Use of secondary mineralizing raw materials in cement production. A case study of a wolframite–stibnite ore

It has been found that certain foreign elements, despite their low concentration in cement raw mix, improve the reactivity of the cement raw mix. The aim of this research is to investigate the possibility of introducing small amounts of minerals, containing these elements, into the cement raw mix. A stibnite–wolframite mineral was selected in order to introduce W, Sb and S in the cement raw mix. One reference mixture and four modified mixtures, containing 0.5%, 1.0%, 1.5% and 2.0% w/w of the above mineral, were examined. The reactivity of the mixture, the sintering reactions, and the structure of the products were studied. In addition, the hydration rate and some typical properties of cements, produced from the modified clinkers, were measured. It was concluded that the added mineral improves the burnability of the cement raw mixture without affecting significantly the hydration rate and the cement properties.     

Incorporation of coal combustion residuals into calcium sulfoaluminate-belite cement clinkers

In recent years, calcium sulfoaluminate-belite (CSAB) cement has been promoted as a sustainable alternative to Portland cement due to lower energy used and less CO₂ emitted during production, while providing comparable performance. However, a potential problem facing the widespread adoption and production of CSAB cement is the cost and availability of raw materials and it is therefore desirable to find alternative raw materials to keep costs competitive. In this study, two CSAB cement clinkers with a similar target phase composition were synthesized from combinations of natural and waste materials (coal combustion residuals). The two CSAB cement clinkers were compared against a CSAB clinker made from reagent-grade chemicals, enabling examination of the effects of impurities on performance. Cements made from the clinkers were examined for hydration rate, hydration product formation, dimensional stability, and compressive strength.     

Rheological behaviour of hydraulic lime-based grouts. Shear-time and temperature dependence

This paper deals with the coupled effect of temperature and fly ash (FA) addition on rheological behaviour of natural hydraulic lime (NHL5) based grouts, currently used in masonry consolidation. The use of a grout injection technique for masonry consolidation may lead to an increase of hydrostatic pressure and lead to structural damage. This means that the thixotropic effects become self-evident in grout design. It was shown that there is a relation between the structuration rate of each grout and the pressure that occurs inside masonry during its consolidation. According to the results, it seems also that there is a grout threshold temperature (T _limit) that separates a domain where the grout build-up structure area is almost constant, from another where flocculation area starts to increase significantly. We believe that in the first region the thixotropic effects are almost isolated from the irreversible effects (due to hydration). For the NHL5 based grout T _limit=20 °C and for the grout with NHL5+15 % of FA T _limit=15 °C. Grouts’ characterization based on maximum resisting time, structuration rate and on the analysis of the hydraulic lime grout behaviour tested at different shear rates was performed using a shear thinning model and assuming that the structure is shear- and time-dependent. The goal is to use this methodology during mix proportioning and design for masonry injection purpose. The tested grout compositions were optimized compositions obtained in previous research using the design of experiments method.     

Synthesis,characterization and properties of calcium ferroaluminate belite cements produced with electric arc furnace steel slag as raw material

This study investigated the use of 10 (M1), 17 (M2) and 27 wt.% (M3) electric arc furnace steel slag (EAFS) as a raw material in the production of calcium ferroaluminate belite cement clinker, after firing at 1320 °C. The thermal behavior of the raw meals was studied by TG/DSC and XRD whereas for the analysis of the clinkers, XRD/QXRD, SEM/EDS and EPMA were employed. The resulting clinker was co-grinded with 5 and 20 wt.% Flue Gas Desulfurization (FGD) gypsum and the properties were determined by a series of tests in accordance to EN standards. The evolution of hydration was investigated by SEM and the development of compressive strength. The results revealed that the formed phases in the clinkers were C₂S, C₄AF and C₄A₃Ŝ. The main hydration products were ettringite, AFm and hydrogarnet. The leached Cr^VI was below 1 ppm in M3. Compressive strength in cements with 5 wt.% FGD gypsum was (in MPa): 18.3 for M1, 14.3 for M2 and 7.8 for M3 at 28 days, whereas for 20 wt.% FGD gypsum, the values were almost doubled.     

Preparation of alinite cement from municipal solid waste incineration fly ash

The feasibility of partially substituting ordinary raw materials with municipal solid waste incineration (MSWI) fly ash in alinite cement production was investigated by X-ray diffraction (XRD), X-ray fluorescence spectrometry (XRF) and scanning electron microscopy (SEM). The physical properties and leaching behavior of the produced cement were also evaluated. Experimental results show that good quality clinkers can be obtained by firing the raw mixes, in which the replacement of MSWI fly ash reaches to 30%, at 1200 °C for 2 h. Alinite cements have higher early strengths at all gypsum additions, while the best result having acceptable early and 28-day strengths is obtained at 5% of gypsum addition. Results also show that the leaching toxicity of heavy metals is far lower than that of the regulatory limit at all testing ages. Based on this study, MSWI fly ash is viable as an effective, alternative raw material in alinite cement production.     

Use of recycled glass as a raw material in the manufacture of Portland cement

Scrap glass is a solid waste from daily recycling. Most of the waste glass is sodium-lime-silicate glass which has, more or less, similar chemical compositions to clay, a raw material in cement manufacturing. Therefore, we utilize the solid waste in cement raw mix by replacing part of the clayey component. In this study, the effects of the glass in cement raw mix on clinker burning were investigated. The experimental results show that the addition of the glass into cement raw mix (1) results in the formation of more liquid phase between 950°C to 1250°C compared with conventional raw meals; (2) decreases C₃S content in the clinker; and (3) increases NC₈A₃ content, which leads to flash setting and poor strength development of the cement. Therefore, it is necessary to increase the SG value [SG=SO₃?100%/(1.292 K₂O+0.85 Na₂O)] of the clinker when the glass is present in the raw mix.     

Effect of boron waste and boric acid addition on the production of low energy belite cement

The effect of boron oxide addition on the production of low energy belite cements has been investigated. Three types of clinkers were prepared with 1.5 wt.% (BC_BA1.5) boric acid, and 1.0 wt.% (BC_BW1) and 6.5 wt.% (BC_BW6.5) boron waste addition. The design of the raw mixtures was based on modified Bogue equations. According to the free lime content and the evolution of the microstructure of the clinkers, firing was performed at 1330 °C, 1350 °C and 1310 °C for BC_BA1.5, BC_BW1 and BC_BW6.5, respectively. Boron addition favored the reduction of the clinkering temperature as well as the stabilization of upper belite polymorphs. According to the present results, late compressive strength development of belite cements depends mainly on the crystal type rather than on the content of belite in the clinker. The results indicate that controlled quantities of boron oxide can be beneficial in the production of belite cement.     

Waste with chrome in the Portland cement clinker production

Hazardous wastes, coming from industries are usually used in the Portland cement production in order to save energy, costs and/or stabilize toxic substances and heavy metals inside the clinker. This work focuses on the effect produced on the Portland cement clinker when it is obtained using tanned leather shavings whit chrome salts as part of the process. The raw materials were clinkered in laboratory with different percentages of shavings, which contained 2% of Cr(2)O(3). DTA-TG of the raw mixtures was performed to evaluate the thermal behavior changes that can take place during the clinkering process, analyzing the crystalline phases obtained by XRD. The milling behavior of clinkers was studied, analyzing also the refractoriness variation on those clinkers. The chrome retention was evaluated by leaching tests. The structural modification determined by the chrome presence in the silicate structure brought consequences in the hydration speed, mechanical resistance and pore distribution.     

Synthesis and hydration of calcium sulfoaluminate-belite cements with varied phase compositions

The production of portland cement is energy intensive and contributes significantly to greenhouse gas emissions. One method of reducing the environmental impact of concrete production is the use of an alternative binder, such as calcium sulfoaluminate-belite (CSAB) cement. The relatively low lime requirement of CSAB cement compared to portland cement reduces energy consumption and carbon dioxide emissions from cement production. Moreover, CSAB cement can be produced at temperatures approximately 200 °C lower than portland cement, further reducing energy and carbon dioxide. Major drawbacks to the implementation of CSAB cements are the lack of standard phase composition and published data on composition-processing-performance relationships. In this study, three CSAB cement clinkers with different phase compositions were synthesized from reagent-grade chemicals. The synthetic clinkers were analyzed for phase composition using X-ray diffraction and phase distribution using scanning electron microscopy. The synthetic clinkers were then tested for hydration rate using isothermal conduction calorimetry to investigate the effects of phase composition and gypsum addition on early-age hydration behavior. A proportioning method for predicting phase composition was refined and an equation for calculating the minimum gypsum content for CSAB cement clinker was developed.     

Red mud addition in the raw meal for the production of Portland cement clinker

The aim of the present research work was to investigate the possibility of adding red mud, an alkaline leaching waste, which is obtained from bauxite during the Bayer process for alumina production, in the raw meal for the production of Portland cement clinker. For that reason, two samples of raw meals were prepared: one with ordinary raw materials, as a reference sample ((PC)Ref), and another with 3.5% red mud ((PC)R/M). The effect on the reactivity of the raw mix was evaluated on the basis of the unreacted lime content in samples sintered at 1350, 1400 and 1450 degrees C. Subsequently, the clinkers were produced by sintering the two raw meals at 1450 degrees C. The results of chemical and mineralogical analyses as well as the microscopic examination showed that the use of the red mud did not affect the mineralogical characteristics of the so produced Portland cement clinker. Furthermore, both clinkers were tested by determining the grindability, setting time, compressive strength and expansibility. The hydration products were examined by XRD analysis at 2, 7, 28 and 90 days. The results of the physico-mechanical tests showed that the addition of the red mud did not negatively affect the quality of the produced cement.     

Effects of porosity and related interstitial phase morphology difference on the grindability of clinkers

The effects of regional clinker porosity and interstitial phase morphology differences on grindability of clinkers have been investigated within the scope of this study. Porosity and phase characteristics of two clinkers from different furnaces which are using the same raw materials were determined by the application of image processing techniques on SEM images of polished surfaces. Comparison of interstitial phase compositions of two clinkers showed that, clinkers with similar phase compositions may have different grindability due to the porosity and phase morphology differences. Porous clinkers usually exhibit a dendritic interstitial phase morphology with an improved grindability. Increasing porosity also leads to greater incidence of the dendritic morphology in porous regions and lower incidence of alkali in the aluminate in dendritic regions.     

Belite cements obtained from ceramic wastes and the mineral pair CaF2/CaSO4

The cement industry is seeking alternative approaches to reduce the high energy and environmental costs of Portland cement manufacture. One such alternative is belite cement. In the present study clinkers with high (36–60%) belite contents were obtained at 1350 °C from raw mixes consisting of ceramic waste and the fluxing/mineralised pair CaF₂/CaSO₄. The factors found to affect the mineralogical composition and the clinker phase polymorphs obtained were the lime saturation factor (LSF), the presence of ceramic waste and the addition of CaF₂ and CaSO₄.The reactivity of these belite clinkers with water was analysed with isothermal conduction calorimetry. A statistical study was then conducted on the findings to determine the effect of each variable when the response signals were peak heat flow rate and the time needed to reach that peak. The statistical analysis identified the optimal experimental conditions to be a LSF of 90%, a CaSO₄ content of 2.60%, and the absence of both ceramic waste and CaF₂.     

Statistical relationship between mix properties and the interfacial transition zone around embedded rebar

The relationship between concrete mix properties and the properties of the interfacial transition zone (ITZ) formed around embedded rebar was investigated. Multiple samples of various mix compositions and bar orientations were prepared so as to represent common concrete technology. Water-to-cement ratios varied from 0.40 to 0.65 and powder (cement + limestone filler) contents ranged from 362 kg/m³ to 564 kg/m³. Over 1300 BSE images of the steel–concrete interface were taken and analyzed automatically. Statistical methods were used to identify correlations between ITZ properties and mix composition or fresh mix properties.A single large void was identified beneath all horizontal bars regardless of concrete composition. The ITZ around vertical bars was more uniform and extended around the entire rebar. No clear relationship was found between ITZ thickness and mix composition or fresh mix properties for either vertical or horizontal bar orientations. The degree of ITZ variability beneath horizontal bars clearly depends, however, on the bleeding properties of the mix. The distance from steel surface to the closest concrete solid, which influences the chemistry over the surface of the steel, is affected by precipitation of hydration products in horizontal bars, but not by mix composition.     

Low-firing binders from magnesium containing carbonate raw materials

This paper presents scientific and experimental data for low-firing hydraulic binders: hydraulic lime and Roman cement based on local mineral raw materials. The binders were prepared by firing representative samples of carbonate–clay magnesian raw materials from Tatarstan. Using X-ray diffraction, we identified the firing products, including a hydraulically active phase, and determined the structural characteristics of its minerals. The compositions of the binders were determined as functions of firing conditions. We examined the influence of the firing temperature and duration of magnesian raw materials in the preparation of binders on MgO activity and demonstrated for the first time the possibility of ensuring an active state of the MgO resulting from firing (up to 21%) and suppressing its negative effect on Roman cement and hydraulic lime hardening processes.     

Clinkers and cements obtained from raw mix containing ceramic waste as a raw material. Characterization,hydration and leaching studies

A clinker and a cement obtained from a raw mix containing ceramic waste as an alternative raw material were characterized in the present study. Their hydration, physical–chemical properties and leaching behaviour in different acid media were also explored. The findings showed that both the clinker and the cement met all the requirements set out in European standards EN 197-1 [1], although they had higher ZnO, ZrO₂, and B₂O₃ contents than an industrially produced reference product.According to the hydration studies, initial hydration was somewhat retarded in the new cement, which exhibited longer initial and final setting times and lower 2-day mechanical strength. The SEM/BSE/EDS microstructural study showed, however, that morphologically and compositionally, the hydration products formed were comparable to unadditioned Portland cement paste products. While low concentrations of Zn and B were observed to leach in acid media, the biotoxicity trials conducted confirmed that these concentrations were not toxic. Zr was retained in the cement pastes.     

Utilization of flotation wastes of copper slag as raw material in cement production

Copper slag wastes, even if treated via processes such as flotation for metal recovery, still contain heavy metals with hazardous properties posing environmental risks for disposal. This study reports the potential use of flotation waste of a copper slag (FWCS) as iron source in the production of Portland cement clinker. The FWCS appears a suitable raw material as iron source containing >59% Fe(2)O(3) mainly in the form of fayalite (Fe(2)SiO(4)) and magnetite (Fe(3)O(4)). The clinker products obtained using the FWCS from the industrial scale trial operations over a 4-month period were characterised for the conformity of its chemical composition and the physico-mechanical performance of the resultant cement products was evaluated. The data collected for the clinker products produced using an iron ore, which is currently used as the cement raw material were also included for comparison. The results have shown that the chemical compositions of all the clinker products including those of FWCS are typical of a Portland cement clinker. The mechanical performance of the standard mortars prepared from the FWCS clinkers were found to be similar to those from the iron ore clinkers with the desired specifications for the industrial cements e.g. CEM I type cements. Furthermore, the leachability tests (TCLP and SPLP) have revealed that the mortar samples obtained from the FWCS clinkers present no environmental problems while the FWCS could act as the potential source of heavy metal contamination. These findings suggest that flotation wastes of copper slag (FWCS) can be readily utilised as cement raw material due to its availability in large quantities at low cost with the further significant benefits for waste management/environmental practices of the FWCS and the reduced production and processing costs for cement raw materials.     

Hydration of tricalcium germanate

The hydration characteristics of tricalcium germanate were examined. Kinetics of tricalcium germanate hydration, and hydration product morphologies and compositions were determined at 5 °C intervals between 5 and 70 °C. Complete hydration was rapidly achieved, X-ray diffraction indicated that tricalcium germanate reacted completely within 2 h at all the temperatures investigated. However, a constant value for an Arrhenius activation energy could not be determined. At hydration temperatures above 45 °C a small heat peak, which preceded the main calorimetric peak, appeared in the calorimetric curves. Calcium hydroxide was rarely observed by SEM for hydration at temperatures below 45 °C. Dense regions of calcium hydroxide were readily observed for hydration above this temperature. In contrast to the hydration of tricalcium silicate, an induction period was not observed nor was an extended period of diffusionally controlled reaction. Calcium germanate hydrate was fibrous with the fibre thickness exhibiting a temperature dependence. Hydration product compositions were determined by thermal gravimetry. Expressing the composition of calcium germanate hydrate as (CaO)_3–x GeO₂·nH₂O, the value of 3–x decreases from 1.68 to 1.59 with increasing temperature from 5–70 °C. The values obtained forn varied inconsistently between 2.4 and 3.3. The unit cell of the calcium germanate hydrate was determined to be monoclinic. Cell parameters werea=1.851,b=1.147,c=0.531 nm and =98.10 °.     

Directed synthesis of alkaline aluminosilicate minerals in a geocement matrix

Geocements were created in accordance with a hypothesis put forward by Prof. V. Glukhovsky that the structure formation processes in the alkaline aluminosilicate binders corresponded to geological transformations of aluminosilicate minerals taking place in nature. At low temperatures, a type of hydration products depends on curing conditions and mix composition. An autoclave curing allows for an intensive synthesis of a well-crystallized zeolite structure, whereas other types of curing result in the formation of an amorphous structure with crystalline inclusions represented mainly by hydroxysodalite. On the contrary to this, after curing at high temperatures, a formation of nepheline, albite or α-cristobalite depends exclusively on the firing temperature and initial geocement composition. Mechanical strength of the geocements may reach 88.5 MPa after low temperature curing and 88.7 MPa after firing at 800 °C. Optimal thermo-mechanical properties of the metakaolin- and fly ash-based geocements may be reached in compositions with a microstructure represented by an average amount of thermostable zeolites, since just these phases are characterized by a smooth dehydration and subsequent re-crystallization into stable anhydrous alkaline aluminosilicates without destruction of a framework. Directed regulation of structure formation at low temperatures is a key question in obtaining a wide range of special materials such as acid-resistant, high-strength, quick hardening, with low leach rates, high adhesion, etc. At the same time, a structure formation at high temperatures is important with regard to creation of heat- and fire-resistant composite materials. Synthesis of analogies to natural aluminosilicate minerals ensures also high durability.     

Thermal Characterization of PZT Ceramics Obtained by Mechanically Activated Mixed Oxides Using Different Pb Sources

In this study, three sets of PZT samples with compositions 57/43 and 55/45 (rhombohedral phase), 53/47 and 51/49 (tetragonal phase) prepared by mechanochemical activation of powder mixtures (during 4?h of milling) and thermal treatment (sintered at 1200?°C for 4?h) were thermally characterized. The three sets of compositions were prepared using different Pb sources (A-PbO, B-PbO₂, and C-Pb₃O₄). The thermal characterization of sintered samples was carried out by photoacoustic spectroscopy and differential scanning calorimetry, to obtain the thermal diffusivity and specific heat (c _p ). The DSC thermograms also allowed the determination of the Curie temperature, and the thermal conductivity was calculated combining the results of the thermal diffusivity, specific heat, and density. The samples obtained with Pb₃O₄ showed a theoretical density higher than 95?%, whereas those obtained from PbO₂ precursors showed a lower densification rate (around 89?%). The samples obtained with Pb₃O₄ with compositions 53/47 and 51/49 also showed the highest values of thermal diffusivity (7.3 ± 0.4)?× 10^?7m²· s^?1 and (6.6 ± 0.3)?× 10^?7m²· s^?1, respectively.     

Potential use of pyrite cinders as raw material in cement production: Results of industrial scale trial operations

Pyrite cinders, which are the waste products of sulphuric acid manufacturing plants, contain hazardous heavy metals with potential environmental risks for disposal. In this study, the potential use of pyrite cinders (PyCs) as iron source in the production of Portland cement clinker was demonstrated at the industrial scale. The chemical and mineralogical analyses of the PyC sample used in this study have revealed that it is essentially a suitable raw material for use as iron source since it contains >87% Fe₂O₃ mainly in the form of hematite (Fe₂O₃) and magnetite (Fe₃O₄). The samples of the clinkers produced from PyC in the industrial scale trial operation of 6 months were tested for the conformity of their chemical composition and the physico-mechanical performance of the resultant cement products. The data were compared with the clinker products of the iron ore, which is used as the raw material for the production Portland cement clinker in the plant. The chemical compositions of all the clinker products of PyC appeared to conform to those of the iron ore clinker, and hence, a Portland cement clinker. The mechanical performance of the mortars prepared from the PyC clinker was found to be consistent with those of the industrial cements e.g. CEM I type cements. It can be inferred from the leachability tests (TCLP and SPLP) that PyC could be a potential source of heavy metal pollution while the mortar samples obtained from the PyC clinkers present no environmental problems. These findings suggest that the waste pyrite cinders can be readily used as iron source for the production of Portland cement. The availability of PyC in large quantities at low cost provides further significant benefits for the management/environmental practices of these wastes and for the reduction of mining and processing costs of cement raw materials.