جستجوی مقالات مرتبط با کلیدواژه "surface free energy" در نشریات گروه "عمران"

Modification plays an important role in asphalt deterioration. Failure occurs when bitumen separates from aggregate particles due to reduced adhesion between asphalt and aggregate compared to adhesion between water and aggregate. In recent years, the use of nanomaterials can be used to improve various asphalt properties. In this study, three types of nanoclay were used to modify styrene-butadiene-styrene modified bitumen (SBS1-). The resistance to failure of modified bitumen was evaluated using surface free energy (SFE2). The results showed that the SFE decreased and the energy ratio (ER3) increased by modifying bitumen with nanoclays, indicating that nanoclays can improve the resistance of these aggregate cohesive systems. After immersion, due to the interaction between water and bitumen, the subsequent degradation rate was observed in both SBS and nanoclay modified asphalt. However, the residual amount of 3D structures in nanoclay modified asphalt was higher than that of SBS modified asphalt, indicating that nanoclay makes the surface morphology more resistant to water damage. Finally, freezing and melting tests were used for the results obtained through SFE tests.

In previous researches, the properties of bitumen and asphalt mixture have been considered for investigation of thermal cracking. In these methods, the roles of different components of the asphalt mixture are not considered. The use of surface free energy and the basic characteristics of asphalt mixture can also be used in the investigation of thermal cracking. In this research, it has been tried to investigate the role of these basic properties of materials in the occurrence of these cracks along with the surface free energy parameters. For this purpose, surface free energy components have been measured for four types of aggregates and eight types of bitumen. Also, the bitumen creep stiffness and m-value were obtained from the bending beam rheometer tests. Asphalt film thickness, aggregate index and the specific surface area of the aggregates have been also determined. For thermal cracking potential, the semicircular bending test was used on 32 different combinations of asphalt mixtures at low temperature. Then, statistical methods have been used for assessing the relationship between the mentioned parameters and the semicircular bending test results. Statistical analysis shows that the basic characteristics of the materials, including the asphalt film thickness, the aggregate index, the free energy of cohesion, the free energy of adhesion, the ratio of basic to acidic components of the surface free energy and the specific surface area of the aggregate have a significant and positive effect on the cracking indices such as semicircular bending fracture energy and fracture toughness.

This research evaluated the effect of epoxy resins on the moisture resistance of asphalt mixtures of each bitumen and aggregate (limestone and siliceous) combination by measuring their surface free energy characteristics. The laboratory method measured the contact angle of several probe liquids called the Sessile Drop method. Bitumen polarity, cohesion energy, adhesion energy, bonding energy, energy parameter related to adhesion performance and energy parameter related to wetting performance of aggregate surface by bitumen for each combination of bitumen and limestone and siliceous aggregates were investigated. The results show that epoxy resins increase the polarity of bitumen, but they do not have a positive effect on increasing the cohesion energy of bitumen. For all the studied bitumen-aggregate compounds containing epoxy resin, the adhesion and wetting performance has increased compared to the compounds containing base bitumen, which indicates the proper performance of this additive in improving the moisture resistance of asphalt mixtures.

One of the most common damages in asphalt mixtures is due to the destructive effects of moisture on the cohesion of asphalt binder and adhesion of asphalt binder-aggregate which is called moisture damage (Xiao et al, 2010). Moisture damage can be divided into two mechanisms, adhesion and cohesion. They are related to the strength loss of asphalt mixtures (Tan and Guo, 2013). Water can penetrate between the surface of asphalt binders and the aggregates. It reduces adhesion between binders and aggregates. Also, water can be absorbed in the asphalt binder. It decreases the cohesion properties of asphalt binders. When the cohesion and adhesion properties of asphalt binder reduce, stiffness of asphalt mixtures reduces. There are several different approaches for improving adhesion and reducing moisture sensitivity in asphalt mixtures. One convenient approach is modifying the asphalt binder with a suitable agent. Most of road and transportation agencies have tried to use anti striping additives to increase adhesion at the aggregate-asphalt interface (Kakar et al, 2015). Liquid anti strip additives are chemical surfactants that decrease the aggregate’s surface tension and improve the surface coverage of aggregates. In contrast in this research, the potential of two types of metallic nano materials in two different percentages (nano AL2O3 and Fe2O3) were evaluated.

In most existing studies to investigate the aging performance of asphalt mixes, the results of mechanical tests are used to investigate the thermal cracking potential of an asphalt mix and less attention is paid to the basic properties of materials that are important in the event of this cracking. Accordingly, the present study investigates the effect of aging on thermal cracking of 12 different compositions of asphalt mixtures through mechanical methods and free surface energy (SFE), which is based on the main properties of the material. Thermal cracking of asphalt mixtures has been evaluated by performing semi-circular bending mechanical tests and thermodynamic tests by determining the SFE components of bitumen and aggregates. The results showed that the parameters of fracture energy and fracture toughness, which are known as indicators of sensitivity of asphalt mix to thermal cracking, for aged asphalt mixtures between 6.3-13.7% and between 6.5-10.7%, respectively. The results of SFE tests show that aging causes an increase in the non-polar component between 1.3-1.5% and a decrease in the acidic and basic free energy components of bitumen between 41.1-53.4% and between 334.2-349.6%, respectively. These results have increased the amount of free cohesive energy from 0.63 to 1.03 (ergs/cm2). Also, aging reduces the free energy of bitumen-aggregate adhesion with a maximum reduction of 2.61 (ergs/cm2). This means that aging reduces the coverability of bitumen on the aggregate surface and the resistance to fracture at the bitumen-aggregate interface.

One of the most common damages in asphalt mixtures is due to the destructive effects of moisture on the cohesion of asphalt binder and adhesion of asphalt binder-aggregate which is called moisture damage. There are several different approaches for improving adhesion and reducing moisture sensitivity in asphalt mixtures. One convenient approach is modifying the asphalt binder with suitable agents. In this research, the effects of two types of nanomaterials in two different percentages (nano ZNO and SiO2), two types of aggregates (granite and limestone), and one base asphalt binder were evaluated. To assess the effect of nanomaterials, the indirect tensile cyclyc loading (similar to resilient modulus test) in dry and wet conditions and surface free energy (SFE) tests have been used. Moisture sensitivity index, which is the percentage of the aggregate surface exposed to water as calculated by using the measured SFE and indirect tensile cyclic results, was considered an index for the moisture susceptibility of mixtures. Mechanicaltest results used in this study show that using nanomaterials significantly improves the moisture strength of samples made with the modified asphalt binder in comparison with the control samples. Results of surface free energy theory show that the nanomaterials increase the cohesion free energy of the asphalt binder that decreases the probability of the occurrence of cohesion failure in the mastic. Also, nanomaterials decrease the acid component and increase the base component of surface free energy of the asphalt binder which increases its adhesion with the aggregates that are prone to moisture damage.

The type of asphalt pavement performance depends on its material properties, manufacturing process and implementation. Surface free energy is an important feature of aggregates and bitumen in predicting the performance of asphalt mixture. Surface free energy indicates the amount of bitumen and aggregate adhesion and the energy parameters related to the moisture resistance performance of bitumen and aggregate. In addition, the mixing temperature of modified bitumen, as part of the modified bitumen preparation method, may have an effective role in the final performance of the bitumen and its composition with aggregates. In this article, the effect of modified bitumens with epoxy resin and their preparation temperature on bitumen surface free energy and moisture resistance of asphalt mixtures is investigated. For this purpose, the modified bitumens containing epoxy resin additive were prepared at 2, 4, 6 and 8 percent (w/w) of bitumen at two temperatures of 90 and 130 °C and surface free energy parameters related to moisture sensitivity were calculated. Results showed different performance between various compositions of bitumen and aggregates for different percentages of additive and bitumen preparation temperatures. In bitumen and silica aggregates, modified bitumen with 6% epoxy resin at 90 °C mixing temperature, and in bitumen and limestone aggregates, modified bitumen with 4% epoxy resin, with 130 °C mixing temperature, showed optimum performance in terms of moisture resistance.

In this research, by using mechanical and thermodynamic methods, the effect of surface coatings of aggregates with crystal calcium carbonate powder on the moisture sensitivity of asphalt mixtures has been evaluated. The results show that the indirect tensile strength of the modified specimens has been increased. as Also, the result of SFE method indicates that, with aggregate surface modification, their acidic and basic components respectively have been reduced and increased. Due to these changes, the adhesion between aggregates and bitumen (which is an acidic substance) increase. In addition, the amount of released energy in the presence of moisture has been reduced for modified specimens, which indicates a reduction in the tendency of the mixture for stripping.

Based on the important effects of filler on performance-related properties of asphalt mixtures, this study investigates the influence of filler type on moisture susceptibility of asphalt mixtures under multiple freeze-thaw cycles. Furthermore, the effect of changing the type of mineral fillers, especially replacing fillers with recycled concrete materials on moisture resistance of asphalt mixture, with sustainable development approach, is evaluated. In this study, first, the indirect tensile strength and the resilient modulus tests are conducted following 1, 3, 6, and 10 cycles of freeze-thaw and then the fracture energy is calculated through the results of indirect tensile test. Next, the surface free energy components of mastics with different types of filler are calculated using the static contact angle measurement method. The results of performance-based moisture susceptibility tests show that replacing natural filler with Portland cement can result in the best performance compared to control mixture, limestone filler, and RCA filler. However, the evolution of mechanical properties of control filler, limestone filler, and RCA filler depends on the number of freeze/thaw cycles. At higher conditioning cycles, TSR values demonstrate a different behavior such that the TSR values of the asphalt mixture containing RCA filler increase up to 15% on average compared to the asphalt mixture containing limestone filler after the first cycle. Although the results of mechanical properties in initial freeze-thaw cycles are similar to surface free energy results. However, these results cannot predict the behavior of asphalt mixtures at higher freeze-thaw cycles.

Moisture damage in asphalt mixtures is defined as loss in strength and durability in present of water. Lack of relationship between distress mechanism in the laboratory and field, lack of measurement of effective properties of materials and their role, lack of modification solution, and other deficiencies of these methods have motivated researchers to present more appropriate experimental methods based on the properties of materials and asphalt mixtures, which could have a determining role in the occurrence of moisture-induced distress. Thus, the present research tries to present a model for predicting moisture sensitivity of asphalt mixtures based on thermodynamic parameters and characteristics of mix design of asphalt mixtures, which could predict the performance of an asphalt mixture against moisture based on the mentioned parameters.Results of this study demonstrated that using antistripping additives can generally improve the performance of asphalt mixtures against moisture; but, type and percent of these additives must be determined considering type of aggregate, type of asphalt binder, and properties of asphalt binder-aggregate mixture. Moreover, based on the presented statistical analyses, the results represented that the parameters of cohesion free energy and adhesion free energy of aggregate-asphalt binder in dry conditions, wettability of aggregate by asphalt binder, specific surface area of aggregates, and apparent film thickness of asphalt binder on the aggregate surface as well as free energy of system during antistripping event and permeability of asphalt mixture considerably influenced the occurrence of moisture damage directly and reversely, respectively.

Using anti-striping additives is the most optimal method to improve the strength of asphalt mix against moisture. In this survey, it is tried to review the effect of using polymeric materials as bitumen modifiers on the reduction of moisture damage of hot asphalt mix. To investigate the effect of polymeric materials, repetitive loading test in dry and wet condition together with thermodynamic parameters have been used. The results showed that using Styrene-Butadiene Rubber (SBR) have led to improve the ratio of wet to dry module of asphalt mixes, showing their strength against moisture damage. Moreover, SBR have increased the conjunction free energy and have decreased the released energy of system in striping event and this indicates drop in system’s tendency to striping. Moisture susceptibility index which is the surface percent of aggregates exposed to moisture have been obtained according to the measuring the components of surface free energy of bitumen and aggregate and asphalt mix module in loading cycles. The results of this index showed similar results to the ratio of dry module to wet module. Obtained results represents that SBR has led to considerable decrease in striping percentage in samples of controlled asphalt mixes.

In this paper the effect of Epoxy Resin polymer on moisture sensitivity of Asphalt mixtures containing Silica and limestone aggregates has been evaluated. Epoxy Resin without hardener and Epoxy Resin curing with hardener in 0, 1, 2, 3, 4, and 5 weight percentages for Asphalt Binder modification have been applied. The method used for evaluating moisture sensitivity of Asphalt mixtures is Surface Free Energy method. In this method, with Surface Free Energy measurements of Asphalt Binder using Sessile Drop method and by using of the extracted values of Surface Free Energy of aggregates of valid reports, the energy parameters related to moisture sensitivity of Asphalt mixtures containing Asphalt Binder and aggregates compound, have been calculated and analyzed. At the end, base and modified Asphalt Binders with Epoxy Resin curing with hardener have been examined with FTIR test. The results show that the Epoxy Resin curing with hardener decreases moisture sensitivity of Asphalt mixtures containing Silica and limestone aggregates. Epoxy Resin without hardener does not have important effect on Asphalt mixtures containing limestone aggregates, but decreases moisture sensitivity of Asphalt mixtures containing Silica aggregates.

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