5 Pavement Testing Techniques to Add to Your Toolbox
When it comes to our everyday lives, we often take the asphalt and concrete beneath our feet for granted. Yet, the quality and longevity of these pavements are vital for smooth and safe journeys. Pavement investigation techniques play a crucial role in maintaining the integrity of our roads. In this blog, we'll explore five essential methods used by engineers and researchers to delve beneath the surface and assess the condition of pavements. From cutting-edge technologies like laser profilometry and ground-penetrating radar to tried-and-true practices such as test pits, trenching, deflection testing, and core drilling, we'll uncover the tools and insights that keep our roads in top shape.
1. Laser Profilometry
Laser profilometry is a technique used for measuring surface typography. The method involves directing a laser beam at a surface and measuring the reflection of the laser using a detector. The reflected light is then examined to derive accurate measurements of the surface features such as height, depth, and shape.
In the pavement industry, laser profilometry is used to assess the condition of the road surface, and to pinpoint areas that require maintenance or rehabilitation. This technique can detect even the slightest variations in the road surface, such as cracks, ruts, and roughness.
Laser Profilometer
Laser profilometry is typically performed using a mobile device, such as a vehicle-mounted sensor or a handheld device. The laser sensor scans the road surface as the vehicle moves along the road, generating a high-resolution 3D image of the surface. Our pavement engineers use the Automatic Road Analyser (ARAN) which is a system capable of collecting detailed data at posted highway speeds. PMS houses two types of Automatic Road Analysers: the ARAN LRMS and ARAN LCMS.
a) The ARAN LRMS is able to measure surface texture and concrete faulting as well as pavement distresses such as cracking and rutting, while other on-board systems simultaneously collect the IRI (International Roughness Index) pavement roughness, all in a single pass.
b) The ARAN LCMS has the same capabilities as the LRMS. However, it differs in one unique way. The LCMS system is capable of automatically extracting crack data including crack type (transverse, longitudinal, crocodile) and severity.
2. Test Pits and Trenching
A test pit is a hole that is dug either by hand or with machinery to uncover what's underneath the surface at a specified depth.
Trenching is similar to test pits, but instead of a single hole, a longer trench is dug to investigate how the subsurface conditions vary across different parts of the construction area. This approach helps us spot changes in the soil composition over a greater distance.
Various soil samplers can be employed to collect samples from these test pits for laboratory analysis and visual assessment.
3. Deflections
Surface deflection measurements are used to evaluate the structural condition of flexible and rigid pavements by measuring the way the pavement reacts to simulated traffic loads.
The magnitude and shape of deflection is affected by various factors such as traffic volume and type, temperature, moisture and pavement structure. This can be evaluated using testing equipment like the Falling Weight Deflectometer (FWD).
The FWD is a non-destructive technique used to measure the deflection of the pavement surface under a controlled load, and the data obtained can be used to assess the thickness, stiffness, and strength of the pavement layers. Essentially, the FWD simulates the load impact like that of a heavy vehicle travelling on flexible pavement. This technique can be visualised in the diagram below.
The diagram shows the FWD measuring the pavement surface deflection at various distances from the load. If the deflection is too high, then it is an indication that the pavement is not strong enough to support the vehicle, resulting in premature pavement failure. The data of the deflection bowl is then used by asset managers to predict the life of the recently constructed or rehabilitated pavement.
Falling Weight Deflectometer
4. Core drilling
Core drilling is a valuable technique used to gather essential information about various aspects of pavement construction and composition. It allows for the measurement of layer thicknesses, assessment of crack type and depth, identification of stripping issues, and the detection of de-bonded layers. Additionally, core drilling serves as a means to obtain critical test specimens for various laboratory evaluations, including mix testing, binder grading, and the assessment of aggregate quality, contributing significantly to the overall quality control and performance assessment of asphalt or concrete installations.
5. Ground Penetrating Radar
In the pavement industry, the Ground Penetrating Radar (GPR) is widely used for locating utility lines, monitoring pavement and runways, locating reinforcement bars, changes in layer thicknesses and voids, as well as moisture determination.
Ground Penetrating Radar (GPR) is a radar system that is used to image the subsurface. The huge advantage of GPR is that it allows crews to safely conduct investigations in a non-intrusive way. It is quick to deploy and easy to operate. But have you ever wondered how GPR works?
Ground Penetrating Radar involves passing a transducer (transmitter/receiver) over the ground surface. The transmitter emits low powered radio energy and reflections from material boundaries and embedded features like metal or voids are recorded by the receiver. The results can be viewed on-screen and recorded to disk.
The sampling occurs so rapidly that the collected data that it essentially forms a continuous cross section, enabling speedy examination of thickness and condition over large areas. GPR works effectively on rough surfaces and through multi-layered media. However, penetration and resolution are impeded when ‘seeing’ through highly conductive materials such as wet clays and soils.
How the Ground Penetrating Radar works
Conclusion
As we wrap up our exploration of pavement investigation techniques, it's evident that maintaining our roads and pavements involves more than simply looking at the pavement with the naked eye. Laser profilometry, test pits and trenching, deflection testing, core drilling, and ground-penetrating radar allow us to see below the surface and ensure the safety and longevity of our paths. These methods, ranging from cutting-edge technology to traditional practices, collectively contribute to the well-being of our transportation networks.