Cementitious compounds

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. 

Styrene-butadiene rubber (SBR) latexes which are compatible with cementitious compounds are copolymers. They show good stability in the presence of multivalent cations such as calcium (Ca++) and aluminum (A1+++) and are unaffected by the addition of relatively large amounts of electrolytes (e.g., CaCl2). Outdoor exposure to... 

The resins used are polymers and copolymers of the esters of acrylic and methacrylic acids. They range in physical properties from soft elastomers to hard plastics, and are used in cementitious compounds in much the same manner as SBR latex. Acrylics are reported to have better UV stability than SBR latex and therefore remain flexible under exterior exposure conditions longer than SBR latex [88]. 

The butadyene styrene latices which are compatible with cementitious compounds are copolymers. Typical physical properties arc given in Table 1. 

Coal fly ash (FA) - FA is useful in many applications because it is a pozzolan, meaning it is a siliceous or alumino-siliceous material that, when in a finely divided form and in the presence of water, will combine with calcium hydroxide (from lime, Portland cement, or kiln dust) to form cementitious compounds... 

Class F fly ash The burning of harder, older anthracite and bituminous coal typically produces Class F fly ash. This fly ash is pozzolanic in nature, and contains less than 20% lime (CaO). Possessing pozzolanic properties, the glassy silica and alumina of Class F fly ash requires a cementing agent, such as Portland cement, quicklime or hydrated lime, with the presence of water in order to react and produce cementitious compounds. Alternatively, the addition of a chemical activator such as sodium silicate (water glass) to a Class F ash leads to the formation of a geopolymer. 

Figure 49 used data from Tables 34 and 35 to present a comparison of binary mixtures of BPD-ROSA with the lime/MKD-ROSA mixtures. The mixture incorporating BPD achieved much a higher compressive strength compared with those made with hydrated lime and MKD. This result is similar to those achieved with binary combinations of BPD-BOS. As mentioned previously, this could be due to cementitious compounds present in BPD resulting in foimation of more cementitious matrix within 28 days. 

An understanding of the complex physico-chemical phenomena associated with the formation and behavior of cementitious compounds is facilitated through the application of many different types of investigative methods. Techniques such as NMR, XRD, neutron activation analysis, atomic absorption spectroscopy, IR/UV spectroscopy, electron microscopy, surface area techniques, pore characterization, zeta potential, vis-cometry, thermal analysis, etc., have been used with some success. Of the thermal analysis techniques the Differential Thermal Analysis (DTA), Thermogravimetric Analysis (TG), Differential Scanning Calorimetry (DSC), and Conduction Calorimetric methods are more popularly used than others. They are more adaptable, easier to use, and yield important results in a short span of time. In this chapter the application of these techniques will be highlighted and some of the work reported utilizing other related methods will also be mentioned with typical examples. 

Francois, M., G. Renaudin and O. Evrard (1998). A Cementitious Compound with Composition 3Ca0-Al203 CaC03-llH20 . Acta Crystallographica Section C Crystal Structure Communications 54 (9) 1214—1217. 

Another field with a large potential for improvements concerns aluminosilicate minerals, which are of great importance in determining the chemistry of water in many types of rock. In backfill clays, aluminosilicates are responsible for the retention (sorption, incorporation) of trace elements and may affect both oxidation potential (incorporation of Fe(II)/Fe(III)) and pH (hydrolysis of silicate and/or exchange of H+). Related classes of compounds (i.e., calcium silicates and calcium aluminates) form the chemical backbone of cementitious materials. The thermodynamic properties of these substances are still largely unexplored. 

CAS 8052-42-4. A dark-brown to black cementitious material, solid or semisolid in consistency, in which the predominating constituents are bitumens that occur in nature as such or are obtained as residua in petroleum refining (ASTM). It is a mixture of paraffinic and aromatic hydrocarbons and heterocyclic compounds containing sulfur, nitrogen, and oxygen. 

ASTM designation of pozzolans is as follows A siliceous or a siliceous and aluminous material, which in itself possesses little or no value, but will, in finely divided form and in presence of moisture, chemically react with calcium hydroxide at ordinary temperatures to form compounds possessing cementitious properties. ... 

Pozzolanas, or pozzolanic materials, are defined as siliceous and aluminous materials that ou their own possess little or no cementitious value, but which will—if preseut iu fiuely divided form aud in the presence of moisture— react chemically with calcium hydroxide at ordinary temperature to form compounds possessing cementitious properties (ASTM C 619-89). The required calcium hydroxide may also be introduced in the form of materials that liberate this compound in the course of their hydration, such as Portland cement. 

Applications. Conduction calorimetry has been widely used for a study ofthe hydration reactions ofvarious cementitious systems. Tricalcium silicate, being the dominant compound in portland cement, determines to a large extent the strength and other properties of concrete. Conduction calorimetric curves of tricalcium silicate and portland cement show five steps during the hydration process (Fig. In the first stage, as soon as... 

One area where environmental microscopes can be more valuable is for the study of cementitious materials containing large amounts of organic compounds, such as latexes or oils, which suffer much more damage under vacuum or simply cannot be put in such conditions. 

Calibration should be done using a proper set of standards. These standards are typical oxides and metals relevant to cementitious materials which include compounds such as wollastonite, jadeite, silica and alumina. It is extremely important that the spectra from the standards be recorded in the same conditions used for analysis, most importantly the beam current. This is because the principle of quantification relies on the comparison between the elemental intensities of the unknown spectrum and those from a set of standards. For convenience, it is useful to define a preset list of elements such as O, Na, Mg, Al, Si, P, S, Cl, K, Ca, Ti and Fe but this can be adjusted as needed. 

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