Concrete is one of the most common building materials that cannot yet fully replace high-tech synthetic counterparts. And yet, a wide practice of improving its individual performance due to special additives has existed for more than a year. Modern additives for concrete are aimed at enhancing various physical and chemical properties that prolong the life of the material and make it more aesthetically pleasing.
General information about additives in concrete
Concrete is a complete building structure, which is created using a special mortar. The usual composition for concrete includes sand, crushed stone and water in different fractions and ratios. The main component, regardless of the purpose of the mixture, will be cement of one brand or another. These ingredients will be enough to produce concrete for different typesworks - from the construction of a capital foundation to the sealing of small cracks on the wall. What are concrete additives? These are building additives, which are also introduced into 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 water resistance (waterproofing), acceleration of hardening, strengthening of the structure, improvement of protective properties against high and low temperatures, etc. The additive itself can be supplied both in liquid and powder form. But the main thing lies in its direct physical and chemical properties, which ultimately affect the characteristics of the hardening concrete.
Types of mineral additives
Basic classification of one of the most popular groups of additives for concrete mortars. 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 binding properties. After being introduced into the solution, they begin an active process of interaction with calcium hydroxide, which is removed from Portland cement during hydration. Which additives for concrete from this category are in the greatest demand? Due to the availability and demanded effect of self-hardening, ground blast-furnace slag has become popular. Enoughinclude lime in the improved mixture, as the target mass begins the process of solidification and compaction of the structure.
As for inert mineral additives, quartz sand (in the form of grinding) is considered the most common representative of this group. However, to start its active phase, a special temperature must be provided to trigger the reactivity. Such means of improving cement mortars are also used during autoclaving. The end effect of the use of inert additives is the regulation of the grain composition and voids in hard concrete. When creating a mortar, an inert additive is usually applied after cement.
Modifiers
Used to correct the mechanical structure of concrete structures, which helps prevent delamination and cracking, as well as improve the water-repellent qualities of the material. Modifiers are available either in liquid form or in the form of a loose mixture that must be diluted with water. During the stirring process, 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 versatility 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 can also reduce material consumption, enhance adhesive qualities and fluidity of the solution.
Plasticizers
Included in the general class of additives that regulate the mechanical properties of concrete and, in particular, its strength characteristics. Actually, the strength of the cement added to the solution after it hardens increases. Plasticizers can also make concrete more elastic - that is, under 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 plasticizers and superplasticizers. The difference lies in the strength of the effect. For example, superplasticizers can increase the strength of the solution up to 10-20%. More importantly, unlike conventional plasticizers, they reduce the need to dilute the cement with water. As a result, cement is saved, and the strength properties of concrete remain at the same standard 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 water demand reduction in the process of preparing the solution exceeds 20%. Ultimately, the finished structure acquires higher strength characteristics, corrosion protection and frost resistance. In addition, the water-repellent additive for concrete minimizes the negative processes of delamination, creep and shrinkage of structures. If the task is to purposefully increase water separation, then stabilizing additives can be used. They increase the water-holding capacity by about 2 times andhomogeneity of cement mixtures, improving concrete performance such as pumpability, workability and curing.
Air entraining and blowing 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 the density and thermal conductivity. This is important when it comes to lightweight and cellular concretes, when microclimatic rather than mechanical characteristics of structures come to the fore. The entrainment of air mixtures can have a beneficial effect on thermal insulation and structural thermal insulation mortars.
Frost resistant additives
This group can also be called temperature resistance regulators - another thing is that the main emphasis in creating recipes is on protecting concrete materials from frost. The action of anti-cold additives begins even in the process of hardening, when the structure is least protected from the negative effects of the environment. At the same stage, concrete additives for waterproofing can be used, since the preservation of dispersed frozen water droplets in the base of the structure will further increase the chances of failure under dynamic loads. Sometimes it is also practiced to supply heat by external means toflooded 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 already during the operation of the structure.
Hardening Regulators
Both additives with an accelerating effect and hardening retarders are used. The change in the polymerization period of the structure of the future concrete should take place without a decrease in the design physical and chemical properties, which is largely ensured by the preliminary heat and moisture treatment of the mortar. At the same time, the electrical and thermal conductivity of the material can also increase. If the additive for concrete for fast hardening usually entails an increase or at least the retention of standard indicators of rigidity and strength, then slowing down the rate of polymerization, on the contrary, reduces these indicators by about 5-10%. The negative effects are justified by the increase in the mobility of concrete and the reduction in the rate of heat release.
Additive technology
It is desirable to work with most additives in special clothing, supplemented with personal protective equipment for hands, respiratory organs and vision. However, the modified concrete itself does not change its 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 surrounding conditions, the type of additive, its characteristics and the requirements for the result. As a rule, manufacturers of concrete admixturesrecommend to contribute approximately 1% of the share of cement used. That is, to create 1 m³ of concrete, you will need about 1.5 liters of additive. 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 downsides to using additives?
Thanks to special additives, modifiers and plasticizers, it is possible to obtain a unique building material in terms of its characteristics, suitable specifically for specific tasks. However, there are also downsides to using these 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 degrade the properties of electrical and thermal 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 deaerate the solution, distribute it evenly over the site or compact it.
Conclusion
Introduction of additives will give the expected effect only under the condition of a comprehensive assessment of the characteristics that need to be endowed with the structure. For example, a waterproofing additive for concrete is best suited if you need to lay the mortar on the foundation. For such a coating, the installation of an additional waterproofer will not be required, since the structure of the structure itself will resistcondensation and groundwater. And this is just one example of the justified use of an additive, but when it comes to complex modification of solutions, a professional analysis of the operational properties of the future design may be required to determine the whole strategy for improving the premix.
