Studies on Portland Cement Admixtures (On the properties and the industrial application of amorphous silica originated in volcanic action, XV's report)

Abstract

Five samples of silicious rocks and three samples of the residue of sulphur smelting, those may be regarded as valcanic origin, were subjected, respectively, to chemical analysis, to the determination of soluble silica, and to lime absorption test. Also the expansion test in saturated lime water as well as in distilled water have been carried out.
The residue of smelting sulphur was found to have 70% of soluble silica and 10-16% of soluble Al₂O₃ and Fe₂O₃, while the silicious rocks were composed almost exclusively, i.e. 90-95%, of soluble silica containing only the small amount of Al₂O₃.
Lime absorption of the residue of smelting sulphur showed at the first rapid, and then the very low increase, while that of the natural silicious rocks increased with rising inflection although the initial values were comparatively small. The expansion in saturated lime water run parallel with the results of the lime absorption. In distilled water, however, no change of length was observed.
Using the mixture of 90% of portland cement with 10% of the sample powder 1:2 mortar specimens were prepared by the method given in JIS R 5201. It was confirmed that the admixtures gave the very good results showing larger strength than portland cement in the 6 month's test. Especially, the residue of sulphur smelting, which contains large quantity of soluble alumina and silica may be regarded as being very promissing since it helps to develope high initial as well as long time strength.