It has been difficult with the conventional polyurethane or epoxy liquid resin systems to fill small gaps formed between the concrete slab and the cement-asphalt (CA) mortar layer of the slab track. It is hard to pour them properly into such small gaps or small cracks in the slab because of their fluidity. Moreover, these thermosetting resins are not easy to harden when applied in a this layer and under a cold atmospheric condition as exothermic heat is lost. Therefore, a radically reactive methyl methacrylate (MMA) liquid resin system has newly been developed for this application. It flows sufficiently to fill such small gaps and cracks as its viscosity is very low (ca. 0.065Pa s at 25). Additionally, it also has advantages to harden very quickly under a wide range of atmospheric temperature, and cure if water exists in gaps or cracks.