effect of a much larger column of concrete.This can also apply increasing loads over time to simulate varying casting rates.The maximum pressure reached was 5.5 psi, which was only approximately 20% of the maximum hydrostatic pressure at the point of measurement.This wall was filled at a relatively slow rate, maximum of 5.5 ft/hr, due to the large dimensions of the structure (5 ft thick, 80 ft long and 28 ft high). A companion test column was fabricated which involved filling a 10.5-ft tall column.The sensors are placed at varying heights and each university uses different height columns.Figure 2 and Figure 3 show results of various mixtures from tests performed at Sherbrooke and UIUC, respectively. Example of Results from UIUC An alternative laboratory set up is used by researchers at Northwestern University.
As in the case of conventional concrete, there are many factors governing the pressure exerted by SCC, including: the stiffening behavior of undisturbed SCC, the casting rate, the height of the formwork, temperature, vibration, and susceptibility to disturbance of the concrete. Lange, University of Illinois Contributing Author: K.This guidance generally limits contractors to short walls or extremely strong formwork.Thus, there is great need for better understanding of the pressures that are actually seen in cast-in-place applications in the field.Several of these walls were instrumented with pressure gages to study the development of pressure on the formwork. One sensor was placed 1.5 ft off the bottom of the wall and the second sensor was placed 6.5 ft off the bottom of the wall.The first hour of pouring was at a rate of 9 ft/hr, the second hour at 4.5 ft/hr and slower for the final hours.
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Since its development, it has been generally assumed that self-consolidating concrete (SCC) would generate hydrostatic formwork pressure due to the rate at which it can be cast and the long time before it starts to set.