Mineral Admixture-Based Rheological Design of Concrete

The use of supplementary cementitious materials (SCMs; e.g., slag, fly ash) to reduce the amount of ordinary Portland cement in concrete construction has increased significantly over the last 20 years. Previous research has shown that, as an important benefit, SCMs can improve the long-term mechanical properties and durability of concrete. However, there is limited and inconclusive information on the relationship between SCM properties and concrete workability. This is particularly important for technologies that require high workability control, such as self-consolidating concrete (SCC).

This thesis provides an experimental-based quantitative assessment and understanding of the effects of the particle size and physicochemical properties of SCMs and their interactions with the primary mixture parameters (such as water-to-cementitious materials ratio, SCM replacement, and reactivity of cement) on the rheology of cementitious paste (i.e., cementitious mixture with no coarse or fine aggregates). The results from this research are intended to improve the mixture design of new construction technologies that require better rheological control, through the use of SCMs. As a specific application, improved design of SCC to achieve better interlayer bonding is investigated. This is important for the construction of large concrete elements, where casting of multiple concrete lifts is required. Specifically, due to the lack of mechanical consolidation when casting SCC, the interfaces between multiple layers can result in reduced mechanical resistance in the final structure.

The specific objectives of this research are to experimentally investigate, develop and validate empirical models for the effects of: 1) SCM properties and their interactions with the primary mixture parameters on the increase of static yield stress on time of cementitious paste before initial set; 2) SCM properties and their interactions with the primary mixture parameters on the viscosity of cementitious paste before initial set; and 3) concrete mixture design (i.e., cementitious paste rheology and aggregate-to-cementitious paste ratio), building process (i.e., layer-to-layer free-fall height and delay time), and their interactions on the layer-to-layer flexural and shear bond strength in multilayer SCC.