Date of Award

1942

Document Type

Thesis - Restricted

Degree Name

Master of Science (MS)

Department

Civil Engineering

Abstract

The extremely variable condition of pavements of various ages and design, together with the early failure of many new pavements, induced a study to ascertain, if possible, the causes therefor. A survey was begun in the fall of 1942 of about 3,000 miles of pavement throughout the state, in which it was endeavored to associate specific pavement condition to the circumstances of its exposure. Agricultural soil maps were used as a base, and the soils as shown by them were correlated to the geology of their formation and deposition, and the character and proximity of bedrock and other subsurface conformations. Certain fundamental relationships appeared to be manifest. Longitudinal cracking occurs in soils of certain characteristics and not in others. "D" cracking is associated only where the pavements, regardless of type of aggregate, were founded in soils of the calcareous glacial drift, and not in others. Faulting occurs at joints with or without load transfer dowels and in a function of the soils. Rhythmic waviness and blowups of rigid pavements are relatable to the soil-moisture conditions of the subgrade soils rather than to temperature stresses within the slab. The study of pumping and the characteristics of the subsequent failure of slabs is indicative of pavement action and stresses other than commonly assumed, and a discussion of this is presented. Aggregate base courses constructed to high densities and supporting impervious bituminous pavements have been found to suffer a complete loss of density and were waterlogged in their lower zones, with the underlying previous material being only slightly damp. The extraordinary destruction of pavements during the last decade is due to a greater incidence of heavy loads coming coincident with a reversal of the meteorological cycle from the general drought conditions of the preceding decade and a half. Due to the presence of an impervious pavement and the energy of moving loads transmitted through the pavements, the moisture conditions in the subgrade soils are not comparable to those in soils freely exposed to the atmosphere. Observations of the position of moisture in the soils and other phenomena of moisture movement, together with a study of literature on the subject, including so-called frost action, lead to the development of an explanation of these phenomena more compatible with observed manifestations than the popular theory of capillarity. The subject is concluded with a discussion on subbase courses, with particular reference, based on experience, to the operation and functioning of freely draining permeable sand or sand-gravel lift or ballast courses.

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