Hi all,
We have a situation here where we have just poured the concrete and need to anchor down a concrete pump as soon as possible. What is the minimum time required in order to install an anchor into green concrete? Anyone have experience on this?
*Posted on behalf of a Hilti customer.
Hi,
Green concrete is typically classified as concrete that is less than 28 days and has not achieved its full compressive strength. Please see below general recommendations for both mechanical and chemical anchoring in green concrete.
Mechanical anchors
To determine the design strength, the concrete strength is always taken at the time of applying the load to the anchor, independently of when the anchor was hammered in and/or torqued up.
Chemical anchors
Tests performed on Hilti adhesive indicate that:
- It is not recommended to install chemical anchors in green concrete before 7 days of concrete curing due to scattered resistance data.
- From day 7 to day 20, the resistance reductions are comparable to those suggested in the EC2 for early age concrete (please see attached). Please note that the cement used in the concrete has significant influence before 28 days and therefore should be taken in consideration by the design engineer. It is also recommended that the installation torque is reduced by the same factor applied to the design resistance.
- After day 20, the reductions are minimal regardless of the cement class and as such no special reductions need to be applied.
Hi,
I always insist to install anchors after 28 days of concrete pour to achieve the design strength. Sometimes we do have to design for green concrete and I have done a very conservative approach to calculate the anchoring strength. Assume reduced bond strength and weaker concrete.
Stephen