RAP Materials Research Articles

Investigating the ANN model for cracking of HMA in terms of temperature, RAP and fibre content

ABSTRACT Using high contents of the RAP material in newly produced asphalt mixtures leads to a reduction in the crack resistance of the mixtures. This shortcoming can be compensated using some methods such as polymer modification, rejuvenation, fibre-reinforcement, etc. In this paper, the effect of Cyclogen as a rejuvenator and glass fibre was investigated on the cracking behaviour of recycled asphalt mixtures. For this aim, the fracture energy and critical value of J integral (Jc)of semi-circular bending (SCB) asphalt specimens in terms of RAP content, Fibre content and testing temperature were investigated in this study and the results were used to develop an experimental model to predict the crack resistance of asphalt mixtures in terms of temperature and fibre and RAP content using the artificial neural network (ANN) and the multiple regression methods. The results indicated that the fracture energy and Jc valueof asphalt mixtures declined by increasing the RAP contentat intermediate temperatures. However, the reduction in fracture energy and Jc valuecould be compensated using the fibres. Both investigated models were appropriate for predicting the cracking behaviour of fibre-reinforced recycled asphalt mixtures. Nevertheless, the level of correlation was much higher for the ANN approach than the multiple regression model.

Improving the tensile strength and durability of asphalt concrete as sustainable surface layer

The construction and maintenance processes of asphalt pavements require many raw materials, high financial cost, and high energy. The sustainability strategy in pavement construction is the use of recycled and waste materials due to significant savings in material, cost, and energy as well as improving the environment through solid waste disposal. The aim of this research is to study the effect of reusing the reclaimed asphalt pavement and crumb-rubber to improve the tensile strength and durability of asphalt mixture as a sustainable method which can be used in construction of surface layer. In this study one proportion of reclaimed asphalt pavement RAP (25%) was used by weight of mixture with virgin and modified asphalt binders. The modified asphalt binders were prepared in three proportions of crumb-rubber (5, 10, and 15%) % by weight of the virgin binder. Many experimental tests were conducted on the modified and recycled mixtures such as Marshall stability and flow, indirect tensile strength and moisture damage induce. The results indicated that the adding of RAP material resulted in slightly improve in the strength and durability, while the adding of crumb-rubber as a modifier for asphalt binder with RAP material has given impressive results in improving the stability, tensile strength, and resistance to moisture damage.

How Can Sustainable Materials in Road Construction Contribute to Vehicles’ Braking?

Vehicles’ braking is a key factor towards safer driving. In particular, tyre–pavement friction is connected with both industry and infrastructure requirements in terms of tyre characteristics and frictional properties of pavement surfaces respectively that both contribute to safe braking. For this reason, tyre–pavement friction is considered as one of the most pressing emergencies in roadway assets in order to reduce skidding related accidents. At the same time, sustainability aspects have been raised in modern infrastructure engineering. Hence, an issue is introduced on how sustainable materials used for pavement construction may contribute to tyre–pavement and consequently vehicles’ braking. For this reason, a laboratory process is developed to investigate the frictional properties of several utilized in pavement wearing courses including both traditional and sustainable materials (reacted activated rubber—RAR and reclaimed asphalt pavement—RAP). Environmental conditions (seasonal temperature changes, rainfall effect and contamination caused by dust formation) are simulated in the laboratory and vehicles’ braking is investigated using the British Pendulum Tester (BPT). Results provide a good explanation for the vehicles’ braking ability under the investigated conditions for both traditional and sustainable materials. Ultimately, it is proved that asphalt mixture types with RAR modifier or RAP material exhibit a satisfactory performance towards providing a safe road surface for the moving vehicles.

KARAKTERISTIK CAMPURAN AC-WC MENGGUNAKAN MATERIAL RECLAIMED ASPHALT PAVEMENT DENGAN TAMBAHAN ASPAL PEN. 60/70 YANG DISUBSTITUSI STYROFOAM

Reuse of reclaimed asphalt pavement material (RAP) is an alternative which applicated for potential enough on the roughness of the road. RAP material can be reused by adding the asphalt and the new aggregate according of the mixture composition so that it is expected will be obtained the quality as planned. One of the efforts made in improving the quality of asphalt mixture RAP material is using a modified asphalt with additional material, such as styrofoam. The use of styrofoam into the asphalt is expected to improve the technical properties of a mixture. The purpose of this research is to know the comparative characteristics of hot mix asphalt (asphalt concrete) type AC-WC that uses RAP material with additional asphalt pen. 60/70 and asphalt pen. 60/70 substitution in the styrofoam by 8%, 10% and 12% against the weight of asphalt based on levels of asphalt left on the material. The initial stages of this study is to conduct an examination of the physical properties of RAP material, then manufacturing a specimen with variations of the addition of asphalt and aggregate new levels based on the job mix diesign (JMD) Bina Marga Aceh (2013). Based on research results, parameter values marshall on all types of asphalt mixture with new aggregate as well as RAP materials and the use of 100% asphalt pen. 60/70 additional or different types of asphalt on OAC has fulfilled the technical specifications defined by the Bina Marga (2014). Best stability values obtained on asphalt mixture using RAP material with additional asphalt pen. 60/70 with 12% styrofoam substitution on OAC JMD Bina Marga Aceh, that amounted to 3,308.72 kg, the lowest value stability retrieved on asphalt mixture using a new aggregate based on the results of Department of Bina Marga Aceh on OAC i.e. of 983.94 kg.

Low- and intermediate-temperature behaviour of polymer-modified asphalt binders, mastics, fine aggregate matrices, and mixtures with Reclaimed Asphalt Pavement material

The long-term effects of SBS-modified binders and rejuvenators on the properties of high-RAP mixtures, especially the cracking resistance, have not been resolved. Therefore, this paper evaluates the cracking resistance of polymer-modified asphalt binders, mastics, fine aggregate matrices (FAMs) and mixtures containing RAP material and a rejuvenator. A series of laboratory tests is performed on different asphalt material scales, including a frequency sweep test; a BBR test for asphalt binders, mastics and FAM mixes; and a dynamic modulus test and the Illinois flexibility index test for asphalt mixtures. Short-term ageing and long-term ageing are also considered for different asphalt material scales. The results show that the asphalt binders and mixes containing RAP materials have similar Glover-Rowe (G-R) values and flexibility index (FI) values to those of the virgin binders and mixtures that are only subjected to short-term ageing. These results indicate that a rejuvenator can partially decrease the stiffness of the RAP material before long-term ageing; however, the cracking resistance of asphalt materials obviously decreases after long-term ageing. Asphalt materials containing RAP are more susceptible than virgin asphalt material to thermal cracking, and the rejuvenator does not improve the long-term cracking resistance of high-RAP material. The correlations between different laboratory ageing conditions for the asphalt binder, mastic, FAM and mixture are analysed. Binders subjected to PAV 20 h ageing present rheological properties equivalent to those of mixes subjected to the long-term oven ageing (LTOA) protocol for 5 d at 85°C. Binders subjected to PAV 40 h ageing present rheological properties equivalent to those of loose mixtures subjected to the LTOA protocol for 12 h at 135°C. The cracking resistance parameters of the binders, mastics and FAMs are also compared with the cracking resistance parameters of the mixture, and the results illustrate that the G-R parameters of asphalt binder, mastic and FAM are well correlated with the G-R parameter and FI parameter of the mixture. Moreover, the G-R parameter can predict the cracking performance of the asphalt mixture.

An investigation on the relationship between FTIR indices and surface free energy of RAP binders

The performance of RAP bituminous mixes depends on the properties of the binder in the RAP material. Surface free energy of a binder, which is a fundamental property of materials, can be used to explain moisture damage, rutting, fracture and healing potential of bituminous mixes. Similarly, different chemical properties of binders can be used to estimate their mechanical properties. The relationship between the surface free energy of the binders and their chemical composition (in terms of functional groups) has been investigated in this study. For this purpose, blends of a virgin binder (VG30 grade) and the RAP binder extracted from a RAP material were prepared. Surface free energy of the binder blends was measured using sessile drop technique. The chemical composition of the blends was obtained using Fourier transform infrared spectroscopy (FTIR) analysis. Different ageing and healing indices were calculated from FIR analysis. Different ageing indices are found to have good correlation with surface free energy and its components. No significant relationship could be observed between healing indices and surface free energy of the binder blends. The correlations presented in the study between different indices estimated from FTIR analysis and the surface free energy components obtained by sessile drop method will be useful in furthering the understanding of the characteristics of binders, especially RAP binders.

Fatigue Performance Analysis of Pavements with RAP Using Viscoelastic Continuum Damage Theory

This paper presents the results of a study to evaluate the fatigue performance of pavements that contain RAP materials. The study is based on two different accelerated loading tests conducted in the United States. Each of these two projects has corresponding pavements with and without RAP mixtures that were constructed over the same aggregate base and subgrade and subjected to the same traffic loading and environmental conditions. The primary reason for selecting these two projects is that they exhibited opposite trends in a comparison of the fatigue cracking performance of their pavements with and without RAP. The asphalt mixtures in the test pavements were characterized using the simplified viscoelastic continuum damage model. The fatigue cracking performance of the pavements was then modeled using the characterized material properties, in situ pavement structures and traffic loads, and climate conditions in FlexPAVE™, a three-dimensional layered viscoelastic finite element program with moving load analysis. The resultant fatigue cracking performance predictions matched the field observations well. Both the simulation results and the field observations also showed that the fatigue cracking performance of the asphalt mixtures that

Correlation between resilient modulus (MR) and constrained modulus (MC) values of granular materials

The resilient modulus (MR) value of unbound aggregates has been widely accepted as the principal mechanical property required in the mechanistic-empirical design/analysis of pavement structures. Resilient modulus measured through repeated triaxial load test is highly desirable to characterise granular materials. However, because of the complexities encountered with this test, other laboratory tests would be desirable if a reliable correlation could be established.Reclaimed asphalt pavement (RAP) and recycled concrete aggregate (RCA) have potential to be used as base and subbase material in substantial percentage to achieve economy and to minimise the undesirable environmental effects linked to the use of virgin aggregates. This paper presents a correlation developed between MR value and constrained modulus (MC) value on the basis of experimental results obtained for 32 reconstituted granular samples containing virgin aggregates, RAP and RCA materials. Proposed model considers the effect of stress state through the experimentally determined MC value while model parameters are correlated to the percentage of RAP materials in the reconstituted blends. Statistical analysis of the suggested correlation by t-test demonstrates encouraging results in terms of its strength and significance.

Modelling of the adhesion between reclaimed asphalt pavement aggregates and hydrated cement paste

Scanning electron microscope images on concrete incorporating 100% RAP material showed the presence of voids between cement paste and RAP aggregates indicating the poor adhesion between these two constituents. Therefore, the LCPC French model, was used with compressive strength data of different RAP concrete mixes to determine the adhesion and threshold parameters of the model. It was found that the adhesion parameter decreases as the RAP content increases while the threshold parameter remained constant for all RAP contents. The model with its described procedure could be used to proportion RAP concretes for any targeted compressive strength.

Use of reclaimed asphalt pavement (RAP) in warm mix asphalt (WMA) pavements: a review

The limit in the use of reclaimed asphalt pavement material (RAP) proportion is restricted due to stiffness and workability issues related to RAP. This problem is addressed with the help of warm mix asphalt (WMA) which increases the proportion of RAP used by producing mixes having same/better properties viz., better workability, reduced viscosity than hot mix asphalt (HMA) at lower temperatures. This paper reviews research conducted on the use of RAP material in WMA pavements. It presents and discusses work done with regard to different recycling methods and on conversion of RAP into HMA. It analyzes the benefits/need of using RAP in WMA in light of previous research findings and the influence on engineering properties of WMA due to RAP introduction. This paper also discusses field performance, environmental/economic impact and some limitations of these mixes.

Sensitivity Analysis of RAP Aggregate Properties on the Performance of Asphalt Emulsion Cold Recycled Mixes

Nowadays, asphalt emulsion cold recycled mixes has been used as binder course in the maintenance and rehabilitation projects of deteriorated asphalt pavements in Jiangsu province, China. The objective of this research was to conduct sensitivity analysis of RAP aggregate properties on the performance of cold recycling mixes based on five asphalt emulsion cold in-place recycling (CIR) projects in Jiangsu Province, China. Firstly, the aggregate properties of five RAP materials, such as sand equivalent, the percentage of flat and elongated particles, angularity and crushing value, were tested from the recovered RAP aggregates. Secondly, the properties of cold recycled mixes were evaluated based on Marshall tests and the indirect tensile strength tests with the same content of asphalt emulsion and cement under similar test conditions. Finally, the linear analysis and pseudo-inverse matrix method was performed to study the correlativity analysis between RAP aggregate properties and the performance of cold recycled mixes. The test results showed that different RAP material has a remarkable influence on the mixes performance. The results indicated that there was not good linear correlation relationship between RAP aggregates characteristics and the performance of recycled mixes, while the pseudo-inverse matrix method showed that the sensitive factors of four indexes of RAP aggregate properties on the performance of asphalt emulsion cold recycled mixes had the same primary and secondary impaction.

Evaluation of the DC(T) test in discerning the variations in cracking properties of asphalt mixtures

As the temperature of an asphalt pavement drops to below freezing point, the asphalt material starts to lose its ductility, and consequently, the asphalt mixture becomes more susceptible to cracking. The disk-shaped compact tension [DC(T)] fracture test has been used to quantify the fracture properties of asphalt concrete at subzero temperatures for more than a decade. The Asphalt Institute laboratory has successfully utilised the DC(T) test in several research studies. As a result of these studies, a valuable database is gathered which represents the sensitivity of the DC(T) test, and exhibits how the test is capable of capturing the effect of various factors on the performance of asphalt mixtures at low temperatures. This paper briefly presents the findings from some of these studies. The paper presents the response of the DC(T) test to the variations in several factors relative to asphalt pavements including the crude source of the asphalt binder, ageing of the asphalt mixture, deficiency in the in-place density, pavement temperature, using a warm-mix agent, using RAP and RAS materials, and chip sealing as a preservation method. The test showed to be well capable of capturing the variations in these factors; therefore, it can be utilised by the pavement managers to assess the changes in the specimens from the asphalt pavements over time to help determine if any maintenance or rehabilitation action is required. Furthermore, the test can be used to evaluate the laboratory-made mixtures and ascertain if they would perform satisfactorily in their designated environmental conditions.

Evaluating the performance of sustainable perpetual pavements using recycled asphalt pavement in China

Abstract The vast highways network in China is moving from the phase of construction to the phase of maintenance, and with the introduction of new technique of perpetual pavement in last decade, it is necessary to consider recycling as one of the promising solutions for rehabilitation of old asphalt concrete pavement and ultimately to convert them into perpetual pavements. The aim is to reuse the existing pavement materials for several reasons, mainly to preserve natural resources such as aggregates, and to satisfy economic requirements by reducing the cost of highway construction and rehabilitation. A detailed testing program has been carried out on recycled asphalt pavements materials (RAP) to evaluate their mechanical and structural characteristics to be used for the construction and rehabilitation of road pavements. Different types of RAP mixes have been stabilized by Portland cement to find the most suitable one from the point of view of design, construction, economy and environment. The analysis of life cycle costs has been carried out using system analysis and management of pavement program (SAMP5). The analysis of life cycle costs showed that the use of Portland cements with small percentages improves the structural characteristics of recycled asphalt materials to be used as stabilized base pavement layers for new or rehabilitated old road pavements and also for the construction and rehabilitation of perpetual pavements. A large amount of savings in construction and rehabilitation cost has been achieved by the use of stabilized RAP materials in addition to important contributions to the environment and preserving of natural resources.

Evaluation of Coarse Aggregate in Cold Recycling Mixes Using X-Ray CT Scanner and Image Analysis

Abstract The performance of cold recycling (CR) mixtures has been widely evaluated, but these studies rarely focused on the internal structure of CR mixtures. The objective of this research is to investigate the distribution, orientation, and shape properties of coarse aggregates in CR mixtures with emulsion by processing a series of sectional images from an X-ray CT scanner. The uniformity index (UI) was derived to describe the distribution of coarse aggregates. The aggregate orientation was obtained by calculating the average angle of inclination θ and the coherence of orientation Δ. The morphological indices, such as the flat and elongated ratio (FER), angularity index (AI), and surface texture index (STI) were used to address the shape properties of CR mixtures. According to the results, the distribution uniformity of CR aggregates becomes worse with coarser gradation. Compaction methods significantly influence the aggregate orientation in CR mixtures. The superpave gyratory compaction (SGC) method makes the best coherence of aggregate orientation, but the static load compacted specimen shows the opposite result. The CR mix tends to have worse uniformity of aggregate distribution, larger angle of aggregate inclination, and more random aggregate orientation compared with the HMA mix. It is estimated that more crushed faces of aggregates are produced in the process of pavement milling and the surface texture of RAP materials decreases with the long-term effects of traffic loading and environment. Adding new coarse aggregates to CR mixtures disturbs the aggregate distribution, but it can improve the average surface texture of aggregates in CR mixtures.

Investigation of the impacts of aging and RAP percentages on effectiveness of asphalt binder rejuvenators

In this study, the ability of five asphalt binder rejuvenators to restore low and high temperature true performance grades of aged binders was investigated. The rejuvenators considered in this study included a Naphthenic Oil, a Paraffinic Oil, an Aromatic Extracts, a Tall Oil, and an Oleic Acid. Several sets of asphalt mixtures containing different percentages (i.e. 25% and 45%) of RAP materials were prepared using PG 76-22 polymer-modified asphalt binder blended with rejuvenators at manufacturers’ recommended dosage. Control mixtures not including the rejuvenators were also prepared. All mixtures were loose mix aged for two hours and six hours to evaluate the impact of aging on the effectiveness of the different rejuvenators. After aging and compaction, the asphalt binder contained in each of these mixtures was extracted and recovered. The true low and high temperature grades of the extracted binders were determined using the Dynamic Shear Rheometer (DSR) and the Bending Beam Rheometer (BBR) tests. The recovered binders were considered RTFO aged due to the mixture aging used in this study. The DSR shear modulus master curves were also utilized to examine the impact of using different rejuvenators on rutting and fatigue cracking. Furthermore, a multi-factor Analysis of Variance (ANOVA) was conducted to evaluate the statistical significance of the differences between results. The results showed that all rejuvenated binders had lower performance grade than that of the control binder without rejuvenation. In addition, rejuvenator’s effectiveness was not affected by aging (from 2 to 6h) and increasing the amount of RAP materials (up to 45%). The rejuvenators were also found to improve the fatigue resistance without substantially influencing rutting performance.

Statistical analysis of the influence of RAP and mix composition on viscoelastic and fatigue properties of asphalt mixes

This study aims at understanding from a statistical point of view the influence of several mix constituents on mechanical properties of asphalt mixes produced with RAP material. The study is developed in two steps. The first section is focused on the qualitative evaluation of the effect of varying certain mix design parameters (aggregate and filler nature, binder content and type) on mechanical properties of mixes containing 20 % of RAP material. Results of the statistical analysis showed that changes in binder nature and binder content have a statistically significant influence on complex modulus of mixes. The second section aims at quantitatively estimating the influence of RAP material content and fresh added binder penetration grade on complex modulus and fatigue life of mixes. Proposed quadratic models satisfactorily fitted experimental data, although some coefficients were not estimated as statistically significant by the software. Observed fatigue and complex modulus performances of mixes containing up to 60 % RAP material are quite encouraging from technical, economical and environmental points of view.

Evaluation of Mix Design Methods for Reclaimed Asphalt Pavement Mixes with Foamed Bitumen

The main objective of this work is to evaluate the use of two mix design procedures for designing bituminous pavement mixes with foamed bitumen. Mix design was carried out following the South African and Caltrans guidelines. The RAP materials used for mix design were collected from the NH-5, Chennai-Tada section. Using foamed bitumen produced from Wirtgen WLB 10 foaming equipment, a mix with RAP material, virgin aggregate and active filler were produced in the pug mill mixer. Marshall compaction effort was used for fabricating the samples. Using the indirect tensile strength test on dry and wet specimens, the optimum binder content was determined. It was seen that the two mix design procedure adopted showed different mix constituents despite using the same RAP source.

Effects of mixing procedures and rap sizes on stiffness distribution of hot recycled asphalt mixtures

The quality of hot recycled asphalt mixture prepared by conventional laboratory procedures tends to be overestimated. This is because the long RAP preheating time, for instance 2h at 110°c might entirely soften RAP and coincidentally enhance the mixing between RAP and virgin materials thus the quality of hot recycled mixture. In order to manufacture the laboratory specimens that better present the quality as produced in the industrial mixing plant, this research employed the mixing method that simulates the mixing mechanism actually occurs in the asphalt mixing plant in which RAP at ambient temperature is mixed with superheated virgin aggregate at 215°c for 2, 4, 6 and 8min before this blend is mixed with virgin binder. The proportion of RAP in the recycled mixture is 40% and bitumen 160/220 penetration grade is used as virgin binder. Two sizes of RAP, 20 and 40mm are used. The stiffness of recycled asphalt specimens composed of different sizes of RAP and prepared by different mixing procedure including the conventional approach is recorded and analysed. The result indicates with short mixing time, RAP tends to work as inert black rock and the complete blending situation only approached if the mixing duration significantly increased. This finding is against the premise that RAP and virgin binder are completely blending in the recycled mixture design literature. However, longer RAP/virgin aggregate mixing times could result in recycled hot asphalt mixtures with higher stiffness modulus and better homogeneity. In addition, RAP size seriously affects the level of blending hence the stiffness variation of recycled mixtures.

RAP Percentage and Warm Mix Additive Influence on Regenerated Asphalt Mixture Performance

The warm mix regeneration technology has prominent economical efficiency that can not only reduce the secondary aging of new asphalt and old asphalt in RAP materials during the production process, but also improve the use proportion of RAP materials. As for the increase of RAP dosage and the warm mix additive added to influence the plant regenerated asphalt mixture performance, this paper adopts two kinds of warm mix additive for the test and analysis of the warm mix regenerated asphalt mixture performance with 20% and 60% RAP. The results indicate that magnify the proportion of RAP percentage makes contribution to further improve high-temperature performance of the regenerated mixture, but it has adverse effects on water resistant damage performance and low-temperature performance. At the same time, adopting the warm mix additive can significantly reduce the adverse effect, so warm mix regenerated technology has better feasibility.

Performance evaluation of Cold In-Place Recycling mixtures using emulsified asphalt based on dynamic modulus, flow number, flow time, and raveling loss

The need for a Cold In-place Recycling using emulsified asphalt (CIR-emulsion) mixture with specific engineering properties calls for the use of a mix design and, recently, a new mix design procedure was developed for CIR-emulsion. As a part of CIR-emulsion mix design process, dynamic modulus, flow number, flow time and raveling tests were conducted to evaluate short- and long-term performance of CIR-emulsion mixtures at various testing temperatures and loading conditions. Based on the test results, the optimum emulsified asphalt content for CIR was determined. Dynamic modulus, flow number and flow time of CIR-emulsion mixtures using CSS-1h (cationic slow setting emulsion) were higher than those of HFMS-2P (high-float medium-setting emulsion modified with a polymer). Flow number and flow time of CIR-emulsion mixtures using RAP materials with softer residual asphalt was higher than those of CIR-emulsion mixtures using RAP materials with harder residual asphalt. The dynamic modulus, flow number and flow time were affected by both emulsion type and residual asphalt stiffness of RAP materials. Raveling loss of CIR-emulsion mixtures with 1.5% emulsified asphalt was significantly less than those with 0.5% and 1.0%.