Hydraulic Cement Additives

Antifreezing agents for cement consist mainly of salts such as calcium chloride, magnesium chloride, sodium chloride, and soda. Calcium chloride is highly corrosive and very restricted in use. Some salts, especially potassium chloride, will affect the curing time of cement. The latter chemical is in fact used to increase the pot life of cement. Likewise, alcohol freezing-point depressants, such as ethylene glycol, can be also included in the composition [1022]. 

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In hydraulic cement slurries, fluid loss additives based on sulfonated or sulfomethylated lignins have been described. 

Homopolymers and copolymers from amido-sulfonic acid or salt containing monomers can be prepared by reactive extrusion, preferably in a twin screw extruder [1660]. The process produces a solid polymer. Copolymers of acrylamide, N-vinyl-2-pyrrolidone, and sodium-2-acrylamido-2-methyl-propane sulfonate have been proposed to be active as fluid loss agents. Another component of the formulations is the sodium salt of naphthalene formaldehyde sulfonate [207]. The fluid loss additive is mixed with hydraulic cements in suitable amounts. 

Addition of rubber particles of 30% to 100% by weight to cement with a grain size of approximately 40 to 60 mesh (0.4 to 0.25 mm) will produce a lightweight cement. The addition of rubber particles also creates a low permeability. The compositions are advantageous for cementing zones subjected to extreme dynamic stresses such as perforation zones and the junctions of branches in a multi-sidetrack well. Recycled, expanded polystyrene lowers the density of a hydraulic cement formulation and is an environmentally friendly solution for downcycling waste materials. 

Foam cement is a special class of lightweight cement. The gas content of foamed cement can be up to 75% by volume. The stability of the foam is achieved by the addition of surfactants, as shown in Table 10-9. A typical foamed cement composition is made from a hydraulic cement, an aqueous rubber latex in an amount up to 45% by weight of the hydraulic cement, a latex stabilizer, a defoaming agent, a gas, a foaming agent, and a foam stabilizer [359,362]. Foamed high-temperature applications are based on calcium phosphate cement [257]. 

E. M. Gartner and R. P. Kreh. Cement additives and hydraulic cement mixes containing them. Patent CA 2071080, 1993. 

Upon addition of water, the hydration reactions initiate, and the hydraulic cement begins to gain strength. This process is very complex, but the strengthening effect is due basically to the formation of three types of hydration products colloidal products such as C2S xH20, which have a size of less than 0.1 p.m submicrocrystalline products such as Ca(OH)2, Al +, Fe +, and S04 phases with sizes from 0.1 to 1 tim and microcrystalline products, primarily of Ca(OH)2, with particle sizes greater than 1 p,m. The most common type of hydraulic cement, Portland cement, usually contains mostly colloidal products. 

Mineral additions may be broadly categorized as pozzolanic materials or latent hydraulic cements. Neither type reacts significantly with water at ordinary temperatures in the absence of other substances. Pozzolanic materials are high in Si02 and often also in AI2O3, and low in CaO they are sufficiently reactive that mixtures of them with water and CaO produce C-S-H at ordinary temperatures and thereby act as hydraulic cements. If they contain AI2O3, calcium aluminate or aluminate silicate hydrates are also formed. Because they are low in CaO, this component must be supplied in stoichiometric quantity. In a composite cement, it is provided by the Portland cement through decreased formation of CH and decreased Ca/Si... 

Portland cement is the most common hydraulic cement. It is formed by clinkering a mixture of powders of limestone, sand, iron oxide and other additives at a very high temperature ( 1500°C). It is mixed with water to form hydrated bonding phases... 

Synonyms/Trade Names Cement, Hydraulic cement, Portland cement silicate [Note A class of hydraulic cements containing tri- and dicalcium silicate in addition to alumina, tricalcium aluminate, and iron oxide.]... 

ASTM C 226. 2012. Standard specification for air-entraining additions for use in the manufacture of air-entraining hydraulic cement. West Conshohocken, PA ASTM International. 

Portland cement n. A hydraulic cement produced by pulverizing clinker consisting essentially of hydraulic calcium silicates and usually containing one or more of the forms of calcium sulfate as an interground addition. 

The most common type of cement used by concrete manufacturers is Portland cement, which is prepared by igniting a mixture of raw materials mainly composed of calcium carbonate or aluminium silicates. Portland cement can be defined as hydraulic cement produced by pulverizing clinker consisting essentially of hydraulic calcium silicates, usually containing one or more of the forms of calcium sulphate as an interground addition . The phase compositions in Portland cement are denoted as tricalcium silicate (C3S), dicalcium silicate (C2S), tricalcium aluminate (C3A), and tetracalcium aluminoferrite (C4AF). 

Coloured cements These are used for decorative purposes. In some standards, the addition of pigments to produce colomed Portland cement is allowed. In other standards (e.g. ASTM), pigments are not allowed constituents of Portland cement, and coloured cements are sold as blended hydraulic cements . 

Portland cement is a hydraulic cement. Hydraulic cements are defined as cements that not only harden by reacting with water but also form a water-resistant product. Portland cement is produced by pulverising clinkers consisting essentially of hydraulic calcium silicates, usually containing one or more of the forms of calcium sulfate as an interground addition. Clinkers are 5-25 mm-diameter nodules of a sintered material which is produced when a raw mixture of limestone and clay is heated to high temperatures (Mehta 1986). The chemical reactions taking place in the cement kiln system can be approximately represented as shown in Fig. 1. 

Concrete admixtures are defined as materials other than hydraulic cement, water, or aggregates that are added immediately before or during mixing. Additives or additions such as grinding aids are added to cement during manufacture. An addition is a material that is interground or blended during the manufacture of cement. Most concrete used in North America contains at least one admixture. The admixtures are added to improve the quality of concrete in the fresh and hardened state. Publications and patents on admixtures are voluminous. Interest in the development of admixtures is evident from the number of patents taken every year. The total number of patents reported in the years 1985, 1986, 1987,1988,1989,1990,1991, and 1992 were respectively 44, 64, 99, 133, 242, 57, 53, and 149. 

Many fly ashes cannot be used as supplementary materials or mineral admixtures because they possess low pozzolanic activity. Some activators may be added to make them hydraulic. The addition of Na2Si03 and Ca(OH)2 to fly ash cement mixtures results in the acceleration of the hydration of cement as evidenced by increased intensities of the endother-mal peak (calcium hydroxide decomposition) in thermal analysis techniques. Strengths are also increased.P Fly ash can also be activated by mixing it with phosphog q)sum and wet hydrated lime. The estimation of ettringite and lime may be carried out by DTA, and the results may be used to explain the strength development in such systems. 

C 204 Test Methods for Fineness of Hydraulic Cement by Air-Permeability Apparatus C 219 Terminology Relating to Hydraulic Cement C 305 Practice for Mechanical Mixing of Hydraulic Cement Pastes and Mortars of Plastic Consistency C 465 Specification for FVocessing Additions for Use in the Manufacture of Hydraulic Cements C 778 Specification for Standard Sand C 786 Test Method for Fineness of Hydraulic Cement and Raw Materials by the 300-nm (No. 50), 150-pm (No. 100), and 75-nm (No. 200) Sieves by Wet Methods lEEE/ASTM SI 10 Standard for Use of the International System of Units (SI) The Modern Metric System... 

The above statement refers to mortar made without addition of any hydraulic substance. But such mortars are now never used at Fort Adams. Hydraulic cement, or burnt clay, or brick dust, or some other similar matter is added to every kind of mortar made at the work, in proportions varying with the purpose to which the mortar is to be applied. The poorest mortar we make contains 1 barrel of hydraulic cement to 3 barrels of unslaked lime and about 15 barrels of sand the cement being added before the sanfl, and while the lime is being reduced under the wheel. 

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