Macro Defect Free (MDF) Cements

Publisher Website
Google Scholar
Abstract
Ordinary cement products based on calcium silicate (Portland cement) or calcium aluminate (refractory, rapid hardening cements) exhibit a number of interesting properties but are deficient in strength and toughness. The purpose of the ICI work on cements was to understand the cause of these deficiencies in order to design improved cement materials. Our early study of existing products showed that strong cements can be produced by high pressure moulding of cement powder, a phenomenon discovered about 50 years ago. Unfortunately this is only practical for small articles such as catalyst supports. A more recent empirical discovery was the improvement in properties of cements extruded using polymer extrusion aids. This process was patented in 1976. The problem was to explain these effects. Review of the literature also revealed a remarkable paradox in the theory of cement strength. Traditionally it had been believed that cement strength depended on the volume of pores in the material, which could be up to 30% porous. In contrast, it was also thought that cement behaved as a brittle material, in which case the presence of long cracks would be most critical. Our contribution was to propose and verify a theory which explained the separate effects of volume porosity and long crack-like pores. The study of cement microstructure and rheology demonstrated that large crack-like pores were the main problem in cements. Processes for removing these pores were developed and shown to give cement products an order of magnitude better than those on the market. The paper describes the progress of this development in detail.

This publication has 7 references indexed in Scilit: