Clinker Minerals Research Articles

Study on Integral Utilization of Alkaline Slag and Fly Ash

The compressive strength of the cementitious materials doubly with alkaline slag and fly ash are investigated in this paper. The optimum mixing way and ratio of weight were found. The hydration properties of cement binders with alkaline slag and fly ash are studied using XRD and SEM. The result shows that alkaline slag can stimulate the activity of fly ash, increase the hydration velocity of clinker mineral and improve the second hydration of fly ash.

Utilization of municipal solid waste incineration fly ash for sulfoaluminate cement clinker production

The feasibility of partially substituting raw materials with municipal solid waste incineration (MSWI) fly ash in sulfoaluminate cement (SAC) clinker production was investigated by X-ray diffraction (XRD), compressive strength and free expansion ratio testing. Three different leaching tests were used to assess the environmental impact of the produced material. Experimental results show that the replacement of MSWI fly ash could be taken up to 30% in the raw mixes. The good quality SAC clinkers are obtained by controlling the compositional parameters at alkalinity modulus ( C m ) around 1.05, alumina–sulfur ratio ( P) around 2.5, alumina–silica ratio ( N) around 2.0∼3.0 and firing the raw mixes at 1250 °C for 2 h. The compressive strengths of SAC are high in early age while that develop slowly in later age. Results also show that the expansive properties of SAC are strongly depended on the gypsum content. Leaching studies of toxic elements in the hydrated SAC-based system reveal that all the investigated elements are well bounded in the clinker minerals or immobilized by the hydration products. Although some limited positive results indicate that the SAC prepared from MSWI fly ash would present no immediate thread to the environment, the long-term toxicity leaching behavior needs to be further studied.

Low energy synthesis of cement compounds in molten salt

The world cement industry is responsible for >5% of the total anthropogenic carbon dioxide emissions blamed for causing global warming. The production of cement clinker minerals by precipitation from a molten salt solvent offers a potential route to energy reduction in cement manufacture. Molten salt synthesis of the major cement compounds β-dicalcium silicate (β-Ca2SiO4, β-C2S) and tricalcium silicate (Ca3SiO5, C3S) has been attempted in fused sodium chloride (NaCl). The synthesis of β-Ca2SiO4 was carried out by the reaction of CaCO3 with SiO2 in molten NaCl (CaCO3-SiO2-NaCl mole ratios 2∶1∶19·2 at 908°C, and 2∶1∶20·4, 2∶1∶13·5, 2∶1∶10·3 and 2∶1∶8 at 1140°C). The product was characterised by powder X-ray diffraction, Raman scattering and scanning electron microscopy. For the synthesis of Ca3SiO5, reactants with a molar ratio of 3∶1 were used (CaCO3–SiO2–NaCl 3∶1∶19·8 at 908 and 1000°C, and 3∶1∶20, 3∶1∶14, 3∶1∶9·9 and 3∶1∶8·1 at 1140°C). In all cases β-Ca2SiO4 was the principal product, with the CaO phase still present and (if any) only small quantities of Ca3SiO5. These observations, coupled with previous studies on the solid state synthesis of Ca3SiO5, indicate that β-Ca2SiO4 is an intermediate compound, requiring in excess of 1140°C to react with CaO in order to form tricalcium silicate.

Analyses of the surfaces of concrete by Raman and FT‐IR spectroscopies: comparative study of hardened samples after demoulding and after organic post‐treatment

AbstractConcrete surfaces were studied by two spectroscopic techniques, FT‐IR (in ATR mode) and Raman, to establish a nondestructive method to analyze the distribution of hydrated and organic phases. The surface composition of ordinary clinker, polished concrete, concrete after demoulding, and coated concrete as used in building construction was studied. The clinker's mineral phases and the polished concrete were first analyzed by Raman spectroscopy to determine a spectrum database of the specific phases located on the surface of the concrete. Then, both spectroscopic techniques were used to analyze, directly, the surface of hardened concrete after demoulding. No impact of roughness or porosity was highlighted using Raman spectroscopy; many cementitious, or hydrated phases (alite, belite, tricalcium aluminate, ferrite, portlandite and ettringite) were clearly identified. FT‐IR in ATR mode only identified some hydrated phases: portlandite and CaOSiO2H2O (CSH), but organic residues from the demoulding oil were characterized by this technique. Furthermore, the convenience of using these techniques together was tested by analyzing the composition of concrete surfaces coated by different organic post‐treatments. FT‐IR spectroscopy was useful to identify the main organic groups at the concrete surface, whereas Raman spectroscopy was especially able to characterize the mineral/hydrated phases under a thick post‐treatment layer (constituted of polyester varnish). Due to their own specificities, these complementary techniques should be used together to easily identify all the mineral phases and organic residues/coatings on concrete surfaces. Copyright © 2010 John Wiley & Sons, Ltd.

Multicompound Model for the Hydration of Portland Cement–Fly Ash Binders

In this study, traditional reaction equations (based on the theory of Powers) are applied to the hydration reactions of portland cement and the pozzolanic reaction of fly ash separately. Moreover, portland clinker is considered as a mixture of four minerals, each with its own sensitivity to the presence of fly ash. The kinetics of the reactions of each clinker mineral have been analyzed by fitting generally known models such as the Avrami and Jander equations to isothermal heat measurements on pastes of cement, fly ash, and water. The proposed model therefore consists of different stages, in which nucleation, phase-boundary, and diffusion reactions become rate controlling. The kinetics of the pozzolanic reactions have been described with similar equations, implementing parameter values based on measured selective dissolution data. Fly ash may accelerate the reaction of a clinker mineral, while at the same time it can decelerate another mineral. Depending on the relative proportions of the clinker minerals, the method can explain the apparent contradiction found in literature related to the acceleration or deceleration effect of fly ash on the cement hydration.

Effect of CuO on the formation of clinker minerals and the hydration properties

The purposes of this study are to explore the mechanisms of Cu element in clinker burning and hydration processes and to make effective use of waste containing copper in cement production. The effect of CuO on clinker mineral composition, C 3S polymorph and size, Cu element distribution and state, compressive strengths, hydration products, non-evaporable water quantity and hydration heat release rate was analyzed by XRD, SEM, DTA, isothermal heat-conduction calorimetry, etc. Results show that as the amount of CuO increases the formation and growth of C 3S grain are accelerated, R C 3S is gradually transformed into M 3 and the content of C 4AF increases; a small quantity of CuO increases the 3-day and 28-day strengths and the hydration degree of clinker, but excessive CuO has adverse effects. Those effects of CuO on clinker burning process are attributed to the formation of low-melting Cu 2O and the dissolution of CuO in C 4AF which decrease the formation temperature of liquid phase and increase its quantity. The effects on hydration process result from the combined action of the following factors: the induction period is prolonged; the hydration reactions in the initial and acceleration periods are accelerated.

Interaction of water vapour with anhydrous cement minerals

The prehydration of industrial cements (CEM I 52·5 R and API Oilwell Class G) and pure cement clinker minerals (C3S, cubic C3A, orthorhombic C3A, C4AF) has been studied at 60 and 85% relative humidity using in situ X-ray diffraction (XRD), calorimetry, environmental scanning electron microscopy and X-ray photoelectron spectroscopy. This combination of techniques identifies the key components involved in the surface prehydration process. Prehydration of cement leads to dramatic retardation of hydration. in situ XRD shows the retardation of portlandite formation after prehydration, supporting the calorimetry results. X-ray photoelectron spectroscopy and ESEM investigations show surface modification after prehydration for C3S, C3A and doped C3A (4%Na2O). Prehydration of cement leads to modification of the surface area and surface charge, which can strongly influence the reactivity of bulk cements. This is relevant to the quality of cement during storage.

Reuse of water purification sludge as raw material in cement production

Abstract 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

Melt differentiation and crystallization of clinker minerals in a CaO–SiO 2–Al 2O 3–Fe 2O 3 pseudoquaternary system

In the CaO–SiO 2–Al 2O 3–Fe 2O 3 pseudoquaternary system, the solid solutions of Ca 3SiO 5 [C 3S(ss)], Ca 2SiO 4 [C 2S(ss)], Ca 2(Al x Fe 1 − x ) 2O 5 with 0.40 ≤ x ≤ 0.57 (ferrite) and Ca 3Al 2O 6 [C 3A(ss)] were crystallized out of a complete melt with 52.9 mass% CaO and Al 2O 3/Fe 2O 3 = 0.70. When the melt was cooled from 1673 K at 80 K/h, the crystals of ferrite with x = 0.40, C 3S(ss) and C 2S(ss) would start to nucleate from the melt at 1630 K. During further cooling, the x value of the precipitating ferrite would progressively increase and eventually approach 0.57 at 1613 K. The resulting ferrite crystals showed a zonal structure, the x value of which successively increased from the cores toward the rims. Actually, the x values of 0.43 and 0.52 were confirmed for, respectively, the cores and rims by EPMA. As the simultaneous crystallization of zoned ferrite, C 3S(ss) and C 2S(ss) proceeded, the coexisting melt would become progressively enriched in the Al 2O 3 component. After the termination of the ferrite crystallization, the C 3A(ss), C 3S(ss) and C 2S(ss) crystallized out of the differentiated melt. The end result was the four phase mixture of ferrite, C 3A(ss), C 3S(ss) and C 2S(ss), being free from the nucleation of Ca 12Al 14O 33 solid solution.

Hydration of calcium sulfoaluminate cements — Experimental findings and thermodynamic modelling

Calcium sulfoaluminate cements (CSA) are a promising low-CO 2 alternative to ordinary Portland cements and are as well of interest concerning their use as binder for waste encapsulation. In this study, the hydration of two CSA cements has been investigated experimentally and by thermodynamic modelling between 1 h and 28 days at w/ c ratios of 0.72 and 0.80, respectively. The main hydration product of CSA is ettringite, which precipitates together with amorphous Al(OH) 3 until the calcium sulfate is consumed after around 1–2 days of hydration. Afterwards, monosulfate is formed. In the presence of belite, strätlingite occurs as an additional hydration product. The pore solution analysis reveals that strätlingite can bind a part of the potassium ions, which are released by the clinker minerals. The microstructure of both cements is quite dense even after 16 h of hydration, with not much pore space available at a sample age of 28 days. The pore solution of both cements is dominated during the first hours of hydration by potassium, sodium, calcium, aluminium and sulfate; the pH is around 10–11. When the calcium sulfate is depleted, the sulfate concentration drops by a factor of 10. This increases pH to around 12.5–12.8. Based on the experimental data, a thermodynamic hydration model for CSA cements based on cement composition, hydration kinetics of clinker phases and calculations of thermodynamic equilibria by geochemical speciation has been established. The modelled phase development with ongoing hydration agrees well with the experimental findings.

Time-resolved combined SAXS and WAXS studies on hydrating tricalcium silicate and cement

The objective of the experiments discussed here was to investigate the hydration process of the clinker minerals tricalcium silicate (C3S) and tricalcium aluminate (C3A) as well as that of ordinary Portland cement in the early stage of hydration (within several hours after the onset of hydration). Small-angle X-ray scattering (SAXS) and wide-angle X-ray scattering (WAXS) patterns caused by microstructural objects (nanometre and micrometre range) as well as by crystalline phases were observed at room temperature and at 40°C. Combined and time-resolved SAXS and WAXS studies in the early stage of hydration (until approximately 21 h) are reported. The experimental results indicate that two types of internal surfaces occurred simultaneously. Smooth surfaces, namely surfaces of Euclidean geometry, coexist with fractal surfaces. Analysis of different segments of a scattering curve showed that the proportions between Euclidean and fractal surfaces changed with time after the onset of hydration. A direct comparison of the structure-forming processes in the nanometre range at different temperatures (room temperature and 40°C) is given by the SAXS results. SAXS/WAXS, in addition to small-angle neutron scattering, represents one of the few relevant non-destructive test methods that provide undisturbed information about the nanostructure and microstructure of hydrating phases. The combination of SAXS and WAXS is a powerful tool for the simultaneous observation of X-ray amorphous (non-crystalline) and crystalline structures.

Effect of barium oxide on the formation and coexistence of tricalcium silicate and calcium sulphoaluminate

Formation and coexistence of tricalcium silicate (C3S) and calcium sulphoaluminate (C4A3\( \bar S \)) minerals in Portland cement clinker containing calcium sulphoaluminate were investigated. The f-CaO content, mineral composite and formation of mineral in the clinker were analyzed respectively by chemical analysis, differential scanning calorimetry(DSC) and X-ray diffraction. The results show that, adding a suitable amount of BaO can improve the burnability of raw meal and promote the f-CaO absorption. Tricalcium silicate and calcium sulphoaluminate minerals can form and coexist in clinkers at 1 234–1 317 °C by the addition of BaO to the raw meal. A suitable amount of BaO expanded the coexistence temperature of two minerals by 58 °.

Creep effects in nanoindentation of hydrated phases of cement pastes

This paper focuses on the nanoindentation of cement pastes and their micromechanical response. Since cement paste is a heterogeneous material at microscale, micromechanical properties have to be assessed separately for its individual material phases, i.e. hydrated products and unhydrated phases. Our study addresses important issues concerning experimental loading paths and their effects on the evaluation of elastic properties using nanoindentation. The effect of creep is shown on a series of multicycle experiments. A wide range of maximum loads and corresponding final penetration depths (approximately 200–1200 nm) are covered in this study. Experimental measurements on both hydrated cement samples and on unhydrated clinker minerals have proved that significant creep deformation can be attributed purely to hydrated phases. Further, it has been found that cement paste exhibits a strong size effect on elastic properties measured by nanoindentation and evaluated by the standard Oliver–Pharr procedure for loading–unloading tests with no dwell period at the peak load. Such property was already reported for plastic materials like metals [Elmustafa AA., Stone DS., Indentation size effect in polycrystalline F.C.C. metals, Acta Materialia 2002; 50 (14): 3641–3650., Wei, Y., Wang, X., Zhao, M., Size effect measurement and characterization in nanoindentation test, Journal of Material Research 2004; 19 (1): 208–217.], due to various effects but creep. As shown in the paper, cyclic loading and using long dwell periods at peak load leads to minimizing of this spurious type of size effect. Moreover, comparison with results obtained for the COC/PE polymer (75% cycloolefin copolymer + 25% polyethylene) has been performed. This polymer has been found to exhibit similar time-dependent behavior as hydrated cement paste.

Preparation of the saving-energy sulphoaluminate cement using MSWI fly ash

MSWI fly ash was used as a major cement raw material in sintering sulphoaluminate cement clinker successfully in the laboratory. Sintering system, mechanical performance, hydration process and microstructure of the clinker was investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray fluorescence spectrometry (XRF), etc. The result shows that the clinker can be sintered properly under the temperature of 1200–1300 °C and sintered time of 120 min. Cl − content in the clinker made with MSWI fly ash is about 1.08%. However most Cl − cannot leach out in water solution from the hardened cement paste during curing age between 1 d and 28 d because of the Cl − being combined in clinker minerals and its hydrates. The compressive strength of the sulphoaluminate cement was high in early age while that developed smoothly in later age.

Effects of Pair-Mineralizer on Burnability of Clinker and Formation of Mineral

The effects of the pair-minerializer (CaSO4,-CaF2) on the burnability of clinker and the formation of mineral are investigated. As experimental results, the addition of F as pair-mineralizer, the burnability of clinker was improved. Especially, the addition of F and SO3 components simultaneously as pair-mineralizer, total amount of free lime in clinker is rapidly decreased compared with the value which mineralizer was added separately. In case of adding K2O only to the raw mixes, the amount of free lime is increased. However, if alkali (K2O) and pair-minerializer (CaSO4,-CaF2) were added simultaneously, the produced amount of clinker mineral is increased due to the formation of stable calcium langbeinite by the combination of alkali (K2O) and sulfate

The influence of phosphorous pentoxide on the phase composition and formation of Portland clinker

The influence of phosphorous pentoxide (P 2O 5) on the phase composition and formation of Portland clinker was studied in laboratory conditions. Phosphorous pentoxide in the form of calcium phosphate was added to common cement-making raw meal in graded quantities up to 5 wt.%. The raw meal properties were studied by thermal analysis. The development of clinker formation by burning for periods ranging from 20 s to 30 min in a special semi-automatic oven with a manipulator was followed using light optical microscopy. The phase composition of clinkers burnt to equilibrium was quantified by the optical point counting method. The entry of P 2O 5 into clinker minerals was determined by electron microprobe analyses. The laboratory tests show that at 0.7 wt.% of P 2O 5 in the clinker the alite (Ca 3SiO 5) content decreases and belite (Ca 2SiO 4) content increases. At a P 2O 5 content of 4.5 wt.% alite formation was totally blocked and the resulting clinker contained free lime in equilibrium with belite.

The influence of mineralogical, chemical and physical properties on grindability of commercial clinkers with high MgO level

This research investigates various methods able to identify possible mineralogical, physical and chemical influences on the grindability of commercial clinkers with high MgO level. The aim of the study is to evaluate the hardness and elastic modulus of the clinker mineral phases and their fracture strength during the comminution processes, comparing samples from clinkers with low MgO level (0.5%) and clinkers with elevated MgO levels (> 5.0%). The study of the influence of mineralogical, chemical and physical properties was carried out using several analytical techniques, such as: optical microscopy, X-ray diffraction with Rietveld refinement (XRD) and X-ray fluorescence (XRF). These techniques were useful in qualifying the different clinker samples. The drop weight test (DWT) and the Bond ball mill grindability test were performed to characterize the mechanical properties of clinkers. Nanoindentation tests were also carried out. Results from the Bond ball mill grindability test were found to be related to the hardness of the mineral phase and to mineralogical characteristics, such as type and amount of inclusions in silicates, belite and alite crystals shape, or microcracked alites. In contrast, the results obtained by the DWT were associated to the macro characteristics of clinkers, such as porosity, as well as to the hardness and mineralogical characteristics of belite crystals in clusters. Hardness instrumented tests helped to determine the Vickers hardness and elastic modulus from the mineral phases in commercial clinkers and produced different values for the pure phases compared to previous publications.

Degree of hydration in cement paste and C3A-sodium carbonate-water systems

This research provides a fundamental understanding of the early stage hydration of Portland cement paste, tricalcium aluminate (C3A) paste at water to cement ratio of 0.5 and C3A suspension at water to cement ratio of 5.0 modified by 2 or 4 mass% of sodium carbonate. A high conversion of unreacted clinker minerals to gel-like hydration products in the cement-Na2CO3 pastes takes place rapidly between 1st to 24th h. Contrary the Ca(OH)2 formation within the same time interval is retarded in the excess of CO32− ions due to intensive rise and growth of CaCO3 crystals in hydrated cement. Later, the conversion of clinker minerals to the hydrate phase is reduced and higher contents of calcite and vaterite relative to that of Ca(OH)2 in comparison with those found in the Portland cement paste are observed. As a consequence a decrease in strength and an increase in porosity between hardened Portland cement paste without sodium carbonate and those modified by Na2CO3 are observed. C3A hydrates very quickly with sodium carbonate between 1st and 24th h forming hydration products rich in bound water and characterized also by complex salts of (x)C3A·(y)CO2·(zH2O type, whereas C3A-H2O system offers C3AH6 as the main hydration product. Higher content of the formed calcium aluminate hydrates in C3A-Na2CO3-H2O system also contributes to early strength increase of Portland cement paste.

P2O5가 클링커 광물조성 및 품질에 미치는 영향

The influence of P₂O? on clinker mineral composition and the cement quality was investigated. When the sewage sludge was used as a raw material in place of clay, the presence of P₂O? in sewage sludge affects the mineral composition and the clinker quality. As the P₂O? concentration in raw mix increases, the burnability of clinker becomes worse and the alite decomposes into belite and free-CaO, so belite increases with the decrease of alite. The early strength of mortar decreases with the increase of P₂O? concentration. On the other hand, later-age strength increases with the increase of belite content. The setting time of cement was delayed with the P₂O? concentration above 0.6 wt%.

Comparative Characterization of Clinker’s Microstructure at Different Temperature Zone during Cement Production

Temperature is an important parameter for transformation of minerals in clinker during cement productions. It influences the formation of alite from belite during calcinations and clinkering processes. The result of microstructure shows that the formation of belite minerals started at temperature nearly 1200°C which is at calcinations zone temperature, followed by formation of I±-belite at higher temperature (around 1300°C), then formation of I²-belite and finally, with the suitable conditions it will form alite minerals. The differences between minerals are identified physically using scanning electron microscope (SEM).