Application of 1H Low-Field NMR Spectroscopy for the Determination of the Concentration and Molecule Weight of Polycarboxylate Superplasticizers

As a type of water reducer, polycarboxylate superplasticizers (PCEs) has been widely used in the concrete industry. The concentration and molecule weight of PCEs have a profound impact on the performance of fresh concrete. Based on 1H low-field nuclear magnetic resonance (NMR) spectroscopy, this paper developed a novel method for the determination of the concentration and characterization of the molecule weight of PCEs. Five types of PCEs with various ether to acid ratios (3:1 to 5:1) and functional groups were synthetized in laboratory conditions, and their molecular structures were characterized by size exclusion chromatography. PCE solutions with concentrations from 0 to 40% were measured using the Carr–Purcell–Meiboom–Gill sequence by 1H low-field NMR. The results showed that the T2 value of the main peak has a linear relation with the PCE concentration. The signal intensity of peaks whose T2 values are smaller than 10 ms of the PCE solutions with a concentration of 20% is linearly correlated to the molecule weight of PCEs.