Rheology of concrete
Rheology may be defined as the science of the deformation and flow of materials. The term rheology deals with the materials whose flow properties are more complicated than those of simple fluids. It is concerned relationships between stress, the rate of strain and time.The rheological principle and techniques are applied to concrete include the deformation of hardened concrete, handling and placing of freshly mixed concrete and the behavior of its constituent parts such as cement slurries and cement paste.
The rheological of fresh concrete like workability includes the parameters of stability, mobility, and compatibility, which are necessary to determine the suitability of any concrete mix. For the purpose of discussion of rheological properties of fresh concrete, these parameters are redefined in terms of force involved in the transmission of mechanical stresses on the concrete.
Table content
- what is Rheology concrete
- Factors Affecting Rheological Concrete Properties
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| Rheology of concrete |
Stability
Stability is a condition in which the aggregate particles are held inhomogeneous dispersion by the matrix, and random sampling shows the same particles size distribution during transportation, placing and compaction.Mobility
The mobility of fresh concrete is its ability to flow under mechanical stresses. The flow is restricted by cohesive, viscous and frictional forces. The cohesive force develops due to adhesion due to adhesion between the matrix and aggregate particles. The viscosity of the matrix contributes to the ease with which the aggregate particles can move and rearrange themselves within the matrix. The mobility of a concrete mix may be evaluated by the laboratory triaxial compression test.Compactability
The compactability measures the ease with which fresh concrete is compacted. Compacting consists of expelling entrapped air and repositioning the aggregate practicals in a dense mass without causing segregation. Compatibility is measured by the compacting factor test. Thus the knowledge of rheological properties of concrete mixtures that can be efficiently compacted in the forms.Factors Affecting Rheological Concrete Properties
Rheological properties of fresh concrete depend upon mix proportions of concrete depend upon mix proportions of concrete. The amount, properties of ingredients, amount of admixtures, the amount of mixing and the time elapsed after the rheology of concrete. The following factors affect the rheology of concrete.- Mix Proportions Of Constituents
- Consistency Of Concrete
- Shaps, Size, and Texture Of Aggregates
- Grading Of Aggregates
- Different Types Of Admixtures
Mix proportions of constituents
If the amount of coarse aggregate will increase in concrete, it will result in loss of cohesion and mobility which is called as harsh concrete and requires great efforts and compaction of concrete. IF the number of fine aggregates will increase, it will result in the increase, it will result in an increase in the cohesion and it results in difficult movement of concrete. It will also increase the drying shrinkage and cracking because a high amount of fine aggregates increase the surface area particles which required more amount of paste to coat the surfaces.If the amount of cement will increase it will result in sticky and sluggish concrete. It aslo reduces the workability of concrete.
Consistency Of Concrete
The consistency of concrete is found out by a slump cone test. An increase in the water content will result in excessive bleeding. Hance a water content more than that required will not improve the rheology properties of concrete. Water content less than the required will reduce the mobility and compatibility which difficulties in placing of concrete.Shape, Size, And Texture Of Aggregate
The shape, size, and texture of aggregate affect the rheological properties of concrete. The rough and angular aggregates will require higher fine aggregates and water content to fill up a higher percentage of voids.In the same way, angular fine aggregates will require higher water content than natural sand.
Grading Of Aggregates
A well graded aggregate result in good workability. Variation in the sizes of aggregates or absence of any particular size of aggregates will affect the workability and void system of concrete. If any aggregates will increase, the concrete mixture becomes sticky. If coarse aggregates increase, the concrete mixture becomes harsh and bleeding will increase, so as aggregates should be well graded to maintain workability.Different Types Of Admixtures
Plasticizer and superplasticizers, air-entraining agents, accelerators and retarders are the admixtures which affect the rheology of concrete. These admixtures are used in the following ways- They increase workability with the same strength and durability.
- They provide the same workability are a strength with less water content.
- they provide the same workability and strength with less cement content.
The plasticizers reduce the water content by 10 percent without any effect on strength, superplasticizer made the concrete flowing which needs less compaction when concrete is placed into corners and around the congested reinforcement.
The air-entraining agents share the rheological properties of concrete. By increasing cohesion and reduce the workability time for a given mixture.