Shigemasa Hasaba

Effectiveness of Various Silica Fumes in Preventing Alkali-Silica Expansion

In order to utilize silica fume as a pozzolanic material for inhibiting alkali-silica expansion, the effect of various silica fumes on expansion of mortars containing beltane opal were investigated. Different silica fumes were found to vary widely in their effect on the expansion of mortars. The properties of silica fume affecting alkali-silica expansion were explored. Pozzolanic activity of silica fumes was evaluated by measuring the amounts of calcium hydroxide consumed by pozzolanic reaction in silica fume-bearing cement pastes. The amounts of calcium hydroxide in portland cement-silica fume mixtures were determined by dsc-tg analysis. Pore solutions obtained from mortars containing three different silica fumes were also analyzed. The silica fume with the highest pozzolanic activity was the most effective in reducing alkali-silica expansion of mortars. However, it was found that reduction in expansion by the addition of silica fume was not necessarily in line with the amount of calcium hydroxide consumed as a whole. Although the concentrations af alkalis and oh-ions in the pore solutions in mortars were reduced to the same level by the addition of three different silica fumes, the reductions in expansions of the three silica fumes-bearing mortars were greatly different from one another. (Author/TRRL)

Fundamental study on utilization of powdered basic oxygen furnace slag as a subbase material.

Recently, the basic oxygen furnace slag produced in a new steel-making process aiming at energy and resource saving is being supplied as fine particles under 5mm size because it breaks down itself due to its high content of f-CaO. In future, this type of basic oxygen furnace slag is anticipated to replace the conventional basic oxygen furnace slag.The objective of this study was to investigate the applicability of this powdered basic oxygen furnace slag as a subbase material. Firstly, the changes in physical and chemical properties, the surface texture and the hydrated products of the basic oxygen furnace slag naturally weathered outdoors. were determined by X-ray diffraction, differential thermal analysis (DTA) and SEM-EDXA analysis. Secondly, the strength test, the CBR test and the expansion test of the compacted basic oxygen furnace slag mixtures were carried out in order to clarify the strength characteristics of the powdered basic oxygen furnace slag as a subbase material and the effect of weathering outdoors on reducing its unfavorable self-deterious properties.The main results obtained are summarized as follows;(1) The major compounds of the powdered basic oxygen furnace slag were β-C2S, C2F, C2S-C3P, Wustite and a considerably large amount of f-CaO and Ca(OH)2.(2) In the powdered basic oxygen furnace slag naturally weathered outdoors, the hydration of β-C2S and f-CaO slowly progressed with age, resulting in the formation of C-S-H gel, Ca(OH)2 and CaCO3 on the surface of particles.(3) The powdered basic oxygen furnace slag became a stable material not showing self-deterious property by weathering outdoors for about three months, and thus it can be used as a subbase material.