Sand Silt Ratio as Design Criteria in Design of Bituminous Paving Mixtures

Highway pavement is a structure consisting of superimposed layers of processed materials above the natural soil sub-grade, whose primary function is to distribute the applied vehicle loads to the sub-grade. The pavement structure should be able to provide a surface of acceptable riding quality, adequate skid resistance, favorable light reflecting characteristics, and low noise pollution. The ultimate aim is to ensure that the transmitted stresses due to wheel load are sufficiently reduced, so that they will not exceed bearing capacity of the subgrade. Flexible pavements will transmit wheel load stresses to the lower layers by grain-to-grain transfer through the points of contact in the granular structure. The wheel load acting on the pavement will be distributed to a wider area, and the stress decreases with the depth. Taking advantage of this stress distribution characteristic, flexible pavements normally has many layers. Hence, the design of flexible pavement uses the concept of layered system. Pavements are a conglomeration of materials. These materials, their associated properties, and their interactions determine the properties of the resultant pavement. Thus, a good understanding of these materials, how they are characterized, and how they perform is fundamental to understanding pavement. The materials which are used in the construction of highway are of intense interest to the highway engineer. Mineral aggregates are used in combination with bitumen to prepare mixtures for a wide variety of purposes. As the aggregates normally constitute 90 % or more by weight of such mixers, their properties and grading have a very significant effect on the characteristics of bituminous mixture such as stability, workability and density. Sand-Silt ratio may be considered as a simple factor to guide the field Engineer in his interpretation of the significance of his daily extraction results.