1. Scope

Keywords

Rationale

The use of colloidal silica, or 'silicon dioxide (SiO2)' in concrete mixtures is increasing, and for this technology to be fully embraced, it is necessary to standardize the types of colloidal silica that can be used in concrete construction and set minimum concrete performance requirements for each type. The remainder of this rationale discusses the need for a standard specification and how a specification will help support application of colloidal silica in concrete projects. Additionally, this rationale is intended to provide insight into why some types of colloidal silica may not be suitable in a particular application while others would be better-suited alternatives, considering a wide range of factors related to concrete chemistry, mixing practices and equipment, durability, effectiveness in reducing binder content, carbon footprint, and more. By establishing requirements for colloidal silica, this standard is to be used to validate the intended, ordered, and delivered colloidal silica properties and performance. Like with other materials, the standard specification cannot determine if the selected colloidal silica is the right choice for a specific project. The user is required to have a basic knowledge of the material, which can be obtained from a variety of sources (Belkowitz, 2015; Land, 2012; Westbrook, 2022). Colloidal silicas are silica-based water based suspensions of finely-divided silica. The suspended phase comprises “colloids”, or particles, which are smaller than 1 um in diameter, in suspension, and are essentially unaffected by gravitational forces due to their size (i.e., they will not settle in the time scale commonly associated with concrete construction). These particles, however, are large enough (i.e., =1 nm) to display marked deviations from the properties of solutions of ionic species commonly associated with concrete.