Written by: Jim Klinger,  ASCC Hotline Operator

Question:  We are attempting to close out a recent construction contract to build a reinforced concrete mid-rise (6 story) assisted living facility. During the course of construction, the typical 8-inch thick post-tensioned (PT) slabs were placed and finished in approximately 25,000 square foot (SF) pours; then tested with a proprietary "Dipstick" for flatness and levelness by the Owner's test agency. All tested slab surfaces met their required F-numbers within the 72-hour time period specified in the construction documents. In addition, all F-number testing was completed (and reported) prior to any stressing of PT tendons and before the start of any follow-on reshoring activities.

Our application for release of retention funds was submitted two months ago following completion (and sign off) of a few minor punch list items (e.g. curbs, pads, and miscellaneous patch items). Unfortunately, we received notice in a meeting today from the general contractor (GC) that our retention payment is in danger of being put on hold, pending resolution of complaints filed by Owner representatives that arose during a recent Architect-Owner job walk.

We were advised in today's jobsite meeting that--in an effort to investigate the reported complaints--one of the GC's project engineers performed an informal floor survey using a self-owned laser scanner. The survey was conducted by a room-to-room scan of the oldest floor e.g. the first elevated PT slab. Neither we--nor the project inspector--were notified in advance that such an unofficial laser scan survey was being performed, let alone even being considered. In addition, such "after-the-fact" testing was not discussed in the project preconstruction conference. Truth be told, the thought never crossed our mind.

Our understanding is that many of the Owner issues are related to the top slab surfaces and flooring at various locations throughout the building. Evidently, for example, the GC's unofficial "heat map" indicates rooms and hallways that feature areas that are in excess of 3/4 inch below the design top of slab elevation. In other words, the GC survey has found areas where the floor slabs may have deflected.

Our position is that the Owner (or the GC) is welcome to survey the floors-at their cost- just as long as the test results will not be used to try and determine contract compliance. That ship has sailed. The Owner's test agency's position is that attempting to determine flatness--after the slabs have been subdivided into so many pieces--by using a Dipstick in accordance with industry standard test methods and protocols will not be possible. Furthermore, the inspector's position is that even the straightedge method--described in industry standard ACI 117-- may not be possible.

(N.B.: Now, here we are--several months after the fact--and all the interior partition walls are in place. This effectively subdivides each original 25,000 SF pour area into a series of small rooms and hallways. In addition, flooring has been installed at most locations within the building. We would think that any movements related to the PT or to slab deflections would be most pronounced at the oldest, lowest floors. There is no way anyone could possibly reproduce the original Dipstick runs established by the inspectors when our work was previously tested--and passed).

We understand that there are several procedural problems with the withholding of our retention payment. After all, our work was tested when it was supposed to be tested, and it passed within the required time window. We are confident that--eventually--this is all going to be resolved and we will be paid. But, in the meantime, the Owner seems insistent on following the GC's lead and proceeding with an investigation. There was some discussion in today's meeting regarding how testing of F-numbers should be performed so long after the fact--when the access boundary conditions (and Dipstick run line locations) have been drastically changed due to the removal of all shoring and follow-on installation of partition walls and flooring.

Although we are relatively new ASCC members, we have become familiar with the ASCC Position Statement collection, especially those related to concrete floor slab finishes; including Position Statement #6: "Division 3 versus Division 9 Floor Flatness Tolerances".  In part, Position Statement #6 addresses surveys of floor flatness that are conducted long after the concrete has been placed, finished, tested, and passed.

Thanks to other ASCC (and ACI) documents, we understand that elevation surveys of PT slab surfaces conducted several months apart can often have completely different results--none of which are the concrete contractor's responsibility to address. Going forward, we are looking to the ASCC Hotline to provide comments and guidance.

 Answer: Welcome to the ASCC Hotline. As you have stated, there are several procedural problems with the Owner's position and proposed course of action, incomplete as it is.

You are correct in noting that your work met your construction document Quality requirements.  It appears that both the concrete slab installation and the subsequent testing were performed in a timely manner, "by the book". And it is no surprise to us to hear that there are areas in the building that--even though the laser scan is unofficial-- apparently have shifted outside of the floor flatness and slab elevation design envelopes as indicated in the construction documents.

You are also quite correct in taking the position that the Owner (or anyone else) is welcome to pay all costs to conduct slab surveys any time they want--as long as the results are not used as an excuse to relieve you of some (or all) of your retention dollars. 

(It should also be noted here that the unofficial laser scan survey conducted by the GC does not constitute "additional testing" as described in ASCC Position Statement #34: "Who Pays for Additional Testing?", since such GC testing was not triggered by failing test results when the original, official F-number tests were conducted by the Owner's test agency).

At this point, we recommend you forward--at a minimum--a copy of ASCC Position Statement #6 to the GC, who should in turn send this information upstream to the design team and the Owner for their consideration.

The questions then become "How should such an after-the-fact, top of slab elevation survey be conducted?  What test apparatus (e.g. instruments) and test procedures should be used?

According to your construction documents, the basic Quality requirements governing the reinforced concrete portion of your scope are derived from industry standards established by the American Concrete Institute (ACI) and ASTM International (ASTM), formerly known as the American Society for Testing and Materials.

For example, general Quality requirements for construction of reinforced concrete slabs (e.g. tolerances for slab formwork, location, thickness, surface finish, etc.) are specified in ACI 117: Specification for Tolerances for Concrete Construction and Materials and Commentary.

On the other hand, specific requirements and protocols for the available test methods used by the Owner's test agency to determine concrete floor surface flatness and levelness numbers (aka "F-numbers") are specified in ASTM E1155: Standard Test Method for Determining Ff Floor Flatness and Fl Floor Levelness Numbers.

ASTM E1155 section 6 contains provisions for the various types of apparatus that may be used.  Type I apparatus options, for example, could include: leveled straightedge, optical level, laser level, or a laser imaging device (e.g. laser scanner).  If a Type I apparatus is not used, then Type II options could include certain inclinometers or floor profiling devices.

The issue of appropriate test procedures and apparatus that should be used to determine F-numbers is addressed--albeit in nuanced fashion--within the ASTM E1155 document itself.  In standard E1155, "Note 3" appears as follows:

At first glance, one might get the impression that all project participants would hold a meeting to discuss, then agree on the exact test apparatus (e.g. laser imaging device, leveled straightedge, "Dipstick", and so on) before embarking on any test program that will be used to enforce contract specification compliance.  Presumably, this mutual, sensible agreement among all project participants could be reached--using pre-bid RFI's--during the bid period.  In practice, however, it is more likely that such discussion and agreement would be reached during the preconstruction conference.   

Well, not so fast.  Upon further review, it turns out that ASTM E1155 Note 3 is only an informative, non-binding suggestion.  In other words, the phrase "should agree" as stated in Note 3 (above) is not equal to "must agree" or "shall agree". The bottom line is the choice of methodology resides with the entity performing the tests.

How do we know this? ASTM Standard E1155 section 1.2 states:

Drilling into the issue deeper, we find guidance presented in the ASTM International "Form and Style for ASTM Standards" document that clarifies the intent of "Notes" that appear in ASTM standards. Section A27.1 of the ASTM style guide appears as follows:

"A27.1 Notes in the text shall not include mandatory requirements. Notes are intended to set explanatory material apart from the text itself, either for emphasis or for offering informative suggestions, which are not properly part of the standard. Clarification of the description of required apparatus or procedure and modifications required or permitted in certain cases belong in the text itself. If inclusion of the contents yields a different result, then that information is considered mandatory for the performance of the standard and shall be located in the text. Notes may be preferable for detailed description of auxiliary procedures (for example, correction of barometric pressure in a test method not primarily concerned with pressure). Table notes are a part of the table and are mandatory provisions."

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NOTE 1: It is not at all unusual for the GC to look to the concrete contractor to provide an agenda for the preconstruction (aka "pre-pour") conference. As it turns out, just such a comprehensive agenda has been prepared jointly by the National Ready Mixed Concrete Association (NRMCA) and the ASCC.  Titled "Checklist for the Pre-Construction Conference", this joint document provides line-item discussion points covering topics that range from Quality testing of fresh concrete (e.g. slump, air) to testing of hardened concrete (e.g. compressive strength acceptance specimens, floor flatness, floor levelness, etc.).

A link to the Joint NRMCA/ASCC Pre-Construction checklist is here:

https://www.nrmca.org/wp-content/uploads/2021/06/1PreconstructionChecklist.pdf

For example, the NRMCA/ASCC preconstruction checklist section B ("Construction Process"), item #18 provides a comprehensive series of discussion points that will help provide clarity regarding floor flatness and levelness, and how such Quality items will be determined.

As many ASCC Hotline callers know, money can often be saved simply by methodically performing our concrete scopes using various ASCC checklists.  Access to the ASCC checklist collection--in addition to the collection of ASCC Position Statements--has proven over the years to be a valuable, proven member benefit. As mentioned above, the GC often requests the concrete contractor draft the agenda for the preconstruction conference. Unfortunately, in the case of the Hotline call described above, the NRMCA/ASCC checklist was not incorporated into the preconstruction meeting.

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NOTE 2: Although not discussed in the Hotline call above, not only are the procedures and apparatus for flatness and levelness testing important, but the qualifications of the device operator are crucial as well. Unfortunately, both ACI and ASTM documents are silent on training, qualifications, or certifications for operators determining F-numbers. This was discussed at length in the September 2023 issue of ACI Concrete International's "Concrete Q&A" titled "Operator Qualifications for Determining F-numbers".

This important item should be discussed in the preconstruction conference, in addition to the topics described above.