Fine Aggregate Matrix Research Articles

Environmental effects on the rheological properties of fine warm RAP-foamed bitumen mixtures using SATS conditioning protocol

ABSTRACT This paper uses the Saturation Ageing Tensile Stiffness (SATS) conditioning to evaluate the combined effects of moisture and oxidative ageing on the rheological characteristics of the Fine Aggregate Matrix (FAM) portion of various Foamed Bitumen Mixtures (FBMs) in combination with Reclaimed Asphalt Pavement (RAP) material produced at 90, 120 and 160°C (i.e. half-warm, warm and hot processes, respectively). A reference fine Hot Mix Asphalt (HMA) with RAP – no foamed bitumen – was also manufactured. Their rheological properties were determined through Dynamic Mechanical Analysis (DMA) tests on specimens tested in their unconditioned and after SATS conditioning states. Rheology of the recovered binders of all FAM mixes before and after SATS conditioning was also studied, and rheological parameters were used to link their long-term performance in terms of cracking susceptibility. The results showed an overall increase in the stiffness of the fine mixtures after the conditioning process, mainly due to oxidation of the bitumen. Although the half-warm and warm fine RAP-FBMs exhibited the highest increase in their complex shear modulus after SATS conditioning, rheological analysis of their corresponding binders indicated that their long-term performance in terms of cracking susceptibility might be superior to those of the hot RAP-FBM, and the HMA-RAP fine mixtures.

Variability of the mechanical properties of Reclaimed Asphalt Pavement (RAP) obtained from different sources

Reclaimed Asphalt Pavement (RAP) is commonly used to manufacture new hot mix asphalt (HMA). The objective of this study is to determine the variability of RAP properties obtained from different projects or sources. To meet this objective, the original particle size distribution of the RAPs, as well as different basic and rheological properties of the recovered binders were quantified. Additionally, in order to assess the differences among the RAP materials and not only of their components (i.e., recovered asphalt and gradation), the rheological properties, mechanical performance and moisture damage susceptibility of fine aggregate matrix (FAM) manufactured using the fine fraction of the different RAP sources (FAM-RAP mixtures) were also evaluated. The results show that there is significant variability in the mechanical response and performance of the evaluated RAPs, suggesting the necessity for considering this aspect when fabricating HMA with RAP obtained from different sources.

Fatigue and self-healing characterization of asphalt composites containing rock asphalts

Fatigue cracking is one of the major distresses that causes early pavement failures. One of the solutions to delay the occurrence of pavement failure by fatigue cracking is to use materials that not only can resist such cracking but also can heal them over time. This is therefore necessary to evaluate the impact of such materials on fatigue cracking resistance and self-healing properties of asphalt mixtures. The increasing use of alternative materials such as rock asphalts has made this need even more pronounced. Fittingly, this paper presents the findings from a study that utilizes a fracture test and a combined fatigue-healing test to evaluate the influence of different sources of rock asphalts-Buton, Qingchuan (QC) and Uintaite Modifier (UM) on the fatigue and self-healing properties of fine aggregate matrix (FAM) mixture. The fracture test results indicate that rock asphalt can effectively improve the cracking resistance of asphalt mortars or FAM. The viscoelastic continuum damage (VECD) analyses of the combined fatigue-healing test results show that rock asphalt can significantly enhance the fatigue cracking resistance of FAM mixture. The results also show that, at same volume concentration of binder, UM rock asphalt and QC rock asphalt enhance fatigue cracking resistance of FAM very similarly but much better than does the Buton rock asphalt. An increase in the concentration of Buton rock asphalt made the FAM mixture even more resistant to fatigue cracking. Similarly, test results show that, at same volume concentration of binder, QC rock asphalt exhibited the best self-healing properties followed by UM and Buton rock asphalt, respectively. This ranking was more pronounced with longer rest period durations. Test results also indicate that, at same rest period, 8% Buton rock asphalt healed better than 20% Buton rock asphalt. In addition, this paper also uses these materials to demonstrate an experimental and analytical approach to quantity both fatigue cracking resistance and self-healing properties using a viscoelastic continuum damage model and a single unified testing protocol with asphalt mortars or FAM. This approach can also be easily applied to evaluate other similar materials such as reclaimed asphalt pavements (RAP).

Simulação computacional do ensaio de módulo complexo em misturas asfálticas

Considerando-se as heterogeneidades inerentes e utilizando-se o Método dos Elementos Finitos juntamente com a Teoria da Viscoelasticidade Linear é simulado computacionalmente, para materiais asfálticos, o ensaio de módulo complexo (que se traduz em um valor absoluto chamado de módulo dinâmico e em um ângulo de fase). O ensaio consiste na aplicação de solicitação (tensão ou deformação) senoidal e na leitura da resposta mecânica (deformação ou tensão). Os materiais estudados são uma Matriz de Agregados Finos (MAF) e uma Mistura Asfáltica Completa (MAC) composta por agregados graúdos, ar e MAF. Tomam-se como dados de entrada os parâmetros de dosagem e as propriedades dos materiais constituintes da mistura. Os resultados das simulações são comparados aos obtidos em ensaios realizados em laboratório. Avalia-se a influência do módulo de elasticidade dos agregados e do volume de vazios sobre o módulo dinâmico da MAC analisada. Os resultados mostraram que para baixas frequências da solicitação, a variação na rigidez do agregado interfere pouco na variação do módulo dinâmico da mistura, tornando-se mais significativa para as frequências mais altas. Ademais, foi possível obter o módulo dinâmico da MAC a partir da simulação, estimando-se o módulo de elasticidade dos agregados. O módulo dinâmico da mistura diminui com o aumento do volume de vazios e apresenta um comportamento aproximadamente linear, principalmente nas frequências mais baixas.

Evaluation of effect of compaction method on the macrostructure of asphalt mixtures through digital image processing under Brazilian conditions

For achieving good performance in the field, the asphalt road surfaces compaction must be adequate. The compaction properties and the mechanical performance prediction in the field are previously established from laboratory specimens. Laboratory compaction is carried out through impact, kneading or vibration and these methods differ from compaction in the field. From this, is necessary to establish a comparison between compaction in the laboratory and in the field in terms of the macrostructure (aggregate distribution in the fine aggregate matrix) and air voids distribution. The aim of this study was to determine the laboratory compaction technique which is most representative of compaction in the field, by testing different methods and compactors. Thus, asphalt mixtures were compacted in a gyratory compactor with different gyration angles (0.75°; 1.0°; 1.25; 1.5° and 1.75°). Asphalt mixtures produced with the aid of a Marshall compactor and a French roller compactor were also analyzed. In addition, specimens compacted in the field, were analyzed and evaluated. Analysis of the compaction methods was studied whether digital image analysis using a software application (IPAS-2). The results showed that the Marshall and the gyratory compactors (gyration angles of 0.75°, 1.25°, 1.0°) were the most representative of the compaction in the field, regarding the macrostructural parameters. However, the Marshall compactor presented the greatest variability in the results. As a result, the gyratory compactor, (gyration angle of 1.25°) was best approximates compaction in the field.

Prediction of dynamic shear modulus of fine aggregate matrix using discrete element method and modified Hirsch model

Dynamic shear modulus of fine aggregate matrix (FAM) has a significant impact on the mechanical response of an asphalt mixture, and micromechanical computational models have proved to be suitable for predicting the modulus of the FAM and the asphalt mixture. However, the model programming is complicated and time-consuming, and it is difficult to be applied directly in pavement design. This study aims at developing a micromechanics-based model which can be used to predict the dynamic shear modulus of the FAM at a variety of frequencies and temperatures. The laboratory Dynamic Shear Rheometer (DSR) tests of asphalt mastics and the oscillatory torsional tests of the FAM are conducted at 7 angular frequencies and 5 temperatures to construct master curves. A three-dimensional discrete element model (DEM) of the FAM is developed to validate the dynamic shear modulus tests. The effects of volumetric and mechanical properties of individual constituents on the simulation results at different frequencies and temperatures are also investigated. After that, the modified Hirsch model is implemented to predict the composite modulus of the FAM. The results show that the DEM is a promising tool to analyze the dynamic shear modulus of the FAM. The modified Hirsch model predicts the dynamic shear modulus of the FAM successfully over a wide range of frequencies and temperatures.

Rheological Characterization of Asphalt Fine Aggregate Matrix Using Dynamic Shear Rheometer.

Asphalt fine aggregate matrix (FAM) is a predominant component directly related to field performances of hot asphalt mix (HMA), it is necessary to investigate material properties of FAM. Prior to preparing FAM specimens, the asphalt content was calculated by keeping the filler–bitumen (FB) ratio the same as in the corresponding HMA. A non-destructive fabrication method instead of coring and cutting methods was developed to compact FAM cylinders, and the joint base was designed to be concentric with the loading axis of testing system. Rheological responses of FAM were studied using the dynamic shear rheometer (DSR). Two repeated tests prove that the FAM compactor and the jointed base meet the requirement of data validation. Results show that rheological performances of FAM are significantly affected by asphalt content, gradation, air void content, and testing frequency. Air void is concluded to be the decisive factor which influences the stability of FAM, and the fiber is demonstrated to play a role on enhancing the flow resistance of FAM-F even though with the richest asphalt content.

Evaluation of Effects of Filler By-Products on Fine Aggregate Matrix Viscoelasticity and Fatigue-Fracture Characteristics

AbstractThis study evaluated ornamental stone fines (OSF) and steel slag fines (SSF) as potential fillers for asphalt mixtures. The fine aggregate matrix (FAM) phase was chosen for performance test...

Using Predictive Models to Estimate the Properties of Binders in Reclaimed Asphalt Pavement Mixes using Fine Aggregate Matrix Mix Testing

A number of predictive models, such as the Hirsch and Al-Khateeb models, have been proposed to determine the properties of asphalt binders from asphalt concrete mix testing results. Fine aggregate matrix (FAM) mix testing can also provide useful insights into the likely performance of asphalt concrete mixes. Consequently, FAM mix testing can be an appropriate means of assessing the predictive power of these models. In this study, FAM mixes prepared with two virgin binders, PG58-28 and PG64-16, and then with different percentages of reclaimed asphalt pavement (RAP) were tested to determine their stiffness and phase angle using temperature-frequency sweeps in a dynamic shear rheometer. The data from the control mixes with no RAP were used along with the rheological properties of the virgin binders to fit the Hirsch and Al-Khateeb models. The fitted models were then used to estimate the properties of the binders in the 15% and 25% RAP FAM mixes. A comparison of the estimated binder properties with the measured binder properties clearly indicated that the fitting parameters are binder dependent. Moreover, the estimated binder moduli deviate from the measured moduli, particularly at high temperatures. The estimated complex shear moduli from the model were found to be consistently higher than the measured shear moduli values of the chemically extracted binders. It was thus concluded that the predictive models studied, in their current form, fail to provide a reliable estimate of the binder properties in mixes containing RAP.

Evaluating the Effects of High RAP Content and Rejuvenating Agents on Fatigue Performance of Fine Aggregate Matrix through DMA Flexural Bending Test.

High percentage reclaimed asphalt pavement (RAP) is prevailing in pavement engineering for its advantages in sustainability and environmental friendliness, however, its fatigue resistance remains a major concern. Fine aggregate matrix (FAM) is a crucial part in the fatigue resistance of asphalt mixtures with high RAP content. Hence, the linear amplitude sweep (LAS) test of FAM has been developed to study the fatigue resistance of asphalt mixtures. However, the torsional loading mode of the LAS test with a dynamic shear rheometer (DSR) is a limitation to simulate traffic load. In this paper, an alternative LAS test for FAM with high RAP content was proposed. Beam FAM specimens were tested using a dual-cantilever flexural loading fixture in a dynamic mechanical analyzer (DMA). To investigate the influence of RAP content and the rejuvenating agent (RA), four kinds of FAM mixes were tested with this method to study their fatigue resistance. The test results suggested that the repeatability of this alternative approach was reliable. A fatigue failure criterion based on maximum was defined. Then, fatigue life prediction models based on viscoelastic continuum damage (VECD) analysis were established according to the LAS test results and validated by a strain-controlled time sweep (TS) test. It turned out that as RAP content increased, the modulus of FAM would be significantly raised, accompanied with a drop in the phase angle. The fatigue life of FAM would be greatly shortened when the RAP binder replacement rate reached 50%. Adding RA could considerably improve the dynamic properties of FAM mixes with high RAP content, resulting in a decrease in modulus, increase in phase angle and elongating fatigue life, but could not recover to the level of virgin binder.

The effect of filler type and content on rutting resistance of asphaltic materials

This research evaluates the effect of filler type and content on rutting resistance of asphaltic materials by using laboratory experiments. To examine the effect of filler type, two traditional fillers (Silica sandstone powder and Portland cement) and a new recycled lime powder (Eggshell) were considered. To investigate the effect of filler content, three different filler contents were used. Marshall Stability test was performed on full mixes in order to determine the optimum binder content of the mixtures. Then, the static creep test was performed on Fine Aggregate Matrix (FAM) samples. The permanent strain after 10 minutes of recovery (PS-660) was considered as the indicator of potential to rutting. It was shown that PS-660 has a good correlation with total strain after 60 seconds of loading (TS-60), permanent strain after 60 seconds of recovery (PS-120), the slope of the primary (θ1) and secondary (θ2) Phases of the creep curve, binder percent of FAM samples (B%), as well as with Marshall Quotient (MQ) value of full mixes. The test results clearly demonstrated that both filler type and content can significantly influence rutting resistance of asphaltic materials.

Development of an alternative test approach for binder blending charts with fine aggregate matrix mix testing

Binder blending charts are used to determine the selection of virgin binder grade of asphalt mixes containing more than 25% reclaimed asphalt pavement (RAP) as part of the Superpave volumetric mix design procedures. However, the extraction and recovery of RAP binder used as part of the binder blending charts process is expensive, hazardous, and poses potential threats to human health and the environment due to the solvents used. An alternative two-phase approach was developed in this study that uses fine aggregate matrix (FAM) mix testing with the help of predictive models. The first phase is to determine the predictive model fitting parameters using the results of virgin binders and virgin FAM mixes. The second phase involves using these model-fitting parameters along with the predictive models to estimate the performance grade of the binders within the FAM mixes containing RAP. The predicted performance grades are compared with the actual performance grade of the RAP/virgin binder blend. The results indicate that the proposed approach can be used to estimate the intermediate and low PG temperatures of the blended binder within the FAM mixes containing RAP with an acceptable accuracy compared to the blending charts approach. The use of FAM mixes also allows consideration of the blending of the RAP and virgin binders, compared with solvent extraction which results in complete blending.

Effect of foaming technique and mixing temperature on the rheological characteristics of fine RAP-foamed bitumen mixtures

This paper evaluates and compares the differences in the rheological characteristics of the fine aggregate matrix (FAM) portion of plant produced Foamed Bitumen Mixtures (FBMs) by means of a mechanical foaming process, and by the incorporation of zeolites in combination with Reclaimed Asphalt Pavement (RAP) material. This evaluation explores, for the first time, the impact of plant production variations for half-warm, warm and hot processes (i.e. mixing temperatures around 90°C, 120°C and 160°C, respectively) on their rheological response. A fine Virgin-HMA, a fine HMA-RAP – no foaming technique -, and a 100% fine RAP mixture were also produced for comparison purposes. Dynamic Mechanical Analysis (DMA) tests were conducted on all evaluated FAM mixtures to determine their linear viscoelastic properties. Results indicate that the rheological response of the fine RAP-FBMs is influenced primarily by the contribution of the RAP binder in the total bitumen blend, and ageing of the fine RAP material, which were a function of the foaming technology and the production temperature of the materials.

Crack modeling of bituminous materials using extrinsic nonlinear viscoelastic cohesive zone (NVCZ) model

Cohesive zone modelling (CZM) has been used to model complex fracture process of various materials including bituminous materials. Among various CZM methods, this study used an extrinsic nonlinear viscoelastic cohesive zone (NVCZ) model implemented in a finite element method to efficiently predict nonlinear-inelastic fracture behavior of bituminous materials from crack nucleation, initiation, and propagation to complete failure. To examine the extrinsic NVCZ model, two fine aggregate matrix (FAM) bituminous mixtures with different fillers were evaluated experimentally and compared with the model’s numerical results. Laboratory tests were performed to obtain model inputs and outputs, and a parametric analysis of the NVCZ model was conducted to investigate the influence of each model parameter in the FAM fracture process. Linear viscoelastic properties were obtained using dynamic frequency sweep tests, and NVCZ model parameters were identified using an integrated experimental-numerical calibration procedure that employed semicircular bending (SCB) tests and finite element simulations. To validate the model, the experimental and numerical simulation results of an indirect tensile (IDT) test were compared. The numerical modeling results agreed well with the laboratory testing results. The outcomes of this study suggest that the extrinsic NVCZ model can be an efficient tool to predict the highly nonlinear and viscoelastic fracture processes of binding constituents in bituminous materials.

Damage assessment of asphalt concrete with composite additives at the FAM–coarse aggregate interfacial zone

Asphalt concrete (AC) is of a three-phase system comprising of coarse aggregate, FAM (fine aggregate matrix) and interfacial zones (ITZ). The interfacial zone between FAM and coarse aggregate plays a critical role which determines the mechanical performance. This paper presents a numerical simulation of the mechanical behavior of ITZ, to quantitatively analyze damage of AC with or without composite additives. The results indicated that damage at the ITZ was initiated from the top area followed by a downward propagation. Both cohesive and adhesive damage of AC with composite additives were less serious than that without composite additives, and the damage severity was greatly affected by the thickness of FAM layer. The most serious damage was observed for the thick FAM layer under a rectangular loading pattern. As such, the adhesive damage area and cohesive damage area of AC with composite additives were found to be 1.7% and 33.8% respectively, less than that without composite additives.

Use of fine aggregate matrix for computational modeling of low temperature fracture of asphalt concrete

In this study, a discrete element computational model is applied to simulate the fracture behavior of asphalt mixtures at low temperatures. In this model, coarse aggregates are explicitly represented by rigid spherical particles. The bonds that connect these particles represent the fine aggregate matrix (FAM), which is defined as the combination of asphalt binder and fine aggregates. The bending beam rheometer (BBR) tests are performed to determine the strength and Young’s modulus of FAM at low temperatures. The model is then used to simulate the semi-circular bend (SCB) tests on the mixtures. The model is verified by a series of BBR and SCB tests on both conventional and graphite nano-platelet modified asphalt materials. The comparison between the experimental and simulated results indicates that the peak load capacity of the SCB specimens is primarily governed by the tensile strength of the FAM. However, in order to capture the entire load–displacement curve of the SCB specimens, one needs to employ a softening constitutive model of the FAM, which requires the information on its fracture energy. Several experimental methods for measuring the fracture energy of FAM are discussed for future prediction of the complete load–displacement response of asphalt mixtures at low temperatures.

Bio-modification of rubberised asphalt binder to enhance its performance

The application of crumb rubber in the asphalt industry has demonstrated many advantages in pavement, yet the challenges associated with its application in pavement construction have limited its usage. In this study, Bio-Binder was used as an additive for crumb-rubber-modified (CRM) asphalt binder to enhance its rheological properties while improving workability and reducing segregation. The product produced by adding Bio-Binder to CRM binder is called Bio-Modified-Rubber (BMR) binder. Rheological studies showed a reduction in the mixing and compacting temperatures of BMR binder in comparison to CRM binder, which consequently leads to improvement in the workability and pumpability of the resulting asphalt mixture. The segregation which was quantified using a phase separation index, reduced from 58% in CRM binder to 33% in BMR binder. In addition, BMR binder showed better fatigue cracking resistance than both CRM and neat binders. Evaluating low-temperature properties of specimens conditioned at −12 °C for 12 h showed that BMR binder had improved low-temperature properties compared to CRM binder. In addition, mixture studies were conducted on the fine aggregate matrix (FAM). It was shown that low-temperature properties of FAM mixes made with BMR were significantly better than those of CRM mixtures.

Investigation on the low temperature property of asphalt fine aggregate matrix and asphalt mixture including the environmental factors

Asphalt fine aggregate matrix (FAM) is an important component of hot-asphalt mix (HMA) pavements at the meso-scale, but the relationship between FAM and HMA is not clear with respect to thermal stress and relaxation capacity at low temperatures. Thus the bending beam rheometer (BBR) was adopted to investigate the low temperature property of FAM and HMA beams. The asphalt content in FAM was calculated by keeping the filler-bitumen (FB) ratio the same as it in the known HMA specimens. FAM and HMA beams were cut and trimmed to meet the geometry requirements. Virgin beams, beams subjected to four freeze-thaw cycles, and aging beams were tested by mean of a constant creep load using BBR. In this study, the time-aging superposition principle was developed to comprehensively interpret the data. Results show that the optimal compaction is a decisive factor to generate a strong asphalt pavement. The size of air voids in FAM and HMA beams contributes to different mechanisms of moisture damage caused by the freeze-thaw cycle. FAM is more sensitive to the sunlight aging, and the time-aging superposition principle is a useful tool to quantitative the effect of aging.

Evaluation of the sensitivity of asphalt concrete modulus to binder oxidation with a multiple length scale study

It is well known that the properties of asphalt concrete mixture are affected by the oxidation of asphalt cement. However, the precise relationship between these two length scales remains largely uncharacterized. In the present study, a multiple length scale evaluation approach is applied to study and quantify the sensitivity of the mechanical properties of asphalt concrete mixture to asphalt cement oxidation. The study involves temperature and frequency sweep experiments on unaged and aged asphalt cement (to establish baseline properties), asphalt mastic (to consider physico-chemical aspects), and Fine Aggregate Matrix (FAM – to consider air voids and aggregate interaction effects). The multiscale approach separates effects of aggregate-binder physico-chemical interactions from those caused by air voids and physical aggregate interactions. Also, all asphalt cements were pre-aged to specific aging levels before preparing respective aged mastics or FAM samples. The methodology adopted for assessment of sensitivity was based on the theory of crossover modulus and second order rate kinetics of asphalt binder oxidation. The results from the analysis indicate that the mechanical properties of mastics are more sensitive to binder oxidation than FAM. Also, mechanical properties of mastics and FAM materials prepared with softer binders are more sensitive to oxidation than those with higher modulus asphalt cements. Finally, it is found that if a laboratory aging procedure is found to match the rheological properties of in-service level of asphalt oxidation at a given level of accuracy, then the expected accuracy in matching the resulting modulus of an asphalt mixture tested after being subjected to that laboratory process will be 1.5–3.6 times higher.

Effects of rejuvenators on high-RAP mixtures based on laboratory tests of asphalt concrete (AC) mixtures and fine aggregate matrix (FAM) mixtures

This paper presents the effects of various rejuvenators on the mechanical characteristics of the asphalt mixtures containing a high percentage of reclaimed asphalt pavement (RAP). Laboratory tests were performed using two different scales of laboratory samples: asphalt concrete (AC) and fine aggregate matrix (FAM) samples with 65% RAP and three different types of rejuvenators chosen from different production technologies. The results of experimental tests on viscoelastic stiffness, cracking behavior, and the permanent deformation of asphaltic materials in both the AC and FAM mixtures were compared. The test results showed rejuvenator-specific effects on the mixture properties, as well as damage-induced performance behavior in both testing scales (AC and FAM). More specifically, rejuvenators generally increased the ductility of the high-RAP mixtures, resulting in their improved cracking resistance of asphalt mixtures. Regarding the linkage between the performance characteristics of the AC mixture and its corresponding FAM mixture, for the all three aspects—stiffness, fatigue cracking, and permanent deformation—the FAM test results generally correlated with the AC test results. This implies that FAM testing could provide key information for predicting the behavior of the AC mixture and thereby act as an efficient tool for screening materials.