Cement Is A Crystalline Compound Of Calcium Silicates And Other

Cement is a crystalline compound of calcium silicates and other calcium compounds having hydraulic properties. LOW HEAT CEMENT PHYSICAL PROPERTIES Appearance Boiling Point / Melt Point above 1200 C Vapour Pressure Per Cent Volatiles Specific Gravity Flash Point Flammability/Combustibility Autoignition Temperature Other Properties Not mixing with water.

A fine, grey powder Some components begin to melt Not applicable Not applicable 3.0 to 3.2 Not applicable Non-flammable; Non-combustible Not applicable explosive. No odour. Hardens on

PHYSICAL DESCRIPTION Physical characteristics of cements are that they are alkaline in nature. The pH of water solution (slurry) of cements can be as high as 13.5. Its specific attribute of low heat evolution means that it is ideally suited for large concrete pours, such as dams and foundations, where peak temperatures and temperature differentials must be controlled to ensure structural integrity by minimising thermal cracking. Its performance in this respect has been proven over a number of years in several major construction projects. This cement also offers excellent resistance to the penetration of both chloride and sulfate ions and as such is particularly suited to the production of concrete that is designed to survive a harsh marine environment. The penetration of chlorides to reinforcement steel is by far the most serious

durability threat to concrete subjected to the ravages of aggressive sea salts.

BCSC LH Cement is recommended for use in mass concrete where reduced heat liberation is important. Due to its superior resistance to both sulphate and chloride salt attack, LH cement may also be used in aggressive sulphate-rich environments or where increased resistance to salt attack is required. Where concrete is expected to be in contact with sulphates or other aggressive salts or solutions, analytical surveys must be completed and appropriate grade of concrete selected. As with Portland cements, the resistance to acid solutions is limited, but concrete life expectancy will be maximised by using BCSC LH Cement at high cement content and low water to cement ratio in fully compacted and cured concrete.

Excess water will have a detrimental effect on the compressive strength and other properties of concrete.

BLAST FURNACE CEMENT Ground granulated blast furnace slag (GGBS or GGBFS) is obtained by quenching molten iron slag (a by-product of iron and steel making) from a blast furnace in water or steam, to produce a glassy, granular product that is then dried and ground into a fine powder. GGBS cement is added to concrete in the concrete manufacturer's batching plant, along with Portland cement, aggregates and water. The normal ratios of aggregates and water to cementitious material in the mix remain unchanged. GGBS is used as a direct replacement for Portland cement, on a one-to-one basis by weight. Replacement levels for GGBS vary from 30% to up to 85%. Typically 40.

Durability GGBS cement is routinely specified in concrete to provide protection against both sulphate attack and chloride attack. GGBS has now effectively replaced Sulfate Resisting Portland cement (SRPC) on the market for sulfate resistance because of its superior performance and greatly reduced cost compared to SRPC. To protect against chloride attack, GGBS is used at a replacement level of 50% in concrete. Instances of chloride attack occur in reinforced concrete in marine environments and in road bridges where the concrete is exposed to splashing from road de-icing salts. In most NRA projects in Ireland GGBS is now specified in structural concrete for bridge piers and abutments for protection against chloride attack. The use of GGBS in such instances will increase the life of the structure by up to 50%

had only Portland cement been used, and precludes the need for more expensive stainless steel reinforcing. GGBS is also routinely used to limit the temperature rise in large concrete pours. The more gradual hydration of GGBS cement generates both lower peak and less total overall heat than Portland cement. This reduces thermal gradients in the concrete, which prevents the occurrence of microcracking which can weaken the concrete and reduce its durability Appearance:In contrast to the stony grey of concrete made with Portland cement, the near-white color of GGBS cement permits architects to achieve a lighter colour for exposed fairfaced concrete finishes, at no extra cost. To achieve a lighter colour finish, GGBS is usually specified at between 50% to 70% replacement levels, although levels as high as 85% can be used GGBS cement also produces a smoother, more defect free surface, due to the fineness of the GGBS particles. Dirt does not adhere to GGBS concrete as easily as concrete made with Portland cement, reducing maintenance costs. GGBS cement prevents the occurrence of efflorescence, the staining of concrete surfaces by calcium carbonate deposits. Due to its much lower lime content and lower permeability, GGBS is effective in preventing efflorescence when used at replacement levels of 50% to 60%. Strength:Concrete containing GGBS cement has a higher ultimate strength than concrete made with Portland cement. It has a higher proportion of the strength-enhancing calcium silicate hydrates (CSH) than concrete made with Portland cement only, and a reduced content of free lime, which does not contribute to concrete strength. Concrete made with GGBS continues to gain strength over time, and has been shown to double its 28 day strength over periods of 10 to 12 years

HIGH ALUMINA CEMENT

High-alumina cement, known also as aluminous cement is not Portland cement. It is made by fusing a mixture of limestone and bauxite with small amounts of silica and titania. In Europe, the process is usually carried out in an open-hearth furnace having a long vertical stack into which the mixture of raw materials is charged. The hot gases produced by a blast of pulverized coal and air pass through the charge and carry off water and carbon dioxide. Fusion occurs when the charge drops from the vertical stack onto the hearth at a temperature of about 1,425° to 1,500°C. A molten liquid is formed and is continuously collected and solidified in steel pans which are carried on an endless belt. Electric arc furnaces also have been used when electric power is cheap. In the United States, the mixture is burned in a rotary kiln similar to that used for Portland cement but provided with a tap hole from which the molten liquid is drawn intermittently. A black solidified sinter is formed and is stored, e.g. in storage piles, from which it is transferred to crushing and grinding mills where it is reduced, without additions, to a fine powder. Aluminous cement is composed of, as percent by weight, from about 36 to 42 percent Al 2 O 3 , about the same amount of CaO, about 7 to 18 percent oxides of iron, about 5 to 10 percent SiO 2 , and small amounts of TiO 2 , MgO and alkalies. A number of other

compounds include minor amounts of, for example, CaO . Al 2 O 3 ; 6CaO . 4Al 2 O 3 ; FeO . SiO 2 ; 2CaO . Al 2 O 3 . SiO and ferrites. The setting and hardening of the cement when mixed with water is probably brought about by the formation of calcium aluminate gels, such as, CaO . Al 2 O 3 . 10H 2 O; 2CaO . Al 2 O 3 . 8H 2 O and 3CaO . Al 2 O 3 . 6H 2 O. One of the notable properties of high-alumina cement is its development of very high strengths at early ages. It attains nearly its maximum strength in less than a day, which is much higher than the strength developed by Portland cement at that age. At higher temperatures, however, the strength drops off rapidly. Heat is also evolved rapidly on hydration and results in high setting temperatures. The resistance of the cement to corrosion in sea or sulfate waters, as well as its resistance to weak solutions of mineral acids, is outstanding.

WHITE CEMENT White Portland cement or white ordinary Portland cement (WOPC) is similar to ordinary, gray Portland cement in all respects except for its high degree of whiteness. Obtaining this color requires substantial modification to the method of manufacture, and because of this, it is somewhat more expensive than the gray product. White Portland cement is used in combination with white aggregates to produce white concrete for prestige construction projects and decorative work. White concrete usually takes the form of pre-cast cladding panels, since it is uneconomic to use white cement for structural purposes. White Portland cement is also used in combination with inorganic pigments to produce brightly colored concretes and mortars. Ordinary cement, when used with pigments, produces colors that may be attractive, but

are somewhat dull. With white cement, bright reds, yellows and greens can be readily produced. Blue concrete can also be made, at some expense. The pigments may be added at the concrete mixer. Alternatively, to guarantee repeatable color, some manufacturers supply ready-blended colored cements, using white cement as a base.

The characteristic greenish-gray to brown color of ordinary Portland cement derives from a number of transitional elements in its chemical composition. These are, in descending order of coloring effect, chromium, manganese, iron, copper, vanadium, nickel and titanium. The amount of these in white cement is minimized as far as possible. Cr2O3 is kept below 0.003%, Mn2O3 is kept below 0.03%, and Fe2O3 is kept below 0.35% in the clinker. The other elements are usually not a significant problem. Portland cement is usually made from cheap, quarried raw materials, and these usually contain substantial amounts of Cr, Mn and Fe. In order to get this color of the White Cement, its method of production is different from that of the ordinary cement. However, this modification in its production method makes White Cement far more expensive then the ordinary cement. The production of White Cement requires exact standards and so it is a product which is used for specialized purposes. White Cement is produced at temperatures that hover around 14501500 degrees Celsius. This temperature is more than what is required by the ordinary grey cement. As more energy is required during the manufacture of White Cement, it goes to make it more expensive than the ordinary grey cement. White Cement is used in architectural projects the use of white cement has been specified. It is used in decorative works and also wherever vibrant colors are desired. White Cement is used to fill up the gaps between marble and ceramic tiles for a smoother and more beautiful finish.

The various raw materials required for the production of White Cement are: Limestone Sand Iron Ore Nickel Titanium Chromium Vanadium

HIGH TEMPERATURE EXPANDING CEMENT

The invention pertains to a composition and a process for plugging a subterranean void where the composition will be subjected to an in situ temperature of about 150° C. or greater in said void. The composition upon hydration at or above the designated temperature exhibits expansive properties making it especially useful for filling the annulus between the casing and the wellbore of a geothermal well. Upon curing, the expansion of said composition provides a tight seal between the casing and the formation and thus prevents communication of fluids between the different zones of the subterranean formation that the wellbore traverses. Cement compositions capable of expansive behavior when slurries thereof are hydrated have been prepared and used for plugging of subterranean voids, e.g. the annulus between the casing and wellbores of gas, oil and water wells. Such compositions have heretofore depended upon the interaction of the calcium and silicon components of hydraulic cements with sulfate-containing compounds such as gypsum and plaster of

Paris. Chem Comp cement is a commercial cement of such a nature. However, when slurries of such expanding cements are subjected to temperatures in excess of about 100° C. they lose their expansive capability.

We have discovered that an expanding, pectolite-containing cement may be formed at temperatures of about 150° C. or greater which has relatively good strength and resistance to degradation by brines at elevated temperatures. The cement is prepared by choosing suitable water-soluble sodium salts of weak acids and combining them with calcium and silicon sources commonly employed in most hydraulic cement compositions. Slurries prepared from the invention cement compositions have sufficiently long thickening times (alone or with conventional retarders) to permit them to be placed in a subterranean void which one desires to plug, in contrast to cement slurries prepared in a similar fashion using sodium hydroxide, sodium sulfate, or sodium carbonate as a source of sodium. The hydratable cement composition of the invention comprises: Component (A) a water soluble sodium salt of a weak acid, a 0.1 molar aqueous solution of which salt has a pH of between about 7.5 and about 11.5; Component (B) a calcium source; and Component (C) a silicon source; wherein the atomic ratios of sodium:calcium:silicon range from about 0.3:0.6:1 to about 0.03:1:1. Aqueous slurries comprising said cement composition intimately mixed with a quantity of water sufficient to fully hydrate the resultant reaction product are useful for plugging subterranean cavities having a temperature of at least about 150° C. A pectolite-containing, expanding cement is formed in the cavity when such a slurry is placed in the cavity and maintained at such a temperature for a time sufficient to permit the slurry to harden and to expand therein. Pectolite is a mineral represented by the chemical formula Na 2 O(CaO) 4 (SiO 2 ) 6 .H 2 O. Helps water proof a cracked foundation.

SULPHATE RESISTANT CEMENT Sulfate Resistant Cement is a specially Sulfate Resistant Cement is a specially blended cement designed to improve the performance of concrete where the risk of sulfate attack may be present. It also provides improved durability for concrete in most aggressive environments, reducing the risk of either deterioration of the structure or structural failure. Suitably designed concrete using this cement technology also significantly reduces concrete permeability. This blended cement product assists in limiting the ingress of chloride ions in concrete exposed to coastal or saltwater environments, reducing the risk of corrosion of reinforcing steel.help improve durability.

RAPID HARDENING CEMENT Rapid Hardening Portland Cement (RHPC) is a type of cement that is used for special purposes when a faster

rate of early high strength is required. RHPC has a higher rate of strength development than the Normal Portland Cement (NPC). The Rapid Hardening Portland Cement's better strength performance is achieved by increasing the refinement of the product. This is the reason that its use is increasing in India. Rapid Hardening Portland Cement is manufactured by fusing together limestone (which has been finely grounded) and shale, at extremely high temperatures to produce cement clinker. To this cement clinker, gypsum is added in small quantities and then finely grounded to produce Rapid Hardening Portland Cement. It is usually manufactured using the dry process technology. Rapid Hardening Portland Cement is used in concrete masonry manufacture, repair work which is urgent, concreting in cold weather, and in pre-cast production of concrete. Rapid Hardening Portland Cement has proved to be a boon in the places where quick repairs are required such as airfield and highway pavements, marine structures, and bridge decks. The Rapid Hardening Portland Cement should be stored in a dry place, or else its quality deteriorates due to premature carbonation and hydration. As the Indian cement industry produces Rapid Hardening Portland Cement in large quantities, it is able to meet the domestic demand and also export to other countries. The cement industry in India exports cement mainly to the West Asian countries. The raw materials required for the manufacture of Rapid Hardening Portland Cement are: Limestone Shale

Gypsum Coke

Normal Portland cements are manufactured by burning an intimately blended mixture of calcareous and argillaceous raw materials to a clinker and grinding this clinker with a small proportion of gypsum to a fine powder. The gypsum is conventionally employed to retard, and thus provide a measure of control over, the setting time of the cement when combined with water. The setting times and rates of strength development attained by ordinary Portland cement, and by so-called rapid hardening cements produced by extra fine grinding of the ingredients, are, however, not sufficiently fast for some applications such as the laying of a factory floor where placing, setting and hardening is required to proceed at such a rate that output from the factory is disrupted as little as possible. Typical setting times for known rapid hardening Portland cement are for instance 150 minutes for initial set and 210 minutes to final set.