Question: Our company's regional hub located in South Florida has been selected to furnish and install approximately 100,000 square feet (SF) of reinforced concrete slab on grade (SOG) for a large, privately owned warehouse developer. Nominal slab thickness is 5 inches, with a 28-day concrete design compressive strength of 3500 psi normal weight concrete (NWC). Typical slab reinforcing is ASTM A 1064 deformed welded wire reinforcement (WWR), specified in the structural drawing general notes as 6 X 6-D2.9 X D2.9. Preparation of subgrade within the building footprint is to be performed by others. Based on our company policy, we do not take ownership of a building substrate until the pad has been inspected, tested and accepted by the geotechnical engineer and its location certified by a licensed surveyor. Both of those hurdles were cleared last week.
To price the job, our bid team divided the building footprint into 5 equal placement areas of 20,000 SF each. Including waste (and various other arcane estimating fudge factors), our estimators determined by calculation that each slab area requires exactly 325 cubic yards (CY) of concrete to complete. All concrete placements, including those that contain mechanical rooms and other back-of-the-house spaces, require a trowel finish.
According to our project schedule, the first order of business after the recent substrate handoff is to furnish and install a layer of 15-mil. vapor barrier, followed by layout and placement of the precast concrete "dobies" that support the sheets of WWR at approximately mid-depth of the slab. Unfortunately, this simple and efficient work sequence that has become routine over the years (and quite profitable--for us, anyway) took a turn for the worse when we received notification that our entire shipment of WWR has been rejected by one of the Owner's representatives. The stated reason for rejection? "We saw the wire mesh being delivered at the jobsite today. It appeared rusty", the email states. "We are recommending that this material be replaced. Let us know if this is a problem". A representative photo of our WWR stockpile onsite is shown below.
Representative photograph of WWR sheets recently delivered onsite.
We are long-standing members of ASCC; members who were active when one of the early Position Statements (Position Statement #3: Coatings that Affect Bond to Reinforcement) was created and published in the ACI Concrete International March 2003 issue--quite likely in response to a similar scenario being revisited today on our project. To oversimplify enormously, by the March 2003 publication date, the collective industry consensus already was that testing performed to determine effects of form release agents, concrete spatter, and...well...bond breakers applied to the bonding surface of reinforcing steel bars proved that such applications "did not affect the bond for concrete strengths of 4000 and 5000 psi."
We are confident the backup information we already have in hand will be sufficient for the engineer to review, reverse the rejection, and allow us to proceed with installation of the WWR that is currently stockpiled onsite. In addition to ASCC Position Statement #3 and excerpts from ACI documents, our WWR supplier is preparing a submittal from the steel mill explaining why the normal, rusty appearance is not a legitimate cause for concern or rejection. Before we respond to our customer, does the ASCC Hotline have any update(s) to the original Position Statement #3 or any additional backup we can submit to expedite resolution? We are in a schedule holding pattern while this issue gets resolved. Please advise.
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Answer: Excellent question; and timely, too. As it turns out, there are several recurring themes and issue updates that can be addressed to help us resolve this Hotline call. We present those in no particular order as follows below.
Many concrete contractors can testify that concrete is a natural product that moves--and then behaves--in mysterious ways. After all, who is there among us that is not dealing daily with at least one of the typical potential costs associated with reinforced structural concrete: shrinkage, curling, deflection, delamination, and--of course--cracking?
Although the chemical processes involved in the manufacture of steel products are somewhat more controlled in the steel mills, there are still a few head-scratchers associated with using steel as a building material as well. Consider, for example, the life cycle of steel wire product eventually used to reinforce concrete slabs such as yours. As soon as the final WWR sheet in a particular bundle is placed on a pallet, the bright metal wire instantly becomes fair game for visible rust to develop. Corrosion experts refer to this first appearance as "flash rust". The rapid initiation of such flash rust is exactly as its name suggests--it appears in a flash, similar to the predictably spontaneous sprouting of weeds we all notice within minutes after we have finished mowing our front lawns. This process, of course, seems to occur even faster when the steel is exposed to a typically humid South Florida market environment. Chances are extremely high that all bundles of WWR being shipped to your market will feature a normal coating of flash rust by the time they arrive onsite.
For more information regarding the manufacture and use of WWR, you can access the Wire Reinforcement Institute (WRI) Manual of Standard Practice at the link given below:
https://www.wirereinforcementinstitute.org/application/files/4416/1711/1814/WWR-500-R-21_MSP.pdf
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It could be argued that one of the riskiest predicaments faced by ASCC concrete contractors in their day-to-day work is the scenario whereby rejection of work product (or the assignation of "suspect work" status) is initiated by a project stakeholder with little or no background in concrete construction or relevant experience with any part of the contract work at hand. This problem can be compounded when the author of the suspect noncompliance is relatively high up in the food chain--perhaps even at project Ownership level.
We note here that--in your case-- the "rejection document" is really nothing more than email traffic that neglects to contain the most essential part of the noncompliance equation: it does not report exactly what part(s) of the contract document requirements have been violated.
In order for us to determine the contractual quality requirements that govern the reinforcing steel material you are furnishing to the project, we reviewed two of the project specification sections that are part of your construction documents, namely Section 03 20 00 CONCRETE REINFORCING and Section 03 30 00 CAST-IN-PLACE CONCRETE. In both cases, these construction document specification sections are silent regarding rust, removal of rust and so on. The reinforcing steel specification does contain a standard requirement that all reinforcing steel delivered to the project be accompanied by mill certifications for Quality Control traceability purposes.
We also noted, however, that you are bound by reference to follow ACI 301-20 Specifications for Concrete Construction. ACI 301-20 Section 5.3.7.6 states that rust is one of the material aspects (including efflorescence, stains, surface deposits) that require removal only if specifically called out in the Contract Documents. On the other hand, ACI 301 section 3.3.1 states "Reinforcement with rust, mill scale, or a combination of both will be considered satisfactory, provided minimum nominal dimensions, weight per foot, and minimum average height of deformations of a hand-wire-brushed test specimen are not less than applicable ASTM specification requirements." In other words, section 3.3.1 gives a qualified inspector an avenue to determine acceptability via testing, even though the construction documents do not specifically call out locations where rust of any nature must be removed.
In your case, the applicable ASTM document is ASTM A 1064 Standard Specification for Steel Wire and Welded Wire Reinforcement, Plain and Deformed, for Concrete. Within this ASTM document, Section 7 Mechanical Property Requirements-Wire, Plain and Deformed specifies testing protocols and tolerance criteria for use in evaluating contract compliance.
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A complicating factor at play here typically presents difficulties for inexperienced (and perhaps even some experienced) stakeholders to wrap their heads around: the fact that seemingly deleterious conditions at first glance (rusted steel, in this case) can in fact be quite helpful. Such a scenario would not be the first time this curious type of phenomenon has been discussed in an ASCC VOICE Guidance column.
Take, for example, the Hotline call described in Guidance installment #9, which appeared in the August 2022 issue of the VOICE. In that episode, the caller wanted to understand the term "bold exposure" that appeared in the project construction documents (this was a term found in the Division 5 structural steel scope documents, not part of the ASCC member's contract scope).
On that project, structural members were fabricated with ASTM A 588 steel, which is intended to be corrosion-resistant with high tensile strength. Also known as "weathering steel" or "COR-TEN" steel, this material was specifically developed to rust on purpose for the steel to protect itself from further rust. This process works just fine if the steel can be "boldly exposed" to an environment that will allow a thin layer (aka "patina") of rust to form on its outer surface. In this case, "bold exposure" is defined as "rain washed-sun dried".
It can take several cycles of rain wash and sun dry before the protective oxide layer is fully activated. Once the steel members have been milled and exposed to ambient air, the surface oxidation process (flash rust) can start within minutes and take up to, say, 6 months to complete. Several state highway departments in the snow belt states specify weathering steel to eliminate initial painting costs and reduce future maintenance and replacement costs--which can be enormous. Architects often specify weathering steel for sculptures and other exposed steel applications due to its pleasing appearance as well. Here in the San Francisco Bay Area market, weathering steel members can be seen at several above-ground BART stations (e.g. Rockridge, Balboa Park), which are exposed to the environment year-round.
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Over this past year, the ASCC Technical Division updated the collection of more than 40 Position Statements. As can be expected, the update to ASCC Position Statement #3: Coatings that Affect Bond to Reinforcement incorporated more than just 20-plus years of advancements in the field of corrosion science related to concrete and reinforcing steel. It also approached the topic of expectation management as well. For example, the revisions to Position Statement #3 described the reactions some project stakeholders may have upon discovery of corrosion by-products (aka rust) on what has been advertised as "new" materials in the field as follows:
"Engineers or inspectors typically direct concrete contractors to clean bars that are coated with materials believed to decrease bond. Form-release agents, bond breakers and cement splatter sometimes come in contact with reinforcing steel before concrete is placed. In the absence of data concerning the types of materials that decrease bond, cautious engineers and inspectors usually require all such material to be cleaned from the reinforcing. However, two studies have provided test data showing that some of these materials don't decrease bond."
For more information, a link to the recently updated ASCC Position Statement #3 is as follows:
https://ascconline.org/Portals/ASCC/Files/Position%20Statements/PS-3_CoatingsAffectBond_webSC-1.pdf?ver=gafefyxrnGEEskWnbyjnrg%3d%3d
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In addition to the contractual requirement for the concrete contractor to follow ACI 301-20 Specifications for Concrete Construction, the project design team is obligated to follow the requirements for reinforcing steel (including WWR) codified in ACI 318-19 Building Code Requirements for Structural Concrete (aka "the Code").
According to the Code, section 26.6.1.2(b) states "Nonprestressed reinforcement with rust, mill scale, or a combination of both shall be considered satisfactory, provided a hand-wire-brushed representative test specimen of the reinforcement complies with the applicable ASTM specification for the minimum dimensions (including height of deformations) and weight per unit length."
This Code requirement is consistent with the inspection and testing protocols for suspect reinforcing material specified in ACI 301-20 section 3.3.1, and Standard Specification ASTM A 1064, both of which are discussed in detail, below.
(N.B.: Commentary section R26.6.1.2(b) associated with the corresponding Code section referenced above is of some significance, since it provides a clear description of acceptable rust products exhibited on reinforcing steel as follows: "Research has shown that a normal amount of rust increases bond. Normal rough handling generally removes rust that is loose enough to impair the bond between the concrete and reinforcement." Translation: "By the time the ironworkers up on the deck have shaken out the WWR sheets, any harmful material has fallen off, leaving whatever incidental rust or rust by-products that remain on each sheet normal and acceptable for use in the work".)
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Based on the above, the best course of action is to request relief from the rejection in writing today, pending receipt of the submittal package currently being prepared by your WWR supplier. Ultimately it is the WWR supplier's responsibility to deliver the WWR to the jobsite--along with supporting backup documentation--indicating compliance with ASTM, ACI and other appropriate contract documents.
In the meantime, your submittal package should include the updated ASCC Position Statement #3, which provides some cover for "cautious inspectors", no matter where they might reside in the project stakeholder food chain. Barring any test results that indicate otherwise, it appears the WWR as delivered to your project jobsite complies with the contract documents.
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