Cements ordinary Portland

Special purpose and blended Portland cements are manufactured essentially by the same processes as ordinary Portland cements but have specific compositional and process differences. White cements are made from raw materials of very low iron content. This type is often difficult to bum because almost the entire Hquid phase must be furnished by calcium aluminates. As a consequence of the generally lower total Hquid-phase content, high burning-zone temperatures may be necessary. Past cooling and occasionally oil sprays are needed to maintain both quaHty and color. 

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. 

Oil well cements are manufactured similarly to ordinary Portland cements except that the goal is usually sluggish reactivity. Eor this reason, levels of C A, C S, and alkafl sulfates are kept low. Hydration-retarding additives are also employed. 

Unfortunately, the protection provided by concrete can be overcome by contamination of the concrete by chloride. Chloride, when entering the concrete as a contaminant of the mix constituents, is to a large extent (about 90%) complexed within the cement matrix and only a small percentage is free in the pore solutions. The present codes of practice ban the use of chloride-bearing additives and restrict the amount of chloride present in concrete. For normally reinforced concrete made with ordinary Portland cement it should be not more than 0.4% chloride ion with respect to the cement content weight/weight. 

Immobilization of Cadmium ions with ordinary Portland cement... 

A.K. Minocha, Pankaj Kumar, Jaswinder Singh, Manish K. Goyal, L.K. Aggarwal, Influence of copper(II), lead(II) and cadmium(II) metal ions on the setting time of ordinary Portland cement. Indian J. Env. Prot, 25,365-368, 2005. 

Fig. 1.15 Adsorption isotherm of calcium lignosulfonate on ordinary Portland cement (Ernsberger).

There has been a considerable study of the effect of various water-reducing admixtures on the pure phases and also on ordinary Portland cement. The following points summarize the general observations. 

As far as the final hydration products of ordinary Portland cement are concerned, there is an indication from isothermal calorimetry [57] that there is very little difference in the presence or absence of a calcium lignosulfonate water-reducing admixture. In this work, the heat evolved per unit of water incorporated into the hydrate has been determined for two cements, with the results shown in Fig. 1.25. It can be seen that the relationship between the amount of heat evolved and the amount of water combined with the cement is maintained whether the admixture is present or not. This work also indicated that the retardation in the early stages is compensated for at later times by an acceleration. 

There is little published data on the effect of air-entraining agents on the chemistry and morphology of cement hydration. However, the limited studies [15] indicate that the normal hydration pattern under isothermal conditions for ordinary Portland cement shown in Fig. 3.14 is modified as follows ... 

Non-ionic materials, such as ethoxylates, do not appear to alter the heat output pattern of ordinary Portland cement. 

Fly ash increases the density, decreases the permeability, and increases the leaching resistance of Ordinary Portland Cement (OPC). It is a truism that The leach resistance of solidified cement-waste systems can be improved by any process which accelerates curing, limits porosity, or chemically bonds fission product or actinide elements. (Jantzen et al., 1984). Supercritical C02 treatment of a modified Portland cement is expected to further increase the density over the untreated material, so that a reduced porosity and improved leachability should result. In addition, the high silica content of fly ash, with its well-known sorbent properties toward actinides and certain other radionuclides, enhances the immobilization characteristics. 

Hills C (1993) Ordinary Portland cement based solidification of toxic wastes the role of OPC reviewed. Cem Concr Res 23 196-212... 

The great majority of Portland cements made throughout the world are designed for general constructional use. The specifications with which such cements must comply are similar, but not identical, in all countries and various names are used to define the material, such as OPC (Ordinary Portland Cement) in the UK, or Type I Portland Cement in the USA. Throughout this book, we shall use the term ordinary Portland cements to distinguish such general purpose cements from other types of Portland cement, which are made in smaller quantities for special purposes. 

In many clinkers, the ferrite phase is closely mixed with aluminate due to a similarity in cell parameters, oriented intergrowth can occur (MIS). The close admixture often renders X-ray microanalysis difficult or unreliable. For ordinary Portland cement clinkers, the compositions found in dilferent laboratories are nevertheless remarkably consistent. Table 1.2 includes an average value based on the results of investigations using X-ray microanalysis (H8,K1,B2,U1,H3,B4) or chemical analysis of separated material (Yl). Table 1.3 includes suggested site occupancies corresponding to these data. 

The specific surface area, like the PSD, is thus a quality whose value depends on how it is defined, and is liable to be affected by any pretreatment or conditions affecting the degree of flocculation. In practice, air permeability methods are widely used. Typical values are 300-350 m kg for modern ordinary Portland cements and 400-450 m kg " for rapidhardening Portland cements. 

Any standard method of matrix inversion, such as the Gauss-Jordan method (N13), may be used to solve the equations. The coefficients in equations 4.11-4.14 may be used without serious error for most ordinary Portland cement clinkers in which the alite composition is not too different from that assumed here. As a byproduct of the calculation described in this section, and using the full compositions of the phases given in Table 1.2, one may calculate a mass balance table (Table 4.3) showing the distributions of all the oxide components among the phases. 

The procedure described above should give satisfactory results for most modern ordinary Portland cement clinkers, but the following points should be noted ... 

Fig. 5.4 (A.B) Types I and II C-S-H, respectively (SEM of fracture surfaces courtesy K. L. Scrivener). (C,D) SEM/STEM pair of ion beam thinned section, showing Type III C-S-H (top, right) and Type IV C-S-H (top, left and bottom, right Jennings et al. (HO)). (A) is of an ordinary Portland cement paste, w/c = 0.5, aged 10 h. (B) is of a paste of an oil well cement, w/c = 0.44, with 2.4% of CaClj on the weight of cement, aged 1 day. (C) and (D) are of a CjS paste, w c = 0.47, aged 330 days.

Unless otherwise stated, this chapter relates to ordinary Portland cements hydrated in pastes at 15-25°C and w/c ratios of 0.45-0.65. XRD powder studies on such pastes have been reported by many investigators (e.g. C38,M67). The rates of disappearance of the phases present in the unreacted cement are considered more fully in Section 7.2.1. Gypsum and other calcium sulphate phases are no longer detectable after, at most, 24 h, and tbe clinker phases are consumed at differing rates, alite and aluminate phase reacting more quickly than belite and ferrite. The ratio of belite to alite thus increases steadily, and after about 90 days at most, little or no alite or aluminate phase is normally detectable. 

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