Concretions coalescence

Fig. 6. Typical lithofacies of the Namorado Sandstone. Fine- and very fine.grained sandstones arranged as turbidite cycles, each capped by shale and siltstone. Pervasively calcite-cemented beds resulted from concretion coalescence. Both individual concretions and calcite-cemented beds are discontinuous on the lateral scale as indicated by core analysis of a recently drilled horizontal well. Concretions show variable shapes and intensity of cementation, and a gradual vertical transition to partially cemented and porous intervals.

Calcium chloride has several industrial applications. The major applications of this compound are in deicing of roads, dust control, imparting stability to roads and buildings, and to improve traction in tractor tires. It is mixed with ice to make freezing mixtures. Hexahydrate mixed with crushed ice can lower the temperature of the cooling bath to below -50°C. It also is used as a desiccant for dehydrating gases and liquids. It is added to cement in various proportions to manufacture different types of concrete. Other uses are in adhesives, to lower gel temperatures, and as a calcium source in liquid feed supplements for dairy cattle. Also, the compound is used to control particle size development and reduce coalescence in plastics. 

It is believed that in the presence of dampproofing admixtures, the surfaces of the concrete, and the internal surfaces of the pores become coated with either a layer of molecules in the case of stearic acid and other fatty acids (Fig. 4.5b) or a layer of coalesced or separate particles of material in the case of waxes and bitumens, etc. (Fig. 4.5c). The end result in both cases is the production of hydrophobic surfaces exhibiting high contact angles to water, as shown in Fig. 4.6. 

Modification of mortar and concrete in the presence of a latex occurs by concurrent cement hydration and formation of a polymer film (coalescence of polymer particles and the polymerization of monomers). Cement... 

The chemical materials used to produce dampproofers are able to form a thin hydrophobic layer within the pores and voids and on the surfaces of the concrete in one of three ways (1) reaction with cement hydration products (2) coalescence... 

The molecular weight, glass transition temperature (T) and size of dispersed polymer particles in the latexes can affect the strength and c loride ion permeability of latex-modified mortar and concrete to a certain extent [87,93] (Tables 6.11 and 6.12). SBR latexes with smaller particle size appear to initially provide lower chloride ion permeability to the mortars, but a difference in the permeability between the smaller and larger particle sizes eventually becomes insignificant as the concrete ages. The initial decrease in the permeability observed with smaller particles is attributed to the fact that smaller particle size coalesce into films faster than the larger particle sizes. 

Patchy or microconcretionary calcite cement, i.e. millimetre- to centimetre-sized specks of calcite cement with spacings that are also typically in the millimetre to centimetre range, seems to be less common than pervasively calcite-cemented concretions and layers, and has only been described from cores (Walderhaug Bjorkum, 1992). The cemented specks may apparently coalesce to form larger calcite-cemented volumes (Plate 4), but owing to the lack of outcrop data it is uncertain what shapes and sizes calcite-cemented volumes formed by the coalescence of calcite cement patches actually have. 

Calcite cement is the dominant cement type in the central basin. Cemented zones can be visually recognized in cores and are from 10 cm to, in a few cases, more than 1 m thick (Boles Ramseyer, 1987). Cement zones cannot be easily traced between wells spaced as close as 100 m, suggesting that the intensely cemented zones are relatively isolated and discontinuous, certainly on a basin scale and in most cases on a reservoir scale. Most cement zones have not been studied in sufficient detail to establish growth patterns. A few detailed analyses of individual zones show that some have a composite history (i.e. variable isotopic compositions) on a scale of less than 0.5 m (e.g. cement zone at North Coles Levee, well NCL 488-29, 2621 m depth), whereas others show little variation (Schultz et al., 1989). Systematic growth patterns, such as are typical for concretions in shales (e.g. Raiswell, 1971 Boles et al., 1985) or in concretions that coalesce to form continuous cemented beds (Bjor-kum Walderhaug, 1990), have not been recognized in the zones studied to date. Apart from extensively cemented zones, calcite occurs as scattered crystals in many samples. 

Further, the availability and proximity of a large source of carbonate material, namely the bioclasts and carbonate intraclasts within the Namorado Sandstone, probably provided supersaturation conditions and sites of nucleation for intense calcite cementation. Sombra et al. (1995) attributed the tabular geometry of calcite-cemented zones to the lateral coalescence of concretions in carbonate clast-rich units in the Namorado Sandstone. 

Although polymers and monomers in any form such as latexes, water-soluble polymers, liquid resins, and monomers are used in cement composites such as mortar and concrete, it is very important that both cement hydration and polymer phase formation (coalescence of polymer particles and the polymerization of monomers) proceed well to yidd a monolithic matrix phase widi a network structure in which the hydrated cement phase and polymer phase interpenetrate. In the polymer-modified mortar and concrete structures, aggregates are bound by such a co-matrbc phase, resulting in the superior properties of polymer-modified mortar and conoete compared to conventional. 

Third Step. Ultimately, with water withdrawal by cement hydration, the close-packed polymer particles on the cement hydrates coalesce into continuous films or membranes, and the films or membranes bind the cement hydrates together to form a monolithic network in which the polymer phase interpenetrates throughout the cement hydrate phase. Such a structure acts as a matrix phase for latex-modified mortar and concrete, and the aggregates are bound by the matrix phase to the hardened mortar and concrete. 

Formation of continuous polymer films in mortar or concrete due to a lower minimum film-forming temperature than the application temperature, and the high adhesion of the polymer films to cement hydrates and aggregates. (The minimum film-forming temperature is defined as the lowest temperature at which the polymer particles of a latex have sufficient mobility and flexibility to coalesce into a continuous polymer films.)... 

Integration of corpuscles can go two ways as a result of isothermal distillation, if corpuscles liquid (Calvin s effect), and as a result colUsions and an adhesion-Concretions. In case of merge of liquid corpuscles, this process name coalescence. So, generally as concretion is called decrease of degree of dispersion, i.e., decrease of number of corpuscles of a disper-soid at their integration [13-18]. 

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