Effect of chemical activator on early hydration of the fly ash-cement system under steam curing

In this paper, the effects of calcium formate (CF) and sodium sulfate (SS) on the early compressive strength, ydration characteristic and microstructure of the fly ash-cement system were investigated and compared. by the tests of mechanical properties, XRD, DSC-TG, MIP, SEM and FTIR. Results show that both the addition of CF and SS can significantly increase the early strength of the fly ash-cement system, and the optimal mixing amounts of CF and SS are 1.5% and 2.0%, respectively; the incorporation of CF and SS can increase the hydration rate of the fly ash-cement system, promote the generation of hydration products, refine the pore structure, reduce the porosity and total pore volume, and transform harmful and very harmful pores into j less harmful and harmless pores. Moreover, the polymerization degree of Si-O tetrahedron can be increased by adding CF, while the addition of SS could only increase the C-S-H gels generation, but does not change. the polymerization degree and chain length of C-S-H. Such results can provide reference for the application of chemical activators in high volume fly ash-cement composites.