Unsaturated Nano-Poro-Mechanics of Century-Scale Creep and Hygrothermal Deformations of Concrete

8:00 am – 9:00 am (1 hour)

Although the poromechanics of saturated materials and of unsaturated materials with capillary porosity has already been developed, a comprehensive model for unstaturated nano-poromechanics has been unavailable. Here we aim at formulating such a model based on Gibbs free energy of the solid-fluid system and on the recently derived and verified Nguyen-Rahimi-Bažant (NRB) isotherm, which corrects the BET isotherm for the effect of hindered adsorbed water in filled nanopores and extends through the capillary range up to saturation. The model is further incorporated into the recent extended micro-prestress theory and hydration model to characterize and predict a wide range of published experimental data, including 1) a complete sorption isotherm of hydrated cement paste (including the capillary range), 2) pore size distribution, 3) autogenous shrinkage, 4) drying shrinkage, swelling and creep 5) water loss or humidity change due to heating, 6) thermal expansion at various humidities, and 7) water loss of specimens caused by compression. The present model is expected to help gain insights into the deleterious moisture effects on long-time deformations, cracking damage, and fracture in concrete infrastructure and thereby indirectly lengthen their service time. Adaptations to shale and coal beds are possible with proper modification, depending on their pore size features.