Jose Garibay

Assessment of Corrosion Potential of Coarse Backfill Aggregates for Mechanically Stabilized Earth Walls

The service life of mechanically stabilized earth walls depends on the rate of corrosion of the metallic reinforcements used in their construction. The assessment of corrosion potential requires an accurate evaluation of pH, resistivity, and sulfate and chloride concentrations of aqueous solutions in contact with the surrounding aggregate. Highway agencies tend to use larger aggregates that contain only a small amount of fine material (passing the Number 40 sieve) in the backfill. Evaluation of the electrochemical parameters of coarse aggregates is challenging because traditional evaluation methods call for the use of fine material. In this study, the suitability of traditional soil characterization techniques for use with coarse aggregates was assessed through leaching experiments performed on coarse limestone and dolomite aggregates from six quarries in Texas. Chemical differences were isolated from size-related kinetic leaching effects by comparing the results from same-sized material collected in the field with material derived from the crushing of larger (≥⅜ in.) aggregates in the laboratory. The testing demonstrated that the fines collected from the field were enriched in chemicals that, when exposed to water, decreased pH and resistivity and increased sulfate concentrations compared with the bulk rock. This was likely the result of sulfur compounds in the atmosphere reacting with carbonate rocks to produce reactive surface layers that were mechanically abraded into the fines. This phenomenon could bias traditional soil testing results and, therefore, the assessment of corrosion potential. This study demonstrated that a more accurate assessment of the electrochemical parameters can be obtained by crushing the coarse material to meet testing size specifications.

Effects of Moisture Variation on Resilient and Seismic Moduli of Unbound Fine-Grained Materials

Moisture variation in a pavement structure due to the environment has a large impact on the moduli of unbounded layers. The moisture variation can affect the performance of the pavement as documented in a number of laboratory and field studies. As such, it is desirable to account for this behavior in the design or evaluation of a pavement. In this study, the effects of moisture variation and compaction effort were investigated through a series of well-controlled laboratory tests on different fine-grained geomaterials. Different sources of fine-grained materials were selected to prepare the laboratory specimens for both resilient and seismic modulus tests. The existing modulus-moisture models were evaluated during the moisture conditioning cycles for the specimens prepared and compacted at different moisture levels. Furthermore, the normalized difference of moisture content at the time of compaction and optimum moisture content was used to explain the trends. A model is proposed to improve the prediction of changes in resilient modulus based upon moisture content. The proposed model showed reasonable agreement with the experimental data.

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.

Overlay Tester Results from Dense-Graded Asphalt Concrete Mixes

Several highway agencies have either implemented or considered implementing laboratory performance tests to estimate the cracking potential of asphalt concrete (AC) mixes during the mix design process. One such popular test, the overlay tester (OT), measures the number of cycles to failure of specimens that are caused by the repeated application of deformation. The major concern about using this test as a reliable characterization of the cracking susceptibility of AC mixes, especially for dense-graded mixtures, is the variability in the specified number of cycles to failure in the performance index. The main objective of this paper is to report a means for improving the consistency of the OT test results on dense-graded AC mixes. An assessment of a specimen preparation process that can yield more consistent results was conducted. The consistency of the traditional number of cycles to failure as well as of the load–displacement response and load reduction curves was investigated by using a modified specimen preparation process. The repeatability of alternative performance indexes, such as the critical fracture energy and crack progression rate, that can be measured from the OT test was also investigated and compared with that of the index for the number of cycles to failure. This study indicated that the raw data from the OT test seemed to be repeatable if the proposed specimen preparation process was consistently followed. Alternative performance indexes that yielded an acceptable degree of repeatability may be readily implemented in the OT test to assess the cracking characteristics of AC mixes.

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.

Compaction Quality Monitoring of Lime-Stabilized Clayey Subgrade Using Intelligent Compaction Technology

This study presents the evaluation of the compaction process on a lime-stabilized clayey subgrade soil using the intelligent compaction (IC) technology. Two test beds with similar clayey subgrade soil were constructed with and without in-situ lime stabilization. These test beds were evaluated using several in situ nondestructive testing devices and an IC-equipped vibratory roller. The results from the study showed significant spatial variability in the in-situ test results and the roller measurements. In comparison to the untreated subgrade, the lime-stabilized test sections demonstrated a reduction in the variability of the roller measurements. The roller measurements on the stabilized section were influenced by the testing time and the underlying support conditions. The laboratory results and the field measurements using the roller and in-situ devices pointed to the improvement in the soil properties after stabilization. The moduli of the stabilized subgrade soil increased by almost two times. Statistical analyses demonstrated the influence of the underlying support condition, the moisture content and the lift thickness variations on the roller measurements.

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.