Mortar and concrete based on calcium sulphate binders

In this study both hemi-hydrate and anhydrite are tested as calcium sulphate binders for structural mortar and concrete. The advantage of using calcium sulphates instead of cement as a binder is the fact that the production of calcium sulphate is more environmental friendly than that of cement. For the calcinations of Portland cement, temperatures up to 1480 °C are needed, while the calcination of for instance hem-hydrate requires a temperature of 170 °C. The global cement industry produces around 1.4 billion tons of C02 per year. This is about 6% ofthe total CO2 production and thus it has a significant influence on the global warming of the earth /1/. Partially replacing cement by calcium sulphate binder could be one way to decrease the C02 production. Applying new methods on gypsum based concrete could result in a type of concrete with a compressive strength up to 30 N/mm2. With the right physical properties like flow ability and segregation resistance this could even be self compacting gypsum concrete (SCGC). Downside of the material is that, unprotected, it can only be used indoors, since it is non water-resistant. The calcium sulphate based concrete that has a compressive strength around 30 N/mm2 can have different potentials of appliance. First of all it could replace cement based concretes where low to medium compressive strengths are required. Another application could be gypsum boards. These gypsum boards may be a good alternative for the use of drywall. The gypsum boards are stronger and can be self supporting, while dry wall has to be supported by a steel frame or wall. When the right aggregates and fillers are used these gypsum boards could even be produced at a lower cost than the dry wall, since the hemi-hydrate can be partially replaced by cheaper materials like sand and gravel. In this study first attempts to develop a competitive concrete based on gypsum are reported. This development follows new mix design methods, based on PSD optimization and oxide balancing, in order to reduce the free water in the hardened gypsum concrete. More detailed information on the study described in this article can be found in the Bachelor thesis of the first author/2/