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.