QUANTIFICATION OF AN INTERMEDIATE PHASE DURING HYDRATION OF CEMENT

Abstract

This paper investigates the intermediate phase（IP）existing as the precursor for the Calcium Silicate Hydrate（C-S-H）, that is the main component and directly affects physical properties of cementitious materials. Although many researches in connection with cement hydration have been carried out, most of them focus on not formation of C-S-H but the dissolution of cementitious minerals. Previous researches showed that the structure of C-S-H is not formed as soon as dissolution of cementitious minerals, dissolved sementitious minerals once become IP as the precursor for the C-S-H and they transpose to C-S-H gradually. It also reported that IP remains even long aged cementitious materials. Therefore transition of IP needs to be considered quantitatively and qualitatively. Bellmann et. al^5） already proposed the method to measure the amount of IP by using ¹H-²⁹Si CP MAS-NMR, but it requires more than 3 weeks to measure only one sample. Thus, it is needed to establish a simplified method for quantification of IP. In this research, three procedures were performed to establish a simplified method and to measure transition of IP；First, the dissolution degrees of cementitious minerals were measured by X-Ray Diffraction（XRD）/Rietveld analysis. Second, the polymerization degrees of silicates were measured by ²⁹Si MAS-NMR. Finally, the amounts of IP were quantified by the difference of the dissolution and polymerization degrees. ²⁹Si MAS-NMR requires about 20 hours to measure one sample which is about only 3％ of measuring time of previous method. As the result, after mixing water and cement, the amount of IP increased with the hydration. The amount of HM reached up to 30％ of all silicate anions when the dissolution degree of calcium silicates was 40％. However, even in the long period, about 5％ of HM still existed. The temperature dependencies of the IP hydration were also discussed. The amount of IP for the sample curing at higher temperature was less than other temperatures, because the curing at higher temperature promoted the phase transition from IP to C-S-H in the short period. However the C-S-H hydrated at higher temperature might form denser structure and it prevented the hydration on the long period. It might be possible to promote the hydration by curing at appropriate temperature and maintaining more amount of HM.