Portland cement surface

Water-Repellent. Three techniques used for water repeUency are modification of cement by the addition of waterproofers, use of repellent additives to the concrete mix, and surface treatment of concrete stmctures with repellents. The modification of portland cement by intergrinding with stearate salts or other water-repellent material can reduce the water permeabiUty of mortar. Considerable controversy exists, however, as to whether these cements produce concrete that is superior to carefully mixed concrete without such additives (79). 

Other Types of Portland Cements. White Portland cementis standard Type I or III Pordand cement with raw materials selected and controUed to have negligible amounts of Hon and manganese oxides, which impart the gray color. The white Pordand cement is used in decorative and architectural appHcations like precast curtain waUs, terra22o surfaces, stucco, tile grout, and decorative concrete. 

Asbestos Cement Asbestos-cement pipe is seamless pipe made of sihca and portland cement, compacted under heavy pressure, uniformly reinforced with asbestos fiber, and thoroughly cured. The interior surface is smooth, does not corrode, and does not tuberculate. Under normal conditions of operation, asbestos cement will handle... 

Quartz fine aggregates and normal Portland cement were used to prepare mortar at a w/c of 0.6. Mortar was cast into 30-mm diameter by 30-mm length cylinders and cured for 3 days. At the end of the curing period the specimens were oven dried at 105 °C until a constant mass was reached. Epoxy was then applied to the curved surface and the specimen was placed such that 1-2 mm of its height was immersed in a 20% NaCl solution. 

Quartz fine aggregate and normal Portland cement were used to prepare mortar with a w/c of 0.5. A cylindrical specimen, 43 mm in diameter and 50 mm long, was cast and cured under sealed conditions for 3 days at 23 °C. The specimen was then oven dried at 105 °C for 1 day prior to exposure to lithium nitrate solution. The specimen was then placed such that the bottom of the cylinder was submerged approximately 1-2 mm into a lithium nitrate solution with Teflon tape applied to the curved surface. 

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. 

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 ... 

The problem with solid—solid reactions is that of sufficiently bringing the reagent molecules together. If the product is liquid or partially liquid, this problem is, to a great extent, obviated, as transport can take place through the liquid phase. The reactions in the rotary Portland cement kiln are an example of this. Adequate mechanical working of the mixture to spread the liquid over the surface of the solids is beneficial. 

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... 

The air-bubble generating and stabilizing process requires a minimum paste consistency. Silica fume particles are smaller than those of Portland cement and addition of silica fume therefore increases the fine fraction of the particles. The higher fraction of smaller particles then increases the surface area causing a greater binding of the water in the mix. This removes the water required for the bubble-generating process. 

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. 

The physical panel size used resulted in more joints between panels than would have been the case in a Portland cement pour, owing to the surface finishing with a screed and the continuous obstruction of the existing support columns. Asphalt expansion strips were placed between panels and were provided with a removable top strip which was filled with a polyurethane compound. Shrinkage of pours in this work was negligible. Shrinkage in sulfur concrete was proportional to the amount of sulfur binder used. 

The rust content (Fc203) of Portland cement, of particular interest to us here, the cement most frequently used for concrete and cement mortars, is usually between 1 and 5%.396 The sand added to the mortar can also exhibit a high iron content (up to 4%). As mentioned in chapter 6.5. 3., a large surface area at the solid-liquid phase limit (iron oxide-cyanide solution) is favorable to the formation of Iron Blue. This is extraordinarily large in cement and concrete mortars (microscopic inte-... 

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