Proton free induction decay evolution during hydration of white synthetic cement

Abstract

Nuclear magnetic resonance (NMR) of protons in hydratlng cement paste(l) can be employed to differentiate between protons whlch are In llquld phases, such as bulk-llke water or very fluld gel, and those embedded In rlgld structures such as crystalline water or hydroxyl groups in portlandlte, CH. As the hydratlon proceeds (2), progresslvely more of the water Inltlally added to the cllnker becomes crystalllne water and hydroxyls of CH. The total amplltude of the proton Nt4R free induction decay (FID) followlng a 90 ° r.f. excltatlon, whlch Is a measure of the total number of protons In the paste, is expected to remaln Independent of the hydratlon time provided there is no loss of water by evaporatlon. Thus, during the hydration the total proton FID amplitude does not change, as Its solld-llke component grows at the expense of its llquld-llke component. The solld-llke FID can be very easily differentiated from the llquld-llke FID as their respectlve shapes differ drastically. Whlle the solld-llke FID is Gausslan, wlth a characterlstlc decay time T on the order of 20 ~s, the llquld-llke FID Is nearly 2