Pressure of normal density concrete

Once the placement rate has been calculated and the concrete temperature determined, the pressure calculations continue. The exercises below illustrate the pressures that may result based on typical placement rates and placement temperatures. It is important to remember that the formulas developed by ACI are based on normal slump normal density concrete.

Demonstration exercise

A wall 10 inches thick, 50 feet long, and 9 feet high is placed at a rate of 4 feet/h. Calculate the maximum pressure developed in the concrete form assuming a concrete temperature of 55°F. Determine the height to which this maximum pressure will extend.

Answer :

Applying the ACI formula for concrete pressure in wall forms (placement rate less than 7 feet/hour),

P = 150 + ((9,000 x R) ÷ (T))
= 150 + ((9,000 x 4) ÷ (55))
= 804.5 psi

Verification: Maximum pressure is 2,000 psf or 150 h, whichever is less:

150h = 150 x 9
1,350 psf > 804.5 psf

The maximum pressure is calculated from the formula.

To determine the height of the maximum pressure, the term 150 h represents the pressure of the concrete in the liquid state and can be equated to the calculated maximum pressure.

P = 150h

which can be written in terms of h as =
h = p ÷ 150

where h represents the distance from the top of the concrete location to where the maximum calculated pressure begins. In this exercise, the distance from the top of the concrete location to the point of maximum pressure is:

h = 804.5 ÷ 150
5.4 pies

Learning exercise

Answer :

Applying the ACI formula for concrete pressure in wall forms for a placement rate not exceeding 2 m / h,

P = 7.2 + ((785R) ÷ (T + 17.8))
= 7.2 + ((785 x 1.2) ÷ (13 + 17.8))
= 37.78 KN/square meter (kpa)

Verification: The maximum pressure is 144 kN/m2 or 23.5 h, whichever is less.

23.5h = 23.5 x 2.75
= 64.63 kPa > 37.78 Kpa

To determine the height of the maximum pressure, the term 23.5h represents the pressure of the concrete in the liquid state and can be equated to the calculated maximum pressure,

P = 23.5h

which can be written in terms of h as =
h = p ÷ 23.5

where h represents the distance from the top of the concrete location to where the maximum calculated pressure begins. In this exercise, the distance from the top of the concrete location to the point of maximum pressure is:

h = 37.78 ÷ 23.5 = 1.61 m