One of the most crucial steps after a concrete pour is to consistently track the temperature. By monitoring the temperature, you will be able to create an optimal curing environment, which will improve the overall strength of your concrete. Maintaining temperatures according to ACI 301-16 standards is also critical for the success of the hydration process. Therefore, before you get ready for your first pour, you need to decide what concrete testing equipment you will use to measure the in-situ temperatures of your concrete elements. This decision will be even more important if you are working on a mass concrete element or in extreme weather conditions. By having a plan and keeping temperatures consistent, you can improve the overall durability of your structure and reduce frustrating thermal cracks.
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When You Need a Thermal Control Plan
If you are working on a mass concrete element, it is essential to have a thermal control plan. Because of the mass effect of these projects, the concrete core can have a high temperature, while the surface tends to be cooler as it is exposed to the external environment. If the temperature differentials are too high, the tensile stress of the concrete will exceed its tensile strength, leading to cracks. A thermal control plan considers things such as the heat output of the concrete mixture, sets a maximum temperature at placement, and explains how you are going to limit risky temperature differentials.
Another situation that requires close temperature monitoring is a cold weather project. Similar to mass concrete, extreme temperatures increase the risk of thermal cracking. Insulation and cooling pipes are two examples of how you can maintain a consistent temperature, but it is important to ensure you are heating and cooling the correct amount. Otherwise, your efforts will not be successful.
Pros and Cons of Concrete Testing Equipment
Options for monitoring concrete temperature include thermocouples, wired temperature loggers, wired concrete sensors with an external wireless transmitter, and fully embedded wireless concrete sensors. Here is a brief overview of each option, as well as the pros and cons to help you with your planning.
A concrete thermocouple consists of two wires of different metals connected at one end to form an electrical junction. They are purchased in a bundle which is then cut into custom lengths based on the distance between the location of where you want to monitor the temperature of your slab and where the measurement equipment is placed. At one end, the two thermocouple metal wires need to be twisted together and at the other end, the two wires are connected to a plug. The wires must always stay connected to the external device, and this is usually where the measurements are displayed. Once the measurements are completed, the unit can be connected to a computer to download the data.
- This method is relatively inexpensive
- As it is an older and less complicated method, it requires less training
- Time-consuming to install and use
- Low accuracy rate
- Some require manual data-analysis, which is labor-intensive
- Wires may be damaged or cut while on-site
Wired Concrete Temperature Loggers
Wired temperature loggers have an electronic circuit board that contains a coin-size battery with an onboard thermistor for temperature measurement. The measurements are recorded and stored on this circuit board at pre-defined intervals. After concrete pouring, users can connect their hand-held unit or data logger to the end of the wires to download the recorded temperature values.
- More rugged than thermocouples and less prone to damage
- The external logger is only used to download data, so it is not regularly exposed to potential damages
- Limited-shelf life
- Like thermocouples, the wires must be properly labelled so they do not get cut or lost
- Difficult to install
Wired Concrete Sensors with External Wireless Transmitter
Wireless data transmitters were developed to remove the hassle of having to collect data with an external device and using a computer to download it. These external units are connected to the end of the wires coming out of concrete to store and transfer the temperature measurements over a wireless network.
- data analysis can be done automatically on the cloud to generate custom alerts and notification for project managers and superintendents even when they are not on the jobsite
- the wire connection to the external unit is still prone to cuts
- The wireless unit can be damaged in a harsh construction environment
- It is a complex system and can be challenging to install
Fully Embedded Wireless Sensors
These are self-contained wireless concrete sensors and loggers that are fully embedded in the concrete. The temperature measurements are stored on the sensor, and that data can be downloaded through various wireless communication protocols. The way the data is downloaded varies between products. Some options require you to be on-site to download your data, but if you have a wireless local hub, you will be able to access the data without even visiting the jobsite.
- Unlike wired systems, the sensors are not prone to potential damages of the site
- The data is securely held on the sensor inside the concrete and can be downloaded with confidence at any time
- the installation and data collection are relatively simpler and faster
- If you have a wireless unit, you do not need to maintain external units, which could lower your overall cost compared to the wired sensor
- the initial purchase cost of these embedded sensors is higher than wired sensors/loggers
- the wireless signal from these sensors can only transmit data through a couple of inches of concrete. So, for deeper locations, a temperature measurement cable is used while the wireless sensor’s transmitter is placed inside the concrete typically on the rebar below the concrete surface.
If you decide to go with a fully embedded wireless sensor, there are several commercial options. These options vary in price, accuracy, and ease of use. Giatec is proud to offer SmartRock, the leading wireless concrete sensor for measuring temperature and strength. The real-time data from SmartRock allows you to decide exactly when to take measures to cool or heat your concrete, which will help you build structures faster, safer, and more economically. Even better, by adding SmartHub, you can eliminate the hassle of visiting your site to retrieve data.
Beton Consulting Engineers
*Editor’s Note: This post was originally published in May 2020 and has been updated for accuracy and comprehensiveness.