What is Self-Compacting Concrete?

Self-Compacting Concrete (SCC) is a type of concrete with high fluidity that flows and takes shape within the formwork without the need for mechanical consolidation operations. The significance of using this type of concrete lies in its ability to meet the required performance requirements for fresh concrete while ensuring the durability and expected stability, and even improving them, without the need for mechanical compaction.

To maintain the integrity of self-consolidating concrete and prevent the segregation of its aggregates and constituent elements, it is essential to use appropriate grading with sufficient fine particles, as well as approved mineral and chemical additives from a quality control unit. This process requires knowledge, expertise, and sufficient experience.

Specifications of Self-Consolidating Concrete

One of the unique features of self-consolidating concrete (SCC) is its performance and the absence of the need for internal vibration. Performance describes the flow characteristics and deformation of fresh concrete. To achieve the necessary performance for producing self-consolidating concrete, this concrete must simultaneously possess the following three characteristics in terms of fresh concrete properties:

• Flowability (flow in a free state): The fluidity of self-consolidating concrete should be sufficient to allow it to flow under its own weight.
• Passability (flow in a confined state): Self-consolidating concrete must be able to pass through the spaces between reinforcements and obstacles.
• Resistance to segregation (stability): Considering the need for homogeneity in self-consolidating concrete, the above two choices must be made under conditions where segregation does not occur.

Considering that the design and construction of self-consolidating concrete differ from ordinary concrete, their mechanical properties will also be different. The increased use of cementitious materials and fine particles, along with uniformity and a better microscopic structure, contributes to improving the mechanical characteristics of self-consolidating concrete compared to ordinary concrete. Depending on the project’s requirements, self-consolidating concrete can be assigned various strength classes such as C40, C50, and so on. Taking into account the improved microstructure of self-consolidating concrete compared to ordinary concrete, according to research conducted, self-consolidating concrete exhibits better results in compressive strength, tensile strength by splitting, modulus of rupture, and modulus of elasticity compared to ordinary concrete.

The use of fine fillers reduces the porosity of self-consolidating concrete. This reduction in the porosity of the self-consolidating concrete matrix leads to decreased permeability and consequently increases the durability of self-consolidating concrete against adverse physical and chemical environmental conditions. This concrete demonstrates better performance compared to ordinary concrete against destructive factors such as carbonation, chloride ion penetration, and resistance to freeze-thaw cycles. According to conducted research, the use of various pozzolans as cement substitutes, such as microsilica, zeolite, slag, etc., improves the durability of self-consolidating concrete in terms of sulfate attacks and alkali-silica reactions compared to ordinary concrete.

Self-Consolidating Concrete Mix Design

For the design of self-consolidating concrete mixtures, flowability and resistance to segregation are two critical aspects that must be considered. To achieve flowability, a low yield stress is required, and to enhance resistance to segregation, an increase in viscosity is necessary. Therefore, efforts should be made to strike a balance between these two parameters in the design of self-consolidating concrete mixtures. In summary, the mix design process, based on the American Concrete Institute Committee 237 (ACI 237R-07), is as follows:

• Selection of the flow spread based on the project’s performance requirements.
• Selection of the size and volume of coarse aggregates based on the spacing between reinforcements, texture, and grading of the aggregates.
• Estimation of the cementitious material content and water requirement.
• Calculation of the volume of paste and mortar.
• Selection of additives.
• Mixing a trial batch.
• Performing necessary tests to evaluate the performance of fresh concrete.
• Adjusting mix proportions based on test results and repeating the process until achieving desired results.

Examples of self-compacting concrete mixtures are shown in the table below:

Advantages of Self-Consolidating Concrete:

1. Pre-production activities: