Suitability of Fumed Lead Blast-Furnace Slag as a Mineral Admixture for Concrete

Abstract

This paper reports the findings from a laboratory evaluation of a metallurgical slag as a pozzolanic admixture for concrete. Lead blast-furnace slag is fumed in a batch process to remove base metal values after which the molten barren slag is water-quenched to produce a glassy, granular product. Chemical analysis shows the principal components of the slag to be silica, iron and calcium with lesser amounts of alumina, zinc and copper. Semi-quantitative x-ray diffraction analysis revealed the slag to be largely amorphous (>60% glass), the crystalline phases being apparently confined to mineral varieties of iron oxide and cuprite. The slag was ground to produce three samples with different Blaine fineness values and tested for compliance with the Canadian Standard for Supplementary Cementing Materials (CSA A23.5). The effect of the slag on a range of fresh and hardened concrete properties was then determined. Concrete mixtures were also cast using commercially available fly ash from a sub-bituminous coal source in Western Canada for comparison. The slag meets all the requirements of Type N, F and C materials and failed only the 45-microns sieve retention maximum of Type G. The results of concrete tests (setting time, compressive strength development, drying shrinkage and rapid chloride permeability) are very encouraging. The incorporation of slag slightly retarded the early strength gain of concrete, but after 28 days the strength of the slag concrete exceeded that of the control concretes of the same W/CM, regardless of the level of slag (in the range 20 to 40%). The strength of slag concrete was higher than that of concrete containing the same level of fly ash and the same W/CM at all ages. The coulomb ratings of the concretes containing slag were lower than those obtained on equivalent control concretes but were higher than those of the fly ash concretes. The results from these preliminary tests indicate that the lead blast-furnace slag is suitable as a pozzolanic admixture for concrete.