A low calcium raw mixture
Prior to further use, the raw materials containing calcium (CaO) and silicon (SiO2) must be processed and an appropriate raw mixture must be designed from the raw material. The CaO supplying component must be available in a reactive form for the following autoclave treatment. This can be achieved by simple decalcination of limestone. However, the molar ratio of calcium to silicon is between 0,5 and 2. That shows a rather low demand in CaO.
Using an autoclave under saturated steam conditions (150-300°C) the autoclave “raw meal” with suitable C/S ratio is processed until special calcium silicate hydrates are formed as an intermediate product. The product from the autoclave has no hydraulic properties. It is stabilised by so called hydrogen bonds preventing it from any further reaction.
The activation grinding step triggers the most important phase transformation during Celitement production. It is at this point, that the stabilizing hydrogen bonds are destroyed. This happens in a so called “tribochemical” surface reaction during co-grinding with other silicates. By this, the new calciumhydrosilicates, named Celitements, are finally formed. To control the reactivity and other important product properties, addition of certain admixtures is possible at this step.
The final product obtained after the reaction grinding already contains appreciable amounts of stuctural water, but can be used and applied just like classical Portland cement. It is also possible to mix it with cement and other hydraulic active substances. During hydration, large amounts of the well known "concrete glue", namely CSH-phases (Calcium Silicate Hydrates) know from hydration of classical cement, are formed.
It is very effortful to characterize or identify Celitement analytically. The processes required for this are complex. For the development and optimization of Celitement, special analytical expertise is required. This is currently being developed together with the partner KIT until final maturity practice. Only the analytical control of all process steps in the production allows the step into industrial practice.
Production of Celitement is achieved at temperatures below 300°C. Compared to OPC clinker (rotary kiln, 1.450°C), low process temperature and reduced limestone content economise substantially on energy. Celitements are compatible to OPC and reveal excellent properties. Phase composition is very homogeneous; i.e. regulation of properties is straightforward and simple, e.g. strength as a funciton of time.
A reliable process control, quality control and optimization of the product up to marketability is only possible if all related materials can be accurately enough characterized and objectively assessed. The efficiency of an industrial plant is highly dependent on the use of automatable systems for production and quality control. Some methods of previous manual analysis of Celitements have never been integrated into the automation of the process control of industrial installations. Along with the KIT, industrially applicable methods and techniques have been developed. These are currently tested either by the industrial partner SCHWENK or in the pilot plant.
The basic principles of Celitement materials and the production process are an invention of Karlsruhe Institute of Technology KIT.