Here at "All about Concrete," we’ll go into great detail about this adaptable building material, covering everything you need to know. This article examines concrete modifiers, including their definition, types, attributes, and qualities.
Admixtures, or concrete modifiers, are materials mixed into concrete to change some of its characteristics. These changes may improve the material’s workability, strength, and durability or add unique properties like quick setting or water resistance. These additives are essential to contemporary concrete technology because they enable engineers and builders to meet particular performance requirements.
Based on their functions, concrete modifiers can be divided into multiple categories. For example, plasticizers increase workability without compromising performance by lowering the water content. Superplasticizers are employed when a greater level of fluidity is needed, and they offer comparable advantages. Tiny air bubbles are added to the mixture by air-entraining agents, which improves freeze-thaw resistance—a critical quality in colder climates.
Accelerators and retarders fall into another category. Accelerators speed up the curing process, which makes them perfect in cold climates where quick setting is required. However, retarders postpone setting, which is helpful in hot climates to avoid premature hardening and cracking.
Concrete modifiers contribute to increased durability as well. Corrosion inhibitors prolong the life of concrete structures exposed to harsh environments by preventing reinforcing steel from rusting. Water reducers, on the other hand, reduce the amount of water present while increasing density and decreasing porosity to improve strength and durability.
Concrete modifiers’ properties are determined by their composition and intended use. Certain modifiers, for instance, can change the hydration process and impact both the initial setting time and the long-term development of strength because they are chemically reactive. Others have no effect and mostly change physical characteristics like viscosity or air content.
In conclusion, concrete modifiers are necessary additions that modify the characteristics of concrete to satisfy particular building requirements. These modifiers enable engineers and builders to design strong, resilient, efficient, and sustainable structures by improving workability, durability, or setting time.
- Types of modifiers
- Additives to change the characteristics of ready-mixes
- Group of plasticizers
- Superplasticizer
- Stabilizing additives
- Air-entraining additives
- Modifiers that change the properties of concrete
- How hardening kinetics is regulated
- Hardening accelerators
- Retarders
- Expansion and shrinkage regulators
- We do not let concrete freeze
- Modifiers of the properties of finished concrete
- Water repellents
- Biocidal additives
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Types of modifiers
Concrete modifiers are substances that come from the chemical industry and can be either inorganic or organic in nature. They are added to mixtures to change their chemical and physical characteristics and to give concrete high performance qualities.
- There are more than 800 varieties of concrete additives in total, and they all have different purposes and combinations of properties. Due to such diversity, choosing the optimal composition for the mixture becomes a very difficult task, accessible, sometimes, only to specialists. However, we will not go into the topic so deeply, and will analyze the most common options that can be useful in home construction.
- To correctly navigate the modifiers, you need to learn to understand their classification, purpose and principle of action. Let"s talk about everything in order.
According to GOST 24211-2003, concrete modifiers, which are most frequently utilized in construction in our nation, can be categorized into three primary groups:
- Additives that regulate the main characteristics of mixtures ready for use;
- Modifiers that change the basic properties of concrete;
- Ligatures that give concrete special properties.
The compositions that give concrete mixtures multiple properties simultaneously are worth mentioning separately. They may be enhancing plasticity and promoting air and gas formation at the same time. Examine the primary effect, which is always expressed more strongly than the others, to categorize such additives.
A significant benefit linked to the application of modifying additives is a favorable economic impact and a superior quality outcome compared to standard counterparts.
- There is an increase in the technological quality of mixtures – mobility, homogeneity improves;
- An increase in strength is achieved with a decrease in the consumption of the astringent;
- An increase in concrete hardening rate, which can significantly reduce the time of construction work;
- You can also reduce the time for heat treatment of hardening concrete;
- It is possible to achieve normal hardening of concrete at negative temperatures, down to -25 degrees Celsius;
- You can increase the strength and moisture resistance of concrete by 1-2 grades;
- The frost resistance of products increases significantly when using appropriate compositions;
- Concrete can also be made resistant to chemical and temperature influences.
Now, let’s examine each kind of concrete additive in more detail.
Additives to change the characteristics of ready-mixes
To be more precise, all additives that modify the liquid mixture’s state fall under this category. These consist of air-entraining, stabilizing, plasticizer, and superplasticizer additives.
Let me go into more detail about each of them.
Group of plasticizers
- Plasticization of a concrete mixture refers to the liquefaction effect achieved by introducing appropriate alloys into its composition.
- This class of substances belongs to surface-active (surfactants). They can be presented in the form of a suspension or powder.
- When they are introduced into a concrete solution, weakly alkaline or neutral compounds are formed, which regulate the workability of the mixture.
- Often such additives are used when molding concrete products, since the mixture retains its mobile state for a long time.
- The density of concrete also increases and cement consumption decreases.
The following categories of additives let you control the mixture’s state in a directed way:
- Technical lignosulfonates (LST). They contain sodium salts, lignosulfonic acids and various minerals.
- SDB or sulfite-yeast brews. They are obtained from pulp production waste.
- SPD – synthetic surface active additive. This is what is used in standard heavy concrete. It is able to reduce the consumption of binder and water by up to 12%. For this reason, it is used for buildings in which the design cement content is very high.
That’s interesting to know! Since SPD has the opposite effect of additives that accelerate hardening, it is always used in tandem with them.
Superplasticizer
Superplasticizers, also referred to as complex additives because of their wider range of effects, also improve the mobility of the concrete mix.
- Superplasticizers are able to liquefy concrete mixtures much more than the previous options. At the same time, there is no loss of concrete strength at any test periods.
- They also belong to synthetic substances, but unlike SPD, they do not slow down its setting speed.
- The consumption of these additives is only 0.1-1.2% of the total volume of the concrete mix.
- Superplasticizers have a limited period of action on liquid concrete – usually this time is only 2-3 hours after their introduction into the solution.
Superplasticizers are categorized differently, as the diagram below illustrates.
They all possess distinct qualities. We won’t go into details right now because you can easily find information on the Internet by yourself if you’d like.
- Superplasticizers are able to reduce the internal friction of particles in the structure of concrete, which is achieved due to the effect of formation on cement grains, as well as fine-grained fillers, read – sand, adsorption shells.
- The main advantage of SP is the ability to use concrete mixtures with a low water-cement ratio in the construction of various structures from reinforced concrete, the class of which exceeds B15. The simplest technological methods are used in this case.
- Superplasticizers are able to increase the strength of finished concrete to 60-80 MPa.
- They allow you to reduce the time of vibration compaction of mixtures with low water-cement ratio to a minimum.
- Increases the speed of forming concrete products.
- They make it much easier to fill in complex shapes.
- The surface of concrete products with the SP additive is more even and smooth – with good compaction, you can even achieve the effect of a polished surface.
- At the same time, cement consumption is reduced and concrete can be prepared using non-standard aggregates.
- Possibility of using prestressing cements, as well as expanding additives for monolithic structures.
Composition C3 is one of the most widely used superplasticizing additives. When weighed against the price-quality ratio, it has excellent qualities.
Let’s use concrete as an example to examine what occurs to it:
- The plasticity of the mixture increases by 1.5 times;
- Mobility increases up to P4, P5;
- The water-cement ratio drops to 25%;
- Concrete is endowed with waterproofing properties up to W10 and above;
- The strength of concrete also increases by 25%;
- The mixture acquires frost resistance class F300;
- Adhesion of concrete to reinforcement frame increases up to 1.6 times.
Yes, the bonuses are really enormous. The surface quality of the concrete improves significantly, and the extra expenses appear insignificant in comparison.
Stabilizing additives
These modifiers, which stop the final mixture from separating, include chemicals and mineral compounds. Its consistency and moisture-retention capacity are also improved. All of this facilitates the solution’s easier passage through pipelines when it is delivered via concrete pumps.
- If stabilizing additives are added to concrete, it will automatically become a self-compacting mixture.
- They reduce the hardness of the mortar, so workability increases. Concrete acquires the interesting property of independently squeezing air out of its mass.
- When the composition interacts with cement grains, a certain microgel is formed on them, preventing the components from delaminating. In this case, the mixture can be stirred easily.
- The first thing these additives are used for is when it is necessary to pour concrete into densely reinforced structures, where the use of a vibrator is ineffective, and often impossible at all.
- The most famous of these additives produced in our country is water-soluble methylcellulose.
- Such an additive can be used together with any type of cement.
- It does not affect the curing time.
Air-entraining additives
When concrete is mixed and allowed to harden, the air in the mixture creates a uniformly distributed pore system within the concrete. This class of modifiers is used to achieve this. To obtain concrete with high frost resistance (F300 and above), this is required.
- It also allows you to reduce the density of concrete to 250 kg / m3, thereby reducing its weight.
- Reduces the water requirement of the solution, consumption of porous materials.
- Increases the deformation characteristics of products and thermal efficiency.
- Allows you to make products with a homogeneous structure.
- Increases the mobility of the finished solution.
- Increases the soundproofing properties of the material.
In the construction industry, knowing concrete modifiers is essential to improving the longevity and functionality of concrete structures. These modifiers—which can be anything from admixtures to additives—are essential for enhancing qualities like workability, resilience to abrasion, and strength. This article intends to shed light on how concrete can be customized to meet particular requirements and environmental conditions by examining its types, properties, and characteristics. Building professionals can produce more durable and effective concrete solutions for a range of applications by using the appropriate modifiers, whether they are accelerating the curing process, decreasing permeability, or increasing flexibility.
Modifiers that change the properties of concrete
Let’s proceed to the following category of additives. These days, compounds that can alter the properties of concrete are of interest to us.
Moreover, this group can be split up into a number of subtypes:
- Hardening retarders and accelerators;
- Additives that regulate expansion and shrinkage;
- Anti-freeze additives.
How hardening kinetics is regulated
Conditions on building sites frequently call for varying the rate at which poured concrete hardens.
- If large objects are being built from monolithic reinforced concrete, slowing down the hardening (provided that the mixture is well-mobile) will help get rid of the formation of "cold" joints.
- If the work is carried out in the hot summer, then from the moment of production until the delivery of the solution to the site, it can begin to set, which greatly affects its workability.
- Also, slowing down the hardening will help to get rid of the formation of cracks when a hydraulic structure is being built.
Concrete’s strength increase or decrease over a specific time period is the criterion used to identify hardening accelerators and retarders.
Hardening accelerators
Cement hydration is accelerated when hardening accelerators are added to concrete. There is a 25% increase in the hardening rate. These additions also positively impact concrete stone formation, resulting in a 20% increase in strength.
The following accelerators are available:
- Potash or calcium carbonate is a white powder with high alkaline properties. Forms a large-porous structure in concrete and accelerates its setting. The consumption of this modifier can be up to 5% of the total mass of concrete.
Counseling! It is not advised to use potash with siliceous fillers as this will cause significant corrosion of the reinforcement frame.
- Calcium chloride – has an incredible indicator of increasing the speed of setting and strength gain – 2 times. Introducing this additive into the solution will increase its temperature by 17 degrees.
Counseling! Since it accelerates the metal’s corrosion, this modifier is not used in the production of reinforced concrete.
- A substance in the form of granules of different sizes and shapes, white in color, water-soluble – how we veiled ordinary salt. Added to concrete in an amount of 4% of the total mass.
Advice: You can experience an anti-freeze effect by increasing consumption.
- Salt significantly accelerates the hardening processes of concrete. It was actively used during the times of mass Stalinist construction, but as time has shown, concrete loses a lot in service life because of it. Everything that was built using this substance has long since been successfully destroyed.
- Sodium aluminate is added to the solution in an amount of 3% of its mass.
That’s interesting to know! When using accelerators in foam concrete products that autoclave to harden, you can cut the amount of binder used by 15% and the amount of time needed for heat treatment in half.
Retarders
In general, all plasticizing additives slow down the concrete’s hardening process if their dosage is exceeded. Recall that these materials create a sort of film around the cement grains, impeding the hydration processes. On the other hand, specific materials are also employed to delay hardening.
Among them are:
- Abbreviated NTP – white crystals that can dissolve in water. Does not cause corrosion of reinforcement, added to the solution in an amount of 0.02 to 0.15%.
- Regular whey, which is a waste product of dairy production. Contains a set of fats, proteins and lactose. Added to the solution during mixing in an amount of 1.5-3%.
- Cementol is a hardening retarder produced in Slovenia. Added to the dry concrete mix in the form of an aqueous solution. Consumption is 0.2-0.8% of the total mass of the mixture.
Expansion and shrinkage regulators
Additives that let you adjust the volume of the concrete mix come next.
The situation when shrinkage cracks appear in concrete is well known to all. This occurs for a number of reasons, including the carbonation of cement, shrinkage during hydration, and changes in concrete brought on by dehydration.
- The first point is due to the fact that moisture leaves the concrete too quickly, and it does not have time to gain optimal strength. This happens when freshly poured concrete is not properly cared for. This phenomenon can be regulated by the water-cement ratio (by reducing it). The principle is simple – the less water initially, the less shrinkage during drying.
- Hydration shrinkage is a chemical process. It occurs as a result of the interaction of cement with water, so eliminating this problem is the most difficult of all.
- This reaction is not affected by the humidity indicators of the environment. Expanding additives are used to reduce this effect. In fact, the lost volume is replenished due to the formation of ettringite.
- Both processes occur in concrete simultaneously, so its current volume does not change.
We do not let concrete freeze
You can work with antifreeze at below-freezing temperatures by using antifreeze additives. Nothing good will happen if you try to pour the solution at a temperature lower than +5 degrees without the right additives. At that temperature, the hydration process does not take place, and the expanding water’s freezing break the bonds inside the concrete, quickly destroying it.
- The simplest conclusion suggests itself from this – antifreeze modifiers prevent water from freezing and accelerate hydration processes in concrete.
- It is not difficult to guess that any hardening accelerators that we wrote about above can be used as such, but there are also specialized compounds.
- Antifreeze reduces the temperature threshold at which water begins to crystallize. At the same time, the setting time of the solution increases. Such an additive does not affect the structure of concrete in any way.
- Sulfate antifreeze modifiers – allow you to achieve the optimal setting speed of concrete. When they are introduced into the mixture, there is an effect of releasing a large amount of heat, which prevents the mixture from freezing.
Modifiers of the properties of finished concrete
Additives that can give hardened concrete specific qualities round out our list. This specifically refers to resistance to biocide and hydrophobization.
Water repellents
Concrete capillaries with these kinds of additives have water-repellent qualities. These additives are made from two classes of materials: water-insoluble silanes, silicones, and siloxanes, and organosilicon compounds in the form of a dry material or aqueous solution.
These kinds of additives are widely available on the market. Products made both domestically and abroad are available.
For illustration, consider the water-repellent GZh 136-41. Concrete will acquire the following qualities when it is added to the solution:
- Fivefold increase in frost resistance;
- Twofold increase in corrosion resistance;
- No efflorescence;
- High water resistance;
- Less binder consumption;
- Accelerated hardening.
Biocidal additives
Nobody is unaware of the significance of these modifiers. Contrary to popular belief, microorganisms can cause damage to concrete.
- Bacteria and fungi living on concrete constantly release organic acids, which lead to carbonization of the material and its accelerated destruction.
- Microorganisms can also affect the metal reinforcement in the thickness of concrete.
- That is why biocidal additives are introduced into its composition when preparing concrete.
You can read the text of the aforementioned GOST to find out more about the selection process for this kind of additive.
Type | Properties and Characteristics |
Plasticizers | Improve workability and flow of concrete, reduce water content |
Superplasticizers | Provide high fluidity and strength, reduce water by 20-30% |
Air-Entraining Agents | Create tiny air bubbles, enhance frost resistance and durability |
Waterproofing Agents | Reduce permeability, enhance resistance to water and moisture |
Accelerators | Speed up setting time, useful in cold weather conditions |
Retarders | Slow down setting time, useful in hot weather conditions |
Corrosion Inhibitors | Protect steel reinforcement from corrosion, increase longevity |
Gaining an understanding of concrete modifiers is essential to improving the longevity and functionality of concrete structures. Modifiers adjust certain characteristics such as strength, workability, and setting time to meet a range of construction requirements. By lowering the cement content and enhancing concrete’s durability and resistance to chemicals, cementitious additives like fly ash and silica fume promote sustainability.
Chemical modifiers that increase workability without sacrificing strength, such as plasticizers and superplasticizers, facilitate simpler application and lower the water content of mixtures. This produces denser, more durable concrete and enhances the pouring and finishing procedures. In the meantime, tiny air bubbles produced by air-entraining agents boost freeze-thaw resistance, which is important for buildings exposed to different climates.
For specialized applications, fiber modifiers such as steel, glass, or synthetic fibers add tensile strength and impact resistance, crucial in reinforced concrete structures. These fibers mitigate cracking and improve structural integrity, making them ideal for bridge decks, pavements, and industrial floors subjected to heavy loads and stress.
In the end, selecting the appropriate concrete modifier necessitates knowing the particular environmental conditions and project requirements. Modifiers are essential to contemporary concrete construction, whether they are used to increase durability, improve workability, or achieve particular aesthetic goals. Engineers and contractors can maximize concrete project performance, longevity, and sustainability by skillfully utilizing these technologies.