Modifying additives for concrete: types, application

Due to its strength and longevity, concrete is a basic building material. However, a variety of modifying additives can be used to meet specific needs and enhance its performance. The qualities of concrete are improved by these additives, increasing its adaptability to various uses.

Modifying additives come in a variety of forms, each intended to accomplish a particular goal. For example, certain additives make concrete easier to mix and pour by improving its workability. Others make it stronger, less prone to shrinkage, or more resilient to adverse weather conditions.

Choosing the best additive for your project can be aided by having a thorough understanding of the various kinds and their uses. There is an additive that can help, whether your goal is to speed up the curing process, increase water resistance, or just make working with the concrete easier.

This article will examine the many kinds of concrete modification additives, their functions, and advantages. By the time it’s all over, you’ll know exactly how to apply these additives to your concrete projects to improve its longevity and performance.

Types of modifiers for improving the technological properties of concrete

Depending on the primary outcome, the most researched and widely utilized additives in our nation (GOST 24211-2003) can be categorized into three groups:

• modifiers that regulate the characteristics of ready-to-use mixtures;
• additives that change and improve the basic properties of concrete;
• chemical ligatures to impart special properties to concrete.

Certain additives, such as those that are plasticizing, gas-forming, air-entraining, etc., have multiple uses. In this instance, the most noticeable action of the modifying additive is taken into consideration when classifying it.

Chemical reagents added to solution compositions are a useful way to directly affect concrete’s architecture as well as its technical and physical properties, resulting in a major economic impact and high-quality indicators of the final product:

• reduce the consumption of binders (up to 12%) with a simultaneous increase in strength up to 25%;
• improved technological qualities of mixtures (homogeneity, mobility, etc.);
• the ability to regulate the rate of hardening and heat release of concrete mortar;
• reduction of heat and moisture treatment time;
• concrete hardening without additional heating at low temperatures (down to -25°C);
• increase frost resistance of products by 2–3 times;
• increase water resistance and strength of products by 1–2 grades;
• increase resistance of structures to various temperature and chemical influences.

This video will teach you how to alter concrete additives so that the building mixture’s composition changes.

Additives that regulate the condition of concrete mixtures

This chapter will address additives that directly contribute to enhancing mixture quality by altering their primary properties while constructing structures in formwork:

• plasticizers;
• superplasticizers;
• stabilizing additives;
• air-entraining additives.

Plasticizers

Plasticization is the term used to describe the liquefaction effect that is introduced into the concrete structure through the use of special modifying ligatures. In order to control the mobility (workability) of cement concretes, plasticizers—surface-active additives—are liquid suspensions or powdered dry mixtures that, when added to a solution, form neutral or slightly alkaline compounds.

Because the compositions used are in a stable mobile state, using these ligatures in the construction of reinforced concrete structures simplifies the product molding process. Furthermore, it lowers the amount of cement needed, lowers the amount of water the solution needs, and simultaneously raises the final concrete’s density.

Among the plasticizers that enable the precise control of cement mixture properties are the following additives:

1. Technical lignosulfonates (abbreviated LST) are a compound of sodium salts and lignosulfonic acids with the addition of various mineral substances.

1. Sulfite-yeast mash (abbreviated SDB), obtained from waste from cellulose production.

1. Synthetic surface active additive (SPA).

The SDB plasticizer is typically used in standard heavy concretes, which greatly improves mixture mobility and allows for an 8–12% reduction in cement consumption and water demand of the solution. Its application is therefore most successful when building structures with a high design cement content.

Some advice: the SDB additive slows down the setting of concrete; therefore, it should only be used in conjunction with additives that speed up solution hardening.

Superplasticizers

Superplasticizers are legitimately the top additive for plasticizing concrete mixtures; they fall into the class of complex regulators of the mixture’s state.

• Superplasticizers, among similar reagents, stand out for their colossal effect of liquefaction of cement mortars without reducing the strength parameters at any test times.
• In their composition, these are synthetic polymer additives that do not slow down the setting of concrete. SP consumption is usually 0.1–1.2% of the total volume of cement.
• When using these plasticizers, it should be taken into account that the effect of SP is limited to 2–3 hours from the moment of their introduction into the concrete solution.

The table (see photo) lists the primary forms of SP.

Superplasticizers have a high effect because they can reduce internal friction in concrete structures by forming adsorption shells on the surfaces of fine-grained fillers and cement grains.

By employing straightforward technological techniques, SP enables the widespread use of concrete mixtures with a low water-cement ratio (W/C) in the construction of any kind of monolithic reinforced concrete structures of strength classes B15 and higher. This results in the following benefits:

• high strength of finished products (60–80 MPa);
• the possibility of using the casting method with short-term vibration of structures, at low W/C, for the production of precast reinforced concrete;
• successfully pour structures of the most complex profile;
• increase the speed of molding products;
• reduce cement consumption;
• improve the surface quality of manufactured products;
• preparation of mixtures on non-standard fillers (fine sand);
• the use of stressing cement or expanding additives in the construction of monolithic structures;
• production of structures from heat-resistant concrete on Portland cement, aluminous cement, slag Portland cement.

Using the example of the most widely used additive, C-3, which has outstanding performance characteristics in the price-quality ratio, we will examine the impact of plasticizers.

The mixture is mixed with plasticizing additive C-3 in the form of an aqueous suspension containing the necessary concentration. The consumer chooses the plasticizer’s composition, taking into consideration the final product’s design features. The type of cement used and the makeup of the aggregates affect how effective the additive is.

By using this plasticizer, you can benefit from the following advantages:

• increased mobility of concrete to P4 – P5;
• improvement of plasticity (location) by 1.5 times;
• Reducing B/C by 25%;
• increases the strength of structures by 25%;
• waterproofing properties W10 or more;
• Frost resistance F300;
• Clutch of mixtures with a reinforcing frame increases 1.6 times.

Stabilizing additives

Compounds that are chemical or mineral-based that stop concrete mixtures are this kind of modifier. Boost its permeability, homogeneity, and capacity to hold water to aid in the better flow of materials through pipelines.

• Concrete, made using stabilizing additives, acquires the properties of self -sealing compositions. Stabilizers reduce the rigidity of the solution, thereby increasing the degree of its placement.
• When a stabilizing additive is introduced into the concrete, a “microgel” is formed on the surface of the cement grains, which ensures the creation of a “load-bearing frame” in the cement paste and prevents the solution from delaminating. Moreover, this design allows the fillers to move easily, which does not change the workability of the concrete.
• This technology allows you to lay mixtures in densely reinforced structures of the most complex configuration without the use of vibrators. During the pouring period, the material self-compacts, squeezing excess water and entrained air onto the surface.

Methyl cellulose that dissolves in water is one of the popular home additives. It is a white, fibrous material that has a faint yellow undertone. This substance reduces shrinkage and delamination, boosts adhesive capacity, and makes it simple to modify the density and rheological properties of solutions.

Because of all of this, the mixture can be transported through pipelines while still meeting all design specifications. Any kind of cement can be used with it; the early strength and curing time are unaffected.

Air-entraining modifying additives

In order to create a system of closed, evenly spaced air pores in the concrete throughout the volume of the structure, air-entraining additives are used to entice a specific amount of air into the cement mixture.

Using air-entraining ligatures enables the following:

• to obtain concrete with high frost resistance FЗОО and more;
• if necessary, to reduce the density of finished products by 50-250 kg/m3;
• to use coarse-grained high-density filler or ordinary quartz sand (instead of porous) for the preparation of lightweight concrete;
• to reduce the consumption of porous materials, reduce the water demand of the solution, improve the thermophysical and deformation properties of products;
• with a low content of fine-grained filler, manufacture products with a monolithic homogeneous structure;
• increase the mobility of the concrete mixture and thereby reduce the time of molding of products, increase the compaction of the mixture, reduce its stratification during delivery and laying in molds;
• improve the sound and heat insulation characteristics of products.

Adding air-entraining additives to a structure is a very efficient way to make it more frost resistant. In order to produce concrete with excellent resistance to frost, the space between neighboring air bubbles must not be larger than 0.025 cm.

Consequently, in order to achieve the desired result, the smallest feasible air cell must be created in addition to the intended air volume.

All of these factors contribute to the implementation of air-entraining compositions, which increase the frost resistance of concrete.

The porous surface of a mixture containing air-entraining additives is typically 1000–2000 cm 2 /cm 3, and the pores themselves are 0.005–0.1 cm in size. In this instance, 4-6% of the cement’s total volume should be the ideal amount of entrained air. Aggregate granularity can be decreased to increase cement consumption.

Concrete can be modified with additives to improve its strength, durability, and suitability for a range of construction applications. These additives are available in various forms, each with a distinct function, including plasticizers, retarders, accelerators, and air-entraining agents. By using them, you can increase resistance to environmental factors, decrease the amount of water content, speed up or slow down the setting time, and improve workability. Concrete structures built with the appropriate additives for a given project can be more durable and effective.

Calculation of concrete composition

Modifiers for changing the main characteristics of concrete

The standard properties of concrete are modified by the following group of modifying compositions:

• hardening regulators (retarders, accelerators);
• shrinkage and expansion regulators;
• antifreeze additives.

Hardening kinetics regulators

Sometimes it’s necessary to lengthen or shorten the time that cement compositions take to harden, depending on the circumstances surrounding the production of concrete products.

The following circumstances may necessitate adjusting the concrete solution’s hardening time:

1. When performing work in hot weather. In the interval between unloading and pouring concrete, early setting of the cement composition may occur, affecting the workability of the mixtures.
2. When constructing large objects, adding retarders in combination with good mobility of solutions can prevent the formation of cold joints during prolonged pouring of concrete.
3. Reducing heat generation and preventing the formation of cracks during the hardening of concrete during the construction of hydraulic structures is achieved by introducing retarding additives.

The relative decrease or increase in concrete strength over a given time period is the criterion used to identify which modifiers fall into the retarder or accelerator category.

The test for hardening accelerator efficacy is a minimum 20% increase in strength in a 24-hour period under typical conditions. Under typical circumstances, retarders are effective when the indicator drops by 30% over the course of seven days.

Retarders

In theory, the plasticization process and all plasticizer additives added in large amounts to the concrete mixture cause the concrete to harden more slowly and lose strength. The reason for this is that plasticizing compositions have the capacity to create adsorption films that enclose cement grains and obstruct normal hydration.

This causes a delay in the kinetics of concrete strength accumulation and a slowdown in the formation of the cement stone’s structure.

Certain materials, both domestically and internationally produced, are well-known for their ability to slow down the hardening process:

1. NTP – Nitrilotrimethylenephosphonic acid. White crystalline powder, easily soluble in water. Has a plasticizing effect and does not contribute to reinforcement corrosion. Consumption 0.02–0.15% of cement volume.

1. Whey is a waste product from dairy production, which is a yellowish liquid whose structure includes protein, fat and milk sugar. It is added directly at the time of concrete preparation in an amount of 1.5-3.0% of the cement mass.

1. Cementol Retarde — a foreign-made retarder-plasticizer (Slovenia). Added to dry concrete mix in the form of a pre-prepared aqueous solution. Recommended consumption — 0.2–0.8% of the total volume of cement.

Apart from the suggested dosages mentioned in the chapter, the ideal additive consumption needs to be ascertained through experimentation based on the product’s design attributes.

Setting accelerators

When hardening accelerators are mixed into the concrete mixture, they initiate the cement hydration process and promote the development of cement stone. Under typical circumstances, the use of setting accelerators results in a 25% increase in the rate of hardening and a 20% or more increase in the strength of the concrete at a young age.

At the moment, cement hydration accelerators come in the following varieties for use in construction:

1. Calcium carbonate (potash) — is a white powder with high alkaline characteristics. Ensures rapid setting of concrete mortar with the formation of a large-porous structure in the finished product. Additive consumption from 1.5–5% of the cement mass. Not recommended for use in combination with siliceous fillers to avoid corrosion of the reinforcement cage.

1. Calcium chloride (CC) — accelerates the setting and strength gain of concrete by 2 times. For example, the introduction of 1% calcium chloride increases the temperature of the solution by 17°C. Not recommended for use in the production of reinforced concrete due to accelerated corrosion of reinforcing parts.

1. Sodium chloride (SCI). Dry white composition, diluted in water. Optimum consumption — up to 4% of the cement mass. With increased consumption, it can be used as an antifreeze additive. Sodium chloride in everyday life is table salt, so, if necessary, you can prepare a mixture with such an additive yourself.

1. AN (Sodium aluminate). Optimum dosage is 3% of the total volume of cement.

When lightweight porous concretes are autoclave treated, the use of accelerators can cut the isothermal heating time in half and the amount of cement used by 10% to 15%.

This video tells how to speed up the hardening of concrete.

Shrinkage and expansion regulators

The three main factors contributing to shrinkage are plastic changes: shrinkage resulting from cement carbonation and hydration, and transformations caused by mixture dehydration.

• Shrinkage from dehydration is associated with rapid drying of concrete, and can last for several months. Humidity changes can be regulated by reducing the water-cement ratio. With a decrease in the amount of free water, the values ​​of shrinkage from drying in the solution decrease.
• Low permeability characteristics also lead to a decrease in the drying rate of concrete. Shrinkage from dehydration can still be controlled by technologically correct methods of caring for the hardening base.
• Chemical shrinkage processes (hydration) are the result of the combination of cement and water during the hydration process and are the most problematic in the technology of precast concrete production.
• This reaction occurs regardless of the humidity indicators of the environment, and is entirely determined by the degree of chemical reaction occurring as a result of cement hydration.
• An effective method for reducing chemical shrinkage is the use of sulfoaluminate expanding additives. The mechanism of action of such additives is based on the chemical reaction of the formation of ettringite, which increases in volume during the formation of the structure.
• In this case, cement hardening is accompanied by two stages: the first stage is chemical shrinkage, and the second is the expansion of the material. Moreover, these processes occur in parallel, reducing the chemical shrinkage of the product.

By varying the quantity and composition of sulfoaluminate expanding compositions, one can actively control the volumetric changes that hardening concrete undergoes.

The multicomponent product Calumex E.A., an organomineral complex modifying additive, is the most effective way to prevent shrinkage. Expanding components in its composition help to prevent shrinkage deformations and produce high-strength concrete even when the foundation is made of extremely mobile mixtures.

Anti-frost additives

There’s a chance that concrete will defrost when it’s cold enough to pour. The moisture in the solution crystallizes and the cement hydration process stops at +5°C and below.

• In addition, water increases in volume during crystallization (freezing), and when expanding, it breaks existing structural bonds, which are no longer restored during thawing.
• Therefore, antifreeze additives include chemical substances that prevent water from freezing in the solution and prolong or shorten the hydration time of the cement.
• As mentioned above, all types of concrete hardening accelerators can act as antifreeze additives, at the required dosage.

In addition to them, there are two other kinds of antifreeze additives that vary based on the chemical components:

1. Antifreeze helps reduce the crystallization temperature of water, and at the same time prolongs the setting time of the solution. However, this type of chemical additive does not affect the formation of the structure.

1. Antifreeze reagents based on sulfates ensure the optimal setting speed of the solution. The effect of these additives is expressed in the abundant release of heat at the moment of combining the component with the hydration products.

Kindly take note! The type of monolithic structure and the air temperature determine which concrete composition and additions are needed. As the temperature drops, the volume of added additives increases proportionately.

The outcomes of tests for corrosion effects, the development of efflorescence on the surface of structures, the necessary setting speed of the solution, and the product’s strength and performance attributes are the criteria for selecting one additive over another.

Calculation of concrete composition

Type of Additive	Application
Plasticizers	Improve workability and reduce water content
Superplasticizers	Enhance fluidity and strength
Accelerators	Speed up the setting and hardening process
Retarders	Delay setting time for better placement
Air-entraining agents	Increase freeze-thaw resistance
Waterproofing agents	Reduce permeability and increase durability
Corrosion inhibitors	Protect reinforcement from corrosion

To improve the qualities of concrete and make it more adaptable and appropriate for a range of uses, modify additives. Whether your goal is to boost durability, increase strength, or improve workability, there’s an additive made to fit your requirements.

Understanding the various additive types—plasticizers, accelerators, and retarders, for example—will help you select the best one to meet the objectives of your project. Every kind has a distinct function and can have a big effect on how well your concrete mix works.

Efficient use of modifying additives can result in superior project outcomes, regardless of the size of the project—small-scale residential or large-scale commercial. The correct additive can improve the workability, durability, and resistance to environmental stresses of your concrete.

It is necessary to give these additives considerable thought and to comprehend the particular needs of your project before incorporating them. By doing this, you can be sure that your concrete will function at its best, producing results that last and living up to the required standards and expectations.

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