Calcareous cement

This process, usually carried out in a kiln and at a temperature well above 600°C, seems to have been practiced as early as the Stone Age (Gourdin and Kingery 1975). Quicklime is a basic component of calcareous cement. Before the cement can be prepared, however, it is essential to slake (disintegrate and break up) the quicklime by the addition of water water reacts with quicklime to form slaked lime, composed of calcium hydroxide ... 

The chemical cement that holds the grains together is also important in characterizing mechanical sediments. A calcareous cement, the most common of which is calcite, will result in a rock that is susceptible to chemical attack. A sediment in which quartz is the dominant cement will be much more stable in some environments. Other chemical cements include gypsum, some salts, and various iron oxides. 

Below the sediments disrupted by cultivation, a unit (Unit A) was found that was about 120 cm thick and that contained a disorderly mixture (almost an inverse time sequence) of Roman, Pharaonic, and Predynastic sherds. The next 15 cm or so was a clay-rich Nile silt (Unit B) in which there was a normal ceramic sequence with sherds dating from about 300 B.C. to about 2500 B.C. Table I describes the typical core sample. The layers of sediments were compacted and, in some cases, partially hardened by a calcareous cement, but in all cases, the samples could be easily crumbled. 

Clinchfield Sand. The Lisbon Formation is unconformably overlain by about 27 ft of interfingering unconsolidated quartz sand and quartz sand containing calcareous cement. The medium-grained, well-sorted quartz sand is stratigraphically equivalent to the basal upper Eocene sand deposit that Herrick (19) described as the Clinchfield Sand. 

VI. Experiments and Observations made With the View of Improving the Art of Composing and Applying Calcareous Cements And Of preparing Quicklime Theory of these Arts And Specification of the Author s cheap and durable Cement, for Building, Incrustation or Stuccoing, and artificial Stone, 8 , London, 1780, pp. xi, 233. 

The history of calcareous cement and concrete is briefly summarized by Lea (1970) and also by Stanley (1979) who describes a number of individual structures significant to the development of concrete technology. A much more in-depth history is given by Mallinson Davies (1987) who also provide a thorough review of the early literature. Jull Lees (1990) give a brief ancient history of lime mortars and poz-zolanic cements. 

Because calcium oxide comprises about 65% of Pordand cement, these plants are frequendy situated near the source of their calcareous material. The requisite silica and alumina may be derived from a clay, shale, or overburden from a limestone quarry. Such materials usually contain some of the required iron oxide, but many plants need to supplement the iron with mill scale, pyrite cinders, or iron ore. Silica may be supplemented by adding sand to the raw mix, whereas alumina can be furnished by bauxites and Al202-rich flint clays. 

Cement is made of calcareous and argillaceous rock materials that are usually obtained from quarries. The process of making cement requires that these raw rock materials be ground, mixed and subjected to high temperatures. 

PawPaw Formation Calcareous marl East Texas, USA Pepper Shale East Texas, USA Pierre Shale South Dakota, USA 29 samples Phosphatic pebbles and cements Dover Sandstone, Pensacola Mountains, Antarctica Phosphorite (typical values)... 

Two types of materials are necessary for the production of portland cement one rich in calcium (calcareous), such as limestone or chalk, and one rich in silica (argillaceous) such as clay. These raw materials are finely ground, mixed, and heated (burned) in a rotary kiln to form cement clinker. 

The thermal conditions at site 504 are very different from those at site 505 (Table 8.4). Physical property measurements at both sites reveal systematic downhole changes and differences between the trends for the two sites. For example, Figure 8.18 shows the porosity-depth curve for the sediments at sites 504 and 505. It is evident that the porosity decreases more rapidly in the higher temperature site 504 calcareous sediments than in the lower temperature site 505 sediments. As would be anticipated from the porosity trends, the compressibility of the sediments decreases systematically with increasing depth. At a similar depth below the sea floor, site 505 sediments are more compressible than those at site 504. All the sediments are over-consolidated, a result of diagenetic cementation. 

These differences in the physical properties of pelagic calcareous sediments at DSDP sites 504 and 505 are a result of the temperature difference between the two sites. A more rapid decrease in diagenetic potential is favored by increasing sediment temperature. The rates of the diagenetic solution-precipitation reactions are increased because of the higher temperature (Baker et al 1980), and the accompanying increased concentrations of ions involved in cementation (Mottl et... 

Figure 8.19. Calculated cement volumes for DSDP sites 504 and 505 calcareous sediments. In the high heat flow area of site 504, cementation starts at a shallower depth and a larger cement volume is observed than at the "cooler" site 505. (After Wetzel, 1989.)...

At shallow depths carbonate cements may cause sands to become brittle and hard. Carbonate which precipitates on the sea floor may also form hard grounds in dominantly clastic sequences. Sandstones may become calcite cemented due to dissolution of biogenic aragonite at relatively shallow depth (less than a few hundred meters). Calcareous sediments flushed by meteoric water at shallow depth or exposed during regression may become rapidly ce-... 

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