Mix proportions, consistency, the qualities of each element contained in the mix, the mixing amount and the additive amount, and the time passed after mixing all influence the rheological properties of concrete. Rheological Properties of Concrete: Factors Affecting Them The following are some of the factors that influence the rheological qualities of concrete depending on its flow characteristics:Concrete amounts to mix Concrete consistency Concrete stiffening and hardening Aggregates’ textures Use of admixtures in concrete.
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Effect of Mix Proportions on Rheological Properties of Concrete
The proportioning of the concrete mixture is done to ensure that it has suitable workability during construction. This would provide complete assurance of the hardened concrete’s performance and properties.
If the concrete mix contains too much aggregate, there will be a shortage of mortar to cover the voids. This reduces cohesiveness and, as a result, the overall mobility of the mix. This mixture is considered harsh and would necessitate more effort in both placement and transportation.
A decreased value of air content also contributes to the harshness. The consumption of fine aggregates would be reduced if the entrained air was increased. Using fine particles or entrained air, in other words, will increase the cohesiveness of the mix, making it difficult to move.
The use of fine aggregate increases the contact surface area, necessitating the use of additional mortar to cover the surfaces with paste.
This is done to keep the mobility. However, this causes issues such as drying shrinkage and cracking.In terms of practical considerations, the mix is designed to have more fine aggregate and cement than is required for an optimal measurement. Because of the high cement content, the concrete mixture becomes sticky. As a result, the blend would be slow in nature. This is most common in standard slump cast in-situ concrete. With a lower water-cement ratio and a higher cement content, the workability of rich mixtures decreases.
Consistency of Concrete Affecting Rheology of Concrete
The consistency of the concrete mix determines the relative water content of the concrete. The concrete fluidity increases as the slump or water content increases, with the goal of making the mix workable. The internal friction of the concrete particles will be reduced as a result of this fluidity disadvantage. Increased fluidity increases the likelihood of segregation and bleeding in concrete. It’s important to remember that adding more water to concrete than is allowed won’t improve its rheological qualities. If there isn’t enough water in the mix, it won’t move properly or compact nicely.When rheological qualities are taken into account, a one percent increase in air entrainment equals a one percent increase in fine aggregate.
Effect of Hardening and Stiffening on Rheological Properties of Concrete
Factors that increase the rate of hydration and hence hardening will lower the concrete’s mobility. The concrete flowability capacity will be reduced due to greater temperatures, rapid hardening cement, and the use of accelerated admixtures.Using dry aggregates or highly porous aggregates would absorb a greater amount of water or have larger surface surfaces that should be wetted. Aggregate Shape and Texture Influence Rheological Properties of Concrete The shape and texture of the aggregates have a significant impact on the rheological qualities of concrete. The use of extremely angular pebbles with a rough texture will necessitate a larger mortar to fill up the voids. This would necessitate a larger fine aggregate content as well as a higher water content.
The angular fine particles have the ability to increase the internal friction inside the concrete mix. However, they require more water than natural sand, which is typically utilised and has a well-rounded form.
Grading of Aggregates influence on Rheological Properties of Concrete
The angular fine particles have the ability to increase the internal friction inside the concrete mix. However, they require more water than natural sand, which is typically utilised and has a well-rounded form.A well-graded set of aggregates ensures high-quality workability. This well grading system aids in the systematic filling of vacancies.There will be a void in the lack of any grade, which will be filled with either cement or fine aggregates. This results in a change in quantity. In fine aggregates, this effect is more significant than in coarse aggregates.The water consumption rises as the fineness of the fine aggregates increases. This will result in a sticky concrete mix.
There is less cohesiveness when the fine aggregates become coarser in size. This combination is believed to be abrasive. There is a risk of bleeding because there is no attachment between them. As a result, correct grading of aggregates is required to assure quality in workability and the other characteristics listed.
The Impact of Maximum Aggregate Size on Concrete Rheological Properties The demand for fine aggregate decreases as aggregate size increases. The overall surface area will be reduced if the fine aggregate content is lower. As a result, the amount of surface area that needs to be wetted will be reduced. As a result, the cement content is reduced, which is required to maintain a steady water cement ratio in the mix.
Effect of Admixtures on Rheological Properties of Concrete
There are many different types of admixtures used in concrete mix designs. These admixtures are chosen based on the requirements and the properties that the concrete must possess.Among the various admixtures, the following have a considerable impact on the rheology of concrete: Plasticizers Agents that entrain the air The admixtures listed above are employed for three distinct characteristics:To increase workability without sacrificing strength or durability To provide workability with a tiny amount of water while also increasing strength To provide both workability and strength with a lower cement content.When thinking about a standard water cement system. In an electrolyte system, particles are suspended, causing the particles to adhere to one another.
The addition of admixture will aid in the prevention of flocculation and, as a result, the flocculated structure, resulting in a change in inter-particle attraction to repulsion.This repulsion is now achieved by using plasticizers or Superplasticizers to build a barrier surrounding the cement particles. The particles with this membrane lose their capacity to attract one another, preventing flocculation. Based on a variety of Superplasticizers, the thickness of this absorbed membrane can be varied. As a result, the flocculation rate can be reduced to zero. There are also repulsive electrical forces formed between the particles, in addition to the foregoing occurrences. The absorption of ionised substances produces them. The viscosity of the plastic will increase as a result of this.
The air entraining agents in the concrete mix will introduce air bubbles, which will change the surface tension of the concrete mix’s aqueous phase. The entrained air bubbles will range in size from 10 to 250 micrometres in diameter. This is accomplished by molecules with a hydrophilic head group with a negative charge and a non-polar, hydrophobic tail.
The entrained air bubbles will form a negative-charged bridge between the cement particles. The rheological properties of concrete are greatly affected by these air entraining agents.Cohesion between the particles is being improved.Bleeding possibilities are reduced.Accelerators and retarders are used in concrete to change the time it takes for it to set.
The amount of each constituent, the qualities of the materials, the amount of mixing, the presence of admixtures, and the time passed after mixing all influence the rheological properties of fresh concrete, just as they do workability. Although these elements have properties of fresh concrete, they are examined here in regard to their impact on concrete flow properties.
The concrete mix is proportioned to give the workability required during placement and compaction to provide the hardened concrete’s specified performance qualities.If a concrete mix has too much coarse aggregate, there will be insufficient mortar to cover the void system, resulting in a loss of mobility and cohesion. This combination is well-known.
The rheological properties of concrete are dependent on the factors like mix proportions, consistency, the properties of each ingredient present in the mix.
Rheology is the branch of physics in which we study the way in which materials deform
The rheological properties of fresh concrete are related to cement hydration and chemical interactions in the cement paste system.