Binder Distribution in Macro‐Defect‐Free Cements: Relation between Percolative Properties and Moisture Absorption Kinetics

Macro‐defect‐free (MDF) cement is fabricated from a calcium aluminate cement and a poly(vinyl alcohol‐acetate) (PVA) copolymer. For the composites studied, it was determined that the interphase regions comprised 63 voi % of the total binder content, while the bulk PVA regions comprised 37 vol% of this phase. Mercury intrusion porosimetry showed that a bimodal pore size distribution developed as binder was removed in increasing amounts from heat‐treated samples. Larger pores with a characteristic diameter above 30 nm resulted from the removal of bulk PVA, whereas smaller pores approximately 5 nm in size resulted from the removal of water and PVA from the interphase regions. Simulation results obtained from a hard‐core/soft‐shell continuum percolation model of the MDF microstructure indicate that both the bulk PVA and interphase regions form percolative pathways through the system. Dramatic changes in both moisture absorption kinetics and flexural strength were observed only when a percolative network of larger pores was present in these composites. Hence, the bulk polymer regions are the dominant transport pathway for moisture in MDF cement. Based on this knowledge, processing guidelines have been developed to improve the moisture resistance of these materials.