Abstract
This study relates to retardation effects of some inorganic compounds on a set of cement mortar. Zinc oxide, Basic zinc carbonate, Copper（Ⅰ）oxide, Copper（Ⅱ）oxide and Basic copper carbonate were used as an inorganic set retarder. Additionally, mixtures of those compounds were tested to examine a combination effect. It was found that retardation effect of zinc compounds was bigger than that of copper compounds. The difference of retardation effect between the zinc compounds was small. And the difference of retardation effect between the copper compounds was also small. Using basic copper oxide and zinc oxide together made the retardation effect bigger than single use of zinc oxide or basic copper carbonate. Particularly, in the case of using a mixture of zinc oxide and basic copper oxide in the ratio of 2：1 by mass, setting of mortar was retarded up to about 10th day. Remixing the mortar shortened the set time, that is to say, decreased the retardation effect. Compressive strength of the mortar at the 28th day was comparable to that of plain mortar. It means those retarders do not affect on the compressive strength at such an age.
