جستجوی مقالات مرتبط با کلیدواژه « Hot mix asphalt » در نشریات گروه « عمران »

In recent years, extensive studies have been conducted on the effect of different nanomaterials on the performance of asphalt mixtures. Also, in the present study, Nano graphene oxide (GO) in the amounts of 0.2, 0.5, and 0.8% by weight of bitumen was used to improve the fracture resistance of HMA asphalt mixture against cracking at negative temperatures. Nano graphene oxide (GO) has been introduced as the material of the century due to its very unique and excellent properties. For this purpose, to investigate the effect of this nanomaterial on the fracture resistance of the asphalt mixtures, the semi-circular bending (SCB) fracture test at temperatures of -5 and -15°C and four different loading modes have been used. In addition, conventional bitumen tests were performed to investigate the effect of Nano GO on pure bitumen in this study. The conventional bitumen tests showed that the addition of Nano GO to pure bitumen increased the softening point, viscosity, and specific gravity and reduced the penetration and ductility in pure bitumen. Also, the semi-circular bending (SCB) fracture test results indicate that using Nano graphene oxide increases the fracture energy of asphalt mixtures and improves the resistance of asphalt specimens to cracking. So that mixtures containing 0.5% of this additive have the best performance. The results show that the use of this amount of additive in the asphalt mixture at -5°C and pure loading mode I increases by 105% and at -15°C and pure loading mode II increases by 60% in the fracture energy.

One of the methods to improve the properties of asphalt mixtures is using additives. One of the additives that have received a lot of attention in recent years is nanomaterials, which have been very popular due to their unique characteristics. In this study, the effects of nanographene on the performance characteristics of hot asphalt mixtures have been investigated. For this purpose, bitumen was modified in 0.1%, 0.3%, and 0.5% (by weight of bitumen) and by performing bitumen tests, the optimal amount of nanographene selected was 0.5%. Then, in order to evaluate the performance characteristics of the mixtures, repeated axial load tests (RLA), indirect tensile strength modulus (ITSM), and indirect tensile fatigue test (ITF) were performed. Besides, in order to evaluate the moisture sensitivity of the mixtures, indirect and compressive tensile tests were performed on the samples in both dry and wet conditions. The results showed a decrease in the final deformation, an increase in stiffness at temperatures of 5, 25, and 40 by 15, 36, and 54%, respectively. Also, in some samples, the fatigue life of modified asphalt mixtures was improved by up to 55% compared to conventional mixtures. Increasing the TSR index in the indirect tensile test indicates an improvement in the performance of the modified sample compared to conventional samples and a decrease in their sensitivity against moisture, to the extent that the indirect tensile strength of the modified sample in dry and wet conditions compared to conventional samples Increased by 23% and 38% respectively.

In this study, the strength of hot and warm asphalt mixtures containing 3% Sasobite in cold regions has been investigated using the principles of fracture mechanics. The effect of temperature and loading modes (tensile and shear) on the fracture toughness of the mixture was investigated using a semicircular samples with an edge crack under three-point bending. The coefficient of critical stress intensity was determined from the results of the fracture test and the shape coefficients were determined from finite element analysis in ABACUS software. In hot and warm asphalt mixtures containing 3% Sasobite, with decreasing temperature, the critical stress intensity coefficient increased in tensile and shear modes. The results showed that the hot asphalt mixture at temperatures of 0, -10 and -20 °C presents significant fracture resistance compared to the warm asphalt mixture in all loading modes. As the temperature decreases, the fracture toughness of both types of both asphalt mixtures increases.

In this study, the effect of fine aggregate angularity was evaluated using Marshall strength ratio and indirect tensile strength tests on moisture sensitivity, sample failure and cracking capability of hot asphalt mixtures. Two types of Qubit crusher (Mix design-1) and hydro-cone (Mix design-2) were used to prepare fine-grained stone materials for the production of hot asphalt. By comparing the parameters of both designs, the results of this study showed that although the grain size of both sands was the same the angulation coefficient of sand produced in Qubit crusher has decreased by 7% compared to sand produced in hydro-cone crusher, which increases by 1.2% the optimal amount of asphalt mixture. Despite this increase in the optimal amount of bitumen in the asphalt mix of mix design-1, the amount of effective bitumen in this asphalt mix decreased by 1%. The reduction of effective bitumen in the asphalt mixture weakened the bond between the bitumen and the aggregate, and accordingly, the moisture durability and resistance in all failure modes of the asphalt mixture of mix design-1was less than that of the asphalt mixture of mix design-2.

The growth of the transportation network has led to a special need to the life cycle cost analysis and increase the lifespan of asphalt mixtures. There are several ways to improve the performance of asphalt mixtures, one of which is bitumen modification using modifiers. In recent years, with the invention and expansion of the production of nanomaterials, special attention has been paid to the use of nanomaterials to improve the rheological properties of bitumen. Accordingly, this study evaluates the effect of copper nanooxide on the rheological behavior of bitumen and the mechanical properties of the asphalt mixture. Therefore, the dynamic shear rheometer is used to determine the specifications of bitumens at medium and high temperatures, as well as fatigue and dynamic creep tests to investigate the performance of asphalt mixtures against fatigue cracking and rutting. The results of bitumen rheological experiments show that the use of copper nanooxide at 1 and 2 percent by weight of bitumen improves the rutting parameter in unaged and short-term aged bitumen from 49-343 and 57-257 percent, respectively, and also improves the fatigue parameter in long-term aged bitumen from 11-40 percent. The results of fatigue tests show that the fatigue life of samples containing 1 and 2 percent of this additive at 5 and 20 °C will improve by 9-16 percent and 6-31 percent, respectively. Also, the results of the rutting potential show that the use of 1 and 2 percent of nanooxide has reduced the permanent deformation change of 13-35 and 18-18 percent, respectively.

It is very important to focus on treatments aimed at strengthening and improving the asphalt layer to increase the life of the pavement. Among the methods to increase the life of asphalt concrete pavement against structural failures that have been discussed in this study include the asphalt mixture modification approach (using Nano-silica) as well as asphalt reinforcement approach (using geogrid). In this study, based on the results of previous studies, the increase in fatigue life of these two approaches and their comparison with the fatigue life of control samples has been investigated. To determine the fatigue life of asphalt mixtures, the fatigue test of 4 points bending (4PB) beams under constant strain conditions (at 3 levels of 500, 700 and 900 micro-strains) has been used. The results show that by addition (in wet method) of Nano-silica to pure bitumen, the fatigue life of asphalt mixture is increased for both samples of Nano-silica modified and geogrid reinforced asphalt mixtures. For example, at a strain level of 500 micro-strain, the addition of 5% Nano-silica increases the fatigue life by about 193.9% (equivalent to 2.94 times) and the installation of a geogrid layer increases the fatigue life by about 212.4% (equivalent to 3.12 times). Also, asphalt mixtures reinforced with geogrid at the strain levels of 500, 700 and 900, respectively, increased the fatigue life of the mixture by about 6.5% (equivalent to 1.06 times), 61% (equivalent to 1.61 times) and 1.8% (equivalent to 1.02 times) compared to the samples modified with Nano-silica.

Today, glasphalt technology is considered as an efficient way to reduce asphalt production costs, reduce fuel consumption, and reduce environmental pollution caused by the production of this type of waste. Despite the advantages of glasphalt, moisture damage is a weak point for these types of mixtures. The present study evaluated the moisture sensitivities of glasphalt and HMA and compared the performance of these two types of mixtures, along with the effects of two types of additives, nano hydrated lime and nano calcium carbonate on moisture damage. The moisture sensitivity of both types of mixtures was evaluated using a modified Lotttman test and a thermodynamic test of Wilhelm plate based on surface free energy methods. The results of the indirect tensile strngth test showed that the resistance of glasphalt in dry conditions was higher than that of HMA. However, glasphalt are exposed to wet conditions with a higher resistance to HMA. The results obtained from the thermodynamic test also showed that the modification of both types of asphalt binder (AC 60-70 and AC 85-100) using nano hydrated lime and nano calcium carbonate increases the total surface free energy and adhesion of the bonding of both types of base asphat binders. This increase improves the strength of mixtures made with this type of asphat binders against moisture damage of cohesion type, which is a positive effect in reducing the moisture damage.

The major national investment in the transportation sector is the creation and construction of pavements. Currently in Iran, most of the pavements are asphalt mixture. It has been damaged by the passage of time, traffic loads, and atmospheric changes. One of the most important types of flexible pavements is the change of permanent forms known as rutting. In recent years, the use of metal melting slag, one of the waste of the metal melting plants, has been considered as an alternative to parts or all rock materials in different layers of metal. in this study, we investigated the use of different percentages of steel slag as a percentage of coarse rock material in gradation of mixture (0 - 25 - 75 - 75 % of slag in alternative rock material)… using the method of mixing marshall, optimum bitumen and other Marshall parameters. In order to investigate the properties of the pure bitumen, penetration point, ductility, viscosity, and degree of fire were performed. Also, the tests of marshall and flow, indirect tensile, moisture susceptibility, resilient modulus, dynamic creep and wheel placement were performed to investigate the effect of the use of فولاد slag on the functional properties of asphalt mixture. The results of this study showed that the compressive strength, indirect tensile strength and tensile strength ratio (saturation to dry of mixtures containing electric arc furnace (EAF) steel slag were higher than control mixture.

Today, modified bitumen is used in the asphalt pavement, extensively. This has improved the properties of the asphaltmixture, including fatigue failure performance. Beside of these additives effect, a phenomenon called asphalt self-healing also increases the fatigue life of the mixture. Since there has not been extensive research on effect of self-healing, design fatigue life is usually considered to be less than the capacity of the mixture, and this action, in addition to adding cost, affects high temperatures performance or in other words, rutting performance. In this study, modified mixtures containing crumb rubber , styrene-butadiene-rubber, styrene-butadiene-styrene and polyethylene polymers were prepared in two groups of same bitumen and same void ratio and subjected to four-point fatigue and rutting tests. Results showed that SBR elastomer polymer with increased bitumen elasticity provides the highest recovery capability (85%) for asphalt specimens. Subsequently, the SBS polymer has the highest fatigue life and 60% recovery capability.

Moisture damage is defined as loss of strength and durability of asphalt mixtures in the presence of water. In this study, the effect of Polyvinyl Chloride (PVC) polymer was evaluated as an asphalt binder modifier on the moisture damage of HMA. Indirect tensile test in dry and 1, 3 & 5 freeze-thaw conditions and thermodynamic method according to the measurements of surface free energy components of aggregates and asphalt binders were used for evaluating the effect of polymeric materials. The results of this study show that using of PVC cause an increase in the strength of the asphalt mixture against the moisture damage. Also, PVC increased the free energy of cohesion and reduced the debonding energy. These cause decreased in the rate of the moisture damage of asphalt mixtures.

Because of important role of pavement quality on the safety and comfort of road users and reducing the operation period costs, the researchers have paved the way for asphalt pavement to produce improved asphalt, to increase its strength and durability against traffic load and conditions Weather. Today polymers are also bituminous modifying additives that are widely used in asphalt. In this study, three polymer with names Styrenine-Butadiene-Styrene, Styrene-Butadiene-Rubber and PolyStyrene were used to improve moisture and rutting asphalt resistance. Styrene-butadiene-styrene has a favorable experience in repair of pavement damage, but imported and due to its price dependence on political occasions, the researchers sought to combine the production of internal polymers efficiently and at reasonable prices Replace it. In this regard, two polymers of styrene-butadiene-styrene and polystyrene were mixed in 25/75, 50/50 and 75/25 combination ratios and 3 and 5% by weight of bitumen in asphalt mixtures. Marshall Stability, Indirect Tensile Strength, Resilient Modulus and Rutting tests were performed on modified specimens. The results showed that the use of polymer blends is much more efficient than the use of polymers individually, and a polymer blend containing 75% styrene butadiene, along with 25% polystyrene, can produce moisture and rutting resistance equal to styrene butadiene styrene.

The behavior of the asphalt mixture depends on the characteristics of asphalt binder, aggregate, filler and mixing design. One of the effective parameters in improving the behavior of asphalt mixtures is to modifying the asphalt binder properties using mineral additives. Accordingly, in this research, we tried to study the behavioral properties of asphalt mixtures made with modified asphalt binder with a type of natural zeolite called Clinoptilolite. For this purpose, this material has been used in two percent mass of asphalt binder (2 and 4 percent). In order to investigate and determine the dynamical properties of base asphalt mixtures and modified resilience of the modulus of experiment with indirect tensile strength, fatigue life by indirect tensile fatigue test and rutting potential using repetitive axial loading have been used. The results obtained in this study indicate that the use of this additive has reduced the asphalt binder thermal sensitivity and increased the viscosity and hardness of it, increasing the modulus and the number of loading cycles that led to failure of asphalt samples. Also, the use of zeolite reduces the final deformation in repeated loading experiments and increases the fatigue life of asphalt mixtures. By increasing the amount of Clinoptilolite from 2 to 4% of asphalt binder mass, the modulus of resilience of asphalt samples increases the elastic properties of the specimens and increases the ability to withstand stress. With increasing temperature, the presence of Clinoptilolite in the samples has led to a reduction in the modulus reduction rate and an increase in the depth of their roughness less than the control samples. This, in turn, reduces the thickness of the asphalt process, reduces the probability of occurrence of the slip phenomenon at high temperatures and reduces cracks caused by fatigue at medium and low temperatures.

Damage in asphalt pavements due to repetitive stresses and strains caused by both traffic loading and environmental factors can manifest itself as fatigue and thermal cracking, respectively. Cracking is considered as a primary distress mechanism in asphalt pavements. Many studies have been carried out on resolving these distresses. One of these ways is the use of polymer modifiers to improve the properties of asphalt binder and asphalt mixtures. Therefore, this research was conducted to study the effects of domestic polymers (with trade names of SBR and PP) in equal proportions on the fatigue properties of asphalt mixtures compared to expensive imported polymer (called SBS). Accordingly, four-point beam fatigue and indirect resilient modulus tests were carried out. It was found that combination of PP and SBR leads to better preservation of fatigue performance of modifed mixes and increases the fatigue life up to 50% compared to SBS-modified mix. Consequently, such polymers combination can be more beneficial than using SBS polymer

Rutting and stripping are among the main distresses that occur in flexible pavements. Moisture damage will result in other distresses such as cracking, raveling and rutting. In this study, rutting and stripping resistance of asphalt mixtures containing different percentages Googas (30, 40 and 50 percent) were evaluated and compared with asphalt mix control under the same conditions. The optimum binder content was obtained from Marshall Method of mix design. The effects of varying googas contents on moisture susceptibility of asphalt mixes were investigated using Indirect Tensile Strength (AASHTO T-283) test. Rutting of this mixes were investigated using Marshall Quotient (ASTM D-1559) test. Marshall Quotient test was performed at temperatures of 45 and 60 ° C. Marshall Quotient test results show that the addition of googas increased the rutting resistance of the asphalt mixes. Indirect tensile test results show that the addition of googas does not increased resistance to moisture susceptibility. Therefore, anti-stripping additives should be used.

One of the important goals of the researchers is reduce the damage of asphalt pavement in order to the increses of safety of road users. The moisture is known as one of the environmental asphalt failure factor which attracted researcher’s attention. The modification would results in failure reduction and maintenance cost. SBS polymer is one of the most widely used polymers to improve the asphalt functional properties, but importing this polymer causes it much costly. So, economic assessments lead engineers to use alternative materials. In this study, in order to improve the properties of binder, a combination of two inexpensive domestic (made by Iran) polymer is used to achieve a compound similar to Thermoplastic elastomers polymer. In this regard, polymer blends of SBR and PP with same amount has been mixed. Then, this combination of polymers has been added to bitumen with ratios of 3, 4 and 5% of weight. On the other side, in order to compare performances, SBS polymer was also used in ratios of 4 and 5% in bitumen of asphalt mixtures. Moreover, in order to provide polymer stability in modified bitumen, namoclay has been added 1.5% of binder weight. Results of Marshall stability test, indirect tensile test, resilient modulus and Texas boiling test has been compared. The results has been shown equal and better performance of mixture contains 5% polymer blends in comparison with mixture contains 5 % SBS; and indicates a 20% increase in moisture resistance compared to the unmodified sample.

Fatigue cracking is one of the main and dominant distresses of hot mix asphalt (HMA) at moderate temperatures. This distress happens mainly because of two reasons: 1) Cohesive fracture in the asphalt binder or mastic phase, and 2) Adhesive fracture at the interface of asphalt binder and aggregate. Therefore, one of the main features of the materials used in asphalt mixtures, which affects their fracture type, is the surface free energy (SFE) of asphalt binder and aggregates. In this study, SFE components of aggregates and asphalt binders were respectively determined by universal sorption device (USD) and sessile drop (SD) tests. Also, to evaluate the effects of adhesive and cohesive parameters on the
fatigue life of asphalt mixtures, the samples prepared with different combinations of asphalt binder and aggregate were examined by indirect tensile fatigue test. Results showed that the asphalt mixtures with limestone aggregates and asphalt binder 85-100 had the highest fatigue life compared to the mixtures produced by other aggregates. This feature can be caused by three parameters: 1) Limestone due to the high specifc surface area has the highest adhesion with asphalt binder. 2) By using the asphalt binder 85-100, greater adhesion energy was created between the asphalt binder and aggregate, which increased the energy required for separating the asphalt binder from the aggregate surface and the occurrence of adhesion rapture distress. 3) By using asphalt binder 60-70 caused less signifcant free energy of cohesion in the asphalt binder which resulted in the increased possibility of distress in mastic