Jim Klinger, Concrete Construction Specialist The Voice Newsletter September 2023

Question:  We were recently awarded the subcontract for a reinforced concrete high-rise tower that features 3-ft thick shear walls with moderate to heavy reinforcing steel congestion. The shear walls in some sectors are up to 4-ft thick. This upcoming project has a fast-track schedule, the so-called "3-day cycle" that has become popular with Owners here in our regional construction market. Based on our experience with similarly congested shear walls, we expect that even with self-consolidating concrete (SCC) there will be honeycomb (rock pocket) conditions that will require timely repair and patching. The following statement appears in our construction documents: "The Contractor is responsible for correcting work that does not conform to the specified requirements, including strength, tolerances, and finishes. The Contractor shall submit the proposed solution for review and approval."  Several brand-name materials that are fair game for concrete repairs and patching are called out in our Division 3 specifications along with this qualification: "Use repair products in accordance with manufacturer's recommendations". For our project, such repair materials are required to meet ASTM C1107: Standard Specification for Packaged Dry, Hydraulic-Cement Grout (Non-shrink).

During the preconstruction collaboration conference specified in ACI 301-20, section 1.6.1, all parties recognized the fact that our proposed repair submittals will have to be prepared, reviewed, and approved quickly in order to avoid schedule hiccups. Since most of the repairs will involve seismic shear walls, the structural engineer wants to review each and every proposed repair on a case-by-case basis. All stakeholders present at the conference (e.g., the concrete contractor, the general contractor (GC), the licensed design professional (LDP), and the Owner's testing and inspection agency) each committed to drop back and develop plans intended to accommodate expedited schedule impacts affecting each stakeholder's respective scope of work. In addition to the proposed repair location and material submittals, the GC asked us to provide in our submittals a list of tests and inspections that the Owner's test agency will need to arrange based on the size of the repair and the type of materials we propose to use in each case. In other words, we have been asked to create an advance repair submittal "template" that is intended to help streamline the repair process.

(N.B.: Although testing and inspection responsibilities are not included in our contract scope, we did not balk at the GC’s request to help predict the work of others in our submittals. For us, such requests are actually routine, especially for large concrete projects.  It would not be at all unusual, for example, to be asked after the contract award how many cubic yards (CY) and how many pump or shoot days we estimated during our bid logistics and schedule analysis. This information helps the Owner solicit bids from the testing agencies, who cannot reasonably know at bid time how we intend to build the job.)

For the most part, simple rock pocket repairs (e.g., within a few inches of the face of wall) are easy enough for us to accomplish.  It is the deeper pockets and voids behind the congested reinforcing steel bars that are at issue. We understand why the Owner wants us to help forecast the testing and inspection scope (there is no way the test agency can forward-price such undefined scope), but therein lies the rub.  Each of the specified repair material options comes with its own unique MPII, some of which is based on unpublished "proprietary" support data. This makes it difficult for us to prepare repair material and procedure submittals in advance, let alone try to forecast the testing and inspection scopes with any degree of accuracy.

We checked in our latest ACI Manual of Concrete Practice (MCP-2015) for guidance related to construction grout applications but were unsuccessful. Can ASCC provide any information that will help us prepare the construction grout repair submittals described above?

Answer: Your question involves just a limited portion of the many possible uses a concrete contractor may have for so-called "construction grout".  Since "grout" is such a wide-ranging yet curiously arcane topic, the discussion below does not include these typically used grout applications: unbonded post-tensioned (PT) stress pockets, bonded PT tendon ducts, precast concrete connections, masonry grout, auger cast piles, pile reinforcement anchorage, and so on.) But strangely enough, while we have excluded discussion of many grout applications above, we find that the best way to assist in your case is to discuss a totally separate construction grout application that almost every concrete contractor knows full well: grouting of steel column base plates.  In other words, it's kind of the same thing...only different.

Any time you have a structural steel building marrying up with a reinforced concrete foundation, there is one structurally significant grout application that has (to date, anyway) not yet been addressed in building codes- including ACI 318- and that is the grout placed under steel base plates. So, you are correct in noting that any guidance regarding base plate grouting and its associated testing and inspection activities are difficult to find. It is our understanding that this issue is currently under advisement in various ACI 318 Code subcommittees, and incorporation of guidelines for certain grout applications, including testing and inspection requirements, may be available on the near horizon.

Generally speaking, base plate grout is given little attention in structural construction documents. "General Notes" sheets, for example, often devote only one or two lines that appear as follows for material:

And as follows for inspection and testing:

Because so little information appears in the construction documents, who then is responsible to determine the materials, placement procedures, testing requirements, and inspection protocols? Is the concrete contractor the one who is responsible for interpreting the individual MPII from each manufacturer? One thing is for sure, when the concrete contractor is presented with such limited information, there are many questions that can (and should) be presented to the LDP via Requests For Information (RFIs) straightaway as follows below. Such RFI questions apply whether the scope is steel base plate grouting or structural repairs in a concrete shear wall. And all of them are the responsibility of the LDP to answer.

What is the compressive strength of the grout required, and how (and when) will that be determined? Should the inspector mold 2-inch square cubes...or 4-inch diameter cylinders? How many samples should be cast? Are the samples to be field cured or lab cured? (Typically grout cubes can break up to 10 to 15 percent higher than companion cylinders cast at the same time.) Does testing of unconfined cubes or cylinders accurately represent the in-situ grout strength in its highly confined condition? Is destructive testing the only truly reliable way to determine the strength of grout under a steel baseplate? And even more to the point, is it possible or feasible to extract core samples in the case of suspect test results?

What grout consistency is required? Depending on the amount of water added, the material could range from plastic (e.g.,"dry pack") to flowable to fluid. Who is responsible for monitoring the amount of water added to the site-mixed powdered grout? Will all of the proportioning, mixing, curing and other procedures prescribed in ASTM C1107 be followed?  If you are familiar with this ASTM Standard, have you ever seen such procedures carried out on your project when your crew is grouting column base plates or patching a shear wall?

For concrete, there is usually a batch-to-placement (BTP) time limit specified by the LDP. Is there such a "shelf-life" time requirement for grout placement?  For "non-shrink" grout, will the inspector really be casting and testing shrinkage bars?

Should a pea gravel "extension" be introduced into the mix?  Most grout MPII requires such an extension whenever the grout layer thickness exceeds 3 inches. What tests and inspections are appropriate when pea gravel extensions are added? At concrete batch plants, for example, addition of water and other constituents are carefully measured and closely monitored using calibrated equipment. Can a similar Quality Control standard of care be expected in the field?

(N.B.: According to several grout manufacturers of MPIIs, the addition of aggregate to the mix is not done for reasons of strength. The pea gravel aggregate is actually introduced to act as a heat sink to cool the grout section when the proprietary cementitious material starts to hydrate and generate heat. Question: given a certain grout layer thickness, do all of the specified manufacturers call for the same amount of aggregate extension? Bonus question: once aggregate is added into the mix...does that not transmute grout into concrete?)

For the proposed repair at hand...is the repair truly a structural fix? Or is the honeycomb repair merely a shallow cosmetic treatment that really might not need to be tested or inspected? Does the Owner want to pay for such level of attention?

As you can see, the topic of construction grout--even for something that seems so simple such as a honeycomb repair--or as important as a load-bearing column base plate condition--can get complicated quickly.  Perhaps these complications are why it has taken the folks who confect concrete building codes so long to address them.