Question: We are preparing to pump, place, and finish a reinforced concrete slab on metal deck (SOMD) in a 4-story (e.g. 4 elevated decks) structural steel-framed office building. Each floor slab has an area of 100,000 gross square feet (GSF), which we plan to complete in 4 each 25,000 square foot (SF) pours per floor, or 16 total placement days. We have scheduled our first concrete placement in two weeks.
To date, our contract scope (pile caps, grade beams, and anchor rods for the steel columns) has been on time and under budget. All foundation concrete placed to date has been tailgated, and the slab on grade (SOG) is now scheduled near the end of the project due to pending Owner (future tenant) design changes. Ownership has been issuing our progress payments in a timely manner, and we have a good relationship with the Owner's inspection team. There are only 3 noncompliance reports (NCR) outstanding that belong to us which are very minor in nature and will be quickly resolved after we pour out the SOMD. The structural engineer has been fair all along, but tends to take a conservative approach to any issues that have arisen.
The metal decking sheets furnished and installed by the steel erector feature 3-inch-deep flutes plus an additional 3 1/4 inches of reinforced concrete "topping", resulting in a nominal concrete thickness at each flute of 6 1/4 inches. The SOMD are designed as normal weight concrete (NWC), reinforced with welded wire mesh reinforcing sheets furnished and installed by others. During the pre-bid period, the metal deck sheets-originally specified as "vented"-were changed to non-vented at our request.
According to the metal deck product data, the neat (aka "exact") volume of concrete required to fill a 3 1/4-inch topping over every 100 SF of floor surface area is 1.466 CY. In other words, a 25,000 SF SOMD placement will require a minimum 367 neat CY concrete purchase. To account for overage, waste, and deck deflection, our estimator carried an additional 1/2 inch of concrete spread over the entire floor area. This adds another 37 CY of NWC--roughly 10 percent-- resulting in a final estimated concrete purchase quantity of 404 CY per pour.
During the SOMD preconstruction conference held at the jobsite yesterday, the concrete pump operator was asked how the pump rubber hose system was going to be primed at the start of each day's placement. Would he use water to prime the pump, or a cementitious grout slurry mix, or a prepackaged proprietary product? The pump operator replied that water would be out of the question, and the final decision has not been made regarding the primer material.
At that point, the structural engineer stated that a pump primer material and placement plan must be submitted and approved before we can begin placing the SOMD. We would like to use a cement slurry mix prepared by our ready-mix concrete supplier, which our estimator agreed to during the concrete material supply buyout after we were awarded the job.
We wish to prime the pump with about 1 cubic yard (CY) of slurry, which--at a 9-inch slump--would be spread out over the pour areas up on each elevated deck and left in place. In other words, the slurry coating would be incorporated into each slab. We did not raise the leave-in-place scenario during yesterday's meeting. Since the engineer is fair--albeit conservative--we wanted to check with the ASCC Hotline first for guidance on how we might successfully package the primer placement submittal and get it approved. Please advise.
Answer: This is a great question, since it features recurring themes fielded here at the ASCC Technical Division. The last time we addressed such various SOMD issues was in "Guidance #23", which appeared in the November 2023 issue of the ASCC VOICE. A memory-refreshing link to Guidance #23 is as follows:
https://ascconline.org/Home/News/articleType/ArticleView/articleId/377/categoryId/33/Guidance-for-Concrete-Contractors23-in-a-Series
January 2025 Pump Primer Update: Three years ago, I was appointed to the American Concrete Institute Construction Liaison Committee (CLC) to serve a three-year term which ends at the conclusion of the upcoming Spring 2025 ACI Convention which will convene in Toronto, Canada March 30-April 2, 2025.
The CLC Committee Mission is stated as follows: "Advise the Board of Direction on the needs of the concrete construction industry as it relates to establishment and operation of committees, programs, and activities to address contractors' needs and problems within the Institute".
Part of the ACI CLC duties performed over the past 3-year term included review of many ACI Practices, Codes, and Specifications under consideration for proposed revisions to existing documents or incorporation into the ACI Collection for new documents. One such review included proposed revisions to ACI SPEC-311.7-18: Specification for Inspection of Concrete Construction. ASCC proposed a revision to section 3.2.4, which originally called for the inspector to "Verify that grout used to lubricate the pump hose is not incorporated into the placement" as described in Guidance #23.
The ASCC proposed revision to section 3.2.4 we submitted to CLC read as follows: "Grout used to prime pump system can be left in place when approved by the Licensed Design Professional (LDP), especially in large placements or slabs on metal deck". In general, the status of any proposed revisions submitted to CLC by ASCC are kept under wraps until the document is made available to the industry as a "public discussion" version.
Last time we checked, the public discussion version of section 3.2.4 reads as follows: "Verify that grout used to lubricate the pump hose is not incorporated into the placement unless approved by the RDPRC (Registered Design Professional in Responsible Charge)". Let's hope this public discussion revision makes it over the finish line when the final ACI SPEC 311.7 is published by ACI.
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Question: More and more we are seeing the prefix "PRC" in titles to certain ACI documents. For example, we noticed a document reference in a recent Concrete International article titled "Converting Core Strengths to Equivalent Specified Concrete Strengths" that appeared in the November 2024 issue of ACI Concrete International. The document reference was "ACI PRC-214.4-21 Obtaining Cores and Interpreting Core Strength Results--Guide". Can the Hotline tell us what the prefix "PRC" stands for?
Answer: The acronym is short for "Practice", and is used in the titles of ACI Guides and Reports. ACI codes feature the prefix "CODE", and ACI specifications feature the prefix "SPEC". A comprehensive listing of ACI documents featuring these prefix designations can be found at this link to the ACI Collection of Concrete Codes, Specifications, and Practices-2024:
https://www.concrete.org/store/productdetail.aspx?ItemID=COL24PACK&Format=HARD_COPY&Language=English&Units=US_Units
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