The macro-fiber content in concrete cast in the field is critical to achieving the desired toughness properties and performance of the concrete structure. Currently, there exists no standard method to determine the polymer fiber content of hardened concrete. A nuclear density/moisture gauge was used on hardened concrete pavements with and without polymer fibers. Polymeric fibers are composed primarily of carbon and hydrogen. Since these elements are substantial neutron thermalizers, the neutron count detector on the nuclear gauge is sensitive to changes in the fiber content. The effects of hydrogen and carbon present in the unreinforced concrete itself were subtracted out by taking readings on specimens without fibers. Polymer fiber volume had a clear and statistically significant effect on the neutron readings. This effect was found to be linear and the polymer fiber volume of hardened concrete could be quickly and accurately be determined. The proposed non-destructive and in-situ test procedure can provide useful information for engineers conducting forensic failures and provide a method of quality assurance for determining the as-built polymeric fiber content of fiber reinforced concrete structures.

The ability to spatially map the stiffness of the foundation layers under concrete pavements with intelligent compaction has created a need to define limits on the allowable stiffness variations in a given construction area as well as the maximum size of a non-complaint area which does not require remedial action. In order to work towards this goal, a two-dimensional finite element analysis was completed to determine the effects of four nonuniform subgrade support conditions (relative to uniform support) on the tensile stresses in a concrete slab under tandem axle loading and temperature curling. The slab responses showed that certain nonuniform subgrade support conditions have a greater impact on the slab tensile stresses relative to the uniform support irrespective if the slab is experiencing curling. A soft support along the longitudinal slab edge and a subgrade with randomly assigned 9 ft(2) (0.84 m2) soft and stiff areas were found to decrease the slab performance relative to a uniform subgrade assumption. In the most extreme case, the nonuniform support with soft longitudinal edges had a maximum stress that was 63 percent greater than the uniform soft support. In this analysis, subgrade nonuniformities produced the potential for bottom-up or top-down fatigue cracking depending on the interaction of the axle location, temperature differential, and local support condition.

This study considered the effects of recycled concrete aggregate (RCA) as a replacement of both coarse and fine aggregate in concrete. The coarse portion was replaced by 100% RCA and the fine portion was replaced with RCA at various amounts up to 50%. In addition, fly ash and ground granulated blast furnace slag were utilized as partial replacements of cement. All mixtures were prepared using the twostage mixing approach and the coarse and fine RCA were in a partially saturated condition. The use of RCA fine aggregate (RFA) reduced the concrete strength. However, it was found that the concrete can have a statistically similar compressive strength to concrete with 100% coarse RCA and no RFA. The shrinkage for almost all recycled concrete mixes was statistically similar at early ages, but at later ages, concrete containing RFA can potentially shrink more, especially if slag and fly ash are used to replace cement. The findings suggest that, with proper design, both RCA and RFA can be used in concrete pavement applications.

Concrete overlays for existing concrete and asphalt roads have been shown to be a viable rehabilitation or replacement option. This research project evaluated three unbonded concrete overlay (UBOL) projects in Illinois with high, medium, and very low truck volumes. The project’s goal was to assess each overlay’s performance including the influence of the interlayer. The project scope included distress surveys, evaluations of interlayer contact conditions through shear wave ultrasound tomography, assessments of structural response through falling weight deflectometer testing, profilometer testing, and core extractions. The findings from the UBOL performance study showed that nonwoven geotextile fabric (NWGF) can be an effective interlayer for concrete overlays under certain conditions. For thin UBOLs, even with macrofibers, steel tie bars should be used across the lane-shoulder joint to maintain shear transfer across a contraction joint or to limit construction joint opening. UBOLs with hot-mix asphalt (HMA) interlayers have historically provided good performance, which was seen in all three projects. For thinner UBOLs, slab geometry, interlayer type and transverse profile, and drainage must be considered in the overlay design. The I-72 eastbound section exhibited 3.8% longitudinal cracks (low severity) at transverse joints in the driving lane after 10 years, which has been linked to a combination of water in the joints, repeated truck loading, and debonding and low severity stripping of the HMA interlayer. For overlays with very few trucks (East Grand Road), the 6-inch slab and 11 feet by 12 feet slab size and the exclusion of dowel across transverse joints did not adversely impact UBOL performance.

Ashes generated from coal combustion, as well as waste incineration, can be a potential source of critical elements necessary for the ongoing transition to electrification and greener energy technologies. For the quantification of critical elements, traditional methods such as acid digestion are time-intensive and can fail to dissolve critical elements in refractory minerals. One potential solution is to adopt alkaline fusion for faster, total digestion. However, the role of flux choice and the subsequent digestion efficiency (DE) is unknown. Here, we report a systematic investigation on the feasibility of alkaline fusion with lithium metaborate (LiBO2) and lithium tetraborate (Li2B4O7) as fluxes for the digestion of two standard reference materials (BCR 176R and SRM 1633c). Our findings suggest that LiBO2 yields higher DE values than Li2B4O7 for several critical REEs and volatiles, such as Pb and Cd. Specifically, for REEs in SRM 1633c, the DE values with LiBO2 are, on average, similar to 16% higher than those with Li2B4O7. Similarly, for Pb and Cd in BCR 176R, the DE values with LiBO2 are similar to 20% higher than with Li2B4O7. These results suggest that LiBO2 is a superior flux for rapid ash digestion.

Large-scale concrete slab tests were conducted in the laboratory to evaluate the effect of multiple wheel gears on the fatigue resistance of concrete slabs. Monotonic and cyclic loading was completed on sixteen fully-supported slabs. The monotonic testing characterized the flexural strength of the concrete slab under the fully-supported conditions relative to the standard simply-supported flexural beam test. The testing program addressed the effects of peak stress ratio, stress range, and stress pulse type on the fatigue resistance of concrete slabs. For low cycle fatigue, stress range was not a significant factor while the applied peak stress controlled the number of repetitions to failure. For high cycle fatigue, peak stress and stress range affected the number of cycles to failure. An S-N curve analyses of the fatigue results showed that the number of repetitions to failure for the tridem pulses was not equivalent to the single pulse repetitions to failure for the same pulse duration, peak stress, and stress range.

Reclaimed asphalt pavement (RAP), when used as aggregate in concrete, is known to reduce the bulk concrete strength and modulus but not dramatically impact shrinkage, durability, or fracture properties, especially at lower replacement levels. This article presents an overview of RAP aggregates in concrete as it pertains to its effect on properties, microstructure, and pavement design. The mechanisms resulting in decreased strength and modulus for concrete containing RAP have been linked to: (1) the larger, more porous interfacial transition zone (ITZ) and (2) the dominance of an asphalt cohesion failure instead of an asphalt-cement adhesion failure. Despite these reductions in mechanical properties, multiple field studies have indicated that concrete with RAP can perform comparably to conventional concrete pavements, particularly when 10-15% RAP is used. The flexural capacity of concrete slabs with 22% RAP has shown similar behavior to virgin aggregate concrete given the similarities in fracture properties. Fatigue and accelerated pavement testing of rollercompacted concrete with high RAP contents (50-100%) have indicated a reduced fatigue life relative to plain concrete, requiring a slightly thicker design. Based on the literature, RAP aggregate replacement levels less than 25% can be used in concrete pavements without a significant change to the structural design.

Construction work zones (CWZ) present safety challenges because of speeding, distracted driving, and improper lane changes. The objective of this research was to enhance CWZ communication and safety for vehicles through pavement signage coded on the road surface. First, an electromagnetic (EM) signature was applied to a pavement surface through a process of magnetizing epoxy-encapsulated chromium dioxide (CrO 2 ) particles. Next, a 3-axis magnetometer array was mounted on a cart to detect the passive EM signature strips and interpret the cart’s speed or upcoming lane maneuvers based on the collected EM signals. Field experiments were conducted in a parking lot with pavement-placed EM strips and a cart equipped with a magnetometer sensor array to demonstrate the CWZ concept. Test case#1 had EM signature strips at a 90° inclination and successfully determined the cart speed by dividing the fixed EM strip spacing by the time between peak signal pulses. Test case#2 with EM strips at 90° and 60° orientations validated the passive sensor system identification of speed and lane-merge action. Differences between the peak response times from magnetometer sensors on the cart’s left, center, and right determined the direction of the upcoming lane merge. The introduction of 3-axis magnetometers improved the data available to calculate and verify speed and maneuver actions by having redundant sensors containing similar interpretation of speed or maneuver action. The study confirmed that pavement signage coded roads and magnetometer array on a vehicle can effectively predict speeds and upcoming maneuvering actions, which should improve overall driver safety and mobility through CWZs.

A study was completed to investigate the changes in fresh and hardened properties when using coarse, fractionated reclaimed asphalt pavement (FRAP) as a partial replacement of virgin coarse aggregate in a ternary blended concrete. The FRAP replacement levels were 0, 20, 35, and 50%. The ternary blended concrete consisted of 65% Type I Portland cement, 25% Grade 100 ground granulated blast furnace slag, and 10% Class C fly ash. Two coarse FRAP sources were investigated: one washed (16 mm maximum size) and one dirty (12.5 mm maximum size). The dirty FRAP source was additionally processed in the laboratory by washing and sieving over a 4.75 mm sieve to reduce the amount of fines and agglomerated sand/asphalt particles. The fresh concrete properties showed that adding FRAP had little to no effect on the air content, increased the slump, and reduced the unit weight. The fresh and hardened concrete characteristics (compressive, split tensile, and flexural strength) demonstrated that replacement levels up to 35% FRAP could be utilized without compromising existing concrete material specifications for paving. Surprisingly, washing the coarse dirty FRAP did not provide any strength benefit over the dirty, unprocessed FRAP for the sources evaluated.

Full-scale test sections were constructed at the University of Illinois and subjected to accelerated pavement testing in order to evaluate IDOT’s options on extended-life continuously reinforced concrete pavements (CRCP). The CRCP test sections included two concrete thicknesses, three steel contents, and the use of single versus double layer reinforcement. Response testing was first conducted on all the test sections in order to monitor the CRCP deformations under fixed loading and variable temperature conditions. Load levels were then applied at the edge of the pavement that would create a punchout failure on the test sections. The measured variables were the vertical and horizontal deformations at cracks and transverse strain near the surface of the slab, along with the temperature profile through slab thickness. The factors controlling the repeated load behavior of the CRC sections were the crack width, the permanent deformation of the support layers, and the steel content. The performance of the CRCP test sections exceeded existing design guide predictions. The main reason for the enhanced performance was the narrow crack width achieved on the test sections and resultant high shear capacity across the transverse cracks.

Built-in curling (BIC) is a permanent upward curvature of the concrete slab produced by irreversible moisture and temperature differences between the top and the bottom of the slab. This residual curvature has been shown to change the performance of concrete pavements. With mechanical loading, built-in curling typically changes the location and magnitude of the maximum tensile stress in the slab as larger regions of the slab are without contact with the support layer. Two existing concrete pavement projects in Chile were selected to characterize their in-situ BIC, document their performance, and determine if existing design procedures can adequately predict and account for their performance differences. In both case studies, BIC had a large effect on pavement performance and the magnitude of the effective built-in temperature difference, which is an important design input to predict the performance life. For one of these projects, premature slab failures resulted due to the initial BIC. The concrete thickness would needed to be increased by 59% or the slab size reduced to 2.00 m x 1.75 m to avoid premature failure of the section due to the high level of BIC. In the second project, the section of the concrete pavement that performed best was constructed at night and had a lower BIC relative to the sections constructed during the daytime in the summer.

The spatial distribution and orientation of fibers in concrete materials can be linked with the measured fracture performance of the fiber-reinforced concrete (FRC). For FRC pavements, the improved toughness performance is used for adjusting the structural design and expected service life of the pavement. The prediction of toughness performance and pavement serviceability can be improved with a better characterization of fiber dispersion in the concrete pavement. In this research study, a flowable fibrous concrete (FFC) mixture was developed containing a synthetic macrofiber at a volume fraction higher than found with existing thin concrete pavements. This FFC mixture is anticipated to have greater toughness induced by more fiber alignment in a thinner (5 cm thickness) concrete inlay pavement. Quantification of synthetic fiber dispersion and alignment in the FFC mixture was made using x-ray computed tomography and imaging analyses. The influences of placement technique and proximity of cast or mold surfaces were investigated and found to impact the fiber spatial distribution and orientation. The image analysis revealed that the number of fibers crossing any vertical plane, which increased for FFC placed under directional flow, was directly related to the measured fracture performance. Fibers were verified to have the desired alignment, allowing more fibers to become engaged in crack opening resistance, when the FRC was placed as a thinner pavement layer and therefore resulting in a more cost-effective use of FRC for pavements.

This paper identifies the key slab loading locations for inducing critical bottom and top tensile stresses on airfield rigid pavements servicing the A-380 aircraft. Finite element simulations were conducted for the A-380’s individual triple dual tandem (TDT) gear and all its main landing gears for a given slab geometry and pavement material properties. The numerical results show that the ratio between the top and bottom tensile stresses of the slab were significantly higher for the main landing gear analysis relative to the individual gear analysis and could be 1.0 for some cases. Furthermore, this initial finite element analysis has shown consideration of the entire main landing gear of the aircraft is necessary if the top tensile stresses are going to be accurately predicted.

The use of steel furnace slag (SFS) aggregates is limited in the United States and abroad, primarily because of the inherent expansion potential of the material, which results from the hydration of the free calcium and magnesium oxides present from the slagging process. When used in concrete, the literature presents contradictory findings, such as that the strength can increase or decrease with the addition of SFS aggregates. Microstructural investigations of the SFS aggregates as well as the interfacial transition zone (ITZ) in mortars revealed that the mechanical properties are strongly dependent on the SFS type and source. Certain SFS types can develop with a porous interior and/or a porous outer layer of different composition, both of which act as weaknesses in the bulk concrete. Depending on the SFS type, the ITZ may also be more porous, which can lead to further weakening of the concrete. Given the potential deleterious expansion of SFS, there are rapid screening protocols, which can quantify both the free lime content (complexometric titration) and expansion potential (autoclave index test) of the SFS. While the literature currently presents limits for the SFS to be used as a base material, no limits are defined for the use of SFS in bound applications, despite the fact that low expansion SFS aggregates are being used in several countries for certain applications.

With the use of mechanistic-empirical rigid pavement design methods becoming more widespread, it is important to note the differences of these methods in terms of their sensitivity to input parameters, conservativeness of the design thicknesses, and failure modes predicted. This study further demonstrated the sensitivity of input parameters such as joint spacing, shoulder type, traffic level, climatic location, and built-in curl level on the fatigue failure mechanisms predicted by several design methods. The use of widen lanes was also found to predict different fatigue failure mechanisms between design methodologies due to the assumptions of each method. An investigation into the sensitivity of the level of built-in curling showed that the thinnest design thickness does not necessarily occur with the absence of this parameter, but is minimized at a built-in curling level of approximately -6°C.

Microcracking at the surface of concrete slabs can result in a reduction in slab strength at the surface and a decrease in the flexural load carrying capacity of the slab especially when undergoing loading that produces top tensile stresses. The majority of this surface cracking is the result of drying shrinkage gradients and slab restraint. The use of an effective initial crack depth (ae) has been previously proposed as a method to model this reduction in slab strength due to surface microcracking. The two-parameter fracture model procedure was modified to make calculations of the effective initial crack depth in three-point bending specimens to examine if reasonable values of ae can be measured in a laboratory setting using fracture mechanics principles. Testing of concrete beams exposed to two curing environments (moist- and dry-cured) indicates that the effective initial crack depth, approximately 50 mm in this study, can be calculated using a dependent relationship between crack depth and compliance values. The procedure was verified by calculating additional fracture parameters of the concrete, which were found to be comparable to values presented in the literature for similar concrete materials and mixtures. The ability to quantify an effective notch depth at the surface of the slab can enable future modeling to determine the effective strength difference of concrete slabs under bottom or top tensile loading conditions.

This research evaluated compacted concrete pavement (CCP) constructed on a local road in Jerseyville, Illinois, and developed a future CCP mix based on a recently proposed roller-compacted concrete (RCC) mix design process using a gyratory compactor. The Jerseyville evaluation provided valuable insights into the batching, hauling, paving, compacting, finishing, and sawing of a pilot CCP project. Specifically, the effects of aggregate packing and fines content on mixture behavior revealed potential areas for improvement in compaction efficiency and strength performance. Furthermore, managing specific construction activities like type and minimum weight of roller compactors, maximum haul time, and moisture management of the CCP can positively impact the field compactability. Lab batching of the Jerseyville constituents using the field batch proportions showed that increasing the voids filled with paste (VFP) could significantly reduce the compaction effort required. A proposed CCP mixture was developed for future use at the Illinois Certification and Research Track (ICART) facility using local Trenton aggregates and a performance-based volumetric design methodology. The four mixtures cast and tested showed that a VFP of 112% with the three-aggregate blend provided the best balance across six key performance categories (paveability, compactability, stability, finishability, strength, sustainability), leading to its recommendation as a suitable starting point for the field CCP mixture.

This report focuses on the calibration of a design framework for continuously reinforced concrete pavement (CRCP) developed in 2009 by using the most recent performance data acquired from existing CRCP sections in Illinois. Field performance data were used to update the fatigue damage to punchout model coefficients in the design framework. A sensitivity analysis was performed on the updated CRCP design program to determine its sensitivity to traffic levels, shoulder type, and support conditions as well as its magnitude relative to jointed plain concrete pavement design curves. Additionally, the new CRCP design charts were compared to AASHTOWare Pavement ME Design predicted CRCP slab thicknesses for the same inputs. Lastly, AASHTOWare Pavement ME Design was run to predict the performance of CRCP overlays in Illinois and compare the performance data of seven unbonded concrete overlays constructed in Illinois. AASHTOWare Pavement ME Design was then used to generate CRCP overlay thickness design tables for different traffic levels, shoulder types, and support conditions.

The performance of concrete pavements and overlays is highly dependent on the uniformity, durability, and stability of the underlying support layers. Erosion of support layers can lead to pavement distresses and a reduction in pavement life. A review of existing erodibility performance tests that assessed stabilized support layers was first conducted to identify and evaluate their suitability for adaptation. The Hamburg wheel tracking device (HWTD) test was selected to assess the erosion potential of asphalt and cement stabilized support layers. Field testing with distress surveys, falling weight deflectometer, and coring was completed to obtain HWTD specimens and link laboratory results to pavement performance. The HWTD test was performed on cores obtained from in-service cement and asphalt stabilized support layers, a cold in-place recycling (CIR) mixture, and cement stabilized laboratory mixtures. As expected, an increase in cement content within cement stabilized mixtures decreases the likelihood of erosion with the HWTD. Additionally, conventional asphalt stabilized base layers were highly erosion resistant. Erosion resistant cement stabilized bases (including full-depth reclamation) should target an average HWTD erosion depth ≤2 to 4 mm (0.08 to 0.16 in.) after 10,000 load cycles based on the functional classification and expected traffic volume of the pavement section. Likewise, asphalt stabilized bases (including CIR and support layers for concrete overlays) should target an average HWTD erosion depth ≤12.5 mm (0.5 in.) after 7,500 load cycles with performance grade 64 binder.