جستجوی مقالات مرتبط با کلیدواژه "خودترمیمی" در نشریات گروه "عمران"

One of the inherent characteristics of asphalt mixtures, related to the viscoelastic properties of bitumen, is called self-healing. Due to the self-healing property, minor damages caused in the asphalt mixture during a loading process can be repaired to some extent during the rest period, and some of the original properties of the mixture can be restored. This study aimed to evaluate the factors affecting the failure characteristics and the self-healing phenomenon in modified asphalt mixtures by conducting tests on semicircular samples (SCB). The results obtained in this research showed that the fracture resistance and fracture energy in modified polymer asphalt mixtures are significantly higher than in the control sample (without modifier). Among the investigated additives, APAO polymer was more effective in increasing strength and failure energy, while SBS polymer showed the least increase in these properties. However, the flexibility index in the sample modified with APAO was lower than in the other investigated mixtures. Investigation of the fatigue behavior and self-healing phenomenon in asphalt mixtures showed that increasing the rest time from 0.8 seconds to 2.5 seconds increased the number of loading cycles until sample failure, indicating the self-healing characteristic of asphalt mixtures. Moreover, among the tested mixtures, the mixture modified with APAO polymer showed the best fatigue performance and self-healing behavior, followed by the mixtures containing SBR and SBS polymers, which performed better than the control mixture.

Nowadays, road transportation plays a major role in the transportation of people and goods; therefore, researchers are trying to reduce environmental pollution and road maintenance costs, and use of natural resources by providing solutions. One of the prominent topics in this field is the self-healing of asphalt, which can be an ideal solution to reduce the mentioned problems. Various methods, such as induction heating, microwave heating, and the use of nanomaterial and polymers, have been suggested by pavement experts to improve the self-healing performance of asphalt pavement. Each of these methods has problems, such as high cost and environmental pollution. This study aims to investigate the self-healing mechanism and improve the self-healing performance of asphalt mixture using capsules containing rejuvenator and to study the methods of evaluating the performance of these capsules in the asphalt mixture. These capsules are a suitable option for improving the self-healing performance of asphalt pavement due to the lack of environmental pollution, disturbance in the traffic flow, and low cost.

Improving the self-healing performance of warm mix asphalt depends on several factors and parameters that are highly interdependent and have significant complexity. In this study, the self-healing performance of warm mix asphalt was investigated using artificial intelligence and artificial neural network of multi-layer perceptron and radial base with two hidden layers. To conduct this study, two additives Sasobit and Zycotherm were used. The three-point bending test was performed at two temperatures of 25 and -16 degrees Celsius and with two crack lengths of 10 and 20 mm, and the fracture toughness, fracture energy and critical load indices were determined for each of the states. Asphalt samples were subjected to induction heating at two frequencies of 87 and 88 kHz and three induction times of 60, 90 and 120 seconds. The results of sensitivity analysis in two artificial neural network models showed that in the MLP network, the fracture toughness parameter had the greatest impact on the output. It was also observed that the test temperature parameter had the highest sensitivity coefficient in the RBF network. The results showed that in the perceptron neural network with two layers in the test section, the root mean square error (RMSE) values increased from 10.46 in the first model to 4.27 in the fourth model. The results of the basic radial artificial neural network showed that the addition of input parameters reduced the root mean square error (RMSE) value of the test section from 10.56 to 4.35. The results of MLP and RBF network estimation have shown that the addition of input variables to the model has increased NS in all three parts of test, train and validation. In this way, in the MLP network, the value of NS in the test section has reached from 0.45 to 0.90 and the estimation accuracy has doubled. In the RBF network, similarly to MLP, with the addition of the NS parameter, the NS value has increased from 0.44 to 0.90. Also, the results of this study showed that in both types of MLP and RBF networks, the value of R2 in the second group was higher than the first group in all test, train and validation sections. In general, the results of this study showed that the artificial neural network has appropriate performance and accuracy due to the nature of learning and the ability to train from the previous laboratory results in estimating the self-healing ability and modeling the complex relationship of the influential input variables, and the use of the proposed intelligent model by reducing the of experiments and cost can be effective in evaluating the self-healing behavior of warm mix asphalt.

In this research, in order to construct environmentally friendly green asphalt mixtures, steel slag with a size of 9.5-4.75 mm to a volume ratio of 60% of aggregates and red mud waste with 50 and 100% ratios of filler has been used as an alternative to limestone filler, and self-healing index and moisture sensitivity of these mixtures have been evaluated. To do that, the semi-circular bending test (SCB) was performed by seven damage-healing cycles using the microwave irradiation heating method. Results indicated that the steel slag and 50% red mud waste in the first healing cycle increased the optimum healing ratio compared to the control sample, respectively; 53.01% and 32.35%. Also, the moisture susceptibility test results showed that the amount of moisture resistance in mixtures containing steel slag and 50% red mud decreased by 16% and 21%, respectively, compared to the control sample. Using 50% and 100% carbonation cake as a replacement for limestone filler in mixtures containing steel slag has increased the moisture resistance by 9% and 13%, respectively. Also, this weakness of moisture resistance in the sample containing 50% of red mud was compensated by using 50% of carbonation cake, and moisture resistance was increased by 12%. According to the obtained results, the use of these waste materials instead of non-renewable natural resources such as aggregates, in addition to preserve the non-renewable natural resources, will improve the healing performance of asphalt mixtures.

Concrete is one of the most widely used constructional materials which is disposed to cracking for various reasons. Cracking is one of the unavoidable defects in concrete. When micro-cracks develop and join together, a continuous network of cracks is formed inside the concrete. Cracks increase the permeability and reduce the impermeability against moisture and aggressive substances such as sulfate ions, chloride ions, and acids. These factors affect the structure durability and reinforcement corrosion and destroy the concrete matrix. The concrete self-healing approaches appear to be an appropriate idea to remove this damage. Among the different self-healing ways which are basically chemical, the Calcium Carbonate precipitation, resulting from the micro-organisms metabolic activities, is a new environmentally friendly strategy. Their ecological variety is high and can be found in different natural settings. In this way, to treat damaged structures, a microbial process is applied wherein the combination of bacteria, urea, and a calcium source forms calcium carbonate crystal that results in crack reduction, impermeability, and improved concrete mechanical properties. Biologically, the calcium carbonate precipitation helps heal the small cracks, fill pores, and bind other materials such as sand and gravel in concrete. These precipitations are the byproducts of the usual metabolic processes such as photosynthesis, urea hydrolysis, and sulfate reduction. To obtain a useful insight in this important researching area and to protect the environment, this article investigates different approaches of using bacteria in concrete, the bacteria potential to heal the cracks. Improving the properties of concrete was examined, and the laboratory results were interpreted. Investigation of the concrete micro-structure indicated the formation of the calcite crystals in the samples and confirmed the promising performance of bacteria in healing micro-cracks, improving the mechanical properties, and the concrete durability in the destructive environments. By reducing structural pores, bacterial participation at a concentration of 105-107 cells/ml led to an increase in compressive strength by and a decrease in the penetration of chloride ions and water absorption to and , respectively. Moreover, the maximum crack healing width at a concentration of 107-109 cells/ml about was mm.

Nowadays, regarding the scarcity and non-renewability of natural resources and environmental issues, the use of waste materials in asphalt mixtures has been very popular. Besides, zinc slag has the potential to absorb microwave radiation because of its conductive nature. The main objective of this study is to investigate the feasibility of using zinc slag as a filler in warm mix asphalt (WMA) mixtures to examine the potential of deicing and self-healing. To evaluate de-icing potential, some tests on deicing potential of asphalt mixtures using microwave heating, including Ice-melting capability test, ice falling time, self-healing during deicing, and stability of WMA samples incorporating different contents of zinc slag filler (0, 35%, 70%, and 100% of total filler weight) were carried out. The results show that if 100% zinc slag filler is used in WMA asphalt mixture, the ratio of self-healing during deicing is the best; additionally, the results indicate that the ice melting speed of the WMA mixture containing 100% BOF filler was 68% higher than that of the control mixture.

Concrete is one of the most used materials in the world. Cracking in concrete is a common problem that occurs due to its relatively low tensile strength. The cracks created in concrete are the main reason for the reduced durability and useful life of concrete structures. Proper and timely repair of primary cracking is necessary in order to prevent its expansion in concrete and reduce the high cost of maintenance. For this purpose, self-healing methods have been developed. Adding microorganisms to concrete mixing and bio-concrete production is an intelligent and environmentally friendly strategy for the repair of concrete cracks. Bacterial species resistant to hard and rough concrete environment such as bacillus, with the production of calcium carbonate precipitation, can be repaired in a continuous hydration process by filling freshly formed fine cracks. The aim of this study was to identify the effective bacterial species and its effect on the strength properties of concrete as a restorative agent.The results show that the changes in the strength properties of bio-concrete by adding Bacillus subtelius at a concentration of 〖10〗^8 (Cells⁄ml), increase the compressive strength by 24.24% and also improve the durability of concrete by bacterial self-healing process.

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.

In cases where the soil normally has undesirable properties and it is not possible to replace the soil, it is necessary to use methods such as compaction, injection, stabilization, reinforcing and other methods for soil improvement. Recently, due to the advancement of engineering science and since many soils and minerals are among the nano materials, their chemical reactions occur at nano scale. In this regard, nano materials are used to improve the geotechnical properties of the soil. Also, the self-healing of clay as one of the positive properties of clay in recent years has been considered by researchers.In this study, in order to investigate the effect of iron oxide nanoparticles on the behanior of clayey-sand soil, three soil types were selected for laboratory tests, including soils with 10, 20 and 30 percentage of clay. The results show that the peak strength of soil stabilized with iron oxide nanoparticles is increased especially sandy soil with lower percentage of clay. Also, the effect of curing time was obvious on the strength development in the restoration process of the soil. The effect of nanoparticles on the peak strength and self-healing characteristics of clayey sand has been shown with a series of SEM images.