Intelligent Compaction Control for Highway Construction Projects

Abstract

This paper gives an overview of traditional compaction techniques used on highway construction projects. It then introduces Intelligent Compaction Control (ICC), which is a newer technology that uses equipment mounted devices to measure relative compaction in base and surface courses during highway construction. It then discusses the main types of ICC and the associated equipment, along with how it can be used on construction projects in terms of Quality Control (QC) and Quality Assurance (QA) processes. Lastly, it uses a case study project do discuss the significance and lessons learned of how ICC can be implemented on additional construction projects.

Introduction

Intelligent Compact Control [ICC] is a rather new and upcoming method being used for the compaction of base and surface courses of flexible pavements. In short, it can be defined as a process that equips conventional rolling equipment with instruments used to monitor and control the material compaction process. The equipped instruments provide operators with graphical information, which then in turn allows them to better manage their operations. This promotes a more efficiently achieved and uniformly compacted surface, yielding a longer and more successful service life. ICC can also be set up with data recording devices that will spatially track compaction operations (Si 2014). This can give the managing agency/owner record of the operation and can even be used as a means of material acceptance.

According to the Federal Highway Administration [FHWA], ICC originally began in Europe during the 1980s and was intended for the compaction of subbases. However, it began to spread to the compaction of flexible pavements in the 1990s when the value of the product was realized further. ICC made it to the United States in the early 2000s, however even today it is still slow to be adapted by state and local agencies (Nieves-Torres [FHWA] 2014). However, entities such as FHWA and certain state DOTs are promoting the widespread use of this technology, as the benefits are beginning to be realized as plentiful.

Significance of compaction

It is no secret that sufficient compaction yields much better performance of pavements over its service life. This is a pavement engineering fundamental, however compaction for roadway construction has remained somewhat consistent over the twentieth century, with minor technological advancements. With that being said, the importance of compaction has been realized for a long time. As far back as 1939, J. T. Pauls and J. F. Goode wrote in Public Roads:“The importance of compaction in highway construction has been long recognized. Recent laboratory and field investigation have repeatedly emphasized the value of thorough consolidation in both the base and surfacing courses. ”Specifically, in flexible pavements, insufficient compaction can lead to decreased stiffness and strength. This includes lower tensile strength, lower static and resilient moduli, and lower stability since there is a higher void content. Additionally, insufficient compaction can lead to reduced fatigue life, accelerated aging, decreased durability, raveling, rutting, and moisture damage (MST 2017; Pavement Interactive n. d. ).

In short, uniform compaction is ideal to minimize long term settlement. High quality compaction ensures long-lasting performance of base and flexible pavement surface courses. There are several methods of traditional compaction measurement, including tools such as a nuclear density gauge, a penetrometer, a deflectometer, and applying a plate load. However, the greatest issue with these measurements is that they are point measurements, meaning that they measure the relative compaction of only that point. According to Caterpillar, on a typical roadway construction project, less than 1% of the surface is actually tested for compaction. This poses a huge issue if uniform compaction is the ultimate goal, as it is hard to get uniform compaction between different point measurements(SCAPA 2013). Additionally, this is one of the largest benefits of ICC as it continuously measures the relative compaction instead of measuring at varying points.

Mechanics of intelligent compaction control

There are many different types of ICC systems, but the most common focus on equipping smooth drum vibratory compactors with instrument devices to measure the “relative stiffness” of the material that they are compacting. A common system, as shown in Figure 1, include an in-cab display panel, a GPS antenna, and a measurement device located within the rotary drum(SCAPA 2013). Figure 1. Typical Components of ICC SystemWhile there are different variations of ICC systems, this is the most common system and is produced/promoted by various roller manufactures. With the display panel in the cab of the roller, operators are able to make real-time decisions to ensure uniform compaction. More sophisticated ICC systems include those that collect the stiffness measurements, analyze the data, make adjustments to the compaction controls via the vibratory roller parameters, and then execute the change automatically to optimize the compaction effort (Nieves-Torres [FHWA] 2017). This type of system that automatically executes the changes is still under refinement and the current ICC systems rely on operator changes to achieve uniform relative compaction.

Types of measurement devices

As mentioned previously, ICC mainly relies on measurements from vibratory rollers. However, there are two types of measurement devices that need to be noted. The first measurement device is called a Compaction Meter Value [CMV], in which an accelerometer is placed within the rotary drum. This device sends waves into the ground and then is able to measure the ‘stiffness’ of what is below by the frequency of response (SCAPA 2013). A diagram showing how the CMV device functions is shown in Figure 2. Figure 2. Compaction Meter Value (CMV) Measurement DeviceThe CMV measurement device can accurately measure stiffness between 3 and 6 feet deep. However, this type of system can only be used on granular base courses or flexible pavements and must only be equipped to a vibratory smooth drum roller (SCAPA 2013). Many manufactures produce this type of system and it can be considered the most common type of ICC today. The other type of ICC equipment is called a Machine Drive Power (MDP) device in which the rolling resistance of the compacting medium is measured and then the ‘stiffness’ is measured from that. Unlike the CMV method, this is an energy-based method and currently, Caterpillar is the only manufacture to produce and market this type of ICC measurement device. MDP devices measure the stiffness accurately between 1 and 2 feet and can be equipped to either smooth drum or padfoot rollers. According to Caterpillar, this type of system is much more versatile as it can be applied to both granular and cohesive types of base courses/soil, as well as flexible pavements. Caterpillar also states that this type of system is the best ICC system as it measures closer to the depth of the lift you are working on and correlates better than a CMV system to portable measurement devices, like a nuclear density gauge (SCAPA 2013).

Analysis of intelligent compaction control

There are several benefits to using the ICC method, but the most prominent is the fact that it provides a more uniform and compact surface. This counteracts the biggest downfall of traditional compaction measurement methods, which is that they only measure at that single point. Instead, ICC continuously monitors relative compact levels and thus will give a better end product. With ICC, compaction efforts can be more focused and efficient. Additionally if ICC is used ahead of flexible pavement laydown, areas of poor subgrade quality can be found and addressed prior to placing pavement. Another benefit of ICC includes its ability to map compaction operations. This information can be loaded into a Geographic Information System [GIS] mapping system. This will then allow the maintaining agency have record of the effort and this is even being tested as a means of material acceptance. With GIS information, agencies can have an idea of potential poor-quality areas that will arise in the future and plan to address them. As with any new technology, there are drawbacks and hesitation associated with it. The largest drawback of ICC includes the lack of both industry and owner familiarity with the technology. According to FHWA, more than 30 states have implemented at least some sort of ICC testing, with Texas and Minnesota being the leaders fore fronting ICC implementation. Other drawbacks of ICC include the difficulty of appropriate specification development by agencies, greater initial expense of new equipment and to retrofit existing equipment, and large training efforts required to gain familiarity of operators, contractors, and owing agencies.

Recommendations for more effective implementation

Since FHWA can be considered one of the leaders in pushing ICC implementation, they have developed a guide for helping state and local agencies implement the technology and develop appropriate specifications. Per FHWA, the most important item in using ICC appropriately is to increase the communication between agencies and industries so that they can collaborate and come up with a fair and reasonable standard. Additionally, they state that greater personnel and equipment familiarity be used, automated GPS validation systems be implemented, and that ICMV roller technology to be further developed so that it can perhaps be used as an acceptance matrix. In addition, the Association of American State and Highway Transportation Officials [AASHTO] has developed a set of recommendations for ICC use, with slight variations to FHWA’s system including items such as GPS verification tolerance, required pre-construction mapping, and the amount of training required for personnel.

Inteligent compaction control used as QC/QA

The project NM 35-1(1) was an 8. 65-mile rehabilitation effort conducted for the Lincoln National Forest in the spring/summer of 2014, being located approximately 15 miles east of Cloudcroft, New Mexico. The main project consisted of milling the existing asphalt surface course, adding a little amount of aggregate base course, and then finishing the surface with an additional 4-inches of SuperPave asphalt pavement. A typical pavement section of both the existing and proposed (now constructed) can be seen in Figure 4. Figure 4. Existing and Proposed Typical Sections for NM PFH 35-1(1) projectThe project was administered by Central Federal Lands Highway Division [CFLHD], a subsidiary of the Federal Highway Administration – Federal Lands Highway program. For CFLHD, this project was seen as a test project in which the applicability of ICC was to be determined for Federal Land Highway projects. When the project was solicited, ICC was an option to the bidding contractors in which they would get an incentive bonus if they utilized the technology. The awarded contractor, Southwest Paving Solutions LLC of Las Cruces, New Mexico, elected to use ICC. As such, there was a lot of publicity for the project from the road construction industry and several high-profile individuals from differing agencies visited and studied the project. Thomas Bonar, the CFLHD project engineer, was chosen to oversee the construction contract administration of this project. Tom was no stranger to road construction, as he had over both 20 years of private sector experience as a contractor and nearly 20 years of public sector experience as a project engineer working on various federal projects throughout the Western U. S.

When Tom was initially briefed on the project, he had his doubts regarding ICC. In an interview, Tom admitted that he was a little nervous about the project using this new technology and that him, like many others of his generation, are reluctant to accept new forms of technology to replace the tried and true methods. Nonetheless, he was anxious to see the ICC system in action as he had a feeling that ICC was going to widely used in the upcoming years(Bonar 2018). Within the original contract, ICC was only to be used for the compaction of the SuperPave asphalt pavement. However, contract modification #001 obligated funds so that ICC could be used on the pulverized asphalt/aggregate base course layer. According to Mr. Bonar, this was the best idea of the project because while compacting this layer, a GPS enabled map was able to be produced and allowed soft spots to be located/addressed that were not areas of sub excavation in the design. Additionally, the map helped provide the stiffness value change indicated on the monitors when compacting over a culvert. Tom was also pleased with the monitors in the rollers because it allowed the operators to take a more proactive approach and ensure that a quality and uniform layer was produced. Overall, Tom was very pleased with the overall quality of the compaction of the grade and pavement. He noted that although acceptance was not based on ICC, the consistently passing tests provided a direct assurance that the process worked. Figure 5. On-Board Monitors Showing “Stiffness” Before and After Completing Rolling PassesAs can be seen in Figure 6, the real-time monitors allow greater flexibility by the roller operators as they can make quick adjustments to ensure optimum compaction levels. The ICC system tracks the GPS location, the number of roller passes, and even the surface temperature of the flexible pavement.

Conclusion

As can be seen, Intelligent Compaction Control [ICC] has many benefits. One of the main benefits is that it provides a more uniformly measured compacted surface, which can promote a longer service life since greater uniformity can be achieved. Additionally, ICC can be considered a more proactive approach rather than reactive since it supplies operators with real-time information. This allows them to take corrective action before it’s too late, specifically regarding flexible pavement compaction. ICC can also be useful for its GPS location services that help map where a roller has been and how many passes it has made. This again provides a more uniformly compact surface if the compaction is spread evenly amongst the surface. However, since ICC is a rather new technology, it is slow to adapt to industry. This can be seen across different materials/methods in construction, such as Glass Fiber Reinforced Polymer [GFRP] bars for reinforced concrete. Many stakeholders, such as state DOTs, can be reluctant to try something until there is ample evidence supporting the idea. Additionally, industry struggles with adapting appropriately developed specifications so that ICC can be used efficiently. Nonetheless, it can be seen that ICC is an up and coming technology that will used more widely in the years coming.