PORE CONNECTIVITY IN AIR VOID SYSTEM OF MODERN AND DECADES OLD IOWA PAVEMENTS

Air void system in Iowa Portland Cement Concrete samples contain can entrained and naturally formed pore networks. Five pre-1950s samples (that contain no entrained air) and eight post-1950s samples (that contain entrained air) were analyzed using mercury porosimetry and thin sections to understand the difference in entrained and naturally formed air void systems that affect the pavement service life. Helium porosity of post-1950s samples was 4 percentage points higher than the pre-1950s samples. 2D thin-section images showed similar porosity (approximately 3 percentage points lower than helium data). Mercury intrusion data shows three modes of pore-throat size distributions in all samples that are correlated with entrained, intergranular air, aggregate dissolution pores, and micropores in the paste. Thin-section images showed the same phases of pore throat size distributions as well as fractures in the paste. Thin-section pores were characterized as circumgranular, coalescent, and moldic. Fractures in post-1950s were characterized as open or closed based on blue epoxy intrusion in the void space. Large pores formed due to aggregate dissolution were connected through fractures and microporosity in the pastes. This complex air void network consisting of entrained and naturally formed pore networks can affect service lives in post-1950s pavements.