Amanda Bordelon

Fracture behavior of functionally graded concrete materials for rigid pavements

Currently, in concrete pavements, a single concrete mixture design and structural surface layer are selected to resist mechanical loading without an attempt to affect concrete pavement shrinkage, ride quality, or noise attenuation adversely. An alternative approach is to design sublayers within the concrete pavement surface that have specific functions and thus to achieve higher performance at a lower cost. The objective of this research was to address the structural benefits of functionally graded concrete materials (FGCMs) for rigid pavements by testing and modeling the fracture behavior of different combinations of layered plain concrete materials and concrete materials reinforced with synthetic fibers. The three-point bending-beam test was used to obtain the softening behavior and fracture parameters of each FGCM. The peak loads and initial fracture energy between the plain, fiber-reinforced, and FGCMs were similar; this signified similar crack initiation. The total fracture energy clearly indicated the improvements in fracture behavior of FGCM relative to full-depth plain concrete. The fracture behavior of FGCM depended on the position of the fiber-reinforced layer relative to the starter notch. The fracture parameters of both the fiber-reinforced and plain concrete were embedded into a finite element–based cohesive zone model. The model successfully captured the experimental behavior of the FGCMs and now can be implemented to predict the fracture behavior of proposed FGCM configurations and structures such as rigid pavements. This integrated approach (testing and modeling) is promising and demonstrates the viability of FGCM for designing layered concrete pavement systems.

Design with fiber reinforcement for thin concrete overlays bonded to asphalt

AbstractA thin concrete overlay bonded to asphalt pavement design approach has been developed by extending an existing ultrathin whitetopping (UTW) design method. A significant contribution to this proposed design method is the incorporation of fiber reinforcement into the structural design and concrete material specification, through the implementation of a residual strength ratio requirement. Climate and traffic inputs were simplified through the use of an equivalent temperature gradient and equivalent single-axle loads (ESALs). A probabilistic concrete fatigue algorithm was also used to allow engineers to select the appropriate level of reliability and the amount of cracking for the UTW project. The new concrete overlay design method is most influenced by the concrete flexural strength, fiber-reinforcement residual strength, slab size, traffic, and the underlying asphalt condition and thickness.

Flowable Fibrous Concrete for Thin Concrete Inlays

A thin concrete pavement wearing surface has been developed using a flowable fibrous concrete (FFC) as a 50 mm (2 in.) inlay on a milled asphalt concrete pavement. The flowable concrete mixture incorporating a hybrid of synthetic fibers was optimized for rapid placement and consolidation. An objective of the wearing surface was to construct reasonable slab sizes and crack widths while ensuring economic feasibility. Laboratory testing demonstrated the FFC has a slump flow diameter value of 400 mm (15.5 in.) and post-cracking residual strength ratio over 47 percent with 0.5 percent volume fraction of synthetic macrofibers. A full-scale demonstration project was cast to evaluate constructability and concrete material performance including placement issues, crack spacing and width development, and interface bonding conditions. Different slab sizes were explored from 1.2 to 3.3 m (4 to 11 ft) with the longer slabs having the earliest and widest cracking up to 1.25 mm (0.05 in.). The joints cracked before day one reside as the largest crack widths measured at later ages. In-situ bonding tests confirmed a good bond between the asphalt and concrete, except in locations where debris from the asphalt layer was not adequately removed.

Fracture Behavior and Properties of Functionally Graded Fiber‐Reinforced Concrete

In concrete pavements, a single concrete mixture design is selected to resist mechanical loading without attempting to adversely affect the concrete pavement shrinkage, ride quality, or noise attenuation. An alternative approach is to design distinct layers within the concrete pavement surface which have specific functions thus achieving higher performance at a lower cost. The objective of this research was to address the structural benefits of functionally graded concrete materials (FGCM) for rigid pavements by testing and modeling the fracture behavior of different combinations of layered plain and synthetic fiber‐reinforced concrete materials. Fracture parameters and the post‐peak softening behavior were obtained for each FGCM beam configuration by the three point bending beam test. The peak loads and initial fracture energy between the plain, fiber‐reinforced, and FGCM signified similar crack initiation. The total fracture energy indicated improvements in fracture behavior of FGCM relative to full‐dep...

Fiber Effect on Interfacial Bond Between Concrete and Fiber-Reinforced Mortar

Field overlay and bridge deck studies have suggested that vertical curling deflections and debonding can be reduced when the overlay contains fiber reinforcement. This study investigates the tensile and shear bond between aged concrete and fiber-reinforced mortar. Three macrofibers commonly used in fiber-reinforced concrete pavement overlays or bridge decks were investigated. The macrofibers were a stretched synthetic, a textured synthetic, and a hooked-end steel fiber. The tensile fracture energy within the fiber-reinforced mortar material and an interfacial tensile bond energy between the fiber-reinforced mortar cast against the aged and sandblasted concrete were all higher than that of plain unreinforced mortar. The peak loads associated with tensile or shear bond failure were not statistically affected with the addition of fibers in the overlay mixture. Overall, the interfacial tensile bond energy did improve as the fiber volume content increased, especially because some of the fracture path occurred through the mortar layer and was bridged by the fibers near the interface surface.

Investigation of ESALs versus Load Spectra for Rigid Pavement Design

The influence of traffic as an input parameter for mechanistic-empirical (M-E) pavement analysis on the percentage of fatigue cracks on slabs or the required slab thickness for jointed concrete pavements (JPCP) was investigated. Site-specific traffic data from Illinois weigh stations exhibiting different axle load and vehicle class distributions were compared against the default traffic inputs used in the M-E pavement design program. The load spectra for several sites were adjusted by changing the annual average daily truck traffic (AADTT) volumes to produce the same equivalent single axle loads (ESALs) for a typical interstate highway design in Illinois. The influence on the required JPCP thickness varied less than 2.0 inch (50 mm) for combinations of all traffic distributions and climate regions given the same level of ESALs. For a given climate station with a fixed ESAL level, there was no significance in cracking level for the load spectra data gathered at different stations across Illinois. Only in extreme overload traffic cases, where a significant percentage of the single axle weights were 50 percent greater than the legal limit, did the distribution of traffic significantly influence the slab cracking performance for a fixed number of ESALs and climate. For JPCP design, the difference between using an ESAL-based design and load spectra design for fatigue cracking prediction was determined to be negligible when using the M-E pavement design program with existing Illinois traffic inputs and a realistic magnitude of overloads.

Properties of Different Pumice Grades Blended with Cement

AbstractThe research focused on determining the effect of fresh and hardened properties of paste, mortar, and concrete using high Si-Al-Na–containing pumice as a supplementary cementitious material...