Concrete is one of the most common building materials that cannot yet fully replace high-tech synthetic analogues. Nevertheless, the widespread practice of improving its individual performance due to special additives has been around for more than a year. Modern additives for concrete are aimed at improving various physical and chemical properties that extend the life of the material and make it more aesthetically attractive.
General Information on Concrete Additives
Concrete is a completed building structure, for the creation of which a special mortar is used. The usual composition for concrete includes sand, gravel and water in different fractions and ratios. The main component, regardless of the purpose of the mixture, will be cement of one or another brand. These ingredients will be enough to obtain concrete for various types of work - from the installation of a capital foundation to the repair of small cracks on the wall. What are concrete additives? These are construction additives, which are also added to the primary composition of the solution, further changing its quality. Obviously, before using them, the task is to improve certain properties of the final structure. Among the most popular effects, one can note an increase in resistance to water (waterproofing), acceleration of hardening, strengthening of the structure, improvement of protective properties before high and low temperatures, etc. The additive itself can be delivered both in liquid and in powder form. But the main thing is its direct physical and chemical properties, which ultimately affect the characteristics of the hardening concrete.
Types of Mineral Supplements
The basic classification of one of the most popular groups of additives for concrete solutions. Mineral additives can be divided into two categories: active and inert. The former are distinguished by the ability to interact in the same medium with water and calcium at normal temperatures. As a result, compounds are formed that provide higher astringent properties. After entering the solution, they begin an active process of interaction with calcium hydroxide, which is removed from Portland cement during hydration. What concrete additives in this category are most in demand? Due to the availability and the sought-after effect of self-hardening, ground blast furnace slag has become popular . It is enough to include lime in the improved mixture, as the target mass will begin the process of solidification and compaction of the structure.
As for inert mineral additives, the most common representatives of this group are quartz sand (in the form of grinding). However, for the beginning of its active phase, a special temperature must be provided that starts the reactivity. Such means of improving cement mortars are also involved in autoclaving. The final effect of the use of inert additives is the regulation of the grain composition and voids in hard concrete. When creating the solution, an inert additive is usually applied after the cement.
Modifying Additives
They are used to correct the mechanical structure of concrete structures, which helps prevent delamination and cracking, as well as improve the moisture-repellent qualities of the material. Modifiers are available either in liquid form or in the form of a granular mixture, which must be diluted with water. During stirring, a neutral solution or low alkaline emulsion is formed. The modifier is one of the most popular additives for concrete, which can be explained by the demand for the effect of improving the mechanical properties of the structure, and the universality of the additive in terms of compatibility with different brands of cement. But this is not all the advantages of modifiers. In some formulations, they also allow to reduce the consumption of materials, to strengthen the adhesive quality and fluidity of the solution.
Plasticizers
They are part of the general class of additives that regulate the mechanical properties of concrete and, in particular, its strength characteristics. Actually, the strength of cement introduced into the solution increases after it hardens. Plasticizers can make concrete more elastic - that is, with dynamic and static loads, the likelihood of cracks and chips will be minimized. In regions with seismic activity, this additive is very relevant. Within the group, additives for concrete for strength are divided into plasticizing and superplasticizing. The difference lies in the strength of the effect. For example, superplasticizers can increase the strength of the solution up to 10-20%. What is more important: unlike ordinary plasticizers, they reduce the need for dilution of cement with water. As a result, cement is saved, and the strength properties of concrete remain at the same regulatory level.
Water reducing additives
If plasticizers reduce the need for water only in the form of their indirect function, then for water-reducing additives this is the main effect. The coefficient of reduction in water demand during the preparation of the solution exceeds 20%. Ultimately, the finished design gains higher strength characteristics, corrosion protection and frost resistance. In addition, a water-repellent additive for concrete minimizes the negative processes of delamination, creep and shrinkage of structures. If the goal is to purposefully increase water separation, then stabilizing additives can be used. They increase the water holding capacity and uniformity of cement mixtures by about 2 times, improving such operational qualities of concrete as pumpability, workability and hardening.
Air-entraining and gas-forming additives
If in the case of water, positive effects are achieved by minimizing its inclusion in the solution during its preparation, then air, gas and foam components can also perform a positive reactive function. By the way, hydrophobic additives are also present in the same group. In the concrete structure, they change the indicators of water absorption and water resistance, reducing density and thermal conductivity. This is important when it comes to light and cellular concrete, when microclimatic rather than mechanical characteristics of structures come to the fore. The involvement of air mixtures can have a beneficial effect for heat-insulating and structural-heat-insulating solutions.
Frost resistant additives
This group can also be called temperature resistance regulators - another thing is that the main emphasis in creating formulations is done specifically on protecting concrete materials from frost. The action of additives against cold begins even in the process of solidification, when the structure is least protected from the negative effects of the environment. At the same stage, it is possible to use concrete additives for waterproofing, since the preservation of dispersed frozen water droplets at the base of the structure will further increase the chances of failure under dynamic loads. Sometimes it is practiced and the supply of heat by external means to the flooded area during the solidification period. For example, diesel heat guns are used for this purpose, and additives are needed to increase the cycles of safe freezing / defrosting during the operation of the structure.
Hardening regulators
Both additives with acceleration effect and hardening inhibitors are used. A change in the polymerization period of the structure of future concrete should take place without reducing the design physicochemical properties, which is largely provided by preliminary heat and moisture treatment of the solution. Along with this, the electrical thermal conductivity of the material can increase. If an additive for concrete for quick hardening usually entails an increase or at least a retention of the standard parameters of rigidity and strength, then a slowdown in the polymerization rate, on the contrary, reduces these indicators by about 5-10%. Negative effects are justified by an increase in the mobility of concrete and a decrease in the rate of heat release.
Additive Technology
It is advisable to work with most supplements in special clothing supplemented with personal protective equipment for hands, respiratory organs and eyesight. However, the modified concrete alone does not change the toxicological and hygienic properties, that is, the degree of its harm to humans remains at the same level as in the standard form. The dosage depends on the environmental conditions, the type of additive, its characteristics and the requirements for the result. As a rule, manufacturers of additives for concrete recommend approximately 1% of the proportion of cement used. That is, to create 1 m³ of concrete you will need about 1.5 liters of admixture. The prepared mixture should be thoroughly mixed with a construction mixer and used after it has been infused for 5-10 minutes.
Are there any negative aspects to using additives?
Thanks to special additives, modifiers and plasticizers, it is possible to obtain a building material, unique in characteristics, suitable specifically for specific tasks. However, there are downsides to the use of such tools. Their main drawback is a chain chemical reaction, during which other qualities of the material also change. For example, waterproofing additives for concrete, which increase its moisture resistance, can worsen the properties of electrical conductivity, and in some cases strength. Another disadvantage is the need to use vibration equipment - depending on the task being solved, the purpose of connecting such equipment may be to dehydrate the solution, distribute it evenly over the site or seal.
Conclusion
The introduction of additives will give the expected effect only if a comprehensive assessment of the characteristics that need to be endowed with the design. For example, a waterproofing additive for concrete is optimal if you need to lay the mortar on a foundation basis. Such a coating will not require the installation of an additional waterproofing device, since the structure itself will resist condensation and groundwater. And this is just one example of the justified use of the additive, but when it comes to complex modification of solutions, it may require a professional analysis of the operational properties of the future design with the definition of a whole strategy for improving the stock mixture.