Factors influencing the time dependence of porosity relaxation in cement during sorption: Experimental results from spatially resolved NMR

Meso-scale Modeling of Anomalous Moisture Transport in Concrete Considering Microstructural Change of Cement-based Material

“…The deviation from the linear relationship at the later stage is mainly caused by the alteration of total diffusivity in the dynamic pore structure of cement paste. This is because the large number of coarse pores, which was induced from the collapse of the C-S-H during the pre-drying process, gradually transforms into fine pores with the pore relaxation rate as evidenced by NMR data (Janota et al 2022;McDonald et al 2020). With the pore relaxation process, the penetration depth gradually deviates from the linear relationship as shown in Fig.…”

“…To quantitatively evaluate the anomalous moisture transport, this study implemented the dynamic microstructural change model that introduces the anomalous behavior based on the microstructure data investigated by Nuclear Magnetic resonance (NMR) (Gajewicz et al 2016;Janota et al 2022;Kiran et al 2020Kiran et al , 2021McDonald et al 2020). The NMR studies on liquid water uptake reported that water absorbed in pores between the C-S-H structure gradually redistributed after rewetting, then induced the change in the pore system [Fig.…”

“…Table 2 lists the moisture transport properties used for the dynamic microstructural model. For the mortar phase, although there is no NMR data representing the microstructure for the reference specimen, the pore fraction used in this study was adopted from the previous NMR studies (Janota et al 2022), which studied moisture transport in OPC. Note that the microstructural data could not be directly applied to the reference experiment regarding the differences in the w/c ratio, curing, and precondition process.…”

“…The anomalous behavior of moisture transport in concrete was reported as the consequence of various phenomena. The NMR study on the microstructure of cement paste clarified that the anomalous behavior is caused by the colloidal behavior of C-S-H (Janota et al 2022;McDonald et al 2020). Whereas the study based on fluorescence imaging reported that the rapid absorption through cracks influences anomalous behavior (Wu et al 2019).…”

“…From our previous studies, the modeling of moisture transport in cracked concrete was proposed based on a couple of numerical methods, a Rigid-Body Spring Model (RBSM) and a Truss-Network Model (TNM), that could effectively couple the mechanical behavior (e.g., volumetric change, cracking) and mass transport (moisture transport), respectively. The anomaly regarding MCCP was introduced in the TNM based on the dynamic microstructural change model (Janota et al 2022;McDonald et al 2020) and the rapid absorption through cracks was explicitly modeled based on microcracks in concrete reproduced by the RBSM. The numerical investigation on liquid water uptake in pre-dried concrete was conducted and validated based on an experiment in our research group (Ogawa et al 2023(Ogawa et al , 2024.…”