The “heat of hydration” is the thermal energy released when cement reacts chemically with water during the hydration process. This exothermic reaction is fundamental to the hardening and strength gain of concrete.
In small concrete samples like cube, this heat is quickly dispersed into the surrounding environment, preventing significant temperature rise.
However in mass concrete, the volume is large enough that the generated heat accumulates internally and gets entrapped, unable to escape the internal region, causing the core temperature of the concrete to rise, sometimes significantly above surface temperature.
As the time progresses the temperature in the core continues to increase, while the outer surface remains relatively cooler (or cools faster), a temperature differential or gradient develops between core and surface.
This gradient can trigger tensile stresses because the inner concrete expands upon heating while the surface remains constrained or contracts.
This difference in the expansion leads to the formation of the thermal cracks.The acceptable temperature difference between the interior and exterior of mass concrete is typically limited to a range of 19°C to 25°C. The specific limit can vary depending on the standards like ACI, Indian Standard Code, or aggregate type, and specific project requirements.
As per ACI 207.1R-05, mixture proportioning (cement content, use of supplementary cementitious materials, water-cement ratio), choice of aggregates, and admixtures are critical to moderating the heat of hydration and thereby controlling temperature rise.
For engineers, understanding the heat of hydration helps in anticipating peak internal temperatures, planning cooling or insulation strategies (pre-cooling, embedded cooling pipes, controlled curing), and selecting appropriate mix proportions to prevent thermal gradients and resulting thermal stress.
Mass Concrete temperature Monitoring system
Mass concrete temperature monitoring device developed by vedantrik technologies is an advanced temperature monitoring and data logging system specifically designed for mass concrete applications like raft, foundations, hot blocks and other mass concretes to prevent thermal stresses and micro cracking.
Wirelength Challenges in Mass Concrete Temperature Monitoring
In mass concrete applications, temperature sensors are typically embedded at multiple levels — the top, middle, and bottom of the pour — to accurately monitor temperature differentials during curing. However, in high-rise building foundations, the raft thickness can reach up to 3 meters or more, creating significant wirelength challenges.
As the sensors are placed deeper within the concrete, the distance between the sensors and the data loggers (which are usually installed at a controlled, accessible location) can exceed 5 meters. This extended wirelength can lead to inaccurate or higher temperature readings.
The commonly used RTD (Resistance Temperature Detector) thermocouples in concrete temperature monitoring are typically accurate only up to a cable length of approximately 5 meters. Beyond this distance, the increase in lead resistance can result in elevated or higher temperature readings. This is particularly problematic because the lead resistance is non-linear and not directly proportional to the cable length, making it difficult to apply standardized correction factors. Consequently, extended cable lengths introduce a significant source of error in temperature measurements.
But the device developed by vedantrik technologies for mass concrete temperature monitoring can give accurate temperature readings even if wirelengths are above 100 meters with accuracy of +/- 1 degree celsius.
The device logs temperature data at user-defined intervals, with a standard recording interval of 30 minutes. The system utilizes high accuracy sensors, which are embedded in the concrete, during casting and remain in place throughout the curing process.
These sensors feed temperature data to the device’s internal storage, which can be accessed later wirelessly using mobile phone or laptop via wifi, the device supports Wi-Fi connectivity, allowing users to access and monitor data in real time through a PC, laptop, or mobile device. By providing accurate and timely temperature data, the system supports informed decisions regarding concrete strength development, enabling optimized construction schedules, timely formwork removal, and improved quality control in mass concrete applications.
