h. divandari

Rutting is one of the most important deteriorations in flexible pavements and a significant amount of annual maintenance and rehabilitation funds are spent for its repair. Permanent deformations increases, which leads to increasing rut depth, can cause irrepairable problems in asphalt pavements. On the other hand, in Marshall method, which is known as the main method of asphalt mixtures mix design in Iran, the lack of a simple test to determine specimen resistance to permanent deformation is sensible. Although there are many devices to measure the rutting nowadays, but none of them have the ability to be used at site level. In addition, prevalent methods of evaluating rutting potential of asphalt mixtures are usually expensive and time consuming. The abovementioned factors necessitate development of a simple laboratory method that not only enjoys an acceptable precision but also is able to predict specimens rutting performance with low cost within the short time. In this research, one type of aggregate, one type of gradation, two types of bitumen, one type of filler, and three bitumen contents were used to prepare Marshall asphalt mixture specimens. After performing the main tests on specimens, IDT test results and Marshall parameters were used to develop a mathematical model to estimate specimen Wheel Track apparatus rut depth. The presented model measures rutting resistance using a combination of indirect tensile strength test results and Marshall parameters. The model is validated using artificial neural network, which makes it possible to evaluate rutting potential while OBC is being determined in a laboratory. Therefore, not only is there no need for expensive instruments of rutting test, but also a remarkable time saving in mix design procedure is achievable.

Pavement deteriorations repair costs allocate a huge part of national budget to itself annually. Inadequate resistance against traffic loading is the main reason for these deteriorations, which will result in pavement life cycle reduction, lower safety condition for road users and increase in maintenance costs. Characteristics of asphalt cement as a basic constituent of asphalt concrete is effective on these problems, a flawed AC can be modified using additives; hence, its properties will improve while the characteristics of asphalt concrete will improve either. Bentonite is used as an additive of asphalt cement in this research. To perform the research program, modified asphalt cement characteristics were surveyed using asphalt cement tests and optimum asphalt content of specimens with various additive contents were determined. The prepare specimens were tested and the results indicates an improvement in asphalt cement and asphalt concrete specimens marshal properties after using bentonite.

Network of roads is a part of assets of each country that can be progressive in different fields and aspects. So, maintenance and repair of this property, is significant. Accordingly, pavement has a very specific effect due to its high costs. The More correct maintenance, lower costs appeared. Asphalt rutting is one of the flexible pavement deteriorations. Rutting has caused high maintenance and repairs costs and several problems for road users for years, so researches are concentrated on this problem. Investigations showed rutting has various origins, although, the most important factor is permanent deformation production due to lack of asphalt shear strength. Predicting asphalt pavement strength against permanent deformation while preparing laboratory mix design can prevent producing asphalt with high rutting potential. However, not only laboratory instruments for this purpose are expensive, but an experienced labor should be used for a considerable time to work with them. These factors made the researchers look for lower cost and time procedures for assessment of rutting in laboratory step. Although the most popular method of determining rutting potential, is loading wheel, but in lots of researches, dynamic creep test is used. Previous studies showed flow number of dynamic creep test is related to rutting potential inversely. In this research which covers a wide variety of aggregates, gradation, bitumen and filler used in Iran a simple model for predicting flow number is developed. Then it was appeared that gyratory shear stress curve which is the one of six output curves of gyratory compactor, can be represented as a logarithmic model. After modeling this curve for all specimens and determining the slope of density for them, a simple model was presented to estimate the flow number by SPSS software. The independent variables of this model were determined from output curves of gyratory compactors. This model was validated by using neural network and genetic algorithm. And its accuracy was confirmed by an appropriate percent of confidence. Flow number can be predicted while asphalt specimens are prepared in order to determine the 9 Developing a Model for Estimating … / Ziari, Divandari, Shafabakhsh and Fakhri optimal bitumen in laboratory by this model. So not only there is no need for expensive equipments to perform rutting and dynamic creep test, but also a reduction in mix design procedure time is achievable and producing of asphalt with high potential of rutting is prevented.

Variation of bitumen useful properties after continuous heat and cold cycles is a weak point of this substance. The temperature of these heating cycles is effective on loss of properties too. Due to problems while transport، hauling and conserving bitumen from production to asphalt plant، the effect of heating cycles and bitumen heating temperature on properties such as penetration degree، softening point and penetration index should be considered. In this paper the mentioned effects were surveyed by performing penetration and softening point test on bitumen samples heated in various cycles and heating durations. The results showed bitumen properties loss intensely after heating cycles and went out of range which should be considered in designs. Finally six models to predict penetration، softening point and penetration index of 67/70 and 85/100 bitumen after heating cycles and in various heating durations were developed.

The Marshall Compaction Method has been used to prepare asphalt mixture samples in laboratories for many years, despite its technical disadvantages. It has since been replaced by the Gyratory Compacting Machine, which came about when the SuperPave mix design method was introduced. Shaft reaction to a specimen with a vertical pressure equal to 600 kPa under a determined angle-applied load is determined, and the specimen is compacted by vertical pressure and mould shear pressure simultaneously. One of the benefits of this new method is that the specimen height is measurable during the compaction procedure in this machine. Since the weight and height are known in the compaction procedure, the specimen density and air void fractions can be determined during the test. During this research study, equilibrium equations were used, and the specimen forces were presented to determine the shear stress in the Gyratory Compacting Machine. The results showed that there is a direct relationship between the shear stress and the mixture rutting resistance. Therefore, by determining the specimen shear stress during mixture preparation, the rutting potential can be measured simultaneously.These results offer the potential for cost and time saving in laboratory experiments, and allow an insight and extra degree of confidence in the experimental methods.

This paper presents the fundamental principles and practice of four commonly used asphalt mixture design procedures in the United States. The methods covered include the Marshall, Hveem, Superpave and GTM mix design methods. Emphasis is placed on comparing them with regards to the three main elements of mix design procedures, namely: 1) Method for preparation and compaction of the asphalt mixtures2) The properties of the compacted specimens to be measured3) Criteria used for selecting acceptable and optimum mix designs