Water porosity

Powers and Brownyard defined the total porosity as the sum of the capillary and gel porosities. Because the term total porosity has been used by some later workers in other senses, we shall refer to such values as total water porosities . As hydration proceeds, the capillary and total water porosities decrease and the gel porosity increases. Table 8.1 gives some values of the three types of porosity obtained from the above formulae, using the data given in Section 8.2.2 as typical. 

Fig. 8.5 Relations between porosities (volume percentages) and water/ccmcnt ratio for mature Portland cement pastes. The experimental data are for pastes at least 8 months old, and the calculated curves relate to a typical cement aged 18 months. Open symbols total water porosities. Filled or half-filled symbols mercury porosities. Curve A total water porosity. Curve B free water porosity. Curve C capillary porosity. References to data O (P20) O (S77) A (F33) V (M68) (S78) (F34) 9 (019) (M68) (D3I) 3 (H4I). In the last two cases, porosities by volume were estimated from data referred in the original sources to masses of dried paste, assuming the tatter to have contained 0.23 kg of water per kg of cement having a specific volume of 3.17 x 10 m kg h...

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. 

Total water porosities are obtained experimentally from the loss in weight when a saturated paste is D-dried or subjected to some procedure regarded as equivalent, such as heating to constant weight at 105 "C. Reabsorption of water by materials thus dried gives identical results (D32). The procedures should be carried out under COj-free conditions. A value for the specific volume of the evaporable water must be assumed this has usually been 1.00 X lO m kg . Fig. 8.5 includes typical values thus obtained. 

Feldman (F33) explained his results in terms of the Feldman-Sereda model as follows. If the paste is D-dried, water is lost from the interlayer spaces. If the sample is immersed in water, this water is reabsorbed, and the total water porosity therefore includes the volurrie of the interlayer space. Methanol does not penetrate into this space, and helium does so only slowly, so that lower porosities are obtained. If the sample is equilibrated at 11% RFI, the interlayer spaces are largely filled, and the lower value is obtained irrespective of the fluid used. The helium porosities reported by Feldman were near to the calculated free water porosities. 

Typical results (Fig. 8.7) show that the distribution moves to smaller values as hydration proceeds. The observed porosity is mainly in the 3 nm to 1 pm range for young pastes, and in the 3-100 nm range for mature pastes. For mature pastes of low w/c ratio, which according to the Powers-Brownyard theory consist entirely of hydration product, nearly all the porosity is below 50 nm (S77). We shall refer to the porosities obtained using mercury at the maximum pressures employed as mercury porosities. Typical values for mature pastes (Fig. 8.5) are somewhat lower than the calculated free water porosities. 

The earlier literature contains several references to missing porosity, meaning the difference between mercury porosities and total water porosities. The difference clearly arises mainly from the failure of mercury to enter vacated interlayer space but has also been attributed to the encapsulation of gel by CH (D33) or to the presence of large (> 15 pm), closed pores that are not entered (A 15). 

These results suggest that, in attempts to relate strength to porosity, the total water porosity should not be used, the capillary or free water porosity or the volume of pores above a certain size being more appropriate. Parrott and Killoh (P30), in relation to their modelling of properties, similarly considered the volume, size and continuity of the larger pores to be the relevant quantities. 

Subsequent studies have shown that K is not related to the total water porosity but depends on the volume and connectivity of the larger pores. Mehta and Manmohan (M75) and Nyame and Illston (N16) found linear relations between log and estimates of the maximum continuous pore radius, obtained from MIP, and other quantities derived from the pore size distribution and degree of reaction. A high proportion of the flow appears to be through pores wider than about 100 nm. Typical values of log K for mature pastes cured at ordinary temperatures range from around - 13.4 at w c 0.3 to around — 11.8 at w/c 0.7 (M75,N16,G67,M76,H47). K increases with temperature (G67,M76). 

Calculations based on reaction stoichiometry and densities of phases support the conclusions from experimental observations that mature pastes of composite cements are more porous than comparable pastes of Portland cements. This is indicated by the results in Table 7.3, 9.4 and 9.6. Similar calculations for 180-day-old pastes of w/s 0.45 indicate free water porosities of about 24% for a typical Portland cement, 35% for a cement with 40% slag, 35% for one with 40% pfa and 32% for one with 30% microsilica. The calculated values are in all cases somewhat higher than observed mercury porosities (F34,F41). 

Samples number Formation Mineralogy Texture Pore-types F m Chargeability M=Ri/(Rr.+Rn) n Water porosity Permeability (mD)... 

Fig. 5 Chargeability factor A/can be predicted by a Fig. 6 Permeability prediction from electrical multi-linear model composed by different behaviour and structures parameters of porous parameters formation factor F, water porosity O, solids, k Katz and Thompson model Hg-specific surface Asp and water permeability k for kjsc Johnson, Schwartz and co-workers different textures. model.

Chargeability factor M depends on the brine/gas saturation of porous solids. Figure 3 gives the relationship between the chargeability and brine saturation for two samples. We noted that the M decreases hardly with the decrease of the brine saturation. The presence of vugs and karsts pore types (sample 9-LS8) seems to speed up the decrease of the M Chargeability factor M can be explained by a multi-linear model composed of different structures parameters such as the formation resistivity factor, water porosity, Hg-specific surface area and water permeability, e.g.. Fig. 5. 

Wood is a hygroscopic, porous, anisotropic and non-homogeneous material. After log sawing, the lumber contains liquid water in fiber cavities (capillary water) and bound water inside the fiber wall (hygroscopic water). Porosity refers to volume fraction of void space. This void space can be actual space filled with air or space filled with both water and air. Capillary-porous materials are sometimes defined as those having pore diameter less than... 

However, these organic-rich and young sediments are mostly extremely rich in water (porosity values up to 0.9) and very soft, so that every sample removal will most likely induce a perturbation of the boundary zone which is, in a crucial way, maintained by diffusion. 

Chu and co-workers at Cornell investigated the combination of PGA and Dacron. They produced knitted fabric grafts composed of PGA and Dacron fibers blended at various compositional ratios. They studied the properties of these bicomponent fabrics in vitro. Their major finding was the achievement of increasing water porosity over time without significant losses in the structural integrity and strength of the specimens. 

Marine specimens are assumed saturated because the volume of gas Vg cannot normally be measured and is therefore neglected. The volume of voids therefore equals the volume of pore water. Porosity is then given by the following ... 

Studies of rock cores from oilfields are used in the petroleum industry to assess the hydrocarbon content of rock strata and the ease with which the oil can be recovered. The GeoSpecT NMR Rock Core Analyser, a 2 MHz TD-NMR from Oxford Instruments, can provide information on the fluids in oil- and water-saturated rock including oil viscosity and clay-bound water, porosity, fluid distribution, and permeability. Rock cores can be studied at high temperatures and pressures and the instrument can provide diffusion and imaging information. 

F formation factor, m cementation factor n saturation exponent water porosity water permrability (mD) ... 

Water porosity Total porosity, hydric properties Little sampling damage Physical decay, structural damage... 

Porosity of. the Teflon core to nitrogen was 24.8 percent. The water filled pore volume was 375 cc, which corresponds to a porosity of 21 percent. The difference between the nitrogen and water porosities is attributed to the wettability characteristics of... 

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