Concrete admixtures are used to improve the properties of concrete under a variety of conditions. Chemical admixtures reduce the cost of construction, modify properties of liquid and hardened concrete and ensure the quality of the finished product.
Chemical admixtures generally fall into the following categories:
Due to the water-based character of many chemical concrete admixtures and their specific composition they are a suitable media for microbial growth. The chemical properties of admixtures are a complex topic requiring in-depth knowledge and experience. Admixtures based on lignosulfonates and sugar components are especially very susceptible to contamination as these raw materials are of natural origin. Admixtures consisting of synthetic raw materials such as polycarboxylates can also be degraded by microbes. Sulfonated naphthalene and formaldehyde containing admixtures show self preserving properties, but these also need to be protected when combined with other ingredients. The preservative has to be compatible with the other components, e.g. defoamers and surfactants. For the preservation of admixtures a broad spectrum of efficacy against bacteria, yeast and mould is essential. Combinations of different biocidal actives are preferred to provide a cost-effective solution.