Portland cement slurries

Figure 15.7. Roofing tiles, extruded from an 80 vol. % fly ash, 20 vol. % Portland cement slurry and treated with supercritical COz...

Inorganic salt derivatives for Portland cement slurries Epoxy resin hardener for composites... 

Uses Dispersant for slurries of calcium carbonate, titanium dioxide, and china clays, esp. for concrete and portland cement slurries Features Replacement in detergents Properties Low vise. high solids Octasperse 590 [Octel Perf. Chem. Thornley]... 

Well cementing materials vary from basic Portland cement used in civil engineering construction of all types, to highly sophisticated special-purpose resin-based or latex cements. The purpose of all of these cementing materials is to provide the well driller with a fluid state slurry of cement, water and additives that can be pumped to specific locations within the well. Once the slurry has reached its intended location in the well and a setup time has elapsed, the slurry material can become a nearly impermeable, durable solid material capable of bonding to rock and steel casing. 

In addition to the four compounds discussed above, the final Portland cement may contain gypsum, alkali sulfates, magnesia, free lime and other components. These do not significantly affect the properties of the set cement, but they can influence rates of hydration, resistance to chemical attack and slurry properties. 

Special grades of gypsum hemihydrate are blended with Portland cement for types with reduced thickening time and setting time. Gypsum requires significantly more water addition. The maximal application temperatures are 70° to 80° C. Sodium silicate is used for cement slurries with diatomaceous earth. It can be used up to 7% by weight. 

A plugging slurry for oil and gas well drilling is given in Table 18-7 [1441]. It is formed by adding water to the Portland cement suspension containing the other three constituents. The bentonite clay powder is premixed with water... 

Incomplete displacement of fluid from the annular space can result in gaps in the cement sheath through which fluids from different formations can intermingle. In this situation, a "squeeze cementing" treatment is required to plug these gaps. Portland cement or rapidly setting sodium silicate slurries can be used in this operation. 

Geothermal cements are also employed to fix the steel wellbore casing in place and tie it to the surrounding rock (8). These are prepared as slurries of Portland cement (qv) in water and pumped into place. Additional components such as silica flour, perlite, and bentonite clay are often added to modify the flow properties and stability of the cement, and a retarder is usually added to the mixture to assure that the cement does not set up prematurely. Cements must bond well to both steel and rock, be noncorrosive, and water impermeable after setting. In hydrothermal applications, temperature stability is critical. Temperature cycling of wellbores as a result of an intermittent production schedule can cause rupture of the cement, leading to movement and, ultimately, failure of the wellbore casing. 

There are three fundamental stages in the process of manufacture of Portland cement, namely. (I) preparation of the raw mixture. (2) production of the clinker. (3) preparation of Ihe cement. Whether the process used is wet or dry. the raw materials are selected, analyzed, and mixed so dial, alter ireatmeni, Ihe product, or clinker, has a desired, narrowly specified composition A factory analysis of slurry, where the wet process is in use. is as follows calcium oxide 44%. aluminum oxide 3.5%. silicon oxide... 

Preparation of Hydrated Silicates. The hydrated silicate specimens used were all in the paste form—that is, mixtures of one of the calcium silicates with a limited amount of water to form a slurry, which sets and hardens as portland cement itself does. These pastes were prepared by the vacuum mixing procedure described by Powers, Copeland, Hayes, and Mann (23), adapted so that the temperature of the mix upon removal from the mixer was the temperature at which the specimen was to be hydrated. The 5° specimens were made by starting with an ice-water mixture the-50° specimens by starting with preheated water. A manostat was incorporated into the pumping system to prevent the pressure from dropping below the vapor pressure of water at the desired final temperature. This was especially important for the 50° mixes, to prevent excessive cooling. 

Lignosulfonates 400-550 Evaporation, precipitation, ultrafiltration, electrodialysis, ion exclusion Additive (oil well drilling muds, Portland cement concrete), dispersing agent and binder (textiles, products of printing industry, mineral slurries), raw material (vanillin, dimethyl sulfoxide, etc.)... 

In most applications, a small amount of binder powders is mixed with a large volume of inexpensive hllers and then the entire mixture is stirred in water to form the reaction slurry. For example, if the phosphate binders are used for manufacturing construction products, invariably the hllers are sand, gravel, ash, soil, or some mineral waste. The phosphate binders provide adhesion between the particles of these hllers and bind them into a solid object. Thus, these mixtures mimic conventional concrete mixmres in which Portland cement binder is mixed with large volume of sand and gravel to produce cement concrete. When phosphate binders are used, the products may be termed as phosphate concrete . In waste stabilization, the waste itself becomes the hller and the hnal product is termed as a waste form . 

Unlike Portland cement, the Ceramicrete slurry sets into a hard ceramic even in the presence of salts such as nitrates and chlorides hence, the Ceramicrete process has a great advantage over conventional cement technology with respect to the stabilization of some difficult waste streams, such as those from Hanford and Savannah River tanks. Wagh et al. demonstrated this advantage in several studies, wherein they produced monolithic Ceramicrete solids by using concentrated sodium nitrate and sodium chloride solutions in place of water to stabilize the waste streams. Details of some of these studies may be found in Ref. [21]. 

Portland cement is an aluminosilicate powder which sets to a solid mass on treatment with water. It is usually manufactured by grinding limestone and clay to a fine powder, mixing with water to form a slurry, and burning the mixture, with a flame of gas, oil, or coal dust, in a long rotary kiln. At the hot end of the kiln, where the temperature is about 1500 C, the aluminosilicate mixture is sintered together into small round marbles, called clinker. The clinker is ground to a fine powder in a ball mill (a rotating cylindrical mill filled with steel balls), to produce the final product. Over 100,000,000 barrels of cement per year is made in the United States. 

The development of the rotary kiln, now predominantly used for the production of Portland cement, started around the late 1870s but the technology was not patented until 1885 (Ransome [B.69]). A rotary kiln (Fig. 6.7-35) is a long refractory-lined steel cylinder that is inclined at about 3-6° to the horizontal. At the lower end is a burner (coal, oil, or gas fired) and the material to be calcined enters on the other end. While passing down the kiln, chemical and physical reactions take place in the oxidizing atmosphere. Hot clinker emerges at the burner end and must be suitably cooled before being milled to yield cement. The rotary kiln process may be carried out with wet (slurry), semi-dry, or dry feed. 

It is well known that portland cement is strongly basic because of the large proportion of calcium hydroxide. Figure 13 shows the viscosity of cement slurries in various liquids as a function of Brookfield shear rates. At 24 vol% cement in organic solvents, it showed lower viscosities than that in water. A strongly basic liquid medium, THF, exhibited the lowest viscosity with Newtonian be-... 

To test the potential of these two pozzolans to lower the pH of Portland-cement mixtures, the pH value of aqueous cement slurries containing PEGS and Silicol P were followed over time (Figure 7). In 1 1 mixtures, both additives shift the pH value below 11 after 4 days. PEGS, however, seems to be a more powerful pozzolan than Silicol P, since in 1 2 ratios, the pH stays below 11.5, while in a similar mixture with Silicol P the pH does not fall below 12.5. 

The lignosulphorrates, byproducts, from the paper industry, were used first, about 1930. Their role of slurry thirmers in Portland cement chrrker production by wet method was well known. 

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