Q: We are planning to bid on a decorative patio on a high-profile project overlooking the Pacific Ocean. The area is known for its continuously changing weather and especially windy conditions.
We would like to try to estimate how the varying weather conditions will affect our productivity. We would specifically like to determine the site's wind velocity, ambient temperature, and relative humidity. To ensure that our work is of the highest quality, our goal is to attempt to work only on days during which conditions are optimal for good concrete curing.
Do you have any ideas on how we can gather this data?
A: Your approach to accurately measure weather conditions before you bid on the job is admirable. Concrete contractors know that weather conditions are directly related to the possibility of plastic shrinkage cracking. Senior editor Joe Nasvik reminded readers in the August 2007 issue of CONCRETE CONSTRUCTION magazine that scientific research on evaporation began more than 200 years ago. And in 1960, researchers converted general information into practical applications for concrete contractors. The American Concrete Institute's nomograph, first developed by Delmar Bloem, helps contractors predict if weather conditions can cause plastic cracking in freshly placed concrete
It can be just as important to know ambient conditions for treating the surface after the pour has been made. Contractor knowledge of the jobsite's relative humidity is important when selecting coating and curing materials. When the contract specifies a non-acrylic sealer or coating, contractors should monitor relative humidity. Manufacturers of these products have now published relative humidity numbers for application purposes.
A good way to monitor ambient weather conditions on the jobsite is with the Kestrel Pocket Weather Meter. Model number 4300 is a hand-held weather instrument weighing only a few ounces and developed especially for the concrete industry.
By positioning the instrument 20 inches above the area that will receive concrete, you can record ambient conditions. This year, the manufacturer added Bluetooth technology to the handheld's capabilities. Contractors can now set up the unit onsite and monitor conditions on a portable computer or other device.
By setting up the unit on the jobsite before you bid, you can develop data by which you can estimate any weather-related issues. By estimating the concrete's placement temperature, you can use the instrument's software to predict the concrete's surface evaporation.
If you determine that the anticipated evaporation rates could exceed 0.20, you know that surface drying conditions are excessive. And you'll be in a position to better select any curing or treatment products.
This effort to gather pre-job weather measurement information should help you avoid unforeseen costs and delays, ensuring a profitable job.
To take a virtual tour on using the Kestrel Pocket Weather Meter model 4300, visit www.kestrelweather.com.
You can win a free Kestrel Pocket Weather Meter by entering the TCPuzzler contest. Visit THE CONCRETE PRODUCER at www.theconcreteproducer.com/tcpuzzler for information on entering.