Written by: Jim Klinger,  ASCC Hotline Operator

Question:  In the June 2022 issue of the American Concrete Institute (ACI) "Concrete International" magazine, the monthly question-and-answer feature column titled "Concrete Q&A" considered the issue of incidental standing water in a mat foundation area being prepared (and inspected) to receive concrete the following day.

In a nutshell, the foundation area comprised edge forms installed all around, with substantial top and bottom layers of reinforcing steel--in place and secured--supported by precast concrete "dobies" resting on a 3-inch-thick unreinforced concrete mud slab.

During the pre-pour inspection, the inspector noticed standing water puddled on the top surface of the mud slab-- incidental remnants of a brief afternoon rainstorm at the jobsite the previous day.  Due to the location of the water, about two inches below the outermost bottom layer of reinforcing steel, accurate measurements of the puddle thicknesses were not possible.  By all anecdotal accounts, however, the puddle thicknesses were estimated to be on the order of 1/2-inch to 3/4-inch deep.  

The inspector notified the general contractor (GC) that the puddled water would have to be removed before he would sign the work off and allow the scheduled next-day concrete placement to proceed.  This left the contractor with few options.  One option, of course, would be to wait until the puddles (now not exposed to direct sun or wind) dissipated via evaporation. Brooming the water--or attempting to blow the water out of the pour area with compressed air--was not possible due to the tight spacing of the reinforcing steel layers.

Another option--cited by the inspector--would be for the placement to proceed as long as the concrete is placed with a full-depth tremie pipe as stated in the ACI Code--namely ACI 318-19 Building Code Requirements for Structural Concrete, section 26.5.2.1(b), which states the following:

"(b) Standing water shall be removed from place of deposit before concrete is placed unless a tremie is to be used or unless otherwise permitted by both the licensed design professional and the building official".

The ACI Code Commentary for this provision--namely Commentary section R26.5.2.1(b)--states the following:

"The tremie referred to in this provision is not a short tube or "elephant trunk". It is a full-depth pipe used in accordance with accepted procedures for placing concrete under water.  Information regarding placing concrete using a tremie is given in ACI 304R.

In our opinion, the ACI 318 "tremie option" for placement does not seem rational for use in incidental "birdbaths" ranging from 1/2 to 3/4 inch in depth.

As it turns out, the Owner advised the GC on that same afternoon that the architect was making some design changes due to a change in future tenancy, and the concrete placement would be delayed by two to three weeks. Any cost impacts would be funded by the Owner.  In other words, no real harm done.

Nevertheless, we are bringing this to the attention of the ASCC Hotline for review and comment. 

Answer:  Based on the response to the ACI Concrete International "Q&A" cited above, the ACI Code Committee is slated to review the provisions in Chapter 26 referenced above regarding standing water and requirements for removal (if any) before placement of concrete in an effort to differentiate between placing concrete in water of any appreciable depth as opposed to placing concrete in a relatively shallow birdbath composed of incidental rainwater.

But there is another important issue not raised above, and that concerns the approval protocols for the application of section 26.5.2.1(b).  Notice that this section is one of the few that appear in the ACI Code that require concurrent review and approval "by both the licensed design professional and the building official" at the same time.

The way we interpret this concurrency requirement, any judgement regarding final approval for a concrete placement to proceed could very likely involve a field review that features the licensed design professional (LDP) accompanying the "building official" (e.g. the inspector) during the inspection such that each condition can be reviewed and permitted--on a case-by-case basis--by both parties. Even more important: this is an opportunity for the concrete contractor to be involved in the conversations.

This case highlights one of those conditions that needs to be addressed during preconstruction meetings.  The procedural problem, of course, with the concurrency requirement is making sure the LDP can be made available to visit the jobsite on rather short notice if appropriate.