مجله مهندسی زیر ساخت های حمل و نقل
سال پنجم شماره 3 (پیاپی 19، پاییز 1398)

The performance of asphalt mixtures against environmental factors such as moisture is important and many of the damages are directly affected by the water entering the pavement and weakening the bond between bitumen and aggregates. On the other hand, Stone Mastic Asphalt Mixture (SMA) is a kind of hot mix asphalt with coarse aggregate skeleton and a high percentage of bitumen and filler, which requires the use of additives due to drain down. Therefore, the objective of this research is to investigate the effects of nanomaterials on the moisture sensitivity of SMA asphalt mixtures. In this research were used, Calcareous aggregate, AC-60/70, two additive Evonik Dgosa in the amount of 0.15, 0.25 and 0.35%, and Zycotherm of 0.05, 0.1 and 0.15% of bitumen weight. AASHTO T283 (modified Lottman test), Resilient Modulus Ratio (RMR), dynamic creep and boiling water test were conducted to control moisture sensitivity and rutting performance. Results showed that Evonik up to 6% and Zycotherm (nanomaterial) up to 16% improve the performance of SMA asphalt mixtures against moisture.Adding Zycotherm (0.15% wt) to the asphalt mixture improves rutting resistance. Also, after analysing of these materials, it can be resulted that the effect of Zycotherm (nanomaterial) on the moisture properties and performance in the mixed state is more favorable than Evonik.

Regarding the growing use of self-compacting concrete(SCC) in roads, highways and airports, designing concrete structures with the sustainable development view is needed. Many researchers are trying to optimize SCC mixture proportions using new materials. Using high content of Portland cement to produce SCC is one of the major challenges. This high content of cement causes higher cost of production. Also higher content of CO2 emission during the production of Portland cement into atmosphere, is one of environmental concerns. In this research, two approaches were adopted to lower the Portland cement: river sand with high content of fine particles and zeolite as the supplementary cementitious materials(SCM) were used. Portland cement was replaced by natural zeolite with the replacement levels of 5,10 and 15 percent in 0.42 and 0.46 of water to cementitious materials ratio. To investigate the rheology of SCC mixtures, slump flow, visual stability index, J-ring, T50, L-box and V-funnel tests were employed. Mechanical properties of hardened concrete were examined in 7, 28 and 90 days of curing, using compressive and flexural bending(third-point loading) experiments; abrasion resistance of concrete according to ASTM C779-A in 28 and 90 days of curing were also examined. Result of fresh concrete tests indicated that using zeolite improved the static stability and segregation resistance of concrete mixtures but increased the required dosage of high-range water-reducer agent(HRWRA). It was observed that , at the age of 7 days, natural zeolite caused compressive and flexural strength reduction; but at 28 and 90 days of curing, significant improvements were observed. Also in lower water to cementitious ratio replacement, zeolite had better impact on both rheological and mechanical properties.

Mechanistic–Empirical Pavement Design Guide (MEPDG) uses dynamic modulus for flexible pavement design and rehabilitation. This parameter could be defined as the viscoelastic property of asphalt materials. Mechanistic–Empirical Pavement Design Guide (MEPDG) uses results of both Falling Weight Deflectometer (FWD) and laboratory dynamic modulus predictive models for determination of dynamic modulus of in-service asphalt layers. In this research, ten asphalt pavement sites were selected in Khuzestan and Kerman provinces in Iran. Field and laboratory testing were performed and dynamic modulus of in-service asphalt layers was determined. Hirsch predictive model for dynamic modulus of asphalt mixes was calibrated and new model was developed for predicting in-situ dynamic modulus of asphalt layers. Performance evaluation and validation of this new model showed very good correlation between predicted and measured values with high prediction accuracy and low prediction bias.Keywords: Dynamic Modulus of Asphalt Layers, FWD, Dynamic Modulus Predictive Models, Hirsch Model, Mechanistic–Empirical Pavement Design Guide (MEPDG).

Nowadays, because of the economical considerations, the application of the high-strength materials has been taken into serious considerations by several researchers. High-strength reinforcement application has many benefits like: decreasing material consumption, project time and peripheral costs. However, due to some of their repercussions such as: decreasing the overall ductility, energy absorption and increasing crack widths, their applications are limited in seismic prone areas. In this research, the effect of high-strength reinforcements on the different types of damage indices in the beam-column connections of rail bridges (designed based on the special seismic instructions) are studied experimentally under cyclic loading. Experimental results show that the application of high-strength reinforcements expedites the failure process of the specimens. Moreover, the results show that the energy absorption of the specimens decreases by using high-strength reinforcements either. However, the effects of high-strength reinforcements as stirrups has less repercussions than the case of using them as longitudinal reinforcements.

Due to the traffic structure in Iran and the excessive occurrence of loads to the surface of the pavement and then to the lower layers, the need to implement a resistant layer against to traffic loads in different weather conditions is quite obvious. In recent years, the upward trend in repair and maintenance costs for pavements has been increasing due to the increase in the amount and frequency of traffic loads on pavements, has led to an increase in the tendency to use modified bitumen and asphalt mixtures, especially in areas with high traffics. Many studies have been done to identify the appropriate additive for use to improve the behavior of bitumen and mixtures. The efficiency and effect of Nano Al2O3 as additive in rubber modified bitumen to improve its performance against rutting and fatigue destroies was evaluated in this study.In order to achieve the objectives of this study, firstly bitumen and 20% rubber powder with different percentages of Nano Al2O3 (0, 0.5, 1.0 and 1.5%) was combined and subjected to physical and rheological tests. The results of this study show that improving the bitumen behavior in moderate and high tempratures can be led to decrease of fatigue and rutting failures. Evaluation on the results showed that using of 20% rubber powder and 1.5% Al2O3 has the best effects on the rheological behavior of bitumen. Also it’s predicted that using of this bitumen can improve the asphalt mixture strength against fatigue and rutting.

One of the most important advances in road construction technology is the use of concrete pavements. These pavements are used in roads that require maximum performance and minimum repairs at the time of use. On the other hand, in recent decades, the use of cementitious composites and common fibers Has become popular to improve concrete performance. In this research, the role of steel and polypropylene fibers in improving the behavior of self-compacting cementitious composites pavements has been investigated. For this purpose, 127cubes specimens, cylinders and discs were made in 11 different mixing design.Two-layer flexural specimens were made in 17 different mixing designs containing steel fibers, polypropylene and a combination of them. On specimens, compressive tests, splitting test, drop weigth impact test and water absorption for half an hour and 72 hours and three point flexural test in accordance with the regulations of the 731 code have been done. the results showed that the more favorable effect of the steel fibers than the polypropylene fibers on the mechanical and impact properties the specimens.

In this paper, the amplification pattern of the ground surface is presented in presence of twin unlined circular tunnels subjected to SH-waves. To analyze the assumed seismic model, a half plane time-domain Boundary Element Method (BEM) was used which has been previously developed for single sub-surface tunnels. First, after presenting a brief formulation of the proposed method and displaying a verification example, the sensitivity analysis was carried out to obtain the seismic amplification pattern of the ground surface by considering the key parameters including tunnels buried depth, interval distance, incident wave angle and response frequency. Finally, by collecting the maximum amplification of different scenarios and applying linear fit on the obtained values, the results were summarized as series of linear equations and tables. The results showed that different situations of buried twin tunnels in urban fabric was very effective on the seismic response of surface. The results of this research can be used to completing and increasing the accuracy of existing codes around the subject of ground surface zonation in presence of twin tunnels.