Portland cement constitution

Roy, D.M. (1983) Portland cement constitution and processing. Part II Cement constitution and kiln reactions. 

Potentially every parameter of cost involved in sulfur concrete is a variable. The cost of sulfur and the cost to modify it, the availability and capacity of mixing equipment and the daily volume of material mixed, and the labor requirement at the mixing installation are variable factors for a specific project. Added to these variables are the normal parameters of a concrete jobsite preparation, form construction and grade delineation, transport, placement, finish, joint practice, and other items constituting the total concrete installation. Finally, a cost comparison must be made versus the local cost of Portland cement concrete, which is highly variable in different locations. 

Alite is the most important constituent of all normal Portland cement clinkers, of which it constitutes 50-70%. It is tricalcium silicate (CajSiOj) modified in composition and crystal structure by incorporation of foreign ions, especially Mg ", AP and Fe. It reacts relatively quickly with water, and in normal Portland cements is the most important of the constituent phases for strength development at ages up to 28 days, it is by far the most important. 

The aluminate phase constitutes 5-10% of most normal Portland cement clinkers. It is tricalcium aluminate (Ca3Al206), substantially modified in... 

According to the ASTM C-884-78, delamination of the polymer mortar layer from the concrete test block or the presence of horizontal cracks in the concrete near the interface shall constitute failure. It is obvious from these results that the RPUMRPE mortar passes the ASTM C-884-78. After thermal cycling, no delamination was found in the specimens. The failure in all specimens in the shear and pull out tests occurred within the portland cement concrete substrate. These results depended on the tensile strength of the concrete substrate. 

M. Torabinejad, C. Hong, F. McDonald, T. Pitt Ford, The chemical constitution and biocompatibility of accelerated Portland cement for endodontic use, Int. Endod. J. 21 (1995) 349-353. 

Basic properties of Portland cement pastes are attributed to the C-S-H gel. Therefore this phase is a field of interest and the subject of numerous investigations [32]. However, in spite of this, the structme and chemical composition of C-S-H cause several discussions. It is the effect of colloidal constitution of this phase and variable, not well defined composition, depending on liquid phase composition, primarily of calcium ions concentration. Moreover, the morphology of this phase transforms as a function of hydration or maturing time of the samples. 

Bates, P.H., "The Constitution of Portland Cement. Some Results Obtained at the Experimental Cement Plant of the Bureau of Standards," Proceedings of the 9th Annual Convention of the National Association of Cement Users, American Concrete Institute, Dec. 10-14,1912,388 pp. 

Maki, I., and Goto, K., "Factors Influencing the Phase Constitution of Alite in Portland Cement Clinker," Cement and Concrete Research, Vol. 12, 1982, pp. 301-308. 

Tavasci, B., "Researchers on the Constitution of Portland Cement Clinker," Giomaledichimica industriale ed applicata, Vol. 16, 1934, pp. 538-552. 

In ordinary Portland clinker (corresponding to ASTM type I Portland cement) tricalcimn silicate is the most abundant phase, present in amormts between about 50% and 70%. Dicalcium silicate usually constitutes 15-30% of the clinker. Typical amounts of tricalcium aluminate are 5-10%, and of the ferrite phase 5-15%. In special Portland clinkers the individual clinker pliases may be present in increased or reduced amounts, or may be absent entirely. Free lime, free MgO and alkali sulfates are minor constituents of Portland clinker that are present only in small amounts or may be absent entirely. Calcium sulfate is only rarely a constituent of Portland clinker, but is intergroimd in limited amounts with it, to obtain Portland cement. In Table 2.1 different types of Portland cement are compared. 

The main product of the pozzolanic reaction is an amorphous or nearly amorphous calciiun sihcate/aluminate hydrate phase similar to that formed in the hydration of calcium silicates constituting Portland cement. 

Ca2Al(0H)g.2H20].0H. In C4AHjc, an additional layer of H2O molecules is present between the principal layers. Tetracalcium aluminate hydrate is not among the hydrate phases formed in the hydration of calcium aluminates constituting calcium aluminate cement however, it may be formed in the hydration of tricalcium aluminate, a constituent of Portland cement. 

The amoirnt of water needed for complete hydration of CA to CAHjq is rather high, and corresponds to a water/solid ratio of m A=1.13. For the formation of C2AHg+AH3 the required w/s is 0.63, and for the formation of CjAHg w/5=0.46 is sufficient. These values are distinctly higher than those needed for the hydration of the calcimn sihcates that constitute Portland cement (C2S and C3S). 

Table 16.1 gives the energy balance of a clinkering process in which a raw meal of typical composition is converted into an ordinary Portland cement clinker. From the table it is apparent that the reaction in which by far the largest fraction of energy is consumed is the conversion of the calcium carbonate constituting the raw meal into calcium oxide and carbon dioxide ... 

Gel pores constitute approximately 28% of Portland cement paste and capillary pores between 0% and 40%, depending on the wic ratio and progress of hydration processes. The voids of entrapped air should not exceed a small proportion that is, 1% of the total volume, otherwise the concrete must be considered as inadequately executed. 

Portland cement presently constitutes over 60% of all cement produced and is a carefully apportioned combination of the oxides of calcium, silica, aluminum, and iron. 

The ferrite phase constitutes about 8-13% of an average portland cement. In portland cement the ferrite phase may have a variable composition that can be expressed as C2(A Fi ) where 0[Pg.46]

The minimum water cement ratio for attaining complete hydration of cement has been variously given from 0.35 to 0. 40, although complete hydration has been reported to have been achieved at a water cement ratio of 0.22.1 In a fully hydrated portland cement Ca(OH)2 constitutes about 20-25% of the solid content. 

The monosulfate group, also known as the AFm phase, is represented by the formula C4ASH12 or C3A CS Hj2. AFm stands for Al-Fe-mono, in which one mole of CS is present. In portland cement this phase forms after the AFt phase disappears. This phase may constitute about 10% of the solid phase in a mature cement paste. In SEM, this phase has a hexagonal morphology resembling that of Ca(OH)2 and the crystals are of sub-micrometer thickness. The principle ionic substitutions in the AFm phase are Fe for AP+, and OH", C03 , Cl", etc. for S04. The density of this phase is 2.02 g/ml. The amount of crystalline hydrogamet present in cement paste is less than 3 %. It is of the type Ca3 Al2(OH)j2 in which part... 

The silicate phases, C3S and C2S together constituting the major portion of the components in portland cement, influence considerably its hydration and strength development. The accelerating influence of CaCl2 on the hydration of C3 S is followed conveniently by estimating at different times the amount of residual unhydrated C3S, the amount of Ca(OH)2, non-evaporable water content, electrical conductivity, heat liberation, etc. 

Calcium sulfate in the form of gypsum or anhydrite is added to the cement in amounts of a few per cent, to act as a set regulator. The rest of the material constitutes ordinary Portland clinker. 

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