Portland cement studied

In Portland cement studies [14] the reductions in initial and final setting times were determined as a function of the number of gram moles of calcium ion introduced and a straight-line relationship was established as shown in Fig. 5.7. 

T. G. Nunes, P. Bodart and E. W. Randall, The hardening of Portland cement studied by H stray field imaging influence of concentration and evaporation rate of water. Proc. Second Int. Conf. NMR Spect. of Cement Based Mater, (eds P. Colombat and H. Zanni), Springer Verlag, Weinheim, 1997, p. 411. 

Portland cement is susceptible to corrosion by CO2 and H2S. The chemical attack by CO2 is called carbonation. A microsample technique has been developed to study the CO2 corrosion in cements, because the corrosion is difficult to monitor with common test procedures [264]. This technique is also advantageous as an accelerated testing method. A polymer-modified cement has been tested in field studies [694]. The addition of silica also improves chemical resistance [146], in particular brine corrosion. 

Slag-mix, solidified mud, and conventional class H Portland cement were evaluated under controlled laboratory conditions to better understand and quantify differences in drillability between these two types of cement under realistic down-hole conditions. The objectives of this study were to refine bit selection and drilling practices for more cost-effective slag-mix plug drilling. 

Cracking can be caused by numerous physical and chemical phenomena in Portland cement materials. For example, freeze-thaw damage and ASR manifest themselves through crack development that may be studied using MRI. In addi-... 

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. 

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 ... 

Flats plant. All of the methods studied eliminated the potential for free liquids and excessive amounts of particulate. The methods included (1) addition of a Portland cement/diatomite mixture, (2) solidification using microwave technology, (3) cementation with Portland cement, and (4) polyethylene solidification. All costs were based on a production rate of 178,840 lb of wet sludge per year. The cost reduction (dollars per pound of sludge) relative to Portland cement/diatomite was 11.68 (1993 dollars) for microwave solidification, 10.45 (1993 dollars) for polyethylene solidification, and 8.07 (1993 dollars) for cementation. Table 1 gives a breakdown of these costs (D1353911, p. 8). 

Kundu, S., Kavalakatt, S.S., Pal, A. et al. (2004) Removal of arsenic using hardened paste of Portland cement batch adsorption and column study. Water Research, 38(17), 3780-90. 

Cement was chosen for the present study because of its low cost, simplicity of use, and stability in most environments. It is, however, rather porous. Also, in the presence of water, hydrolysis reactions promoted by the high pH of the cement can cause conversion reactions resulting in the release of iodine from many compounds. Type III Portland cement was chosen because of its early strength (curing time 8 days). 

Clark, W. E. "The Isolation of Radioiodine with Portland Cement. Part 1 Scoping Leach Studies," Nuc. Tech. 36 215-221, 1977. 

The inherent instability of sulfur-infiltrated concrete in aqueous media illustrated in this study may be the most important factor in utilization, because it will affect long-term durability of the concrete in many natural settings. The Ca(OH)2 produced by the hydration of portland cement is a principal reactant in the leaching process, and while it remains sulfur could be extracted, leaving the matrix vulnerable to other destructive processes. The removal rate of sulfur will vary greatly, depending mostly upon the pH of the immersion medium thus, the concrete deteriorates in alkaline sulfatic soils but is relatively stable in the corrosive neutral sulfatic solutions from the sodium sulfate plant. 

Gutt and Smith (GI6) reviewed earlier work on the effects of SO3 on the formation of Portland cement clinker, and to augment the available information studied part of the Ca0-Al203-Fe203-Si02-CaS04 system at 1400°C. They concluded that, if AI2O3 was present and MgO absent, even small proportions of SO3 could restrict or prevent formation of C3S. The effect was lessened, but not eliminated, if MgO was present, and it was noted... 

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 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. 

Silicate anion structures in Portland cement pastes have been studied by the methods described in Section 5.3.2 for calcium silicate pastes. Trimethylsily- i lation (TMS) studies (L20,T12,S69,T36,L31,M43,M44) show that, as with C,S. the proportion of the silicon present as monomer decreases with age and that the hydration products contain dimer, which is later accompanied and eventually partly replaced by polymer (>5Si). Some results have i indicated that fully hydrated pastes of cement differ from those of CjS in that substantial proportions of the silicate occur as monomer (S69,L31), but the results of a study in which pastes of CjS, P-CjS and cement were compared (M44) suggest that the differences between the anion structures of cement and CjS pastes are probably within the considerable experimental errors inherent in the method. The recovery of monomer from unhydrated P-CjS was only 66% and results for cement pastes can only be considered semiquantitative. 

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