Substances that are added in small amounts to the transmission during production or before casting are called additives that serve to improve the properties of concrete. Additives can be divided into chemical and mineral depending on their origin:
1) Chemical additiveof chemical additives are listed below.
They provide the same consistency of concrete when using less water. The strength of concrete increases as the amount of water used in fresh concrete decreases. They are divided into reducing and super-reducing.
They extend the curing time of concrete. They are useful when transporting concrete over a long distance at high temperatures.
Unlike retarding agents, these additives reduce the time of concrete solidification. They are used in some cases, when casting formwork and castings at low air temperature, to ensure that the concrete hardens before the start of frost.
c) Reducing permeability
These are additives that allow a limited amount of air to pass through, but ensuring that concrete is waterproofing in place depends on good work and proper placement techniques.
Several types of additives can be used simultaneously in some concrete mixes. But you should pay attention to the interaction of additives. Chemical additives are an integral part of concrete in the construction industry because of their aforementioned properties.
2) Mineral additives
Slag, fly ash, silica, rock sand... etc., stored in silos as crushed powder, as well as cement. Various inert substances are called "mineral additives". Mineral additives do not have a binding property like cement, but when used together they perform a similar task, so they significantly save cement. Mineral additives are also used in the production of high-strength concrete.
In TS EN 206, chemical additives are defined as "a material added to concrete in small quantities compared to the cement mass during the mixing process in order to change some of the properties of the concrete mortar". It does not contain inert or pozzolanic mineral additives. (for example, silica). But these substances can be found in a chemical additive.
It is generally recognized that chemical additives contribute to the durability and stability of concrete structures. Properties that give chemical additives include workability and improved self-compaction of concrete, additives with anti-frost effect. They allow you to work with concrete at sub-zero temperatures.
The properties of chemical additives have been defined in the standard series TS EN 934-chemical additives-for concrete, mortar.
Part 2-Concrete additives
Chapter 3- additives for the concrete
Chapter 4-Additives to the mix concrete
Chapter 5-Concrete additives for pouring
The use of chemical additives was defined in TS EN 206.
TS EN 934-2 contains the following types of additives:
Water-reducing additives/ fluidization
High level of water-repellent / super-fluidizing additives
Increasing the air (gas) content
Retarders/water reducing / fluidizing additives
Retarders /water-reducing / super-fluidizing additives
Accelerators / water-reducing / fluidizing additives
Other additives do not contain TS EN 934-2, but can be used if they comply with TS EN 206-1 A.
a) Increasing frost resistance
Additives that increase the frost resistance, strength and corrosion resistance of concrete and concrete products are a mixture of air-entrapping and plasticizing components used in accordance with a strictly defined ratio. The use of such additives increases the durability of concrete, as well as frost resistance, water resistance and corrosion resistance. The use of such additives increases the mobility of concrete mixes, without any reduction in the strength of the finished concrete. Moreover, the use of such additives helps to reduce the water demand of concrete mixes by 25% of the total weight, without reducing the degree of their mobility.
These additives create small air bubbles that are evenly distributed inside the concrete, which increases the impermeability and frost resistance of the concrete.
Increasing corrosion resistance
Increasing protective properties in relation to steel reinforcement
Properties of concrete additives
In addition to special concrete mixes, such as high-strength concrete, the maximum dosage is 5.2.6 TS EN 206. depending on the weight of the cement in the composition. For dosages less than 2 g / kg, the chemical additive should be added by mixing with water.
The performance of concrete additives is controlled by TS EN 934-2 in accordance with the main and secondary functions of the additives. Production standards are shown in Table 1.
In addition to the General requirements for the production process, there are General requirements that apply to all chemical additives.
Effect on solidification time
Impact on strength
Effect of concrete on air content
Amount of water-soluble chloride
Amount of alkali
The performance of chemical additives depends on the type of concrete. The experimental mixture (with a chemical additive) is compared with the control mixture (without additives). The chlorine and alkali content is also determined by measurement.
The maximum chloride content that can be present in concrete is defined in TS EN 206-1. TS EN 934-2 limited the maximum chloride content to 0.1%.
The maximum alkaline content must be determined by the manufacturer for each chemical additive in accordance with TS EN 934-2.
Determination of concrete additives
The additives will be used in the developed concrete. The concrete manufacturer must select the most appropriate additive that will provide certain concrete properties. The type of additive used in the finished concrete is indicated on the invoice.
In developed concrete, additives are often used to improve the following properties.
Acceleration of solidification
Other characteristics (for example, fast sealing)
TS EN 934-2 Chapter 3.1.3. in order to obtain the necessary amount of concrete to achieve the desired result, it is necessary to conduct a series of tests with the materials that will be used on the construction site.”
Composition developers should consider the following;
Supplements of the same type from different manufacturers can give the expected result in different doses.
The effect of additives varies depending on the cement and mineral additives and inert materials used in concrete.
The dosage is different for each brand and type of concrete. This information is provided by the manufacturer.
The compliance and effectiveness of additives must be monitored during production.