Hot Asphalt Mixtures Research Articles

Study on Low-Temperature and Fatigue Performance of High RAP Content Hot Recycled Asphalt Mixture Based on the Degree of Blending (DOB).

This paper selected three kinds of AC-20 hot-mix recycled asphalt mixtures with high RAP content (30%, 40%, and 50%). It obtains a mixture of different degrees of miscibility by changing RAP preheating temperatures and mixing temperatures. The calculation formula of the degree of blending (DOB) of RAP asphalt interface recycling is proposed. The DSR test quantitatively characterized the DOB mixture's low temperature, and fatigue properties were tested by beam bending test and four-point bending fatigue test. The prediction models of the recycled mixture's low temperature and fatigue properties were proposed. The RAP preheating temperature is the most critical factor that dominates both transfers of RAP asphalt to the surface of new aggregate and the effective blending of old and new asphalt. DOB has a significant great influence on low-temperature performance and fatigue performance. The DOB of recycled asphalt can be improved by adjusting and optimizing the process parameters of plant hot recycled mixture to effectively improve the recycled mixture's low-temperature crack resistance and fatigue lifetime. The optimal RAP dosage and mixing process of required performance can be obtained based on the prediction models to save experimental time and cost.

Investigating the effect of using unclassified fractionated reclaimed asphalt pavement materials on the properties of hot mix asphalt

Reclaimed Asphalt Pavement (RAP) incorporation is bounded by many specifications that limit its increased utilization. One of them, which many road agencies adopt, is the allowance of RAP from known single origin “classified RAP” only to be utilized in new mixtures. A lot of asphalt plants cannot afford space for multiple small RAP stockpiles in their yards and are forced to accumulate “unclassified” RAP materials collected from several projects into a single zone, hence, the “classified RAP” specification restricts the benefits of their utilization. In this context, this study aimed to investigate the pros and cons of using unclassified fractionated RAP with 15%, 25% and 45% percentages in Superpave asphalt mixtures. Complex modulus testing was performed on three replicates of each asphalt concrete (AC) mixture to evaluate the dynamic modulus |E*| and phase angle Φ properties over a range of temperatures and loading frequencies. As well, Flow number (FN) test was conducted to assess the rutting potential of the mixtures. The results showed that no significant difference existed between |E*| and Φ values of conventional hot asphalt mixture (HMA) and other RAP mixtures over the full analyzed range of frequency which indicates that the utilization of low, medium or high percentages of unclassified RAP materials may be indeed appropriate. Finally, the results of the flow number test and the simple performance indicator were compared and used to rank the rutting resistance of the assessed mixtures.

Mechanical performance of asphalt mixture composed of asphalt binder modified with sunflower oil

Warm Mix Asphalt (WMA) refers to a variety of asphalt mixtures produced at lower temperatures than those conventionally used to produce hot mixture asphalt. These reductions in the production temperatures provide social, economic, and environmental gains. This study aimed to investigate the mechanical properties of asphalt mixtures composed of asphalt binders modified with sunflower oil at the addition contents of 1%, 2%, and 3%. Indirect tensile strength, resilient modulus, water sensitivity, dynamic modulus, rutting resistance, and fatigue life of the asphalt mixtures were evaluated. Results showed that the mechanical performance of asphalt mixtures composed of oil-modified asphalt binder decreased compared to that of the mixture with neat asphalt binder, even though all of them are suitable for application in surface courses according to the current technical requirements for asphalt concretes. However, asphalt mixtures with sunflower oil-modified binders presented enhances in adhesion, which indicates less susceptibility to moisture than their equivalent non-modified.

Migration behavior of reclaimed asphalt pavement mastic during hot mixing

The production of hot central plant recycling asphalt mixture (RHMA) is more complex and uncertain than conventional hot mix asphalt. An adequate blend of virgin and aged asphalt is essential to recovering the performance of aged asphalt in reclaimed asphalt pavement (RAP). Therefore, the amount of aged asphalt migrating from the RAP into the recycled material system determines the level of blending and the durability of RHMA. To reveal the influencing factors of migration rate, we used fine aggregates in RAP as tracers to measure the RAP mastic concentration in the blended mastic. The considered factors included mixing time, asphalt-aggregate ratio, rejuvenator content, mixing sequence, RAP pseudo ratio, and RAP agglomeration rate. Then, the migration behavior of aged mastic was investigated from the viewpoints of the temperature field and microscopic features using the infrared thermogram and CT scan techniques, respectively. In addition, FTIR, GPC, and AFM were used to study the influence of migration of RAP mastic on the composition of blended asphalt. Finally, the effect of RAP mastic migration on moisture stability of RHMA was investigated using moisture induced sensitivity test, freeze-thaw indirect tensile test, and water immersion rutting test. The results show that the migration rate of RAP mastic during hot mix can be improved by reducing RAP content, raising the preheating temperature of RAP, extending the mixing time, increasing the asphalt content, and using dry mixing method, whereas the amount of regenerator has no significant effect. The temperature is the essential factor affecting the migration level. The RAP mastic migration is highly synchronized with RAP aggregate movement under forced mixing. Furthermore, increasing the migration level of RAP mastic can significantly increase the proportion of aged asphalt in blended asphalt. At last, the higher RAP mastic migration can prevent void development in RHMA under freezing-thawing and hydrothermal washing, thereby improving the moisture stability of RHMA and alleviate peeling aggregates and mastic. This study contributes to current knowledge by explaining the essence of RAP mastic migration during hot mixing, the results should be interested by road contractors, producer of RHMA, and academic society.

Viability of recycled asphalt mixtures with soybean oil sludge fatty acid

• The use of 3 and 5 % SFFA as asphalt binder modifier reduced the maximum PG temperature of the virgin one. • 5% SFFA indicated 40% of RAP as the viable content to the mixture by using the blending chart method. • Recycled asphalt mixtures showed a better mechanical performance and strength gain with SFFA. • The addition of RAP resulted in a higher circularity index for the recycled mixtures. • Production and recovery costs of recycled asphalt mixtures are lower than traditional mixtures. The growing demand for advantages and energy and the increase in the economy justify the reduction of the circular environmental impact, which seeks to reduce the circular environmental impact. The use of recycled asphalt pavement (Reclaimed Asphalt Pavement – RAP) in the production of hot asphalt mixes (Hot Asphalt Mixtures – HMA) has been used in paving due to virgin materials. However, the use of high percentages to its RAP damage is susceptible to failure at low temperatures due to fatigue. The addition of rejuvenating agents can restore the properties of the recovered binder. In this sense, research that addresses solutions with industrial parts and by-products is likely to bring solutions that foster a tendency to work from a circular economy perspective, based on the economy and the circulation of waste and by-products between different sectors including engineering of paving. This work evaluated soybean oil sludge fatty acid (SSFA) at contents of 3 and 5% as a rejuvenator for recycled asphalt agents with 40% RAP, analyzing the possibility of technical, economic, and environmental feasibility. The latter, considering the potential for circularity of materials. Asphalts were mixed with mixtures for mechanical analysis through tests of resistance to attraction, susceptibility to moisture, modulus of resilient, modulus, permanent formation, and fatigue. The circularity assessment was performed through the circularity index (MCI), verifying the recycling potential of the RAP, and the net value presented (NPV) was calculated to analyze the costs of recycled asphalt mixtures. In addition to making RAP, it improved the resistance to permanent deformation, and the SSFA showed a rejuvenating effect on recycled asphalt mixtures, improving fatigue performance at the tested contents. The recycled mixtures showed the highest circularity indexes. The incorporation of accruals increased as accrued SSFA costs did not increase. Therefore, recycled asphalt mixtures proved to be more technically, environmentally, and more viable than the conventional asphalt mixture, especially the mixture with 3% SSFA.

Study of the mechanical behavior of asphalt mixtures in terms of creep and Superpave compaction parameters

This was a study on the mechanical behavior of hot asphalt mixtures with regard to permanent deformation, considering static creep tests and the parameters derived from the Superpave compaction curve. For the asphalt mixture production, mineral aggregates and two types of asphalt binder (CAP 50/70 and AMP 60/85) were used. These mixtures were designed using the Superpave methodology and compacted in the content and number of gyrations according to the design. For the design condition, asphalt mixtures using the conventional CAP 50/70 asphalt binder showed better workability and lower deformation than asphalt mixtures with the AMP 60/85 polymer binder. Furthermore, the influence of asphalt binder content on the behavior of asphalt mixtures in relation to permanent deformation and compaction indices was studied, considering the maximum number of gyrations in the design. Regarding this investigation, asphalt mixtures with higher asphalt binder content tend to show higher permanent deformation and better workability. Complementarily, the compaction curve indices (Construction Densification Index, CDI; modified Traffic Densification Index, TDIm and Locking Point, LP) were correlated with parameters obtained from static creep tests (total deformation after the recovery period, Dt; creep modulus, CM and curve inclination, Icurve) through curves obtained by the correlation between these indices. Based on this analysis, a good correlation was found between the results of static creep tests and compaction indices, showing the potential of these indices for predicting the mechanical behavior of the analyzed mixtures in relation to the development of permanent deformations.

Evaluating the properties of hot asphalt mixtures modified by Metakaolin

The mineral filler has an important role in filling the voids between aggregates inside the asphalt matrix. This study investigates the effect of using Metakaolin (MK) as a modifier on the mechanical properties of hot mix asphalt. MK was added to the mixtures as a part of the filler used. As known, the hot mix asphalt (HMA) consists of coarse aggregate, fine aggregate, filler material, and asphalt binder with or without existing modifiers. The components of the HMA were subjected to validation tests to check the validity of the materials for producing HMA The asphalt binder used was bitumen 60/70. Tests performed on bitumen were penetration test, softening point test, flash and firing point test. The optimum asphalt content based on the designed control mix was 5.2%. the control mix has no content of MK. MK was added as a partial replacement of filler used (limestone powder). Mk was added to the HMA by replacing 20%, 40%, 60%, 80%, and 100% of the filler. A comparative study was performed to evaluate the effects of HMA modification by MK. Marshall quotient (MQ) increases by 10.37% for the mix modified by 40% MK. MK has significant effects on the indirect tensile strength (ITS).

Field performance of bitumen emulsion Cold Central Plant Recycling (CCPR) mixture with same day and delayed overlay compared with traditional rehabilitation procedures

Cold Recycled Mixtures (CRM) offer many benefits, including cost-effectiveness and sustainability. Large existing Reclaimed Asphalt Pavement (RAP) stockpiles that represent an environmental and storage challenge can be used for bitumen emulsion Cold Central Plant Recycling (CCPR). A pavement rehabilitation demonstration project using Cold Recycled Mixture with Bitumen Emulsion (CRM-E) as binder course with 100% RAP was carried out on August 25, 2020. The project was divided into three sections to evaluate the mill and pave strategy using CRM-E as an alternative to traditional Hot Mixture Asphalt (HMA). The wearing course was the same asphalt concrete for the three sections. The difference between Section 1 and 2 that used CRM-E was to either pave the asphalt concrete overlay on the same day or to delay its application for 3 days to give additional time for the CRM-E to cure. Section 3 had no CCPR and consisted of two HMA layers. The field performance of the rehabilitated sections was monitored in 4 phases after 14 days, 3 months, 6 months and 12 months. The performance of the sections was assessed based on Falling Weight Deflectometer (FWD), field rutting measurements and cracking distress surveys. Cores were also taken over time to compare the CRM-E and HMA binder course properties in terms of resilient modulus, dynamic creep, indirect tensile strength and tensile strength ratio. The research showed that CRM-E and HMA performance was similar in terms of FWD deflections, field rutting, in situ cracking, and moisture resistance of the field cores. CRM-E showed superior performance in terms of resilient modulus and dynamic creep compared with asphalt concrete binder course based on testing of field cores taken after 6 and 12 months. The research showed that same day CRM-E HMA overlay is a viable construction option.

Multi-scale finite element simulation of asphalt mixture anti-cracking performance

This study investigates the anti-cracking performance and cracking mechanisms of asphalt mixtures. The results of experimental tests were compared with simulated tests of asphalt mixtures based on the multi-scale finite element method (FEM). The FEM considered the mesostructure of the asphalt mixtures, the internal viscoelasticity of asphalt mortar, and the asphalt mastic-aggregate interface. Coarse aggregates were generated based on the polygonal random aggregate generation and placement method. Numerical cracking models of the asphalt mixtures were established by the multi-scale FEM and fracture tests were simulated according to the experimental test conditions. The reliability of the simulations was verified by comparison with the experimental test results. The influences on cracking behavior were investigated, with an energy-saving and economical alternative mixture—cold recycled mixture (CRM)—used for comparison. The simulations were highly accurate and could effectively simulate the asphalt mixtures’ cracking processes and mechanisms. The cracking behavior was directly related to notch length, test temperature, void content, and mixture type. A significant difference in the macroscopic anti-cracking performance of hot mixture asphalt and CRM was found. According to the simulations of crack development, there is a 'critical point' of crack propagation from the interface to the interior of the mortar. The mesoscale influences on the cracking behavior of asphalt mixtures are discussed and ranked in terms of importance.

Using nano silica to enhance the performance of recycled asphalt mixtures

Understanding how the physical properties of Nano-silica material affect the ultimate implementation of the asphalt binder is an essential study area that has been disregarded previously. The current investigation aims to determine whether or not it was possible to change the asphalt binder with Nano-silica (NS) depending on the qualities of the asphalt binder under consideration. Using nano-silica (2, 4, and 6 percentage by weight of asphalt), a penetration grade asphalt cement with 60/70 was developed. Nano silica and asphalt cement were first tested for their qualities. The NS modified asphalt binder was ready for use in the experiment after being heated to 160°C and mixed with a shear mixer at 2000 rpm for 60 minutes. The softening point temperature and penetration index of the NS modified asphalt binder, as well as the Brookfield rotational viscosity and ductility data, were also evaluated. Based on the rheological performance of the NS modified asphalt binder, increasing Nano silica content increases stiffness while decreasing temperature sensitivity. The addition of 4% Nano silica (NS) asphalt binder improved its basic properties and allowed it to be used in hot weather. By adding 4% NS to the hot recycle asphalt mixture, the Marshall stability is increased by 32.5%, the flow is reduced by 21.4%, the unit weight is maintained, and the amount of air voids in the mix, as well as other mix qualities, are kept at acceptable ranges. It'll also boost the ITS by 37.8%. In general, adding NS to asphalt mixtures improves their qualities.

Properties of recycled hot asphalt mixture added with mastic asphalt component

The use of natural aggregates can be reduced by utilizing Reclaimed Asphalt Pavement (RAP). In field, there have been many simple recycling applications of RAP with addition of new asphalt and stone ash as road pavement on community housing areas. The objective of this experiment is to provide engineering properties of the mixture. Asphalt pen 60/70 was softened or rejuvenated with 11% SAE 10 engine oil, to obtain asphalt pen 180/200. The mixtures were produced by adding the RAP with 10% and 20% rock ash and soften asphalt, in hot mix process. The added asphalt content was varied by 2%, 2.5%, 3%, 3.5% and 4% by weight of the RAP, and compacted at 2x50 Marshall blows. The mixture of RAP with 10% stone ash at 3% added asphalt gave better performances compared to the mixture with 20% stone ash, in which the stability value was 3380.5 kg, flow 3.08 mm, Marshall Quotient of 1097.65 kg/mm, VIM 3.077%, VMA 18.95%, VFB 83.84%, Cantabro 9.02%, ITSM 5422 MPa, creep slope 0.267, and fatigue with load of 700; 900; 1100 KPa failed at 6101; 1471; 831 load repetitions. The mixture well meet the specification for typical mixtures for low to medium trafficked roads.

Method for the Evaluation of the Homogeneity of Asphalt Mixtures by 2-Dimensional Image Analysis.

In order to evaluate the homogeneity of asphalt mixture quantitatively, the distribution characteristic of internal phases of asphalt mixture were identified based on digital image processing technique and stereology theory, and the homogeneity coefficient (i.e., K) was proposed. At the same time, the trend of variation and reliability of homogeneity of asphalt mixture were analyzed by changing the nominal maximum aggregate size, aggregate gradation and asphalt content. The results suggest that the homogeneity of asphalt mixture could be comprehensively described using DIP technique combined with stereology theory. The smaller the K, the better the distribution homogeneity of the asphalt mixture. An improvement in the homogeneity of an asphalt mixture is achieved with the decrease of the nominal maximum aggregate size and a finer aggregate gradation. The asphalt content corresponding to the optimal homogeneity of the internal structure of asphalt mixture specimen is the optimum asphalt content. According to the experimental study, the suggested values of the homogeneity coefficient were given, which provides theoretical support to control the construction quality of the hot mixture asphalt.

Assessment of Virgin Binder-Blended Rejuvenators and Antistripping Agents for Hot Recycled Asphalt Mixture

Assessment of Virgin Binder-Blended Rejuvenators and Antistripping Agents for Hot Recycled Asphalt Mixture

Analysing the potential use of a low-grade magnesium carbonate by-product as a filler in hot asphalt mixtures

ABSTRACT Climate change and the depletion of natural resources are causing society to adopt more environmentally sustainable approaches. In areas such as construction and civil engineering, waste and by-product valorisation could help in the fight against climate change, reducing the consumption of raw materials. Thus, the use of residues or by-products in asphalt mixture manufacturing as road pavement layers has great potential due to their characteristics. This study aimed to characterise a flotation sterile (low-grade magnesium carbonate; LG-MC) generated in the beneficiation process of natural magnesite and to analyse its potential as a filler in asphalt mixture manufacturing. The physical, chemical, and microscopic properties of LG-MC were characterised and its potential use as a filler for asphalt mixtures was evaluated using the UCL (Universal de Caracterización de Ligantes) method. The optimum filler/bitumen ratio for LG-MC was 1.49, higher than the 1.33 of calcium carbonate. Results showed a protective effect of LG-MC against ageing both in the short and long- term, reducing losses from abrasion.

Influence of mobilized RAP content on the effective binder quality and performance of 100% hot in-place recycled asphalt mixtures

Hot in-place recycling (HIR) is a promising technique to consume 100% recycled asphalt pavement (RAP) for pavement surface rehabilitation. When RAP aggregates are incorporated in asphalt mixtures, a proportion of the RAP binder can be mobilized by the virgin binder or additive and achieve a homogenous binder blend, named “the effective binder blend.” There exist two major concerns of using 100% RAP in HIR mixes: 1. How much of the RAP binder can be mobilized to coat aggregates? 2. What are the contributions of the mobilized RAP binder to the performance of HIR mixes? This study firstly developed an approach to quantify the mobilized RAP content in HIR mixes. Afterward, the effective binder blends were prepared in the laboratory, based on the mobilized RAP and virgin asphalt percentage. Finally, the dynamic shear rheometer test and sessile drop method were adopted to characterize the effective binder qualities, while AMPT and Ideal-CT tests were utilized for mixture performance evaluation. Results showed that the mobilized RAP binder altered the binder qualities of the effective binder blends and also the effective asphalt content in HIR mixes. The binder qualities, including rheological properties and surface free energy, contributed to the different stiffness and cohesion of the effective binder blends in HIR mixes. However, the effective asphalt content proved to dominate the cracking resistance of HIR mixes.

Fatigue analysis of hot recycled asphalt mixtures with RAP incorporation

Asphalt coatings are the most commonly used in paving services in Brazil, explained by the availability of material and the applicability of the technique. Throughout their service life, pavements are subject to traffic stresses that cause damage to the coating, most commonly fatigue cracking and permanent deformation. Thus, the need for new pavements and the need to perform rehabilitation services result in the generation of waste. Because of this, the allocation of this waste in the pavement was now performed more frequently, like this, and this research aimed to evaluate the fatigue life of hot recycled asphalt mixtures, with the incorporation of RAP (reclaimed asphalt pavement) at 25%, 45%, and 100% as a substitute for part of the materials. The dosing process, which occurred according to the Superpave specification, focused on the analysis of the mechanical behavior of the mixtures in aspects of strength, deformation, adhesion, and cohesion. The results indicated a good performance of the mixtures with proportionality in the values obtained with the incorporation of RAP. Because fatigue is associated with stiffness, mixtures with higher incorporations tended to have a shorter fatigue life. Above all, the results indicated a good mechanical performance, proving the feasibility of the technique in paving works.

Experimental study of the tensile strength of hot asphalt mixtures measured with indirect tensile and semi-circular bending tests

This paper examines the tensile strength performance of hot mix asphalt without and with reclaimed asphalt pavement (RAP), different gradations, asphalt content, and test temperatures applying the Indirect Tensile Test (IDT) and the Semi-Circular Bending Test (SCB). Laboratory test results indicated the dependence of the tensile strength on the study variables, with evident trends for the type of test and the test temperature. A reasonable correlation between IDT and SCB tensile strength was verified. There is also a good correlation between IDT and SCB when data reported in previous research is incorporated.

The Utilisation of Waste Bamboo Shells as A Filler in The ACWC Mixture on Marshall Characteristics

Roads as transportation system infrastructure that are routinely used to support human activities every day must have adequate quality. The increase in the number of public and private vehicles results in the use of roads that continue to increase to the potential road damage if they do not have adequate quality. One of the factors of the quality of road infrastructure is the road pavement. This study is to examine the effects of bamboo shell powder as Filler on the ac-WC hot asphalt mixture on the characteristic value of Marshall. In this study we used Marshall Testing. This research was carried out in laboratories, starting from literature studies, material collection, material testing, determination of mixed plan asphalt levels, preparation and manufacture of test objects and Marshall testing. This study found bamboo shells to be one of the mixed materials in the hot asphalt mixture so that it becomes an asset for residents in the future.

Functional and field performance of epoxy asphalt technology – state-of-the-art

There is an increasing demand for high strength and more durable materials in the asphalt technology market. In response to the demand, epoxy asphalt mixture (EAM) is one relatively new technology for use as a paving material in flexible pavements. There are various research works carried out on the laboratory and field performance of EAM. However, comprehensive research covering functional and field (F&F) performance of EAM is lacking. The main purpose of this review is to bridge this gap via the analysis of the functional properties of EAM. Consequently, the field performance of EAM in different case studies is reviewed and the serviceability of EAM in various transportation infrastructure is investigated. This paper also reviews the life cycle cost and maintenance of EAM. The major findings indicate that EAM shows superior F&F performance compared to the traditional hot and warm asphalt mixture. Additionally, the use of EAM is beneficial in the structure of pavements in tunnels and on bridge decks. In conclusion, the higher F&F performance of EAM supports the development of better performing pavements for various applications.

Empirical Property of Asphaltic Binder PA 50/70 Modified with Mixture of Industrial Waste

The incorporation, by wet, of 10% w/w from the mixture of two solid wastes, rubber from waste tires and oily petroleum sludge, in proportions 15/85% w/w (M1) and 85/15% w/w (M2) on asphalt binder CAP 50/70 (PA-M1-10 and PA-M2-10) was evaluated against the unmodified binder, regarding the empirical properties: apparent viscosity, flux activation energy, penetration, softening point, specific mass, adhesion to stone aggregates, machining, and compaction temperature, and indirect tensile strength test (ITS) of its hot asphalt mixture (HMA). Test results showed that the modifiers do not significantly change the values of empirical properties under analysis, except the flow activation energy. Modified samples had a lower value when compared to the binder PA 50/70, and the penetration of modified binder PA-M2-10, which for having a higher concentration of rubber tire made it harder, changed to binder class 40-50, according to standard ASTM D946-09A. The ITS behavior of HMA's processed with modified binders showed compatible values with the unmodified binder, meeting the standard ASTM D6931-12.