مجله مهندسی زیر ساخت های حمل و نقل
سال چهارم شماره 1 (پیاپی 13، بهار 1397)

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.

With starting plastic deformation around the tunnel, the pressure on the tunnel roof increases due to the weight of the plastic area, which influences on the tunnel stability. In this paper, with considering strain-softening rock mass around the tunnel and plastic region weight and using the generalized Hook-Brown failure criterion, the stress and displacement equations around the tunnel were rewritten and solved by the semi-analytical method. The results show that considering the weight of the plastic region caused the distribution of stress around the tunnel are changed and the amount of displacement and radius of the plastic region increases. This becomes more importance in conditions with larger plastic radius. Also, by investigation of the effect of Hook-Brown criterion parameters on the displacement around the tunnel, the importance of each of the parameters is shown. The results show that Hook-Brown parameters in plastic condition have a greater effect on the displacement around the tunnel than in peak conditions.

Concrete, as one of the most widely used building materials, has brittle behavior. Concrete pavement design factor is the 28-day concrete flexural strength. Adding fibers to concrete is effective on the ductility behavior, impact resistance, energy absorption, crack resistance, abrasion resistance, and tensile strength of the concrete and prevents crack expansion. For this purpose, a laboratory research was conducted to investigate the effect of different combinations of macro-synthetic fibers on the flexural strength of fiber-reinforced concrete, including flexural strength, average residual strength and flexural toughness. In this study, concrete specimens were constructed according to ASTM C1609, ASTM C1399 and ASTM C79 standards and were evaluated with four different macro-synthetic polymer fibers. Results of the experiments showed that adding fibers to concrete joints, the flexural strength increased by 3.31-16.96 percent. Also, the flexural toughness and average residual strength increased by addition of the fibers. Meanwhile, due to the soft break of regular concrete, flexural toughness and average residual strength could not be computed.

One of the requirements for mechanistic-empirical design of asphalt pavement is determining the viscoelastic properties of asphalt mixture, including dynamic modulus and phase angle. Since the dynamic modulus test of asphalt mixture is time consuming and expensive, some prediction models have been proposed by various researchers. The purpose of the present study was to investigate some of the available predictive models to determine the viscoelastic properties of hot, warm and RAP-contained asphalt mixtures. For this aim, asphalt mixtures with two types of gradation (with a nominal maximum aggregate size of 9.5 and 19 mm) representing the mixtures prepared for surface and binder layers, as well as three kinds of bitumen, including neat bitumen, Sasobit-modified bitumen and reclaimed bitumen, were designed according to Superpave method. Dynamic shear rheometer and dynamic modulus tests were performed on the bitumen and the mixtures, respectively. The empirical model of NCHRP 1-40D and micro-mechanical models of Hirsch and its modified form were evaluated for estimating the dynamic modulus of asphalt mixtures using laboratory measurements. It was found that the empirical model of NCHRP performed very well after calibration (R2> 0.95) and then the semi-empirical and micromechanical models of modified Hirsch and Hirsch had a good performance. All models had a better predictability for the modulus of fine graded mixtures. It seems that the considered models are not successful in taking into account the resistance from aggregates interlocking. Application of dynamic modulus prediction models is suitable for implementation of the new design method at Level 2.

Properties of asphalt mixture change with time. These changes directly affect operation of the asphalt mixture. This issue makes the road maintenance important. One of the methods of road maintenance for preventing deeper problems is using rejuvenator materials in improving the rheological and mechanical properties of the aged tar; thus, the pavement will not contront different cracks and future failures will be prevented. The main purpose of this study was to prove the effect of rejuvenator materials on asphalt mixture ageing, specialy in field cases and in situ application. Four compounds were made as rejuvenator and were sprayed over the pavement. After removing a 1.5 cm layer from top of the sample, the corresponding tar was extracted and DSR, penetration value and softening point tests, before and after applying the rejuvenator materials, were carried out. Since the friction of rejuvenated surface is an important issue for road specialists, British pendulum test was also performed in order to make sure about friction of pavement surface for reopening. Results showed that in penetration value, DSR and softening point tests, all of the 4 compounds rehabiliated the properties of asphalt mixture and their differences were not significant. Results of British pendulum test showed proper performance of the rejuvenating materials, for surface friction of the pavement, after being applied.

By the research on the behavior of fracture toughness in asphalt mixtures, it has been suggested that several components have been proposed to test the mode III (KIIIc) fracture toughness of asphalt mixtures. But until now, a standard piece not been provided for testing fracture toughness (KIIIc) of asphalt. Such specimen should have appropriate geometric and loading conditions. In addition, it could be compatibility with the most common features in the inherent of tested materials and provide repeatable, reliable and integrity data of fracture resistance in asphalt mixture. ENDB is one of the specimens that could provide these items for calculating KIIIC of asphalt materials. It seems to be a good choice in comparing with other samples due to advantages such as ease of construction, cracks creation and simulation facilities of mode I loading for investigating of asphalt fracture behavior. The aim of this study was to investigate the effect of geometry and characteristics of asphalt mixtures on the behavior of ENDB fracture toughness. Using the finite element software (ABAQUS), geometry and meshing of the desired part have been performed. The result of this research can help in selecting and introducing the appropriate standard specimen and appropriate specifications of asphalt mixtures to determine the amount of KIIIC of asphalt mixtures to researchers. The important results of this research can be mentioned as the effect of thickness on the degree of fracture toughness in loading mode III. So the fracture toughness in the specimen with a higher thickness increases, and with the decrease in the percentage of air void and the test temperature, the degree of toughness of the fracture also increases.

Porous concrete pavement reduces surface runoff volume, prevents flood and reinforces groundwater resources. In this research, effects of replacing concrete aggregates (25, 50, 75 and 100%) by pumice, scoria and zeolite lightweight aggregates in porous concrete on physical properties including compressive strength and porosity were investigated. Preparation of concrete samples and testing was performed in the Concrete Technology Laboratory of Semnan University. Statistical analysis of the results was performed by using SAS 9.4 software. Results showed that by replacing lightweight aggregates in the porous concrete and removing the course aggregates, certain trend was observed among the samples. As the porosity increases, the compressive strength of the samples is reduced. The highest average compressive strength in porous concrete samples was observed in substitution of 50 and 25 percent scoria with aggregates (11.08 and 10.76 Mpa, respectively). The highest average porosity was observed in the sample containing 100% pumice as aggregates, which was 55.95% more than the control sample. Based on the obtained empirical relationship (R2=0.9), the compressive strength of porous concrete can be estimated for different porosities of porous concrete samples. Due to the abundance, economical values, high porosity and reduction of urban runoff, the proposed lightweight natural aggregates of this study have great potential to be used in pavements, especially in areas with low traffic.