The present study attempts to investigate different factors affecting the resilient modulus of hot mix asphalt. So a fractional factorial analysis of experiment was carried out considering five factors, each at two different levels. These factors were the maximum nominal aggregate size, specimen diameter and thickness, the load pulse form and duration. During the course of analysis, two types of hot mix asphalts with different maximum aggregate sizes were taken into consideration, while Marshall compaction method was used to prepare the specimens. Furthermore, measuring the resilient modulus, sinusoidal and triangular load pulse forms were applied. Finally, our investigation examined the different factors interrelations which affect the resilient modulus. Analysis of the factorial experimental design showed that the maximum nominal aggregate size was the most important factor affecting the resilient modulus, then the load duration, the specimen geometry (thickness and diameter), and finally the interactions between the different factors.

One of the key parameters to design flexible pavements is the resilient modulus of HMA. For determining the resilient modulus of asphalt concrete, commonly the indirect tension test has been used which includes loading the sample with a haversine pulse with duration of 0.1s and a rest period of 0.9 seconds at different temperatures. Due to the viscoelastic nature of asphalt mixes and the influence of loading time, rest period and loading waveform on the resilient modulus of HMA, this paper deals with the effect of loading time, rest period and loading waveform on the resilient modulus of HMA. To reach this end, the resilient modulus test using the indirect tension test method was carried out on the asphalt mix specimens prepared with both unmodified and SBS-modified bitumen. Then, the resilient modulus of specimens were determined using haversine and square loading at three different temperatures of 5, 25 and 40oC by varying the duration and rest period of applied load and results are compared to each other. Some models have been presented to predict the resilient modulus of HMA by regression analysis. According to the experimental results, the most significant factors to enhance the resilient modulus of HMA were the reduction of temperature, increase of loading time and SBS content in asphalt mixture, and finally the reduction of the rest period to loading time ratio. The most important factors to decrease the resilient modulus of HMA were increase of temperature; change the haversine waveform to square waveform, and increase of loading time.

Soil materials and road pavement construction materials are subjected to dynamic and repetitive loading of different intensity from vehicle traffic. To account for the cyclic nature of material loading and its non-linear behavior, the concept of the resilient modulus has been adopted. It is a fundamental property of unbound pavement materials, as it quantifies the stiffness of the material under repeated loading. Its real value depends on the actual material parameters—e. g., maximum dry density, moisture content, compaction method, and the number and magnitude of repeated loads—and on the state of stress of the actual pavement structure. The resilient modulus value is therefore not constant for a given material type but varies over a certain interval depending on the above-mentioned parameters and the actual test conditions. Therefore, the method of determining the resilient modulus must take into account all the above factors. The standard method for resilient modulus determination is the cyclic triaxial test, but the cyclic CBR test procedure is also used. It uses standard California Bearing Ratio (CBR) test equipment, and thus it is a very simple and very economical testing method. In the presented paper, the influence of loading force and number of loading cycles on the deformation characteristic and resilient modulus of the analyzed soil is investigated. A total of 72 soil specimens are tested at two different levels of loading force and six different numbers of loading cycles. The obtained results confirm that the resilience modulus increases with increasing loading force value and with increasing number of loading cycles. For the soil analyzed, the resilient modulus ranges in the interval 31-83 MPa.

Resilient modulus and California Bearing Ratio (CBR) in unbound granular materials are the key technical characteristics of layers in a flexible pavement design. Among the factors affecting these two parameters, the aggregate gradation is the most important. Using particle size distribution curve developed by AASHTO, together with other considerations mentioned in the related regulations have yielded desirable results in many cases. However, many roads loaded by heavy vehicles, for which all technical instructions of standard regulations were observed, have undergone deformations caused by subsidence of layers. According to the related technical documents, one hypothesis could be the proximity of aggregate gradation to the boundary areas. Therefore, the aim of this study was to determine the effect of changes in the scope of aggregation in the border areas on strength parameters. For this purpose, effects of aggregate grading variation on two types of aggregates, i. e. limestone and quartzite (as determined by AASHTO) were investigated using specific gravity, CBR, and resilient modulus tests. The results showed that, in the gradation boundaries determined by AASHTO, the difference between specific gravity values was insignificant. In the CBR and resilient modulus tests, however, there was a significant difference between test results in the upper and lower limits of gradation. In addition, gradation variation had a lower impact on resistance parameters in quartzite aggregate compared to limestone aggregate. Therefore, under special utilization conditions, materials with highest values of technical specifications should be used, since even materials whose technical specifications are in the standard range may not behave as expected in real world situations.

In order to consider the effect of loading time and temperature on the stiffness modulus of asphalt mixtures in current mechanistic-empirical pavement design methods, such as Mechanistic-Empirical Pavement Design Guide (MEPDG), the quasi-static analysis assuming elastic behavior of asphalt mixtures is employed instead of dynamic analysis assuming viscoelastic behavior of asphalt mixtures. In current procedures, quasi-static analysis of pavement is commonly accomplished by dynamic modulus. Nevertheless, previous studies have shown that the dynamic modulus is greater than the resilient modulus due to consideration of rest period for determination of resilient modulus of asphalt mixtures. Due to this reason, utilizing dynamic modulus for quasi-static analysis of pavements results in decreasing reliability of pavement design. This paper aims to propose a new method for quasi-static analysis of flexible pavements on the basis of resilient modulus master curves of asphalt mix under three loading waveforms of square, triangular and haversine. In the proposed method, the resilient modulus master curves under different loading waveforms are developed based on measured complex moduli and by employing linear viscoelastic theory. Comparison of fatigue life and rutting life resulting from the quasi-static analysis of pavement based on the dynamic modulus and resilient modulus shows that the pavement life is overestimated when the dynamic modulus master curve is used instead of resilient modulus master curves. Also, this paper shows that for more accurate quasi-static analysis of flexible pavements and to consider loading waveform as well as the rest period on the stiffness of asphalt materials, the dynamic modulus values should be used with the assumption of f=1/2mt instead of f=1/t.

A porous asphalt mixture (PAM) is distinguished by its different porous structures, which allow water to move through it as quickly as possible, making drainage an essential component. Porous asphalt pavement (PAP) can maintain its permeability because the mixture contains voids that are interconnected with one another. Permeability, on the other hand, decreases as the proportion of particles in the gradation and the level of compaction increases. To generate various air-void structures, permeability was evaluated with specimens made from varying sizes and shapes of aggregates. The equipment that was used for this research was specifically designed. When compared directly with permeability, the findings indicate that the combination of multiple forms is not directly comparable. The permeability of PAM was observed to be affected by a variety of air void densities, which were observed. While there was a beneficial influence on permeability, there was a negative impact on the Resilient Modulus (MR), which was detected when there was an increase in the void content. The amount of air voids in the mixture substantially impacts the performance of porous asphalt mixtures. Open-Gr-I viscosity grade (VG30) bitumen has a permeability value of 0.394 cm/s, and the resilience modulus value for open-Gr-II mixtures that use a modified binder is 3494 MPa. Both of these values are relative to the permeability value. The drainage and stiffness metrics for the several combinations investigated in this study were considerably impacted by the gradation, the kind of binder, and the temperature conditions. Stormwater management is possible in PAP and improves the groundwater table.

Due to the sharp reduction in budget of civil projects and road construction, the need to use local soil as the base is felt as a way to reduce the final cost of projects. Therefore, this research examines the characteristics of untreated and treated base soil with 3% lime, including uniaxial compressive strengths and indirect tension (Brazilian) test and resilient modulus with different curing times, as well as after performing tests of wet-dry cycles and freezing-thawing. Uniaxial and Brazilian samples with a diameter of 10. 1 cm and a height of 11 cm were made in 3 layers with the same thickness and dry density of 2. 2 g/cm3 and initial moisture of 6% and 8%. The results show that the addition of lime significantly increases the CBR values and shear strength of the soil. Soil treatment with lime improves its resistance against wetting-drying cycles, but it is not suitable against freezing-thawing cycles. Also, based on the tests to determine the resilience modulus, a comparison was made to determine the relationship between CBR values of untreated and treated soil with lime under hot-dry weather conditions. The results showed that the modulus values of dry untreated soil and lime treated soil are equal. The CBR value (maximum value based on penetration of 2. 5 mm or 5 mm) in untreated soil is equal to the same value for penetration of 1. 25 mm in lime treated soil. Therefore, for design purposes, it is recommended to use correlation relations of resilience modulus and CBR values for penetration of 1. 25 mm for soil treated by lime.

In this study, the effect of temperature, binder content and compaction on the resilient modulus of hot mix asphalt (HMA) were studied. The samples were prepared by using gyratory compaction method. The resilient modulus of samples that were prepared with different binder content and compaction effort were determined by Indirect Tensile Method (ASTM – D4123). To increase the accuracy, the tests were conducted on two similar samples and the results were discussed by using both tests. The results show that with increasing temperature, decreasing binder content and increasing compaction effort, the resilient modulus of hot mix asphalt increase. Based on the results of this study, the variation of resilient modulus with temperature, binder content and gyration number was estimated by using a mathematical model. Comparison of the prediction of this model with experimental results shows that the model is acceptable.

this research aimed to investigate the effects of using waste polyethylene terephthalate (PET) on the resilient modulus of asphalt concrete. To this end, waste PET was added into asphalt concrete at different dosages of 0, 2, 4, 6 and 8% (by the weight of binder) and the resilient modulus of the mixtures was evaluated at different temperatures of 5, 25 and 45°C. Coarse and fine PET particles were added into asphalt concrete. Response surface methodology in Design Expert software was utilized for designing of experiments, developing a model for prediction of resilient modulus and evaluating the main and interaction effects of different factors on the resilient modulus of asphalt concrete. A polynomial model was well fitted to the test results relating temperature and PET content to the resilient modulus. Analysis of variance in Design Expert software implies that the model is highly capable for prediction of resilient modulus. Temperature, PET content and PET size are found to be effective on the resilient modulus. The resilient modulus of the mixtures was found to increase with increasing PET size and content, while it decreases with increasing temperature. However, the decrease of resilient modulus with PET size is not significant. It was found that there is no interaction between temperature and PET content with PET size, while interaction effect was found between temperature and PET content. Higher reduction of resilient modulus with increasing temperature was found to be in the mixtures containing higher PET content.

In this study the effect of PET content and particle size on resilient modulus and fatigue property of asphalt concrete has been investigated. PET was added to the mixture at different contents of 0, 2, 4 and 6% (by the weight of binder) with two different sizes as fine and coarse particles. The mixtures were subjected to resilient modulus test at 3 different temperatures of 5, 25 and 40°C and strain controlled fatigue test at 20°C. It was found that the samples containing coarse particles have similar trend at different temperatures, in which, the resilient modulus increases with increasing PET content. Similarly, in the mixtures containing fine PET particles, at 5°, the resilient modulus increases with increasing PET content. However, at 25 and 40°C, the mixture containing 2% PET has the highest resilient modulus with values of 3.5 and 0.808MPa, respectively. The mixtures containing fine particles have higher fatigue life and lower flexural stiffness than the control mixtures. In the mixtures containing 4% of coarse particles the highest flexural stiffness and lowest fatigue life, with the values of 3803MPa and 16260, respectively is obtained. The highest fatigue life for both fine and coarse PET particles is obtained with 6% of PET content, which are 100000 and 63250, respectively. It is concluded that the resilient modulus of the mixtures containing coarse particles is higher than the mixtures containing fine PET particles, but, the mixtures containing fine PET particles have higher fatigue life than the mixtures containing coarse particles.