Studies on Effect of Wheel Configuration-Temperature and Type of Binder on Rutting Characteristics of Bituminous Concrete Mix
This report presents the investigation of rutting characteristics of bitumen mixes using plain bitumen (VG-10) and modified binders (CRMB-60 and PMB-70). The report will be of particular interest to engineers in the public and private sectors with responsibility for the design, construction, maintenance and rehabilitation of HMA pavements. The present work is aimed at understanding the properties of mix and the machine parameters which influence the deformation causing ruts for mixes. The rutting was caused on the beam specimens prepared in the laboratory. The study includes the influence of different types of binders, air voids, and along with the applied loads on the rutting characteristics. The results are analyzed to formulate regression equations. It is found that modified binders resist rutting compared to plain binders. PMB-70 binders perform better than VG-10 and CRMB-60 binders under the laboratory induced applied pressures and number of passes.
Evaluation and Selection of Aggregate Gradations for Asphalt Mixtures Using Superpave
The design of asphalt mixtures is a complex process that requires the proper proportioning of materials to satisfy mixture volumetric and mechanical properties. The majority of time spent in the mix design process is used in evaluating and selecting aggregate gradations to meet project requirements. The latest set of requirements for asphalt mixtures is the Superpave system, developed during the Strategic Highway Research Program. This system incorporates materials selection, evaluation of trial aggregate structures, selection of design asphalt binder content, moisture sensitivity, and, in some cases, determination of performance properties of the selected asphalt-aggregate blend. The selection of a design aggregate structure reduces to selecting an aggregate gradation that will meet minimum volumetric and densification criteria, and selecting an aggregate structure that will provide adequate resistance to permanent deformation, fatigue, and thermal cracking. In the Superpave volumetric mix design process, achieving voids in mineral aggregate (VMA) is the most difficult task facing the mix designer. One phase of this evaluation focuses on providing Guidelines to achieve VMA requirements with Superpave mix designs. This phase was accomplished by evaluating the existing database of information on Superpave mix designs at the Asphalt Institute. The second phase examines the relationship between properties determined during the Superpave volumetric mix design process, and material properties determined by mix analysis tests.
The crystal structure of stilpnomelane. Part II. The full cell
Summary The structural formula of stilpnomelane averaged from 37 representative literature analyses and based on the determined structure is (Ca,Na,K)4(Ti0·1Al2·3Fe35·5Mn0·8Mg9·3)[Si63Al9](O,OH)216·nH2O. Ferrostilpnomelanes have up to 12 R 3+ cations in the octahedral sheet, ferristilpnomelanes commonly have between 24 and 30 R 3+ cations, rarely up to 37. The two groups can be distinguished by accurate X-ray powder diffraction, ferrostilpnomelanes having d 001 less and a greater than have ferristilpnomelanes. The unit cell is triclinic, a = b∼21·8 Å, γ = 120°, d 001∼12·2 Å, P . Hexagonal groups or ‘islands’ of 24 silicon-oxygen tetrahedra co-ordinate to the octahedral sheet, the centres of the ‘islands’ are displaced by 5a/12, 8b/12 on either side of the octahedral sheet as a result of warping of this sheet to permit articulation with the smaller tetrahedral sheet. The 24-tetrahedra ‘islands’ are linked laterally by 6-member rings of inverted tetrahedra, which in turn link at their apices to like rings connecting the next sheet of ‘islands’. Thus a single tetrahedral layer is 4 tetrahedra thick and has symmetry 6/m. The 6-member rings of tetrahedra act as hinges permitting up to 0·5 Å extension or contraction of the tetrahedral sheet to accommodate variations in the octahedral sheet dimensions with varying R 2+/R 3+ ratio.