Where self-compacting concrete is used: pros and cons, installation features

Because of its special qualities, self-compacting concrete, or SCC, is a versatile building material that has grown in popularity in a variety of construction applications. SCC requires no mechanical vibration, unlike traditional concrete, and flows easily through crowded reinforcement and into complex forms. Because of this, it’s a great option for tasks where accuracy and usability are essential.

The ability of SCC to cut labor costs and time is one of its main advantages. It requires less labor and is easier to install because vibration is not needed. This feature not only expedites the construction schedule but also improves safety by lowering the possibility of mishaps related to the operation of vibrating machinery.

SCC does not, however, come without disadvantages. Because of the materials and admixtures required to give it its self-compacting qualities, it may cost more than regular concrete. Additionally, because the flowability of SCC can be sensitive to changes in material properties or environmental conditions, care must be taken in the mix design and quality control to ensure consistent performance.

SCC is frequently utilized in a range of construction projects in spite of these difficulties. Large-scale infrastructure projects like bridges and tunnels benefit from its ease of placement and ability to create smooth finishes, which makes it perfect for architectural applications. SCC is still a popular choice in contemporary construction because of its versatility, which provides both practical and aesthetic advantages.

Self-compacting concrete, or SCC, is a very adaptable building material that flows into forms with little assistance from mechanical vibration. It is frequently utilized in intricate constructions, architectural features, and locations with dense rebar arrangements, where conventional concrete might find it difficult to equally fill voids. Smoother finishes, lower labor costs, and increased safety from less manual handling are the main benefits of SCC. But there are disadvantages as well, like increased material costs and the requirement for exact mix design and quality control. For SCC to work as well as it can, proper installation methods that pay close attention to mix and placement are essential.

Definition

Many people are curious about the characteristics of self-compacting concrete. Self-compacting concrete, or SBC, is a novel building material that, even when a fine-mesh reinforcing grid is applied to the surface in multiple layers, will still sag and compact under the force of gravity and its own weight while filling nearly the whole area of the formwork. SCC is used to make shotcrete concreting and reinforced concrete (particularly if the concrete has a lot of reinforcement) for long-lasting seamless floors and ceilings. Working with the concrete mass is simple and convenient due to its high mobility, density, and viscosity.

Advantages

The primary benefit is installation speed, as the mixture can be compacted without further manipulation after pouring. Consequently, there are no flaws because the solution entirely fills the available space.

The formwork’s shape can be readily recognized due to the smooth and aesthetically pleasing surface that results from hardening, which frequently allows you to save money on cosmetic finishing. The material’s ease of use, durability, and high rate of adhesion to reinforcement all have an impact on the structure’s mechanical strength.

With the right knowledge and expertise, it is possible to construct structures of different geometries because the composition has a high viscosity and holds its shape well (which is impossible when using ordinary concrete, since it is too loose for such purposes). Apart from the aforementioned benefits, the work team can reorganize itself to undertake supplementary duties and reduce labor expenses as the material can be poured rapidly enough without requiring compaction. Additionally, SUB offers better insulation against noise and vibration, which is frequently a pretty important factor, for instance, when building any production facilities inside city limits.

Disadvantages

Notwithstanding the aforementioned benefits, SUB has a number of drawbacks. The most significant is the mixture’s high cost, which results from the need to produce a larger volume of cement, sand, and plasticizers during production than with regular cement in the same volume ratio.

The mobility of the concrete mixture is another drawback, but this can be easily leveled if the work crew is experienced and sufficiently professional.

Properties

When compared to ordinary concrete, self-compacting concrete mixtures have the following mechanical and physical characteristics:

1. Ultimate tensile strength – significantly higher than that of ordinary concrete.
2. Ultimate compressive strength – similar to the previous indicator, but with the condition that when preparing the concrete mixture there was strict adherence to the recipe (this is especially true for the proportional ratio of water).
3. Creep index – as mentioned earlier, this coefficient is somewhat higher due to the use of plasticizers, chemical modulators, sand and Portland cement in the mixture, but this indicator does not exceed the permissible standards.
4. Adhesion – the adhesion indicator with reinforcement also has an increased value due to the high density, creep and hardening rate.
5. Shrinkage – depends on the amount of cement glue. SUB and ordinary cement are approximately equal in this indicator.
6. Elasticity – 15% lower compared to ordinary cement-sand mass. This is due to the reduced content of the fraction of dry fine-component mixtures (sand) and a fairly low content of the fraction of large-component composition (crushed stone).

Important: It is important to note the unique characteristics of concrete structures separately. The mass of the structure also rises as a result of the higher density at the same volume. When constructing a structure, this needs to be considered because the building might sag once the composition hardens. Consequently, it is advised to modify and design surfaces and ceilings that are thinner; fortunately, the material’s strength permits this.

Composition

The following elements (based on 1 m3) make up the self-compacting concrete solution:

• water (170-180 kg);
• portland cement (530 kg);
• sand (650 kg);
• fine crushed stone (950 kg);
• plasticizer (3-4 kg);
• fly ash (filler) (200 kg).

This is a typical concrete composition calculation. To improve adhesion and lower the chance of cracking during shrinkage, different chemical modifiers and fillers can be added to it in addition to these basic ingredients.

Application and features of laying

SUB is utilized in the building of many different things, especially hydraulic structures (piers, port buildings, breakwaters, dams for hydroelectric power plants).

1. In the production of precast reinforced concrete elements and structures.
2. For the construction of monolithic seamless floors.
3. For strengthening and reinforcing buildings and supporting structures.
4. In the construction of objects that require an initially high-quality flat surface that does not require additional processing (for example, a runway).
5. When constructing various structures from concrete with a high content of reinforcing elements.
6. For the construction of fences or thin-walled rooms (for example, when the building requires a minimum weight of load-bearing and supporting floors).

When applying self-compacting concrete, it’s important to keep in mind a few of its characteristics and subtleties. For instance, the concrete mix takes a lot longer to set as a result of the higher superplasticizer content. Self-compacting concrete loses its ability to self-compact after being moved in a concrete mixer for longer than an hour. Long-term transportation also negatively affects plasticizers, which reduces the mobility of the solution. Experts advise against cutting costs and instead producing SCC on the construction site.

The mass may become heterogeneous if concrete is transported to the work site via a pipeline that is longer than 200 meters due to the possibility of delamination. Additionally, this point needs to be considered very carefully. When filling, try to avoid using long supply pipelines. Delamination and a heterogeneous composition can have a detrimental effect on the outcome and greatly diminish the final structure’s mechanical and physical qualities.

Make sure there is no liquid present before adding self-compacting concrete to the formwork. Even a tiny bit of water can cause compositional issues. The adhesion coefficient will be greatly increased if any water is present, and it is preferable for the surface to be mostly dry. All of the components must be supplied continuously when pouring SCC; otherwise, homogeneity could be broken and the final product’s quality could suffer. Since the solution doesn’t require compaction, it should be left undisturbed for a while. Any manipulations could cause the homogeneity to be disrupted and result in uneven surfaces once it has hardened.

Important: Special chemical thinners can be used to restore the quality of the self-compacting mixture if it has thickened and lost some of its properties during storage or transportation. These thinners are fed directly into the concrete mixer and mixed until the mass is homogeneous and the original properties are restored.

When making the working mixture, the following additives can be added to improve the quality attributes of class B15 concrete:

• sand and crushed stone of smaller fractions – when used, the strength increases significantly, but the viscosity also increases (since the surface area of ​​the fine fraction particles in total is significantly larger than the large fraction;
• adding micro- and ultra-dispersed filler to the mixture also significantly increases the strength reduces the risk of corrosion on the reinforcement and the appearance of cracks during shrinkage and subsequent operation.

Diagnostics

Only nations that are members of the European Union use regulatory data, stringent guidelines for manufacturing conditions, and diagnostics of self-compacting concrete mixtures in the building industry. Based on rheology and hydrodynamics, a "rheological" method of analysis is used to evaluate the workability and fluidity of concrete mortar. The following quality indicators are followed when performing analysis and diagnostics:

1. Strength characteristics.
2. Mixture viscosity.
3. Degree of water drainage.
4. Media stratification coefficient.
5. Mobility (determined in centimeters by the size of the standard cone settlement).
6. Workability (estimated by mobility indicators).

An experiment mathematical model is used to analyze the aforementioned features:

• percentage ratio of superplasticizer additive: 0.8, 1, and 1.3 of the total mass;
• percentage ratio of stabilizers: 0.05, 0.1, 0.15, and 0.3 of the total mass.

Samples for the analysis are cubes with a side length of 10 cm. Following solution preparation, each sample’s workability index was ascertained, and it was then put in a room with ideal humidity and temperature levels. The samples are examined for strength on the first, third, and seventh days of the hardening process, as well as after 14 and 30 days. Following receipt of the statistical data, a summary table is created, upon which the stratification coefficient and water drainage analysis are carried out.

Production and transportation

Like any other liquid construction mixture, concrete compacts itself, so specific transportation circumstances are needed. Similar to regular concrete mortar, SCC experiences gradual stratification as the mixture separates into fractions. This causes the quality indicators to drop dramatically, which has an adverse effect on the finished product.

It’s important to follow these guidelines to prevent such outcomes:

1. Transportation of the composition for two to three hours is impossible, the maximum time in motion is one hour. If the mixture is in a static state for more than an hour, stratification into fractions and precipitation begins. Therefore, long-term (and, incidentally, short too) mixing is desirable only in concrete mixers.
2. Weather conditions directly affect the quality of the final result. It goes without saying that atmospheric precipitation should not get into the concrete, this will change the percentage ratio of water. It is also not recommended to leave the mixture in direct sunlight for a long time, as this will increase the temperature of the mixture and negatively affect the consistency.
3. After the concrete mixture has been delivered to the construction site, it is necessary to add a thinner to it to optimize the consistency (it is more difficult to work with a thickened solution, plus self-compacting indicators are reduced).

In the construction industry, self-compacting concrete (SCC) has shown to be a flexible and effective material. Because of its special qualities, it can flow and settle without the need for mechanical vibration, which makes it the perfect material for projects involving intricate formwork or heavily reinforced areas. This feature enhances the final structure’s quality and durability while also accelerating the construction process.

The ability of SCC to cut labor costs and time is one of its key benefits. Employee productivity is increased since there is no longer a need for vibration, freeing them up to concentrate on other important duties. Furthermore, SCC offers a flawless surface and smooth finish, which is especially advantageous for exposed concrete surfaces or decorative applications.

There are, however, a few disadvantages to take into account. Because SCC requires certain additives and a more exact mix design than conventional concrete, the cost of materials may be higher. Additionally, due to its high fluidity, SCC needs to be handled carefully when being transported and placed in order to avoid segregation and guarantee consistent quality throughout the pour.

To get the best results when installing SCC, it is essential to adhere to best practices. This entails careful planning, choosing appropriate mix designs, and making sure the formwork is strong and taut to support the fluid pressure. Building professionals can fully realize the advantages of SCC and create aesthetically beautiful, long-lasting structures by taking care of these factors.

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