The formation of cements

A comprehensive study on the formation of cement catalytic systems was performed by X-ray diffraction, thermal analysis, electronic diffuse-reflectance spectroscopy and IR-spectroscopy. Table 1 presents characteristics of some of the investigated catalytic systems. 

The critical evaluation of the results in Table 9 leads to the following conclusion it seems that the mechanical behaviour of the cements formed improves when more red gypsum is added to the cements, thereby approaching the resistance values of the commercial cement. In faet, in the YC sample (10 % red gypsum) the mechanical resistance values are similar to those for the commercial cement. This is important, as it supports the use of red gypsum as an additive in the formation of cements and because it is possible to reduce the amount of clinker used, with all the economic benefits that tliis entails (cost savings). In this sense, it is necessary to remember that the commercial cement taken as reference in our study is approximately 97% clinker and 3 % natural gypsum. 

The fluorine containing compounds are added to the raw cement mix to accelerate the formation of cement minerals. The effect of additionof fluorides sueh as LiF, NaF and KF on the reactions in the system CaC03-Si02 has been followed by DTA.t l The results are shown in Fig. 7. In the absence of the additions, the curve (solid line) shows a slope at about 920°C while those treated with the fluorides exhibit a slope at a temperature of about 700°C, indicating early commencement of reactions. The effectiveness of other mineralizers have also been examined by DTA. The influence of mineralizers such as ZnO, CuO, and Mn02 on the formation of alite from a mixture of calcium carbonate and a silica-bearing material such... 

The physicochemical characteristics of concrete depend on the behavior of the individual components of portland cement as well as on the cement itself. The second chapter provides essential information on cement and cement components so that the informationpresented in subsequent chapters can easily be followed. In this chapter, the formation of cement, the hydration of individual cement compounds and cement itself, physicochemical processes during the formation ofthe pastes, the properties ofthe cement paste, and the durability aspects of concrete are discussed. 

Sometimes primary cementations are not successful, for instance if the cement volume has been wrongly calculated, if cement is lost into the formation or if the cement has been contaminated with drilling fluids. In this case a remedial or secondary cementation is required. This may necessitate the perforation of the casing a given depth and the pumping of cement through the perforations. 

The chemistry of cement slurries is complex. Additives will be used to ensure the slurry remains pumpable long enough at the prevailing downhole pressures and temperatures but sets (hardens) quickly enough to avoid unnecessary delays in the drilling of the next hole section. The cement also has to attain sufficient compressive strength to withstand the forces exerted by the formation over time. A spacer fluid is often pumped ahead of the slurry to clean the borehole of mudcake and thereby achieve a better cement bond between formation and cement. 

Cement is then placed across the open perforations and partially squeezed Into the formation to seal off all production zones. Depending on the well configuration it is normal to set a series of cement and wireline plugs in both the liner and production casing (see Figure 16.2), to a depth level with the top of cement behind the production casing. 

Deflocculation and Slurry Thinning. Sihcates are used as deflocculants, ie, agents that maintain high sohds slurry viscosities at increased sohds concentrations. Soluble sihcates suppress the formation of ordered stmctures within clay slurries that creates resistance to viscous flow within the various sytems. Laboratory trials are necessary, because the complexity of the systems precludes the use of a universal deflocculant. Sihcates are employed in thinning of limestone or clay slurries used in the wet-process manufacture of cements and bricks, clay refining, and petroleum drilling muds (see also... 

Calcium Chelates (Salicylates). Several successhil dental cements which use the formation of a calcium chelate system (96) were developed based on the reaction of calcium hydroxide [1305-62-0] and various phenohc esters of sahcyhc acid [69-72-7]. The calcium sahcylate [824-35-1] system offers certain advantages over the more widely used zinc oxide—eugenol system. These products are completely bland, antibacterial (97), facihtate the formation of reparative dentin, and do not retard the free-radical polymerization reaction of acryhc monomer systems. The principal deficiencies of this type of cement are its relatively high solubihty, relatively low strength, and low modulus. Less soluble and higher strength calcium-based cements based on dimer and trimer acid have been reported (82). 

Factors that affect cell formation are the type of cement, the water/cement ratio and the aeration of the concrete [6]. Figure 12-1 shows schematically the cell action and the variation of the pipe/soil potential where there is contact with a steel-concrete structure. The cell current density is determined by the large area of the cathode [see Fig. 2-6 and Eq. (2-44)]. In industrial installations the area of steel surface in concrete is usually greater than lO m ... 

The adhesion of the tobermorite particles to each other and to the embedded aggregates is responsible for the strength of the cement which is due, ultimately, to the formation of -Si-O-Si-O bonds. 

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