More than a century ago, essayist and writer Charles Dudley Warner said, “Everybody complains about the weather, but nobody does anything about it.” Concrete producers and their contractor-customers can relate with the sentiment as they strive to deliver a high-quality product in all kinds of weather conditions.
But it takes a wily professional to show that perhaps producers can do something concrete not only about product quality, but also about climate change.
On a trip to Phoenix last summer, Frank Kozeliski, a materials engineer from Gallup, N.M., and a TCP Industry Influencer in 2008, performed a simple test to demonstrate concrete's potential role in preventing the urban heat island. “Asphalt surfaces are hotter than portland cement concrete surfaces,” reports Kozeliski. “I never realized how hot the Phoenix metropolitan area really was, so ever the engineer looking to document a problem, I used my infrared thermometer to measure surface temperatures of various parking lots.”
While his wife was in the shops, Kozeliski remained in his pickup truck with the air conditioner on to survey various surface temperatures. To his amazement, asphalt pavement surface temperatures averaged 146.5° F. He then checked the concrete sidewalks, curbs, and gutters, recording temperatures averaging nearly 30 degrees cooler. The thermometer located in the rearview mirror showed an ambient temperature of 112° F, while the water in the nearby fountain was 93° F.
Kozeliski continued his experiment over next few days in the heat, even asking his wife to open her window at a stop sign to check the asphalt surface temperature. “We saw an average 15-degree difference between the surface temperatures of the asphalt pavement and nearby concrete sidewalks,” he said.
Handheld temperature sensors can measure concrete's contribution in reducing the heat island. But producers and contractors should also be aware of emerging technologies that can play important roles during the pour.
The redesigned Kestrel 4300 Construction Weather Tracker is a portable instrument that enables QC technicians to monitor environmental conditions at a pour. This version is now equipped with Bluetooth technology, enabling measurements and data to be logged directly into a laptop or other receiver.
Some producers have used the real-time capability to connect directly to their batching system to help monitor concrete mixing temperatures. The new unit was unveiled at World of Concrete in February.
The Kestrel Pocket Weather Meter is a complete hand-held weather station, capable of measuring every major environmental condition at a jobsite, including barometric pressure, altitude, density altitude, temperature, humidity, wind speed, wind chill, dew point, wet bulb temperature, and heat stress. It also offers a crosswind calculation feature.
The 4300 model was custom configured for concrete construction. Engineers have highlighted the key ambient measurements with which producers and contractors can mitigate the occurrence of plastic shrinkage by properly assessing the weather and fresh concrete conditions. Evaporation rate is a critical environmental indicator that concrete contractors use to avoid plastic shrinkage cracks in concrete installations, especially flatwork. Plastic shrinkage cracks occur when the surface of the concrete dries too quickly and shrinks before the bed has cured enough to resist cracking.
The new Bluetooth feature also enables producers to be proactive in the jobsite prep. By positioning the instrument 20 inches above the pour, technicians can roughly predict wind and temperature patterns. By estimating the concrete's placement temperature, they can use the handheld's software to predict the concrete's surface evaporation. If your predication determines that the anticipated evaporation rates could exceed 0.20, technicians can alert the contractor that surface drying conditions are excessive.
And contractors can be in a position to better select any curing or treatment products after the pour has been made. Contractors' knowledge of the jobsite's relative humidity is important when selecting coating and curing materials. When the contract specifies a nonacrylic sealer or coating, contractors should monitor relative humidity. Manufacturers of these products have published relative humidity numbers for application purposes.