Jim Klinger, Concrete Construction Specialist
The Voice Newsletter February 2025 

Full Disclosure: Anyone who has cast ice cubes in their kitchen freezer can confirm there is an unseen side effect that occurs during the transformation of liquid water into solid ice--namely a substantial increase in volume.  Material science textbooks say that--under certain boundary conditions-- a volume increase of about 9 percent can be expected once the phase change process is complete.

Kitchen ice cube molds typically allow ice crystals to form and expansion to occur free of restraint or confinement.  But what would happen if the molds restrained the material from expanding?  What sort of internal forces would develop? And even more to the point, how could restrained freezing of water affect concrete performance and durability?

To get a feel for the kind of forces that can develop when restrained or confined water freezes, physics and chemistry professors like to perform a popular "shock and awe" demonstration in university lecture halls packed with an unsuspecting audience of first-year engineering students.

This writer was one of several hundred students enrolled in an introductory chemistry course called CHEM103 during the 1983 spring semester at the University of Maryland. Despite the passage of more than 40 years, the demonstration was indeed one of shock and awe--a sensory event easily retrieved from this old man's memory bank.

Unfortunately, video documentation of the 1983 Maryland demonstration is unavailable. But perhaps the next best alternate is a video posted recently by the British Royal Society of Chemistry (RSC). Although the smaller scale of the RSC "ice bomb" demonstration results in a less violent (and quieter) aftermath, there is no mistaking the lesson learned.  When it comes to resisting forces developed when confined water freezes, materials notoriously weak in tension--such as concrete--don't stand a chance.

The RSC video is available at the link below. As described above, there was a notable difference between the Maryland and RSC demonstrations related to scale. The Maryland cast iron sphere was larger than a softball. The temperature was lowered by way of a plastic 5-gallon bucket; half full of liquid nitrogen and loosely capped with an 18-inch square makeshift plywood lid. When the cast iron sphere ruptured, the bucket was shattered, the plywood lid was sent sailing, and the explosion was not only heard, but felt.

https://www.youtube.com/watch?v=YpQwQx2lMGk

So what can we take away from this?  No matter how you personally feel about it, the construction industry has a love-hate relationship with the curious chemical compound called water.  Some trades are devoted to keeping water out at all costs--others want to keep water in.  All it takes is the smallest of leaks to totally wreck a project.

Things get a little convoluted when it comes to the concrete business.  On the one hand, we need water to initiate the essential chemical reaction called hydration that occurs when water is mixed with cement. After that, we might even want to use a little water here and there for curing purposes. On the other hand, however, many project stakeholders seem to be spending piles of time and money in a concerted effort to divert water off of--and away from--our work product.   

What follows below is just a watered-down sip of how water in two of its forms can affect a concrete contractor. But if you think about it for a while, you will see straightaway that this ASCC Hotline call is just the tip of the iceberg.

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Question: We are in the preconstruction phase of a privately financed concrete construction project located south of the 30-degree latitude line. Work items in our contract scope include reinforced concrete foundations and tilt-up wall panels. There is also a significant quantity of exterior paving slabs intended for employee and customer parking.

The project Owner is a well-known manufacturing company based in the Chicago, Illinois metropolitan area. At any one time, their active jobsites can be seen in almost every geographic region across the USA.  Despite having a national presence, we understand their project designs are typically performed by architects and engineers based in Chicago--above the 40-degree latitude line.  And therein lies the issue driving our call to the ASCC Hotline for guidance.  Here's why.

The structural drawing general notes feature a blanket requirement calling for the use of air entraining admixtures in all project concrete; including the foundations, tilt-up panels, and parking slabs in our scope.

During the pre-bid period, our estimators were aware of this requirement. Since this is a private project, we made a business decision to not submit any pre-bid RFI's regarding the use of air entraining admixtures.  Further, we did not qualify our bid proposal calling attention to air entrainment. We have been placing structural concrete in our regional market since 1959, and in all those years neither we--nor our concrete supplier--have ever been required to provide air entrained concrete. During the post-award buyout of the ready-mix concrete, none of the three price quotes we solicited from the local ready-mix suppliers included any cost of air entraining admixtures.

Shortly after we selected our successful concrete supplier, mix designs were proportioned without air entrainment and submitted to the design team for review. Last week, we learned the design team has rejected our mix design submittal.

Our customer--themselves a national general contractor (GC) with extensive experience in our regional market--agrees with our position and arranged a virtual meeting with the licensed design professional (LDP) to discuss the rejected submittal. That meeting took place this morning.  The LDP explained that their hands are tied; that their construction documents were prepared in accordance with the ACI Code durability requirements outlined in Table 19.3.1.1. (The version of the ACI 318 Code used for design purposes and referenced on the structural drawings is ACI 318-19 Building Code Requirements for Structural Concrete, hereinafter referred to as "ACI 318").

We (including the GC and the ready-mix supplier) explained our position that--based on our collective experience in our regional market--the geographic location of the jobsite poses almost no risk of freeze-thaw deterioration. The LDP asked us to provide substantiation, and we arranged to meet again ASAP.

Looking back on it, we acknowledge that we should have raised the issue of air entrainment during the pre-bid period. Nevertheless, we are convinced that the structural design prepared above the 40-degree latitude line includes assumptions of exposure conditions that do not apply to our project.  We are looking to ASCC for advice on how best to substantiate our position and help convince the LDP that air entrainment should not be required.

Answer:  The LDP is correct in saying that their design is based on the durability requirements stated in ACI 318. They are well within their right to take that position, no matter how conservative their Code interpretation may seem to you. So the question then becomes "How tight are the LDP's hands really tied?" 

As all ASCC Hotline callers know, the Quality of hardened concrete is judged by three characteristics, namely compressive strength, durability, and dimensional stability. In other words, the hardened concrete must be strong enough to carry design loads, durable enough to withstand various types of deterioration, and must remain in the right place after hardening. 

ACI 318 defines "durability" as "the ability of a structure or member to resist deterioration that impairs performance or limits service life of the structure in the relevant environment considered in the design".  ACI 318 section 19.3.1 describes four basic durability exposure categories:  deterioration caused by freeze-thaw (Category Type F), deterioration cause by sulfate attack (Type S), deterioration caused by water (Type W), and deterioration caused by corrosion (Type C).

At issue in your case is exposure category type F, freeze-thaw. According to ACI 318 commentary section R19.3.1, the risk of concrete damage is a function of water saturation when the concrete temperature cycles from freeze to thaw, described in an example as follows: "If the top 3/8 in. of a slab or outer 1/4 in. of a wall is saturated, those portions are vulnerable to damage from freezing and thawing, regardless of how dry the interior may be".

According to ACI 318, the rationale supporting the requirement for air entrainment is "for any portion of a member to be resistant to freezing and thawing, that portion of the concrete needs to have sufficient entrained air and adequate strength".

It is crucial to note here that ACI 318 is replete with "check and balance" provisions intended to assist in rinsing out "grey area" issues such as yours. Resolution can be accomplished by applying healthy doses of engineering judgment. The concept really isn't all that complicated, but it is certainly often overlooked.

For example, ACI 318 commentary section R1.3.2 advises the LDP audience as follows: "The minimum requirements in this Code do not replace sound professional judgment or the licensed design professional's knowledge of the specific factors surrounding a project, its design, the project site, and other specific or unusual circumstances to the project".

Additional support for your position can be found in ACI 318 commentary section R19.3.1 as follows: "The likelihood that concrete in a member will be saturated depends on project location, member location and orientation in the structure, and climate.  Records of performance of similar members in existing structures in the same general location can also provide guidance in assigning exposure classes".

On your project, there are three classes of structural concrete that require exemption from the air entrainment requirement: foundations, tilt-up wall panels, and exterior parking slabs.  Based on the above, we recommend the following items be included in your request for relief from the LDP.

The first item that can easily be compiled by your project engineer is a weather history recorded as close as possible to the project jobsite.  This information should be considered by the LDP consistent with the two ACI 318 excerpts cited above.  Put another way: prove to the LDP that a waiver of the air entrainment requirement is a very low-risk proposition. This argument can be most effective for exemption with the foundation and parking slab mixes.

The next item that should be included in your submittal is a project concrete placement schedule.  When will the foundation concrete and parking slab concrete actually be placed?

Finally, for the tilt-up wall panels, the most significant document that can be brought to bear is the position statement prepared by the Tilt-up Concrete Association (TCA) that addresses the use of air entraining admixtures in concrete proportioned for use in tilt-up wall panels.  A link to the TCA air entrainment position statement is given below:

https://tilt-up.org/tilt-uptoday/2023/09/22/collective-position-on-specification-of-air-entrainment-in-concrete-for-tilt-up-panel-construction/

The TCA position statement is summarized as follows: "Tilt-up concrete panels are vertically oriented slabs of concrete with limited exposure to conditions of saturation.  Furthermore, since these wall panels are primarily vertical and located above grade conditions, they have virtually zero exposure to conditions of deicing salts.  Therefore, the Tilt-up Concrete Association believes that the use of air-entraining admixtures is not required to protect the surface of the panels from delamination due to freezing and thawing cycles during saturated conditions".

The TCA position statement does not mean, of course, that the LDP does not need to investigate the weather conditions likely to be experienced by the concrete members built in your regional market. But based on the above, we believe you stand a good chance of getting relief from the LDP. Let us know how it turns out.

Note: You took a risk at bid time by not carrying the cost of air-entraining admixtures in your price.  In the unlikely event the LDP enforces the requirement, you will have to absorb that cost.  At the same time, it may be beneficial to view this through a lens focused on the Owner's side.  No matter how it goes, the Owner never pays the cost of the admixtures, and stands to save on testing and inspection costs if the waiver is granted as well.