These materials are quite different from polymer-modified mortars in that they do not contain any hydraulic cement. They consist of a synthetic resin binder incorporating a hardener and filler such as well-graded powder, sand or coarse aggregate. These are mixed on site, placed and then allowed to cure giving a material with generally good mechanical properties (in terms of compressive, tensile, flexural strengths), adhesive bond strength, and chemical and abrasion resistance. Applications of these materials include repair mortars and crack injection formulations, adhesives, grouts for mechanical fixings, floor finishes such as sealers and toppings, and pre-cast drainage channels and pipes. Several recent and detailed reviews are available (CIRIA, 2000).
The most widely used resins include those of the following generic types: epoxies, unsaturated polyesters, methacrylates, polyurethanes, vinyl esters and furans. Their chemical nature allows the formulation of a wide variety of products ranging from low viscosity solvent systems for void impregnation and crack injection to heavily filled products much like conventional mortars.
Thermosetting resins are used so that, when combined with curing agents or catalysts at ambient temperatures, they undergo further polymerisation (cross- linking) to give a three dimensional structure. The correct degree of cross- linking is very important in that it determines the glass transition temperature of the polymer and other long-term properties.
The amount of curing agent or catalyst governs the rate of reaction at a given temperature so that, if the material were applied on site at low ambient tem- peratures of say ~10ëC, more is required, whilst at higher ambient temperatures of say ~35ëC the converse is true. In addition, the reactions are influenced by the exothermic nature of polymerisation, the thickness of the coating and variations in ambient temperature. Most reactions do not proceed to completion but, if reactive polymer matrix composites are formulated appropriately, a sufficient degree of cross-linking is attained at ambient temperatures to give the required service properties.
