Under what conditions can the strength of concrete be equal to the strength of the cement used?

Under the condition that humans live to be 250-300 years old, it is possible.

The strength grade of cement is determined by the compressive strength of the mortar prepared with standard sand. Theoretically: under the condition of the same water-cement ratio and the same mortar cement content (concrete refers to the cement content per unit volume of the mortar part), the strength grade of concrete and cement is the same.

Because, at this time, the difference between concrete and mortar is only that concrete contains coarse aggregate and occupies part of the space, and the mortar part of the two is the same. Actually, the water-cement ratio of concrete is slightly lower, or the amount of cement of concrete mortar part is slightly higher, and the strength grade of concrete can generally be the same as cement strength grade. Because, the aggregate gradation and aggregate cleanliness in the concrete are not as good as the standard sand, which will reduce the strength.

The strength grade of cement is determined by the compressive strength of the mortar prepared with standard sand. Theoretically: under the condition of the same water-cement ratio and the same mortar cement content (concrete refers to the cement content per unit volume of the mortar part), the strength grade of concrete and cement is the same.

Because, at this time, the difference between concrete and mortar is only that concrete contains coarse aggregate and occupies part of the space, and the mortar part of the two is the same. Actually, the water-cement ratio of concrete is slightly lower, or the amount of cement of concrete mortar part is slightly higher, and the strength grade of concrete can generally be the same as cement strength grade. Because, the aggregate gradation and aggregate cleanliness in the concrete are not as good as the standard sand, which will reduce the strength.

This problem, first of all, the concrete strength in China's national standard is to test the concrete strength with a cube test block of 150mm, and the cement strength is tested with a strip specimen of 40*40*160mm, the strength of cement is called the cement mark, these two strength values can not be compared, second, for the concrete grade to be configured, the cement that is higher than the concrete grade is generally used, such as the cement grade that is twice the strength of the concrete, in the configuration of concrete, The amount of cement used will not exceed 500 kilograms per cubic meter, so this question raised by the landlord is difficult. If you want to make the configured concrete reach the strength of the cement label used, there are also ways, such as high-efficiency admixtures, reinforcing agents and so on.

The main factors that determine the strength of concrete are the cement strength grade and the water-cement ratio, because the strength of concrete mainly depends on the strength of cement stone and the adhesion between its aggregates, and the strength of cement stone and the adhesion between it and aggregates depend on the strength grade of cement and the size of the water-cement ratio. In the case of the same cement strength grade, the strength will decrease with the increase of the water-cement ratio. However, if the water-cement ratio is too small, the mixture is too dry and hard, and under certain tamping molding conditions, the concrete is difficult to form and compact, so that the strength decreases.

In addition, under the same water-cement ratio and the same test conditions, the higher the cement strength grade, the higher the strength of the cement stone, and thus the higher the strength of the concrete prepared by it.

In addition, the factors that affect the compressive strength of concrete are aggregate, age and curing.

The main reason for determining the strength of concrete is the rationality of the mix ratio, followed by the curing method and curing conditions after the concrete is formed.

The main factors that determine the strength of concrete are the water-glue ratio and porosity, the higher the cementation strength, the higher the concrete strength, the lower the porosity, the higher the concrete strength.

The main factor that determines the strength of concreteIt is the cement strength grade and the water-cement ratio. The effective measure to improve the strength of concrete is to use high-grade cement and reduce the water-cement ratio (such as the use of high-performance superplasticizer and the addition of high-strength mineral admixtures such as silica fume).

The strength grade of cement is determined by the compressive strength and flexural strength.

The strength grade of cement is a sign of cement strength, the measurement index is the compressive strength of cement, and the testing standard is mainly the strength of cement mortar after 28 days of induration. For example, if the compressive strength after 28 days is detected, the strength grade of the cement is set as grade or grade.

Cement is available in eight strength grades. The strength grade with r indicates that the cement is early strength cement. Strength grades can be used in some house construction. Above the strength level can be used for the construction of larger bridges or factories, as well as some important pavements and the manufacture of prefabricated components.

The main factors that affect the strength of concrete are as follows:

Influencing factor 1: cement strength.

Concrete is an artificial stone made of cement as cementitious material, sand and gravel as aggregate, and mixed with water. Therefore, whether the concrete strength is high or low, first of all, we have to look at the strength of the cement, that is, to understand the grade of cement - the cement grade is not high, it is not worthy of high-strength concrete, which is a prerequisite.

Influencing factor 2: water-cement ratio.

The water-cement ratio, also known as the water-cement ratio, refers to the weight ratio of the amount of water used in concrete to the amount of cement used. The water-cement ratio is the main parameter that determines the strength, durability and a series of other physical and mechanical properties of concrete, and each type of cement corresponds to an optimal ratio, which is too large or too small to affect the strength and other properties. In general, the water-cement ratio is inversely proportional to the strength of concrete.

Influencing factor three: aggregates.

Coarse aggregate also has a certain impact on the strength of concrete, the technical person in charge should determine the coarse aggregate on the spot, when the stone strength is equal, the surface of the gravel is rougher than the pebble surface, it is stronger than the cohesiveness of the cement mortar than the pebble, when the water-cement ratio is equal or the mix ratio is the same, the concrete of the two materials is prepared, the concrete strength of the crushed stone is higher than that of the pebble.

The influence of fine aggregate varieties on the strength of concrete is smaller than that of coarse aggregate, but the quality of sand also has a certain impact on the quality of concrete, and the mud content of sand should be strictly controlled within 3%.

Influencing factor 4: admixtures.

The quality of concrete is closely related to the type, amount and mode of admixture, and it is also one of the important factors affecting the strength of concrete.

Influencing factor 5: maintenance work.

The strength of concrete can only ensure normal development under the condition that temperature and humidity are suitable, and it should be maintained in accordance with the provisions of the construction code. In summer, it is necessary to prevent exposure to the sun, and make full use of the time when the temperature is high and low in the morning and evening to pour concrete; Minimize the transportation and pouring time, prevent exposure to the sun, and increase the collapse of the mixture when it comes out of the tank; Intermittent watering should not be done during curing, because the temperature of the concrete surface rises when it is dry and cools when it is watered, and this alternating effect of cold and heat will reduce the strength and crack resistance of the concrete. In winter, it is necessary to keep warm and prevent frost damage, and the comprehensive heat storage method and steaming method are generally adopted for winter construction.

If you want to effectively improve the strength of concrete, in addition to doing the above work, you can also strengthen the concrete with the help of concrete sealing curing agent material. Concrete sealing curing agent is a widely used concrete sealant, hardener and dustproof agent in the construction industry, which is often used in factory workshops, underground garages and other places, and is an important means to create high-strength floors, dust-free floors and impermeable floors.

The main factors affecting the strength of concrete: before the hardened concrete is subjected to external force, the chemical shrinkage and physical contraction caused by cement hydration cause the change of mortar volume, and the tensile stress is extremely unevenly distributed at the interface between the coarse aggregate and the mortar, resulting in the formation of many fine cracks on the interface. In addition, because of the water leakage after concrete molding, some of the rising water is prevented by the coarse aggregate particles, so it accumulates at the lower edge of the coarse aggregate, and the concrete becomes an interface crack after hardening.

When the concrete is stressed, these pre-existing interfacial cracks will gradually expand, lengthen, and converge to form visible cracks, resulting in the loss of continuity and complete destruction of the concrete structure. The strength test also confirms that the failure of the normal ratio of concrete is mainly due to the failure of the bonding interface between the aggregate and the cement stone. Therefore, the strength of concrete mainly depends on the strength of cement stone and its bond strength with aggregate.

The bond strength is closely related to the cement strength grade, water-cement ratio and aggregate properties, and the strength of concrete is also affected by the construction quality, maintenance conditions and age.

The measures to improve the strength of concrete are mainly as follows:

1) Adopt high-strength grade cement.

Increasing the strength grade of cement can effectively improve the strength of concrete, but because the increase of cement strength grade is restricted by raw materials and production technology, it is often unrealistic and uneconomical to achieve the purpose of improving concrete strength by simply improving cement strength.

2) Reduce the water-cement ratio.

This is an effective measure to improve the strength of concrete. Reducing the water-cement ratio of concrete mixture can reduce the porosity of hardened concrete, significantly increase the cohesion between cement and aggregate, and improve the strength. However, reducing the water-cement ratio will reduce the workability of the concrete mixture.

Therefore, there must be corresponding technical measures, such as the use of mechanical strong vibration, doping to improve the workability of admixtures, etc.

3) Damp heat curing.

In addition to the use of steam curing, autoclaving curing, winter aggregate preheating and other technical measures, the storage of cement itself hydration heat can also be used to improve the growth rate of strength.

4) Age adjustment.

As mentioned earlier, the strength of concrete continues to increase as it ages. Practice has proved that when the age of concrete is 3-6 months, the strength will be increased by 25-50% compared with 28dIf the concrete in some parts of the project can only be used at full load after 6 months, the strength grade of this part can be appropriately reduced to save cement.

However, the specific application should be approved by the design and management unit.

5) Improve the construction process.

If mechanical mixing and strong vibration are used, the concrete mixture can be poured more evenly and densely under the condition of low water-cement ratio, so as to obtain higher strength. In recent years, new construction technologies such as high-speed stirring method, secondary feeding mixing method and high-frequency vibration method developed abroad have been applied in domestic projects, and good results have been achieved.

6) Add admixtures.

The addition of admixtures is one of the effective ways to improve the strength of concrete, and both superplasticizer and early strength agent play an obvious role in the strength development of concrete.

When the strength of cement is constant, the strength of concrete mainly depends on ().

Correct answer: cement with the amount of regret holes.

Answer: Lack of burning D

The choice of cement strength when mixing concrete:

Answer]: Buried mold d

Analysis] The strength of concrete mainly depends on the strength of cement stone and its bond strength with the aggregate surface, and the strength of cement stone and its bond strength with aggregate are closely related to the strength grade, water-cement ratio and aggregate properties. In addition, the strength of concrete is also affected by the construction quality, curing conditions and age.

Answer: Family Rock] :d

Textbook p129

For the brigade limb concrete with higher strength grades, the cement strength grade should be times of the concrete Zhaozhen soil strength grade.