Concrete Temperature Testing Now Mandatory for Certified Pre-Cast Plants

Why Temperature Monitoring in Precast Concrete is Important

Weather fluctuates, and especially in regions where you can go from 25 degrees Celsius one day, to minus 2 the next, people often struggle with dressing appropriately to maintain a comfortable level of heat. Not only do we have subjective experiences of feeling ‘hot’ or ‘cold’, temperature fluctuations have an objective and observable effect on our bodies as well. These physiological symptoms are due to the fact that temperature is not a simple, one-dimensional measurement in units of degrees but rather is multi-dimensional, affecting properties such as density, volume, pressure, chemical reactions and more.

Just as with a healthy body wherein appropriate internal temperatures are required to be maintained, high quality pre-cast concrete relies on appropriate curing temperatures. If not properly cured, then the concrete is susceptible to thermal shock or thermal cracking and the entire structure will in turn suffer.

Controlling temperature is important for fresh concrete as it can affect cement hydration reactions, setting time, compressive strength gain and workability. Its temperature depends on a number of factors such as other materials included in the mix, the ambient temperature, the mixing equipment and forming equipment. The temperature of these items in comparison to the concrete itself is known as temperature differentials and if not properly corrected for, is said to be the leading cause of thermal shock and cracking.

For precast plants that are located in colder climates, the following should be complied to avoid thermal shock and cracking:

i) Control maximum internal temperature
ii) Insulate the surface of the concrete for gradual cooling
iii) Cover precast products as a means of reducing temperature differential

For plants in warmer climates, the following is suggested:

i) Minimize the temperature difference between the concrete form and concrete

ii) Use supplementary cementitious materials to help control the temperature

iii) Spray water on aggregates to control internal concrete temperature and maintain appropriate moisture content

As of January 2017, the 12th Edition NPCA QC Manual QCM-001, Rev. 3, 1-1-17 now makes it mandatory for precast plants to measure concrete temperature in order to be certified manufacturers. As stated in 4.5 CURING CONCRETE, 4.5.1. General, “The highest internal concrete temperature shall be determined by testing”. Further, under 4.5.4 Plant Requirements, it is now mandatory that one must verify that concrete does not exceed a maximum temperature, per Section 4.5.1, for the highest heat generating mix designs, largest concrete mass and hottest curing conditions.

Giatec Scientific Inc. offers an advanced, wireless system for temperature and maturity strength monitoring that can provide the end user with the information they require to meet the above demands and to avoid structural failure due to thermal cracking and shocks.

The SmartRock2 provides real-time analysis of temperature and strength in situ. By embedding the wireless sensors into the concrete by connecting its metal wires together around the rebar, you can measure the temperature development of fresh concrete to the hardened stage at regular intervals. Having this information ensures optimization of concrete formulation, optimization of the construction process and cycle-time optimization.

The wireless capabilities of the SmartRock2 means that wires are not required to run through the site which could be easily damaged or cut off due to high traffic on site or poor practices demonstrated by workers. The SmartRock2 also utilizes Bluetooth technology, mobile apps and easy data sharing. Further, using a free app-based program on your android or tablet allows for features to be easily added with free software upgrades as well as a database of mix calibrations. It also eliminates the need to upload your data at an off-site location – saving time and resources.

Sources: http://precast.org/2016/07/thermal-shock-concrete/
Image credit: Steve Wijangco at NABA Group