FHWA DEMONSTRATION FINDS TREASURE UNDER THE INTERSTATE

Interstate 40 (I-40) is a major east-west transcontinental highway running through the southeastern and southwestern portions of the United States from North Carolina to California. Much of the pavement surfacing on I-40 within the states of Arizona and New Mexico is so badly potholed as to create a safety hazard for drivers. In response, the New Mexico Department of Transportation (NMDOT) recently closed down the eastbound lanes of I-40 near Gallup for three consecutive nights, entirely shutting down for repairs all eastbound lanes of the Interstate to all automobile and truck traffic, a dramatic course of action in this day and age. NMDOT spokesperson Delane Baros announced the following day that this same section of highway would likely have to be shut down again as the new repairs started to fail almost immediately, and then adding, “The reason being is because the bulk of the soil underneath is clay, and then the subgrade is just completely saturated with moisture.”

Following wet winter weather conditions, some potholing and pavement failure on I-40 is not abnormal, but the severity of the problem this year is particularly troubling. The Governor of Arizona recently held a press conference to inform residents that millions of dollars will be made available for repair work on Interstate 40 and the State of New Mexico issued a press release announcing that they are conducting a study for the reconstruction of I-40 all the way from Albuquerque to the Arizona state line, a project of approximately 150 miles. The current estimated cost for that highway improvement project in New Mexico is $830 million. With Average Annual Daily Traffic (AADT) of 20,000 cars and trucks, 30% of which is truck traffic, that works out to approximately four trucks and ten cars per minute impacting the I-40 pavements on an around-the-clock basis. At that traffic volume, with both cars and trucks swerving in and out of their lanes to avoid potholes and distressed areas, these pavement failures are creating serious hazards for road users and nightmares for the road maintenance crews. Earlier this year, the local county sheriff blamed potholes on I-40 as the cause of multiple crashes and remarked that the pothole problem is only getting worse. As history has proven, these repairs will only function as temporary Band-Aids until a more permanent and sustainable solution is implemented to preserve the life of these pavements for decades of safe, maintenance-free service, and not just a few years.

“The reason being is because the bulk of the soil underneath is clay, and then the subgrade is just completely saturated with moisture.”

TIMELY DISCOVERY OF A SOLUTION

Timely then is the recent discovery of the outstanding performance of one segment of an I-40 reconstruction project that incorporated innovative stabilization product technology in two miles of its construction. As recently confirmed by Mr. Eugene Hosteen, NMDOT’s current Area Maintenance Supervisor in charge of the maintenance of the I-40 pavements in this area of the state, two miles of eastbound I-40 pavement remain smooth-running and free of repairs after 23 years in service with “nothing more than a fog seal applied” to the pavement surface in recent years. While other I-40 pavements in this area of New Mexico are currently potholed and have been subject to complete reconstruction and numerous repairs throughout the same period of years, the trouble-free performance of this one section of I-40 stands out as exceptional. Even more so, this two mile segment of eastbound I-40 was historically NMDOT’s worst area in the entire 150 mile length of I-40 between Albuquerque and the Arizona border. Last reconstructed in Year 2000, this two mile section of I-40 featured use of advanced liquid stabilization products with the encouragement of the Federal Highway Administration (FHWA) New Mexico Division Office. The project was designated as a FHWA Demonstration Project, and involved the full-depth reconstruction (complete removal and disposal of asphalt pavement, aggregate base materials and saturated soils below pavement elevation) of four miles of I-40, identified as Milepost 93 to Milepost 97, and included the two miles featuring the stabilization of both the subgrade soils and aggregate base course materials.

WORST I-40 PAVEMENT BETWEEN ALBUQUERQUE AND AZ STATE LINE

This four mile section of Interstate reconstruction just happened to include the two mile section of eastbound lanes that Will Williamson, NMDOT’s Area Maintenance Supervisor at that time, identified in his experience as “THE” worst maintenance problem between Albuquerque and the Arizona state line. The eastbound lanes of Interstate 40 that he was speaking about were located between Milepost 94 and Milepost 96 (MP 94 – MP 96), within the limits of the I-40 MP 93 – MP 97 reconstruction project. This section of I-40 transects the Acoma Indian Reservation and runs through a mountainous valley, much of which is underlain by the El Malpais lava fields. One of the lava flows runs parallel to the south side of I-40. This lava flow interrupts the natural downslope drainage under the highway and acts as a dam that traps water within the silty clay and organic soils deposits located immediately beneath the eastbound lanes. This unique geology creates a worst case condition of trapped groundwater directly underneath a pavement supporting heavy truck traffic. Many other sections of I-40 are plagued with high groundwater, but the two miles between MP 94 - MP 96 were considered by NMDOT Maintenance as their very worst pavement problem. The worst case.

PREDICTIONS BASED ON CONVENTIONAL PAVEMENT DESIGNS

The MP 94 – MP 96 section of eastbound I-40 had previously required full depth reconstruction every 2 to 3 years, while the westbound lanes constructed on more solid ground were far less problematic. During reconstruction of the eastbound lanes in Year 2000, NMDOT District 6 Engineer Larry Maynard commented that he anticipated another full depth reconstruction project of this same section would be required in less than three years. Ron Clark, the Superintendent for contractor WW Construction (WWC), predicted failure and reconstruction within two years. He mentioned in a testimonial letter that it was very difficult to work on top of the native soils under the eastbound lanes that were composed of “soft wet silt, clay and dark stinking organic soils.” NMDOT and WWC had worked together reconstructing many other sections of I-40 between Albuquerque and the Arizona state line during this same period of years, so both men were speaking from extensive experience when making these predictions.

Prior to year 2000, when the I-40 MP 93 – MP 97 project was completed, and during subsequent years, NMDOT was relying on conventional pavement designs during reconstruction of other sections of I-40, and basically increasing the thickness of the asphalt pavement and the aggregate base course layers as a continuing response to the ongoing pavement failures. Their primary method of dealing with localized subgrade failures during these reconstruction projects was deep excavation of saturated soils and replacement with virgin and recycled aggregate materials reinforced with a combination of geogrids and geotextile fabric products. Nothing was done during these projects to treat the moisture sensitive clay subgrades under the pavement structural section. Consequently, none of these pavement reconstruction projects have matched the extended performance of the Eastbound MP 94 – MP 96 pavement installation that incorporated base course materials and subgrade soils treated with the EMC SQUARED System liquid stabilizer products as part of the FHWA Demonstration Project. The pavements constructed on top of these EMC SQUARED stabilized subgrade and base course layers were constructed over worst case ground conditions, with an asphalt pavement section that was reduced in thickness by two (2) inches, yet they remain free of potholes and repairs twenty-three (23) years later. The eastbound MP 94 – MP 96 pavements will soon exceed the service life predicted by the District Engineer and by the Construction Superintendent by a factor of eight (8) times, with no sign of failure currently anticipated.

INNOVATIVE TECHNOLOGY SOLVES AN UNSOLVABLE PROBLEM

Potholes in highway pavements are widely understood to be the result of base and subgrade failures under the pavement, failures generated by the presence of water in the base materials and subgrade soils. Until measures are taken to keep water out of the base and subgrade layers, potholes and pavement failures will continue to be a costly and dangerous problem. Ever thickening layers of moisture and frost susceptible base course materials will not eliminate the problem. Thicker layers of asphalt pavement will not eliminate the problem of water in the base course layer. Suction and capillary attraction will continue to draw moisture and pull ground water upwards into moisture susceptible base materials, particularly when placed on top of moisture susceptible subgrade soils. Geogrids and geotextile fabrics may add tensile strength and reduce the upward flow of clay particles via capillary water into the base layer, but they do nothing to keep the base material and the subgrade soils dry and able to retain the strength that was assumed in the pavement design. The addition of cement and lime chemicals to base or subgrade layers can increase the strength of the layer, but there is no historical evidence that they eliminate the moisture susceptibility problem itself, the problem that continues to draw water in and saturate base course and subgrade layers. For example, the I-40 MP 93 – 97 lanes reconstructed in year 2000 were previously constructed with asphalt pavement placed on top of cement treated base (CTB) and that pavement didn’t last three years. The EMC SQUARED treatments instead keep the moisture content in the base course layer and subgrade in a stable state, without major fluctuations, while also functioning as a moisture barrier impeding the upward and downward movement of water within the pavement structural section. The moisture barrier aspect of the EMC SQUARED System stabilizer treatments is the clue to understanding why the I-40 eastbound MP 94 – MP 96 pavements, constructed on the EMC SQUARED Subgrade and EMC SQUARED Base Course layers, can remain smooth running and free of repairs 23 years later, even with ground water trapped in the native soils immediately below the stabilized subgrade and base course layers.

COHESIVE FORCES BRIDGE UNDERLYING SOFT SOIL DEPOSITS

The exceptional performance of freeway and highway pavements constructed on foundation materials stabilized with EMC SQUARED System liquid stabilizer products is not unique to New Mexico. The solution to solving the frequent failures of the I-40 pavements in New Mexico involved utilization of the EMC SQUARED stabilizer products to keep water out of the treated layers. After 23 years of trouble-free service, the long term benefits of the EMC SQUARED stabilizer treatments for extending pavement service life are now obvious, but also noteworthy is the advantage the contactor achieved by applying the EMC SQUARED treatments during construction, giving themselves the ability to continue construction uninterrupted by the delays that they would have otherwise experienced while digging out and repairing soft spots in their subgrade and backfilling with layers of aggregate and geosynthetic reinforcement. These unique stabilizer products also produce a reaction in soils that rapidly generate increased internal cohesive forces that help the stabilized layer quickly bridge saturated soils below the subgrade. Such bridging performance is unique to the EMC SQUARED System stabilizer products.

MONITORING OF FHWA DEMONSTRATION PROJECT

Ray Pederson, the FHWA Area Engineer who was on site throughout the construction of the eastbound lanes, was aware of the particularly complicated geology underneath this section of Interstate when he made the decision to monitor on an ongoing basis the entire MP 93 – MP 97 project. Ray was a Professional Engineer (P.E.) with a Materials Engineering background. His intention was to evaluate whether the use of the EMC SQUARED System liquid stabilizer products, or the other chemical and mechanical stabilization products used during this challenging highway construction project, significantly contributed to extending pavement service life. The variation in the underlying ground conditions and the number of different methods of stabilization made this a complicated monitoring task, but Pederson was determined to make something of value out of this Demonstration Project. To his great credit, it was his 13-year monitoring effort that finally led to the uncovering of a treasure trove of information that otherwise would have remained buried without his perseverance. The clues that led him to his findings were being accumulated annually by state crews operating high-speed profilers to measure the smoothness, or the rate the pavement was developing roughness in the form of International Roughness Index (IRI) measurements. IRI measurements are the international standard for evaluating highway pavement performance. They provide the basis for predicting the amount of service life remaining in a particular segment of highway pavement.

UNCOVERING THE CLUES TO FIND THE TREASURE

As FHWA Area Engineer Pederson reported in his September 8, 2013, letter, where he compared the performance of various different chemical and mechanical stabilization measures used during the construction of the MP 93 – MP 97 project, which is included as page 13 of summary (https://stabilizationproducts.net/docs/18809.pdf), nothing more than routine maintenance operations were conducted during his 13 years of monitoring. A thin bituminous treatment (Novachip) was applied to the westbound lanes in 2008 and to the eastbound lanes in 2009, and the following year an Open Graded Friction Course was applied to the entire project and adjacent sections of highway as a safety measure.

Pederson was onsite during the 1999 – 2000 construction phases of the I-40 MP 93 – MP 97 project. He was aware of the fact that the eastbound lanes were constructed on top of the worst case ground conditions in this length of Interstate 40, while the westbound lanes were constructed on a more solid native subgrade. During construction, one mile of the subgrade soils under the westbound MP 93 – MP 97 lanes had been left untreated, with no chemical stabilizer product applied. The soft spots in this one mile section of subgrade were over excavated and replaced with aggregate materials reinforced by a combination of geotextile and geogrid products, but the subgrade soils were otherwise left untreated. The remaining three miles of subgrade soils were treated with lime chemical. The second phase of the MP 93 – MP 97 project used the EMC SQUARED liquid stabilizer products during the construction of eastbound lanes from MP 94 to MP 96. In the case of the construction of the eastbound lanes, two out of the four miles of subgrade were left untreated, with localized repairs conducted on an as needed basis, in similar manner as the untreated subgrade on the westbound side.

STAYING ON TASK AND FOLLOWING THE CLUES TO THE SOLUTION

Area Engineer Pederson was aware that the different ground conditions underlying the westbound and eastbound pavements were fundamentally influencing the IRI test results. He concluded that the monitoring program must incorporate the two different starting points for the IRI measurements and separate monitoring of the westbound and eastbound lanes in order to properly measure and compare their rates of deterioration over time, and not just their initial smoothness at the time they were constructed. He went on to collect the IRI monitoring results over a period of ten years. He also made comparisons with the different methods of subgrade construction that were used under the westbound pavements and the under the eastbound pavements, in each case comparing pavement smoothness above the stabilized subgrade to the pavement smoothness above the sections of subgrade that were not chemically treated or reinforced with the geosynthetic products. This analysis allowed him to demonstrate that both the lime treatment and EMC SQUARED treatments were clearly beneficial in helping retain pavement smoothness and prolong pavement service life. The first take away that he achieved in analyzing the data from this Demonstration Project was that chemical stabilization of the subgrade soils under I-40 in this area of New Mexico is highly cost-effective, in this case using either lime or the EMC SQUARED System stabilizer products.

Pederson was also assigned as Area Engineer to two other NMDOT construction projects on I-40 that were in progress during this same period of years, and he reported that the smoothness test results for the pavements constructed above these chemically stabilized subgrades were superior to those of the new segments of I-40 pavement being constructed at both ends of the MP 93 – MP 97 project without use of chemical subgrade treatments. The IRI data also confirmed over time that the EMC SQUARED System applications were more effective than lime treatment in preserving pavement condition and prolonging service life, and once again more effective than the geosynthetic products in preserving pavement smoothness and service life. Using the Theoretical Design Life calculations developed by NMDOT to interpret the IRI data, Peterson was accurate in his prediction that the EMC SQUARED System treatments would be by far the most effective treatment measure for extending pavement service life. For additional perspective, the EMC SQUARED System treatments were also the lowest cost to purchase and fastest to install.

LESSONS TO BE LEARNED

Given the current pothole epidemic that is seriously endangering the safety of I-40 highway users in Arizona and New Mexico, along with the revelation by NMDOT that they recognize pothole pavement failures are caused by saturated clay subgrades, the conclusion could be drawn that the Department of Transportation should expand approval and use of stabilizers products that counteract the movement of water into highway subgrade soils. As proven by this FHWA Demonstration Project on Interstate 40, there is an affordable alternative to short-lived conventional construction. Interstate Highways can be designed with moisture-resistant foundation materials that have the year-round solid support that asphalt pavements require to provide decades of pothole-resistant service.

VIDEO TOUR OF EASTBOUND I-40 MP 94 - MP 96 ABOVE EMC SQUARED STABILIZED SUBGRADE AND BASE COURSE

Take a one minute video tour of the eastbound MP 94 – MP 96 segment of Interstate 40. This pavement was constructed on top of subgrade and base course layers treated with the EMC SQUARED System products to keep water out of the base course materials and subgrade soils. This section has been 23 years in service over worst case ground conditions without need for repair or reconstruction. The video footage was taken in April 2023, in the midst of the current epidemic of hazardous potholes that have made other sections of Interstate 40 in both Arizona and New Mexico truly life-threatening to drive, and that have caused repeated shutdowns of the Interstate for pothole repairs.

FOR AN EVEN DEEPER DIVE

For a deeper dive into the related construction history and the monitoring results of the 13 year study conducted by the FHWA Area Engineer, visit https://stabilizationproducts.net/docs/18809.pdf

NOTE: If you are interested in the studies conducted by independent soil and pavement materials testing laboratories, whose results give evidence as to the how and why the performance of EMC SQUARED System stabilizer products prolonged the service life of the FHWA Demonstration Project on Interstate 40, look for the next newsletter coming soon. In case you missed one, earlier newsletters describing laboratory and field tests, as well as projects in North America can be found here: https://stabilizationproducts.net/newsletters.html

For a summary report on other smooth running highways built on EMC SQUARED subgrades constructed above deep deposits of expansive clay soils, visit
https://stabilizationproducts.net/docs/18791.pdf and
https://stabilizationproducts.net/docs/18468.pdf