Moisture sorption and mechanical properties of polymer-cement waterproofing membranes investigated by LF NMR

This study investigates the impacts of environmental humidity on moisture absorption and mechanical properties of polymer-based waterproofing membranes. Membranes of polymer-CaCO₃, polymer-white cement composites and pure polymer were used for measurements after treated in different relative humidities (RHs). Results indicate that the humidity treatment greatly changes the mechanical properties of the membranes and increasing RH from 0 % to 100 % leads to reduction of tensile strength by 60–80 %, which is believed to originate from the plasticizing effect of the absorbed moisture. LF NMR (Low field NMR) enables quantification of moisture distribution in the polymer-filler composites and three types of water, i.e. the water stored inside polymer matrix (O/O water), the water located in interfacial regions between polymer phase and fillers (I/O water), and the free water in air voids are detected with increasing T₂ values. The absorbed moisture majorly accumulates in the O/O interfacial region during the humidity treatments with RH of 0∼80 %, which is because of the larger O/O interfacial area compared with the I/O interface. A large amount of free water appears only at RH of 100 %. A core-shell structure of the polymer domains with dry core and moisturized shell, is interestingly found during the moisture absorption process of the membranes, based on the LF NMR measurements using MSE sequence. It is surprisingly found that the drop of tensile strength of the membranes upon moisture absorption is majorly related to the growing shell thickness of the polymer domains whereas the moisture accumulated in the I/O interfacial region plays a minor role.