Cement-based

The nitrogen content for plastics is usually about 11%, for lacquers and cement base it is 12%, and for explosives it is 13%. The standard plasticizer added is camphor. 

Portland cement is classified as a hydrauHc cement, ie, it sets or cures in the presence of water. The term Portland comes from its inventor, Joseph Aspdin, who in 1824 obtained a patent for the combination of materials referred to today as Portland cement. He named it after a grayish colored, natural limestone quarried on the Isle of Portland, which his cured mixture resembled. Other types of hydrauHc cements based on calcium materials were known for many centuries before this, going back to Roman times. Portland cement is not an exact composition but rather a range of compositions, which obtain the desired final properties. The compounds that make up Portland cements are calcium siHcates, calcium aluminates, and calcium aluminoferrites (see ). 

This type of cement has been further improved by the substitution of -hexyl van ill ate [84375-71-3] and similar esters of vanillic acid [121 -34-6] and/or syringic acid [530-57 ] for eugenol (93—95). These substituted cements are strong, resistant to dissolution, and, unlike ZOE and EBA cements, do not inhibit the polymerization of resin-base materials. Noneugenol cements based on the acid—base reaction of zinc and similar oxides with carboxyhc acids have been investigated, and several promising types have been developed based on dimer and trimer acids (82). 

Calcium Chelates (Salicylates). Several successhil dental cements which use the formation of a calcium chelate system (96) were developed based on the reaction of calcium hydroxide [1305-62-0] and various phenohc esters of sahcyhc acid [69-72-7]. The calcium sahcylate [824-35-1] system offers certain advantages over the more widely used zinc oxide—eugenol system. These products are completely bland, antibacterial (97), facihtate the formation of reparative dentin, and do not retard the free-radical polymerization reaction of acryhc monomer systems. The principal deficiencies of this type of cement are its relatively high solubihty, relatively low strength, and low modulus. Less soluble and higher strength calcium-based cements based on dimer and trimer acid have been reported (82). 

Concrete is a particulate composite of stone and sand, held together by an adhesive. The adhesive is usually a cement paste (used also as an adhesive to join bricks or stones), but asphalt or even polymers can be used to give special concretes. In this chapter we examine three cement pastes the primitive pozzolana the widespread Portland cement and the newer, and somewhat discredited, high-alumina cement. And we consider the properties of the principal cement-based composite, concrete. The chemistry will be unfamiliar, but it is not difficult. The properties are exactly those expected of a ceramic containing a high density of flaws. 

Don t connect the piping to the pump until the cement base and grouting is fully cured, and all foundation bolts are tightened. 

Cement-based grouts will not bond well to the platform load-bearing surfaces. Over a period of time, lubricating oils will severely degrade both cement groups and concrete. This problem is further aggravated because... 

Young, J.F. (1985) Very high strength cement-based materials. Mater. Res. Soc. Symp. Proc. 42. 

Major categories of industrial waste solidiflcation/stabilization systems are cement-based processes, pozzolanic processes (not including cement), thermoplastic techniques, organic polymer techniques, surface encapsulation techniques, and self-cementing techniques (for high calcium sulfate sludges). Vitrification (discussed previously) can also be considered a solidification process. 

Cement- based Applicable Applicable impeded setting Applicable Applicable (contaminant is neutralized by the basic cement) Applicable Applicable if an additive used to prevent spalling... 

Advantages Cement-based solidification systems are an economically feasible process having the following advantages ... 

Figure 44. Cement-based stabilization process (Roy F. Weston).

Zinc will initially react with cement-based materials with the evolution of hydrogen. This reaction can be controlled by the presence of soluble chromate either in the cement (over 70 ppm) or as a chromate passivation treatment to the zinc surface. Zinc can therefore be used to provide additional protection to steel in concrete. It is more effective in cmbonated concrete than in chloride-contaminated concrete. 

This concept covers most situations in the theory of AB cements. Cements based on aqueous solutions of phosphoric acid and poly(acrylic acid), and non-aqueous cements based on eugenol, alike fall within this definition. However, the theory does not, unfortunately, recognize salt formation as a criterion of an acid-base reaction, and the matrices of AB cements are conveniently described as salts. It is also uncertain whether it covers the metal oxide/metal halide or sulphate cements. Bare cations are not recognized as acids in the Bronsted-Lowry theory, but hydrated... 

Polyelectrolytes are polymers having a multiplicity of ionizable groups. In solution, they dissociate into polyions (or macroions) and small ions of the opposite charge, known as counterions. The polyelectrolytes of interest in this book are those where the polyion is an anion and the counterions are cations. Some typical anionic polyelectrolytes are depicted in Figure 4.1. Of principal interest are the homopolymers of acrylic acid and its copolymers with e.g. itaconic and maleic adds. These are used in the zinc polycarboxylate cement of Smith (1968) and the glass-ionomer cement of Wilson Kent (1971). More recently, Wilson Ellis (1989) and Ellis Wilson (1990) have described cements based on polyphosphonic adds. 

This cement also has a low setting exotherm, lower than any other aqueous dental cement (Crisp, Jennings Wilson, 1978), which means that it can be mixed swiftly as there is no need to dissipate heat. This property also gives it an advantage over bone cements based on modified poly(methyl methacrylate) which have high exotherms. 

Resistance to acid erosion depends on brand and varies from 0 04 to 0-54% per hour (Setchell, Teo Kuhn, 1985 Wilson et al, 1986a Walls, McCabe Murray, 1988). It would appear that cements based on copolymers of acrylic and maleic acids are less durable than those based on poly(acrylic acid). The extent of erosion varies inversely with the time allowed for the cement to cure prior to exposure (Walls, McCabe Murray, 1988). 

Recently, Oldfield Ellis (1991) have examined the reinforcement of glass-ionomer cement with alumina (Safil) and carbon fibres. The introduction of only small amounts of carbon fibres (5% to 7-5% by volume) into cements based on MP4 and G-338 glasses was found to increase considerably both the elastic modulus and flexural strength. There was an increase in work of fracture attributable to fibre pull-out. A modulus as high as 12-5 GPa has been attained with the addition of 12% by voliune of fibre into MP4 glass (Bailey et al, 1991). Results using alumina fibre were less promising as there was no fibre pull-out because of the brittle nature of alumina fibres which fractured under load. 

Wilson, A. D. (1975c). Dental cements based on ion-leachable glasses. In von Fraunhofer, J. A. (ed.) Scientific Aspects of Dental Materials, Chapter 6. London and Boston Butterworths. 

In vivo studies have indicated that zinc phosphate cements erode under oral conditions. Also, cements based on zinc oxide, including the zinc phosphate cement, are less durable in the mouth than those based on aluminosilicate glasses, the dental silicate and glass-ionomer (Norman et al., 1969 Ritcher Ueno, 1975 Mitchem Gronas, 1978,1981 Osborne et al., 1978 Pluim Arends, 1981, 1987 Sidler Strub, 1983 Mesu Reedijk, 1983 Theuniers, 1984 Pluim et al., 1984, Arends Havinga, 1985). However, there is some disagreement on whether the zinc phosphate cement is more durable than the zinc polycarboxylate cement. 

Sugama Kukacka (1983b) described cements based on magnesium oxide and a 56% aqueous solution of ammonium polyphosphate (APP). The po wder was a fine magnesium oxide that had been calcined above 1300 °C and had a surface area of 1 to 5 m g . The reaction was strongly exothermic the cements set within 3 minutes and developed an early strength of 13-8 MPa after 1 hour and over 20 MPa after 5 hours. 

Sychev, M. M., Medvedeva, I. N., Biokov, V. A. Krylov, O. S. (1982). Effect of reaction kinetics and morphology of neoformation on the properties of phosphate cements based on magnesium titanates. Chemical Abstracts, 96, 222252e. 

The mechanism by which sulphur has these observed effects is as follows. Immersion of native magnesium oxychloride cement in water brings about a slow dissolution which creates pores. When those pores are filled with sulphur, sites of possible stress concentration at points of contact between particles are modified. Similar effects occur when sulphur is used to impregnate hydraulic cements based on Portland cement and silica (Beaudoin, Ramachandran Feldman, 1977). 

This chapter is devoted to a miscellaneous group of aqueous acid-base cements that do not fit into other categories. There are numerous cements in this group. Although many are of little practical interest, some are of theoretical interest, while others have considerable potential as sustained-release devices and biomedical materials. Deserving of special mention as biomedical materials of the future are the recently invented polyelectrolyte cements based on poly(vinylphosphonic adds), which are related both to the orthophosphoric acid and poly(alkenoic add) cements. 

In 1968 Wilson published an account of his early search for alternatives to orthophosphoric acid as a cement-former with aluminosilicate glasses. Aluminosilicate glasses of the type used in dental silicate cements were used in the study and were reacted with concentrated solutions of various organic and inorganic adds. Wilson (1968) made certain general observations on the nature of cement formation which apply to all cements based on aluminosilicate glasses. 

Cements based on phytic add set more quickly than their glass polyalkenoate or dental silicate cement cormterparts, but have similar mechanical properties (Table 8.2). They are unique among add-base cements in being impervious to acid attack at pH = 2-7. Unfortunately, they share with the dental silicate cement the disadvantage of not adhering to dentine. They do bond to enamel but this is by micromechanical attachment - the cement etches enamel - and not by molecular bonding. Lack of adhesive property is a grave weakness in a modern dental or bone... 

Table 8.2. Properties of cements based on phytic acid Prosser et al, 1983)...

Ellis, J., Anstice, M. Wilson, A. D. (1991). The glass polyphosphonate cement a novel glass-ionomer cement based on poly(vinylphosphonic acid). Clinical Materials, 7, 341-6. 

Civjan, S. Brauer, G. M. (1964). Physical properties of cements based on zinc oxide, hydrogenated resin, o-ethoxybenzoic acid and eugenol. Journal of Dental Research, 43, 281-99. 

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