The Building Code and the Post-Tensioned Institute (PTI) - Part 2

In our last article, we went over the flow of scope within the building code.  We idealized that like a highway with exit signs for ease of understanding.  This article is going to focus specifically on DC10.5 and where it gets scope from the IBC.  Using our highway analogy, we are looking specifically for the exit signs leading to the PTI DC10.5.

As we previously mentioned, the exit sign is located in Chapter 18 of the IBC.  Specifically, the exit is located in Section 1808.6.2.  In the last article, we discussed that, even though this section pertains to expansive soils, the DC10.5 document clearly addresses expansive, stable and collapsible soil types regardless of the IBC language.  The 2024 IRC confirms this fact in Chapter 5 where the full title of the DC10.5 document is shown correctly.

Once we have exited the IBC and entered into the destination of the PTI DC10.5 standard, there is no reason to go back, or to access other standards, unless specifically instructed to do so within the standard.  In the case that the standard does not address a specific structural criteria, then that criteria should be found back in the previous standard (IBC).  So using our highway analogy, we made it to DC10.5 town, but they may not have all the things we need to stay there and we may have to go back to the last exit.

In order to stay in the DC10.5, we need to consider the items required for us to reside there.  In the case of the PT slab-on-grade, we need concrete strength and durability requirements in order to complete our journey.  So the question is do we have that information?

Within DC10.5, concrete strength is addressed by specifying a minimum compressive strength of 2500psi.  The required compressive strength is increased to 3000 psi when slabs may be subjected to freezing and thawing or deicing chemicals under the section on durability.  There is no return to the IBC or to other standards like ACI required.

Water-soluble sulfates are addressed by requiring a sulfate resistant cement like type II or type V cement.  The DC10.5 document goes on to require a minimum of 3000 psi concrete strength at even higher levels of sulfates.  Therefore, very high levels of sulfates and potential for freezing and thawing can trigger the increased compressive strength of 3000 psi.

Chlorides are addressed by requiring encapsulation of the tendons and tendon anchorages where high levels of chlorides exist.  There are also recommendations to protect convention rebar products by utilizing things like epoxy coated rebar.

From PTI DC10.5, there are no references to ACI pertaining to durability.  Nor are there references back to the IBC since the PTI receives scope as a standalone document.  Normally, this would be the end of the story, except that we have many “experts” that get lost along the road.  They attempt to import unnecessary requirements into the DC10.5 where they do not belong.  These “experts” are often influenced by a need to find fault at any cost – even if it means throwing objectivity and logic aside.

Although we have shown that the destination is clearly within the DC10.5, these “experts” insist on returning to the IBC and moving on to Chapter 19, which deals specifically with concrete.  In their “expert” opinion, the DC10.5 document cannot stand on its own.  Therefore, they make a U-turn and take the road back into the IBC.

Chapter 19 of the IBC directly references ACI318.  This is often where the “experts” immediately exit the IBC and refer to the durability requirements located in ACI318.  The ACI318 durability requirements also have a reference out to another ACI document, ACI201.  They have exited the IBC at the destination that aligns with their opinions, and they rest their case.  The “experts” cannot see that they have arrived in the wrong place by going the wrong way down a one-way street.  Even if they could justify getting back to the IBC on the one-way street, they cannot even see that they missed yet another sign.

Just relying upon the reference to ACI at the beginning of Chapter 19 is not enough.  That is because the IBC specifically mentions durability.  Under IBC section 1904 “Durability”, the first sub-section, 1904.1, specifically lists ACI318 durability requirements as the standard for the IBC.  However, just as you plan to exit there is another sign – an exception.

The exception pertains to Group R-2 and R-3 occupancies, and there are numerous types of residential structures that fall under these two categories (residential what the “R” means).  R-2 occupancies contain sleeping units or more than two dwelling units where occupants are primarily permanent in nature.  A couple of examples would be apartments or condominiums.  R-3 occupancies are those that do not align with R-1, R-2, or R-4.  The R-3 occupancy therefore includes one-and-two-family homes.

The only durability requirement under the exception is that the minimum concrete compressive strength shall be 3000 psi.  The durability exception turns the exit sign from the IBC to the ACI into a “DO NOT ENTER” sign for the ACI.

Because neither of the paths, DC10.5 or IBC1904.1, lead on to the ACI nor do they restrict the water-to-cement (w/c) ratio, the w/c ratio is clearly not a restriction that is imposed by either of them.  While it is true that the ACI318 and ACI201 documents do limit w/c ratio as part of their durability requirements, it does not matter since neither one of those documents have scope given to them by the parent code, the IBC, or at the true destination within DC10.5.

While the focus here is on the IBC as the historic exit ramp to the DC10.5 document, mentioning the IRC is important because there now exists another exit ramp to the DC10.5 from the IRC.  The IRC indicates that concrete slab-on-ground floors are to be constructed per ACI332 or the provisions of R506 – which includes DC10.5 under R506.2 specifically addressing PT slab-on-grade.  Therefore, the final destination from the IRC is DC10.5.

While the reference out of the IRC may seem insignificant to this discussion, it is extremely important.  Neither the IBC nor the IRC refer out to ACI pertaining to PT slab-on-grade.  If they did, then there would be a conflict between ACI318 and ACI332.  This provides further justification showing that DC10.5 is stand-alone.

In order to better summarize this post and how so many people, including self-proclaimed “experts”, get this wrong, we will present another highway road map.  The only destination addressing durability for PT slab-on-grade is Chapter 4 of the PTI.

One additional thought on the topic of “experts”, everyone should keep in mind that anybody can claim to be an “expert”.  In the words of Don Henley:

In post #3, we will explore how PTI deals with the ACI debate as well as the w/c ratio!