The Building Code and the Post-Tensioned Institute (PTI) - Part 3

As previously discussed in our last two articles, there is no ACI scope related to post-tensioned slab-on-grade (PT-SOG) foundations, especially pertaining to durability.  We have already shown the flow of the building code itself, being much like a highway with various exits, does NOT link the PT-SOG foundations to ACI durability requirements.  In part two, we demonstrated that the PTI DC10.5 document handles its own durability requirements because of its independence from ACI.

In this article, we will move on to the PTI’s own stance regarding the independence of residential (don’t forget that this includes apartments, condos, townhomes, as well as one-and-two-family dwellings) PT-SOG foundations from ACI.  We will also be learning from an ACI and PTI legend, Mr. Ken Bondy, about how water-to-cement (w/cm) ratio is indirectly addressed in DC10.5 while not specifically mentioned.  These additional facts show that, as our previous roadmap indicates, DC10.5 is independent from durability requirements of ACI (318, 201 by reference within 318, 332, and 360R).

We will begin with PTI Technical Note 21 (TN21), Issue 21 – July 2017, which was published by the Technical Advisory Board (TAB) of the PTI.  This technical note should have ended any doubt that ACI318, and by reference ACI201, was never intended to govern PT-SOG foundations.  The following points are highlights from the TN21.

While TN21 uses ACI318-14 for its facts, there exists improved and clarified verbiage within ACI318-19.  According to TN21, ACI318-14 Section 1.4.7 states that, “This Code (ACI318-14) does not apply to design and construction of slabs-on-ground, unless the slab transmits vertical loads or lateral forces from other portions of the structure to the soil.”  The first thing “experts” grab ahold of is the statement about transmitting vertical loads or lateral forces to the soil, which all foundations do.  However, the commentary R1.4.7, clearly states, “Detailed recommendations for design and construction of slabs-on-ground and floors that do not transmit vertical loads or lateral forces from other portions of the structure to the soil, and residential post-tensioned slabs-on-ground, are given in the following publications:

  • ACI360R
  • PTI DC10.5-12".  (DC10.5-19 is the most current)

So, utilizing our highway exit sign analogy as before, there are two exits that exist covering conventionally reinforced concrete slabs that do not transmit loads to the soil via ACI360R and covering residential and light commercial PT-SOG slabs that do transmit loads to the soil through PTI DC10.5-12.

In the most current ACI at the time of this post (ACI318-19), the Section 1.4.6 states, “For one- and two-family dwellings, multiple single-family dwellings, townhouses, and accessory structures to these types of dwellings, the design and construction of cast-in-place footings, foundation walls, and slabs-on-ground in accordance with ACI332 shall be permitted.”  However, the commentary for section 1.4.6 then indicates an exit route to DC10.5-12 for expansive soils.  That begs the question “experts” often ask, what about stable soils?  The commentary goes on to refer to section 1.4.8 for stable soils which ultimately lands at the ACI360R standard.  Entering Chapter 10 of ACI360R-10 for design of post-tensioned slabs-on-ground, we find reference to the PTI as an applicable design procedure under section 10.2.4.  Once again, all roads and all exits have ended within the PTI DC10.5 document.

Here is where we really need ACI and the IBC both to clean up their references.  ACI318-19 was released prior to the release of DC10.5-19, which addresses both stable and expansive soils like those that we previously mentioned for the 2024 IRC.  At the time of this article, the ACI360R-10 document has not been updated for 8 years (since the 2016 errata).  It references the third edition of the PTI released in 2004.  The commentary section for ACI318-19 section 1.4.6 simply needs the words “stable or expansive soils” to replace “expansive soils” –similar to the 2024 IBC in chapter 1808.  This would eliminate the twisting and turning paths to DC10.5 document that currently exist.  Please note that DC10.5-19 deals with both expansive and stable soils where DC10.5-12 only dealt with the expansive soils, but addressed stable soils by reference back to the DC10.1-08 (3rd Edition).

Finalizing our focus on TN21, we will leave it to the reader to glean the rest of the information compiled there, but we can summarize TN21 with this point at the bottom of page 1 (underline added by Felten Group):

“This Technical Note is to clarify that the post-tensioned residential slabs-on-ground were never intended to be governed by the ACI 318 Building Code.”

To summarize, PTI clearly states that the DC10.5 document is stand-alone via TN21.  PTI DC10.5-19 goes on to clarify its scope in the commentary of Chapter 1.  “…This standard is intended to be a stand-alone document uniquely developed for the design of post-tensioned concrete foundations on expansive and stable soils and is supported by the performance of many thousands of existing conformant foundations.  As such, it is intended that this standard be independent of ACI 318 and the conflicting parts of the general building code into which this standard is incorporated.”

That brings us to the legend himself: Mr. Ken Bondy.  Mr. Bondy published an article in the February 2008 of the PTI Journal in Volume 6 Issue 1.  It is important to note that this article was reviewed under the PTI Journal publication policies.  Mr. Bondy’s article is titled “CodeRequirements for Sulfate Durability in Residential Concrete”.  He does such a good job providing the code change history and the where and why “the sulfate table” that is in the ACI code originated.  Mr. Bondy goes on to describe the sulfate litigation history leading up to the time of the journal entry where “experts” were attacking residential foundations across the southwest United States based on the sulfate requirements of ACI 318 (and ACI 201 by reference).  Particularly, regarding the w/cm ratio listed in the ACI sulfate table.

Interestingly, Mr. Bondy notes that in historical practice the w/cm ratio did not apply for residential concrete design and construction.  As a result, this is where the “experts” were able to show non-compliance to ACI 318.  He continues to explain the typical compressive strengths used were between 2000 and 3000 psi, which equated, in his estimation, to w/cm ratios of 0.8 and 0.6, respectively.  Therefore, the w/cm requirements for sulfates (0.45 or 0.5 depending on conditions) of the ACI table were violated.

At the time Mr. Bondy wrote his journal entry, ACI332 had not yet included limitations in the form of w/cm ratio.  It now does, but recall from our previous two articles that ACI 318, 201, and 332 do not have scope on the DC10.5 document.  Some of the early engineers in the PT-SOG field did not have the same scope that we have today.  As a result, they reacted to the many lawsuits regarding sulfate durability allegations by changing their plan specifications and that “… has resulted in a significant increase in the cost of many new homes in California, Nevada and Arizona, with no related benefit.”

Mr. Bondy answers the question: Why different durability requirements for residential concrete?  He presents facts from the position of plain concrete and factors of safety in the range of 30 under the light residential loads.  In addition, he makes the point that reducing the w/cm ratio from 0.6 to 0.45 effectively changes the service life of the concrete from 150 to 200 years, while the materials in the structure on top of the concrete only have a service life of roughly 75 to 100 years.

Finally, after going through the various durability requirements for PT-SOG within the PTI, which do not (then or now) include limitations on w/cm ratio, Mr. Bondy summarizes as follows:

“…They (the codes) will include a requirement for sulfate-resistant cements, but they will not require direct limitations on w/cm, which are difficult to control in fresh concrete and impossible to evaluate precisely in hardened concrete.  This will clarify and refute the erroneous allegation that the mere reference to a sulfate-resistant cement by a licensed design professional somehow also triggers a requirement for a limitation in w/cm.  In this model code, w/cm ratios will be indirectly controlled, when necessary, by specifying a minimum concrete compressive strength.  These new code criteria are consistent with long-standing successful practices for sulfate durability in residential slabs and foundations.  They should help in reducing opportunistic lawsuits which have resulted in increased costs to homeowners with no related benefit, and are based simply on a lack of clarity in code wording rather than a real deficiency in performance.”

The PTI DC10.5 code follows Mr. Bondy’s conclusion through its durability requirements, which do not include w/cm ratio, rather, cement type and compressive strength when necessary.  Bearing in mind TN21 and Mr. Bondy’s article, it is very easy to see that PTI DC10.5 is stand-alone and intentional regarding how it addresses concrete durability by cement type and compressive strength and not w/cm ratio.

The last post ended with a quote from a song regarding “experts”, but this article will end with a story about “experts”.

It is a story about a fictional builder named Virtuous Homes who was attacked by out-of-state “experts” just as described by Mr. Bondy’s article.  Virtuous’ legal counsel Mr. Netherlands, hired “experts” that had no experience with PT-SOG to fend off the out-of-state attackers who were savvy with years of opportunistic litigation against homebuilders, led by Mr. Hatchetman.  One of Virtuous’ “experts” in particular, Mr. Leaftwig, had not designed post-tensioned slabs in at least 15 years prior to Mr. Hatchetman’s attack on Virtuous Homes.  Mr. Leaftwig could not stand against Mr. Hatchetman’s claims regarding durability needing to follow w/cm ratio and concrete compressive strength per ACI318.  Mr. Leaftwig’s inability to fend off Mr. Hatchetman using the information in these three articles needlessly cost Virtuous Homes large sums of money.

After suffering through unnecessary financial loss because of Mr. Leaftwig’s lack of knowledge, Virtuous Homes and Mr. Netherlands asked Mr. Leaftwig, with his inadequate understanding of the building code combined with lack of design in PT-SOG, to be an “expert” turning the attack on the insurance policies of their trades.  Mr. Leaftwig and Mr. Netherlands regurgitated Mr. Hatchetman’s attack on the w/cm ratio and concrete compressive strength because of their collective lack of knowledge.  They were essentially invalidating every home Virtuous Homes had ever built on stable soils.  To their own detriment, they were able to convince the arbitrator, Mr. Mustard, that w/cm and compressive strength per the ACI both applied to the PT-SOG foundations in question because they were on stable soil, not expansive soil, as the building code stated.

By a technicality, Virtuous not only paid more in damages than they need to, they invalidated all the PT SOG foundations they built (and continue to build) on stable soils.  The domino effect ripples through the industry as more “experts” look to cash in on the vulnerability, insurance rates go up, fees for subcontractors go up, and the cost to provide housing goes up.

In the end – nobody wins.