What is the C25 concrete mix ratio

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What types of concrete are there?

Fresh concrete

The concrete in which the cement paste has not yet set is called fresh concrete. During the setting of the cement paste, the concrete is called young concrete or green concrete. After the cement paste has set, it is called hardened concrete.

Ingredients and composition

The composition of the concrete depends on many parameters, such as: B. strength class and environmental conditions. With normal concrete of strength class C25 / 30, a cubic meter has the proportions of 285 kg of cement, 200 l of water and 1900 kg of aggregate, which corresponds to a mixing ratio of 1: 0.6: 7.

consistency

The consistency of the fresh concrete should be selected so that it can be conveyed, installed and practically completely compacted without significant segregation. The decisive property of fresh concrete is its workability. The fresh concrete consistency must be determined before construction begins and must be adhered to during construction. As the flowability increases, the concrete becomes more expensive. When pumping the concrete, the concrete consistency should be at least in the plastic range, i.e. H. Slump class F2, better F3. To check the consistency, there are standardized methods suitable for construction sites, the spreading test, the slump test and the compaction test. The subsequent admixing of water to the finished fresh concrete, e.g. B. on arrival at the construction site, is not permitted according to German regulations, because this can have a negative impact on the w / c value and, as a result, the material properties. However, ready-mixed concrete may be mixed with superplasticizers on site to improve workability. The maximum permissible amount is 2 liters / m³, which turns plastic concrete into easily flowable concrete.

 

Consistency ranges of the fresh concrete according to DIN 1045-2

Consistency area

Slump classes

Compaction dimension classes

Suitable compaction measures

 

class

Slump [mm]

class

Degree of compaction

 

very stiff

-

-

C0

≥1,46

Strong stamping, very intense shaking

stiff

F1

≤340

C1

1,45?1,26

Very intense shaking

plastic

F2

350?410

C2

1,25?1,11

Shake

soft

F3

420?480

C3

1,11?1,04

Shake

very soft

F4

490?550

 

 

Poking or shaking lightly

flowable

F5

560?620

 

 

Poking or shaking lightly

very flowable

F6

≥630

 

 

Poking or shaking lightly

SVB

-

>700

 

 

self-compacting

Strength classes

Compressive strength is one of the most important properties of concrete. DIN 1045-1: 2001-07 for the reinforcement of reinforced concrete structures prescribes an assessment by testing after 28 days using cubes with an edge length of 15 cm (test cubes) or 30 cm long cylinders with a diameter of 15 cm. Based on the determined compressive strength, the concrete can be assigned to the strength classes. A C12 / 15 has the characteristic cylinder compressive strength of 12 N / mm² and a characteristic cube compressive strength of 15 N / mm². The C in the nomenclature stands for English concrete (German: concrete). In the course of the harmonization of the European standards, these concrete strength classes have been standardized across Europe in the current generation of standards. The previously valid designation in Germany was, for example, B15.

Compressive strength classes for normal concrete according to DIN 1045-1 and DIN1045-2 *

Surveillance

Strength class

characteristic cylinder

Mean value of the cylinder

Average tensile strength (N / mm²)

class

compressive strengthfck (N / mm²)

compressive strengthfcm (N / mm²)

1

C8 / 10 *

8

-

-

1

C12 / 15

12

20

1,6

1

C16 / 20

16

24

1,9

1

C20 / 25

20

28

2,2

1

C25 / 30

25

33

2,6

2

C30 / 37

30

38

2,9

2

C35 / 45

35

43

3,2

2

C40 / 50

40

48

3,5

2

C45 / 55

45

53

3,8

2

C50 / 60

50

58

4,1

3

C55 / 67

55

63

4,2

3

C60 / 75

60

68

4,4

3

C70 / 85

70

78

4,6

3

C80 / 95

80

88

4,8

3

C90 / 105

90

98

5

3

C100 / 115

100

108

5,2

Stress-strain relation of concrete for different strengths

Site concrete

Concrete installation with hose bucket

Construction site concrete is concrete that is produced in a dedicated plant directly on the construction site, in contrast to ready-mixed concrete, which is delivered by mixer vehicles from a stationary plant. In Germany, this is only common on construction sites with a large demand for concrete, which may only be accessible via long journeys. One example is the major construction site in Berlin around Potsdamer Platz. For years there was a great need for concrete for the residential and business complexes, the road and underground tunnels and the train stations. The construction site concrete works deliver all concrete strength classes and types like a stationary system, provided that they are technically and personally designed for this.

Ready-mixed concrete

Ready-mixed concrete is concrete that is produced centrally in stationary concrete mixing plants and then delivered to the construction sites with concrete mixing vehicles. Another name for ready-mixed concrete is Precast concretebecause it has already been mixed and only needs to be added. The production of ready-mixed concrete is specified in the European standard EN 206.

In-situ concrete

With In-situ concrete This is concrete that is processed on site on the construction site and sets there, usually in a formwork, in contrast to precast concrete parts, which are installed directly after they have hardened. In-situ concrete is either delivered to the construction site as ready-mix concrete or produced there as construction site concrete. After pouring into the formwork, the in-situ concrete must be compacted, that is, trapped air bubbles are removed with vibrating machines.

Shotcrete

Shotcrete is concrete that is conveyed with compressed air in pipes or hoses to a spray nozzle, where the concrete is applied over a large area and thus simultaneously compacted. This concreting process is particularly important in tunnel construction when securing exposed rock or loose rock surfaces, but also in the renovation and reinforcement of concrete and reinforced concrete structures.

Underwater concrete

Underwater concrete is concrete that is installed underwater. Special concreting methods, such as the use of stationary funnels (contractor method), are necessary to ensure that the concrete does not separate during concreting. The concrete must have good cohesiveness and good workability. For this, the cement content should be at least 350 kg / m³. Underwater concrete is used in particular for diaphragm walls and in the groundwater as a barrier layer for floor slabs.

Rolled concrete

Rolled concrete or HGT concrete (hydraulically bound base course) is earth-moist concrete that is installed and pre-compacted with a road paver or a laser-controlled grader using a wheel loader in layers about 18-20 cm thick. The redensification takes place with rubber-tyred rollers. Rolled concrete has a low cement content (180 kg / m³) and a coarse grain size of 0-32 mm and is mainly used in road construction and industrial floors.

Spun concrete

Spun concrete is concrete that is compacted with rapidly rotating steel formwork. This results in a low water-cement ratio of 0.3 and thus a dense and very strong concrete. Above all, pipes, masts and piles are manufactured using this process.

Vacuum concrete

Under Vacuum concrete is a process in which a vacuum pump and suction mats are used to generate a negative pressure after concreting. This removes some of the water not required for hydration from the fresh concrete. The special treatment of the fresh concrete z. B. reduces the formation of shrinkage cracks. The result is denser and more wear-resistant concrete surfaces. In addition, this process enables high strengths to be achieved very early on, which means that the surface can be used earlier and the concrete is more frost-resistant.

Concrete

Concrete that is subsequently applied to existing concrete is referred to as concrete.

Screed concrete

Screed concrete is a special concrete for the production of floor layers in buildings. It fulfills special requirements, including by limiting the grain size (generally up to a maximum of 8 millimeters) of the aggregates, so that thin layers of a few cm thick with good surface properties (especially resistance, smoothability) can be produced.

Aerated concrete

Aerated concrete (formerly aerated concrete) is a mineral material that is produced by chemical foaming of a mortar mixture. The alkaline mortar suspension reacts with the formation of gas with powders of base metals such. B. aluminum. Since aerated concrete contains almost no aggregates, strictly speaking it does not meet the definition of concrete. Before hardening in pressurized saturated steam in the autoclave, the blocks are cut into wall elements, insulating elements or stones. Compared to conventional concrete, aerated concrete has low strength and low thermal conductivity due to its low bulk density. Components made of aerated concrete, like those made of reinforced concrete, can contain reinforcement to absorb the tensile forces. In addition to the wall modules and mostly unreinforced wall elements, reinforced beam and ceiling elements can also be produced (at the factory), which are assembled as prefabricated parts at the construction site.

Fiber concrete

At the Fiber concrete Fibers are added to the concrete to improve the tensile strength and thus the breaking and cracking behavior. These fibers are embedded in the matrix (cement stone). They act as reinforcement. With higher tensile loads, cracks appear in the concrete. By using a fiber concrete, the cracks are distributed in many very narrow and therefore normally harmless cracks.

Short or long fibers laid in the direction of tensile stress can be used. Long fibers are mostly used in the form of glass fiber textile mats. One then speaks of textile-reinforced concrete or else Textile concrete.

Fiberglass Normal glass reacts with the alkalis in the concrete. This is why alkali-resistant glass fibers must be used (e.g. AR glass fibers).

Steel fibers A wide variety of steel fibers are used. (Stainless, structural steel, bent up, not bent up,?)

Plastic fibers The Kevlar fibers developed in the USA are of particular interest here, as they have properties that are just as good as the other fibers.

Carbon fiber Carbon fibers have the highest modulus of elasticity of the fibers listed here.

Polymer concrete (PC)

In contrast to normal concrete, polymer concretes contain a polymer (plastic) as a binding agent that holds the aggregate (aggregate) together. Cement is only used in polymer concrete, if at all, as a filler, i.e. as an extension of the aggregate into the finest grain range and does not have any binding effect. Polymer concretes are mainly used in the renovation of existing components. Due to the short pot life (hardening time) of the polymers of less than a day, long closing times for roads and bridges can be avoided.

The most common polymer matrix for polymer concrete (PC = Polymer Concrete) is unsaturated polyester resin (UP resin). By mixing different grain sizes, filling levels of over 90% (m / m) can be achieved. The most important applications in Germany are pipes and gutter systems that are cast entirely from polymer concrete. In its area of ​​application, polymer concrete has significantly better mechanical and chemical properties than cement concrete. The gel time (or in short: gel time) of these resins can be adjusted individually by the amount of catalysts (mostly cobalt salts) and hardeners (mostly methyl ethyl ketone peroxide) used.

Polymer concrete (also called mineral cast) is also widely used in the manufacture of machine frames. Thanks to its very good vibration damping, great accuracies can be achieved in lathes or milling machines. The polymer (binder) consists mainly of epoxy resin.

Gravel concrete, drain concrete

Grit concrete contains grit of one grain as well as cement and water. After setting, there is a coherent cavity system through which water can drain off. This means that there is less risk of frost in winter. Grit concrete is used in road and path construction as well as when setting curbs, etc. Stone concrete is often produced today in bridge construction using polymeric binders, since otherwise the relatively large inner surface when using hydraulic binders leads to rapid leaching of the same and to the formation of sintering in and on drip spouts and on the underside of the structure.

Grit concrete is not always drain concrete, as the grit is also used to produce grading curves for ready-mixed concrete in grain groups 2/8, 8/16 and 16/22.

Asphalt concrete

Asphalt concrete is a name for a mixture of bitumen and aggregate.

Mineral concrete

Mineral concrete is a name for a highly compacted mineral mixture, usually with the use of a high proportion of broken grain. The grading curve is to be built up according to the Fuller parabola; an optimal water content for compaction is to be set. Segregation must be avoided during installation. Without a binder, mineral concrete becomes a highly stable building material that is used, for example, in road surfaces. A common product is the graded gravel base layer as a frost protection material according to ZTVT-ST B95 0 - 32 mm. Strictly speaking, since it is made without cement, it is not concrete.

Concrete concrete

Concrete concrete is a name for a concrete with the addition of chippings, rubble or the like, which was sometimes used in the past. It is therefore more permeable to water (more porous) and of poor quality. The English name for concrete? Concrete? can be found in the word.

Blue concrete

As blue concrete is the name given to a particularly resistant type of concrete that was used in particular for the construction of bunkers before and during World War II

Recent developments

Self-compacting concrete

Using suitable formulations or additives, it is possible to produce concrete that does not require any externally applied compression energy (vibration). This concrete is called SVB (self-compacting concrete) or SCC (self-compacting concrete).

High strength concrete

High-strength concretes are produced with the help of cements with high compressive strength, high-performance plasticizers and possibly with extremely fine additives (silica dust).

Ultra high strength concrete

Ultra high strength concrete (UHFB), internationally known as? Ultra High Performance Concrete (UHPC)? denotes, represents the result of continued research on the basis of high-strength concrete. Due to its preferably small maximum grain diameter and the high reactivity of its solid constituents, the parallel designation? reaction powder concrete? or? Béton de Poudres Réactives? (? BPR?) Or? Reactive Powder Concrete? (? RPC?) Its technological characteristics very aptly. It achieves compressive strengths of over 200 MPa and? mixed with fibers? Tensile strengths of 15 and flexural strengths up to 45 MPa. In Germany, several bridges in the Kassel area were built with UHFB.

Infralight concrete or ultralight concrete

With a dry bulk density of a maximum of 800 kg / m³ one speaks of infra-light concrete or ultra-light concrete. A lower weight limit for this type of concrete is currently around 350 kg / m³ from a technical point of view. The low density results from the special production, different lightweight concrete aggregates and the structure of the infra-lightweight concrete. Light clay granules are used for production, e.g. B. Liapor. The compressive strength is so low that it cannot yet be used as structural concrete. Investigations are currently being carried out in this regard at various institutes in Germany. In addition to its low weight, the main advantages of this concrete are its low thermal conductivity. With a lambda of around 0.18 W / mK, this decisive property is around half as high as the values ​​for lightweight concrete according to DIN 1045.

Translucent concrete

By inserting optical fibers, the Hungarian Aron Losonczi succeeded in producing translucent concrete elements. The? Luminous concrete? is called? LiTraCon? (Light Transmitting Concrete). The concrete has a glass fiber content of 3-5% and the almost loss-free light transmission through the optical fibers makes it possible to see light, shadows or even colors even with walls up to twenty meters thick.[6] In contrast to fiber concrete or textile concrete, optical fibers are used here, which allow the light to be transmitted. Commercially available AR glass fibers that are stable in concrete are too thin for the phenomenon of total reflection in the range of visible light.

Paper concrete

Papercrete or paper-concrete is a building material that is light and has high strength. Of course, other fiber and metal processing wastes can also be used, such as the Textile concrete. The decisive factor is the mixture (papercrete ~ 60 paper? 20 dust / mineral? 20 fine cement). Simple geodesic domes have already been built with this material, and metal mesh reinforcement (reinforcement) can also be used.

Glass foam concrete

Glass foam concrete or "Vetrocell" concrete is a concrete mix that uses glass foam instead of sand and gravel. The building material is hard and load-bearing, but also very light. The glass foam also achieves very good thermal insulation properties.The compressive strength is 8 to 47 MPa, with a density of approximately 800 to 1600 kg / m³ and a thermal conductivity between 0.12 and 0.38 W / (m K).

Self-cleaning concrete

There are more recent developments to obtain facades with self-cleaning concrete surfaces. Similar to the lotus effect, the surface must either be highly water-repellent (superhydrophobic) or water-attracting (superhydrophilic). The second way in particular seems to be promising, whereby both methods of subsequent surface treatment and the addition of concrete are used in the mixing process. By using hydrophobic alkaline silicate solutions, similar effects can also be achieved with older concrete. Such additives can also have a positive effect on the abrasion and compressive strength.

Acid-resistant concrete

With these concretes, the aim is to greatly increase the chemical resistance. This is achieved when the three-dimensionally cross-linked calcium hydroxide structure of the cement stone matrix is ​​interrupted and the amount of C.a(OH)2 is limited.

Source own and Wikipedia in June 2009