The Effects of Hydration Retarding of Portland Cement by <tex>$MgSiF_6.6H_2O$</tex>

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J. Korean Ceram. Soc. > Volume 34(2); 1997 > Article

Journal of the Korean Ceramic Society 1997;34(2): 163.

규불화마그네슘에 의한 포틀랜드 시멘트의 수화 지연효과

한상호, 이경희, 정성철, 김남호¹

명지대학교 무기재료공학과
¹동양 중앙 연구소

The Effects of Hydration Retarding of Portland Cement by $MgSiF_6.6H_2O$

ABSTRACT

The retarding effects of MgSiF6.6H2O on the hydration of portland cement were studied. The setting time, flow value and compressive strength of mortar were measured and the mechanism of retardation was also studied by ion concentration in solution, SEM, BET, and X-ray diffraction. The results are as follows ; 1. Setting time was delayed by the addition of MgSiF6.6H2O. 2. The flow value of mortar decreases depending upon the amount of MgSiF6.6H2O. 3. The compressive strength was almost same or some increase on 28 days hydration. 4. The main retardation mechanism of MgSiF6 on the hydration of portland cement may be explained by the following hypothesis. MgSiF6 depressing the Ca++ and K+ ion concentration of cement paste solution be-cause of the recrystalization of K2SiF6 and CaF2 phase. The new products of K2SiF6 and CaF2 deposit on the surface of unhydrated cement powder and harzard the mass transfer through these layer. The low con-centration of Ca++, K+ ion in solution was decreasing the hydration rate of portland cement.

Key words: Magnesium hexafluorosilicate hexahydrate, The retarding hydration, Cement mortar