Physical Characteristics of Some Indiana Argillaceous Carbonates Regarding Their Freeze-Thaw Resistance in Concrete

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 dolomites and dolomitic limestone 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 distributions. Results indicate the poorly performing ledges are highly argillaceous, fine grained, limestones and dolomites with insoluble residues of from 20-45 percent consisting of low plasticity silts to medium plasticity silty clays. Illite is the predominant clay mineral. 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 insolubles consisting of silty concentrations of streaks and laminations. Insoluble residue content of silt and clay size and pore characteristics, as measured by either the mercury intrusion method or the pore index test, are the most reliable indicators of freeze-thaw durability. Nondurable aggregates are characterized by a residue content in excess of 20 percent, a large pore volume with small pore diameters, most being less than 0.1 microns, and a pore index value more than 50 ml. Additional tests including sulphate soundness, unconfined freeze-thaw, and absorption-adsorption tests were conducted and their results correlated with percent insoluble residue. The purpose is to develop a simpler, reliable, and more economical test to exclude nondurable argillaceous carbonate aggregates. (Author)