Performance Characteristics Comparisons of Various Asphalt Mixture Technologies

Due to the use of many warm-mix-asphalt (WMA) additives in the market, the effect of long-term aging on these WMA mixtures is generally unclear; hence, it is necessary to simulate their performance in the laboratory. The objective of this study was to investigate the influence of various WMA additives on the moisture susceptibility of mixtures containing moist aggregates following a long-term aging process. Mass loss (percentage), indirect tensile strength (ITS) of dry and conditioned specimens, deformation (flow), and dissipated energy values were measured. The experimental design included two aggregate moisture contents (0% and approximately 0.5% by weight of the dry mass of the aggregate), two lime contents (1 and 2% lime by weight of dry aggregate), one liquid antistripping agent (ASA), five WMA additives, and two aggregate sources. A common long-term aging procedure was used in this study. The test results indicated that long-term aging improved the moisture resistance of WMA mixtures regardless of WMA additive, ASA, and moisture content. In addition, aggregate source affected the moisture resistance regardless of WMA additive, ASA, and aggregate moisture content. The effects of various WMA additives on the dissipated fracture energy of unaged mixtures are generally similar except that mixtures with Asphamin have relatively lower dry dissipated fracture energy. In addition, the aggregate type affected the dissipated energy value of WMA mixtures regardless of aging states.

Laboratory evaluation of the effect of nano-organosilane anti-stripping additive on the moisture susceptibility of HMA mixtures under freeze–thaw cycles

Different laboratory tests have been available to predict and compare the mechanical and engineering properties of asphalt mixes under different loading and environmental conditions. However, to predict and/or evaluate long-term performance of asphalt mixes, indirect tensile fatigue and cyclic compressive laboratory tests have been utilized for many years. Most recently, the Asphalt Pavement Analyzer (APA) has been receiving much attention in the United States and Canada as a proof test for early detection of asphalt mixes susceptible to premature rutting and fatigue failure. In addition, the shear strength of asphalt mixes has been recognized by the Strategic Highway Research Program (SHRP) as one of the strong candidates to describe and possibly predict long-term performance of newly constructed asphalt pavements. However, the correlation among these different test methods as well as the correlation between them and the pavement's long-term performance still needs to be assessed. This investigation addresses these two points, where asphalt cores corresponding to five different mix types were tested in four different laboratory procedures. The parameters determined for each mix were the indirect tensile strength, resilient modulus, shear strength, shear modulus, and rut depth in the APA. The results of the indirect tensile strength and resilient were in excellent agreement, and the results of the shear strength, shear modulus, and rut depth were very close. However, the two groups had considerable differences, indicating that a single test may not be enough to predict the full extent of the asphalt long-term performance. For the covering abstract see ITRD E118503.

As the construction industry continues to evolve globally, there is a need to develop best practices geared towards achieving sustainable construction. Asphalt concrete’s demand has been increasing steadily with an estimated global demand of 122.5 million tons in 2019. This is driven primarily by the growth in construction activities in developing countries as each country works towards enhancing its transportation facilities to cater to the ever-expanding population. Hence, there are needs to develop newer and more efficient means of asphalt consumption. One of such is identifying cheaper or waste materials for use in Asphalt production. This study, therefore, examined the viability of waste marble dust (WMD), an industrial waste produced during the shaping and polishing of marble blocks and also during its extraction from the mines, as a mineral filler in Hot-mix asphalt (HMA) concrete. Engineering properties such as Marshall stability and flow, Void characteristics, Indirect tensile strength and Tensile strength ratio properties were examined. It was observed that the addition of WMD steadily increased the Marshall Stability and indirect tensile strength values and lowered the voids percentages. The study’s major finding is that waste marble dust is highly suitable as a mineral filler in HMA and a 3% by volume addition of WMD in HMA at 4.5% binder content produced the most optimal mix for use in road pavements.

The effect of matric suction on stress-strain relation and strength of three Alfisols

In recent decades, the utilization of the warm mix technologies in pavement constructions is increasing rapidly with rise in public environmental awareness. The durability of a pavement highly depend on the behavior of the pavement against aging induced failures. Therefore this study encompasses the evaluation of short- and long-term aging characteristics of four kinds of Warm Mix Asphalt (WMA) additives. Additives distinctly assessed in this study, consist of two non-foaming (organic and chemical) and two foaming(synthetic and natural zeolite) additives. In order to appraise the proportion of hardening of mixtures containing dierent kinds of additives, indirect tensile strength (ITS) values of both short- and long-term aged specimens were determined. Based on relative aging indices derived from the ratio of ITS values of aged and unaged specimens, comparisons were made between the additives assessing the impact of their utilization on aging characteristics of WMA.

Fibre is one of the most popular additives in hot mix asphalt (HMA). However, there are few research studies about the application of fibres in cold recycled mixture with asphalt emulsion. In this study, five popular fibres are introduced to the emulsion recycled mixture, including polyester fibre, polypropylene (PP) fibre, polyacrylonitrile (PAN) fibre, lignin fibre, and basalt fibre. The optimum pre-mixing water (OPW) content, optimum emulsion content (OEC) and optimum fibre content of recycled mixtures reinforced by fibres are determined. The indirect tensile strength (ITS), moisture susceptibility, bending cracking at low temperature, rutting and fatigue life of mixtures with these fibres are investigated. The test results indicate that the OPW and OEC of recycled mixture are influenced by types and contents of fibres. Although different fibres lead to obviously different ITS values, the optimum content for each fibre is near 0.3% by weight of RAP. All five fibres improve the performance properties of the emulsion recycled mixture. The improved percentages depend on the type of fibres. Polyester fibre has higher improvement on fatigue life than the other fibres. Therefore, polyester fibre is recommended as the most effective fibre to improve the emulsion recycled mixture.

The resilient modulus is the modulus to be used with the elastic theory during any analysis of a flexible pavement. It is well known that most paving materials (e.g., asphalt pavements) are not elastic but experience some permanent deformation after each load application. With respect to the complexity of the Rubberized Asphalt Concrete (RAC) containing Reclaimed Asphalt Pavement (RAP), the Indirect Tensile Strength (ITS) and resilient modulus evaluation of modified mixtures are important to understand. The aging of binder containing crumb rubber obviously alters the visco-elastic and plastic characteristics of the modified mixtures. The deformation of the mixture under repeated loading, nearly completely recoverable, should also be considered. The experimental design included the use of two aggregate sources, one rubber type (ambient), four rubber contents (0%, 5%, 10%, and 15%), one crumb rubber size (-40 mesh [-0.425 mm]), and four RAP contents (0%, 15%, 25%, and 30%). The findings indicated that an increase in the rubber content in the modified mixture leads to a decrease in ITS and resilient modulus values regardless of rubber content, and this increase also improves the aging resistance and increases the viscous characteristics of the modified binder. However, as RAP content increased, not only the viscosity and G*sinδ values of the modified binder increased, the ITS and resilient modulus values of the modified mixtures also increased.

With the growing need for sustainable and long-lasting paving materials, researchers have turned to innovative additives to improve the performance of bitumen and asphalt mixtures. Conventional bitumen often fails under heavy traffic loads and harsh climatic conditions, necessitating modification. This study aimed to improve the performance of bitumen and hot mix asphalt (HMA) by co-modifying them with a 4% styrene-butadiene-styrene (SBS) polymer and varying ratios of novolac resin. The results offered that the optimum ratio was 2% Novolac with 4% SBS. The physical and mechanical properties were evaluated through penetration tests, softening point, penetration index, dynamic shear rheometer (DSR), Marshall Stability tests, indirect tensile strength (ITS), tensile strength ratio (TSR), and wheel tracking. The modified mixture offered an improvement in penetration index from -1.89 to +1.3, a 38.7% increase in stability, a 40.9% increase in indirect tensile strength (ITS), and a 66.2% increase in moisture resistance. In comparison, the depth of permanent deformation was reduced by 58%. These results indicate significant improvements in stability, moisture, and deformation resistance, making it a promising option for developing more efficient asphalt mixtures. It also aligns with sustainable construction goals by reducing the need for frequent maintenance and extending pavement life.

Modeling and performance evaluation of asphalt mixtures and aggregate bases containing steel slag

Using hot asphalt mixtures (HMAs) is very common in flexible pavement construction due to its mechanical properties of durability, water resistance, and riding comfort. It proved to substantially reduce the applied stresses from vehicular traffic to subgrade. However, these types of pavements can undergo different types of distress such as cracks and rutting, which could be the result of weak mixing of the asphalt mixture and/or increasing traffic volumes. Therefore, the need to improve the mechanical properties of hot mix asphalt mixtures using different additives and modifiers was raised. Different materials have been recently used to reinforce asphalt concrete. For the construction of road pavements, using fibers in a HMA has emerged as a significantly more appealing option due to their strengthening properties. The alteration of asphalt binder is expected to benefit from carbon fibers (CFs) more than other types of fiber. In this study, an experimental study is carried out to investigate the effects of adding CFs to the asphalt mixtures with grades of (40–50) which comply with the Iraqi specifications. Twelve Marshall specimens were tested for stability and flow, 24 specimens for moisture failure testing, and two specimens for the rutting resistance of the asphalt mixture. The optimum bitumen content of 5.0% was used to prepare all the specimens. Different percentages of CFs by weight of asphalt (0, 0.2, 0.4, and 0.6%) were implemented to study the performance of paving mixtures. The way to mix the disperse the CFs homogeneously is by dry state (after separating the fibers manually) for 10 min, and then the asphalt was added; the mixture was heated to 165°C and mixed for at least 20 min. The results showed that the optimum properties of the HMA were reached by adding 0.4% CF to the HMA. Marshall stability was increased by 48%, the flow was decreased by 23%, and in addition, rut depth was reduced by 50%. The unit weight and the percentage of air voids in the mix were maintained and, along with other mix properties, are preserved within acceptable limits. Moreover, the indirect tensile strength has increased by 88.6%. Furthermore, moisture susceptibility reached 88%. Therefore, the addition of 0.4% CFs improved the performance of HMA at a high temperature of 60°C, which is close to the paving temperature in Iraq, by reducing the rutting of the asphalt mixture, which is considered the most dangerous tiling problem in Iraq. By improving the performance characteristics of asphalt mixture, the durability of the pavement will increase, and the riding will be more comfortable.

Evaluation of open-grade friction course (OGFC) mixtures with high content SBS polymer modified asphalt

Increasing rubber content in asphalt mixtures is recognized as a practical approach to consume fast-growing waste tires. The reacted rubber technology using the dry process was developed to address the rubber swelling and poor performance of rubber asphalt mixtures. Although the tire rubber has proved to increase the low-temperature performance, fatigue life, cracking resistance, and rutting resistance of asphalt mixtures, the impacts of high content tire rubber on the mixtures’ internal structures have not been revealed. This study is a preliminary research that utilized the laboratory and numerical simulation approach to investigate the strength, skeleton structures, and stress distribution of the tire rubber asphalt mixtures. The discrete element method (DEM) was employed to establish asphalt mixture models with a high content of tire rubber. New modeling procedures were developed to incorporate coarse aggregate shapes and rubber particles. Indirect tensile strength (ITS) values of specimens with rubber content up to 4.5% by mass were tested in laboratory and simulation. The results from DEM simulation had better consistency than the laboratory results. However, the test results showed that as the rubber content increased, the ITS of asphalt mixtures significantly decreased. Besides, the simulation indicates that the ITS decreased linearly as the percentage air void increased. The specimen ITS value decreased by half as the void ratio reached 15%. Furthermore, the internal structures and stress distribution of specimens with different rubber content were analyzed. The gap gradation proved to have a functional capacity of accommodating fine aggregates and rubber particles, all while forming a coarse aggregate skeleton.KeywordsAsphalt mixturesReacted and active rubberDry processIndirect tensile strengthDiscrete element methodInternal structure

The rubber which is generated from scrap tyres (tires), identified by crumb or powdered rubber. Day after day, discarded or scrap tyres create huge environmental problems. As long as the scrap tyres are regarded as a non-decade material those disrupt the clean environment. Using this rubber in pavement and asphalt has become a great interest and proposal for researchers for overcome this issue in recent years. Researchers and engineers discovered another way to improve asphalt concrete, by adding crumb rubber (CR) into asphalt concrete. This is done by two methods; first method rubber placed in bitumen and completely or partially reacted with bitumen, this will become binder modifier (wet process). Second method replacing this rubber with fine aggregates which are not dissolved completely with bitumen (dry process). In this study crumb rubber is added into mixture initially by substituting rubber with amount of fine aggregate. Thereafter laboratory tests; penetration, ductility, softening point, elastic recovery and moisture susceptibility test were conducted. These tests were performed, investigated and compared to evaluate the effect of indirect tensile strength (ITS) on asphalt concrete modified with several ranges of crumb rubber. It has been shown that (0%) is control sample, while (2, 4, 6, 8 and 10) are percent of rubber by the total weight of aggregate. One of the critical issues in asphalt pavement is moisture damage. The existence of moisture play a great role in reducing the stiffness of the asphalt mix as well as makes the chance for stripping of the asphalt from the aggregate. This study evaluates the strength loss by comparing two methods of ITS test, which are conditioned (tested in saturated state) and unconditioned (tested in dry state) samples. Marshall Mix method was applied for preparation of total 24 samples for both states of ITS. The results show that for conditioned samples 6% of CR gives the highest value of tensile strength, (892) Kpa. While in unconditioned samples, 10% of CR gives even higher value of strength, compared to conditioned and control sample, (933) Kpa. According to AASHTO T 283-14, the tensile strength ratio (TSR) results of all samples are within the standards, using the minimum value of 80%. For asphalt modified with (2, 4, 6, 8 and 10) % of CR, the TSR values are (95.3, 97.7, 97.4, 93.6 and 90.9) % respectively. Moreover the results are discussed in detail in this study. As summary, the optimal dose of CR is 4% which gives better performance for penetration, softening point, elastic recovery and tensile strength ratio.

This research investigated the size effect of hydrated lime on the moisture susceptibility of warm-mix-asphalt (WMA) mixtures with selected additives. A superfine hydrated lime used in the study was produced from regular hydrated lime (RHL) by a Los Angeles abrasion machine. The superfine lime was measured to be 660 nm, approximately half of the RHL size of 1.3 µm, a sub-nano-sized hydrated lime (SNHL). Scanning electron microscope (SEM) pictures were taken to observe the difference of the crushed lime in size, shape, and texture. Experiments for antistripping properties, such as indirect tensile strength (ITS), tensile strength ratio (TSR), flow, and toughness were conducted on WMA mixtures containing SNHL and RHL as control samples. A total of 18 mixtures and 108 specimens were prepared from three types of aggregate, three WMA additives, and two types of lime. The results indicated that the microstructures of the SNHL and RHL are irregular: the lime particles have fractured and rough surfaces with sharp angles; some small spherical particles in the nano size were found in SNHL but not in RHL. Also, WMA mixtures using SNHL have greater ITS and TSR than those using RHL; an increases of 8% in ITS and 10% in TSR by using SNHL over RHL were observed for the WMA mixtures investigated. Finally, the antistripping properties of WMA mixtures containing SNHL were affected predominately by aggregate type and the WMA additive.