Special applications for temperature measurement in asphalt paving

The asphalt and with that the temperature of our material starts at the mixing plant.

From there the material is transported with trucks to the jobsite. Depending on the paving mode they directly or indirectly unload into the paver's hopper or the hopper of a so called feeder machine (MTV = material transportation vehicle or a so called Shuttle Buggy). After paving process the mat is compacted to achieve the finished road.

Through the whole process chain of road construction the temperature of the asphalt will drop slightly. More or less depending on the used technics, materials and machines. Doing good here is very important for homogeneous surface temperatures and with that, as we know, for the quality of the road. Because of that the temperature should be measured and controlled at each step.

Following stations are considered:

• Loading the truck at mixing plant
• Transport to the jobsite
• Unloading to the paver
• Paving process
• Asphalt compaction

Truck loading

The mixing plant is where it starts when it comes to temperatures.

No matter in which market or country: The heat needs to be powered into the aggregates of the asphalt. Depending on the material type and stone dimensions this is more or less. Despite this it is very impressive that modern asphalt mixing plants (some are powered by gas, others by carbon dust) have heating power up to 30MW (thirty Mega Watt!). These are 30.000kW of heating power. Compared to a normal hair blower of 1kW quite alot and we should keep in mind that we try to save energy wherever we can.

This power for heating can only be aplied once at the mixing plants. Even the huge Shuttle Buggies and feeder machine can only heat a very small amount in addition. Most of the time the heating is only to prevent the bitumen to stick to the metal. Modern mixing plants already do have several temperature probes for sure inside. But most of them do not have a measurement when the material is loaded to the truck. This should be the first point where our temperature measurement starts.

Transport to the jobsite

Directly after loading the truck we can see temperatures vanish from the asphalt. The truck's metal is heated up and acts like a huge heat conductor. All surfaces of the asphalt will cool down. Some more, some less. Depending on insulation and ambient conditions. This way the temperature segregation starts.

From here on there are any factors and conditions that may lead to more or less segregation. Only by measuring and reporting the temperatures we can learn how to improve this process chain. And depending on where we have to measure we also have to find the right method to do so. Not every measuring principle is working good. This is easy to see if looking to the thermal Pictures and thinking of how normally the temperature is measured by probes that are stick into the asphalt. Even though different measurement types are not directly comparable. So there are alot of things that need to be considered.

Unloading to the paver

Knowing that the paving itself as well as unloading of the material differs in various ways depending on countries, requests and demands it is not easy to measure the temperature at this moment when material gets from the trucks to the jobiste.

First variable is the trailer of the truck itself that varies. Others are the different hopper or feeder machines. Even totally different ways of paving like "Windrow Paving" in the US will need special ways for measuring. So, there is no universal or best way for this.

Paving process

Measuring temperatures in-situ while paving is more comfortable again because the material is remixed by the auger for example. By that the temperature can be monitored before the mat is paved.

Depending on the technique used this can be achieved by single IR sensors together with the MOBAmatic II or the Pave-IR system of MOBA. Here Pave-IR shows all of its benefits compared to single IR measurements or infrared camera pictures. It will deliver a detailed documentation of the thermal profile together with useful additional data.

With a "picture" (better a comprehensive documentation) like that we now see what all steps before can result in. Stepwise we can learn by that and turn screws that influence the thermal segregation of an asphalt mat. We know how important not only one temperature of the asphalt is but even more the homogenious surface of it should be the goal to achieve an uniform compaction. This way we will get the base for a long lasting road of high quality.

Asphalt compaction

During the paving jobsite the asphalt's compaction is one of the last steps and with that one of the most important ones. Even though the uniform temperature of the mat is the base for a good and even surface and compaction value the temperature window depending on the asphalt type needs to be correct when the roller is going over. For that the temperature information is another very helpful value for the roller driver. Again there are various ways to achieve these measurements and present the readings to the driver. Also here the best solution might vary from market to market and is depending on the driver's needs.

Knowing this, open and specified interfaces as well as easy adaptable systems are important. For both, systems like Pave-IR (for the paver) and MCA (for the roller) are prepared to help operators in a meaningful and easy way.