Concrete Formwork Pressure: What You Need to Know?

It is imperative to know and comprehend all factors that can affect the concrete formwork pressure as this will determine a successful pour. As soon as concrete is placed, it is important to consider the various factors that have a role to play in determining the height of pour and placement rate.

 

Unit Weight-Concrete

The unit weight may vary geographically. Typically, it is 140-150 pounds/cubic foot. Concrete that weigh less have lower concrete formwork pressure. On the other hand, concrete that weighs more is likely to increase the pressure.

 

Height of the Concrete Pour

This is the overall height of the wall where the concrete is placed during a pour. In case the concrete fails to achieve the initial set between the lifts, this is what the pressure should be. Typically, it would be a good practice to place the concrete so every lift would be able to reach the initial set.

 

Setting Time

Below are the common factors that affect the set up time of concrete. When concrete has been set up, there will be zero concrete pressure.

 

Concrete Mix Chemistry

This greatly affects the pressure of the formwork. The factors would include the following: slag, retarders, fly ash, and cement type. All of these contribute to increasing the pressure. Also, accelerators can speed up the setting time aside from reducing pressure.

 

Concrete Temperature

When there is higher temperature, then there will be shorter setting time. Ambient temperature affects the temperature of the concrete, thus, one need to have a slower rate of placement during winter time.

 

Depth and Vibration Method

Any method, both internal and external needs to be performed by a lift. In case of disturbance, the lift will be affecting the setup of the previous lift. This leads to increasing the concrete’s unset height, thus creating greater pressure.

 

Rate of Placement

This also affects the pressure of the concrete. In case of slow placement, the pressure will be lesser. The rate is measured in feet per hour.

Thickness of the Wall

In theory, the thickness of the wall does not really affect the pressure in the formwork. But, having a narrow wall can lead to lower pressures due to bridging effects.

In general, the main factors that can affect the pressure of the formwork include temperature, concrete mix, and rate of placement. Keep in mind that the rate of placement needs to be lower in winter than in summer.

With this information, you can gain the right insights that you can actually use as you make the decision of placing concrete. This will make you more cognizant of the factors that affect the pressure. Moreover, understanding these things will be a big help to maximize the use and benefits of a formwork.