Proper CO2 Levels are Critical for Concrete Curing
Builders and engineers know that concrete laid during cold weather construction is prone to many problems including soft surfaces caused by the concrete freezing during curing. However, pouring concrete floors indoors was always possible by heating the building interiors with salamanders or other flame-based heating devices.
Unfortunately, poured concrete in heated areas still posed a problem. The surface often remained soft, and builders were forced to come up with various tricks to harden it in order to complete the project. Only after several weeks or months did the building owner realize that the poured concrete did not perform as required.
This was a challenge faced by one of our clients who was pouring concrete for a parking garage in Chicago. The concrete wasn't performing as required and everyone involved in the project wanted to know why.
Research discovered that the CO2 given off by the open-flamed salamander heaters was the culprit. Flame-based heaters in enclosed areas have been shown to product between 1.6 and 5.6% CO2 by volume. While these CO2 levels would be deadly in an enclosed area, the danger was mitigated due to the relatively large area of the project.
Concrete that cures while exposed to elevated CO2 levels was found to have significantly softer surfaces than concrete hardened in fresh (0.04% CO2 by volume) air.
As a result, our client purchased several pSense handheld CO2 data loggers for their new concrete pouring projects. The pSense is used for spot-checking CO2 levels and as a portable data logger to verify to their client that the concrete was never subject to high CO2 levels during curing.