Rashadul Islam

Coefficients of Thermal Contraction and Expansion of Asphalt Concrete in the Laboratory

AbstractThe research reported in this paper investigates the coefficient of thermal contraction (CTE) and coefficient of thermal expansion (CTE) of asphalt concrete (AC) under different conditions in the laboratory. As a first step, the CTC and the CTE of AC at different temperatures ranging between −20 and 55°C were measured using field samples to examine the temperature effect. Then, the difference in the CTC and the CTE values in the vertical and horizontal directions (cross anisotropy) were evaluated using field samples. The influences of air void (AV), aggregate type, and aggregate gradation on the CTC and the CTE values were also investigated using laboratory prepared SuperPave gyratory samples. The deformation measuring devices, LVDTs, were calibrated using a zerodur to eliminate the temperature effect on the LVDTs. Results show that the CTC and the CTE values of AC are nonlinear with temperature and vary with aggregate type. However, gradation of aggregate and AV of sample do not affect the CTC an...

Effects of Large Freeze-Thaw Cycles on Stiffness and Tensile Strength of Asphalt Concrete

AbstractThis study investigates the stiffness and tensile strength degradation behavior of asphalt concrete (AC) on long-term freeze-thaw (FT) conditioned samples in the laboratory. In the first step, beam samples (363×63×50  mm) are prepared in the laboratory using a kneading compactor and conditioned at different numbers of full-day FT cycles up to 150. The flexural stiffness of control and FT conditioned beam samples are determined using a beam fatigue test apparatus. In the second step, circular (100-mm diameter) samples of 50-mm thickness are prepared using a SuperPave gyratory compactor and conditioned in a FT chamber similar to the beam samples. The indirect tensile strength (ITS) of control and FT conditioned circular samples are determined by indirect tensile strength (IDT) tests at different temperatures. Results show that the flexural stiffness of the FT conditioned samples decreases with FT conditioning, whereas the ITS of AC does not change significantly with FT cycles. It is highly expected ...

Measuring Fatigue Damages from an Instrumented Pavement Section due to Day-Night and Yearly Temperature Rise and Fall in Desert Land of the West

This study measures the fatigue damage due to temperature fluctuations and, hence, the fatigue life of asphalt concrete using data from an instrumentation pavement section in the desert land of New Mexico for real time climate conditions. As a first step, fatigue life prediction models have been developed for both vehicle and temperature fluctuations based on stiffness and strain of Hot Mix Asphalt (HMA) collected from the instrumentation section located on Interstate 40 (I-40) in New Mexico. In the second step, traffic and thermal strains at the bottom of asphalt concrete are measured by Horizontal Asphalt Strain Gauges (HASGs). In the third step, using these strain values, fatigue damage at the bottom of asphalt concrete is determined. Results show that thermal damage is responsible for 98.2% of total fatigue damage in asphalt concrete. In addition, yearly temperature fluctuation produces greater damage (95.8% of total damage) than the damage caused by daily temperature variations (2.4% of total damage).

Effects of Reclaimed Asphalt Pavement on Hot-mix Asphalt

This study examined the effects of reclaimed asphalt pavement (RAP) on the structural properties and performance of hot-mix asphalt (HMA) and the rheological properties of asphalt binder in the laboratory. As a first step, dynamic modulus (|E*|) and indirect tensile strength (ITS) tests were conducted on a set of HMA samples prepared with RAP and a set of HMA samples without RAP. The moisture susceptibility of samples with and without RAP was evaluated based on the |E*| ratio of wet to dry conditioned samples. Bending beam rheometer tests and direct tension tests were conducted on virgin binder, extracted binder, and RAP and aggregate mastics (mixture of binder and RAP and aggregate passing #200 to #50 sieves) to evaluate the low-temperature cracking. The results show that RAP materials caused an increase in |E*| and a decrease in ITS and had a negligible effect on moisture susceptibility. The RAP samples produced 15 % less permanent strain in |E*| testing than samples without RAP, which means that the RAP mixes were less susceptible to rutting. However, RAP mixed binder was more susceptible to low-temperature cracking as measured by the m-value (slope of the curve of stiffness versus time) and brittleness.

Determining Coefficients of Thermal Contraction and Expansion of Asphalt Concrete Using Horizontal Asphalt Strain Gage

Thermal strain occurs in asphalt pavement from thermal contraction and expansion due to temperature decrease and increase, respectively. No standard procedure to measure thermal strain is available. This study determines thermal strain per unit increase or decrease in temperature (also referred to as coefficient of thermal contraction or thermal expansion (CTC or CTE)) in an instrumented pavement section on Interstate 40 (I-40) in New Mexico. Firstly, the Horizontal Asphalt Strain Gages (HASGs) are calibrated for temperature to measure thermal strain. In the second step, the thermal strain variations in fall, winter, and summer are determined. For validation, the CTC and the CTE values are measured in the laboratory on three field collected cylindrical cored samples using Linear Variable Displacement Transducers (LVDTs) and temperature sensors. The LVDTs are also calibrated using a cylindrical zerodur block to account the temperature effect on it. Results show that field CTC and CTE values are close to the laboratory findings.

Clustering Vehicle Class Distribution and Axle Load Spectra for Mechanistic-Empirical Predicting Pavement Performance

AbstractPast studies have determined the effects of the pavement mechanistic-empirical (ME) default (Level 3) values of vehicle class distribution (VCD) and axle load spectra (ALS) on pavement performance. However, it is still not clear how the clustered VCD and ALS affect the ME predicted pavement performance. In this study, traffic data from 10 weigh-in-motion (WIM) stations were gathered and analyzed to develop the VCD and ALS values using arithmetic average and clustering methods (Level 2). Next, using Level 2, Level 3, and site-specific (Level 1) inputs of VCD and ALS, the pavement ME predicted performance was determined. The results show that the predicted performance by the cluster (Level 2) data are very close to those of the site-specific data (Level 1). Performance generated by the ME default values (Level 3) are significantly different from those generated by the site-specific or cluster values. When comparing the performance of the ME design default (Level 3) with those of the statewide averag...

Field Validation of the Arching Phenomenon of Earth Pressure Cell to Measure Vertical Stress in Flexible Pavement

Earth pressure cell (EPC) is used to measure vertical stresses at different depths of pavement due to traffic loading. Typically, it is considered that this sensor is not affected by arching phenomenon. As the sensor is made up of steel, its stiffness is greater than the surrounding soil materials. Therefore, the sensor may report greater stress for arching action compared to the actual value. This study investigated the arching effect by finite element model (FEM) and validates the results by field data from installed EPCs due to traffic and falling weight deflectometer (FWD) loads on an instrumented pavement section in New Mexico, USA. Results show that vertical stress response measured on the top of subbase (445 mm depth) and top of subgrade (645 mm depth) increases up to 2.72 and 2.21%, respectively, for arching action. The vertical stress on top of base decreases with increase in EPC stiffness. Field measured vertical stresses under traffic and FWD loads at different depths agree with these FEM outputs.

Crack Propagation in Hot Mix Asphalt Overlay Using Extended Finite-Element Model

AbstractThis study investigates the crack propagation behavior of asphalt materials through the use of damage models using the principles of the disturbed state concept (DSC). Traction–separation c...

Developing Temperature-Induced Fatigue Model of Asphalt Concrete for Better Prediction of Alligator Cracking

AbstractCurrently, the fatigue performance of asphalt concrete (AC) is predicted according to repeated traffic-induced tensile strain at the bottom of AC layer. Cyclic thermal strain caused by day-night temperature fluctuation is not considered because of the fact that there is no closed-form solution or model available for calculating thermal fatigue damage. This study, for the first time, develops a closed-form equation for calculating the temperature-induced fatigue damage of AC. To generate data, beam fatigue testing was conducted on three Superpave mixtures in the laboratory. The mechanical beam fatigue test data were correlated with the actual cyclic temperature loading test data. The developed model was then calibrated for field condition. Finally, the model was used to evaluate fatigue damages of randomly chosen 34 long-term pavement performance (LTPP) test sections from 19 states in the United States. Fatigue damage determined by the traditional pavement design software (which considers traffic-i...

Measuring the cross-anisotropy of hot-mix asphalt

This study measures the cross-anisotropy of gyratory, kneading and field-compacted hot-mix asphalt samples of two sizes. One set of cube samples were subjected to compression through the top face and the other set through the side face. In addition, two sets of beam samples were tested for flexure stiffness using load on both the top and side faces. Results show that the side faces can sustain an average compressive stress of 0.89, 0.91 and 0.77 times of the top faces for kneading, gyratory and field-compacted cube samples, respectively. The average flexure stiffness of the side face is 0.85 times of that of the top face. For comparison, finite element model (FEM) was developed to predict pavement stress–strain under wheel load. In addition, stress–strain data from a field-instrumented pavement section on Interstate 40 in New Mexico were collected. The FEM-simulated vertical stress shows a close match with collected stress at cross-anisotropy value of 0.8.