Capillary Water Absorption of Portland Cement Mortar Added with Large Quantities of Blast Furnace Slag

Abstract

A series of experiments was carried out with an idea that better blast furnace cement may be produced by the combination of the portland cement of normal fineness with finer blast furnace slag. The granulated slag was ground to nearly 5000cm2/g of Blaine fineness to mix, in different ratios, with the portland cement of 3000cm2/g. Using the mixture and normal sand the specimens of 1:3 mortar of the size 40×92φmm were formed, and after water curing the water absorption under the pressure of about 3mm of H2O was measured with an apparatus of the author's own design. Similar experiments were carried out, using the slag of the fineness of about 3000, 4000 and 5000cm2/g in order to know the effect of grain size. The strength of the mortar specimens 40×40×160mm in size were also tested.The following results were obtained:(1) Blast furnace cement containing 60, 70 and 80% slag of the size of about 5000cm2/g showed the absorption as low as 3-15% of pure portland cement after the age of 2 or 3 weeks.(2) The effect of grain size on the absorption fell gradually with age.(3) The absorption decreased with the increasing fineness of slag.(4) In early ages the difference of absorption between two cements containing 3000 and 4000cm2/g slags was far larger than those between 4000 and 5000cm2/g slags.(5) The difference of absorption caused by the fineness of slag decreased with the increasing age of specimen.(6) Compared with portland cement blast furnace cement showed a smaller ratio of absorption/evaporation telling that it had a higher drying rate than pure portland cement notwithstanding the lower surface of the specimen was always in contact with water.(7) Furthermore, it was noticed that the blast furnace cement gave a larger amount of bleeding water and a smaller content of air when filled in mould.(8) The blast furnace cement of 5000cm2/g powder gave higher two weeks strength than portland cement.