Stone Matrix Asphalt Mixtures Research Articles

Performance properties of rubberized stone matrix asphalt mixtures produced through different processes

Performance properties of rubberized stone matrix asphalt mixtures produced through different processes

Effect of coarse aggregate morphology on the mechanical properties of stone matrix asphalt

The aim of this study is to examine the effects of morphological characteristics of coarse aggregates on the rutting and fatigue performance of stone matrix asphalt (SMA). A total of twenty-two coarse aggregate fractions were analyzed, and different aggregate blends were used to prepare different SMA mixtures following the job-mix formula in Virginia State. Specimens from eight types of SMA mixtures, with three replicates each, were tested for rutting resistance with an asphalt pavement analyzer (APA). Six types of the SMA mixtures were tested for fatigue resistance with a modal mobile load simulator (MMLS) in conjunction with a portable seismic pavement analyzer (PSPA). Rut depth obtained from the APA and seismic modulus difference obtained during MMLS trafficking were linked to morphological characteristics of coarse aggregates. Statistical analysis showed that flatness ratio and elongation ratio had no measurable influence on rut depth. The regression analysis demonstrated that rut depth increased with the increase of sphericity, angularity and texture, which indicates that rutting resistance of SMA can be improved by using more equi-dimensional and angular coarse aggregates with rougher texture. However, angularity and texture were found to have little influence on seismic modulus difference. Sphericity was shown to have a negative influence on seismic modulus difference, and flatness ratio was shown to have a positive effect on seismic modulus difference, which indicated that using more spherical and less flaky coarse aggregates reduces the degradation of stiffness, resulting in improved fatigue performance of SMA mixtures. The performance results suggest that flat and elongated aggregates should be used only in limited amounts.

The rheological behavior of bitumen and moisture susceptibility modified with SBS and nanoclay

ABSTRACTThe effect of styrene–butadiene–styrene (SBS) and nanoclay additive on performance of pure bitumen and stone matrix asphalt (SMA) mixture was investigated. Different samples with various percentages of nanoclay (2%, 3%, 4%, and 5%) and SBS (0% and 5%) by weight of bitumen were prepared, and the rheological and chemical behavior of bitumen (rotational viscosity, dynamic shear rheometer, SEM, and FTIR), the indirect tensile strength and moisture susceptibility of different mixtures were evaluated. Based on the results, using nanoclay and SBS polymer can improve the rheological behavior of base binder and the resistance of SMA mixtures against moisture damage.

Designing a Skid-Resistant and Durable Asphalt Mixture Based on the Stress Concentration Distribution Rate

This article uses pressure-sensitive film and accelerated load kneading machine to study the large-skid pavement. The stress distribution of static contact between tire and asphalt pavement under different pavement roughness and kneading time is investigated. The present study reports on the establishment of a relevant quantitative evaluation method to evaluate asphalt pavement skid resistance and durability by the stress concentration distribution rate. By designing different gradations of SMA-13 (stone matrix asphalt mixture) and GAC-13 (discontinuity dense grading of AC-13, 13 is nominal maximum aggregate size) asphalt mixture, using the stress concentration distribution rate to evaluate the initial stage and the late skid resistance. Therefore, we elected the asphalt mixture with superior performance and durability of skid resistance. The present results provide a reference for engineering applications.

Effect of Fibers on Mixture Design of Stone Matrix Asphalt

Lignin fibers typically influence the mixture performance of stone matrix asphalt (SMA), such as strength, stability, durability, noise level, rutting resistance, fatigue life, and water sensitivity. However, limited studies were conducted to analyze the influence of fibers on the percent voids in mineral aggregate in bituminous mixture (VMA) during the mixture design. This study analyzed the effect of different fibers and fiber contents on the VMA in SMA mixture design. A surface-dry condition method test and Marshall Stability test were applied on the SMA mixture with four different fibers (i.e., flocculent lignin fiber, mineral fiber, polyester fiber, blended fiber). The test results indicated that the bulk specific gravity of SMA mixtures and asphalt saturation decreased with the increasing fiber content, whilst the percent air voids in bituminous mixtures (VV), Marshall Stability and VMA increased. Mineral fiber had the most obvious impact on the bulk specific gravity of bituminous mixtures, while flocculent lignin fiber had a minimal impact. The mixture with mineral fiber and polyester fiber had significant effects on the volumetric properties, and, consequently, exhibited better VMA over the conventional SMA mixture with lignin fiber. Modified fiber content range was also provided, which will widen the utilization of mineral fiber and polyester fiber in the applications of SMA mixtures. The mixture evaluation suggested no statistically significant difference between lignin fiber and polyester fiber on the stability. The mineral fiber required a much larger fiber content to improve the mixture performance than other fibers. Overall, the results can be a reference to guide SMA mixture design.

Evaluation of rutting performance of stone matrix asphalt mixtures containing warm mix additives

Permanent deformation or rutting, one of the most important distresses in flexible pavements, has long been a problem in asphalt mixtures and thus a great deal of research has been focused on the development of a rheological parameter that would address the rutting susceptibility of both unmodified and modified bituminous binders. In this research, three warm mix additives (Sasobit, Rheofalt and Zycotherm) were used to modify 60-70 penetration grade base binder. The rutting potential of both modified and unmodified binders were evaluated through the multiple stress creep recovery (MSCR)-based parameter, nonrecoverable compliance (J nr) and recovery parameter (R). Several performance tests carried on stone matrix asphalt (SMA) mixtures comprising different nominal maximum aggregate sizes (NMASs, 9.5, 12.5 and 19 mm), like Marshall stability, dynamic and static creep and Hamburg wheel tracking tests to evaluate their rutting performance. The objective of this work is to correlate MSCR test results to performance. Results indicate that for the range of the gradations investigated in this work, increasing the nominal maximum aggregate size of the gradation would increase the permanent deformation resistance of the SMA mixture. Addition of 3% sasobit to base binder leads an increase in J nr100 about 82%. Addition of 2% rheofalt to base binder leads an recovery increase of about 9.76 % and 27.44% in stress levels of 100 and 3200 Pa, respectively. The results reveal that rutting resistance of mixtures improves as J nr decreases. The use of the MSCR test in the rutting characterization of bituminous binders is highly recommended based on the results of this work.

Effects of Nominal Maximum Aggregate Size on the Performance of Stone Matrix Asphalt

It is well known that the performance of hot mix asphalt (HMA) in service life is closely related to a proper aggregate gradation. A laboratory study was conducted to investigate the effects of nominal maximum aggregate size (NMAS) on the performance of stone matrix asphalt (SMA). The volumetric characteristics and performance properties obtained from wheel tracking tests, permeability test, beam bending test, contabro test are compared for SMA mixes with different NMAS. The results indicated that voids in mineral aggregate (VMA) and voids filled with asphalt (VFA) of SMA mixtures increased with a decrease of aggregate size in aggregate gradation. SMA30 had the lowest optimum asphalt content among all the mixtures. Increase of NMAS contributed to improvement of the rutting resistance of SMA mixtures. However, a decrease of NMAS showed better cracking and raveling resistance. Permeability rate of SMA was primarily affected by the air voids (AV) and break point sieve, but was also sensitive to aggregate gradation to some extent, with reduced NMAS corresponding to less permeability rate. Based on the test results, SMA5 and SMA13 are suggested to be used as a water-proof layer in bridge deck pavement, and SMA20 and SMA30 are suggested to be used as binder course in asphalt pavement, which needs to possess superior rutting resistance at high temperature.

Back-calculation method for determining the maximum RAP content in Stone Matrix Asphalt mixtures with good fatigue performance based on asphalt mortar tests

This paper presents a simple method to determine the amount of Reclaimed Asphalt Pavement (RAP) that can be added to Stone Matrix Asphalt (SMA) mixtures without compromising the fatigue resistance. Dynamic Shear Rheometer tests (DSR) on binder and mortars composed with fine RAP particles, called Selected Recycled Asphalt Pavement (SRAP) are used together with the Nielsen model to back-calculate the norm of the complex modulus of the bituminous blend of fresh and RAP binder. Fatigue properties are derived from parameter G*sinδ and Linear Amplitude Sweep tests. The analysis indicates that a limiting SRAP binder content of 23% can be included in SMA mixtures with satisfactory fatigue performance.

Quantification of Aggregate Morphologic Characteristics as Related to Mechanical Properties of Asphalt Concrete with Improved FTI System

AbstractThis paper introduces the improved Fourier transform interferometry (FTI) system, which captures three-dimensional (3D) high-resolution images of aggregates. The improved FTI system uses the two-dimensional (2D) fast Fourier transform (FFT2) to rapidly measure aggregate morphologic characteristics from these images, including sphericity, flatness ratio, elongation ratio, angularity, and surface texture. Eight aggregate fractions, used in two different stone matrix asphalt (SMA) mixtures, were imaged and the calculated aggregate morphologic characteristics were found to be in good agreement with manual measurement results. The influence of aggregate morphologic characteristics on the mechanical performance of asphalt concrete is further examined on mixtures from Culpeper and Staunton in terms of dynamic modulus, flow number, and fatigue performance in laboratory experiments. Experimental results show that the mechanical performance of Staunton asphalt concrete samples was better than that of those ...

Evaluation and optimisation of stone matrix asphalt (SMA-13) mix design using weight-matrix method

The mix design of the stone matrix asphalt (SMA) mixture is critical to its performance and thereby has attracted considerable attention. In this research, abiding by the principals of orthogonal experimental design, a series of laboratory tests are conducted to assess and optimise the SMA-13 mixture mix designs. Different levels of three critical factors, gradation, asphalt-aggregate ratio, and fibre contents, are applied in the factorial experimental designs. Five performance measures, residual stability, dynamic stability, fatigue lifespan, bending strength, and coefficient of friction, are tested. With the laboratory testing results, weight-matrix analysis is employed to identify the impact of different levels of different factors on overall performance. Based on the results, the influences of the three factors are ranked: gradation, asphalt-aggregate ratio, and fibre contents, from the most influential to the least. Furthermore, analyses are conducted to determine the optimum SMA-13 mix design for four representative climate zones in China. Results are verified with the compared mixture groups.

Comparison of Stone Matrix Asphalt mixtures with polymer-modified bitumen and shredded waste plastics

Stone Matrix Asphalt (SMA) is a gap-graded bituminous mixture characterised with its improved rut resistance and durability. It has comparatively higher proportion of coarse aggregates and binder mastic with bituminous binder and mineral filler. Drain down of mastic content at various stages of construction is a common issue with SMA, and generally, some fibre additives are used to stabilise the mixture or a modified bitumen is used as the binder material. In this study, shredded waste plastics (SWP) are used instead of other stabilising additives, to prepare SMA mixtures with conventional viscosity graded (VG) 30 bitumen. Mixtures were prepared with four different levels of SWP content, and another mixture without any stabilisers was also prepared using polymer-modified bitumen (PMB). Specimens were prepared in superpave gyratory compactor (SGC) for all mixtures at different bitumen contents to determine volumetric and Marshall properties, and optimum bitumen content (OBC) was calculated for each mixture. Tensile strength, moisture susceptibility, rutting resistance and fatigue behaviour were also determined for all mixtures at corresponding OBC. From the available results, the optimum level of SWP in SMA mixture was determined as 8% by weight of bitumen. The study showed that even though mixture with PMB performed the best, SMA with 8% SWP provided comparable results. Based on the present investigation, waste plastic in suitable dosage can be recommended in SMA, instead of a stabilising additive.

Performance properties of rubberized stone matrix asphalt mixtures produced through different processes

The study investigated the dynamic modulus, rutting resistance, moisture susceptibility and fatigue resistance of rubberized Stone Matrix Asphalt (SMA) through laboratory performance tests. Rubberized SMA mixes were produced by three processes: the dry process, the wet process and the terminal in the laboratory. For comparison purposes, SMA mixtures containing styrene–butadiene–styrene (SBS) modified binder and virgin asphalt of PG 67-22 were also evaluated and compared to rubberized SMA. Dynamic modulus and direct tension fatigue tests were performed using the Asphalt Mixture Performance Tester (AMPT) system. Rutting resistance and moisture susceptibility were analyzed by Hamburg wheel tracking test using asphalt pavement analyzer (APA). The results showed that: (1) the incorporation of CRM improved the high temperature dynamic modulus, the resistance to rutting and fatigue life of SMA mixes. (2) The introduction processes of CRM (dry process and wet process) may have effect on the high temperature dynamic modulus and rutting resistance, while no significant influence on the moisture susceptibility and fatigue life. (3) The use of combination of SBS and CRM in the terminal SMA significantly improved the resistance to rutting and fatigue cracking. (4) The rubberized SMA with 10% CRM had the lower performance properties than SBS SMA, regardless of the dry process or the wet process.

Fatigue Performance of Rubberized Stone Matrix Asphalt by a Simplified Viscoelastic Continuum Damage Model

AbstractThe study investigated the fatigue performance of rubberized stone matrix asphalt (SMA) in the dry process and compared its fatigue characterization with SMAs with other typical binders. Five SMA mixtures were used with the following asphalt binders: (1) virgin asphalt of PG 67-22, (2) crumb rubber modifier (CRM) modified in wet process, (3) CRM modified in dry process, (4) terminal-blend binder, and (5) styrene-butadiene-styrene (SBS) modified binder. Dynamic modulus and direct-tension fatigue tests were performed using the asphalt mixture performance tester (AMPT) system. In addition, improved linear amplitude sweep (LAS) tests were performed on the binders by a dynamic shear rheometer (DSR). The fatigue test data were analyzed by the simplified viscoelastic continuum damage (S-VECD) theory. The results showed that (1) dynamic modulus of the rubberized SMA in the dry process was similar to that of the wet process and higher than that of SMA with virgin asphalt, although a little lower than those...

Experimental investigation on mineral and organic fibers effect on resilient modulus and dynamic creep of stone matrix asphalt and continuous graded mixtures in three temperature levels

Two fiber types were used in this study to evaluate resilient modulus and dynamic creep behavior of stone matrix asphalt and continuous graded hot mixed asphalt versus various fiber contents in three levels of temperature. Generally, continuous graded mixtures presented better mechanical properties in both resilient modulus and dynamic creep tests. Fibers have shown great effect not only on asphalt drain-down, but on mechanical properties of samples. Considering the temperature effect, the higher the temperature is, the higher fiber content is required to improve mechanical characteristics of asphalt concrete.

Laboratory characterization of compaction and damping properties of Stone Matrix Asphalt

Stone Matrix Asphalt (SMA) is referred to gap graded Hot Mix Asphalt (HMA) that is designed to maximize rutting resistance and durability by using a structural basis of stone-on-stone contact. SMA mixture designs with gap graded aggregate gradations and polymer modified binders often have special field compaction requirements. To better understand differences in compaction behavior between SMA and dense graded HMA mixtures, laboratory tests were conducted on field collected loose samples at typical field densities and loading conditions. The goal of the first phase of this study was to investigate the growth of density and the mobilized shear stress in the specimen as a function of applied normal stress, gyration numbers, and the compactive effort. In the second phase, damping ratio tests were performed on the compacted samples at close to field compaction temperatures by applying dynamic loading at various frequencies and different confining pressures to determine the mixture damping properties. The test results indicated that SMA mixtures with the gap graded aggregate structure achieved higher densities in comparison to HMA mixtures. The frequency of dynamic loading had a significant effect on the damping ratios of the SMA mixtures and the effect of confining pressure, linked to proper lift thicknesses in the field, was found to be dependent on compaction pressure levels as well as mixture properties.

Laboratory evaluation of the effect of gilsonite on the performance of stone matrix asphalt mixtures

This study investigates the benefits of modifying asphalt and stone matrix asphalt (SMA) mixtures in flexible pavement. Sixty to seventy penetration-grade asphalt cement and Iranian natural bitumen (gilsonite) were subjected to physical and performance tests. Physical and conventional tests were conducted on modified and unmodified bitumen (penetration, softening point, ductility and viscosity). Performance tests, including Marshall stability, indirect tensile strength, moisture susceptibility, resilient modulus and rutting resistance, were conducted on unmodified and modified SMA mixtures. Results of conducted tests on the modified asphalt binders with 5%, 10% and 15% gilsonite show that using gilsonite improves performance of SMA mixture.

Laboratory performance of stone matrix asphalt mixtures with two aggregate gradations

Stone matrix asphalt (SMA) is a gap-graded bituminous mixture which can be used in surface layer of high volume pavements. The mixture has higher concentrations of coarse aggregates, providing strength and rut resistance to the mixture, and higher asphalt content giving durability. There must be a proper stone-to-stone contact between the coarse aggregates of SMA, and hence aggregate gradation is an important factor in this mixture. In the current study, two aggregate gradations, with nominal maximum aggregate sizes (NMAS) 16 and 13 mm were adopted to prepare SMA mixtures and their laboratory performances were compared. Polymer-modified bitumen (PMB) was used as the binder material and no stabilising additive was used, since drain down was within permissible limits for both mixtures with PMB. Conventional cylindrical specimens were prepared in superpave gyratory compactor with bitumen contents 5.0 %, 5.5 %, 6.0 %, 6.5 % and 7.0 % by weight of aggregates, and volumetric and Marshall properties were determined. Tensile strength, behaviour to repeated loading etc. were checked for cylindrical specimens prepared at optimum bitumen content, whereas specially prepared slab specimens were used to check the rutting resistance of SMA mixtures. From the laboratory study, it was observed that, out of the two SMA mixtures, the one with NMAS 16 mm performed better compared to the other. These improved properties may be attributed towards the larger coarse aggregate sizes in the mixture.

Analysis on the cooling effect of a heat-reflective coating for asphalt pavement

A type of self-made heat-reflective coating was applied on the surface of different types of asphalt concrete. The temperature of the asphalt mixture specimens with coatings that have different application rates was measured. By calculating the temperature difference between the specimen with and without the coating, the results show that the cooling value first increases and then becomes flat as the application rate of the coating increases. With the same coating application rate, dense-graded asphalt mixture has the best cooling effect, followed by the stone matrix asphalt (SMA) mixture, and finally, the open-graded friction course (OGFC) asphalt mixture has the lowest cooling effect of the tested specimens. The reason is that the OGFC asphalt mixture has a high per cent of air voids and part of the coating will penetrate into the air voids, so less coating is available to reduce the temperature. The SMA mixture has a higher texture depth than the dense-graded asphalt mixture, which compromises the cooling effect of the coating. The cooling mechanism was analysed through microscopic analysis methods, and the reflective spectrum was measured by ultraviolet–visible–near-infrared spectrometer. Results show that the coating has a high reflectivity due to the addition of fillers, which reduces the heat absorption of pavement. The Infrared spectra of the coating and fillers in the middle infrared region were tested by the Fourier transform infrared spectrometer. It indicates that the fillers have good thermal radiation ability in the atmospheric window. Accordingly, the coating presents a good cooling ability in this region, which can further reduce the temperature of the pavement. Pictures from the scanning electron microscope prove that there are many fillers scattered on the surface of the coating, which can bring about a good cooling effect.

Influence of Fiber Type on Road Performance of Stone Mastic Asphalt

Stone Matrix Asphalt (SMA) is a gap-graded mix that is gaining popularity worldwide. Various types of fibers are used as additions in SMA asphalt mixture. However, there is not sufficient information available for the selection of different fibers with regard to different applications of SMA pavement. In this paper, SMA-13 using three different fibers: lignin fiber, polyester fiber and basalt mineral fiber, is used as an example. Based on the Marshall test, Schellenberg Binder Drainage test, Cantabro test, Residential stability test, Freezethaw cycle test, Rutting test and Bending test of small beam of the mixtures, the influences of different fibers on road performance of SMA mixture were investigated. The results show that SMA-13 mixtures using mineral fibers exhibit optimal high temperature and low temperature stability; while SMA mixtures using lignin fibers exhibit optimal water stability.

Evaluation of fatigue life of CRM-reinforced SMA and its relationship to dynamic stiffness.

Fatigue cracking is an essential problem of asphalt concrete that contributes to pavement damage. Although stone matrix asphalt (SMA) has significantly provided resistance to rutting failure, its resistance to fatigue failure is yet to be fully addressed. The aim of this study is to evaluate the effect of crumb rubber modifier (CRM) on stiffness and fatigue properties of SMA mixtures at optimum binder content, using four different modification levels, namely, 6%, 8%, 10%, and 12% CRM by weight of the bitumen. The testing undertaken on the asphalt mix comprises the dynamic stiffness (indirect tensile test), dynamic creep (repeated load creep), and fatigue test (indirect tensile fatigue test) at temperature of 25°C. The indirect tensile fatigue test was conducted at three different stress levels (200, 300, and 400 kPa). Experimental results indicate that CRM-reinforced SMA mixtures exhibit significantly higher fatigue life compared to the mixtures without CRM. Further, higher correlation coefficient was obtained between the fatigue life and resilient modulus as compared to permanent strain; thus resilient modulus might be a more reliable indicator in evaluating the fatigue life of asphalt mixture.