Discussion Paper: How Many Components in a Grout Mix?

This article is presented to stimulate thought and discussion on how many additives should be included in high-mobility cement based grouts (HMG). The number of components used varies from just two (cement and water) to as many as ten. The ideal number will depend on many factors. The goal of this article is not to provide an ideal number nor to provide a recipe for formulating grouts, but rather to provide some relevant information and discussion on the subject of grout components. Additives range from chemicals specifically designed to affect cement hydration and the rheology of suspensions, to naturally occurring minerals, clays and sands. A description of some of the more common additives, the characteristics they modify and typical dosages is provided. A table describing the most common quality control test is also included. Both fluid and set characteristics of grouts are briefly described, including bleed, segregation, resistance to pressure filtration, control of particle agglomeration, a nti-washout characteristics, evolution of rheology and cohesion with time, set time, matrix porosity, ultimate strength, resistance to chemical attack, and durability. A range for the water/cement ratio and the proposed components for a base formulation for an uncomplicated HMG are identified. Discussion on modification of the base formulation to adjust to application specific challenges is then provided.