Literatürde Macro-Defect-Free (MDF) cement olarak adlandırılan büyük boşluklarından arındırılmış çimento-polimer kompozitleri veya kısaca MDF çimento olarak adlandırabileceğimiz malzeme 1980 'li yılların başında çimento bazlı malzemelerin özellikle eğilme dayanımlarının artırılması amacıyla geliştirilmiştir. MDF çimentolar, ağırlıkça % 80'den fazla oranda çimentonun az miktarlarda polimer ve su ile karıştırılması ile elde edilir. Bu karışıma yüksek eğilme dayanımları elde edebilmek için kauçuk endüstrisinde de kullanılan kalenderleme işlemi uygulanmaktadır. Bu esnada çimento ve polimer arasında çapraz bağların olduğu düşünülmekte ve bu durum yüksek eğilme dayanımlarının temel sebebi olarak açıklanmaktadır. Ayrıca, bu malzemeyi üretimden sonra bir miktar basınç ve sıcaklık altında küre tabi tutmanın da eğilme dayanımının artırılmasında önemli etkisi vardır. Öyle ki normal çimento hamuru ile ancak 5-10 MPa eğilme dayanımı elde edilebilirken, MDF çimento ile 200 MPa'ı aşmak rahatlıkla mümkündür. Hatta bazı araştırmacılar 300 MPa'ın da üzerine ulaşarak çeliğin dayanımına yaklaşmışlardır. En yüksek dayanımlar alüminli çimento ve polivinil alkol-asetat (PVAc) kopolimerleri kullanılan kompozitlerde elde edilmektedir. Öte yandan, bu kompozitlerde çok önemli dürabilite problemleri söz konusudur. Özellikle bu malzemenin suyla temas etmesi halinde dayanımı büyük oranda düşmektedir. Bu çalışmada farklı PVAc ve alüminli çimentolar kullanılarak üretilen çimento-polimer kompozitlerinin dayanım ve dayanıklılık özellikleri incelenmiştir. Çalışmanın 1. bölümünde hidroliz dereceleri farklı PVAc'ların kullanılmasının MDF üzerindeki etkisi incelenirken, alüminli çimentoların AI2O3 yüzdesindeki değişimin etkilerinin incelenmesi 2. bölümü oluşturmaktadır. Bu sayede MDF çimento üretimi için en uygun malzemeler belirlenmeye çalışılmıştır.

Macro-Defect Free (MDF) Cements, which are cement-polymer composites, had been developed and patented by the scientists from Imperial Chemical Industry (ICI) in order to increase especially the flexural strength of cementious materials by decreasing large voids at the early 1980 's in London. These new composite materials were produced by adding small amount of polymer and water into the cement and processed in a different method inspired by rubber production. The most important property of this composite is its unusually high flexural strength. Although, generally more than 80% (by weight) of this composite is cement, it has 20-30 times higher flexural strength than conventional cement paste. 150-300 MPa flexural strengths are easily achieved which are close to the strength of ordinary steel and it was a very important development if we compare it with ordinary cement paste which has only 5-10 MPa flexural strength. Inventors of the MDF cements attributed this high flexural strength to the elimination of macro voids in the material during processing and they thought that polymer was a rheological aid and inert filler. However, further studies have proved that crosslinking reactions between the ions of cement and polymer chains are also very important to obtain such high flexural strengths. In addition, pressing the material under moderate temperature after production is another reason for improving mechanical properties. Different cement and polymer types can be used for the production of this composite material. However, highest flexural strengths are always obtained when Calcium Alumina Cements (CAC) as cement and Poly (Vinyl alcohol) Acetate (PVAc) copolymers as polymer were used. On the other hand, this composite has serious durability problems under water effect. Significant amount of swelling are observed and the strength of this composite decreases in water storage even in very short time. In this study, MDF cements were produced by using CAC-PVAc copolymers and effects of ingredients on the water sensitivity were investigated. In the first part of the experimental studies, MDF cements were produced with different type of PVAcs which differ in their hydrolysis degrees. Secondly, MDF cements were also produced with four different types of CACs which differ in their AI2O3 content and their effects on water sensitivity were investigated. Biaxial flexural strength tests were conducted on the specimens after storing in both dry and humid conditions. Purpose of these tests was finding the most suitable PVAc and CAC type with respect to both mechanical and durability properties. Seven different types of PVAc were used in the first step. Their hydrolysis degrees were changing between 79.6 to 99.1%. MDF cements were successfully produced with 5 of 7 different PVAcs, except those with fully hydrolyzed PVAc (98.4%) or car-boxy lated PVAc (96.0%). All mixtures were affected from moisture in different rates between 45% and 80% depending on PVAc type. However, the PVAc at the lowest hydrolysis degree (79.6%) gave the lowest strength loss (45%). Increasing the degree of hydrolysis of PVAc increased the strength loss of MDF specimens stored in water. In the second step, MDF cements were produced with 4 different types of calcium alumina cement, which their alumina contents were changing between 42 to 79%. Water/cement ratio was changing between 0.09 and 0.19 while the polymer/cement ratio was kept constant at 0.07. Twenty five different batches were prepared in order to produce MDF cements, which differ in their water contents. Production was successful with all 4 different types of calcium alumina cements. The highest biaxial flexural strength was obtained as 257 MPa on CAC 70 composite, which was prepared by cement with 70% AI2O3 content and water/cement ratio of 0.15. The lowest biaxial flexural strength was 70 MPa and belongs to the CAC 79 composite, which was prepared with 79% AI2O3 content cement and water/cement ratio of 0.19. Although, the production of MDF becomes harder for highest level of AI2O3 (79%) than those with lower AI2O3 content there is a slight increase on properties with the increasing content of Al2O3upto 70%. As conclusion, MDF cements, which were produced with low hydrolysis degrees PVAcs, and alumina cements, which have highest AI2O3 content up to 70%, showed higher flexural strength and better durability properties under water effect.