- Testing
- Formwork
Technical Resource:
Formwork
Pressure
Laboratory Tests
There are several means of studying formwork pressure with SCC in the laboratory. One method used by researchers at the University of Sherbrooke and the University of Illinois at Urbana-Champaign (UIUC) uses a PVC tube with sensors mounted to the tube. Researchers at both universities use diaphragm sensors that measure total pressure and are in physical contact with the concrete material during the test. These experimental devices are used to study pressure drop over time. 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.
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Figure 2. Example of Results from University of Sherbrooke |
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Figure 3. Example of Results from UIUC |
An alternative laboratory set up is used by researchers at Northwestern University. Their testing apparatus utilizes a short column of concrete, 300 mm, in a steel mold. Figure 4 is a picture of their test set-up. 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 cylinder has two pressure cells mounted on the sides. One is used to measure total horizontal pressure and the second sensor is used to measure pore water pressure. The general procedure is to fill the cylinder and then apply an ever increasing load until a pre-determined maximum load representing a particular column height. That load is maintained for several hours to simulate the end of filling and the material at rest.
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Figure 4. Northwestern University Laboratory Set-Up |
It has been found through many laboratory trials that the particular material chosen for the formwork is of great importance in studying formwork pressure. Initial tests at UIUC were performed using cardboard tubes as might be used in the field to pour columns. These proved to be problematic in studying formwork pressure. The cardboard material absorbs moisture from the concrete and swells. This small displacement of the sensor causes the sensor to lose contact with the concrete, and this results in errant measurements of lateral pressure on the form material. A comparison of a plain cardboard tube, one with a plastic liner, and 2 PVC pipe configurations are shown in Figure 5.
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Figure 5. Effect of Formwork Material on Measured Lateral Pressure |
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