An Inventory of Granular Materials in Indiana

Of the many improvements in the design of highway pavements during the past two decades, it is doubtful that any have been more important to the life and service of the pavement than the incorporation of the granular base course as a design feature. The true significance of the base course can be more thoroughly understood if one considers the merits of this practice. First, the properly designed base course increases the load-carrying capacity for a given pavement structure and therefore increases its ability to support wheel loads. Second, the granular base course, if properly designed, serves as a drainage installa­ tion, thus enhancing the rapid removal of surface water and thereby alleviating the tendency for water to accumulate beneath the pavement. This is of extreme importance, since surface water and soil moisture always complement pumping, frost heaving, subgrade softening, and materials disintegration. Highway engineers have been quick to recognize the value of base courses; however, even as late as ten years ago, when many of our exist­ ing highways were being built, there were numerous instances where the loads and the volume and intensity of traffic did not warrant the addi­ tional cost of base-course construction. However, with the advent of the modern motor-freight truck, the wheel loads and the heavy truck traffic have been increasing constantly. This has been particularly true since the start of the national emergency, thereby accelerating the dis­ tress and failures of many of our pavements. And as one might suspect, other things being equal, the pavements having the granular base courses as well as those on gravel terraces and granular soil areas are showing superior performance. In view of these introductory statements on base-course design and construction, it seems reasonable that post-war highway plans w ill be unanimous in the adoption of the granular base course for roads carry­ ing heavy traffic and located in certain soil areas. And with the vast