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.     

Ceramic wastes as alternative raw materials for Portland cement clinker production

The cement industry has for some time been seeking procedures that would effectively reduce the high energy and environmental costs of cement manufacture. One such procedure is the use of alternative materials as partial replacements for fuel, raw materials or even clinker. The present study explores the reactivity and burnability of cement raw mixes containing fired red or white ceramic wall tile wastes and combinations of the two as alternative raw materials.The results showed that the new raw mixes containing this kind of waste to be technically viable, and to have higher reactivity and burnability than a conventional mix, providing that the particle size of the waste used is lower than 90 μm. The mineralogical composition and distribution in the experimental clinker prepared were comparable to the properties of the clinker manufactured with conventional raw materials. Due to the presence of oxides such as ZnO, ZrO₂ and B₂O₃ in tile glazing, the content of these oxides was higher in clinker made with such waste. The mix of red and white ceramic wall tile waste was found to perform equally or better than each type of waste separately, a promising indication that separation of the two would be unnecessary for the purpose described above.     

Utilization of steel slag for Portland cement clinker production

The aim of the present research work is to investigate the possibility of adding steel slag, a by-product of the conversion of iron to steel process, in the raw meal for the production of Portland cement clinker. Two samples of raw meals were prepared, one with ordinary raw materials, as a reference sample ((PC)(Ref)), and another with 10.5% steel slag ((PC)(S/S)). Both raw meals were sintered at 1450 degrees C. The results of chemical and mineralogical analyses as well as the microscopic examination showed that the use of the steel slag did not affect the mineralogical characteristics of the so produced Portland cement clinker. Furthermore, both clinkers were tested by determining the grindability, setting times, compressive strengths and soundness. 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 steel slag did not negatively affect the quality of the produced 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.     

Incorporation of waste materials into portland cement clinker synthesized from natural raw materials

For every ton of portland cement that is manufactured, approximately half a ton of carbon dioxide is released from calcining limestone. One method of reducing the carbon dioxide from portland cement production is to reduce or eliminate the use of limestone through replacement with calcium oxide-bearing waste materials. In this study, portland cement clinker was synthesized using minimal limestone content and maximal waste material content, specifically fly ash and blast furnace slag. The synthetic cements were characterized using X-ray diffraction, scanning electron microscopy, and isothermal calorimetry. Results show that portland cement clinker can be successfully synthesized from a maximam of 27.5% fly ash and 35% slag. The synthetic cements possessed early-age hydration behavior similar to a commercial Type I/II portland cement. However, the presence of sulfur impurities contained in waste materials significantly affected phase formation in portland cement clinker.

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Dredged sediments used as novel supply of raw material to produce Portland cement clinker

The maintenance of waterways generates large amounts of dredged sediments that are an environmental issue. This paper focuses on the use of fluvial sediment to replace a portion of the raw materials of Portland cement clinker, which would otherwise come from natural resources. The mineralogy of the synthetic cement was characterised using X-ray diffraction and scanning electron microscopy and its reactivity was followed by isothermal calorimetry. Comparisons were made to a commercial ordinary Portland cement (CEM I 52.5). Compressive strength measurements were conducted on cement pastes at 1, 2, 4, 7, 14, 28 and 56 days to study strength development. The results showed that Portland cement clinker can be successfully synthesised by using up to 39% sediment. The compressive strengths developed by the cement made from sediment were equivalent to those obtained with the reference at early ages and 20% higher at long term.     

Examination of grinding techniques for the reuse of by-products of cement production

The purpose of the letter is to explore an effective way to substantially utilize by-product of cement production by developing an environmentally friendly, sufficiently performing, and cost-effective cementitious product for future concrete materials. The study involves properly blending fly ash with cement kiln dust to create a cementitious material in which the material deficiencies will be converted into benefits. The activation process chosen, in order to facilitate and enhance hydration of the two materials, is mechanical grinding. Properties are determined through the use of heat of hydration test, particle size test and compressive test. The results show that such a material is feasible with additional study.     

Contribution of limestone to the hydration of calcium sulfoaluminate cement

Calcium sulfoaluminate (CSA) cements can be blended with mineral additions such as limestone for properties and cost optimization. This study investigates the contribution of limestone to the hydration of a commercial CSA clinker regarding the hydration kinetics, hydrate assemblage and compressive strength. Nine formulations were defined at M-values of 0, 1.1 and 2.1 (M = molar ratio of anhydrite to ye’elimite) without and with medium and high limestone contents.Calorimetric results indicate that limestone accelerates the hydration reaction especially at M = 1.1, probably due to the filler effect. The phase assemblages were calculated by thermodynamic modeling using Gibbs Energy Minimization Software (GEMS). With increasing limestone content the formation of ettringite and calcium monocarboaluminate is predicted at the expense of calcium monosulfoaluminate. With increasing M-value more ettringite is predicted at the expense of the monocarbonate and less calcite takes part in the hydration reactions.The modeled results compare well with the experimental data after 90 d of hydration, except that calcium hemicarboaluminate was found instead of monocarbonate, which is assumed to be due to kinetics considerations.The lowest compressive strength occurs in ternary formulations, whereas in the absence of calcium sulfate, strength is significantly higher.The results presented here indicate that in CSA cements, limestone accelerates early hydration kinetics, takes part in the hydration reactions at M < 2, and has a positive effect on strength development in systems without anhydrite.     

Reuse of water purification sludge as raw material in cement production

The feasibility of partial replacement of siliceous raw material for cement production with water purification sludge (WPS) was investigated by X-ray diffraction, free-lime analysis, compressive strength testing and toxicity characteristics leaching procedure (TCLP). It is found that WPS has no negative effects on the consumption of free lime and the formation of clinker minerals. The samples with WPS from 4 to 10 wt.% have higher 3 days and 7 days strengths than the control. After 28 days, however, only WPS replacements <7% increased the strength of samples. It is noteworthy that heavy metals in WPS were almost completely incorporated into the clinkers, and up to 28 days the heavy metals were not detected in the leachates. From the above results of clinker minerals, compressive strength and leaching tests, it can be concluded that WPS has the potential to be utilized as an alternative raw material in cement production.     

Rheological and hydration characterization of calcium sulfoaluminate cement pastes

Calcium sulfoaluminate (CSA) cements are currently receiving a lot of attention because their manufacture produces less CO₂ than ordinary Portland cement (OPC). However, it is essential to understand all parameters which may affect the hydration processes. This work deals with the study of the effect of several parameters, such as superplasticizer (SP), gypsum contents (10, 20 and 30 wt.%) and w/c ratio (0.4 and 0.5), on the properties of CSA pastes during early hydration. This characterization has been performed through rheological studies, Rietveld quantitative phase analysis of measured X-ray diffraction patterns, thermal analysis and mercury porosimetry for pastes, and by compressive strength measurements for mortars. The effect of the used SP on the rheological properties has been established. Its addition makes little difference to the amount of ettringite formed but strongly decreases the large pore fraction in the pastes. Furthermore, the SP role on compressive strength is variable, as it increases the values for mortars containing 30 wt.% gypsum but decreases the strengths for mortars containing 10 wt.% gypsum.     

Micro-mechanical properties of calcium sulfoaluminate cement and the correlation with microstructures

To investigate the micro-mechanical properties of calcium sulfoaluminate cement and the correlation with the microstructures, we apply a variety of advanced techniques of microstructural and micro-mechanical characterization, including scanning electron microscopy with backscattered electron and energy-dispersive X-ray spectroscopy detectors, X-ray fluorescence, X-ray diffraction and nanoindentation. For the first time, the micro-mechanical properties of material microstructures present in a calcium sulfoaluminate cement are estimated. In the calcium sulfoaluminate cement used in this research, two type of hydration product microstructures with the differentiable microstructural morphologies, compositions and micro-mechanical properties are identified and investigated. The correlation of the micro-mechanical properties with the microstructures shows that the hydration product microstructure containing more ettringite has lower indentation modulus and hardness than that containing more aluminum hydroxide.     

Waste ammunition as secondary mineralizing raw material in Portland cement production

This paper presents a laboratory scale simulation that aims to investigate the possibility of partially substituting ordinary cement raw mix with waste ammunition materials (WAM), originated from a shooting range in Athens, Greece, in Portland cement clinker production. One reference and twelve modified mixtures, containing 0.5%, 1.0%, 1.5% and 2.0% w/w of three blends of corresponding types of waste ammunition materials, were examined. It was concluded that the three used WAM blends, improve remarkably the burnability of the cement raw mixture, even though in a different extent, without affecting considerably the hydration rate and the cement properties. In spite of the high volatile matter in the WAM, primarily due to high levels of lead present, incorporation degree of the heavy metals present in the WAM blends in the mineralogical clinker compounds was rather high during the sintering process. Leaching tests showed that the heavy metal concentrations in the leachates were kept low.     

An alternative to Portland Cement for waste encapsulation--the calcium sulfoaluminate cement system

Currently, Portland Cement (PC) is used extensively in the solidification/stabilisation of a wide variety of wastes. In the nuclear industry, low and intermediate level radioactive wastes are encapsulated or immobilised within composite PC cement systems based on high replacement with blast furnace slag or fly ash. However, the high alkalinity of these PC-based systems will corrode reactive metals found in some wastes releasing hydrogen and forming expansive corrosion products. Alternative cement systems could provide a different hydration chemistry, which would allow wastes containing these metals to be encapsulated with lower reactivity. Calcium sulfoaluminate (CS A) cement is one such cement. It combines economy of cost and low emission of CO(2) with rapid strength gain and compatibility with other construction materials. Hydration provides an internal pore solution where the pH is considerably lower than that of PC. The main hydration product, ettringite, can incorporate a number of ions into its crystal structure, making it an ideal candidate for waste immobilisation. This paper details some results from a commercial CS A system that examines aspects of mixing, hydration of different formulations and aluminium corrosion behaviour. The fluidity of mixes can be adjusted by changing the formulations. All designed mixes were set within 24 h with little bleeding and the pH values were in the range of 10-11.5. In addition, a significant reduction in Al corrosion was observed compared to a composite OPC system. Although these results provide encouragement for the idea that CS A cement can provide a possible alternative to PC in the immobilisation of difficult and reactive wastes, further investigation is needed.     

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.     

CCD比色测温系统在水泥篦冷机中的应用

本文介绍一种基于CCD比色法的水泥篦冷机熟料温度场测量系统。详细论述了该系统的测温原理和系统结构，分析系统参数的选择原则。通过实验测定，结果表明，该测量系统可以测量篦冷机熟料温度场的分布，满足篦冷机熟料温度场测量要求。     

Investigation into the stabilization/solidification performance of Portland cement through cement clinker phases

This research studied the influence of individual heavy metal on the hydration reactions of major cement clinker phases in order to investigate the performance of cement based stabilization/solidification (S/S) system. Tricalcium silicate (C3S) and tricalcium aluminate (C3A) had been mixed with individual heavy metal hydroxide including Zn(OH)2, Pb(OH)2 and Cu(OH)2, respectively. The influences of these heavy metal hydroxides on the hydration of C3S and C3A have been characterized by X-ray diffraction (XRD) and differential scanning calorimetry-thermogravimetry (DSC-TG). A mixture of Zn(OH)2, Pb(OH)2 and Cu(OH)2 was blended with Portland cement (PC) and evaluated through compressive strength and dynamic leach test. XRD and DSC-TG data show that all the heavy metal hydroxides (Zn(OH)2, Pb(OH)2 and Cu(OH)2) have detrimental effects on the hydration of C3A, but only Zn(OH)2 does to the C3S at early curing ages which can completely inhibit the hydration of C3S due to the formation of CaO(Zn(OH)2).2H2O. Cu6Al2O8CO(3).12H2O, Pb2Al4O4(CO3)(4).7H2O and Zn6Al2O8CO(3).12H2O are formed in all the samples containing C3A in the presence of metal hydroxides. After adding CaSO4 into C3A, the detrimental effect of heavy metals increases due to the coating effect of both calcium aluminate sulphates and heavy metal aluminate carbonates. The influence of heavy metal hydroxide on the hydration of C3S and C3A can be used to predict the S/S performance of Portland cement.     

Use of sulfoaluminate cement and bottom ash in the solidification/stabilization of galvanic sludge

Solidification/stabilization (S/S) process can improve the physical characteristics of wastes, reduce their leaching and limit the solubility of their heavy metals. The identification of binders able to assume the fixation of contaminants is essential for the success of the technique. In this study, calcium sulfoaluminate cement was added to another waste, bottom ash, in order to treat galvanic sludge. The properties of the resultant solid matrix (MS) were determined: setting time, compressive strength and products of hydration. Solid matrix composed of 77% waste and only 23% cement presented initial setting time lower than 4 h and 28 day-strength of 6 MPa. SEM investigations showed that contaminants present in the galvanic sludge (Cr) were encapsulated in the hydrated phases and particles of bottom ash.     

Influence of polyether polyol on the hydration and engineering properties of calcium sulfoaluminate cement

The aim of the present paper was to investigate the efficiency of polyether polyol as shrinkage-reducing admixture on pastes and mortars prepared with calcium sulfoaluminate cement (CSA). CSA was prepared by mixing CSA clinker and re-crystallized gypsum in different proportions. Three types of polyether polyol were added at a dosage of 1.5 wt% of CSA when hydrating pure pastes and standard mortars. The engineering properties of mortars (compressive strength, drying shrinkage) and the microstructure of pastes were investigated. The results show that polyol reduces drying shrinkage of CSA-based mortars without affecting the nature of hydrates formed. The effect of polyol mainly depends on its molecular weight.