Hydration investigation of negative temperature concrete at early age based on low-field nuclear magnetic resonance

Few control indexes and detection methods have considered the microstructure properties of negative temperature concrete. As such, construction-focused quality control of negative temperature concrete is still a problem that needs to be solved. In this paper, low-field nuclear magnetic resonance (LF-NMR) was used to monitor the in-situ distribution and dynamical variation of liquid water content in cement paste at both thawed (20 °C) and frozen (−15 °C) states. Results showed that LF-NMR could determine the optimal antifreeze dosage and pre-curing time. LF-NMR was also able to evaluate the properties of negative temperature concrete at early stages, and these properties coincided with the results of compressive strength test. Both LF-NMR and differential scanning calorimetry thermal gravimetric analysis (DSC-TGA) revealed that the main positive effect of the antifreeze on negative temperature concrete is the alleviation of frost heave stress, and not the promotion of hydration. Additionally, a theoretical hypothesis was proposed to explain the reason why concrete with low water/binder ratio is more sensitive to freezing damage at the early stages.