Rutting of Asphalt Pavement

Posted: August 26th, 2021

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Rutting of Asphalt Pavement

Background Information

Definition of Rutting

Rutting is a collective term used to describe a permanent deformation in an asphalt pavement surface over time, which is generally presented by the wheel paths being engraved in the road. Asphalt pavements are flexible, and this is depicted during the summer months when the ring binders of the older asphalts begin to stick on the shoe soles (Chakroborty et al. 257). Rutting occurs as a result of deformation or consolidation of pavement layers caused by insufficient pavement thickness, weak asphalt mixtures, and lack of compaction. Illinois Department of Transportation (IDOT) has specifications on asphalt road design, which engineers should adhere towhen developing construction or implementing maintenance to prevent rutting (Pavemen et al.58-65). These guidelines regulate the development of the asphalt roads on the thickness of the base, aggregate content of the hot mix asphalt, and how the tarmac is rolled. Hence, it is crucial to maintain a firm and robust sub-base in asphalt construction. In this way, it will help minimize the occurrence of rutting as it provides the primary foundation on which the road is built.

Why is Rutting an Issue?

Weight administration and the number of asphalt rollers should be adhered to, which can be achieved by the use of GPS systems and sensors in the rollers. As such, the hot mix asphalt (HMA) should be three to four times to withstand the temperature of the HMA that has to be set approximately 175- 320 degrees Fahrenheit (Kandhal, Prithvi & Cooley 24). Such conditions would guarantee adequate compaction. Temperature requirements should also be observed during compaction when forming the sub-base as improper temperatures cause surface degradation. The asphalt mix should also be mixed thoroughly in appropriate proportions to strengthen the road internally(Koch et al. 352). It makes the road to permanently resist deformation as a result of stress from loaded vehicle tires. Fine aggregate and angular aggregates can also be added to the mix, which increases the friction, thus enhancing the combination and resistance of asphalt against rutting.

Moreover, precarious conditions can occur on the roads due to rutting as the depressions can hold water, causing hydroplaning, which lead to vehicular collisions(Koch et al. 352). The high costs of replacing such ways result in an economic loss. The reason is that repairing roads due to rutting usually involves cutting the section of the road and replacing it with a new one. In some cases, it consists of replacing even the sub-base. More so, rutting leads to potholes and cracking on pavements, especially when the sub-base mix during development was poorly done (Chakroborty, et al. 256). As a result, this further increases substantial maintenance costs. Therefore, engineers should adopt compaction technology, observe the set standards in constructions, and ensure quality control to avoid the costly effect of ruts.

Types of Rutting

There are four types of rutting caused by overstretching the underlying sub-base layers of pavement, as discussed in the following sections. Overstretching leads to overstressing of the existing state of the structure, which eventually results in insufficient thickness from the power of the sub-base materials (Mirzapour et al. 1). As such, the moisture can permeate into the foundation, thereby further weakening the sub-base layers. Thus, coupled with repeated traffic over the structure, it becomes permanently deformed.

Mechanical Deformation

Mechanical deformation is also referred to as subgrade displacement of the asphalt pavement. It results from consolidation in the base, sub-base layers. It is characterized by alligator cracks in the asphalt roads (Mirzapour et al. 1).Mostly, it occurs due to inadequate mechanical structural capacity or insufficient compaction of the subgrade layers of the pavement.

Plastic Deformation

It refers tothe deformation of the asphalt mixes near the pavement surface. Usually, it is characterized by the formation of a depression at the center of a road (Mirzapour et al. 3). As such, it causes sides of the rut because the structural material is squeezed out on both sides from under the way(Mirzapour et al. 1).Plastic deformation emerges due to high road temperatures, particles, and poor quality of design mixture, which lowers the mat stability.

Consolidation Rutting

Consolidation rutting is caused by insufficient compaction of the mat during construction or from an inadequate sub-base design mixture. A few rollers can cause consolidation rutting (Kandhal, Prithvi & Cooley 54). This is especially when asphalt pavement is subjected to material cooling before achieving the target density and high fluid content (Mirzapour et al. 1). Once construction is completed, traffic condenses the mat on the wheel path, thus forming a single basin-shaped rut on the asphalt road.

Pavement Surface Wear

It is the actual wearing of the surface particles by traffic due to studded tires. It typically occurs on rigid pavements(Mirzapour et al. 1). It is because of the damage of surface aggregate and impairment of asphalt pavements due to moisture damage, especially frominadequate drainage systems on the roads.

Causes of Rutting

Rutting is caused by several factors, which include improper asphalt content or excessive asphalt, moisture susceptibility, inadequate mix, and structural design for carrying the particular load. The following discussion discusses each of these factors.

Improper Asphalt Content/Too Much Asphalt

Proper hot mixed asphalt layer thickness and adequate contact pressure should also be thoroughly checked in the construction of asphalt pavement. A thicker layer is better as it will be able to resist rutting as the segment is stiffer(Koch et al. 352). The moisture in the asphalt content and poor compaction during construction also lead to rutting. A weak sub-base is susceptible to higher strains from traffic loading, thus a higher possibility of rutting. The provision of weak clayey subgrade layers leads to corrugation at the surface, increasing groove at the surface, and an upsurge in roughness.

Moisture Susceptibility

Inadequate drainage systems n rainy seasons, make water from entering the road from the sides and the top leading to rutting (Chakroborty et al. 32). Moisture content is retained on the pavements, especially if there is an open bituminous layer. Thus, the top layer is detached from the lower tiers.

Inadequate Mix and Structural Designs to Carry Loads

When mixing the tarmac, all factors should be mixed using the ideal quantities to ensure rutting does not occur. When the temperature of bitumen mixes is not appropriately maintained, it can lead to pavement failure due to overheating. In this case, the binding property of asphalt is reduced (Chakroborty et al. 32). Equally, when the temperature of the bitumen mix is lowered,the compaction will be poorly affected, thus resulting in longitudinal corrugations.

Rut Measuring Devices

Regular data collection on road conditions is crucial for maintaining the value of the asset and for proper monitoring. The data collection involves use of traditional and modern techniques (Hu et al. 132). The conventional methods include the manual collection of data. These are methods for conducting visual assessments of the pavement conditions using a ruler and either a straight edge or a wire (Koch et al. 352). It is a simple approach to use. However, the main challenge is that it may result in irregular readings from broad intervals or large-scale measurements. Thus, the weaknesses in the traditional systems led to the advanced developmentapproaches, which are friendly and reliable to use.

           Modern data measuring devices can use ultrasonic, lasers, and optical devices. The use of the ultrasonic involves having sensors at nearly 100-millimeter intervals and measuring up to 3 meters across the pavement. The measurements are done in an environmentally protected housing. Besides, the use of Point Lasers is crucial in giving the point elevation by the simple use of a 3-point laser scanning. The method is faster than the use of ultrasounds in data collections as the transverse profile recording by point lasers is done at intervals from 10 mm (Firoozi et al. 17). Optical methods are another automated method that uses transverse profile digitized images for analyzing and estimating rut depths. The approach involves using flat planes of laser lights that are shone onto the road being measured with a camera looking at the resulting line and recording it as raw data (Chakroborty et al. 32). Another method is the optical approach, which often involves the use of the instantaneous profile laser scanner. It is applied in instantaneously measuring the heights of the rut, where it results in the laser creating bright lines on the surface of the soil. The laser also provides measurements for a continuous profile. Question 5: Test Methods for Rutting Evaluation

Test methods that are used in characterizing the permanent deformation responses of asphalt pavement materials are classified as fundamental, empirical, and simulative tests. The following discussion examines each of these classifications.

Fundamental Tests

The use of fundamental tests involves the application of triaxle and uniaxial approaches. The methods include conducting creep tests by applying static loads to HMA specimens. Afterward, permanent deformations are measured (Miljković et al. 409). The creep tests can be done in confined and unconfined modes. The loads’ tests in this method are more sensitive than using creep tests to determine the HMA mix variables.Further, the Direct Shear Test is used in the prediction of rutting by measuring the shear strength of properties. It involves shear loading tests to determine HMA shear characteristics.  Also, the shear is repeatedly measured at constant height teats, uniaxial strain, and stress ratios (Mohammad et al. 2418). Here, Superpave shear tester-shear dynamic modulus is used, which is the output or result of the sheer frequency sweep tests. Thus, fundamental analyses involve applying shear strains that are available for simulating the road traffic impact.

Empirical Tests

The empirical tests involve methods such as the Marshall, hveem, lateral pressure indicator, and the use of the Corps of Engineering Gyratory Testing Machine. The marshal test is the simplest to implement, and the test procedures are standardized (Hu et al. 123). The method is also widely used hence easily applied. However, it cannot correctly rank mixes used in permanent deformations (Bahia et al. 86). On the other hand, the Hveem approach takes the shortest time and handles triaxle loads. It needs a California kneading compactor. Yet, the method is not widely used, like the marshal method (Chakroborty et al. 32). Further, the lateral pressure method tests rutting during compaction, and it sometimes results in a problem in data interpretation. The Gyratory testing machine is applied in the simulation of action rollers during the construction phase (wen et al. 300). Therefore, the main challenge is that it cannot handle correctly rank mixes that can be applied in permanent deformations.

Simulative Tests

Simulative Tests are among the new methods for predicting performance in HMA performance. The tests employ f mechanistic approaches. It is a modification of Georgia loaded wheeler tester. Georgia loaded wheeler tester was developed in 1996 and is applied in HMA mixtures in the evaluation of moisture resistance and rutting fatigue (Hu et al. 15). Testing in this approach involves the use of Test beams that can be either cylindrical or beamed with the test temperatures ranging between 40.6 -64 degrees centigrade (Wen, Haifang & Bhusal 28). Another test in this category involves the use of the Hamburg Wheel-Tracking Device, which is applied in the specification requirements,particularly in Germany, for evaluating stripping and rutting in some of the country’s most traveled roads (Schram et al. 91). As such, therefore, testing is done by the use of the Superpave gyratory compact samples and the linear kneading compactor.

            French Rutting Tester is another simulative test method mostly used in France to prevent HMA pavements from rutting. It can simultaneously test two HMA slabs, where samples are mostly compacted with LCPC laboratory’s rubber tied compactors (Ouni et al. 60). The Purdue University Laboratory Wheel Tracking Device tests specimens that are compacted in laboratories or cut from roadways. The wheel was developed to assist in the HMA evaluation, its moisture sensitivity, or rutting material (Doyle et al. 149). These methods are used to assess the quality and structural content of pavement, thereby establishing the extend of rutting.

Methods for Improving Rutting Resistance

The main techniques used to improve rutting resistance include adding plastic waste to asphalt and the use of geosynthetics. By adding plastic waste to the binder, the viscosity level of the asphalt increased, thereby increasing its stiffness (Wen, Haifang & Bhusal 18). In this case, the rutting resistance is improved at standard operational temperatures. Similarly, Geosynthetics utilizes synthetic materials to enhance the performance of roadways against rutting. Other methods of strengthening rutting resistance on pavements include asphalt concrete reinforcement, which is the structural measure to increasecapability against a variety of pressures (Schram et al. 302). Thus, improving its strength capabilities and granular layer reinforcement,thereby reducing the mechanisms of rut depth through Geosynthetic strengthening.

Conclusion and Recommendations

Asphalt pavement rutting in road construction is among the most destructive roaddistresses, particularly in urban environments characterized by busy intersections. Pavement rutting poses safety hazards,especially during wet weather seasons, because of hydroplaning that result from water collection in pavement ruts.  Notably, ruts occur when traffic loading displaces the bitumen made material that forms part of the pavement structure.  The evaluation of rutting involves the use of some methods. The common one is simulation tests that are done using several methods in evaluating rutting performance. At the same time, evaluation can be done through the application of empirical and other fundamental tests. Therefore, it is always crucial to evaluate the structural integrity of the pavement since it affects the safety of road users.    

Works cited

Bahia, H. U., Coenen, A., & Tabatabaee, N. (2013). Mixture design and compaction. In Advances in Interlaboratory Testing and Evaluation of Bituminous Materials (pp. 85-      142). Springer, Dordrecht.

Chakroborty, Partha, Animesh Das, and Pijush Ghosh. “Determining the reliability of an asphalt mix        design: the case of the Marshall Method.” Journal of transportation engineering 136.1 (2010): 31-37

Doyle, Jesse D., and Isaac L. Howard. “Rutting and moisture damage resistance of high reclaimed asphalt pavement warm mixed asphalt: loaded wheel tracking vs. conventional methods.” Road Materials and Pavement Design 14.sup2 (2013): 148-172.

Firoozi Yeganeh, Sayna, Amir Golroo, and Mohammad R. Jahanshahi. “Automated rutting measurement using an inexpensive RGB-D sensor fusion approach.” Journal of       Transportation Engineering, Part B: Pavements 145.1 (2019): 04018061.

Golalipour, Amir, et al. “Effect of aggregate gradation on rutting of asphalt pavements.” Procedia-Social and Behavioral Sciences 53 (2012): 440-449.

Hu, Meng, Jiupeng Zhang, and Xiaoming Huang. “Analysis of rutting characteristics of semi-rigid base asphalt pavement.” Journal of Highway and Transportation Research and                Development 28.6 (2011): 15-18.

Kandhal, Prithvi S., and L A. Cooley. Accelerated laboratory rutting tests: evaluation of the asphalt pavement analyzer. Washington, D.C: Transportation Research Board, National Research Council, 2003. Print.

Koch, Christian, et al. “Machine vision techniques for condition assessment of civil infrastructure.” Integrated Imaging and Vision Techniques for Industrial Inspection. Springer, London, 2015. 351-375.

Miljković, Miomir, and Martin Rodenberg. “Rutting mechanisms and advanced laboratory testing of asphalt mixtures resistance against permanent deformation.” Facta Universitatis-Series: Architecture and Civil Engineering 9.3 (2011): 407-417.

Mirzapour Mounes, Sina, et al. “Improving rutting resistance of pavement structures using geosynthetics: An overview.” The scientific world journal 2014 (2014).

Mohammad J., et al. “Image-based discrete element modeling of hot mix asphalt mixtures.” Materials and Structures 48.8 (2015): 2417-2430.

Ouni, Anissa Eddhahak, Anne Dony, and Johan Colin. “Probabilistic parametric approach for rutting evaluation: application to hot and warm asphalt.” International Jurnal of Engineering 15.1. (2014): 15 – 65.

Pavemen Patel, Arti, et al. “Developing QC/QA specifications for hot mix asphalt concrete in       Illinois.” Transportation research record 1575.1 (1997): 66-74.

Radhakrishnan, Vishnu, et al. “Evaluation of wheel tracking and field rutting susceptibility of dense bituminous mixes.” Road Materials and Pavement Design 20.1 (2019): 90-109.

Schram, Scott, R. Christopher Williams, and Ashley Buss. “Reporting results from the Hamburg wheel tracking device.” Transportation Research Record 2446.1 (2014): 89-98.

Wen, Haifang, and Sushanta Bhusal. “A laboratory study to predict the rutting and fatigue behavior of asphalt concrete using the indirect tensile test.” Journal of Testing and Evaluation 41.2 (2013): 299-304.