Jim Klinger, concrete construction specialist The Voice Newsletter November 2022
Full disclosure: I was ransacking the garage trying to find that one missing part from our George Foreman grill when I uncovered a couple of collector's items. There was a slightly dented blue metal hard hat- an old "Jackson hat", a real beauty- issued in 1979 when I took my first concrete construction job with Miller and Long. And then pops up another construction gem from 1979, a video of the movie "Steel", starring Lee Majors, George Kennedy, Art Carney and Jennifer O'Neill. To this day, "Steel" is the only movie ever made that actually takes place on an active construction jobsite**. Filmed during erection of the 22-story Kincaid Tower in Lexington, KY, the plot involves a retired steel superintendent (Majors) who returns to high-rise construction just in time to debut the industry's first three-day cycle by erecting nine floors worth of steel in three weeks after tracking down his old crew, beating the bad guys and at the same time making some serious time with Jennifer O'Neill. During a brief lull in the action and after several martinis, Oscar-winner Art Carney has just about had it with the steel construction business and pipes up with this piece of sage advice for the intrepid good guys: "I think it'll all be over soon, though. I don't think there'll be much high steel business anymore. I think it'll be replaced by reinforced concrete. But a man can't get very excited about cement".
**N.B. Although this is technically correct, there are purists who will insist that there was a popular full-length music video that was filmed on an active concrete construction jobsite that deserves honorable mention. It was 1987, and the World Wrestling Federation (WWF) filmed the classic "Piledriver" to promote Koko B. Ware's upcoming match in "Saturday Night's Main Event" on an ASCC member jobsite in Oakland, CA. Many legendary WWF stars were there, from Vince McMahon to Hulk Hogan. In one sequence, the Hulkster can be seen at the end of the pump hose, placing concrete for an elevated podium slab. Similar to "Steel," these were committed to celluloid without the blessing or benefit of any corporate HR or Safety Dept. review. And Vince McMahon never did make good on his promise to deliver several cases of beer and other party favors to the concrete guys who had to clean up the mess after the video was filmed, the least of which was the pour crew who had to deal with the mess Hogan left on the deck.
Top of column elevation tolerance: ACI 117-10 section 4.4.4 tells us that the top of wall elevation tolerance is plus/minus 3/4 inch. There is no top of column elevation tolerance specified. Columns that frame into slabs or beams are usually formed and placed so the column concrete at each construction joint protrudes slightly higher than the elevation of the formed beam or slab soffit. This allows the soffit formwork to butt into concrete and minimize loss of concrete at that opening. When column cold joints are below the slab or beam soffit, forming at the opening in the form soffit is more complex and more concrete leakage is likely. For these reasons, ASCC contractors often place the top of columns (and walls that frame into slabs) on the plus side of that tolerance.
Engineers may require the concrete contractor to chip out concrete above the adjacent slab or beam soffit due to a belief that the slab shear capacity is reduced by the column "overpour" intrusion into the slab (or beam). Unfortunately, this requirement is not included in the construction documents, is usually enforced by inspectors on-site, and results in additional cost to the contractor. ACI 318-19 "Building Code Requirements for Structural Concrete," does not include any guidance for handling this issue, and we cannot find published data regarding the intrusion of "overpoured" column concrete on shear capacity.
The ASCC Technical Division is looking for your experience with "overpours" at top of columns. Have you had to chip column concrete out? Do you have photos? Specifically photos of how the column is formed when the column top is below the soffit form and of how bad the concrete divots look on the column when it is below the soffit. Has the EOR ever put in writing why and how far you had to chip the concrete down?
We know this is a long-standing cause of confusion in the industry and are working to help resolve this to eliminate recurring hassles and cost impact.
Let us know. Keep those cards and letters coming.
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ASCC Hotline Question: We are scheduled to complete several projects here in the next few months, including sidewalks and exterior slabs. Are there any papers or articles we can share with the project Owners that describe the ill effects of deicers on young concrete?
Answer: There are several sources that can be cited. The first is ACI 302.1R-15 Guide to Concrete Floor and Slab Construction. In section 13.5-Scaling, ACI tells us that scaling can be caused by use of deicing chemicals because "deicers lower the freezing point of water that can increase the number of freezing-and-thawing cycles and can increase the propensity for resaturation of concrete during the thawing period." ACI 302 section 8.4.3 also tells us "the use of any deicing chemicals is not recommended in the first year of slab service."
The Portland Cement Association (PCA) recommends a "drying period should be at least 1 month of relatively dry weather before the application of deicing salts." Even application of sealers to new concrete can be as risky as gas station sushi. According to the PCA, "Concrete placed in the late fall should not be sealed until spring because the sealer may cause the concrete to retain water that may exacerbate freeze-thaw damage."