Cure Time Versus Loading Schedule
Adhesive anchors are being installed to anchor a temporary fall-protection post base to an exterior concrete wall. The product data gives a cure schedule based on concrete temperature: at 50 F the minimum cure before loading is substantially longer than at 70 F. The concrete surface temperature measured with an infrared thermometer reads 48 F in the morning shade; the ambient air is 62 F and rising. The crew plans to install anchors at 7:00 a.m. and tension the anchors and attach the post at 11:00 a.m. the same day, citing the 70 F column of the cure chart because 'the air will warm up.' The anchors are 3/4 inch diameter, and the specification requires the manufacturer's published cure time to be met before any load is applied.
1. Which temperature governs the cure time, and is the 11:00 a.m. loading acceptable?
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The concrete/hole temperature governs, not the air temperature.
- Adhesive cure is driven by the temperature of the materials in contact with the adhesive - the concrete and the rod - not the ambient air. The infrared reading of 48 F on the concrete surface (and the hole will be at or near that) places the installation in the colder cure column, which requires a longer cure than the 70 F value the crew wants to use.
- 'The air will warm up' is not a valid basis: the cure clock starts at installation, and early cure occurs at the colder substrate temperature. Loading at 11:00 a.m. (4 hours) is very likely inside the required cure window for 48–50 F.
- Conclusion: Loading at 11:00 a.m. is not acceptable unless the measured substrate temperature at installation and the manufacturer's chart for that temperature show the 4-hour interval is sufficient. At 48 F it typically is not. The inspector should require the crew to use the colder-temperature cure column and delay loading accordingly, or take approved measures consistent with the product data.
- Document the measured substrate temperature at the time of installation, not just ambient air.
2. What records and controls would you put in place to prevent a recurrence on this project?
Read the worked answer
- Temperature record at installation: measure and log concrete surface and hole temperature (and rod temperature if conditioned differently) at the time each batch is placed, using a calibrated thermometer; do not rely on ambient air or forecast.
- Cure-time determination: have the crew post the manufacturer's cure chart at the work area and mark the governing column based on the measured substrate temperature; record the earliest permitted load time for each anchor group.
- Hold point: establish a hold on loading/tensioning until the recorded cure time has elapsed; the inspector verifies before the post is attached or anchors are tensioned.
- Cold-weather provisions: if substrate temperatures fall below the product's permitted range, stop and consult the manufacturer/EOR - some products prohibit installation below a minimum temperature.
- Documentation: cartridge product name, batch, expiration, mix nozzle, hole cleaning, embedment, and cure start/end times in the daily report so the loading decision is auditable.