Epoxy Repair Mortars

Epoxies have an excellent resistance to abrasion. The abrasion resistance of a particular system depends upon the type of formulation and conditions. For example coatings have the capacity to resist abrasion from rubber wheels, whereas screed floorings, repair mortar and self-levelling floors can resist thousands of cycles from steel wheels. 

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. 

Epoxy resin mortars have been used in repairing or conserving massive concrete structures. It has been found that the adhesive properties of epoxy resins modified with polysulfides is... 

The anodic process can be stopped by applying a coating to the reinforcement that acts as a physical barrier between the steel and the repair mortar. For this purpose only organic coatings, preferably epoxy based, should be used. Protection is entirely based on the barrier between the reinforcement and the mortar, and passivation of steel cannot be achieved because contact with alkaline repair material is prevented. This method should be used to protect depassivated areas of the reinforcement only as a last resort, i. e. when other techniques are not applicable and only for small specific applications [1,4]. It may be used, for instance, when the thickness of the concrete cover is very low and it is impossible to increase it to the proper level, so that the repair material cannot provide durable protection to the embedded steel. 

Bonding agents may also be applied in some cases on the concrete surface in order to enhance adhesion of the repair mortar. These may be cementitious systems (cement paste or fine mortars), polymer latex or epoxy systems [4]. Epoxy systems should be used carefully since they create a moisture barrier between the substrate and the repair material, which can result in failure of the repair if moisture is trapped in the concrete. 

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.

Epoxy resin composites are well suited for applications in moist environments they are used as epoxy resin mortar, cold curing anchoring compound in building construction, repairs to bridge pavement, and high-quality floor coverings in industrial facilities. 

Epoxy-Bonded Mortar or Concrete for Concrete Repair... 

Epoxy-bonded mortar or concrete is used for repairs involving shallow replacement of concrete. Epoxy-bonded mortar is used for depth of replacement less than 40 mm, while epoxy-bonded concrete is used in depths between 40 and 140 mm (USER 1997). Shallow concrete replacements are subject to poor curing conditions as a result of moisture loss to evaporation and to capillary absorption by the existing concrete element with subsequent poor bond to the existing structure. The use of epoxy-bonded mortar or concrete can be used to ensure adequate bond between the old and the new material... 

Materials Used for Epoxy-Bonded Repair The epoxy resin used for epoxy-bonded mortar repairs (less than 40 mm depth) should be two component, 100 % solid type, meeting the requirements of specification ASTM C-881 (2010) for type III, grade 2 (medium viscosity), class B or C (depending on the ambient temperature). 

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. 

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-... 

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. 

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. 

ACI 503.4 Standard specifications for repairing concrete with epoxy mortars. 

A spalled concrete surface is the beginning of continued disintegration of the concrete. If the cost of replacement is at all comparable with the cost of repair, replacement is recommended. Replacement is also recommended when changing the level of the final surface is impractical. Otherwise, the concrete can be resurfaced with new concrete, epoxy topping, latex mortar, or iron topping. 

If the disintegration is shallow, it may be possible to use a latex-fortified or an epoxy mortar to patch the area. The mixtures of latex and cement and sand described under Repairing Surfaces of Pavement and Slabs may be used. An epoxy mortar may also be used, but it may not blend readily with the surrounding concrete in color or appearance. 

The corrosion of buildings and concrete structures is a major area of concern to engineers and builders. Repairs to concrete structures are essential to maintain their integrity. The design of the structure should have sufficient accessibility for repairs as shown in Fig. 8.47. During repair, spalled concrete is taken out ensuring that the salts have been sufficiently removed and the steel is cleaned. The concrete is replaced by a suitable mortar or concrete with proprietary additives. It has been observed in recent years that epoxy coated reinforcement provides an excellent protection against reinforced concrete corrosion. 

Areas less than 10 mm thick can be hand repaired by applying proprietary cementitious mortar with or without polymer modifier. Polymeric mortars can provide physical protection to concrete but do not provide an alkaline environment. The substrate must be kept sufficiently wet to minimize the loss of water during repairing. Proprietary bonding coats may be added to provide strong bonding to the substrate. They are formulated from epoxy polymer or polyester polymer and they can be used without a primer. 

Repairing Existing RC Structures Using Epoxy Resins and Bonded Mortar... 

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