EVALUATION OF METHODS FOR PREDICTING DURABILITY CHARACTERISTICS OF ARGILLACEOUS CARBONATE AGGREGATES FOR HIGHWAY PAVEMENTS

ABDUL SHAKOOR, Purdue University

Abstract

Argillaceous carbonate aggregates are particularly prone to freeze-thaw failures, yet standard acceptance tests commonly do not prevent their use. Recently several Indiana highways have experienced such extensive pitting and popouts of highly argillaceous carbonates that resurfacing was required within one year. Coarse aggregate from three quarries and from pavement cores were studied to determine petrography, insoluble residue and clay contents, and pore size distribution. Results indicate the poorly performing ledges are highly argillaceous, fine grained, dolomites and dolomitic limestones with insoluble residues ranging from 20-50% consisting of low plasticity silts to medium plasticity silty clays. Illite is the predominant clay mineral (by x-ray diffraction). Aggregates with poorest performance are not necessarily those with the greatest insoluble residue percentage; the nature and mode of insolubles control extremes of deterioration. Rocks with more clay as insolubles, evenly distributed throughout the rock, are less durable than those with greater total insolubles consisting of silty concentrations of streaks and laminations. Insoluble residue content of silt and clay size and pore characteristics, as measured by the mercury intrusion or the Iowa pore index test, are the most reliable indicators of freeze-thaw durability. Nondurable aggregates have a residue content in excess of 20%, a large pore volume with small pore diameters, most being less than 0.1 microns, and an Iowa pore index value more than 50 ml. Additional tests including sulphate soundness, unconfined freeze-thaw and absorption-adsorption tests were conducted and their results compared with percent residue, mercury porosimeter data, and pore index values. Sulphate soundness and freeze-thaw tests are found to pass some unsound aggregates and reject some sound ones. Also, the criteria based on D-cracking are found to be more stringent than those required to prevent pitting and popouts. Use of D-cracking criteria will exclude many aggregates which can be safely used in bituminous pavements. The purpose of this research is to develop a simpler, more economical test to exclude nondurable argillaceous carbonate aggregates.

Degree

Ph.D.

Subject Area

Geology

COinS