COMPUTED TOMOGRAPHY ANALYSIS OF AIR VOID SYSTEM IN IOWA PAVEMENTS CREATED FROM AGGREGATE DETERIORATION

Some portland cement concrete pavements in Iowa have shown negligible deterioration despite long service lives (>75 years). These pavements were built with no entrained air, a modern method to reduce cold-weather concrete deterioration. More recent pavements (<20 years old) contain fractures within both aggregate and paste resulting in lower performance. Thirteen concrete cores from Iowa pavements spanning 15-100 years of service were collected and analyzed by image analysis (ASTM C457) and helium pycnometry. Both methods showed increasingly higher porosity in younger pavements. These cores were also subjected to computed tomography analysis that allowed us to calculate pore and grain sizes. Pores with the size and shape of coarse aggregate grains in samples >50 years old suggested that dissolution could produce a well-connected air void network through fractures in paste despite lack of air entrainment during construction. This pore network has likely permitted sufficient drainage to allow these pavements to escape significant deterioration over their service lives.