Epoxy-Cement Systems

These resin cement systems require only moderate capital investment, yet can yield dramatic results. For example, the many thousands of cracks in the Los Angeles City Hall produced by the 1971 earthquake were repaired by the use of 20 thousand gallons of an aluminum and ceramic filled epoxy resin mortar.— Likewise, wood whose cracks have been sealed by polyurethane mortars is suitable for continuous lathe cutting for veneer manufacture. 

With the development of epoxy resin systems as toppings, it was only natural that these systems would have been adapted in terrazzo applications. The advantages of epoxy-based terrazzo include rapid cure, as compared to conventional cement terrazzo, and lightweight of 1-3 lbs. per square foot, as compared to 10-20 lbs. per square foot for Portland cement terrazzo. 

In recent years, there have been some interesting developments in epoxy-modified mortar and concrete in Germany. The developments include a one-component epoxy resin system for the cement modifier and a dry mortar using epoxy resin. The former does not need any hardeners added at the construction site. The latter is produced as a dry mixture of an epoxy resin with a hardener, cement, and aggregates, and can be applied by adding only water in the field. 

The slot in the interfaces for passage of the belt is formed by two "L"-shaped sapphire pieces which are attached to the stainless-steel flange or vacuum closure bar by epoxy cement. The belts used are either 0.05 or 0.075 mm thick and the slot tolerance is set to be 0.075 mm greater than the belt thickness (i.e., either 0.125 or 0.15 mm). The belt width is 0.317 cm and the slot width is 0.325 cm. A ribbon 0.32 cm wide travelling at a speed of 2.5 cm/sec will carry away a liquid film 0.2 mm thick from a solvent flow of 1 ml/min and if the solvent film can be evaporated without loss of solute, then the ribbon will transport virtually 100% of the solute into the mass spectrometer. Sample utilization will then depend only on the efficiency of the flash vaporization step. In practice, some sample is lost by spray processes and the flash vaporization cannot be fully efficient for all compounds. Nevertheless, yields in the range of 25-40% have been attained with an LC/MS ribbon interface system. It follows that the quantity of column eluent taken from the ribbon will be twenty times greater than that taken by the wire and provide significantly improved sensitivity. 

Epoxy resins are the strongest adhesives known they are extensively cross-linked systems. They can adhere to almost any surface and are resistant to solvents and to extremes of temperature. Epoxy cement is purchased as a kit consisting of a low-molecular-weight prepolymer (the most common is a copolymer of bisphenol A and epichlorohydrin) and a hardener that react when mixed to form a cross-linked polymer. 

Epoxy resin has superior properties such as high adhesion and anticorrosion, and has widely been used as adhesives and anticorrosives in the construction industry in the world. Provided the incorporation of the epoxy resin into cement mortar can give its superior properties to the mortar, it is possible to produce a highly polymer-modified cement mortar. The first patent of an epoxy-modified cement system was taken by Donnelly in 1965 [1]. Since the patent, 30 or more papers on the epoxy resin modification of the cement mortar and concrete have already been published [2]. Most epoxy resin-based cement modifiers dealt with in the papers are specially compounded by the manufacturers, and the procedures for mixing them to fresh mortar and... 

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]. 

A sand filled epoxy compound will have lower stresses because the coefficient of thermal expansion will have been reduced and will have been brought closer to the coefficient of thermal expansion of Portland cement concrete. Some of the requirements for an epoxy system, based on a polysulfide-modified epoxy binder, are typically as follows ... 

The third approach has been the direct addition of epoxy resin and curing agent to cement. This can be accomplished, but generally requires the addition of 20% to 50% of the resin curing agent combination to obtain the desired properties. This approach is a compromise, resulting in a system which is economically impractical. 

Because of the generally bad to poor results of past attempts, it became apparent that an entirely new and different approach to the water dilutable epoxy system had to be followed, whereby the resin emulsion could be added to cement in small quantities and still affect the desired increase in properties. The proper ties desired would be as follows ... 

The shear strength of the epoxy-episulfide resin system ranges from 6,400 psl to 7,500 psl, comparable to 6,500 psi for Zimmer and 6,230 psl for Simplex acrylic cements. 

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