Monitoring positions in precast production

Maturix™ is a system for monitoring the maturity development in concrete elements in real-time. The strength is accurately estimated over time using the ASTM C1074 standard practice for maturity-based strength. This can be used to document that the temperature differences across a concrete element complies with the standards, or simply to detect the demolding time in a more accurate manner.

It is important, when considering how to use Maturix™, that the purpose of the monitoring is known, since this affects the positioning of the thermocouple during the curing cycle.

The flexibility of the Maturix™ allows for endless monitoring possibilities, but an example of two different monitoring philosophies can be given:

 

Monitoring slowest curing position

One of the most used monitoring philosophies is “Monitoring for slowest curing position” in a concrete element. The objective of this philosophy is to determine the strength development in the position of the element with the slowest strength and maturity development – and as a result of that, being able to know the minimum strength of the element overall.

This is relevant if you want to determine the demolding time of an element, since it will often be the minimum strength that determines whether the element can be removed from the mold or not.

The example can be illustrated using a standard wall with a door, see picture below.

This element will be cast with two lifts in the top of the element to allow for easy transportation of the element after demolding. The minimum strength requirement for the element for the lifts to stay in place is 15 MPa.

Maturix™ can be used to determine the earliest possible time for demolding. In the illustration, the green circles represent (1 + 2) two possible monitoring positions for placing the thermocouple during the monitoring.

When looking at which of the two positions will develop maturity fastest, it naturally depends on different parameters. The fastest developing position, will be the position that develops and maintains the most heat throughout the curing process. If you are not certain about which position it is, this can be investigated by placing a thermocouple in both positions.

Once the concrete reacts with water it will develop heat. Due to the concentration of mass, the thicker the concrete element (or the more material surrounding the position), the higher heat development – and as a result of that, the faster maturity development.

In the picture above, the heat concentration in the element can be seen. This shows us that position no. 1 will have a higher heat development than position no. 2, which means that the correct position for the thermocouple will position no. 2, when you are looking for the slowest curing position.

 

Monitoring fastest curing position

Another monitoring philosophy can be to monitor the fastest curing position in the concrete element. This can be helpful if an element has a very differentiated size – where a part of the element is substantially thicker than the rest of the element – or if the element is cast in multiple phases, where a second cast should be able to bind with the first cast. This will require a controlled curing of the first cast (not too fast) in order for the second cast to be able to bind to the first cast.

Using the same picture as above, the fastest curing position in the element is in the middle of the large section of the wall (position no. 1). The large amount of mass surrounding the point will cause the heating in the exotherm phase of the curing process to accumulate heat and reach a higher temperature than the outer areas of the element.

Positioning a thermocouple at position no. 1 will tell you the fastest maturity and strength of the element at this moment.

When considering positioning of the thermocouple, it should always be remembered what the result really shows – and what information you are actually searching for.