‘Concrete Rheology’ or ‘Rheology of Concrete’ is the study of how matter flows and deforms, and it describes how force, deformation and time interact with each other. The word ‘rheology‘ comes from the Greek word “rheos,” which means “to flow.”
From gases to solids, concrete rheology can be used to any substance. The deformation of hardened concrete, the handling and placement of freshly mixed concrete, and the behaviour of its constituent parts, notably cement slurries and pastes, are all examples of some of the major rheological principles and techniques applied to concrete.
The rheology of fresh concrete like workability includes the parameters of stability, mobility and compactability.
Rheological concepts can also be used to describe the mechanical behaviour of solidified cement paste, which shows both elastic and inelastic deformations.
Factors Affecting Rheological Properties of Concrete
The general properties which mainly effect the rheology of concrete are as follows:
- consistency of concrete mix
- mix proportions
- shape and texture of aggregates
- size of aggregates
- grading of aggregates
- admixtures
- hardening
- mixture adjustments
Consistency
The relative water content in the concrete mix is determined by the consistency of the concrete as assessed by the slump test. Greater fluidity and lower internal friction are produced by increasing the water content or slump above that required to form a workable mix.
As a result, adding more water to concrete than is required will not increase its rheological qualities. A low slump or water content, on the other hand, reduces mobility and compactibility, which might make placing and consolidation more difficult.
Mix Proportions
An excessive amount of coarse aggregate in a concrete mix will result in a lack of mortar to fill the void system, resulting in a loss of cohesion and mobility. This type of mixture is known as harsh, and it takes a lot of work to place and compact.
An excessive amount of fine aggregate or entrained air in a concrete mixture, on the other hand, will significantly increase cohesion and make the concrete difficult to move.
Shape & Texture (Aggregates)
Because of the rough and angular aggregate particles, a higher percentage of voids will be filled by mortar, demanding higher fine aggregate levels and, as a result, a higher water content.
An angular fine aggregate, like well-rounded natural sands, increases internal friction in the concrete mixture and demands more water.
Size of Aggregate
Increases in aggregate maximum size minimize the fine aggregate required to maintain a given workability, reducing the surface area to be wetted and thus the cement content required to keep a consistent water/cement ratio.
Grading of Aggregate
Workability is enhanced by a well-graded aggregate. Gap graded aggregate has an impact on the void system and workability. In fine aggregate, these impacts are more severe.
Admixtures
The admixtures used in the mix have a significant impact on concrete rheology. Plasticizers and superplasticizers, air-entraining agents, accelerators and retarders are all examples of admixtures.
Hardening and Stiffening
The use of rapid hardening cement, gypsum-deficient cement, and accelerating admixtures all accelerate the rate of hardening, reducing the mobility of concrete.
Mixture Adjustment
Paying close attention to a mixture’s rheological qualities can help you save money on construction and materials. The qualities of the materials utilised, as well as the field circumstances, have a significant impact.