Soheil Nazarian

Moisture Content-Based Longitudinal Cracking Prediction and Evaluation Model for Low-Volume Roads over Expansive Soils

AbstractThis paper summarizes a methodology for using moisture content (MC) together with soil index properties to study and predict the progression of longitudinal shrinkage cracking (LSC) along low-volume roads through finite-element analysis. Extensive laboratory tests were performed on soil samples retrieved from six representative clayey sites in Texas, including five high plasticity index (PI greater than 25) sites and one low-PI site. Field measurements of moisture content, suction, and crack development were carried out at five representative farm-to-market roads constructed over the high-PI clayey materials in southern and eastern regions of Texas for verification. Compared to the prevailing suction-based approach, the MC-based approach offers more flexibility in terms of incorporating different drying/wetting paths into numerical modeling by laboratory-based material constitutive models. The estimated critical moisture content thresholds and locations of LSC showed good agreement with the field ...

Correlating the resilient modulus and seismic modulus of subgrade materials incorporating moisture and density variations

Resilient modulus tests are commonly used to determine the representative modulus of geomaterials as well as to establish their nonlinear behaviors. Such tests are complex and time consuming and therefore only performed during high priority construction projects. In comparison, seismic modulus tests are rapid, nondestructive and provide low-strain linear elastic moduli. Although, seismic moduli are measured at lower strains than those imparted to pavements by vehicular traffic, it is desirable to relate the moduli from these two tests since the seismic modulus tests lend themselves to a convenient tool for quality management of compacted geomaterials. Several geomaterials were comprehensively tested with the resilient modulus and seismic modulus devices at different moisture contents. The laboratory seismic moduli were several times greater than the corresponding representative resilient moduli. However, a reasonably well-correlated relationship was observed between them. This relationship was further improved and strengthened by incorporating moisture-density parameters of the materials.

Methodology for Determining Performance Life of Hot-Mix Asphalt Mixtures

A critical component of the life-cycle cost analysis for staged design and rehabilitation of flexible pavements is to estimate the service lives of various hot-mix asphalt (HMA) mixtures, which in some cases is carried out subjectively. This paper describes a process for using the existing data to develop an objective and data-driven process for estimating the service lives of common HMA mixtures. Spatial information along with construction records and distress and functional condition logs are merged to assess the “cradle-to-grave” service lives and deterioration patterns, statewide or regionally. One of the most challenging steps was linking separate databases to compile a comprehensive pavement performance database. The end result was an online tool that enabled the extraction of HMA service life data and descriptive statistics of several thousand road sections. The probabilistic performance life of each common mix was then estimated through an integrated approach of survivability analysis that considers the historical longevity of mix types, the age of the HMA surface course, distress history–based life predictions, field case study life predictions, and department of transportation personnel perceived service lives. The results as applied to Texas data showed bimodal longevity distributions of service life. In general, the mean service life of the analyzed dense-graded mix met or exceeded the mean perceived service life expressed by two dozen pavement engineers statewide. However, a fraction of the projects exhibited shorter lives because of a number of technical and institutional factors. Overall, the proposed methodology proved to be a consistent process when assessing HMA service life.

Alternative methodology for assessing cracking resistance of hot mix asphalt mixtures with overlay tester

Several highway agencies have either implemented or considered implementing performance tests to predict the cracking potential of asphalt concrete (AC) mixes in the laboratory setting. One such test, the overlay tester (OT), simulates the opening and closing of the cracks induced by daily temperature variations and tensile strain generated by the traffic load. The variability of the OT results is expressed as a major concern in reliably characterising cracking potential of the AC mixes. A more fundamental analysis process and more mechanistic performance indicators were implemented that consider the two stages of the cracking mechanism (i.e. crack initiation and crack propagation). The repeatability of the proposed performance indices, critical fracture energy and crack progression rate, seems to be better than the current criterion based on the number of cycles to dissipate 93% of the initial maximum peak load. The proposed cracking methodology and associated preliminary failure limits seem to characterise and discriminate satisfactorily the cracking resistance of AC mixes. Given its promise in this study, the proposed OT test method is recommended as a routine test during the mix-design process of AC mixes to predict and screen their cracking susceptibility.

Performance of the Overlay Tester in Monotonic and Cyclic Loading Modes

The overlay tester (OT) is considered by several highway agencies as an index test to evaluate the cracking resistance of asphalt mixtures in the laboratory. The OT simulates the reflective cracking mechanism of the opening and closing of joints and/or cracks. The repeatability of the number of cycles to failure measured with the OT is expressed as a concern in reliably characterizing the potential of hot mix asphalt (HMA) mixes to cracking. The work presented in this paper was performed mainly to analyze the repeatability of the number of OT cycles to failure and the fracture energy (FE) measured with the cyclic and monotonic OT methods. The load-displacement curves from the cyclic and monotonic OT tests were compared to select the promising alternative parameters that could serve as surrogate cracking parameters. The performance of the OT test may improve if alternative parameters, such as the maximum load and fracture energy are used to estimate the cracking resistance of the HMA mixes.