Effects of Mixture and Aggregate Type on Over-Compaction in Hot Mix Asphalt in Tennessee

Correct compaction is vital for asphalt mixture service life. An adequately compacted mixture with inferior properties can achieve better performance than a mixture with excellent properties but poorly compacted. This study investigated resistance to damage caused by over-compaction by utilizing the locking point concept. Over-compaction might cause damage to the aggregate structure and decrease service life. The locking point is defined as the moment during mixture compaction at which an aggregate skeleton is developed and becomes stable. Beyond the locking point, more compaction energy does not significantly increase mixture density and can damage aggregate particles. A total of 15 mixtures was utilized and evaluated using the gyratory compactor. Among them, five dense-graded plant mixtures contained different aggregates and binders, and 10 laboratory mixtures (three types: the surface, the base, and stone mastic asphalt [SMA]) were designed with the most popular coarse aggregates in Tennessee: hard limestone, soft limestone, gravel, and granite. The results of this study show that the highest locking point was reached by the mixtures containing gravel. The SMA mixtures have, on average, lower locking points than the dense-graded mixtures. Most of the dense-graded mixtures made with crushed stones failed in the range of +20 to +30 gyrations, whereas the samples made with gravels failed in the range of +30 to +40 gyrations, indicating that gravel seems to be the most resistant to damage.

Performance Characterization of Stone Mastic Asphalt using Steel Fiber

Stone Mastic Asphalt (SMA) is a gap-graded hot mixture designed to provide higher resistance towards permanent deformation and rutting potential by 30% to 40% more than dense-graded asphalt, due to its stable aggregate skeleton structure. However, compared to other types of hot mix asphalt, SMA unfortunately has some shortcomings in term of its susceptibility towards moisture-induced damage due to its structure and excessive bitumen content in the composition. This research aims to assess the performance of a SMA mixture with steel fiber by enhancing overall stability, abrasion resistance, and, most importantly, moisture susceptibility. This study involved the incorporation of various steel fiber proportions of 0%, 0.3%, 0.5% and 0.7% by the total weight of mixture. The steel fiber modified SMA was made up of 6.0% PEN 60/70 bitumen content. The performance of SMA were evaluated through Marshall stability and flow test, Cantabro loss test and indirect tensile strength test. The results obtained from the testing showed that the incorporation of steel fiber is significantly effective to enhance the resistance towards moisture damage, while increasing the stability and reducing the abrasion loss of SMA mixture, compared to conventional mixture. Overall, it can be concluded that the addition of steel fiber in asphalt mixture specifically SMA, has improved the mechanical performance in the application of asphalt pavement with the optimum steel fiber proportion of 0.3% by the weight of mixture. The developed models between the independent variables and responses demonstrated high levels of correlation. The study found that Response Surface Methodology (RSM) is an effective statistical method for providing an appropriate empirical model for relating parameters and predicting the optimum performance of an asphaltic mixture to reduce flexible pavement failure.

THE EFFECT OF STABILIZING ADDITIVES ON THE STABILITY OF ASPHALT CONCRETE TO THE EFFECTS OF WEATHER AND CLIMATIC FACTORS

The article presents the results of studies on the influence of stabilizing additives from industrial waste on the change in the physical and mechanical properties of asphalt concrete as a result of the influence of weather and climatic factors. Microporous waste from the pulp and paper industry of high density (corrugated cardboard), mineral fillers from limestone and waste from wet magnetic separation of ferruginous quartzites in a stable and activated state and a bituminous emulsion are used as initial components. As a criterion for assessing the influence of weather and climatic factors on the physical and mechanical properties of the stone mastic asphalt, the coefficient of degradation of their values was used. It is found that after one and three years of conditional exposure to weather and climatic factors, there was an increase in the tensile strength at splitting and a decrease in the compressive strength at temperatures of 20 and 50 °C of samples of all compositions of the stone mastic asphalt, which is associated with the aging of the binder and the separation of the bitumen film from the surface of mineral materials and components of the stabilizing additive. It is shown that as a result of the introduction of mineral fillers into the composition of stabilizing additives, their bitumen-retaining ability increases, which indicates an increase in the structuring effect of the stabilizer and helps to slow down aging. The most effective was shown by a stabilizing additive containing freshly ground wet magnetic separation waste, which is explained by their high adsorption capacity in relation to an organic binder. It is found that the stone mastic asphalt using the developed stabilizing additive undergoes significantly less degradation as a result of the influence of weather and climatic factors than asphalt concrete on a traditional Viatop stabilizer.

Reducing Environment Pollution by Reusing of Alum Sludge Waste in Stone Mastic Asphalt Mixtures

Globally, a huge quantity of alum sludge waste is produced as a by-product material from drinking water treatment plants that utilize aluminum salts as an essential coagulate and is the most generally produced water treatment remaining sludge around the world, which causes a serious environmental problem. Direct discarding of this substance has ecological effects. Hence, it is important to reuse this alum sludge waste material in such a manner to diminish its detrimental impacts on the environment. This research investigates the possibility of reusing alum sludge waste as a partial replacement of cement filler in stone mastic asphalt (SMA) paving mixtures. For this investigation, the alum sludge was used as a filler material in SMA mixtures in two modes; dried alum sludge at 110°C and burned alum sludge at 700°C. Different percentages of alum sludge were used as a replacement by the total weight of mineral filler at 0, 20, 40, 60, 80, and 100%. The results showed that using alum sludge as a substitution of filler in SMA mixtures reduces the performance of the mixtures in terms of Marshall properties and tensile strength for both dried and burned alum sludge compared with a standard mix. However, the performance of the mixtures containing burned alum sludge gave a better performance than the mixtures containing dried alum sludge.

Performance Studies on Stone Mastic Asphalt Mixes with Reclaimed Asphalt Pavement

Stone mastic asphalt (SMA) is a gap graded mix which is categorised by more quantity of coarse aggregate, high asphalt content and fibre. Due to stone on stone contact and presences of high filler content, it acts as a stiff matrix and reduces the rutting due to heavy traffic load. This research presents a study on fatigue performance RAP replaced SMA mixes using VG 30 as binder along with elastomer as a modifier and results were compared with conventional SMA mix. The specimens prepared were tested using several laboratory test procedures: Marshall mix design, indirect tensile strength, moisture susceptibility, drain down test and Repeated load fatigue test. Test results showed Marshall Properties of the RAP mix improved up to a RAP content of 30% without elastomer modifier and RAP content up to 60% with elastomeric modifier. From the moisture susceptibility test results, the elastomeric modified SMA mix showed high resistance to moisture damage when compared to conventional mix and 30% RAP replacement mix. Repeated load fatigue test was conducted for different stress load and temperature and results showed elastomeric modified SMA mix offered high resistance to deformation across all stress level and temperature when compared to conventional and optimum RAP mix. As a fatigue loading increased resulted in decrease of number of fatigue cycles and increased in the initial tensile strain of the mix. As the percentage of RAP addition increased the initial tensile strain decreased.

Reutilization of Recycled Cellulose Diacetate From Discarded Cigarette Filters in Production of Stone Mastic Asphalt Mixtures

In this paper, recycled cellulose diacetate (rCDA) derived from cigarette butts was used as a fiber stabilizer to develop stone mastic asphalt (SMA) mixtures. The characterizations of rCDA were investigated by scanning electron microcopy (SEM), a Fourier transform infrared spectrometer (FTIR), and a thermogravimetric analyzer (TGA). Volumetric stability, temperature stability, moisture stability, and fatigue performance of SMA mixtures with rCDA were tested to obtain the pavement performance. Results showed that rCDA appeared to have a tough surface texture with a curly and corrugated structure, which facilitated the enhancement of the cohesion bond with the asphalt binder. TG-DTG indicated that the maximum weight loss (62.48%) obtained at temperatures ranging from 294.1°C to 376.0°C was due to decomposition and degradation of organic matters. When 0.4% rCDA was used in the asphalt mixture, the dynamic stability was 4,105 cycles/mm. The ultimate flexural strength and flexural stiffness modulus were 3,722 MPa and 9.7 MPa. It indicated that the temperature stability of 0.4% rCDA was superior to 0.3% polyacrylonitrile fiber (PAN), while inferior to 0.3% polyester (PET). The value of tensile strength ratio and residual Marshall stability were 80.2 and 75.3%, respectively. The fatigue life of 0.4% rCDA was technically like that of 0.3% PAN and 0.3% PET at lower stress levels. All results concluded that the optimum content of rCDA in asphalt mixtures was 0.4% by mass of the binder.