Waterproof of Membranes
Waterproof membranes have been used extensively to minimize the ingress of chloride ions into concrete.
The requirements for the ideal waterproofing system are straightforward, it should:
- be easy to install,
- have good bond to the substrate,
- be compatible with all the components of the system including the substrate, prime coat, adhesives, and overlay (wherever used),
- maintain impermeability to chlorides and moisture under service conditions, especially temperature extremes, crack bridging, aging, and superimposed loads.
Polymer impregnation consists of filling some of the voids in hardened concrete with a monomer and polymerizing in-sib. Laboratory studies have demonstrated that polymer impregnated concrete (PIC) is strong, durable, and almost impermeable. Maximum polymer loading's are achieved by drying the concrete to remove nearly all the evaporahle water. removing air by vacuum techniques, saturation with a manometer under pressure. and polymerizing the monometer in the voids of the concrete while simultaneously preventing
evaporation of the monometer.
Chemical initiators, which decompose under the action of heat or a chemical promoter, are used exclusively in field applications. Since prolonged heating and vacuum saturation are difficult to achieve, increase processing costs substantially, most field applications have been aimed toward producing only a surface polymer impregnation, usually to a depth of about 25mm. Such partially impregnated slabs have been found to have good resistance to chloride penetration. Some of the disadvantages of PIC are that the monomers are expensive and that the processing is lengthy and costly.
Polymer Concrete Overlays
Most monomers have a low tolerance to moisture and low temperatures, hence the substrate must be dry and in excess of 4OC (40 F). Aggregates must be dry so as not to inhibit the polymerization reaction.
Workers should wear protective clothing when working with epoxies and some other polymers because of the potential for skin sensitization and dermatitis. Manufacturers recommendations for safe storage and handling of the chemicals must be followed. A bond coat of neat polymer is usually applied ahead of the polymer concrete.
Latex-modified Concrete Overlays
Latex modified concrete is conventional Portland cement concrete with the addition of a polymeric latex emulsion. The water of suspension in the emulsion hydrates the cement and the polymer provides supplementary binding properties to producer a concrete having a low water cellulite ratio, good durability, good bonding characteristics and a high degree of resistance to penetration by chloride ions. all of which are desirable properties in a concrete overlay.
Tlie latex is a colloidal dispersion of synthetic rubber particles in water. Styrene-butadiene latcxes Ge used most widely. The rate of addition of the latex is approximately 15 percent by weight of the cement.
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