Effect of Cement Hydration on Concrete Form Pressure

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Title: Effect of Cement Hydration on Concrete Form Pressure

Author(s): Elwood L. Ore and J. J. Straughan

Publication: Journal Proceedings

Volume: 65

Issue: 2

Appears on pages(s): 111-120

Keywords: admixtures (concrete);cements;concretes;fly ash;formwork (construction); hydration;pressure;research;retarders;vibration;water-reducing agents.

Date: 2/1/1968

Abstract:
The pressure of concrete on forms as affected by cement hydration and individual concrete ingredients at 70 F (21 C) was studied. The effect of cement hydration was investigated by comparing the behavior of concrete with and without a water-reducing, set-retarding agent to a nonhydrating mix-ture containing fly ash which had about the same plastic properties as concrete. Oil filled pressure cells were adapted to measure pressure in a form 10 ft (3.05 m) high x 3 ft (0.91 m) wide x 1 ft (0.30 m) thick. Results indicate that under these conditions, a workable concrete having a 3 to 4 in. (76 to 102 mm) slump does not behave as a fluid for any appreciable time without some outside energizing force such as vibration. The arching action of the aggregate is the earliest factor to limit the lateral pressure to 5 to 6 psi (0.35 to 0.42 kg/cm2) equivalent to 5 to 6 ft (1.52 to 1.83 m) of head, with the method of placement and vibration used. Hydration of the cement tended to limit form pressure under the normal vibration used but did not prevent an increase in pressure brought about by revibration until after 4 hr. The effect of set-retarding agent on cement hydration did not significantly alter the pressure.