Improvement in Water Resistance of Macrodefect-Free(MDF)Cements by Application of Hot Press Molding Process
Yoshihiko OHAMA, Toshimitsu KOBAYASHI and Katsunori DEMURA
Abstract:In general, MDF (macrodefect-free) cements are produced by using portland cements and water-soluble polymers, and applying mechanochemical processing techniques at very low water-cement ratios, and have flexural strengths of 50 to 70MPa under dry conditions. However, MDF cements have a poor water resistance because of the nature of the water-soluble polymers used, therefore, the precast products made of MDF cements have not been commercialized in the world. MDF cements using a portland cement, a water-soluble polyacrylamide, an epoxy resin and a phenol resin are prepared with various mix proportions by applying a kneader mixing process, hot press molding process and heat cure, and tested for water resistance through a change in flexural strength and water absorption during water immersion. The effects of the mix proportions for the hot press molding process on the water resistance of MDF cements are examined to find out the effective processing techniques for improving their water resistance. As a result, the water resistance of MDF cements is markedly improved by applying the hot press molding process and heat cure to them with the optimum mix proportions, I.e., a polyacrylamide content of 6.0%, an epoxy resin content of 6.0%, a phenol resin content of 2.0% and a water-cement ratio of 8.0%. The application of the hot press molding process to MDF cements is considered to be effective for the simplification of their manufacturing process. Key Words:flexural strength, macrodefect-free(MDF) cement, polyacrylamide, epoxy resin, phenol resin, hot press molding process, heat cure