Hydration Portland cements

Gypsum, 4 582-601 5 467, 785t 23 576 forms and composition, 4 583t hardness in various scales, 7 3t in Portland cement, 5 467 in Portland cement hydration, 5 477t thermal reduction of, 23 577 thermodynamics and kinetics of formation- decomposition, 4 586-588 Gypsum board, 4 600-601 Gypsum processes, obtaining sulfur from, 23 576-577... 

Fig. 2.14 Conduction calorimetric curves for Portland cement hydrated in the presence of SMF.

Conduction calorimetric curves of Portland cement hydrated isothermally containing various quantities of triethanolamine are shown in Fig. 5.3 [8]. On initial contact with water each sample evolves heat (not shown in figure) that can be attributed to heat of wetting, hydration of free lime and reaction of C3 A with gypsum to form... 

The reactions of C3A and C4AF with water, alone or in the presence of calcium hydroxide or sulphate or both, have been widely studied for the light they may cast on the mechanism of Portland cement hydration, and... 

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. 

Fig. 11.1 Concentrations in the aqueous phase of Portland cement hydrated at w/c = 2.0 in water or in sucrose or EDTA solutions. After Thomas and Birchall (T49).

Si NMR has also been applied to a hydration study of actual Portland cements, the broad spectra of which are composed of the spectra of the component tricalcium silicate and p-dicalcium silicate (Figure 4.40) (Barnes et al. 1985). Integration of the Si spectra of the discrete cement silicates and Portland cement hydrated under identical conditions allowed a comparison of the hydration characteristics (Figure 4.41) and... 

I. Muller Influence of cellulose ethers on the kinetics of early Portland cement hydration. PhD thesis, Westf ischerWilhelms-Universitat Munster. (2006)... 

Concrete is a composite typically composed of aggregate and cement paste. It is the connection between these phases - the interfacial transition zone (ITZ) that is most important.. The ITZ is the weakest link in the composite system with lowest mechanical properties of the three [1-4], The ITZ can affect the overall elastic module and the stress distributions in a concrete material. The ITZ is comparatively more porous than that of bulk cement paste, and often less well bonded to the aggregate [3]. This region can have a low formation of calcium-silicate-hydrate (C-S-H gel), a product of Portland cement hydration responsible for the good mechanical properties and durability [5]. 

L. J. Parrot, M.Geiker, W. A. Gutteridge and D. Killoh Monitoring Portland Cement Hydration Comparison of Methods. Cement and Concrete Research, 20, (1990), p. 919-926. 

Fig. 4.38 Concentrations of some ions in solution during the Portland cement hydration with sucrose (according to [101])...

When mineral filler is used to improve mixture consistency and to adjust mixture breaking and curing properties, it can be Portland cement, hydrated lime, limestone dust, fly ash or other approved filler complying with the requirements of the appropriate standard. The percentage of filler added typically ranged from 0% to 3%, by weight of aggregate. 

Chen, Y, and Odler, I. (1992b) The progress of Portland cement hydration effect of clinker composition, in Proceedings 9th ICCC, New Delhi, Vol. 4, pp. 24-30. 

Odler, 1., and Woimemann, R. (1983) Effect of alkalis on Portland cement hydration. Cement and Concrete Research 13,771-777. 

Unlike Portland cement, hydrated aluminous cement pastes are resistant to diluted acid solutions with pH>4. This also includes natural waters containing dissolved CO2. One factor responsible for the good acid resistance of this cement is the absence of free calcium hydroxide among the formed hydrates, a phase that is easily soluble even in dilute acids. At the same time hydrous alumina is not dissolved at pH values down to 4. At very high pH values, such as those existing in alkah hydroxide solutions, corrosion of hardened aluminous cement may occur. Under these conditions AHj is dissolved in the liquid phase in the form of alkali aluminates. 

Some anions exhibit a distinct accelerating effect on Portland cement hydration. They include halides, nitrate, nitrite, formiate, thiosulfate, and thiocyanate. Their activity depends not only on the dosage used, but also on the identity of the associated cation. 

The way in which organic compounds are bound within the hardened Portland cement paste, and their effect on hydration and the stmcture of the Itydrates formed, may vary greatly. Compounds that are insoluble in water usually have no effect, whereas those that are at least partially soluble may or may not slow down the rate of hydration, alter the stmcture of the hydrated paste, and decrease its strength. Compounds that exhibit an adverse effect on Portland cement hydration include various phenols, chlorophenols, and ethylene glycol, whereas metlianol or ethanol have almost no effect (Gmtzek, 1992). 

The low strength of the transition zone is attributed to higher porosity and to the orientation of large CH crystals with weak intercrystalline bonds. Hadley (1972) has shown that hollow grains composed of Portland cement hydration products, which increased porosity, appeared more often in the interface than in bulk cement paste. These are known as Hadley grains, where the pores and voids may appear in the form of clusters, which create critical flaws. 

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