Pore, capillary coarse

Concrete is a composite material composed of cement paste with interspersed coarse and fine aggregates. Cement paste is a porous material with pore sizes ranging from nanometers to micrometers in size. The large pores are known as capillary pores and the smaller pores are gel pores (i.e., pores within the hydrated cement gel). These pores contain water and within the water are a wide variety of dissolved ions. The most common pore solution ions are OH", K+ and Na+ with minor amounts of S042" and Ca2+. The microstructure of the cement paste is a controlling factor for durable concrete under set environmental exposure conditions. 

The saturated zone is formed by porous material in which all the pore spaces are filled with water. The water table is defined as the depth at which pore water pressure equals atmospheric pressure. If a hole is dug down to the saturated zone, the location of the water table can be easily determined it is at the depth to which water accumulates in the hole. In coarse porous material, the location of the water table itself very nearly approximates the transition between saturated and unsaturated material in a fine-textured porous material, enough water may move upward by capillarity to cause complete saturation of a measurable thickness above the water table (the capillary fringe). 

The ability of soil to hft water from the water table level depends on capillary action. It has been calculated that the following soil types can lift water to the indicated heights (a) fine gravel - 0.1 m (b) coarse sand - 0.5 m (c) fine sand - 2 (d) silt - 10 m (e) clay 50 m. Estimate the average pore size in each soil type. 

When disperse phase of the coarse emulsion wets the membrane wall and suitable surfactants are dissolved in both liquid phases, the process results in a phase inversion namely a coarse OAV emulsion is inverted into a fine W/O emulsion (Figure 6.1c), and vice versa (Suzuki et al, 1999). The main advantage of this method is that a fine emulsion can be easily prepared from a low concentration coarse emulsion at high rates. For polytetrafluoroethylene (PTFE) membrane filters with a mean pore size of 1 im, the maximum dispersed phase volume fraction in phase-inverted emulsions was 0.9 and 0.84 for O/W and W/O emulsions, respectively (Suzuki et al., 1999). Flow-induced phase-inversion (FIPI) phenomenon was observed earlier by Akay (1998) who used a multiple expansion-contraction static mixer (MECSM) consisting of a series of short capillaries with flow dividers. Hino et al. (2000) and Kawashima et al. (1991) inverted a W/O/W emulsion made up of liquid paraffin. Span 80 (a hydrophobic surfactant), and Tween 20 (a hydrophilic surfactant) into a W/ O emulsion by extrusion through polycarbonate membranes with a mean pore sizes of 3 and 8 im. Inside the membrane pores, surfactant molecules are oriented with their hydrophobic groups toward the wall surface and with hydro-phihc groups toward the solubilized water molecules as a result of a lamellar structure formed inside the pores. The structure ruptured at the pore outlets. 

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