MATERIALS LABORATORY RESEARCH
Fatigue Characteristics for Airport Pavements
Developing design methodologies for airport pavements requires new consideration of fatigue failure in the pavement under the unique aircraft loadings associated with airport operations. This project examines a new fundamental energy/damage approach to the accumulation of damage under intermittent heavy loads on very thick asphalt pavements. This Dissipated Energy approach unifies fatigue behavior and provides the means to integrate such disparate elements as loading pulse times, shapes, and rest periods between loadings into the thickness selection. A design approach based on this methodology will more accurately include airport conditions and provide a more reliable and economical pavement design.
Concrete Distress Identification
Starting in the early 1990s, studies at UIUC supported by IDOT demonstrated concrete deterioration due to alkali-silica reaction. Through microscopic examination of affected concretes, it was found that the reaction involves chert in the sand; and many sands in Illinois that are potentially reactive. Chert is a granular form of microcrystalline quartz, not a distinct mineral, but rather a type of rock; and it is often found in limestone (a common rock in Illinois). Some chert is reactive with alkalis and causes expansion and deterioration of concrete, but some chert is not reactive. The objective of this research is to explore whether there are microstructural or crystal-chemical features to distinguish reactive chert from non-reactive chert.
Subgrade Soil Support and Stabilization
As part of the O’Hare Modenization Program, this applied research provides testing and analysis to establish subgrade support conditions and stabilization requirements in support of the new designs and rehabilitations of pavements at the Chicago O’Hare International Airport. Based on field testing and soil sampling at the new O’Hare North Runway (9-27) site, laboratory testing is undertaken to establish pavement design inputs for subgrade support, soil stabilization requirements with respect to need for stabilization, stabilization admixture(s) selection, and stabilization depth. To ensure adequate airport pavement foundations, subgrade support is estimated for various combinations of subgrade stabilization treatments and prepared subgrade conditions.
Performance and Acceptance of Self-Consolidating Concrete (SCC)
Self-consolidating concrete (SCC) is a high-performance cementitious material that is designed to flow into formwork under its own weight. The ease of placement of SCC has the potential to reduce construction manpower, increase the rate of construction, and produce cost savings. This technology is rapidly gaining acceptance.
Research and development of SCC at UIUC focuses on uniformity of SCC and acceptance criteria. The goals of this research are to understand how SCC mixture characteristics may change hardened properties and impact performance or long term durability. Laboratory and field monitoring of SCC formwork pressure are used to evaluate construction practices and develop a predictive model. Mechanical properties such as creep, shrinkage, and stress development are studied, and a predictive modeling approach for shrinkage stress is being developed to assess the impact on design stresses and cracking.
Development of Performance Guidelines for Hot-Poured Crack Sealants
Preventive maintenance is the most effective approach to delay road deterioration, extend its service life, and save public funds. While crack sealing is one of the most common preventive maintenance techniques, sealant failure is common within the first three years of application. This research is geared towards developing performance guidelines for hot-poured crack sealants. The project outcome includes the development of testing procedures to predict sealant performance in the field utilizing rheological behavior of sealants at a wide range of temperatures; quantify the effect of aging on sealant performance; and investigate the adhesion capability of sealants to crack walls. In addition, the project will result in developing performance specifications to identify and categorize sealants based on crack parameters and environmental conditions.
Fracture Behavior of Fiber Reinforced Concrete Slabs
Discrete fibers have shown to improve the toughness of concrete materials based on small-scale laboratory specimens. A testing program was conducted to determine the fracture behavior of concrete slabs reinforced with steel and synthetic, discrete fibers, wire mesh, and plain concrete under monotonic loading. Large-scale slabs were cast, instrumented, and tested. The research explored the effects of various fiber types and volume fractions on the full-scale monotonic behavior of concrete slabs-on-ground. Relationships between the small-scale concrete toughness results and the concrete slab flexural capacities were derived. A design method was also proposed to incorporate the use of fiber into existing concrete pavement design procedures based on these experimental findings.
Materials Testing and Permanent Deformation Model Development for NAPTF Base/Subbase Layers
By studying the measured performances and deterioration behavior of the FAA’s National Airport Pavement Test Facility (NAPTF) airport pavements, rutting accumulated in granular layers is studied through improved testing and modeling. The work areas consist of sampling and advanced laboratory testing of granular base/subbase aggregates, determining the most damaging field stress states affecting aggregate performance, development of material characterization and laboratory performance based models, and finally, based on laboratory performance-based evaluation, development of specifications for field construction and compaction of unbound granular layers. The research findings are intended to identify pavement deterioration mechanisms under heavy aircraft loading to advance science and technology in making rut resistant airport pavement structures.
Reflective Crack Control Treatment and Design Procedures
In A new integrated approach through an NSF GOALI (Grant Opportunities for Academic Liaison with Industry) project, researchers at the University of Illinois have collaborated with researchers from industry to vigorously expand experimental fracture testing methods and basic knowledge of fracture mechanisms in asphalt pavements and overlay systems. The project has addressed the aforementioned problem through a highly-integrated approach involving laboratory fracture testing, numerical simulation, and field validation studies. Laboratory investigations have led to the development of two new fracture tests: a single-edge notched beam (SE[B]) test suitable for mode I and mixed-mode fracture testing and a practical disk-shaped compact tension (DC[T]) test. Simultaneously, progress in the development of cohesive-zone fracture models suitable for the modeling of crack initiation and propagation in asphalt concrete mixtures has been accomplished.
