Optimizing the Gradation of Fine Processed Reclaimed Asphalt Pavement and Aggregate Blends for Unbound Base Courses (original) (raw)
Related papers
The Effect of Aggregate Gradation on Design Mix using Modified Bitumen
2017
Pavements undergo different type of stresses through out there life. Out of which rutting and fatigue are major distresses. To combat these problematic aspects of roads we have to deal from the root level of design mix (BC) and find a suitable cure for it.Aggregates are most important building component used in the construction as well as in the pavement industry. It is the reason for which aggregate characteristics and gradation greatly affect the performance of asphalt pavements and should be studied carefully. For preparation of mixes two types of gradation are considered i.e., Dense gradation and Open Gradation as per MORT&H (5 th Revision) specifications. The mix with modified asphalt (CRMB 55) is evaluated under Marshall Test to obtain the optimum binder content and also the strength factor of the mix is evaluated by the test. After finding out the OBC, Indirect Tensile Strength test and Texas Boiling Test are carried out to investigate the preferability of the mixes. The rese...
2019
Stone matrix asphalt (SMA) is a gap-graded hot mix asphalt with a high percentage of coarse aggregate and a high asphalt content. SMA is the typical gap-graded mixture used in Virginia that is intended to maximize rutting resistance and durability with a stable stone-on-stone skeleton held together by a rich mixture of asphalt binder. The field performance of SMA in Virginia has been generally excellent. However, several SMA pavements have undergone premature failure, and factors related to both pavement structure and materials have been identified as causes for the poor performance. A detailed forensic study recommended a specification change for gradation of SMA-9.5 mixtures to provide improved stability. The Virginia Department of Transportation adopted a new aggregate gradation in 2012 for these mixtures. Aggregate morphological characteristics, including sphericity, flatness ratio, elongation ratio, angularity, and texture, have been recognized as major factors influencing the performance of aggregate and asphalt mixtures. The current study demonstrated via laboratory methods the stability of mixtures conforming to the Virginia Department of Transportation's new grading specification and the effects of aggregate morphology and asphalt binder properties on stability. SMA mixtures designed and produced by different contractors using aggregates from different quarries in Virginia were included in the study. SMA mixtures and samples of the aggregates used in production were obtained for laboratory evaluation of the structural stability and aggregate characteristics of the mixtures. All mixtures met the criterion of VCA MIX < VCA DRC, indicating good stone-on-stone contact and a denser coarse aggregate fraction. Flow number and asphalt pavement analyzer results showed better rutting resistance of all mixtures with revised gradation. In both confined and unconfined flow number tests, polymer-modified binders (PG 64E-22 or PG 76-22) showed a lower flow number slope compared to that of PG 70-22 (PG 64H-22) binders, indicating better rutting resistance. SMA mixtures with polymer-modified binder also showed excellent fatigue performance. All mixtures showed a maximum number of cycles of 1,200 in the Texas overlay test, showing the excellent reflection crack resistance of these mixtures. Regression analyses were conducted between weighted mean morphological characteristics and performance parameters. Aggregate morphological characteristics were found to play an important role in the mechanical performance of SMA mixtures and the uncompacted void content of the coarse aggregates. Results showed that using more spherical (equant), angular, or better-crushed rough coarse aggregate particles in SMA mixtures can improve the resistance of the SMA to rutting. In addition, aggregates with fewer flat and elongated aggregate particles can contribute to better rutting performance of SMA mixtures. Results also showed that better rutting resistance can be obtained using polymer-modified binders even if the aggregate morphological characteristics are slightly less favorable.
Beni-Suef University Journal of Basic and Applied Sciences
Background The depletion of natural resources has led to the need of looking out for alternatives of primary construction materials. The use of reclaimed asphalt pavement (RAP) has become a common practice as it reduces economic burden and saves natural resources and energy. This study is based on partial replacement of fresh natural aggregate with reclaimed aggregate. The project is divided into two phases; first one discusses the mechanical viability of replacing 10%, 20%, 30%, 40%, 50% and 60% of fresh aggregates with reclaimed aggregates. The second phase involves the study conducted on a 9.8 KM dense bituminous macadam (DBM) layer, constructed using the most optimum mix from the first phase of study. Finally, a cost analysis of the pavement was conducted to assess its economic viability. Results In the light of MORTH guidelines, laboratory results showed improvement in the Marshall parameters till 30% replacement of fresh aggregates. Eventually, the DBM layer was constructed us...
— Stone Mastic Asphalt (SMA) mixtures rely on stone-to-stone contacts among particles to resist applied forces, and permanent deformation. Aggregates in SMA should resist degradation (fracture and abrasion) under high stresses at the contact points. Current practices for asphalt mix design and acceptance testing rely on volumetric properties. Vital to the calculation of mix volumetric properties are specific gravity measurements of the mixture and the aggregate in the mixture. For the Motorways wearing course,SMA stone grid must fulfil the mineralogical-petrographic condition to be on rock of igneous and/or metamorphic origin but of silicate composition, specific weight and LA method on resistance to fragmentation. During the construction of the Kosovo motorway for wearing course was used the SMA as asphaltlayer for providing longer lifetime to the road construction. The super-pave mix design for SMA wearing course has been composed considering the available stone with high mineralogical and petrographic composition. The stone used for the wearing course on this motorway has resistance to crushing of LA =18 which is below the standard criteria for heavy traffic roads and motorways wearing courses. Thespecific weight of used stone was 3100 kg/m3which is about 15% heavier than standard weight. For this specific stone were prepared special super-pave design mix with binder content 4.5% which was well below than typical SMA composition of 6.0−7.0% binder rather of mixture was 3100 kg/m 3. In this paperwork it is described the design mix of SMA composed with relatively high specific weight and their impacts on asphalt mix design properties used in Kosovo Motorway.
ASPHALT MIXTURE DESIGN CONCEPTS TO DEVELOP AGGREGATE INTERLOCK
From the beginning of asphalt mixture design it was desired to understand the interaction of aggregates, asphalt, and the voids created during their compaction. In asphalt mixture design, guidance is lacking in the selection of the design aggregate structure and understanding the interaction of that aggregate structure and mixture volumetric properties. This paper presents mixture design concepts that utilize aggregate interlock and aggregate packing to develop an aggregate blend that meets volumetric criteria and provides adequate compaction characteristics. The presented concepts rely on coarse aggregate for the skeleton of the mixture with the proper amount of fine aggregate to provide a properly packed aggregate structure. The objective is to utilize aggregate packing concepts to analyze the combined gradation and relate the packing characteristics to the mixture volumetric properties and compaction characteristics.
Transportation Research Record: Journal of the Transportation Research Board, 2013
Finding innovative ways to incorporate reclaimed asphalt pavement (RAP) into highway base course applications will provide both environmental and economic benefits by allowing in situ recycling of material for projects such as widening or shoulder addition. RAP is a well-drained granular material; however, 100% RAP has low bearing strength and creeps under load. The objective of this research is to develop methods to improve RAP's strength while reducing creep to an acceptable level through blending with high-quality crushed-limestone aggregate, by chemical stabilization with asphalt emulsion or portland cement, or both. RAP–aggregate blends with and without chemical stabilization were compacted by the modified Proctor method, cured, and tested for strength and creep. Strength was tested by the limerock bearing ratio (LBR), a variant of the California bearing ratio test. Specimens were tested dry and soaked to evaluate retained strength. One-dimensional creep testing was perform...
DEVELOPMENT OF A MIXTURE DESIGN PROCEDURE FOR STONE MATRIX ASPHALT (SMA)
2000
Stone Matrix Asphalt (SMA) has been used successfully in Europe for over 20 years to provide better rutting resistance and to resist studded tire wear. Since 1991, the use of SMA has increased steadily in the United States. At present, some states routinely use SMA even though a standard mixture design procedure is not available. A mixture design procedure that provides guidance on material properties, aggregate gradation, determination of optimum asphalt content, and mixture properties is needed. This paper presents a mixture design procedure for SMA mixtures developed by the National Center for Asphalt Technology. Data for the development of the procedure was collected from a laboratory study conducted with various samples of aggregates, fillers, asphalt binders, and stabilizing additives. Compacted mixtures were tested to evaluate the effects of aggregate structure, asphalt binder, and binder-fine aggregate mortar. Specific conclusions from this study were: 1) The Los Angeles abrasion loss showed good correlation with aggregate breakdown; 2) it appeared that the 3:1 or 2:1 flat and elongated particles provided much better classification for the various aggregates than a 5:1 ratio; 3) the flat and elongated particle ratio showed excellent correlation with aggregate breakdown; 4) in a SMA mix, the percent passing the 4.75 mm sieve must be below 30 percent to ensure proper stone-on-stone contact; 5) the percent passing the 0.02 mm sieve did not show a correlation with mortar stiffness. However, the dry compacted volume, as obtained from the Penn State test method, did show a good correlation with mortar stiffness and can be utilized to characterize the shape of fillers. Generally, a more angular filler tends to produce a higher air voids result in this test; 6) In-place results from about 86 projects showed that very little rutting has occurred in SMA pavements constructed in the United States since 1991. However, for the pavements with air voids falling below the 3 percent range, some rutting was observed; 7) a VMA significantly lower than specified VMA can be obtained due to aggregate breakdown. Hence, the mix designer must consider aggregate type, compactor type and compactive effort along with the gradation in meeting the required VMA criteria. Specifying a minimum asphalt content can result in different requirements for aggregates with different specific gravity; 8) Fifty blows of Marshall hammer were found to be approximately equal to 100 revolutions of the Superpave gyratory compactor in terms of resultant density. The Superpave gyratory compacter was found to produce less aggregate breakdown than the Marshall hammer; 9) Fiber stabilizers were found to be more effective in reducing draindown than polymer stabilizers. However, mixes modified with polymer showed better resistance to rutting in laboratory wheel tracking tests.
EFFECT OF AGGREGATE GRADATION ON THE STIFFNESS OF ASPHALT MIXTURES
Aggregate gradation plays an important role in the behaviour of asphalt mixtures. Packing of aggregate is a very important factor that will be affected by changing the aggregate gradation. Many researchers have investigated different ways of describing packing both theoretically and practically. Bailey ratios have recently been used to understand the volumetric properties of mixtures. In this paper, the Bailey ratios have been used, and two further ratios have also been introduced to allow the asphalt mixture gradation to be fully understood. Thirteen different aggregate gradations have been chosen within the 14 mm asphalt concrete specification to investigate the effect of particle size distribution on the stiffness of the mixture. It was found that variation in aggregate gradation has a significant effect on asphalt stiffness, even within specification limits, and a reasonable correlation between the set of ratios investigated and the Indirect Tensile Stiffness.