State of the art of macro-defect-free composites

Macro-defect-free (MDF) composites, developed and patented by scientists from Imperial Chemical Industries in the early 1980s, are very high strength cement–polymer composites. The preparation of MDF composites is different from the production of conventional cement paste in that high shearing with a roller mill as well as moderate pressure (about 5 MPa) and moderate temperature (about 80–100 °C) are applied during the production. Very low water/cement ratio (w/c) levels are achieved (as low as 0.10) in this composite, much lower than in other cement-based materials. Of the many unique properties exhibited by MDF composites, surely the most remarkable is their high flexural strength. This is generally attributed to their low porosity and to cross-linking reactions between cement and polymer. MDF composites may reach a flexural strength of 200–300 MPa levels, whereas ordinary cement pastes have generally around 5–10 MPa. However, serious durability problems are observed in MDF composites, particularly their significant reductions in strength when immersed in water. Comprehensive information about MDF composite research will help in understanding the reasons behind the high strength, microstructure and water sensitivity of MDF composites. This review summarizes the materials, production methods, properties, microstructure, hydration reactions, durability and potential application areas of MDF composites as published since 1981.