During the winter months, when snow has taken over every inch of not only your driveway, but also your jobsite, it can be incredibly frustrating to carry on with regular construction operations.
If you are working on a concrete structure, the process of monitoring temperature and strength of your in-situ elements becomes even more time-consuming in these weather conditions. It is during these months of dropping temperatures that monitoring your concrete becomes much more critical as the rate of strength development decreases and durability can be compromised. For this reason, accurate and consistent readings of your concrete elements are important so that the quality of your structure is optimized.
What is Cold Weather Concreting?
In the American Concrete Institute (ACI) 306: Guide to Cold Weather Concreting, “cold weather” is defined as three or more consecutive days of low temperatures, specifically ambient temperatures below 40°F (4°C) and air temperatures below 50°F (10°C) for more than any 12-hour period. To ensure proper strength development in these ambient conditions, some placement specifications include;
- Concrete temperatures must be maintained higher than 40°F (4°C) for 48 hours after a pour.
- All concrete surfaces must be protected within the first 24 hours after being placed to prevent freeze damage.
- Concrete temperature cannot reach freezing levels before reaching a specific strength (3.5 MPa/500 psi) or the overall structure will have a reduced strength.
Techniques to Improve Strength Development in Cold Weather
- Protective insulation blankets
- Insulated formwork
- Heaters and other heat sources
- Optimize your concrete mix
Monitoring Concrete Strength in Cold Weather
The most common method for monitoring the strength of in-situ concrete is the use of field-cured cylinders. These samples are cast and cured according to ASTM C31 and tested for compressive strength, usually by a third-party lab, at various stages. Usually, if the slab has reached 75% of its designed strength, engineers will give the ‘go-ahead’ to their team to move on to the next steps in the construction process.
However, when pouring in cold weather, ACI 306 specifically recommends not using this method as field-cured cylinders “can cause confusion and unnecessary delays in construction”. This is largely because it makes it difficult to maintain the cylinders in the same conditions as your structure.
It is, therefore, recommended that other in-place testing methods, like maturity testing, be used for monitoring concrete strength.
What is Concrete Maturity?
The maturity method or ASTM C1074: Standard Practice for Estimating Concrete Strength by the Maturity Method, is a non-destructive testing technique. This method allows you to estimate the early-age and compressive strength of in-place concrete in real-time. It is based on the principle that concrete strength is directly related to its hydration temperature history. In other words, maturity is a value that represents the progression of concrete curing. A mix calibration is required to implement this concept in a project. The goal of the calibration is to determine a relationship between maturity and strength for a specific mix.
This method allows you to eliminate field-cured cylinder testing and switch to wireless sensors for both temperature and strength monitoring. Wireless sensors, like SmartRock™ are placed within the concrete formwork, secured on the rebar, before pouring. Temperature data is collected by the sensor and uploaded to any smart device within an app using a wireless connection. This information is then used to calculate the compressive strength of the in-situ concrete element based on the maturity equation that is set up in the app. This strength data is considered to be very accurate and reliable as the sensors are subject to the same curing conditions as the in-situ concrete slab.
Using Wireless Concrete Maturity Sensors to Measure Strength
When you use SmartRock™ on your jobsite, you get temperature and strength data uploaded on your mobile device every 15 minutes. This is done using a wireless signal, meaning you have to be onsite to collect this information. However, it is much easier than having to search for wires under blankets to collect data with a logger, if you were to use wired sensors. This also improves safety standards on your site as wires won’t get in the way of other operations.
Equipped with real-time results, contractors can improve the heating process, decrease energy costs, and save time in their project schedule by knowing when to move on to subsequent construction operations, such as; formwork removal or post-tensioning.
Remote Monitoring with SmartHub™
The main limitation of the maturity method is the maximum allowable distance between the sensor and the surface of the concrete. Since concrete can block wireless signals the sensors usually need to be placed within a certain distance from the surface to ensure connectivity. With SmartRock™ that distance is up to 26 feet (8 meters).
However, with SmartRock’s latest feature, the SmartHub™ remote monitoring system, you no longer have to worry about being onsite to gather this important data. SmartHub™ was developed to help users gain access to their concrete data at any time and in any location.
The system works by automatically collecting concrete temperature and strength data recorded by your wireless SmartRock™ sensors and uploading it to the Giatec360 cloud dashboard via LTE/Wi-Fi connection. Real-time data is then synced to your team’s mobile devices, allowing you to always know the temperature and strength of your concrete. With the Hub, SmartRock™ user are therefore able to eliminate unnecessary time, money, and labor associated with collecting and analyzing data.
Access Your Concrete Data 24/7 With SmartHub™ in Three Easy Steps
1. Install the Hub
As a rugged, waterproof design, the SmartHub™ can withstand any weather conditions. All you have to do is secure the device on your jobsite.
2. Open the SmartRock™ App
On the tablet provided, open your SmartRock™ app and sign in with the Hub user that can be created on the Giatec360 web-dashboard.
3. Get Real-time Results
Once logged in, the SmartHub™ will automatically scan your jobsite for SmartRock™ sensors and collect temperature and strength data which are then uploaded to the Giatec360 cloud and synced to your team’s mobile app.
Optimize Your Cold Weather Concreting Project Schedule with SmartHub™
When working in cold weather conditions, the faster you can gather concrete strength data, the better. With a remote monitoring system, like SmartHub™, there is no need to visit the site to get this data, it is sent directly to your mobile device in real-time. You can set up the Hub and not have to worry about when you are going to get concrete strength data.
With the Hub’s smart alert system, users can set up notifications to let them know when their concrete has reached specific temperature gradients or strength thresholds. This critical information helps optimize project schedules and identify any problems with the curing process, such as a broken-down heater and a drop in temperature. With the SmartHub™ remote monitoring system you can therefore make quick decisions immediately before they result in delays on your project, ensuring your jobsite it faster, safer, and more efficient.