Performance Of Hot Asphalt Mixtures Research Articles

Rutting performance of asphalt mixtures containing treated RCA and reinforced by carbon fibers

This study examined the rutting performance of hot asphalt mixtures containing treated RCA and reinforced by carbon fibers. The methodology involved substituting RCA instead of coarse virgin aggregates in the several percentages (20, 40, 60, 80, and 100%) that were treated by being submerged for 24 hours in an acetic acid solution with a concentration of 0.1M. Carbon fibers were added in several percentages of 0.15, 0.25, and 0.35% by the entire weight of the mix to produce cylindrical specimens (4×2.5 inches) for evaluating the Marshall and volumetric properties, and rectangular slabs (30×40×5 cm) for evaluating rutting resistance. The study finds, that incorporating RCA and carbon fibers did not substantially affect the volumetric characteristics of asphalt mixtures, but Marshall's stability increased. The combination containing 60% RCA and 0.35% carbon fibers showed the greatest increase in Marshall stability, which was 35.81% over the control mixture. The addition of RCA led to a reduction in the rutting performance, whereas the addition of carbon fibers increased it, as seen by a decrease in rutting depth. The combination incorporating 40% RCA and 0.35% carbon fibers exhibited a minimum rutting depth of 40.64% lower than the control mixture. The combination incorporating 20% RCA and 0.35% carbon fibers exhibited the maximum level of dynamic stability, which was 1.64 times greater than the control mixture.

The Effect of Wetfix and Nanohydrated Lime Additives on Bitumen Aging and the Cohesion and Adhesion Failure Mechanisms of Hot Asphalt Mixtures

Aging due to sunlight and the passage of time is an effective element in the occurrence of moisture damage in hot asphalt mixtures. Still, the effects of this parameter are scarcely considered in the experiments examining the moisture damage potential. Accordingly, this study investigated the effect of aging on the performance of hot asphalt mixtures and examined the improvement of moisture damage performance by using antistripping additives via mechanism and functional tests. Two types of aggregates (limestone and granite) with different degrees of moisture sensitivity, two types of bitumen (PG64-16 and PG58-22) with different performances, and two additives (Wetfix liquid additive and nanohydrated lime) as bitumen modifiers were used. Bitumen samples and asphalt mixtures were subjected to short- and long-term aging. The pull-off test was performed to explore the aging effect on different failure mechanisms (cohesion and adhesion), and the indirect tensile stiffness modulus (ITSM) test was conducted to study the asphalt mixture’s performance against moisture damage. The results specify that aging, in terms of hot asphalt mixture hardening in dry and wet conditions, decreased the MSR (resilient modulus wet to resilient modulus dry ratio), and this decline was greater in long-term aging. The pull-off test results exhibited that aging, especially in the long term, decreased the asphalt mixture’s adhesive strength in dry and wet conditions; this decline in adhesion was greater in the wet than in the dry state, and this difference decreased the wet-to-dry adhesion strength ratio (the pull-off ratio). The additives relatively improved the yield modulus of the asphalt mixture, but their effect was greater in the wet state. A comparison of the pull-off test results in cohesion and adhesion failure demonstrated that Wetfix was more effective in improving bitumen–aggregate adhesion, whereas nanohydrated lime was more effective in enhancing bitumen adhesion. The resilient modulus (Mr) ratio in wet-to-dry conditions indicated that nanohydrated lime had better effects on the overall performance of the aged asphalt mixture against moisture damage. To investigate the effect of additives on the performance of asphalt mixtures, a t-test was performed in all modes of control, short-term aging, and long-term aging. The findings showed the effect of Wetfix and nanohydrated lime on increasing the modulus of elasticity of the samples.

Comparative environmental performance of pavement structures considering recycled materials and regional differences

The construction of pavements incorporating reclaimed asphalt pavement (RAP) is taking place around the world, implying the necessity to quantify their net environmental impacts. Life cycle assessment (LCA) is a popular method to analyze the environmental impacts of a product along the whole value chain, providing guidance to practices and technologies from environmental perspectives. However, the LCA research of RAP-modified pavement is seldom performed in Brazil. In addition, as an important source of uncertainties, there is also need of discussion regarding the geographical and technological characteristics in the LCA of pavements. For these motivations, this paper performs a cradle-to-gate LCA to compare the environmental performance of asphalt pavement in Brazil and Switzerland, using the practical rates of RAP use. The functional unit was defined based on the same traffic volume and service life of asphalt pavements, where the mix design and pavement structures follow the standards of the two countries. The results showed that RAP recycling can improve the environmental performance of hot asphalt mixtures in both countries. Binder amount has a high environmental burden and its reduced use by adding RAP has a positive environmental effect. Type of fuel also plays an important role in LCA. In Brazil, it is not recommended to use heavy oils as fuel during the mixing process if other options such as methane gas is available. The results show that the Swiss production of asphalt mixture had lower environmental impact. Nevertheless, a strategic location of material suppliers and mixing plants could lower the transportation distances, improving its environmental performance.

Effect of Aggregate Gradation and Morphology on Porous Asphalt Mixture Performance

Previous studies have reported the effects of aggregate gradation and angularity on the pavement performance of hot asphalt mixtures, while little work has been done on the role of aggregate gradation and morphology related to porous asphalt (PA) mixture performance. The primary objective of this article was to evaluate the effects of aggregate gradation and morphology on the mechanical properties and volumetric characteristics of PA mixtures. Ten PA mixtures, prepared by regulating the percentages of aggregate passing 9.5-, 4.75-, 2.36-, and 1.18-mm sieves and using two types of aggregate sources, were compared by evaluating air voids, shear strength, Marshall stability, indirect tensile strength, and micromorphology. The analytic hierarchy process method was used to analyze the priority weights of various influencing factors on PA mixture performance. The results indicate that aggregate gradation had significant effects on the performance of the PA mixtures. There was an excellent linear relationship between the percentages of aggregate passing the 9.5-, 4.75-, and 2.36-mm sieves and the respective mixture air voids. Increasing the proportion of 4.75–9.5-mm aggregate particles in the PA mixes did not contribute to its moisture damage resistance. The percentage of 2.36–4.75-mm aggregate fractions was the most critical influencing factor for the PA mixtures’ mechanical properties and volumetric characteristics. Additionally, aggregate morphology does affect PA performance. The permanent deformation resistance and moisture resistance were notably improved as the aggregate sphericity value increased. Based on the test results, the mechanical properties and volumetric characteristics of PA mixtures can be optimized depending on engineering requirements by regulating the aggregate gradation and type.

Using of Plastic Wastes as Additives in Bituminous Mixes

Plastic wastes are everywhere in today’s lifestyle and are growing rapidly specially in a developing country like Egypt. As these are non-biodegradable, there is a main issue facing the community concerning the handling of this plastic rubbish. On the other hand, different forms of increased distresses in flexible pavements such as cracking and rutting as well as moisture damage ratio should be faced and reduced by modifying the performance of hot asphalt mixtures. The reclaimed plastics that originally made of polymers have been used as an anti-stripping modifier to reduce the appearance of distresses in asphalt pavement surface and increase the resistance against moisture damage. In this research, the recycled plastic wastes have been used according to dry mixing process using contents (0.0, 2.0, 3.0, 4.0 and 5%) from the total weight of hot asphalt mixture. The optimal bitumen content has been derived for each polymer content by using Marshall procedure. The performance of modified bitumen mixtures have been recognized using Marshall quotient (as indicator of the stiffness), static indirect tensile strength and tensile strength ratio (as indicator of moisture damage resistance), dynamic modulus value (as indicator of stiffness of the asphalt mixture when tested in a compressive and repeated load test under different temperatures) and flow number (as indicator of permanent axial deformation resistance). The results obtained that the addendum of plastic rubbish to HMA improves its characteristics such as stability, strength, resistance to moisture damage and permanent deformation. The addition ratio of 3% polymer provides better pavement performance. Moreover, it has an economic importance where it reduces the exhaustion of natural asphalt in paving works by about 14.5%.

Evaluating the mechanical performance of hot asphalt mixtures modified with metakaolin as filler

Filler has an essential effect on the behavior of the hot asphalt pavement mixtures (HMA) through reducing the voids in the aggregate skeleton and reducing the temperature susceptibility of the asphalt binder layer. Recently the use of Metakaolin as a Pozzolanic admixture has been investigated to enhance the strength of cement concrete mixture. In this study, an experimental assessment of the mechanical properties of the HMA modified by Metakaolin as partial replacement of cement mineral filler was conducted. Five mixtures containing 0, 25, 50, 75, and 100 Metakaolin replacements percentages of ordinary cement were prepared at their optimum asphalt content. The Marshall properties, temperature susceptibility, and moisture damage are investigated for these mixtures. It was found that the addition of different proportions of Metakaolin filler as replacement of cement has a significant influence on the mechanical behavior of the HMA. The result illustrated that The Marshall's Stability, Flow and, density grow as the Metakaolin content grows until 50%, then the value starts to decrease at 75 and 100%. The air voids and voids in mineral aggregate decrease with increase the Metakaolin content to the lowest value at 50% of Metakaolin. The indirect tensile strength increases continuously as the Metakaolin content increases at 25, 40, and 60 oC, while temperature susceptibility decreases as Metakaolin content increases. The resistance to moisture damage has been improved by adding Metakaolin filler. It is concluded that the hot asphalt mixture can be modified by using Metakaolin as partial replacement mineral filler at 50% and optimum asphalt content of 5.2 %.

Performance of Hot Asphalt Mixtures Containing Plastic Bottles as Additive

This study focuses on evaluating the resistance of polymer modified asphalt mixes and the role played by asphalt in the realm of construction is undeniably important. Addition of polymers(PB) as additives to asphalt helps to improve the strength and water repellent property of the mix and as well as helps environment in various ways and at the same time, analyzing its lower maintenance activities and service life is most important. The use of inexpensive polymers, in this case, waste polymers has without any doubt proven to be the most convenient way of reducing the cost of construction and at the same time maintaining quality. The main resolve for this research was to establish the effects of the use of plastic bottles on hot asphalt and its mixtures. In order to put this into perspective, varying percentages of asphalt mixtures were calculated and subjected to laboratory tests. The two-factor variance analysis (ANOVA) was conducted to determine the significance at various confidence limits. The results indicate that the inclusion of Polyethylene Terephthalate (PET) had a particularly substantial effect on the properties of asphalt. Consequently, it can encourage the re-utilization of waste in the manufacturing industry in an ecologically friendly and cost-effective way.

Analysis of Factors Influencing on Compaction Performance of Hot Asphalt Mixtures by Orthogonal Test

The compaction can directly affect the performance of asphalt pavement, while the mixing temperature, the molding temperature, the temperature of aggregates and the rolling times can all affect the compaction performance. The L9(34) orthogonal tests and indoor tests were used to analyze the influence of the main factors on the examination indicators. The results show that molding temperature have a significant effect on the physical and mechanical properties of SMA13 asphalt mixtures when the confidence level α is 0.10. Finally, quantitative analysis is performed to study the optimal compaction technology of molding temperature and rolling times.