ANALYSIS OF CARBONATE QUARRY BLOCK STONES USING PETROGRAPHY, GEOCHEMISTRY AND PORE THROAT SIZE DISTRIBUTION TO PREDICT HIGHWAY PAVEMENT PERFORMANCE

Iowa aggregate sources are selected for use in portland cement concrete pavement based on properties that correlate with high durability and safety. Favorable properties have been shown to be low clay content, end-member limestone or dolostones, and low “secondary” pore volume as measured by the Iowa Pore Index apparatus. This secondary pore volume is hypothesized to be correlated to microporosity abundance.

This study seeks 1) to evaluate the commonly used rock properties (e.g. pore size distribution and geochemistrythat correlate to high quality in individual lithofacies from Iowa aggregate sources, 2) to identify any depositional and diagenetic controls on lithofacies quality, and 3) assess what changes, if any, are caused to rock pore throat size distribution by crushing.

Block stones were selected representing a spectrum of aggregate quality from quarries across Iowa. Core plugs were drilled from block stones and subjected to helium and mercury porosimetry as well as having their depositional and diagenetic characteristics interpreted using thin section petrography.

Block stone core plug helium porosities range from less than 1% to 24%. Porosity varies among different rock types from a single source. Transmitted and fluorescence petrography reveals many sources have abundant blocky calcite cement and complex diagenetic histories. Samples with identifiable depositional features reflect a variety of environments.

Current analytical work focuses on 1) analyzing block stone core plugs via mercury porosimetry to identify pore throat size distribution and 2) comparison to previous, similar analyses of crushed rock from identical sources to account for changes caused by crushing.