(limestone, clay, and minor amounts of iron ore and silica). Resulting pellets, known as clinker, are then milled with gypsum (CaSO 4 .5H 2 O) to form the Portland cement.Basalt is widely used as an aggregate for concrete, particularly in regions where quartz-feldspathic rocks are not available, and represents ca. 5% of the market for aggregates in Brazil [4]. Basalt quarries for aggregate production generate two types of large-scale residues: (a) quarry fines produced AbstractLarge volumes of waste materials are produced by crushing of basaltic rocks for aggregate production, which is widely used in regions that lack rocks of granitic or gneissic composition. Two types of waste materials are produced (a) quarry fines, which are in part used as fine aggregates in concrete and (b) vesicular basalt, a porous variety of basalt that is useless as aggregate. This paper presents a procedure to use basaltic mine-tailings as raw-mixtures for Portland cement by adjusting the proportion of the other rawmaterials (limestone, clay, iron ore). It is demonstrated that there is no need for additional fluxes to the basalt-bearing raw-mixtures, since the setting of the chemical parameters is enough to guarantee clinker formation. Two series of experimental clinkers were synthesized with raw-mixtures containing residues from a basalt quarry that produces aggregates for concrete. Experimental clinkers were produced from raw-mixtures with similar lime saturation factors, silica and alumina modules, which were set by adjusting the proportions of limestone, clay and iron ore to the varying proportions of basaltic materials added to them. One series of clinkers was made with basalt quarry fines, which are in part used as fine aggregate, but also accumulate as mine-tailings. Other series was made using vesicular (porous) basalt, a variety not resistant enough to be used as aggregate. It is demonstrated that the basaltic composition is fully compatible with clinker production, and no addition of fluxes or other additions is required. Composition of the raw-mixtures was checked by chemical analysis. Quantitative phase analysis of the clinkers was made by optical microscopy point counting, together with qualitative X-ray diffraction. All mixtures produced clinkers with acceptable proportions of major and minor crystalline phases, inside the range of common industrial Portland clinkers.

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The present study regards the effect of sulfur in dicalcium silicate (Ca 2 SiO 4 ), a major crystalline phase (20 to 40 wt.%) of the ordinary Portland cement clinker. Dicalcium silicate is also known as C 2 S (2CaO.SiO 2 ) or belite. The synthesis of the C 2 S samples was made with high purity reactants with addition of sulfur as CaSO 4 .2H 2 O, mixed according to the stoichiometric proportion 2Ca:(1-x)Si:xS, in which x corresponds to the cationic proportion of sulfur, with values ranging from 0 to 20%. Added amounts of SO 3 in the samples were 0.23, 1.39, 2.77, 4.60 and 9.71wt.%. Chemical composition of the samples was determined by X-ray fl uorescence before and after sintering. Large-scale sulfur loss by volatilization leads to an excess in calcium and consequently to formation of increasing amounts of tricalcium silicate with increasing sulfur content in the starting mixture. Mineralogical composition of the samples and cell parameters of C 2 S polymorphs were determined by X-ray diffraction and Rietveld refi nements. Structural analysis of diffraction data indicates that the presence of sulfur stabilizes the intermediate temperature polymorph β C 2 S, with increasing unit cell volume. The reactivity with water (heat of hydration) of the samples was measured by differential scanning calorimetry, which was strongly infl uenced by the highly reactive tricalcium silicate.

This paper presents results on the composition of Portland clinkers produced with non-conventional raw-materials and fuels, focusing on the distribution of selected trace elements. Clinkers produced with three different fuel compositions were sampled in an industrial plant, where all other parameters were kept unchanged. The fuels have chemical fingerprints, which are sulfur for petroleum coke and zinc for TDF (tire-derived fuel). Presence of carbonatite in the raw materials is indicated by high amounts of strontium and phosphorous. Electron microprobe data was used to determine occupation of structural site of both C3S and C2S, and the distribution of trace elements among clinker phases. Phosphorous occurs in similar proportions in C3S and C2S; while considering its modal abundance, C3S is its main reservoir in the clinker. Sulfur is preferentially partitioned toward C2S compared to C3S. Strontium substitutes for Ca2+ mainly in C2S and in non-silicatic phases, compared to C3S.

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