Repair Procedures

The procedures developed for the repair of the longitudinal cracks involved enlarging the crack to permit the placement of polymer concrete. Polymer concrete (PC) consisting of aggregate with a polymer binder had been previously investigated and reported for the repair of portland cement concrete (1-4). PC develops very good bond to portland cement concrete.

Several methods for enlarging the crack were investigated. Sawing was not feasible for following the irregular cracks. High pressure water jetting was not feasible.

Since polymer concrete does not bond well to wet surfaces and it would have been necessary to permit the cracks to dry before placing the PC.

The polymer concrete is placed by filling the enlarged crack with clean dry concrete sand and pouring methyl methacrylate (MMA) monomer system over the sand until it is completely saturated.

The monomer system consists of 95 percent MMA and 5 percent trimethylol propane trimethacrylate (TMPTMA). Benzoyl peroxide (BzP) initiatior, in dispersion form, is added at a level of about one percent (2.5 percent for 40 percent dispersion) and a promoter, dimethyl-para-toluidine (DMPT), is added at a level of 0.5 percent, both by weight of the MMA system. The levels of BzP and DMPT are dependent upon the ambient temperature .

It is essential that monomer be reapplied to keep the sand saturated since Monomer is lost due to evaporation and due to leakage in the crack at the bottom of the enlarged crack.

In some repairs silicone caulking was used to seal the crack below the PC to minimize monomer loss. In other repairs polymethyl methacrylate (PMMA) powder was mixed with the sand before it was placed in the crack. PMMA powder acts as a thickner and prevents leakage of the monomer.

Most repairs, however, have been made without the silicone sealant or PMMA powder. The objective has been to have monomer penetrate into the crack and bond the concrete.