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Chemical Portland cements

The Shoe grouting system is considered nonhazardous and nonpolluting. Sodium silicate is essentially nontoxic. Formamide is toxic and corrosive, but does not present a serious hazard if normal safety precautions are followed. Shoe chemical grout materials are two to five times more expensive than Portland cement, depending on the sodium silicate to formamide concentration ratios. Installed costs are generally more similar to those for cement grouts. [Pg.227]

Portland cement is manufactured by two basic processes, the wet process and the dry process. The dry process uses approximately 25% less energy per ton of Portland cement and is used to produce about 68% of the U.S. Portland cement. Both processes start by mixing selected raw materials, cmshed and/or milled to approximately s in. (1.9 cm) diameter, in the correct ratios to give the final desired chemical composition. [Pg.322]

Cement. Portland cement, a mixture of calcium siUcate and calcium aluminate minerals, is produduced by the calcination of argillaceous limestone or mixtures of limestone and clay (see Cement). Although other clays can be used, ka olin is preferred because of its alumina and siUca content and low level of impurities. It is especially desirable in the manufacture of white cement and other types requiring careful control of chemical composition. Air-floated ka olin, because of its low cost, is usually used. [Pg.210]

Cement and Concrete Concrete is an aggregate of inert reinforcing particles in an amorphous matrix of hardened cement paste. Concrete made of portland cement has limited resistance to acids and bases and will fail mechanically following absorption of crystalforming solutions such as brines and various organics. Concretes made of corrosion-resistant cements (such as calcium aluminate) can be selected for specific chemical exposures. [Pg.2457]

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. [Pg.1179]

The commercial product is actually a blend of different cements. This blending leads to a more constant quality. The chemical composition of Portland cement is typically 60% to 69% CaO, 18% to 24% Si02, 4% to 8%... [Pg.127]

Portland cement is susceptible to corrosion by CO2 and H2S. The chemical attack by CO2 is called carbonation. A microsample technique has been developed to study the CO2 corrosion in cements, because the corrosion is difficult to monitor with common test procedures [264]. This technique is also advantageous as an accelerated testing method. A polymer-modified cement has been tested in field studies [694]. The addition of silica also improves chemical resistance [146], in particular brine corrosion. [Pg.149]

Cracking can be caused by numerous physical and chemical phenomena in Portland cement materials. For example, freeze-thaw damage and ASR manifest themselves through crack development that may be studied using MRI. In addi-... [Pg.296]

Portland cement is a fine, soft, powdery substance that acts as a critical component in producing Portland cement concrete. When mixed in contact with water, the cement will hydrate and generate complex chemicals that eventually bind the sand and gravel into a hard, solid mass, known as concrete. [Pg.185]

Although low in volume compared with other foundry solid waste, baghouse dust may still be used beneficially in the production of portland cement. This opportunity arises from its attractive mineral composition silica, clay, and metal fines, which are needed in the cement kiln. Also, special efforts may be undertaken to characterize its chemical composition and purity. [Pg.186]

Unconfined compressive strength of cohesive soil Unconfined compressive strength index of chemical-grouted soils Slump of portland cement concrete... [Pg.189]

Surface bonding mortar or cement is mentioned in some building codes as an approved dampproofing treatment, but not as a waterproofing treatment. A number of manufacturers produce cements and mortars impregnated with fibrous glass or other fibers. Some of these may be chemically unstable in the alkaline environment of Portland cement. [Pg.1284]

Concretes made with Portland cement have a specific weight of 140 to 150 Ib/ft (2,242 to 2,400 kg/m ). Concrete absorbs the heat of a fire when chemically bound water is released from a crystalline structure and is reduced to lime. Dense concretes can be formed in place, or pneumatically sprayed to the required thickness using steel reinforcement. The corrosive effect of chlorides on the steel surface in moist saline environments (coastal or other chloride environments) dictates the use of protective primers and topcoat sealers. Major advantages of dense concrete are ... [Pg.147]

Chemical hxation is another possible process to handle drilling fluids. A typical process uses a mixture of potassium or sodium silicate with portland cement to turn a drilling fluid into a soil-like solid that may be left in place, used as a landhll, or even used as a construction material [13]. [Pg.276]

The replacement of Portland cement by fly ash class F (ASTM C 618) has been found to reduce the rate of slump loss in a prolonged mixed concrete, and the extent of the reduction is greater with increased cement replacement (Fig. 7.37). Fly ash also was found to be beneficial in reducing slump loss in concretes with conventional water-reducing and retarding admixtures [95], The effect of fly ash on reducing slump loss can be attributed to chemical and physical factors. It was found that the surface of fly ash particles may be partly covered with a vapor-deposited alkali sulfate that is readily soluble [103, 104], Thus the early hydration process of Portland cement is effected because sulfate ions have a retarding effect on the formation of the aluminates. Indeed, fly ash was found to be a more effective retarder than an... [Pg.490]

Reports of incompatibility between Portland cement and chemical admixtures have increased over the past 10 years. Rapid set, accelerated stiffening, increase in time of set, lack of water-reduction are some of the reported problems. Such effects produced by the interaction of the composition of the cement and that of the chemical admixtures has been often referred to as cement-admixture incompatibility . This is discussed below. [Pg.525]

Pozzolanic S/S systems use portland cement and pozzolan materials (e.g., fly ash) to produce a strucmrally stronger waste/concrete composite. The waste is contained in the concrete matrix by microencapsulation (physical entrapment). It is a chemical treatment that uses commercially available soluble silicate solutions and various cementious materials such as cement, lime, poz-zolans, and fly ash. By addition of these reagents and rigorous mixing, the waste is fixed or stabilized. Contaminant mobility is reduced through the binding of contaminants within a solid matrix, which reduces permeability and the amount of surface area available for the release of toxic components. [Pg.880]

Use lower doses of chemicals than traditional treatments such as lime or Portland cement. [Pg.927]

Although many Ca-rich fly ashes are self-cementing, strength gain is usually too slow for most practical applications. Moreover, aluminosilicate rich ashes are essentially unreactive with water. The most important application of fly ash is as a partial replacement for Portland cement. In this application, Portland cement furnishes much of the early strength, up to 1 month, while the high alkalinity of cement chemically activates the ash such that its slow reaction with cement components and water contribute increasingly to... [Pg.217]

The Romans pioneered the use of hydraulic, or water-cured, cement. Its unique chemical and physical properties produced a material so lasting that it stands today in magnificent stmctures like the Pantheon. Yet the formula was forgotten in the first few centuries after the fall of the Roman Empire and wasn t rediscovered until 1824 as Portland cement. One Roman version was based on a burned mixture of two major components volcanic ash—called pozzolana—from Mount Vesuvius, which destroyed Pompeii and nearby towns in... [Pg.444]


See other pages where Chemical Portland cements is mentioned: [Pg.44]    [Pg.44]    [Pg.227]    [Pg.322]    [Pg.322]    [Pg.295]    [Pg.120]    [Pg.905]    [Pg.54]    [Pg.180]    [Pg.5]    [Pg.168]    [Pg.169]    [Pg.172]    [Pg.182]    [Pg.185]    [Pg.185]    [Pg.185]    [Pg.244]    [Pg.11]    [Pg.454]    [Pg.120]    [Pg.125]    [Pg.289]    [Pg.375]    [Pg.525]    [Pg.53]    [Pg.53]    [Pg.211]    [Pg.218]   
See also in sourсe #XX -- [ Pg.394 ]




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