Portland cement paste microstructure

Harrisson ct til. (H4.H49) represented the results of X-ray microanalyses of individual spot analyses in all parts of the microstructure other than unreacted clinker grains on plots of Al/Ca ratio against Si/Ca ratio and of Mg/Ca ratio against Al/Ca ratio (Figs 9.1 and 9.2). If the analyses of the material formed in situ from the slag are excluded, the plot of Al/Ca against Si Ca is broadly similar to those obtained for pure Portland cement pastes, and may be interpreted in the same way (Section 7.2.5). 

Halse and Pratt (H57) reported SEM observations on pastes hydrated at various temperatures. In those hydrated at 8°C or 23 C, the main feature was fibrous material that was considered to be hydrous alumina, but which could also have been partly dehydrated CAH,q. The hydrating grains of cement were surrounded by shells of hydration products, from w hich they tended to become separated in a manner similar to that observed with Portland cement pastes (Section 7.4.2) though the authors recognized that this could have been partly due to dehydration. Two-day-old pastes hydrated at 40"C showed spheroidal particles of CjAH and thin, flaky plates of gibbsite. In pastes mixed with sea water, hydration took place more slowly, but no other effects on microstructural development were observed. 

Shi, C. et al. (1992a) Composition of the microstructure and performance of alkali-slag and Portland cement paste, in Proceedings 9th ICCC, New Delhi, Vol. 3, pp. 298-304. 

The prineiple hydration produets of slag cements are essentially similar to those found in pordand eement pastes. The microstructure of slag cement pastes is also similar to that of portland cement pastes. X-ray microanalysis has, however, shown that the C/S ratio of C-S-H product in hydrated slag cement is lower than that found in portland cement paste. 

Whilst the microhardness values of hydrated portland cement paste lie between those for Reg Set cement paste with 2 and 5% CaCl2, the modulus of elasticity values for hydrated portland cement paste are higher than for any of the Reg Set cement pastes. It is suggested that the processes of microstructural deformation occurring in microhardness and modulus of elasticity measurements are influenced in different ways by bond formation during the hydration of Reg Set cement in the presence of CaCl2. 

Lothenbach, B., F. Winnefeld, C. Aldei E. Wieland and P. Lunk (2007). Effect of temperature on the pore solution, microstructure and hydration products of Portland cement pastes . Cement and Concrete Research 37(4) 483—491. 

Figure 3.16 Automatic dilatometry using webcam and the EPFL procedure (see Table 3.1) on replicate samples of portland cement paste (CEM I 52.5R, w/c = 0.4, mixed 2 min at 1600 rpm). (After Berodier, E.. Impact of the supplementary cementitious materials on the kinetics and microstructure development of cement hydration, PhD thesis, Ecole Polytechnique Federale de Lausanne, Switzerland, 2014.)...

Richardson, I. G., and G. W. Groves. 1993. Microstructure and Microanalysis of Hardened Ordinary Portland Cement Pastes . Journal of Materials Science 28 (1) 265-277. 

Backscattered electron and X-ray images obtained in the SEM (021,U17,S68) show that the microstructures of hardened pastes of cement or CjS with pfa broadly resemble those of pure Portland cements, though, as would be expected, there is considerably less CH. Reaction rims may be seen around the pfa particles in sufficiently old pastes. 

The structure of concrete-like materials may be considered at different levels (cf. Section 2.4). The lowest level, where the required resolution of observation is of the order of a few Angstroms, is used mostly for examination of the microstructure of cement paste. The main interest is concentrated between so-called micro- and macro-levels, which means between the size of Portland cement grains or of small pores of a few micrometers in diameter, up to tens of millimetres for maximum grains of coarse aggregate and the diameters of steel bars. 

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