Amin ready-made nano concrete
Concrete (in French: Béton) in a broad sense is any substance or combination that consists of a sticky substance with the property of cementation. In general, concrete is concrete made by Portland cement, which is produced by mixing fine and coarse aggregates, Portland cement and water. After enough time, this mixture turns into a stone-like substance. Coarse aggregate is usually gravel or crushed stone and fine aggregate is sand. During the hardening or curing of concrete, cement chemically combines with water to form strong crystals that bind the aggregates together, a process called hydration. During this process, a significant amount of heat called heat of hydration is released.
Additionally, concrete shrinks slightly, especially as excess water evaporates, a phenomenon known as drying shrinkage. The process of hardening and the gradual increase in concrete strength that occurs with it does not end suddenly unless it is artificially interrupted. Instead, it degrades more over long periods of time, although, in practical applications, concrete is usually set after 28 days and is considered at full design strength.
Concrete may be prepared from different types of cement as well as pozzolans, furnace slag, additives, sulfur, additives, polymers, fibers, etc. Also, heat, water vapor, autoclave, vacuum, hydraulic pressure and various compressors may be used in its construction.
After water, concrete is the most consumed material on earth. Concrete does not rot or burn. It is relatively inexpensive and can be used to create any building, from low-rise paving to sturdy structural frames to beautiful exteriors and interior finishes. Concrete is also the only major structural material that is usually produced on site. Concrete does not have useful tensile strength.
Maigre concrete (in French: béton maigre) which is also called cleaning concrete in Persian and lean concrete in English means weak concrete, is a type of concrete with a low percentage of cement, whose main task is to create a uniform surface for the foundation and prevent Direct contact with the soil. It provides a smooth surface for the foundation to be placed on and acts as a barrier to moisture or other chemicals in the soil such as sulfates that can attack and weaken the concrete.
Aggregates in concrete make up approximately three-fourths of its volume, and cement mortar and water make up one-fourth by volume. Aggregates used in concrete are divided into three categories.
• Aggregates with a small volume (light aggregate) used in the production of lightweight concrete. Such as pumice, tuff, diatomite, clay, shale, etc
• High-volume aggregates (heavy grains) for making heavy concrete such as serpentine, magnetite, steel, iron, barite and limonite
• Aggregates with normal volume and weight that are used in making normal concrete mix.
Portland cement is made by mixing and grinding limestone and clay at a ratio of 3:1, and baking the homogeneous and uniform powder under 1000 degrees, so that CO2 is separated from limestone and chemical water from clay. In the heat below 1200 degrees Celsius, lime is combined with silica and clay. In the heat above 1200 degrees, the top of the round seeds gets hot and they stick together while sweating and become clinker lumps. Cement is produced by cooling the lumps and then grinding them with some gypsum.
The quality of water in concrete is important because the impurities in it may affect the setting of cement and cause disturbances. Also, inappropriate water may have an adverse effect on the strength of concrete and cause stains on the surface of the concrete and even rusting of the reinforcement.  In most of the mixes, the water suitable for concrete is water that is suitable for drinking.  The solids of such water It will rarely exceed 2000 parts per million ppm, usually less than 1000 ppm. This amount is equal to 0.05 of the weight of cement for a water-to-cement ratio of 0.5. The potable water criterion for mixing is not absolute, and a potable water may not be suitable for concreting due to having a high percentage of sodium and potassium ions, which carries the risk of alkaline reaction of stone grains. as
As a general rule, any water whose PH (acidity level) is between 6 and 8 and does not have a salty taste can be used for concrete. Dark color and smell do not necessarily prove the presence of harmful substances in water.
Amount of water consumed
The amount of water used in concrete is very important. In order to complete the reaction process of cement with water, a certain amount of water is needed. If this amount is less than that, part of the cement does not receive enough water for reaction and remains unreacted. If more than the required amount of water is added to the concrete mixture after the completion of the reaction, some water will remain freely inside the concrete, which will cause its porosity after the concrete hardens and, as a result, reduce its strength. For this reason, it is necessary to be careful not to use too much water inside the concrete in order to achieve high strength.
The amount of water required to complete the reaction is defined as the water-cement ratio parameter. This ratio for ordinary Portland cement is about 25%. With this amount of water, the concrete will lack the necessary efficiency and usually the ratio of water to cement used in construction workshops is more than this amount. In determining the mixing ratio of concrete, a parameter is considered that includes the moisture content of aggregates before adding water to concrete, which is important in determining the amount of water needed. This excess moisture (or moisture deficiency) is the amount of excess moisture (moisture deficiency) of the aggregates from the saturated state with the dry surface of SSD or (Saturated Surface Dry).
Processing (concrete curing)
Concrete processing (in English: Curing) means maintaining concrete moisture until the reaction between cement and water is completed.
With the continuation of hydration (chemical combination of water and cement), the resistance of concrete increases, and this reaction is the reason for increasing the strength of concrete or cement setting. The relative humidity must be at least 80% for the hydration process to proceed. If the humidity drops below this value, the processing is stopped, and if the relative humidity returns to above 80%, the hydration process will start again. Due to the evaporation of a part of the water required beforeCompletion of the reaction between water and cement (which takes several days) leaves some of the cement in the concrete mixture unreacted. After concreting, immediate attention should be paid to the curing process. This action can be done by temporary insulation, water spraying or steam generation. From a practical point of view, it is recommended to keep concrete moisture for 7 days. If this is not possible, the minimum concrete processing time should not be less than 2 days.
Aggregates in concrete make up almost three quarters of its volume, so their quality is of particular importance. In fact, their physical, thermal and sometimes chemical properties affect the performance of concrete. Natural stone grains are usually formed by weathering and erosion or by artificially crushing the parent rocks. Of course, this should not be forgotten about aggregates. If the surface of the aggregates is covered with mud, its surface should be cleaned, even if possible, it should be washed if necessary.
Size of stone grainsConcrete is generally made of aggregates of different sizes, the maximum diameter of which is between 10 mm and 50 mm. On average, aggregates with a diameter of 20 mm are used.  The size distribution of the particles called “aggregate granulation” is common. In general, grains with a diameter greater than four or five millimeters are called sand and those smaller than that are called sand. The lower limit of sand is generally 0.07 mm or slightly less. Materials with a diameter between 0.06 mm and 0.02 mm are called silt and smaller materials are named clay. Mud is a soft material that contains relatively equal amounts of sand, silt, and clay.
The most important and common minerals of aggregates used in concrete are:
Silica minerals (quartz, opal, calcite, trimite, cristobalite), feldspars, mica minerals, carbonate minerals, sulfate minerals, iron sulfur minerals, ferromagnesium minerals, iron oxide minerals, zeolites and clay minerals.
Classification based on appearance
In the ASTM standard, stones are divided into five groups in terms of their appearance: completely rounded corners, rounded corners, moderately rounded corners, relatively sharp corners and sharp corners.
In the BS standard, this designation is: round-cornered, shapeless-irregular, flaky, sharp-cornered, long, long flaky.
Admixtures are substances other than Portland cement, aggregates, and water, which are added in a round or liquid form, as one of the components of concrete and to modify the properties of concrete, shortly before or during mixing. is added.
Additives are divided into two groups: chemical additives and mineral additives.
Common types of concrete additives are as follows.
• Concrete hydration rate accelerator (hardening).
• Concrete setting speed reducer.
• Bubble-forming additives create bubbles with spherical and very fine geometry inside the concrete. Encapsulating admixtures are used intentionally to create and stabilize microscopic air bubbles in concrete.
Concrete softener, which is used to reduce the water content of concrete.
• Additives that include pigments that can be used to change the color of concrete and beautify it.
• Concrete antifreeze
• Concrete glue
• Concrete hardener
Use of retarder in concrete admixtures: The job of concrete retarder additives is to delay the setting of concrete. Retardant concrete additives are used in bulk concreting or hot weather conditions. Concrete retarding additives are suitable for preventing shrinkage cracks caused by entrapment in back-to-back concreting. Concrete retarding additives are used to transport concrete over long distances.
Among the concrete additives, we can mention micro silica gel, microsilica gel, Silicafium gel, as well as various types of grout.
Fiber lubricants are also types of concrete additives.
Usually, instead of using a specific cement, it is possible to change some of the properties of the conventional cement used by combining it with an additive. Notably, the terms “mixing materials” and “additives” should not be used synonymously, because mixing materials are materials that are added to cement during the production stage, while additives are added to concrete during the mixing stage.
Chemical additives are basically: water reducers, retarders, and setting accelerators, which are classified under the headings of C, B, and A types, respectively, in the ASTM regulations. Classification of additives in BS standard also
It is similar. In addition, there are other additives whose main purpose is to protect concrete from the harmful effects of freezing and melting.
There are additives that accelerate the hardening of concrete and increase the initial strength of concrete. Some examples of accelerators are sodium carbonate, aluminum chloride, potassium carbonate, sodium fluoride, sodium aluminate, iron salts, and calcium chloride.
There are additives that delay the setting time of concrete. These materials are useful in very hot weather when the normal setting time of concrete is shortened and also to prevent cracks caused by setting in consecutive concreting.
Sugar, hydrocarbon derivatives, soluble zinc salts and soluble salts can be mentioned as some examples of retarders.
For example, if we add 0.05 weight of sugar cement to concrete with a precise control, it will delay its setting for about four hours. Consumption of 0.2 to 1 percent of cement weight prevents cement from setting.
These additives serve three purposes
1. Achieving a higher resistance by reducing the ratio of water to cement
2. Achieving specific efficiency by reducing the amount of cement used and consequently reducing the heat of hydration in the concrete mass.
3. Simplicity of concreting by increasing efficiency in forms with massive reinforcement and inaccessible positions
To see the water reducers with descriptions and performance diagrams, see in full detail.
Water reducing additives are classified as type A; But if the additives cause a delay in setting at the same time as reducing the need for water, they are classified as type D. If these accelerate the setting, they are called E-type.
These materials are among the strongest types of water reducers, which are named as strong lubricants in America and as type F in ASTM. There are also additives that, while reducing water drastically, also cause some delay in setting and are classified as type G.
Two examples of strong lubricants are concentrated sulfated melamine formaldehyde or concentrated sulfated naphthalene formaldehyde. Basically, the use of sulfated acids accelerates the dispersion process. Because they are absorbed on the surface of the cement particles and give them a negative charge, and this causes the particles to repel each other. This process increases workability at a specific water-cement ratio.
Nano technology in concrete
So far, many studies have been conducted in the field of improving the quality of concrete, most of them have examined the change in the composition of concrete (which is called concrete mixing design), however, the use of additives and also replacing the common materials used in concrete with new materials. It has always been of interest. A series of new materials that have been able to improve the mechanical and physical properties of concrete are nano materials. Nano materials can completely transform the world of concrete due to their properties at very small levels.
Light concrete or autoclaved aerated concrete
One of the important issues of the building is to lighten the weight of the structure in order to be more stable against the force of the earthquake. in buildings
Metal and concrete framework, partitions and internal walls only have the role of separating the space, which has a direct effect on reducing the weight of the structure if the materials used in these components are lighter. Hablex bricks have a low specific weight so that they do not sink to the bottom of the water and are placed on the surface of the water.
Specific gravity of concrete
The specific gravity of concrete is checked in two ways: real (by reducing its voids) and apparent (its apparent volume), and from this point of view, concrete is grouped into three categories: normal concrete, light concrete, and heavy concrete.
• Ordinary concrete
Made with ordinary aggregates and cements of one to five types of Portland and with a specific weight of 2200 to 2500 kg/m3.
In its construction, instead of silica sand, porous grains such as pumice or pumice are used, or with methods (such as adding aluminum gel) to increase the volume of concrete. The specific weight of this type of concrete is 33% to 50% of the specific weight of ordinary concrete; It means that concrete with a specific weight of 800 kg/m3 can be made
float on water. This concrete is mostly used for facades, separating walls, false ceilings and places where resistance is not considered. It may also be used in lightweight reinforced concrete (most high-strength reinforcements). Working with this type of concrete can be done in two ways: making light prefabricated blocks and in-situ concreting. Light concrete has been used in the roof and walls in the reconstruction of Hoizeh city.
• heavy concrete
It is among the concretes that have special applications. This concrete is designed for use in the construction of nuclear power plants (and to prevent atomic leaks and environmental pollution); And this kind of material is called heavy concrete due to the use of fine steel grains in the form of sand, which has a specific weight of more than 2600 kg/m3 of this concrete, which is more than ordinary concrete made with silica sand.
In the construction of this type of concrete, instead of sand, steel, cast iron or barium sulfate is used to prevent the leakage of any harmful rays such as X, gamma and other rays.
The specific weight of heavy concrete is 1.5 to 2.5 times that of ordinary concrete (3500 to 6000 kg per cubic meter).
Among the structures reinforced with this concrete in Iran, we can mention Bushehr nuclear power plant and Arak heavy water power plant.
By trapping atomic rays, steel grains prevent them from leaking into the surrounding environment. Damage to heavy concrete causes nuclear contamination, which occurred in the Fukushima nuclear power plant in Japan following an earthquake and tsunami.
Additives or concrete seasonings
materials, including water, cement and aggregate, which are added before or during the making of concrete, and in determining the proportions
Mixing (unless concrete water reduction is considered) is not calculated.
These materials are round or liquid and change one or more properties of concrete with the aim of modifying some of these properties. Although sometimes some of the characteristics of concrete may be disturbed, this work should not be outside the scope of the standard. These additives must be compatible with the national standards of Iran, including the 2930 standard, or in case of failure of the required standards, with one of the valid international standards.
Concrete chemical additives
According to Iran’s concrete regulations (ABA), chemical additives are divided into the following five groups:
1- Bubble maker
2- Water reducer
Concrete delay admixtures are ordinary water reducers and strong water reducers.
The use of concrete with pozzolan to reduce the amount of cement and also the use of concrete with pozzolan to reduce the speed and amount of heat obtained from the cement dewatering process.
The topic of additives is a broad topic and today in developed countries it is difficult to find concrete that does not use additives. For further study, you can refer to reliable sources.
Cement-like concrete additives
Cement-like concrete additives are one of the types of mineral concrete additives according to Iran’s concrete regulation (ABA). These materials have hidden hydraulic properties and when they are properly activated, they acquire cement properties and are more similar to ordinary cement than fly ash and other pozzolanic materials.
Concrete mineral additives
According to Iran’s concrete regulations (ABA), these materials in the form of very fine mineral particles improve some properties or provide special properties in concrete. Mineral admixtures can improve the workability and cohesiveness of fresh concrete as well as the strength and impermeability of hardened concrete, and change the color of concrete. These materials are divided into the following three groups:
1- Neutral mineral additives and concrete pigments
3- Cement-like concrete additives
All kinds of single-purpose additives
1. Retardant additives
2. Fastening additives
3. Fast hardening additives
4. Aerogenic additives
5. Water retention additives
6. Additives that reduce water absorption
Cement substitute material
including pozzolans and cement-like materials based on the national standards (numbers 3433 and 6171) of Iran and with the aim of providing one or more of the following characteristics;
• Reduction of cement consumption
• Reducing the speed and amount of water intake
• Increase concrete bending
• Increasing concrete reliability by reducing water permeability
Silica or silica and aluminum materials with no or low adhesion value that react with calcium hydroxide in the presence of water and form compounds such as Portland cement. Pozzolans are either natural, in raw or calcined forms, and mainly consist of non-crystalline volcanic ash; or industry including silica fume (micro silica, product
Byproduct of electric arc furnaces of ferroalloy and ferro-silica industries, a material with strong pozzolanic activity), fly ash (a by-product of coal fuel, including: silica, alumina and iron and calcium oxides), and rice husk ash
It has hidden hydraulic properties, which, if properly activated, become cement properties and react like Portland cement only in water play environments. The most widely used cementitious material is the slag of iron smelting furnace.
It is one of the modern materials that transmits some of the light rays and is somewhat like glass.
• Reinforced concrete
• Portland cement
• Concrete salt
• Friedel salt
• Gypsum stone
• Concrete structures