Cement Cementitious

Chem. Descrip. Magnesium oxide CAS 1309-48-4 EINECS/ELINCS 215-171-9 Uses Ingred. in oxychloride and oxysulfate cements cementitious matrix for construction applies. for mfg. of commercial, industrial, sparkproof, and decorative terrazzo floors, flooring for railroad boxcars, industrial fireproof coatings, fire-resist, marine interior deckings, variety of building units... 

Fiber-Reinforced Cementitious Material. Use of asbestos (qv) has been legally restricted in Europe and the United States as being ha2ardous to health. In asbestos cement, which had consumed 70—80% of total asbestos, PVA fiber has been used in large amount as a replacement for asbestos. PVA fiber has a strength of at least 0.88 N/tex (9 gf/dtex) and can therefore provide the necessary reinforcement for cement the fiber has excellent adhesiveness to cement (qv) and alkaU resistance, and is not a health ha2ard. 

Silica and Alumina. The manufacture of Pordand cement is predicated on the reaction of lime with siUca and alumina to form tricalcium sihcate [12168-85-3] and aluminate. However, under certain ambient conditions of compaction with sustained optimum moisture content, lime reacts very slowly to form complex mono- and dicalcium siUcates, ie, cementitious compounds (9,10). If such a moist, compact mixture of lime and siUca is subjected to steam and pressure in an autoclave, the lime—silica reaction is greatiy accelerated, and when sand and aggregate is added, materials of concrete-like hardness are produced. Limestone does not react with siUca and alumina under any circumstances, unless it is first calcined to lime, as in the case of hydrauhc lime or cement manufacture. 

S. H. Kosmatka, Cementitious Grouts and Grouting, EBlllT, Pordand Cement Association, Skokie, Dl., 1990. 

Polymer-modified cementitious floor toppings are now widely used instead of separately laid granolithic toppings. The polymers used are normally supplied as milky white dispersions in water and are used to gauge a carefully selected sand/aggregate/cement mix as a whole or partial replacement of the gauging mortar. They must always be mixed in a forced-action mixer. 

Acid-base (AB) cements have been known since the mid 19th century. They are formed by the interaction of an acid and a base, a reaction which yields a cementitious salt hydrogel (Wilson, 1978) and offers an alternative route to that of polymerization for the formation of macro-molecular materials. They are quick-setting materials, some of which have unusual properties for cements, such as adhesion and translucency. They find diverse applications, ranging from the biomedical to the industrial. 

One example is silicate cement where orthosilicic acid, chemically generated in solution, condenses to form a silicic acid gel. Another is refractory cement where a cementitious product is formed by the heat treatment of an acid orthophosphate, a process which again involves condensation to form a polyphosphate. 

The essential property of a cementitious material is that it is cohesive. Cohesion is characteristic of a continuous structure, which in the case of a cement implies an isotropic three-dimensional network. Moreover, the network bonds must be attributed to attractions on the molecular level. Increasingly, recent research tends to show that cements are not bonded by interlocking crystallites and that the formation of crystallites is incidental (Steinke et al., 1988 Crisp et al., 1978). The reason is that it is difficult to form rapidly a mass which is both cohesive and highly ordered. 

A final point needs to be made. Theory has indicated that AB cements should be amorphous. However, a degree of crystallization does sometimes occur, its extent varying from cement to cement, and this often misled early workers in the field who used X-ray diffraction as a principal method of study. Although this technique readily identifies crystalline phases, it cannot by its nature detect amorphous material, which may form the bulk of the matrix. Thus, in early work too much emphasis was given to crystalline structures and too little to amorphous ones. As we shall see, the formation of crystalUtes, far from being evidence of cement formation, is often the reverse, complete crystallinity being associated with a non-cementitious product of an acid-base reaction. 

Another feature of the metal ions that are typically involved in cementitious bonding in AB cements is that most of them fall into the category of hard in Pearson s Hard and Soft Acids and Bases scheme (Pearson, 1963). The underlying principle of this classification is that bases may be divided into two categories, namely those that are polarizable or soft, and those that are non-polarizable or hard. Lewis acids too may be essentially divided into hard and soft, depending on polarizability. From these classifications emerges the useful generalization that hard acids prefer to associate with hayd bases and soft acids prefer to associate with soft bases (see Section 2.3.7). 

Of the ions most often implicated in cementitious bonding in AB cements, Ca ", Mg " and AF are classified as clearly hard Zn " by contrast falls into the category that Pearson designated borderline , as... 

The phosphate bonded cements described in this chapter are the products of the simple acid-base reaction between an aqueous solution of orthophosphoric acid and a basic oxide or silicate. Such reactions take place at room temperature. Excluded from this chapter are the cementitious substances that are formed by the heat treatment of aqueous solutions of acid metal phosphates. 

For the native cement exposed first to water, there was a dramatic and rapid drop in microhardness, 30-40 % in the first hour, and 55-60 % at eight hours. Compressive strength was assumed to have undergone a similar decrease, since it is linearly related to microhardness for cementitious materials (Beaudoin Feldman, 1975). Scanning electron microscopy revealed clearly the differences that occurred on soaking in water. 

The chief problem in studying the chemical nature of AB cements is that many are essentially amorphous, so that the powerful tool of X-ray diffraction (XRD) analysis cannot be used. Some AB cements do exhibit a degree of crystallinity, but rarely in significant amounts indeed, complete crystallinity is usually a sign that the reaction product is not cementitious. The literature contains numerous examples of workers being misled by the results of XRD analysis into neglecting the presence and significance of the amorphous phase. 

Petrifix A process for solidifying aqueous wastes, converting them to a solid form suitable for landfill. Cementitious additives are used, based on the compositions used by the Romans for making Pozzolanic cements. Developed by Pec-Engineering, Paris, France. In 1979 it had been used in France and Germany. 

Sealosafe A family of processes for encapsulating inorganic and organic wastes in a cementitious material suitable for landfill. The product, known as Stablex, is made from a cement and an aluminosilicate and may incorporate pulverized fly ash. Developed by C. Chappell in the United Kingdom in the 1970s and now operated in a number of countries. Offered by the Stablex Corporation, Radnor, PA. The environmental acceptability of the product has since been criticized. 

Cementitious materials use a hydraulically setting cement such as Portland cement as a binder with a filler material of good insulation properties, e.g., verminculite, perlite, etc. Concrete us frequently used for fireproofing because it is easily installed, readily available, is quite durable and generally economical compared to other methods. It is heavy compared to other materials and requires more steel to support that other methods. 

C. Park, "Hydration and solidification of hazardous wastes containing heavy metals using modified cementitious materials," Cement and Concrete Research, 30, 429, 2000. 

Cement hydration and epoxy polymerization occur simultaneously to form a structure that is similar to the latex-modified cementitious system. Epoxy systems develop high strength, adhesion and have low permeability, good water resistance and chemical resistance. A major advantage of this system is that it can be cured under moist or wet conditions. According to a recent study, the epoxy-modified mortars can be made without the hardeners with superior properties to those obtained with conventional epoxy mortars [89, 90]. 

Mix proportion aspects that should be considered in the design of highly flowable mixtures include (1) cement content (2) fines content (3) type of superplasticizer (4) the presence of other admixtures in the mix (5) type of cement or cementitious material (6) dosage of the admixture (7) sequence... 

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