مجله مهندسی زیر ساخت های حمل و نقل
سال هشتم شماره 3 (پیاپی 31، پاییز 1401)

The present research seeks to investigate the modification of bitumen emulsion with polyphosphoric acid and study the feasibility of using steel slag powder as an alternative to conventional rock material filler in the design of microsurfacing mixture in an attempt to improve the ultimate performance of the mixture. For this purpose, firstly, polyphosphoric acid was used to modify the bitumen emulsion at 0.4, 0.8, 1.2, and 1.6 wt% (by weight of residual bitumen). Next, the optimally modified bitumen emulsion was used in different microsurfacing mixtures. Five different mixtures of micro surfacing containing steel slag filler at 0, 2.5, 5.0, 7.5, and 10.0 wt% (by total weight of aggregates), as an alternative to material passing through 0.075 mm sieve, were prepared. The asphalt mixtures were assessed by means of wet cohesion test, wet track abrasion test, loaded wheel-displacement, and loaded wheel-sand adhesion tests. Results of the bitumen tests showed that the use of the polyphosphoric acid tends to improve the bitumen properties in terms of decreased penetration, increased softening point, and reduced thermal sensitivity. With increasing the dosage of the polyphosphoric acid to up to 0.8 wt% by weight of the residual bitumen, significant changes were seen in the penetration and the softening point, which led to improved performance of the bitumen emulsion. Results of the asphalt tests on the samples showed that the mixtures containing steel slag filler at 7.5 and 10.0 wt% outperformed the other mixtures. Indeed, the mixture containing steel slag at 7.5 wt% could improve the cohesion, abrasion resistance, bleeding resistance, and vertical displace resistance by 29.2, 64.5, 18.6, and 44.0%, respectively. The corresponding figures for the mixture containing the slag at 10.0 wt% were 25.0, 64.3, 23.3, and 42.9 wt%, respectively.

With the social and economic developments, as well as the new roads that are being built every year, the need for a smooth and durable pavement that has a longer service life is fully felt. In addition, it is no secret that the use of traditional asphalt mixes causes many environmental problems due to the use of bitumen, which is a non-renewable source. Therefore, researchers have been looking for a solution to improve pavement performance and find a suitable alternative to bitumen. One of these alternative materials is derived from biological sources, commonly referred to as BioAsphalt. In this study, the possibility of using lignin and waste engine oil, which are bio-asphalt materials, in bitumen to improve its properties was investigated. The lignin used in the study was extracted from black liquor. Waste engine oil was also taken from a car repair shop. The samples are PG64-22 as control sample, samples containing 5% and 10% lignin, samples containing 4% waste engine oil, and samples containing both additives. Superpave tests including RV, DSR, BBR, RTFO, PAV and MSCR were performed on all samples at different temperatures to fully examine the samples rheologically. The results showed that the addition of lignin or WEO or a combination of both, can improve the rheological properties of bitumen. Also using waste materials in bitumen can be useful from an environmental and economic point of view.

Considering the important economic and environmental benefits of low energy asphalt mixture and the need to know and study more about this asphalt due to little research, in this article, the linear viscoelastic properties of this type of asphalt are evaluated using dynamic modulus test. Due to the mechanical weakness of this asphalt mixture and considering its environmental nature, an additive compatible with the environment was selected to modify it. Therefore, crumb rubber in three levels of 10, 15 and 20% by weight of asphalt binder was used to modify the samples. Controlled and modified asphalt samples were designed and compacted according to the superpave method and were tested to determine the dynamic modulus and their viscoelastic properties at different temperatures and frequencies. The master curve of asphalt mixtures showed that at high temperature (low frequency) the highest dynamic modulus belongs to low energy asphalt mixtures with 15% rubber powder. Therefore, this mixture has the highest rutting strength compared to other mixtures. On the other hand, comparison of the master curve of asphalt mixtures at low temperature (high frequency) showed low stiffness of low energy asphalt samples without additive and low energy asphalt with 15% additive and their resistance to cracking, respectively. Evaluation of the viscoelastic properties of the test specimens also confirmed the fact that the highest elasticity belonged to the low-energy asphalt sample modified with 15% crumb rubber and the most viscous mixture was the hot asphalt sample.

Providing adequate skid resistance is one of the most important issues in the construction of concrete pavements and due to the lack of sufficient friction, smooth concrete pavements can only be used in the places where skid resistance doesn't matter so much; such as parking lots and warehouses. Although there is no comprehensive instruction for texturing on concrete pavements, methods such as grooving, burlap or broom dragging, and exposing the aggregates are used to texture the concrete pavements.In this study, the method of grooving is studied using British pendulum sand patch tests.Therefore, grooves in three different center to center spacings(12.7 mm, 19 mm, 25.4 mm), three different widths (2.5 mm, 3.2 mm, 3.8 mm) and three different directions(transverse, diagonal and longitudinal) were created on concrete specimens.The results of this study indicate that increasing the spacing of the grooves or decreasing the width of them, decreases the depth of the texture.The friction value in every three direction of the grooving decreases by increasing the spacing between the grooves; while increasing the widths of the grooves leads to an increase in the friction values at first; but then the value decreases in the wider grooves.The results show that the transverse grooves lead to the highest skid resistance.

Soil slopes may need to be stabilized due to geometrical conditions, material parameters, and applied loads. Geosynthetics-reinforcement is one of the solutions to stabilize soil slopes, especially under surcharge. The use of geocells as a 3D geosynthetics reinforcement has become very widespread. In this study, using small-scale physical model tests, the role of geocells in evaluating the behavior of strip foundations resting on soil slope with an angle 70° has been investigated. The results showed that in order to increase the bearing capacity of the foundation resting on a steep soil slope, a certain number of geocells are needed and if more than three layers are used, the bearing capacity of the foundation increases. The bearing capacity of soil slope reinforced by three and four geocell layers is 3.6 and 4.9 times that of unreinforced ones, respectively. Due to the membrane behavior of geocells, it causes that the load transfers to the subsoil layers, and if number of reinforcing layers is low, the slope will be failed under relatively low-intensity surcharge. The use of geocells increases the stiffness of the soil slope and reduces the rotation of the foundation and the horizontal displacement of the slope crest compared to the unreinforced case. Also, the use of a sufficient number of geocell layers makes the slope able to absorb more energy and withstand more displacements before failure. Increasing the geocell spacing from 75 to 100 mm has reduced the efficiency of the reinforced slope so that the bearing capacity has decreased by about 35% compared to the geocell with smaller spacing. Also, the stiffness of the reinforced slope decreased by increasing the reinforcement spacing. The bearing capacity of a foundation with an embedment depth of 100 mm is 1.3 times the bearing capacity of a foundation located on a reinforced slope.

The proposed models to assess the security risks of bridges are generally designed based on the product of three-factor: probability (O), vulnerability (V), and importance (I). In this paper, the importance of bridge (I) and its changes due to the uncertainty of network topology during future network development programs were discussed. To measure and compare the relative importance of bridges, two groups of unique importance and the network-based importance of bridges were considered. Given that the network-based characteristics of bridges change during network development, a numerical example was presented to compare different decision-making approaches in selecting bridges (with and without considering the changes in the importance of bridge networks due to network changes). In this example, the Ahwaz inter-city transportation network was examined. The results showed that some bridges, such as B3, which were not important in the initial, became important during the development process. In contrast, in some bridges, such as B5, the relative importance was high at first, but during the development process, their relative importance decreased. It was also observed that a number of bridges such as B1, B6, and B7 are always important. In contrast, bridges such as B4 are always considered insignificant and network changes do not place them among the important bridges in any period.

In recent decades, the use of alkaline materials in concrete has found a wide perspective in the concrete industry due to its pozzolanic properties and the presence of aluminosilicate materials with high filling and adhesion properties. The use of this type of concrete (due to its superior advantages over ordinary concrete) in paving roads can improve the strength and increase the useful life of roads. In this laboratory research, a mixture ratio of normal concrete with a cement grade of 450 kg/m3 was made. A mixture ratio was also made of activated alkali concrete based on blast furnace slag to compare and evaluate the modulus of elasticity of concrete under ambient temperature and heat of 500 ℃, at the age of 90 days. Next, X-ray Diffraction Spectroscopy (XRD) and Scanning Electron Microscope (SEM) tests were carried out in order to further investigate and verify the results of the modulus of elasticity test, at the processing age of 90 days at ambient temperature and It was done on concrete samples under the heat of 500 ℃. The modulus of elasticity at ambient temperature was 32 GPa for ordinary concrete and 35 GPa for activated alkali concrete, which had a difference of 8%. By applying heat to concrete samples, the amount of modulus of elasticity drop in normal concrete reached 59% and in activated alkali concrete 42%. The results of the XRD and SEM tests were in agreement with each other and overlapped with the results of the modulus of elasticity test.