Leila Hashemian

Effects of Seasonal Variation on the Load-Bearing Capacity of Pavements Composed of Insulation Layers

Seasonal variation in the subgrade resilient modulus is likely caused by external factors, such as precipitation and freeze–thaw cycles. One of the strategies for minimizing the impact of this variation on the subgrade modulus is to use insulation layers to prevent frost penetration. This study investigated the effects of the use of insulation layers on pavement performance in the fully instrumented Integrated Road Research Facility in Edmonton, Alberta, Canada. Three insulated sections of the test road were comprised of bottom ash (BA) (100 cm) and polystyrene boards of two thicknesses (5 and 10 cm), and the adjacent conventional section was considered the control section (CS). The resilient modulus and the effective modulus of pavement were backcalculated with the data obtained from falling weight deflectometer testing conducted at the test road during a 1-year monitoring period, from July 2014 to July 2015. Temperature and moisture probes, installed across the depth of the sections, were used to determine the frozen, thawed, or recovering condition of the pavement. The study results revealed that polystyrene boards protected subgrade soil from freezing and thawing effects. The minimum ratio of the backcalculated subgrade modulus of each test to the resilient modulus of the test performed in September was 0.94 in the BA section, and the ratio of the CS could decrease to 0.88 in the recovering period. Comparison of the load-bearing capacity of insulated sections and the CS indicated that, unlike BA, polystyrene boards significantly decreased the load-bearing capacity of the pavement.

Laboratory Investigation of Pavement Backfilling Materials for Micro-Trenching in Cold Regions

This study investigated the performance of different materials in a micro-trench composite backfilling design. Laboratory tests were conducted to evaluate the effect of cold temperatures and freeze/thaw cycles on a cement grout and seven preparatory cold asphalt mixes. To compare the performance of cold mix asphalt and epoxy grout with hot mix asphalt as the host material, rutting tests and dynamic modulus tests at different loading frequencies and temperatures were conducted. Finally, laboratory scale micro-trench samples were prepared using different backfilling materials and were loaded using a wheel tracker after freeze/thaw conditioning. The results showed that cement grout could effectively be used to secure the conduit inside the trench. It was also concluded that using high-quality cold mix asphalt, a compatible material with hot mix asphalt, could improve micro-trench durability compared with epoxy grout.

The Effect of Bottom Ash on Soil Suction and Resilient Modulus of Medium-Plasticity Clay

The effect of adding bottom ash to medium-plasticity clay as a soil stabilizer was evaluated in this study by performing triaxial resilient modulus tests. Two log–log resilient modulus prediction equations found in the literature (MEPDG and NCHRP 1-28) were selected and calibrated for mixtures of bottom ash and clay at different moisture contents. It was found that, with 25% bottom ash in the mixture, the resilient modulus increased between 5% and 23% under different stress states. The soil total and matric suctions of the mixtures were indirectly measured using the filter paper method, and the total suction parameter was incorporated in the two log–log prediction models. The nonlinear regression analysis revealed that the average goodness-of-fit statistics for one of the modified models showed highly satisfactory performance in predicting the resilient modulus values.

Field Measurement and Modeling of Vertical and Longitudinal Strains from Falling Weight Deflectometer Testing

AbstractThis study investigates longitudinal tensile and vertical compressive strains at the bottom of the hot mix asphalt (HMA) layer subjected to a falling weight deflectometer during different s...

Field Evaluation of Load-Bearing Capacity of Tire Fill Embankment Pavements

Tire-derived aggregates (TDAs) are produced by shredding scrap tires. These materials have desirable engineering properties and can be appropriately used in pavement embankment fills. Several pavements have been constructed using TDA fill embankment; however, the seasonal performance of the pavements composed of these materials has not been widely investigated., This study investigates seasonal changes in load-bearing capacity of tire-filled embankment pavements after two years of construction in comparison to conventional pavement in a test road in Edmonton, Alberta, Canada. Three sections were constructed using different TDA materials, including passenger and light-truck tires (PLTT), off-the-road (OTR) tire particles, and a mix of PLTT and local subgrade soil, which was placed adjacent to a conventional section that acted as a control section. Falling weight deflectometer (FWD) tests were conducted in different seasons, and the back-calculation results revealed that although the subgrade of the TDA sections showed higher deflection and a lower resilient modulus compared with the control section, the load-bearing capacity of the TDA sections was greater than that for the control section. The section constructed using a mix of TDA material and soil showed almost the same performance as the control section.

The effect of insulation layers on pavement strength during non-freeze–thaw season

Abstract This paper examines the effect of integrating insulation layers on pavement strength using falling weight deflectometer testing data conducted on an instrumented test road in Edmonton, Alberta, Canada. The insulated sections of this road consisted of a -metre-thick bottom ash layer and two polystyrene layers at thicknesses of 5 and 10 cm, while the adjacent conventional section functioned as the control section (CS). For the purpose of strength comparison, the effective modulus and structural number of insulated sections were compared to a conventional CS in a non-freeze–thaw season. The durations of pavement freezing, recovering and fully recovered (non-freeze–thaw) periods were established by monitoring the moisture variations in different pavement layers. The results indicated that using insulation layers generally reduces pavement strength, and this reduction is more pronounced in the insulated section with thicker polystyrene.

Characterization of Permanent Deformation Behavior of Silty Sand Subgrade Soil Under Repeated Load Triaxial Tests

The performance of pavement structures is highly dependent on the performance of the subgrade layer, because it is the last layer underlying all the other pavement layers. The development of permanent deformation in subgrade material under traffic loads can cause pavement distresses such as fatigue cracking and rutting. This paper presents an evaluation of permanent deformation behavior of a silty sand subgrade material in the laboratory at various stress ratios and stress levels. It was found that the shakedown behavior of the material fell within plastic shakedown and plastic creep for stress ratios below 1.0 and a stress ratio of 1.5, respectively. A statistical prediction model for permanent deformation based on the test results is suggested.

Laboratory Investigations of Cold Mix Asphalt for Cold Region Applications

Cold mix asphalt (CMA) can be a quick, environmentally friendly, and low-cost option for utility-cut backfilling on urban streets and most highway agencies prefer it as a pothole patching and pavement surface repairing material over hot mix asphalt (HMA) during winter and wet seasons. However, applying poor quality CMA may result in premature patching and backfilling failures, reduce pavement’s integrity and longevity, and impair drivers’ safety. Additionally, CMA’s lack of stability and durability while exposed to heavy traffic, moisture, and freeze-thaw conditions may accelerate further deterioration. This paper focused on evaluating and comparing twelve CMAs through laboratory tests to determine properties that may cause poor performance in cold climatic regions. Taking into consideration the identified CMA distresses, this study conducted Marshall Stability and flow, indirect tensile strength (ITS), cohesion, and adhesiveness tests on nine proprietary and three conventional cold mixes, including both open- and dense-graded materials. Most mixes had low adhesion properties and high sensitivity to freeze-thaw cycles. An analysis of variance showed that aggregate grain size distribution and bitumen content had a significant effect on CMA’s performance.

Investigation of Rutting Resistance and Moisture Damage of Cold Asphalt Mixes

AbstractCold-mix asphalt (CMA) is considered a convenient and rapid solution for pavement pothole repair projects. Despite the wide use of CMAs, reliable procedures for quality control and screenin...

Three Years’ Monitoring of IRRF Instrumented Test Road

The IRRF’s test road, nearly 500 m in length, is unique to Western Canada. Situated in Edmonton’s east end, the road consists of two test sections and a control section designed to investigate the use of Tire Derived Aggregate as embankment material and the performance of bottom ash and polystyrene board as insulation layers in cold climate conditions. During construction, the road was instrumented with more than 250 pavement and geotechnical sensors. The installed geotechnical instrumentation monitors compression behaviour, internal temperature, and drainage characteristics of the test sections, while the pavement instrumentation monitors the mechanistic responses of the pavement to traffic and environmental conditions. Data collected from these sensors is relayed in 15-s intervals to the IRRF’s laboratory facilities, where it is used to study pavement performance. Various activities are scheduled to study how seasonal changes affect the pavement. Falling weight deflectometer tests are conducted monthly on the test road to monitor seasonal changes in the pavement layers’ moduli, while the effects of temperature, moisture variations, and traffic loads on the different pavement layers are also evaluated. This paper summarizes the effect of seasonal variation on pavement responses as a result of 3 years’ monitoring of the control section, tire embankment and insulated sections of the IRRF instrumented test road. By analyzing several Falling weight deflectometer testing results and temperature data collected from different instrumented sections during the time of monitoring, this paper investigates the impact of freeze and thaw on subgrade soil resilient modulus and the benefits of using insulation layers to protect the subgrade soil.