Cement phase composition

Bogue potential cement phase composition of cements... 

In calcium aluminate clinkers the lower or higher Cj2A, amounts are present, which causes set acceleration of cement paste. Sometimes in the sintered clinkers even the CjA phase can be present, due to the local inhomogeneity of the raw mixture, in which the larger limestone grains can occur. Calleja [16] proposed the simplified formulae for the calculation of calcium aluminate cement phase composition. 

Behte cements are not a technological novelty too. Portland cements produced in thirties, in XXc, had a considerably lower hme saturation factor and highbelite content. It was linked with much slower strength development and therefore it caused the gradual changes of cement phase composition, with the increase of alite content. 

Portland cement Belite cement Sulfobelite cement Sulfoalite cement Phase composition of clinker (%)... 

QPA by XRD has become a prominent characterisation technique in cement science and more recently also in cement production. Properties such as strength development or durability are closely related to the cement phase composition. Early analyses were mostly based on the Bogue calculation... 

XRD is quickly becoming a standard tool in cement materials science. If appropriately used, a wealth of information on cement phase composition can be retrieved, both qualitatively and quantitatively. Flowever, cement and hydrated cements in particular are complex multicomponent materials. The application of a common material characterisation technique such as XRD to the quantitative analysis of cement is therefore fraught with inherent challenges and practical problems. For the large majority of research problems, standardised black box operation and data analysis procedures cannot deliver meaningful results and deeper insights and practical experience with the technique are a prerequisite for good analytical practise. 

ASTM C845 Type E-I (K) expansive cement manufactured ia the United States usually depends on aluminate and sulfate phases that result ia more ettriagite formation duriag hydration than ia normal Portland cements. Type K contains an anhydrous calcium sulfoaluminate, C A SI. This cement can be made either by iategraHy burning to produce the desired phase composition, or by intergrinding a special component with ordinary Portland cement clinkers and calcium sulfate. 

In the cements of this type a number of phases are known to be present. For example, in the zinc oxychloride cement two discrete phases, corresponding to the composition ZnO. ZnCl. H O in the ratios 4 1 5 and 1 1 2 respectively, are known to occur (Sorrell, 1977). Similarly, in the magnesium oxychloride cement, phases corresponding to Mg(OH)a. MgClj. HjO in the ratios 5 1 8 and 3 1 8 have been shown to exist and have been studied by X-ray diffractometry (Sorrell Armstrong, 1976). 

Early workers, and some later ones, ignored the fact that aluminium is always found in the orthophosphoric acid liquid of the practical cement its presence profoundly affects the course of the cement-forming reaction. It affects crystallinity and phase composition, and renders deductions based on phase diagrams inappropriate. Nevertheless we first describe the simple reaction between zinc oxide and pure orthophosphoric acid solution, which was the system studied by the earliest workers. 

The presence of the additive results in the formation of a homogeneous structure of the plugging rock, with an improved uniformity of the phase composition of the system and a more compact distribution of the dispersed particles. An increased strength of the cement rock is also obtained. 

Portland cement clinker potential phase composition is presented in Table 4. It could be seen that the C3A content in the clinker was 9.46% which is important for the cement hydration rate and cement sulfate resistance. Common Portland cement is not resistant to the sulfate influence because of the significant C3A content, whose hydrates react with sulfate ions resulting in expansive compounds. Portland cement with the higher resistance to sulfates must have low C3A content. Moderate to high content of mineral alite - C3S (54.72%) is usual for the Serbian cement plants and enables the addition of higher quantities of mineral admixtures without influencing the quality of final cement. 

Table 4 Potential phase composition of Portland cement clinker...

Matrix Bonding Infrared Absorption Studies. It is possible that some form of reaction could occur between liquid sulfur and the hydrated cement phases to produce a chemical bond which would contribute to the strength of the composite, perhaps more noticeably with filling of the... 

A knowledge of the relevant high-temperature phase equilibria is necessary for understanding the factors that govern acceptable bulk compositions for Portland cement clinker, the conditions under which the latter can be manufactured, and the phase composition and microstructure of the resulting material. This chapter deals with these equilibria and with the phases to which they relate, with the exception of the major clinker phases, which were described in Chapter I. Some anhydrous phases primarily of interest in relation to other types of cement are also considered here. Principles underlying the preparation of anhydrous silicate, aluminate and other high-temperature phases are outlined. 

As with LSF, the approach is applicable to cements if CaO is further corrected by deducting O.7SO3. Because minor oxide components are ignored, the total for the four main phases plus free lime will not add up to 100%. It is implicit in the approach that all the MgO is assumed to occur as periclase. The phase composition calculated by Bogue s method is related to the LSF in that a ratio of 38 to CjA 0.546, calculated without correcting the CaO content for free lime, corresponds to an LSF > 1.0 (D2). 

Particle size distribution, phase composition and cement properties... 

The potential uses of XRD powder diffraction in the study of clinker or anhydrous cement include the qualitative and quantitative (QXDA) determination of phase composition, and the determination of polymorphic modification, state of crystallinity and other features of individual phases. In principle, information on compositions of phases is obtainable through cell parameters, but, due to the lack of adequate reference data, XRD is generally less satisfactory for the clinker phases than X-ray microanalysis. Table 4.2 gives the pattern of a typical Portland cement, with indications of the assignments of peaks to phases. 

The calculation of phase composition from bulk analysis for cements presents no special difficulties if the content and composition of the gypsum and any other admixture are known, as the analysis can then readily be corrected to give the composition of the clinker. If they are not known, an assumption must be made as to the amount of SOj in the clinker, so that the contribution of the gypsum to the CaO content of the cement may be estimated. Further assumptions and corrections may have to be made to allow for impurities in the gypsum or other additives (e.g. calcite). 

Several studies on the quaternary systems of CaO-SiOj-HiO with NajO or K,0 have been reported (K19,S52,M52). Alkali greatly lowers the concentrations of CaO in the solution and raises those of Si02. The solid phase compositions are difficult to study. Determinations based on changes in concentration on adding CH to alkali silicate solutions are subject to considerable experimental errors, while direct analyses of the solid are difficult to interpret because the alkali cations are easily removed by washing. Suzuki ei al. (S52) considered that they were adsorbed. Macpheeef /. (M52) reported TEM analyses of the C-S-H in washed preparations obtained by reaction ofCjS (lOg) in water or NaOH solutions (250 ml). The C-S-H obtained with water had a mean Ca/Si ratio of 1.77 that obtained with 0.8 M NaOH had a mean Ca/Si ratio of 1.5 and a mean NujO/SiOj ratio of 0.5. These results do not appear to be directly relevant to cement pastes. The pore solutions of the latter may be 0.8 M or even higher in alkali... 

The experimental considerations applying to calcium silicate pastes (Sections 5.1 and 5.2) are equally relevant to cement pastes. Of the methods so far used in attempts to determine the degrees of reaction of the individual clinker phases as a function of time, QXDA (C39,D12,T34,P28) has proved much the most satisfactory. Procedures are essentially as for the analysis of a clinker or unreacted cement (Section 4.3.2), but it is necessary to take account of overlaps with peaks from the hydration products, and especially, with the C-S-H band at 0.27-0.31 nm. The water content of the sample must be known, so that the results can be referred to the weight of anhydrous material. If a sample of the unhydrated cement is available, and its quantitative phase composition has been determined, it may be used as the reference standard for the individual clinker phases in the paste. 

There are probably no effective direct methods at present for determining either C-S-H or AFm phases in cement pastes in both cases, this is probably attributable to the low degree of crystallinity. Odler and Abdul-Maula (015) found that determination of AFm phase by QXDA was only semiquantitative. Postulated quantitative phase compositions of cement pastes may, however, be tested by comparing observed and calculated TG curves (Section 7.3.3). 

The essential input data are (a) the bulk chemical composition of the cement, (b) the quantitative phase composition of the cement and the chemical compositions of its individual phases, (c) the fraction of each phase that has reacted, (d) the w/c ratio, (e) the COj content of the paste and an estimate of how it is distributed among phases, and (0 the composition of each hydrated phase for the specified drying condition. If (b) is unknown, it may be estimated as described in Section 4.4, and if (c) is unknown, it may be estimated from the age as described by Parrott and Killoh (P30), or, more simply though less precisely, by using empirical equations (D12,T37). If the phase composition by volume and porosities are to be calculated, densities of phases are also required. 

Table 7.5 Coefficients in equation 7.3 for predicting the cumulative heat evolution in a cement paste of given age from the potential phase composition of the cement (for w/c = 0,4 and 21°C) (C38)... 

Major influences on the kinetic curve of a cement include the phase composition of the clinker, the particle size distribution of the cement and the RH and temperature regimes during curing. Other influences include the w/c ratio, the content and distribution of admixtures, including gypsum, the reactivities of individual clinker phases and probably others, such as the microstructures of the clinker and of the cement particles. 

In Section 7.3.3, a method was described for calculating the quantitative phase composition of a cement paste by weight and by volume for various drying conditions. Fig. 8.5 includes porosities thus calculated for 18-month-... 

Regulated-set cement and jet cement are modified Portland cements in which the normal aluminate phase is replaced by CuA CaF, through the use of a raw mix containing CaF,. Uchikawa and Tsukiyama (U2I) gave chemical (Table 10.4) and phase compositions of two jet cements. Botli contained approximately 60% of alite, 20% of C, i A CaF,. 1% of belite and 5% of ferrite. Admixtures are required to control the rate of reaction of the C, 1 A CaFj and the nature of the products. One of the cements included a proprietary retarder based on citric acid, togetlier with 2"/o of CaC O, . The other contained 2.5% of hemihydrale. In each case, Na,S04 (T o) and anhydrite were also present. The specific surface areas were around 550 m kg . 

G65 Grudemo, A., Strength-structure relationships of cement paste materials. Part I. Methods and bctsic data for studying phase composition and microstructure (CBI Research, 6 77), 101 pp., Swedish Cemcnl and Concrete Research Institute, Stockholm (1977) also private communication quoted by L.-O. Nilsson in Report TVBM-1003, Division of Building Materials, University of Lund, Sweden (1980). 

---