10.1 Pre-Placement Inspection Checklist & Subgrade Preparation
Key Takeaways
Under model IBC Table 1705.3, reinforcement, cast-in anchors and formwork geometry are generally periodic inspection tasks. Concrete placement is continuous.
ACI 301-20 Sections 5.3.1.3 and 5.3.1.4 address the preparation of form contact surfaces, reinforcement and the specified slab-on-ground base.
In cold-weather work under ACI 301-20, contact surfaces against ground, subbase or a mud mat must be above 32°F. Remove snow, ice, frost and other contaminants before placement.
Read the applicable vapor-retarder requirement and approved details for laps, penetrations, damage repairs and protection from construction traffic.
Record the location and measured condition of discrepancies. Notify the contractor and follow the applicable escalation and correction procedures.
10.1 Pre-Placement Inspection Checklist & Subgrade Preparation
Inspect the features that fresh concrete will conceal. Use the approved drawings, specifications and statement of special inspections to establish what must be checked and who is assigned to check it. Coordinate access so the reinforcement, embedments, forms and supporting surfaces remain visible long enough to inspect.
1. Identify the inspection assignment
Model IBC Table 1705.3 lists periodic inspections of reinforcement placement (item 1), cast-in anchors (item 3) and the shape, location and dimensions of the concrete member being formed (item 14). Item 7 lists continuous inspection of concrete and shotcrete placement for proper application techniques. Item 6 separately addresses fresh concrete tests and fabrication of strength specimens before placement. Use the approved statement of special inspections and the applicable jurisdiction’s code for the work in question.
A pre-placement inspection record documents the work observed, conformity or discrepancies, notifications and correction. Under model IBC Section 1704.2.4, report discrepancies to the contractor for correction and, if uncorrected, to the building official and the registered design professional in responsible charge before completion of that phase. Follow any project hold point and document the result. Authority to dispatch batches or approve changes comes from the applicable project process and designated parties.
2. Check subgrade, base and weather protection
Under ACI 301-20 Section 5.3.1.4, remove contaminants from the slab-on-ground contact surface, prepare subgrade and base as specified, and apply the ACI 117 elevation tolerance for the base. Where the contract applies ACI 117-10 Section 4.4.5 to the fine grade of soil immediately below the slab, the elevation tolerance is ±3/4 inch. Use the approved geotechnical criteria for density, test method and locations. ASTM D698 and D1557 are different laboratory compaction methods. A percent compaction reading must identify the specified reference and field result.
For example, the approved specification requires at least 95% of the laboratory maximum dry density determined by ASTM D1557. A field dry density of 114 lb/ft³ divided by a laboratory maximum of 120 lb/ft³ gives , or 95%. This meets the stated density criterion at that location. Check finished elevation, bearing condition and any required test records separately.
Verify moisture conditioning according to the approved base and placement details. Remove standing water and loose or contaminating material. Where work falls under ACI 301-20 Section 5.3.2.1(b), verify that the contact surface is above 32°F for placement against ground, subbase or a mud mat. Check the actual surface at the placement location and confirm the approved cold-weather protection. Warm concrete at discharge does not satisfy a separate temperature requirement for the contact surface. Remove snow, ice and frost from surfaces, steel and embedded items as applicable.
3. Check the vapor retarder before it is covered
For the slab-on-ground scope of the 2021 model IBC Section 1907.1, the prescriptive provision uses 6-mil polyethylene between the base or subgrade and floor slab, with seams lapped at least 6 inches, or another approved equivalent. The section has exceptions, including outdoor flatwork that will remain unenclosed. Use the approved project details for a thicker or higher-performance product where specified. ASTM E1745 is a product specification and ASTM E1643 addresses selection, design, installation and inspection.
Match the roll label and approved submittal. Check seam overlap, seals at penetrations and perimeter, and treatment of punctures using the specified product instructions. For example, StegoHome Wrap instructions specify a 6-inch minimum seam overlap and taped seams. They also specify a repair patch overlapping a hole by at least 6 inches in every direction, with all edges taped. A 2-inch by 3-inch tear with straight edges would require at least a 14-inch by 15-inch rectangular patch placed to achieve the stated overlap. Recheck the repaired area and the chair legs that can damage it.
4. Inspect the work that concrete will conceal
| Location | Evidence to record |
|---|---|
| Forms | Check the approved geometry, line, level and member dimensions. Inspect the contact surfaces and joints for debris, defects or leakage paths. |
| Form access | Under specified ACI 301-20 Section 2.2.2.6, provide temporary openings where needed for cleaning and inspection. Verify cleanout closure and secure fit before placement. |
| Reinforcement | Match bar size, grade, location, quantity and spacing to the approved drawings. Measure specified cover to the applicable steel surface using ACI 318-19 Table 20.5.1.3.1 for nonprestressed cast-in-place members. |
| Bar supports | Confirm the approved type, seating and stability under placement activity. A correct chair height cannot make up for a base that sinks or a span between chairs that allows the mat to sag. |
| Anchors, plates and sleeves | Check required marks, orientation, location, fastening and applicable embedment under ACI 318-19 Sections 26.7 and 26.8. Submit unshown items or changes for review as applicable. |
| Construction joint | Confirm the approved location and specified roughness where required. Check cleaning, laitance removal, immediate prewetting and removal of standing water under Section 26.5.6.2. |
Where a form release product is specified and ACI 301-20 Section 2.3.1.15 applies, verify application before reinforcement, removal of excess and protection of steel and any joint face that will receive fresh concrete. Use the applicable plan for forms, shoring and access around congested reinforcement. If something changes after the pre-placement check, recheck the affected location and record the disposition.
ACI 301-20 Section 5.3.2.1(b) applies to a slab placed against a subbase in cold weather. What temperature condition must the inspector verify at the contact surface?
It is above 32°F.
It may be frozen if the delivered concrete is above 70°F.
It may be at 28°F if the mixture contains an accelerator.
It must be at least as warm as the delivered concrete.
The approved slab vapor retarder is StegoHome Wrap. A patch over a rectangular 2-inch by 3-inch tear must extend 6 inches beyond the tear on every side. What is the smallest rectangular patch that can meet the stated overlap?
8 by 9 inches
14 by 15 inches
12 by 12 inches
6 by 6 inches
The base of a deep wall form cannot be accessed from above and sawdust is visible. What does ACI 301-20 Section 2.2.2.6 require where temporary access is needed?
Leave the base unexamined if it is below 10 feet.
Use the openings to drain bleed water throughout placement.
Provide temporary openings for cleaning and inspection and verify the form is ready before concrete placement.
Replace the cleanout with vents at the top of the form.
Sections you finish are checked off in the contents.