Individual presentations of the best papers submitted to the Aggregates Committee. Three main areas are covered:
1) Testing of granular material,
2) Assessing and modeling waste / by-product materials for use as aggregates,
3) Assessing the effect of particle shape, texture and basic mix characteristics on aggregate performance in pavement use
Evaluation of Iron Tailings as Aggregates in Asphalt Mixture
Liping Cao (email@example.com), Harbin Institute of TechnologyShow Abstract
Jie Zhou, Harbin Institute of Technology
Zhiwen Tian, China State Construction Silkroad Construction Investment Group Co., Ltd.
Zejiao Dong, Harbin Institute of Technology
Iron tailings are solid waste yielded during the beneficiation process of iron mine, which not only occupy a great quantity of land, but also cause serious pollution to environment. The aim of this study is to evaluate the feasibility of iron tailings as aggregates in asphalt mix. A suite of laboratory tests were conducted on iron tailings and asphalt mixtures containing iron tailings. Aggregate property tests involved composition characteristics, microstructure, physical and mechanical properties, weather resistance, and adhesion to asphalt. Pavement performance tests included rutting resistance, thermal cracking resistance, and moisture susceptibility. The test results showed that iron tailings had a relatively poor adhesion to asphalt due to acidic chemical composition and smooth surface texture, but the adhesion difference between it and conventional aggregates can be narrowed by utilizing high-viscosity asphalt binder. In addition, although iron tailings had lower density, higher water absorption, flat and elongated particle content, silt dosage, crushing value, and LA abrasion loss in comparison to basalt, these properties met the specification requirements. The asphalt mixtures with iron tailings possessed satisfactory high-temperature property and water stability. By means of using limestone as fine aggregate or applying modified asphalt with superior properties, various key pavement performances were enhanced significantly and mixes can be used in paving application. Therefore, iron tailings are a promising material and the replacement of natural mineral aggregates with it will contribute to the future development of road engineering and mining industry.
Compressibility Assessment of Roadway Embankments Using Tire Derived Aggregates (TDA)
Auchib Reza, Memorial University of NewfoundlandShow Abstract
Kamal Hossain, Carleton University
Ashutosh Dhar, Memorial University of Newfoundland
On average, one tire per capita per year is generated in Canada as a waste tire, which either goes to landfill or stockpile. Researchers across the world are trying alternative uses of scrap tires. Among many civil engineering applications, roadway embankment construction using tire-derived aggregates (TDA) is the most popular and ecologically viable due to large amount of consumption of material in the embankment. However, its deformability/ compressibility under applied load is an important consideration for design of tire shred embankment. The mechanical behavior of tire shreds is dependent on stress levels, which shows nonlinear viscoelastic-plastic behaviour. There is a lack of quantitative information on the compressibility characteristics of tire shred embankments. In this study, the finite element (FE) method is applied to assess the compressibility of the tire shred embankment. Nowadays FE method is being increasingly used in deformation analysis of pavements. Linear and nonlinear compressibility analysis of tire shred embankment is performed, assuming a multilayer elastic-isotropic system. The results show that deflections of the road calculated from nonlinear elastic analysis are significantly higher than those calculated using linear elastic model. The analysis also shows that small size tire shreds (50 mm) experience less deflection compared to large size tire shreds (300 mm). Resulted deflections obtained from FE calculations are then compared with the results from an analysis using a multilayer computer software, KENLAYER, available in published literature. Finally, the paper presents the key features of tire compressibility of different sizes of tire shreds observed during the FE analysis.
Anisotropic Resilience Modulus Model of Granular Materials Based on Particle Characteristics
Zefeng Tao, Tongji UniversityShow Abstract
Zengyi Wang, Tongji University
Jianming Ling, Tongji University
Yu Tian, Tongji University
Juewei Cai, Tongji University
Granular materials are widely used for base or subbase in pavement structure. It typically exhibits strong anisotropic properties which is related to stress state and particle characteristics. Conventional design procedure for flexible pavements underestimates the anisotropy of resilience modulus. This study established an anisotropic resilience modulus model for granular materials, considering gradation and particle shape characteristics. Vertical and horizontal resilience modulus of certain granular materials was measured via self-developed triaxial tests, to obtain corresponding model parameters and anisotropic coefficient. Gradation and particle shape models were established to quantify the granular material characteristics, and the parameters were regressed. Particle shapes were obtained via image processing, and the ratio (η) of particle sphericity to roundness was chosen as a shape parameter. Results show that η increases with the dwindling of particle size, and the average values of η for graded gravel and natural laterite are 0.54 and 0.63, respectively. The η distribution curves indicate that the proportion of relatively anisotropic particles, rather than extremely anisotropic particles, results in the difference of particle shape characteristics. The regression relationship between anisotropic calculation parameters and model parameters of vertical resilience modulus, gradation and particle shape was established. Thus, the horizontal resilience modulus and anisotropic coefficient can be predicted, via conventional resilience modulus tests and gradation and particle shape analysis. This study shows that the anisotropy of granular materials, decreases with the increase of coarse particles and the uniformization of gradation curve, and increases with the increase of anisotropic particles and the polarization of η distribution.
Structural Modelling of Recycled Materials for Rehabilitating Urban Heavy Haul Arterial Roadways
Curtis Berthelot, PSI Technologies, Inc.Show Abstract
Rielle Haichert, PSI Technologies
Jody Berthelot, PSI Technologies
Roberto Soares, PSI Technologies
The “Green Street” Program investigated the use of on-site recycling and off-site recycled portland cement concrete and asphaltic concrete materials to construct test sections during the 2009 construction season. This study includes a review of the 8th Street East test sections constructed in Saskatoon, Saskatchewan and subsequent structural testing and modeling performed 7 to 9 years after initial structural rehabilitation construction. The structural modelling performed in this study investigated the effects of heavy construction truck traffic on the rehabilitated sections (recycle and conventional) seven years after initial construction. Material constitutive properties used for the structural modelling were derived from falling weight deflection measurements taken 7 years after construction to provide realistic in situ material properties within the actual field state conditions of the road test sections. Based on the numerical three-dimensional modelling results, it was found the recycle test sections generated significantly lower primary strain behavior relative to the conventional test section. Of particular interest, for urban cross sections, the horizontal shear strain state generated under the curb and sidewalk adjacent to the loaded lanes were significantly lower.
Feasibility of Using More Highly Polishable Aggregates in Asphalt Surface Mixture: A Case Study for West Virginia Division of Highways
Fan Gu (firstname.lastname@example.org), Auburn UniversityShow Abstract
Michael Heitzman, 3d-Radar
Buzz Powell, Auburn University
Vincent Allison, West Virginia Division of Highways
This study aimed to evaluate the feasibility of using more highly polishable aggregates (e.g., dolomite) in asphalt surface mixtures that are typically used by West Virginia Division of Highways (WVDOH). Asphalt slabs containing different percentages of dolomite coarse aggregates were abraded by the three-wheel polishing device (TWPD). The dynamic friction tester (DFT) was used to measure the friction deterioration of these asphalt slabs. The laboratory DFT test results indicated that increasing dolomite content in asphalt surface mixtures resulted in a faster deterioration rate at the early polishing stage (i.e., 5,000 – 20,000 polishing cycles). In addition, asphalt surface mixtures containing more than 50% dolomite coarse aggregates had a terminal DFT friction coefficient measured at 20 km/h less than 0.30, which would significantly reduce roadway safety when using for asphalt pavements. At the NCAT Pavement Test Track, two sections were built in 2018 that used 70% and 90% dolomite coarse aggregates in the asphalt surface course. DFT and locked-wheel skid trailer (LWST) tests were conducted to determine the friction performance of these two sections and confirmed that replacing sandstone coarse aggregates by 70% and 90% dolomite aggregates resulted in asphalt surface mixtures with fairly low long-term skid resistance. A shotblasting treatment was applied to enhance both the microtexture and macrotexture of the test sections. After 2.3 million ESALs of traffic, both sections exhibited better friction performance. Through the pavement performance evaluation, the shotblasting treatment was found to have no detrimental impact on cracking, rutting, and surface roughness of asphalt pavements.
Invited Student Paper: Using Artificial Intelligence to Estimate Nonlinear Resilient Modulus Parameters from Common Index Properties
Laura Camarena, University of Texas, El PasoShow Abstract
The Mechanistic Empirical Pavement Design Guide (MEPDG) considers a hierarchical approach to determine the input values necessary for most design parameters. Level 1 requires site-specific measurement of the material properties from laboratory testing, while other levels make use of equations developed from regression models to estimate the material properties. Resilient modulus is a mechanical property that characterizes the unbound and subgrade materials under loading that is essential for mechanistic design of pavements. The MEPDG resilient modulus model makes use of a three-parameter constitutive model to characterize the nonlinear behavior of the geomaterials. Since the resilient modulus tests are complex, expensive, and require lengthy preparation time, most state highway agencies are unlikely to implement them as routine daily applications. Therefore, it is imperative to make use of models to calculate these nonlinear parameters. Existing models to determine these parameters are frequently based on linear regression. With the development of machine learning techniques, it is feasible to develop simpler equations that can be used to estimate the nonlinear parameters more accurately. This study makes use of the LTPP database and machine learning techniques to improve the equations utilized to determine the nonlinear parameters crucial to estimate the resilient modulus of unbound base and subgrade materials.
INCORPORATING LOAD CYCLE NUMBER AND SHEAR STRESS RATIO IN A SIMPLE PERMANENT DEFORMATION MODEL FOR UNBOUND MATERIAL
Phillip Ooi (email@example.com), University of HawaiiShow Abstract
A power model (ε = A.N^B) to estimate permanent strain ( ε ) from single-stage repeated load triaxial (RLT) testing can simulate both shakedown and incremental collapse. When the exponent B < 1, the ε versus load cycle number (N) plot concaves downwards, resembling that of a material that shakes down. When B > 1, the same plot concaves upwards, mimicking that of a material that incrementally collapses. A and B must be related to the shear stress ratio (SR = 1/factor of safety), a measure of how far the RLT specimen is away from static failure. A power model was developed for a virgin and a recycled concrete aggregate utilizing 2 independent variables (N and SR) with A and B both functions of SR . A methodology to quantify SR that considers non-linearity of the Mohr-Coulomb failure envelope, cohesion due to suction in the unsaturated RLT specimens and that estimates an appropriate mobilized shear stress is presented. For the two unbound materials tested, A was found to decrease non-linearly with increasing SR while the relationship between B and SR is quite linear. The resulting model with four fitting parameters was able to simulate the RLT test data quite well overall. The fitting parameters can be derived using linear regression and were all statistically significant with a confidence level exceeding 95%. Once B is known, the shakedown limit can be estimated by setting B < 1. An appropriate margin of safety should be incorporated to limit the permanent strain.
New Turner-Fairbank Alkali-Silica Reaction Susceptibility Test for Aggregate Evaluation
Jose Munoz (firstname.lastname@example.org), SES Group and AssociatesShow Abstract
Chandni Balachandran, SES Group & Associates, LLC
Terence Arnold, Federal Highway Administration (FHWA)
The ASTM C1260 and ASTM C1293 are generally accepted as being the best available accelerated tests to evaluate the alkali-silica reactivity of aggregates used in concrete. Unfortunately, these tests have limitations such as the significant amount of false-positive and false-negative results in ASTM C1260 and the alkali leaching in ASTM C1293 that reduce their accuracy. This paper introduces an alternative test method, the Turner-Fairbank alkali-silica reaction (ASR) susceptibility test (T-FAST) that overcomes traditional limitations of both ASTM standards. In the new test, the ASR was accelerated by exposing the aggregates to a 1 N NaOH solution, three different amounts of CaO, and two temperatures for 21 days. The reactivity index (RI), calculated based on the 21-day concentrations of aluminum, calcium, and silicon in liquid phase, was used to assess the alkali-silica reactivity of 24 well-known aggregates—17 coarse and 7 fine. The results agreed with the classification of the same based on ASTM C1293 and historic field performance available in the literature. The aggregate-alkali threshold, the alkali concentration at which the ASR reaction was triggered, of specific samples measured using the T-FAST matched values previously reported in the literature. The alkali threshold determined for a river sand from Arkansas helped to understand the unexpected ASR distress observed in the field for an aggregate traditionally categorized as nonreactive. This case is a good example of mismatch in the information between accelerated-ASR standard tests and field performance.
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