جستجوی مقالات مرتبط با کلیدواژه « مقاومت لغزشی » در نشریات گروه « فنی و مهندسی »

Appropriate skid resistance is one of the important requirements in road paving; because this factor plays a decisive role in the safety of vehicle traffic, especially in rainy conditions. The fine texture of the asphalt surface, which primarily depends on the characteristics of the aggregates used in the asphalt mixture, plays a fundamental role in creating friction and skid resistance between the pavement and the vehicle tire; Therefore, it is necessary to ensure the proper quality of the aggregates before preparing the asphalt mixture. Because institutions and researchers have proposed various tests for this purpose, in the present study, while introducing each of these tests, the specifications limits for the parameters obtained from each of the tests have also been presented. The investigations show that no single test can indicate the optimal performance of the aggregate in the required skid resistance in the asphalt pavement; Meanwhile, a specific limit cannot be introduced for the output of these experiments. The suggested limits or values obtained from research and experiences can be considered as a primary guide in determining the test criteria related to the performance of aggregates in creating an appropriate skid resistance in asphalt pavement.

Seasonal variations in skid resistance have been a recurring phenomenon that has been studied by many researchers. The impact of seasonal variations will vary across geographic regions, due to different amounts of rainfall. During the summer months, especially during prolonged dry periods, small rock chips on the surface continuously become fine-grained particles as vehicles move and act as a polishing agent. During long rains (winter months), fine matter disappears and the heavier and more coarse sand acts as a polishing agent, resulting in slippery resistance to surface texture. Increase the coarseness. Many variables affect the measurement of skid resistance. It is not yet possible to fully investigate the possible influence of various factors affecting the seasonal variations in skid resistance. Precise measurement of seasonal variation in skid resistance is a relatively complex task. This paper introduces and investigates various methods of seasonal slip resistance correction available in the world and evaluates their feasibility of usage in Iran.

Threshold level of skid resistance is a process that is widely used in the pavement management to minimize the measured skid resistance at standard level for activating the maintenance of each section of the pavement with less skid resistance than this threshold. Road accidents during wet weather are a major concern for road engineers in rainy season. Road safety studies show that about 20% of all road accidents occur during wet weather, and resistance to wet roads has a major impact on wet weather accidents. Due to the lack of predictability of the ability to withstand skidding levels under different rainfall patterns, a minimum slip resistance threshold for safe driving in wet climates should be considered. In our country, these thresholds and management methods have not yet been defined. Monitoring the slip resistance of pavement surfaces is an integral part of a typical pavement management system. This paper shows how, using a scientific approach, the minimum threshold of skid resistance in different points of a road network is determined using different methods in the world that have been used so far. It is worth noting that other advanced methods are also used in different countries that are not addressed in this article.

Pavement friction and skid resistance are some of the most important factors affecting road accidents frequency and severity. Texturing is using due to improve frictional properties of surface during the construction of concrete pavements. In this research, in order to create macrotexture on the concrete surface, techniques such as perpendicular and parallel brushing (according to traffic direction), turf and burlap dragging on fresh concrete, and grooving hardened concrete were used. Mean Texture Depth and Skid Resistance of concrete surface, were measured using Sand Patch and British Pendulum tests, respectively. The results showed that the pavement macrotexture affects skid resistance. For turf dragged, parallel brushed, and non-textured sample, R-squared of the obtained relation between British Pendulum Number and Mean Texture Depth was more than 0.8. According to the results, among the created textures, perpendicular brushing of fresh concrete, with the average British pendulum number of 103.5, reached the highest skid resistance and by increasing the Mean Texture Depth, the British Pendulum Number increases. The result also showed in non-textured samples increase/decrease in Mean Texture Depth result in high increasing/decreasing in British Pendulum Number.

Concrete pavements are performing the as asphalt pavements. Their skidding resistance level eventually reduced by the flow of traffic, environment, climate change, pollution etc. During their service life. Cause of many road and highway accident, especially in wet condition is lack of skid resistance. Surface of the road must always have a proper texture, which includes both micro texture and macro texture. Mechanical retexturing treatment is about correcting skidding resistance level of the road that improves the return of any leakage of resistance, texture depth, or both. Most of the processes can be done at any time of the year in the toughest weather conditions. These methods can be used as a short to medium term remedial tool for repairing high risk sites and many processes can be replicated. The most appropriate technique to be used in any situation depends on the nature of the level and the downtime that needs to be addressed. All methods for reducing skid resistance are different, and the choice of technique should always be done according to the quality and the specific nature of the procedure. In this paper different methods of re-texturing have been analyzed and place of their usage have been materialized.    

Restoration of lost texture road pavement is one of the most important ways to keep high-traffic highways safe. Even with the most advanced building materials and technologies of today, busy highways will eventually lose their skid resistance due to excessive traffic and weather effects. Rain, snow, and ice, along with the high traffic volume of vehicles, can eliminate road surfaces or polish them. Losing friction means dangerous situation occurs when the stopping distance increases and leads to an accident. There are accident prone places on the roads, squares, roundabouts etc. There is a need to restore skid resistance for polishing reasons of these surfaces. Skid-resisting resistive procedures, in turn, provide a higher level of safety. Now using multiple re-texturing techniques, roads can be re-used at its best performance again, which is also very cost-effective and does not require the implementation of a new pavement. In this paper, different methods of enhancing of the skid resistance of polished asphalt surfaces are investigated and the position of the use of each method is determined.

The friction of a pavement surface indicates safety of a pavement. Pavement friction properties depend on pavement surface’s microtexture and macrotexture characteristics. Recently, considerable attention has been paid by researchers to find new methods and procedures for more accurate and quick measurement of the pavement skid resistance. Most of the proposed approaches in this regard have been in the range of non-contact methods, the use of laser and digital images. It has been found that image processing as a non-contact method with adequate precision and high speed can prove to be a promising and effective approach for further research on determining the pavement skid resistance. In this paper an intelligent system based on image processing is introduced which analyzes the texture of the pavement and presents a new index for pavement skid resistance by taking the effects of horizontal, vertical and diagonal components of its texture into consideration. By comparing the results of the proposed system and the corresponding British pendulum test results (BPN) it can be said that, the proposed system through using the image processing technology and more accurate assessment of pavement textures is capable of better recognizing the pavement textures and can produce repeatable results associated with the pavement skid resistance.

Skid resistance characteristics of road marking materials affect road safety appreciably. The two componenet road marking materials that are extensively used in pedestrian crossings should have skid resistance properties in order to assure safety of both pedestrians and cyclists. In this research evaluation of skid resistance and other physical properties of a two-component road marking material (that is extensively used in Tehran), were determined. Several mineral additives were used, namely Waste Glass, Silica and Leka (an expanded clay). British pendulum testing was conducted on all the samples and their skid resistance values (SRV) were determined. In addition to skid resistance, abrasion resistance, reflectivity and also adhesive properties of the samples were determined.Testing results showed that conventional road marking materials had poor skid resistance characteristics. With using the above mentioned additives the problem could be partially solved. Comparing the results it was shown that among the various additives, waste glass had performed better. In fact, the results showed that application of %10 waste glass resulted in SRV increase from 21 to 40. This also reduced abrasion resistance of the road marking material for some 10 percent and provided greater reflectivity.

Porous asphalt is a kind of open-graded asphalt mixture that characterized by containing a large proportion of interconnected air voids. Many countries have used porous asphalt since many years ago¡ but due to unfamiliarity and some ambiguities of contractors and consultants with this kind of asphalt¡ it has not been used appropriately in Iran. In this paper the performance of porous asphalt constructed in a section of Ghaemshahr-Sari road¡ is explained and evaluated. Laboratory and field studies show that porous asphalt containing polymer modified bitumen and cellulose fibers has adequate strength and durability; also it decreases the noise and increases the permeability and skid resistance.

Slipperiness of the road surface is one of the factors which increase the risk of accident. In fact slip occurs when the coefficient of friction between the tire and road surface is not enough to keep the adherence between the two. Skid should not be considered as a separate issue, but to solve this problem, we should optimize properties of tire and road which leads to decrease in possibility of skid. This is a fact that the less the skid resistance value, the more accidents in fall and winter which have more rain. Road friction changes with change of many factors such as properties of pavement surface, properties of tire, moisture of road and performance of vehicle. There is a need to manage skid resistance systematically to maintain the level of safety performance of roadway surfaces. This study focused on the development of a skid resistance deterioration model based on the analysis of skid data inventory collected in Tehran.This field study has been performed by examining the statistical information related to traffic and accidents and case study of a street with heavy trafficin inTehran as follows. Hot mix asphalt was provided from factories of municipality of Tehran and was distributed and tests of hot mix asphalt were done by Marshal test; then British pendulum method was used to determine the microtexture, and sand patch test was used to determine mean surface macrotexture depth. Finally by repeating the test in time intervals within 18 months and investigating the relationship between the data and test results, charts of state of changes of skid resistance over time were presented which indicated that slip resistance of asphalt pavement decreases by time and traffic crossing. First this decrease is more and then gradually declines. By comparing the results with standard it is concluded that the skid resistance of asphalt pavement should be improved after 7 months. result shows the variation of pavement skid resistance versus pavement age.Also by investigating the statistical reports given by the road police in the aforesaid street it was found that about 50% of the accidents are related to function of brakes of vehicles and friction resistance and comparing the statistics reveals that after the road surface is improved by asphalt, accidents in case study street decreased by 25%. After that with comparing the number of accidents in the studied street in the second 6-month of year and during the year especially in accident prone points it was found that number of accidents in the second 6-month is 70% of the whole year. This indicates the particular effect of weather condition in rainy season and decrease of skid resistance of pavement due to roads surface wetting on number of accidents.

To make the slippery roads surfaces safe during the winter, highway authorities usually must either apply rock salt (NaCl) or other chemical de-icers to melt ice and snow or spread sand to provide traction. Since usage of these materials may have negative environmental and physical impacts, therefore, their properties must be known to provide adequate space for improvement and to compensate for any short comes.In this research we are only concerning with the physical impact of the issue which is lowering skidding resistance of the surface as a result of applying rock salt to melt the snow and ice. Road surface type snow and ice melt more rapidly on a concrete surface because it gives up heat more rapidly. Since asphalt absorbs more solar radiation, it is therefore have more heat available for melting snow. This is why snow melts rapidly next to bare asphalt pavement areas. Even when the temperature of the pavement is below freezing point, it holds some heat and can help melting snow and ice. Changing ice or snow into water (brine) requires heat from the air, the sun, the pavement, or traffic friction. The surface temperature of a snow- or ice-covered road determines de-icing salt amounts and melting rates. As temperatures go down, the amount of salt needed to melt a given quantity of ice increases significantly. Using salt brine to pre-wet is becoming more common because of its lower cost.In this research it was established that the presence of salt brine on the surface will lower down the skidding resistance of the surface considerably. It is necessary to have adequate drainage system on the roads that enables the melted snow and ice which have concentration of high amount of salt content to be clear off the surface as soon as possible. It is better to apply salt as needed than to over-treat initially. It has been established that on the location in which the harsh maneuvering, acceleration and deceleration is needed aggregate of higher Polished Stone Value (PSV) be used than it was believed to be used before.

Rapid improvement in vehicle manufacturing technology has caused increases in vehicular speed, thus making ever increasing needs for improvements in vehicle break and skid resistance of road surfaces. International studies have shown increase in average speed, resulted greater damages when accidents occur. Concrete surfaces in general and road surface characteristics in particular have not neen improved in the same manner and wet skid resistance is generally low.The main aim of this research which has been carried out at Tarbiat Modares University is to evaluate the effect of concrete surface macro texture and its type, nominal size and effect of aggregate shape on skid resistance. In this research, the skid resistance is measured by using British portable skid resistance tester, commonly known as British pendulum and macro texture is measured using the sand – patch method.Skid resistance is an important factor for reduction of raod accidents. When this resistance is less than the optimum limit, special provisions should be considered for the surface areas. The best practice for controlling the skid risk is prevention. This means that during construction of the roads, it is necessary to achieve a suitable and long life skid resistance, by taking into account the principal techniques. The present research and its findings showed that the following points are of great importance:1.The diagrams 5 and 7 illustrate the fact that the skid resistance has a direct relationship to the size and shape of aggregates. Aggregates with largest sizes (4.75mm) created the highest resistance.2.Diagram 3 shows that the troweled surfaces (lacking the macro texture) have had the minimum skid resistance.3.It also shows that the macro texture developed on the surface of concrete road through harsh brush and fine aggregates with size 2.6 mm. has had the best skid resistance

One of the effective factors in road safety and accident reduction is to combat road surface slipperiness. The greater the coefficient of friction at the contact patch, the greater will be the degree of vehicle control in bringing it to a halt, thus helping reduce accidents.Asphalt pavements are used extensively throughout the world in general, and in Iran in particular. Thus, in this research hot asphalt mixes (3 types) have been studied for their relative performance in skid resistance. In this research, British Skid Resistance Tester (commonly known as the Pendulum) has been used to evaluate the skid resistance of laboratory made samples and the macrotexture of these surfaces have been measured using the sand-patch technique.In this research, by keeping the aggregate type the same, three types of asphalt mixes that is; pervious macadam, stone mastic asphalt and asphalt concrete are made and evaluated that are different in respect of macrotexture, nominal size, aggregate grading and the percentage of large to small aggregate fractions. Samples made measure 30 x 30 cm with a thickness of 5 cm which are the same as a complete wearing course layer in the field. As asphalt pavements are extensively used in Iran and in the world in addition to mechanical specifications of the asphalt mix the skidding resistance should also be considered. The results show that:1.Among the porous asphalt, SMA asphalt, and the asphalt with continuous grading (concrete asphalt), the porous asphalt is advantageous from the skidding resistance point of view.2.The nominal size of the mix affects the skid resistance of the size, and in the range of 4.75 to 19 mm. nominal size that were studied in this research. The less the nominal size of the mix, the more will be its skid resistance.3.Investigations show that the content of aggregates passed through sieve No. 4.75mm. affects the skid resistance of the nominal size measured by the English pendulum and the skid resistance of the aggregates has a reversed relationship with the aggregates passed thought the same sieve.4.In the asphalt with continuous concrete asphalt grading, the reduced skid resistance between nominal size of 4.75 and 9.5 mm. is not considerable, however it is influential on other parameters like Marshall Stability

Road maintenance and management is one of the most important tasks for road administration in every country. Application of preventive maintenance has been the subject of research for several years. Chip Seal is an option in preventive maintenance reducing the cost and time of rehabilitation. The outcome of the previous researches has revealed that spending a small portion of total cost for maintenance resulted in reduced pavement rehabilitation costs. In this paper after introducing and identification of chip seals, the design and construction of different chip seal is presented. The main purpose of this research is introducing different type of chip seal and evaluating their performance in the laboratory. To fabricate the chip seals effort was made to use the facilities available and simulate the real conditions in the country. In this research, friction, permeability and coating properties of different chip seals was evaluated to make a comparison between different chip seals.