جستجوی مقالات مرتبط با کلیدواژه « Asphalt concrete » در نشریات گروه « عمران »

In this research the effects of different aging conditions on the raveling and cracking resistance of asphalt concrete made by two types of aggregates, namely limestone and siliceous source have been investigated. Asphalt samples made by siliceous and limestone aggregates were made and were subjected to short-term and 5 and 7-day long-term aging conditions. After that, they were tested using Cantabro mass loss and semi-circular bending test at ambient temperature. Results reveal that the mixture made by limestone aggregates has more raveling and cracking resistance than the mixture made by siliceous aggregates. These results were found to be due to rougher texture and more angularity of limestone particles and also having more MgO and CaO content in their chemical compositions. Results also reveal that aging results in reduction of raveling resistance, fracture energy, fracture toughness, ductility and critical load sustained before fracture in semi-circular bending test. The effect of aging on these properties was found to be dependent on the type of aggregates and the considered property. In terms of raveling resistance, the aging is more effective on the mixture made by limestone aggregates; however, the fracture properties and cracking resistance of the mixture made by siliceous aggregates are more affected by aging than the mixture made by limestone aggregates.

In this study the effect of aggregate source on the ageing of asphalt binder ageing in asphalt mixtures has been investigated. Limestone and siliceous aggregates have been used for making specimens with the same binder and aggregate gradation. The mixtures were tested after subjecting to short and long term ageing, and the properties of the mixtures after each ageing condition have been evaluated and compared.  Marshall Stability, flow and Marshall Quotient (MQ), indirect tensile strength (ITS) and moisture susceptibility have been investigated. Results reveal that the mixture made by limestone aggregates has higher Marshall Stability, Marshall Quotient, and indirect tensile strength than the mixture made by siliceous aggregates, while the mixture made by siliceous aggregates has higher moisture susceptibility. The difference between the moisture susceptibility of the mixtures is more after ageing. Results also show that ageing results in increase of Marshall Stability, Marshall Quotient, the ITS in dry condition, and decrease of Marshall flow and tensile strength ratio.  It was found that long term ageing condition of 7 days at 85°C, results in 13 and 62% improvement in Marshall stability and ITS, respectively, in the mixture made by limestone aggregates, while these values for the siliceous aggregates are 17 and 32%. The effect of ageing on the Marshall Properties and moisture susceptibility for the mixture made by siliceous aggregates is higher than that for the mixtures made by limestone aggregates. However, the effect of ageing on the ITS in dry condition is higher for the mixture made by limestone aggregates.

Soil shear strength is affected by various factors such as grading, compaction percent of materials, vertical load level, shear rate and other factors. When placing soil and other material in the vicinity , the interaction problem is discussed . Such conditions are observed in embankment dams with asphalt concrete cores, in which determining the mechanical performance of the interfacing materials has great importance. In this research, a laboratory study has been conducted to characterize the interface behavior of soil materials of filter and asphalt concrete in the core, through direct shear test. For this purpose, specimens containing soil materials from classes GC and GP at the same relative density were tested under different shear rates and the strength parameters were determined. On the other hand, for considering the impact of the relative density of the materials on strength characteristics, specimens containing materials from GP class at both medium and high relative densities were tested at different shear rates and the desired parameters were determined. Based on the results, in GC interface materials, the interaction ratio has diminished at small shear rates and increased at elevated shear rates. The amount of increase and decrease of the interaction ratio was equal to 2.36 percent. In GP interface materials, the ratio of interaction has increased by 2.3% with a higher shear rate. Also, for constant shear rates, increasing the compaction percent of materials from GP class in the interface, from medium to high level, has resulted to reduced interaction ratio. Increasing the shear rate in materials with moderate and high relative density also followed, respectively, the increase and decrease of the interaction ratio .

Asphalt mortar and asphalt mixture are viscoelastic materials due to the presence of bitumen in their structures. The master curves of dynamic modulus and phase angle developed through the horizontal shifting of the results using the appropriate shift factors are commonly used to describe the viscoelastic properties of asphalt mortar and asphalt mixture. In this study, constructing master curves of dynamic modulus and phase angle of asphalt mortar and asphalt mixture using the least number of test temperatures and frequencies was investigated. The dynamic modulus test was performed on asphalt concrete and asphalt mortar samples at six temperatures and frequencies. Then, the Laboratoire Central des Ponts et Chaussees method was used to determine the shift factors for constructing master curves. Also, the modified Christensen-Anderson-Marasteanu model was fitted on the master curves to predict their viscoelastic properties at an arbitrary temperature and frequency. In addition, the master curves and the fitted models which are created by using test results at two frequencies and six temperatures, six frequencies and three temperatures, or three frequencies and three temperatures, could provide the same predicted values and patterns as the original fitted model with more than 92% accuracy. So, as a result, it is possible to develop the master curves of the viscoelastic properties of asphalt mixture and asphalt mortar with a lower number of test results that have similar accuracy to the original master curves and reduce the time and cost of experiments up to 50%.

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.

Composite modification is increasingly used to alleviate the detrimental problems associated with asphalt modifiers and meet the massive demand for asphalt pavement. In this study, nano-Al2O3 composite modifications at three concentrations of 1%, 2%, and 3% by weight of asphalt binder were implemented in neat and modified asphalt binders to improve their performance at high and intermediate temperatures. These binders were evaluated in terms of their physical, rheological, and high-temperature storage stability properties. In addition, nano-Al2O3 composite modified binders were utilized in asphalt concrete and investigated for their resistance to cracking, permanent deformation, and moisture damage. The nano-Al2O3 composite modifications were made using neat, polymer-modified, and crumb-rubber (CR) modified asphalt binders. Adding nano-Al2O3 to the asphalt binders was found to improve stiffness, high-temperature storage stability, permanent deformation resistance, and cracking tolerance. Moreover, the composites of nano-Al2O3 with neat and modified asphalt binders were found to provide improved resistance to permanent deformation, cracking, and moisture damage in hot mix asphalt concrete. The composite of 2% nano-Al2O3 showed the best performance in terms of resistance to permanent deformation, the composite of 3% nano-Al2O3 showed the best performance in terms of resistance to moisture damage, the composites of 2% nano-Al2O3 with polymer and CR-modified asphalt binders both showed the best performance in terms of resistance to cracking, and the composite of 3% nano-Al2O3 with AC20 showed improved resistance to cracking.

This study aimed to investigate the properties of asphalt concrete containing reclaimed asphalt pavement (RAP) and waste polyethylene Teraphthalate (PET). Different dosages of PET including 0, 3, 6 and 9% (by the weight of total binder of control mix) were added to asphalt concrete containing 0, 10, 20 and 30% of RAP and the properties including Marshall stability and flow, indirect tensile strength (ITS), moisture damage resistance, dynamic creep and constant stress fatigue resistance have been evaluated. Results reveal that RAP inclusion improves Marshall Stability, resistance against permanent deformation, tensile strength and fatigue resistance. In addition, moisture sensitivity of asphalt mixture containing RAP is less than the control mix, and, for the mixtures containing the same PET content, inclusion of 20% RAP results in the highest tensile strength ratio (TSR). Results also show that PET results in decrease of Marshall Stability, permanent deformation and fatigue resistance. Moreover, in the mixtures containing the same RAP content, ITS and TSR of the mixtures containing 0 to 6% of PET are higher than those of the control mixture. From the results in this study it can be inferred that using RAP and PET simultaneously can result in better properties than the control mixture and using RAP allows using higher PET content without scarifying the properties.

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.

This study investigates the effect of using waste engine oil (WEO) on some engineering properties of hot mix asphalt concrete containing different percentages of reclaimed asphalt pavement (RAP). Different percentages of WEO, namely 0, 5, 10 and 15% (by the weight of asphalt binder) have been added to the mixtures containing 25, 50 and 75% (by the weight of aggregates) of RAP and the volumetric properties, Marshall stability, flow, Marshall quotient and dynamic creep properties of the mixtures have been investigated and comparedwith control mixture without any waste material. Results show that the addition of RAP into the mixtures increases the air voids content, while, the air voids content decreases with increasing WEO content. Also, the optimum binder content of the mixtures was found to increase with increasing RAP content and decrease with increasing WEO content. In addition, the Marshall quotient of the mixtures decreases with increasing RAP content. The Marshall quotient of the mixtures containing 50 and 75% of RAP increases with increasing WEO. Dynamic creep test results show that the resistance against permanent deformation of the mixtures increases with increasing RAP content. In addition, the resistance against permanent deformation decreases with increasing WEO content. With the same RAP content, the highest resistance against permanent deformation is achieved by adding 10% of WEO. Results of this research show that, using waste engine oil as a rejuvenator of aged asphalt, enables to use up to 75% of waste asphalt in production of new asphaltic concrete.

In this research, the effects of using different amounts of waste tire by dry and wet method, on the long term aging and moisture damage of a typical asphalt concrete have been investigated. Results show that in both methods of mixing, there is an optimum tire content by which the highest dry and conditioned indirect tensile strength is achieved. The optimum tire content for the dry and wet method was found to be 1 and 10%, respectively, by which, the indirect tensile strength in dry and wet method was found to be 20 and 18% higher than the control mixture. However, the conditioned indirect tensile strength of the mixtures containing the optimum rubber content in dry and wet method was found to be 0 and 17% higher than that of the control mixture. The experiments on the for both method mixing, the aged specimens  show that aging results in a slight increase in the indirect tensile strength of the control mixture and the mixtures containing different percentages of crumb rubber. Also the results show that long term ageing results in the increase of moisture susceptibility in the mixtures containing crumb rubber added by the wet method. However, the mixtures containing crumb rubber added by the dry method have a less susceptibility to moisture after long term ageing than that before long term ageing, for which a tensile strength ratio (TSR) of 0.98 was obtained.

Asphaltic concrete has been used as waterproofing core in embankment dams, since 1948. The large majority of embankment dams' central core is made of clay worldwide. However, as clay is increasingly difficult to find at new construction sites, asphalt concrete was used as a replacement core material. Cores made of clay has also some other disadvantages such as, low shear strength, compressibility, long construction time, requiring higher amount of material and accurate controls during construction, etc. These are in favor of using asphalt concrete, which has advantages such as less sensitivity to weather conditions, less width of core, healing behavior of bitumen, high shear strength etc. In this application, granular materials are used around the asphaltic concrete as filter, which makes a complicated behavior in the interface and needs to be researched by experiments and modeling. This paper describes experimental work and the results of investigating the mechanical behavior of the interface between aggregates and asphaltic concrete. Small scale shear strength test has been used in this study, in which the shear surface is considered as the interface. The effect of bitumen penetration grade, moisture, density and angularity of aggregates on the shear strength parameters at different levels of vertical stresses and a constant shear rate was studied.

In this research, in order to study the effect of using PET on the performance of asphalt concrete containing rubber modified and unmodified binder, PET particles were added into the mixtures in different dosages of 0, 2, 4, 6, 8 and 10% (by the weight of binder). After determination of the optimum binder content of the mixtures, the specimens were made and subjected to Marshall, indirect tensile and dynamic creep tests. The dynamic creep tests were performed using a universal testing machine (UTM-10) by applying a vertical stress of 300kPa at a temperature of 40°C, to investigate the resistance against permanent deformation. Results show that adding PET into the mixtures improves the Marshall stability and Marshall Quotient compared with those for the control mixture. However, the trend of variation with PET content is different for the unmodified and rubber modified mixtures. While the Marshall stability and Marshall quotient increase with increasing PET content in the rubber modified asphalt concrete, they reach to the highest value by adding 4% of PET into the unmodified mixture, and after that they decrease with increase of PET content. The indirect tensile test results show that the indirect tensile strength (ITS) of the mixtures made by rubber modified and unmodified binder and containing air voids content within 6.5 to 7.5%, reaches to its highest value by adding 2% of PET. However, for the mixtures containing air voids content within 3-5% ITS decreases with increasing PET content. Dynamic creep tests reveal that the resistance against permanent deformation decreases with increasing PET content in both mixtures, with a lower reduction in the mixtures made by rubber modified binder. Comparing the results of Marshall Quotient and dynamic creep tests show that the deformation behavior of PET modified mixtures is different under static and dynamic loading. While, the mixtures resistance against deformation under static loading is improved, under dynamic loading they show less resistance than the control mixtures. Also, results of this research show that PET is less effective on the rubber modified mixtures than the unmodified mixtures.  

In order to investigate the effect of nylon fibers on the performance of asphaltic mixtures, 12mm long nylon fibers in different contents of 0.1, 0.2 and 0.3% (by the weight of total mixture) were added to a typical asphaltic concrete. After determination of the optimum binder content of the mixtures, the volumetric properties of the mixtures containing different percentages of nylon fibers were analyzed. Then, the fiber reinforced mixtures were subjected to Marshall Stability, flow an indirect tensile strength tests. In addition, in order to evaluate the permanent deformation behavior of the mixtures, using UTM-10, dynamic creep tests were conducted under different stress levels of 200 and 400kPa, and at different temperatures of 40, 50 and 60°C. Dynamic creep curve, flow number and the creep strain slope (CSS) were used for analysis of the results. Then, the creep behavior of the mixtures was modeled using the three-stage model developed by Zhou et al. The resistance against moisture damage of the mixtures were also evaluated using the tensile strength ratio (TSR) and Marshall Stability ratio (MSR). The results showed that the mechanical properties of the mixture such as the Marshall stability, Marshall Quotient and the indirect tensile strength of the mixture can be improved by modifying with 0.1% of nylon fiber. Also, the moisture sensitivity of the mixtures decreases with increasing fiber content, up to the fiber content of 0.1%, after which, increases with increasing fiber content. The results of dynamic creep tests and modelling the creep curve using the three=stage model showed that the mixture containing 0.1% of nylon fiber has the highest length of primary creep region and flow number and the lowest creep stain slope, indicating that its resistance against the permanent deformation is the highest.

In this research the effects of waste polymer of PET on the performance of asphaltic mixtures containing rubber asphalt are investigated. To this end, two different sizes of waste PET particles were added into an asphalt concrete at different percentages of 2, 4, 6, 8 and 10% (by the weight of asphalt binder). After determination of the optimum binder content of each mixture, they were subjected to different tests of Marshall Stability, indirect tensile strength and dynamic creep tests. Dynamic creep tests were conducted using UTM-10 under 300kPa and temperature of 40°C for evaluating the permanent deformation behavior of the mixtures containing different percentages of PET. The results showed that the addition of PET into the asphaltic mixtures containing rubber asphalt resulted in the improvement of Marshall Stability and Marshall Quotient compared with the control mixture without PET, with the highest stability was obtained for the mixtures containing 10% of PET. The indirect tensile strength tests results showed that, for both sizes, the highest indirect tensile strength was obtained by the addition of 2% of PET, beyond which the indirect tensile strength decreased with increasing PET content. The dynamic creep test results showed that the mixtures containing PET have a different behavior under dynamic loading compared with that under static loading. It was found that the addition of PET results in the reduction of resistance against permanent deformation under dynamic loading, such that, the resistance decreased with increasing PET content. The Marshall stability, indirect tensile and dynamic creep tests results showed that the mixtures containing finer PET particles have a higher resistance than those containing coarser particles.