It is well known in the art that the setting and hardening of a hydraulic binder or of a mixture which contains a hydraulic binder can be accelerated through the adding of a setting accelerator or hardening accelerator. Typical examples of binders are cement, like Portland cement, lime, slake limes, gypsum and mixtures thereof and typical examples of mixtures which contain such a binder and further components are mortar and concrete.
The most commonly used setting accelerators however are substances with strongly alkaline properties, like alkali metal hydroxides, alkali metal carbonates, alkali metal silicates and alkali metal aluminates. Substances with strongly alkaline properties however are undesired due to health risks which they can cause when persons are handling such substances, and specially etching of the skin of the worker, harmful effects onto the respiratory system, specially the lungs, and irritation of the eyes and even an etching of the cornea can occur.
Furthermore the introduction of alkali metal ions into mortar or concrete has an adverse effect onto the properties of the construction material. For example, through the incorporation of strongly alkaline setting accelerators into concrete, the final compressive strength of the hardened construction material is lowered, and the shrinkage is increased, which may result in the development of cracks in the construction material. Thus the stability and the lasting quality and durability of the building is deteriorated.
A further group of frequently used setting accelerators and hardening accelerators contains chlorides like alkaline earth metal chlorides. Any chloride containing materials however are undesired at a construction site because they have a corrosive effect onto the different equipments used at the construction site and also the corrosion of reinforcing bars and nets is increased through chloride ions.
Furthermore it is well known in the art that any set accelerators which contain chlorides reduce the chemical resistance of the construction material drastically, specially the sulfate resistance of the hardened cement or concrete.