Advances in concrete strength and temperature monitoring: what new technology can do for you

New innovations for monitoring concrete strength and temperature, as well as technological advances that make sharing this information easier, can help construction companies build faster while ensuring concrete quality and site safety. This technology offers multiple advantages over traditional concrete monitoring methods. Chris Bainter of FLIR Systems discusses some of the technological advances in the concrete industry and how they can benefit the construction industry by allowing companies to build faster while improving safety.

Engineers understand the value of being able to more accurately predict the compressive strength of concrete. Accurate estimations save time and money, as concrete is on the critical path of almost every project. With a better understanding of in-situ strengths, engineers can develop mix designs best suited for optimal strength gain, while at the same time producing a higher-quality product, potentially preventing cracks, delamination, poor performance or even structural collapses. These improvements can be achieved while at the same time reducing material costs.

Today, some concrete contractors rely on field-cured specimens to measure concrete strength for workflow purposes. These samples are cast in cylinders, cubes, or beams and cured on-site to try to duplicate the structures’ strength profile as closely as possible. The method relies on destructively testing a sample for strength estimation, but destructive testing does not accurately predict early-age concrete strengths. There are several reasons why: first, the cylinders have smaller volumes but larger surface areas, so they retain less heat. In addition, their temperature history may differ due to curing conditions, causing a different rate of strength gain. Finally, mistakes in how the cylinders are handled, prepared and tested can cause low failure strengths.

Furthermore, the construction industry often relies on traditional methods when required to monitor temperature in mass concrete pours. Specifically, thermocouples are frequently used for monitoring overall and differential temperatures. Thermocouples can become disconnected or damaged in the harsh construction environments. This loss of data is unacceptable and can be very costly.

Advantages in innovation

The good news is that many of the high-tech solutions to pitfalls of traditional monitoring methods are gaining acceptance throughout the construction industry. These new methods help improve quality control, speed time to completion, lower material costs and reduce labour costs.

The maturity method is a proven, nondestructive strength estimation technique that accounts for the effects of time and temperature on the strength development of actual in-place concrete structures. Using a sensor, the maturity method very accurately estimates the strength of an in-place structure by combining strength data from laboratory or field-cured cylinders with the temperature profile of the actual structure. The resulting strength data are available in real time, anytime during the curing process.

For this method to work optimally, many contractors monitor temperature using sophisticated embedded loggers, which use thermistors. Many thermistors now have the added ability to transmit collected data wirelessly. These fully embedded sensors help engineers meet very strict temperature monitoring specifications more easily, while using the concrete itself as a ‘vault’ to protect these critical data.

“We’ve always been able to measure temperatures, but that was at the very least inconvenient and in the worst cases even dangerous,” explains Jim O’Daniel of FLIR Construction Solutions, which makes concrete maturity solutions. “With the technology available today, you can just look at your phone or check your e-mail and know things are good.” Maintaining proper temperatures is critical when the least dimension of the pour is greater than 3ft or 1m, so they must be monitored and controlled to ensure quality concrete. Overall temperature is critical but so is differential temperature. When differential temperatures – that is, the difference between a core and a surface temperature, become too great (usually 35°F/20°C) – the risk of thermal cracking increases. With accurate temperature data, contractors can take action when needed and they are able to prove they have done the job right.

Many of the newer maturity and temperature loggers offer peace of mind by tracking time and temperature data as often as every minute over a 180-day period. They can ensure adherence to tough temperature monitoring specifications by logging critical data for any construction application and help construction engineers regulate thermal protection by measuring and documenting temperature profiles.

A new entry into the concrete solutions space is loggers combined with thermal imaging cameras. These cameras detect heat and display the levels as a range of colours on-screen while also providing temperature measurements. This technology is useful for comparing  surface temperatures to logged data, or for monitoring thermal blankets or formwork to detect heat loss.

“Combining thermal imaging of surface temperatures with data from within the concrete gives us a bigger picture. We can see how thermal insulation is performing and associate that data with logger readings,” says O’Daniel. 

The newest technology comes with a host of new software options, much of which is now cloud-based. The right software can help construction managers improve oversight by monitoring the entire maturity system – from anywhere, at any time – through the cloud. “Pushing data automatically to the cloud really is the key today. Engineers can make informed decisions quicker, they can be much more proactive and the result is faster, safer concrete construction,” explains O’Daniel.

The latest systems allow for automatic e-mail alerts on potential problems with strength, overall temperature and temperature differentials. This information allows construction managers to act quickly based on real-time data, rather than having to send workers to the site every six hours to gather required temperature information. Moreover, data on critical concrete strength and temperature data is stored safely in the cloud – ensuring its integrity while still giving everyone visibility.

Looking to the future

New technology is making it easier for construction companies to maintain critical rotation schedules by providing more accurate temperature data, real-time strength information and streamlined reporting and oversight. Construction managers can increase capacity and production by knowing immediately when the concrete is ready for the next phase of construction. At the same time, they can reduce the costs of energy consumption for heating, prevent project delays and cut overall operative hours – while increasing on-site safety and the potential lifetime durability of the concrete placement.

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