Capillary Water Absorption of Blended Portland Cement Mortar

Abstract

The tests of capillary water absorption and of the strength of the mortar of portland cement blended with (1) 20-70% of fly ash, and with (2) 20-50% of siliceous earth mined, respectively, from Yorii and Beppu districts, were carried out.The fly ash from a coal power station was used partly as it was, and partly after grinding in laboratory.The siliceous earths, sun dried, or dried at 110°C, were ground to a finer size than portland cement, and a part of which was calcined at 750°-840°C.All these materials, after passing through the respective pretreatments were subjected to the tests.The blending with fly ash gave a by far larger absorption than pure portland cement, partly because of the same mix-proportion by volume used for preparing mortar regardless of the substitution ratio, which made W/C by weight of blended cements larger.The siliceous earths, both Yorii and Beppu, showed by far smaller absorption than pure cement at the age of 4 and 5 weeks. The effect of calcination on the reduction of the absorption of blended cement was obvious in Yorii brand, while it is not clear in Beppu brand. When the blending with siliceous earth decreased the absorption of cement the ratio of absorption to evaporation (A/E) decreased with decreasing absorption, indicating that the smaller absorption does not run parallel with smaller evaporation. In other words it may be concluded that a blended portland cement will tend to dry when exposed to air. It may be said that the cements blended with Yorii or Beppu earth are suitable to use in wet surroundings.Bending strength of Yorii-earth mortar after 3 weeks was nearly the same with, or larger than that of pure cement, but its compressive strength showed less development.Calcination of Yorii earth made the strength larger. The strength of the simply dried Beppu earth at the age of 5 or 6 weeks was larger than that of pure cement. Calcination showed no good effect on the strength in the case of blending with Beppu earth.