Some general information about temperatures

One very important factor for the quality of a road is the temperature of the asphalt with which the road is build. Since a long time this is not a secret anymore but experiences from the last years are showing correlations between some of the other important factors in road building (like compaction, evenness, segregation, etc.) and the temperature. Especially in relation to a homogenies thermal distribution of asphalt. In Germany authorities and construction companies start to think about finding a way to analyse the quality of a job and the material not only by one temperature measurement of the delivered material but even more by analysing the thermal segregation of the whole job. By this we can learn a lot to understand the whole process in a better way and new possibilities of improving the quality of it arise.

Measuring temperature is not new at all. Depending on what and why should be measured there are several ways and solutions to achieve it. Mostly, the temperature can be taken by a probe that gets into contact with the material you want to measure. But it is also possible to measure contact-free by using the heat radiation of a material. This radiation is the infrared emission of its surface. Both methods have advantages and it is depending on what, how and where temperature needs to be measured to determine which method works best.

An essential part of asphalt is its binder bitumen. Bitumen itself is a very temperature dependant material and only with the help of this a good road quality can be achieved. One of the main reasons why it is that important to take care of the asphalt material temperature. On one side it is not good to have asphalt with temperatures too low, on the other side too hot temperatures can have a bad influence, too. So, depending on the material type and its consistence it is important to work with the asphalt within a certain temperature window.

Source: http://www.familie-und-tipps.de

Here are some crucial factors with most influence to the temperature of asphalt:

• temperature at mixing plant
• material transport to jobsite
• material transport on jobsite (truck to paver)
• material transport inside paver (hopper to screed)
• ambient conditions (for sure)
• surface / layer course
• layer thickness and material itself

Source: http://de.wikipedia.org

Unlike a common opinion the paver’s screed heating cannot really have an influence to the asphalt temperature itself. In a modern mixing plant the power for heating the stones/aggregate can reach up to 30MW. In relation to only some kW powering the screed heaters (by gas or electricity) it is only possible to “smoothen” the surface and prevent the asphalt from sticking to the metal. But on the other side a defective screed heating can lead to a rough surface that can cause future potholes and cracks.

Source: http://www.schaumasphalt.info

Current efforts in temperature measurements are very much depending on countries. But even inside a country it may vary. Here are some examples from Germany:

Source: http://assets.knowledge.allianz.com/

Mixing plant

• temperatures taken during mixing internally
• some plants take temperature right during loading the truck
• no standard in taking these temperatures nor a standard of handing this information to the jobsite

Material transportation

• until this year only manual measurements on the jobsite (by some companies)
• no standard, no measurement on the truck itself or when unloading
• based on authorities request temperatures of probes/samples are taken

Source: http://tti.tamu.edu

During paving

• single measurements by probe are taken during paving (by some companies)
• no documentation needed
• no standard procedure existing

Before/during compaction

• temperature only taken with some compaction assistant systems
• normally no information about material temperature available for roller driver

Source: http://tti.tamu.edu

When speaking about temperature measurements during paving you can often hear following feedback:

“What’s the benefit of this? When I am measuring wrong temperatures it is too late. The asphalt is laid.”

If we would agree to this we would not have any reason to measure at all. Because even if you cannot influence it directly it should be a

strong argument to make it better and to improve the process with next jobsite. Furthermore people who know how to look at the real-time data are

already able to optimize screed heating or the auger speed and height for example.

If this understanding is existing the feedback changes to:

“We can now see what we only could guess before.”

“It is a great tool to improve the whole paving process sustainable and get a better road quality on the long run.”

“It is offering a new way to document and analyse the work that has been done.”

“Using Pave-IR Scan already results in continuously good asphalt temperatures delivered by the mixing plant.”

The old guiding principle proves to be true again:

Before you can improve something, you have to measure the current situation.