DR-FTIR method for the study of early hydration of cement

Paper in proceeding, 2008

A method has been developed to study early hydration reactions of ordinary Portland cement using freeze drying and Diffuse Reflectance Fourier Transform Infrared Spectroscopy (DR-FTIR). The hydration process was studied after 3 minutes up to 2 hours. The cement samples were mixed and after different hydration times the samples were placed in frozen liquid hydrogen to stop the hydration process. The samples were freeze dried under vacuum and analyzed with DR-FTIR. Measurements were also made on cement that was only dried in vacuum. The results showed that the freezing of the cement instantly stopped without any further hydration. This makes it possible to monitor chemical changes during very early hydration stages of cement by using the freeze drying combined with DR-FTIR. It was also possible to dry the samples with only vacuum, but then it was not possible to study the hydration process on a short timescale. Comparison between frozen and non-frozen samples showed that the freezing do not cause any detectable differences. This clearly indicates that the freezing do not change the chemical or physical structure of the samples to any larger extent. The freezing of the samples gave a much better time resolution and made it easier to handle the samples technically as they could be stored in the liquid nitrogen and put in the freeze drier together. The vacuum dried samples on the other hand had to be put in the drier at specified times. After a sample is put in the drier, vacuum has to be established and the sample must be sufficiently dry for the hydration to stop. This limits the time resolution of the vacuum technique in this study at best to a few minutes. The limiting time step of the freezing technique is the time for freezing the samples, which in this study was a few seconds.