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 (≥ 3/8 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

Improvement of Base and Soil Construction Quality by Using Intelligent Compaction Technology: Final Report

Report on a project to capitalize on the new specification for implementation of IC technology developed through TxDOT research project 0-6740. The specific objectives of this project included: (1) developing and deploying a training program for the TxDOT engineers and inspectors, (2) supporting the districts in implementing the IC technology in their districts, (3) implementing a field monitoring program to quantify the benefits of the IC technology, and (4) assisting TxDOT Construction Division in evaluating and adopting the new IC specification. The activities to achieve these objectives, the lessons learned from the pilot implementation projects, and the conclusions are included in this report

Development of a Numerical Simulation Tool for Continuously Reinforced Concrete Pavements

DTRT13-G-UTC36The accurate modeling of the main features of continuously-reinforced concrete pavements (CRCP) is of primary importance in a mechanistic-empirical pavement design procedure. The use of the finite element (FE) method as a comprehensive tool for modeling the responses of rigid pavements, CRCP in particular, has been limited because of the complexity of calculations in modeling material nonlinear behaviors, which are difficult to describe mathematically and computationally. Significant amount of research has been conducted to improve the design of CRCPs under traffic, environmental, and thermal loads. To develop a reliable model that better represents the behavior of CRCP, a clear understanding of the design features that impact CRCP responses is essential. Researchers from the University of Texas at El Paso developed NYSLAB to analyze the response of comprehensively jointed concrete pavements (JCPs) under different geometric configurations, foundation models, temperature gradient profiles and traffic loads. This tool has the capability to analyze pavements under nonlinear thermal profiles across the thickness of the slab and capture the frictional tractions between the slab and foundation. All the complications related to appropriate discretization and modeling are handled internally by the software. This research study aims to expand the capacity of NYSLAB by integrating a CRCP model that is capable of predicting the responses of a critical section within a CRCP pavement structure subjected to traffic and environmental loading conditions. Unlike JCPs, CRCPs use reinforcing steel rather than contraction joints for crack control. Therefore, the development of a new FE model that defines the complex interaction between the reinforcement steel and concrete as well as the slab-foundation interaction due to friction and temperature changes will be implemented into the proposed tool

Evaluation of Level 3-4 Intelligent Compaction Measurement Values (ICMV) for Soils Subgrade and Aggregate Subbase Compaction

1034039Intelligent compaction (IC) is a roller-based innovative technology that provides real-time compaction monitoring and control. IC can monitor roller passes, vibration frequencies/amplitudes, and stiffness-related values of compacted materials or intelligent compaction measurement Values (ICMV). Various ICMVs have been introduced since 1978. Based on the five levels of ICMV in the 2017 FHWA IC Road Map, the current implementation of ICMV in the United States has been limited to Levels 1 and 2. However, Level 1 and 2 ICMVs fail to meet the FHWA IC Road Map criteria. To achieve the full potential of IC technology, Level 3 and above ICMVs are needed to gain the confidence of agencies and industry and the adoption of IC to soil and base compaction. This project aims to (1) evaluate Level 3-4 ICMV systems against Level 1 ICMV systems for soils, subbase, and base compaction and (2) develop a blueprint for future certification procedures of IC as an acceptance tool. This study also aligns with the goals of the ongoing HWA IC for foundation study and the TPF-5(478) pooled fund study. This final report details the ICMV background, field test efforts, analysis results, and an IC specification framework for compaction acceptance

Mechanistic-based field evaluation of pavement foundation

For the last few decades, practitioners have understood the importance of the properties of pavement foundation layers on the performance of rigid and flexible pavements. With the pavement community’s widespread interest in implementing a new mechanistic empirical pavement design program (ME-PDG), the importance of accurately quantifying the stiffness and thickness of the foundation layers has become even more critical.ASCE, Geo Institute, Soy In

Comparison of Theoretical and In Situ Behaviors of a Flexible Pavement Section

The use of nondestructive testing (NDT) devices has provided pavement engineers with a simple method for determining pavement layer moduli. Moduli obtained with the NDT devices are used in mechanistic pavement design. Therefore, it is important to determine accurately the elastic moduli of pavement systems. Through a case study, some concerns with the deflection-based NDT of pavements are examined. The main objectives were (a) to establish the accuracy of a backcalculation methodology, (b) to determine the closeness of the theoretical and measured deformations within a pavement cross section, and (c) to assess the impact of the established accuracies on the design of pavement sections. These items are discussed through an example from one instrumented site. The instrumentation and algorithm used to determine in situ deflections are briefly described. A total of seven state-of-the-art NDT devices were employed. Particular attention was devoted to the effects of the load-induced nonlinearity associated with the large magnitude of loads imparted by the NDT devices to the pavement. On the basis of the case study, it was found that some differences in the deflections predicted the use of backcalculated moduli and measured deflections. It was also shown that load-induced nonlinearity may be one of the reasons for the poor match between the measured and theoretical deflection basins. Mechanistic pavement design has been used more frequently in recent years than in earlier years. The backbone of mechanistic pavement design is nondestructive testing (NDT). To confirm the validity of mechanistic models and NDT methods, it has become important to monitor the behavior and performance of pavements under actual loads. As such, much effort has been focused on instrumenting pavements. One response parameter usually measured is the deflection within the body of the pavement. Multidepth deflectometer (J) or geophone units (2) can be used to obtain this information. One site was instrumented with geophones and tested with seven NDT devices. The main objective of this study was to determine how well layered elastic theory in conjunction with NDT devices can predict the behavior of pavements. To achieve this objective, several steps were taken. The first step was to determine the effects that the load level and the sensor locations might have on backcalculated moduli. For each NDT device, and each load level, up to 19 deflections were available, 12 within the pavement section and the rest on the surface. Eight combinations of deflections were used in backcalculation. On the basis of these results, a thorough discussion of the effects that the load level, location, and number of deflection sensors and type of NDT device may have on backcalculated moduli was carried out. Department of Civil Engineering, University of Texas at El Paso, El Paso, Tex. 79968. The second goal was to determine how well the deformations, stresses, and strains are determined. A comprehensive comparison of stresses and strains from various types of NDT devices used is also included in this paper. BACKGROUN

Asphalt Testing: Enhancing the Roads

At the University of Texas at El Paso, the Center for Transportation Infrastructure Systems is conducting several asphalt tests to ensure the quality of the asphalt and the safety of the public. The tests determine special engineering properties of the material such as the strength and aggregate-asphalt ratio that are crucial to the life span of the asphalt on the field. The five tests that are conducted are: Maximum Theoretical Specific Gravity Test (GMM) – used to find the density of the material Bulk Specific Gravity Test (GMB) – determines the air pockets (air voids) in the material using the previous test Gradation Test – calculates the asphalt and aggregate content Hamburg Wheel Tracker Test – used to determine the rigidity of the material Indirect Tensile Test – determines the tensile strength The purpose of the project is to modernize an asphalt database that is a result of many years and the collaboration of many engineers. Paving the roads with better and stronger material will improve the highway and interstate systems. Transportation and communication will be easier and more efficient

Extracting damping information from resilient modulus tests

In addition to the dynamic moduli, the damping properties of the different pavement layers are required by most algorithms used for modeling the dynamic responses of pavement caused by moving or impact loads. The importance of the damping properties in estimating the proper responses is well documented in the geotechnical engineering community. The dynamic moduli are typically estimated in the laboratory using the cyclic triaxial (resilient modulus) tests. The feasibility of estimating the damping properties with resilient modulus tests is explored in this paper. The most promising algorithm among the alternatives studied was preliminarily established from the resilient modulus tests carried out on 17 gravel bases, sandy subgrades, and clayey subgrades. The selected method was used to develop a database for further evaluation. The damping coefficient was correlated to the applied stresses, the measured strains, and the nonlinear stiffness parameters (k(1)-k(3)) obtained from a nonlinear constitutive model commonly used in mechanistic-empirical pavement analysis methodology.info:eu-repo/semantics/publishedVersio