Thermokinetic Study On Hydration Of Cementitious Materials

The heat flow of hydration of Portland cement consists of the heat of hydration and its rate, which have great effects on the engineering stability of concrete, especially the one of the massive concrete. For constructions in summer, the heat of hydration will gather in concrete for a long time, making the temperature increase, even as high as 75℃in three days. Thus temperature difference and temperature stress are formed, causing concrete cracking. In order to control the temperature and the corrosion resistance, fly ash, slag and silica fume, as mineral admixtures, are used widely in the massive concrete and the engineering applications of hydraulic concrete.This paper relies on the National Key Basic Research and Development Plans (973):modern concrete gelling paste microstructure formation mechanism. In the condition of different mineral admixtures and different W/C, the property of hydration heat flow and the microcosmic morphology of C3S and Portland cement are tested and observed the trace hot test method and EEM. The hydration heat kinetics characteristics are studied according to the hydration heat curve. Major work and achievement as follow:The heat flow of hydration of C3S and Portland cement with different mineral admixtures are tested and analyzed. The influence of fly ash, slag and silica fume on the hydration heat of C3S and Portland cement are studied too. As the study shows, fly ash and slag can reduce the rate and delay the NG stage. The heat of hydration and its rate, both of C3S and Portland cement, decrease with increasing content of Silica fume in different degrees. However, Silica fume can shorten the NG stage of C3S while prolong the NG stage of Portland cement. When W/C>0.3, Qmax, the final heat of hydration of all of the experimental samples, will be a setting value and the half-life period—t50 decreases as W/C increases. Thus show that the rate increases as W/C increases.When W/C=0.35, the Krstulovic-Dabic model study shows that the dynamics process of C3S is the NG-D type at normal temperature. Fly ash can't change it. The dynamics process of C3S is yet the NG-D type when the content of slag is 20%. However, when the content of slag is 30% or 50%, the dynamics process of C3S will turn into the NG-I-D type. The effect of silica fume is similar with slag for the dynamics process of C3S. The dynamics process of C3S is the NG-D type when the cement of silica fume is 10%. But it will turn into the NG-I-D one as the cement is 15% or 20%. The dynamics process of Portland cement is the NG-I-D type. It doesn't matter whether there is fly ash or slag. The process is the NG-D type when the cement of silica fume is 10% or 15%. However it will turn into he NG-I-D one when the cement is up to 20%. Besides, the relationship of the transformation points of hydration process and the dimensionless feature size of different systems are analyzed. In this experimental condition, when there are fly ash, slag and silica fume, hydration reaction is controlled by the NG stage, with the dimensionless feature size more than 0.95. And hydration reaction is controlled by the diffusion reaction stage when the dimensionless feature size is less than 0.84.The thermal spectrum reconstruction of the heat flow of hydration of Portland cement and samples with one of fly ash, slag or silica fume, which is obtained according to Chemical thermal dynamic, show that the reconstruction curve fits the real process well.