Expanding concrete: properties, areas of application, manufacturing nuances

From sidewalks to skyscrapers, concrete is used everywhere and is renowned for its sturdiness. However, not all concrete is made equally. One particular variety, referred to as expanding concrete, stands out due to its special qualities. Because this type of concrete can expand and contract in ways that conventional concrete cannot, it creates new opportunities for building and maintenance.

The purpose of expanding concrete is to expand slightly as it hardens. This capacity to expand comes in especially handy in situations where accuracy and close fits are essential. It’s frequently used, for example, to seal against water and other elements or to fill gaps or joints where a precise fit is required to maintain structural integrity.

In order to create expanding concrete, certain ingredients are added to the mixture, which causes the concrete to swell as it cures. To guarantee that the concrete expands at the proper rate and doesn’t lose strength, this process needs to be carefully controlled. In order to get the desired effects, proper formulation and mixing are essential.

Choosing the appropriate materials for your needs can be facilitated by knowing how expanding concrete works, whether you’re working on a small repair job or a large construction project. Its special qualities allow you to approach a variety of tasks more accurately and effectively.

Volumetric deformations of structures

Colloidal and crystalline formations are created during the hydration of cement during the production of reinforced concrete. These formations can have varying effects on the deformation processes taking place in the cement stone.

The compaction of colloidal formations during the mixtures’ hardening phase leads to the emergence of shrinkage cavities. Additionally, under specific temperature circumstances during the cement stone’s hydration process, the crystals formed may expand in volume, causing the concrete to expand thermally and resulting in the development of cracks on the surface of buildings.

Shrinkage deformations

Two categories of shrinkage are distinguished based on the mechanisms involved.

1. shrinkage stress (expansion)
2. shrinkage deformation.

The humidity and temperature of the surrounding air affect how strong these deformations are.

Changes brought about by shrinkage deformation, when coupled with the concrete’s linear expansion, greatly lessen the structures’ resistance to cracking and their longevity. Shrinkage is mostly caused by a process that reduces the mixture’s linear dimensions over time as a result of physicochemical reactions taking place in the product’s structure at that particular moment.

There are various stages to shrinkage processes:

• plastic deformation occurring at the moment of setting of the mixture;
• shrinkage caused by subsequent hardening of mixtures (up to 28 days);
• deformations occurring at a mature age (more than 28 days).

The shrinkage coefficient, which is typically less than 1.5%, is a conditional percentage ratio of the change in the material’s initial volume compared to its final value.

Linear temperature deformation

A volumetric change in a material’s structure brought on by changes in internal or external temperature is known as linear expansion.

• Coefficient of linear expansion of reinforced concrete (α). This is a relative increase in the linear dimensions of structures with an increase in temperature by 1 K under standard conditions.
• Coefficient of thermal expansion of concrete. Its value depends on the temperature and relative humidity of the environment. This parameter is inextricably linked with the thermal conductivity of the material.

Note: The product’s capacity to retain or transfer heat through its structure is indicated by the latter value. This parameter rises with increasing density.

• Coefficient of linear expansion of concrete. Equal to 0.00001 (°C) -1 – that is, when the temperature rises to +50°C, the linear expansion will have a value of 0.5 mm/m.
• Coefficient of expansion of concrete. Also depends on the brand of cement and the composition of the fillers.

The coefficient of thermal expansion of cement stone varies from that of filler. As a result, these components react differently to changes in temperature, which causes volumetric stresses in the product’s structure and aids in the development of cracks in the material’s exterior and interior.

A wide range of precautions are offered in modern construction to prevent shrinkage, thermal expansion, and cracking:

• expansion joints in concrete (deformation or temperature);
• increasing the frequency of reinforcement of structures;
• dividing monolithic surfaces into separate autonomous blocks, etc.

All of these techniques, meanwhile, come with a hefty construction cost tag and don’t always yield the desired improvements in operational characteristics. Expanding and stressing binders are the best solution to get rid of the aforementioned issues.

Expanding and stressing concretes

Stressing concretes are blends made from stressing cements that have the capacity to expand during the first hardening stage and stretch the reinforcement that is in direct contact with it. As a result of these processes, the reinforcement experiences self-stressing, or compression.

• Moreover, reinforcing bars are stretched regardless of their direction and arrangement in the structure of the product, which helps to obtain biaxial volumetric self-stress of structures.
• The mechanism of action of expanding materials is based on the creation of controlled directional crystal formation during the hardening of cement stone, which helps regulate the process of volumetric deformations in the plastic structure of the product.
• The use of expanding rapid-hardening concrete, due to controlled linear expansion, allows to significantly compensate for the effects of shrinkage deformations, increase crack resistance and service life of buildings and structures.

Properties

• with a standardized value of compression;
• with compensated shrinkage, but with non-standardized self-stress (compression).

Apart from these classifications, expanding fine-grained mixtures for restoration and repair can be identified as a distinct group.

Pretensioned concrete’s primary attributes (GOST 32803-2014) are as follows:

1. For heavy ones, the following classes are provided for compression: B20-B90; for tension – B_t0.8—B_t4.0.
2. For light: for compression — B10—B40; tensile strength — classes B_t0.8—3.2.
3. Taking into account the magnitude of stress, concrete is classified into the following grades: Sp0.6—4.0.

Some guidelines: expanding mixtures with standardized compression are classified as classes Sp 1.2–4.0, and self-stress grades Sp 0.6–1.0 are classified as concrete with compensated shrinkage.

1. By frost resistance F200—F
2. By water resistance: heavy — W12—W20, light — W8—W
3. This material has high strength (40–70 MPa). Moreover, the growth of this value is especially intensive at an early age (28 days). After three months, the tensile-compressive strength increases by 30%, and by 40% upon reaching 6 months.
4. No reinforcement corrosion.
5. High sulfate resistance.
6. Gas permeability is 40 times lower compared to heavy concretes on Portland cement.

Application

The following characteristics of this material enable its efficient application in precast and monolithic reinforced concrete structures:

• in the construction of load-bearing elements and roadways of bridges, which increased the load-bearing capacity by 12-16%;
• for the construction of energy facilities of thermal power plants, hydroelectric power plants, nuclear power plants, etc.;
• in the prefabricated construction of subway tunnels;
• in the construction of stress-bearing structures for sports purposes (indoor sports arenas, etc.);
• in the production of high-pressure reinforced concrete pipes;
• for equipping roof coverings and installing durable industrial floors;
• widely used in the installation of reliable waterproofing coatings applied by shotcreting.

Materials

Using both large and small natural aggregates, shrinkage-free cement and stress-bearing cement are the foundations for the production of expanding concrete.

Binders

Expanding cements are blends made of Portland or aluminous cement plus specific additives that provide the structure of the cement stone more volume during the first hardening stage.

As additives typically behave:

• gypsum;
• clay -earth slag;
• Calcium hydroalumines.

Hydraulic aboaling compounds of calcium are formed during the hydration and cement stone processes. It is during these formations that the effect of the structure’s expansion arises, compensating for shrinkage phenomena.

The most popular varieties of cements are as follows:

1. Waterproof expanding cements (WRCs) obtained by mixing clay -earth cements (70%), calcium hydroaculumate (10%) and fine milk gypsum (20%).

1. Waterproof unsuccessful cements (VBC), consisting of the same components as (VRC), but taken in other proportions and in other volumetric relationships. These cements are able to form a cement stone of high water resistance, withstanding water pressure up to 0.70 MPa.

1. Expanding cement (EPC) obtained by fine grinding and mixing of Portland cement (60%), high-alumina blast furnace slag (5–7%), gypsum (7–10%) and mineral additives (20–25%).

1. Gypsum-alumina expanding cements (GAEC), consisting of a mixture of finely ground alumina blast furnace slag (70%) and ground gypsum (30%).

1. Pressure cements (PC) are produced on the basis of Portland cement (60–70%), alumina cement (18–20%) and gypsum dihydrate, jointly ground to a specific surface area of ​​at least 3500 cm2 /g (see. photo).

Fillers

Concrete’s large and small aggregate content, which can account for up to 80% of the mixture’s volume, greatly affects the product’s chemical and physical characteristics. An ideal combination of these elements can drastically cut down on the amount of cement used, which has a big impact on the product’s cost.

Furthermore, fillers and binders together can enhance the technical properties of structures:

• increase strength and restrain deformations;
• reduce creep;
• take on the effect of linear stresses and partially compensate for shrinkage.

Large aggregates such as gravel and crushed stone with fractions ranging from 5 to 70 mm are used in the preparation of expanding solutions. This material must meet the same standards as conventional heavy concretes (GOST 10268-80).

The strength values of the rocks that are used to make the aggregates determine their overall strength. The GOST specifies that coarse-grained aggregates have an average density of 2000–3000 kg/m3.

Suggested grade for large aggregates

The most common type of quartz sand used as a fine aggregate is small fractions (GOST 8736-93) with a density of 2000–2800 kg/m3. The higher the fraction, the denser the concrete.

Properties	Expanding concrete expands slightly as it sets, filling gaps and cracks for a tighter fit.
Areas of Application	Used in foundation repairs, sealing joints, and in structures where tight fits are crucial.
Manufacturing Nuances	Requires precise mixing and curing to ensure proper expansion and strength.

The construction industry has found many uses for expanding concrete, which is a creative and adaptable material. Because of its special capacity to swell after setting, it’s a great material for stabilizing buildings, filling gaps, and fixing broken concrete. This feature not only increases a building’s structural integrity but also increases its lifespan.

Expanding concrete’s strength and durability make it ideal for large-scale infrastructure developments as well as smaller-scale projects. This kind of concrete performs consistently under a range of circumstances, making it suitable for use in both large-scale commercial and residential construction projects. Its resilience to environmental elements like moisture and temperature fluctuations also guarantees that it will continue to work over time.

Care must be taken when manufacturing expanding concrete to ensure that the mix proportions and material quality are appropriate. Achieving the desired expansion properties during mixing and curing requires careful attention to detail. Although the procedure might appear difficult, improvements in materials and technology have made it easier for contractors and builders to complete.

Incorporating expanding concrete into construction practices can significantly improve the efficiency and durability of projects. By understanding its properties and applications, builders can make informed decisions that enhance the safety and longevity of their structures. As the construction industry continues to evolve, expanding concrete stands out as a valuable innovation that meets the demands of modern building challenges.

Expanding concrete is a special kind of concrete that can alter its volume in specific situations. It has many benefits for a range of building applications. This article explains its basic characteristics, such as its ability to expand and contract, and demonstrates its many uses, which range from repairing infrastructure flaws to precisely forming architectural forms. We’ll also delve into the nuances of its production process, illuminating what makes this material unique and how it’s crafted to satisfy particular requirements in the construction sector.

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