Alite volume

Parrott and co-workers (P30,P32,P35,P33) described a more sophisticated method for modelling the hydration process. The fraction of the total water porosity that was below 4nm was calculated by multiplying the volume fraction of C-S- H by an appropriate factor, which depended on whether the C-S-H was formed from alite or belite, the temperature and the amount of space available. The constants assumed were based on experimental data obtained using a procedure based on methanol sorption (Section 8.3.4). The effect of drying was allowed for (P35) by introducing a factor of 0.7 - -1.2(RH — 0.5) for 0.5 < RH < 1, or of 0.7 for RH 0.5. These refinements allow some deviation from the Powers-Brownyard postulate of a fixed volume ratio of gel porosity to product. Typical results for the volume fractions of pores larger than 4 nm in mature pastes of a cement with an alite content of 56% were approximately 0.26, 0.16 and 0.07 for w/c ratios of 0.65, 0.50 and 0.35, respectively (P32). For the two higher w/c ratios, these results are near the capillary porosities of Powers and Brownyard, but for w/c 0.35 the latter value is zero. 

Parrott et al. (PI9) used butane. sorption to determine the volume of pores smaller than 50 nm. For a 28-day-old alite paste of w/s 0.59, a volume porosity of 27% was obtained. 

Figure 5.12 Industrial scale installation for the detonation synthesis of diamond at the Alit Corp. in Zhitomir (Ukraine). The reactor s volume is about 100m ( Alit Corp.).

The crystal lattice constants of alite (a,b,c) and unit cell volume (V), determined by XRD, were studied in relation to alite double refraction (Ono, 1984). Alite with high double refraction was characterized by long a and short b and c, V was decreased, and (a/bY was large. Laboratory-prepared alite, burned at high temperature for a long time, had a small V, large (a/ bY, and a high double refraction. Therefore, XRD can be used in much the same way as the microscope in the quality control of clinker. 

Linear traverse methods, which record crystal chord lengths and calculate volume and weight percentages as well as specific surfaces of alite and belite, have recently been used to study clinker thermal history and... 

XRE gives the total amount without differentiating between the amounts in exsolved regions and in solid solution in alite. The microscopy techniques permit the selection of regions without clusters. With SEM techniques, because of the large interaction volume, subsurface clusters not visible from the surface may be included, but the relatively large distance between exsolved regions makes this unlikely. The STEM technique allows a localised analysis of the composition, since the interaction volume is small because of the small thickness of the sample. Table 8.1 compares the results obtained with the different techniques to the calculated amount of each element from the synthesis recipe. 

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