Non-destructive measurements of¹H,²³Na and³⁵Cl profiles in cementitious materials with NMR

It is widely acknowledged that chloride-induced corrosion is one of the main degradation mechanisms in civil structures based on reinforced concrete. Gaining insight into the transport phenomena can improve the assessment of durability aspects of existing structures. At the moment there is lack of experimental data on this topic that can be used to validate or discredit the wide range of models available in literature. While such models might be correct, erroneous input is bound to lead to false predictions (i.e., the garbage in, garbage out principle). Nowadays there is a wide range of non-destructive techniques available. While most of these methods are able to detect chloride content non-destructively, of them are able to measure moisture and ion transport simultaneously. For research a method that can measure combined moisture and ion profiles with high accuracy and high temporal and spatial resolution would be desired as to verify transport models. Using a specially designed Nuclear Magnetic Resonance (NMR) setup quasisimultaneously the¹H,²³Na and³⁵Cl content can be measured in cementitious materials. As the gyromagnetic ratio of the selected nuclei is too far apart to be combined into one insert we have opted to use the main field of a 1.5T whole body MRI system (Philips Intera). The sensitivity of the current setup is sufficient to monitor the intrusion of seawater in cementitious materials. The relaxation of¹H,²³Na and³⁵Cl can be used to obtain pore-size information, and thereby information on the pore-ion concentration distribution during transport. Moreover the setup has shown that by multi nuclei measurements more insight could be gained on interactions with the cement matrix. It is seen that the Na/Cl ratio changes during the hydration, indication a chemical/ physical interaction with cement matrix.