Epoxy mortars

When exeessive vibration is deteeted in the gear box of a eompressor train (Figure 21-14) and is transferred to the platform below, a dampening effeet ean be ereated by inereasing the rigidity of the support below. This effeet ean be aeeomplished by first filling the platform eavity and then the gear-box support with epoxy mortar. 

Another aspect of epoxy resin mortar floorings which needs careful attention is that their coefficients of thermal expansion are approximately three times that of concrete. This, coupled with the relative low thermal conductivity of epoxy mortar, can cause stresses to be induced at the resin mortar/concrete interface under conditions of thermal shock (e.g. thermal cleaning), resulting in break-up of the flooring due to initial failure in the concrete. Two approaches have been tried to overcome this problem ... 

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]. 

Epoxy mortars are suitable for horizontal, vertical and overhead applications. Advantages of these mortars are... 

Polyester concretes are used as a repair material in a similar fashion to epoxy mortars. They are also two-component systems. The material has a pot-life of usually 45 minutes at ambient temperatures but it is possible to adjust the pot-life by controlling the amount of catalyst. Formulators market the product in winter and summer grades. 

Epoxy Mortars Epoxies are the strongest resin mortars, have the best bond strength to other CRM materials, and resist many solvents, mild to moderate acids, non-oxidizing and alkaline media. Their useful pH range is about 2-14, and their thermal limit is approximately 230°F. Besides their excellent alkali and dilute acid resistance, epoxy mortars handle many organic chemicals and sodium hypochlorite at low temperatures. Epoxies should not be exposed to acetic acid and its esters. Epoxy mortars have the best physical and mechanical properties of all the resin mortars. 

Epoxy mortars, although susceptible to damage from water, are not seriously affected by thermal effects in the ambient upper ranges, and as long as the materials are kept covered, little difficulty is usually experienced. 

Epoxy mortars for patching applications are the most highly filled materials. With the proper selection of silica sand mixture as the filler, the filler concentration can be as high as 95 wt%. This, and similar materials produced Ifom a reactive polyure-... 

Epoxy mortars with the following composition have been used in oil-wells 1.0-2.5 wt % epoxy resin, 0.1-0.2 % curing agent,... 

Of course, floors in a structure receive the greatest abuse, where deterioration occurs in such areas, epoxy resin systems have been widely used for repairs. Industrial floors are now constructed with initial specifications calling for an epoxy mortar, usually, 1/4 inch in thickness, to provide a diemically and physically resistant surface. Slip-resistant aggregates may be embedded in such epoxy toppings. The same tech-... 

Priming is often necessary before placement of the mortar. A small amount of the mixed epoxy binder may be used to be applied to the surface on which the epoxy mortar is to be bonded. The volume of a batch of epoxy mortar should not exceed that which can be placed within one hour. Working time of the mixture may be extended by spreading the mixture out to prevent the development of an.excessive exotherm. 

A primer adhesive is first applied to a properly prepared concrete surface. A thin coat of epoxy mortar is then applied with a trowel. While this thin coat is still wet, a fiberglass membrane is rolled into the mortar. The edges of the membrane should be overlapped 2 inches. The mortar will squeeze up through the voids in the fiberglass mesh, resulting in adhesive base to which the final epoxy mortar will adhere. While this first application of mortar is still tacky, the second layer of epoxy mortar is applied over the glass cloth. This second layer may then be screeded and leveled. ... 

Expanded metal lathe and/or wire mesh may be utilized in the same way as fiberglass membrane, particularly, when applying an epoxy mortar onto a wodden floor. It is recommended that a preliminary repair of a wood floor be made first by securing 3/4 inch Douglas fir plywood to the v/ooden substrate by proper nailing. 

A typical formula for an epoxy mortar is given in Figure 4 ... 

Figure 4. Epoxymortar topping The epoxy mortar topping is prepared in kits.

Epoxy mortars are less frequently used in CRM than other resin bonded systems due to higher cost, lower maximum service temperature, and narrower range of chemical resistance. However, because of their excellent bond strength to concrete, epoxides are frequently used for acid brick floors over concrete. They also have applications in alkali exposure. 

Chem. Descrip. Aliphatic polyamine adduct (80%) in water Uses Hardener for water-reducible coatings on min. or metallic substrates, hydraulic epoxy mortars... 

Uses Epoxy for water-reducible primers/coatings on min. substrates, adhesives and water-washable jointing compds. for tiles, hydraulic epoxy mortars... 

Uses Diiuent for epoxy systems, for soiv.-free coatings and floorings Features General purpose low toxicity improves adhesion to most substrates incl. oily metal ( 5-10 phr) improves trowelability of epoxy mortars add to resin or curing agent Properties Gardner7 max. liq. sp.gr. 1.04 dens. 8.6 Ih/gal vise. 100cps... 

Fig. 6.3. Free shrinkage strains in repair mortars, (a) Epoxy mortar, (b) Styrene Butadiene Rubber modified mortar, (c) Magnesium phosphate modified mortar, (d) Ordinary Portland cement mortar.

In old buildings timber often fails where it enters a masonry wall or in roofs at the junction of rafter and tie beam where the truss is supported on the wall plate. In both cases leaking water over a long period has resulted in wet rot. The repair process consists of replacing the decayed timber with reinforced epoxy mortar. The reinforcement may consist of steel plate or bars which are drilled or set deep into the sound portion of the timber to ensure a good bond and load transfer. Fig. 6.23 shows bonded dowel bars used to repair the end section of a column or beam while Fig. 6.24 illustrates a typical repair to a roof truss. 

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