Transportation
PAVE-IR thermal IR profiler
PaveScan RDM asphalt density assessment tool
quality assurance engineer, who maintains that there are numerous problems with random testing. It is not suitable for heterogeneous ma- terials and will not find defects on paving projects. Giessel believes the method is based on two false premises. The first is the assumption that soils and other road construction materials will fall on a “Gaussian” distribution (a normal curve), which he said they almost never do. The second false assumption is that we should care most about the average density values one gets from random testing. This is just not so, Giessel said, “Random sampling is a really good way to get the average, but when you are doing one test that represents one square foot every 500 tons, there are thousands or hundreds of thousands of square feet we have not even looked at. Also, the average spot is never what gives us a problem or a failure on the road — it is the weak spots. Random testing never finds your low spots and your weak spots so there is little to no probability of locating pot-hole size defects.” Replacing the status quo Giessel has been challenging the two false premises in recent years and became a firm believer in replacing the random sampling/statistical ap- proach with continuous, full-coverage testing methods. The system he favors uses three components: IC, a paver-mounted IR thermal profiler/ scanner, and GPR rolling density meter. With IC, compaction rollers are equipped with accelerometers and computers that measure surface density and rebound, or relative stiff- ness. This is related to the materials’ Resilient Modulus, a measure of material stiffness that is used for designing traffic loads. IC offers geo-located data, continuous, full-coverage real-time compaction of the entire hot mix asphalt mat, along with temperature mapping at the time of the roller pass. Next is an IR thermal profiler mounted on the paver, which provides a continual map of the temperature of the asphalt as it is laid down right behind the paver. The thermal IR scanner provides geo-located data, a complete map of asphalt mat surface temperature that is viewable in real time, and calculates the degree of thermal segregation every 150 feet, providing a permanent temperature record.
The Alaska Department of Transportation & Public Facilities (ADOT&PF) is on the front line when it comes to promoting new tech- nologies that give them continuous, full-coverage asphalt pavement density testing for road paving projects. Unlike traditional random sampling, continuous testing uses multiple inputs to “look” for failure zones and has a high probability of detecting defects before they lead to premature failures. The system they opted for combines intelligent compaction (IC), a paver-mounted infrared (IR) thermal profiler/scan- ner, and ground-penetrating radar (GPR) rolling density meter. Now, ADOT&PF is moving toward a system that will tie project acceptance to data from this system. They plan to offer bonuses for increasing the asphalt compaction averages — and require remediation for compac- tion below the standards. For the last 40 years, state departments of transportation across the United States have been basing quality measurement testing for road paving proj- ects on random sampling of materials. For example, one lot of asphalt is 5,000 tons, which is divided into 10 sub lots of 500 tons each. Quality assurance (QA) personnel use a random number generator to select where each sub lot would be sampled while placing the mix on the grade to check for oil and aggregate gradation. They then randomly select a separate location to take a core in the paving mat and at any longitudinal joints between two lanes. QApersonnel then use statistical methods on these random samples to generate information on the theo- retical distribution of road paving material properties, and to calculate the average density of material placed. This method does not sit well with Rich Giessel, ADOT&PF statewide ADOT&PF’s continuous, full-coverage asphalt testing system detects pavement defects before they lead to premature failures. By Rob Sommerfeldt Sampling paradigm ensures pavement quality
53
march 2018
csengineermag.com
Made with FlippingBook Annual report