Strength of epoxy-modified

Figure 7.3 Compressive strength of epoxy-modified concretes.

Figure 7.5 Polymer-cement ratio vs. flexural strength of epoxy-modified mortars without and with hardener.

Figure 2 represents the effects of type of hardener and polymer-cement ratio on the flexural and compressive strengths of epoxy-modified mortars. The... 

Figure 4- exhibits the effects of nonionic surfactant content, HLB and antifoamer on the flexural and compressive strengths of epoxy-modified mortars with a modified polyamide-amine hardener content of 55%> a polymer-cement ratio of 4-0% and a water-reducing agent content of 3 0 %, which are the optimum values recommended from the above test results. The flexural strength of the epoxy-modified mortars with a nonionic surfactant of HLB 9 5... 

The use of elastomeric modifiers for toughening thermoset resias generally results ia lowering the glass transition temperature, modulus, and strength of the modified system. More recendy, ductile engineering thermoplastics and functional thermoplastic oligomers have been used as modifiers for epoxy matrix resias and other thermosets (12). 

L.2.3 The compressive strength of epoxy grout shall be a minimum of 83 MPa (12,000 psi) in 7 days when tested by ASTM C 579 method 8, modified. 

Li and Netravali [121] modified an UHSPE fiber surface using allylamine plasma deposition to improve its adhesion to epoxy resin. The shear strength of the modified surface increased by a factor of 2-3 when measured by pull-out test using a U-shaped epoxy resin. The epoxy resin and a curing agent were mixed and molded into U-shaped form without disturbing the fiber (see Fig. 8). 

IMPACT STRENGTH OF ATBN MODIFIED EPOXY COATINGS... 

Scarito and Sperling (14). The impact strength of the modified SIN system was indeed improved, but the glass transition temperature of the composite decreased substantially relative to the epoxy control. 

Ohama, V., Demura, K., and Endo, T. (1992) Strength properties of epoxy-modified mortars without hardener, m. Proceedings 9th ICCC, New Delhi, Vol. 5, pp. 512-511. 

Figure 5.5 Effect of CTPEHA content on impact strength of a modified epoxy network. Reprinted with permission from D. Ratna, A.K. Banthia and RC. Deh, Journal of Applied Polymer Science, 2001, 80,1792. 2001, John Wiley and Sons...

As polymer-cement ratio increases from 30 to 60%, generally the extensibility, strength and chemical resistance of epoxy-modified mortars are considerably improved, but their adhesion, waterproofness, carbonation depth, chloride ion penetration depth and drying shrinkage are nearly constant. Of the improved properties, the large extensibility is very interesting. 

ASTM D883 defines a filler as "...a relatively inert material added to a plastic to modify its strength, permanence, working properties, or other quaHties or to lower costs." EiHers (qv) that modify the properties and characteristics of epoxies are employed in epoxy resins for a variety of reasons. Then principal functions are to control viscosity, reduce shrinkage and the coefficient of thermal expansion, effect a cost reduction, and color the epoxy resins. 

Aqueous dispersions are used in fiber bonding, paper coating, friction and abrasive appHcations, and laminates and wood bonding. PhenoHc dispersions improve the strength of latex-contact adhesive appHcations. Epoxy-modified phenoHc dispersions are prepared by dispersion of the phenoHc epoxy resin. The systems are used for baked primer appHcations and bonding requirements. Minimum baking conditions are 20 min at 150°C (25). 

Heat resistance is an important characteristic of the bond. The strength of typical abrasive stmctures is tested at RT and at 300°C. Flexural strengths are between 24.1 and 34.4 MPa (3500—5000 psi). An unmodified phenoHc resin bond loses about one-third of its room temperature strength at 298°C. Novolak phenoHc resins are used almost exclusively because these offer heat resistance and because the moisture given off during the cure of resole resins results in undesirable porosity. Some novolaks modified with epoxy or poly(vinyl butyral) resin are used for softer grinding action. 

During the temperature ramp period, pressure is applied. How much pressure is applied depends on the adhesive and the type of assembly. Honeycomb assemblies are limited by the compression strength of the honeycomb core, so cure pressure is typically limited to 50 psi for aluminum core of standard density. Metal to metal assemblies can withstand higher pressures and usually have fewer bondline voids when cured at higher pressures. Metal-to-metal assemblies bonded with standard modified epoxies are cured at 90 psi. 

Wimolkiatisak, A.S. and Bell, J.P. (1989). Interfacial shear strength and failure modes of interphase modified graphite-epoxy composites. Polym. Composites 10, 162-172. 

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]. 

Cements that harden by the loss of solvent generally are to be avoided because the solvent can be lost only be diffusion thru the expl. Diffusion may be slow and the solvent may modify the properties of the expl. Two types of cement that have been used for this purpose are catalytic setting cements, like epoxy resins, and contact cements. Compatibility of the materials to be used should be checked. Compatibility of epoxy resins with most explosives depends upon the catalyst or hardener used (Ref 8). Data regarding bond strengths and other pertinent properties also have been compiled (Refs 5 6)... 

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