What Is Concrete Compressive Strength?

The strength grade of concrete refers to the compressive strength of concrete. According to the "Concrete Strength Inspection and Evaluation Standard" (GB / T 50107-2010), the strength grade of concrete should be determined according to its cubic compressive strength standard value. Use symbol C and cube compressive strength standard value (in N / mm ^ 2; or MPa).

Concrete strength grade

The compressive strength of concrete is obtained through tests. A cube test piece with a side length of 150 mm is used as the standard compressive strength test piece for concrete below the latest standard C60 strength in China. According to GB / T50081-2002 Standard for Testing Methods of Mechanical Properties of Common Concrete , cubes with a side length of 150mm are made under standard curing conditions (temperature 20 ± 2 , relative humidity above 95%), and they are cured to 28d age. The ultimate compressive strength measured by the standard test method is called the standard compressive strength of concrete cubes and is expressed by fcu, k. According to GB50010-2010

One of the main indicators of concrete quality is compressive strength. It is not difficult to see from the expression of concrete strength that the compressive strength of concrete is proportional to the strength of concrete cement. It is calculated according to the formula. When the water-cement ratio is equal, the label is high.

Cement has much higher compressive strength than concrete formulated with low-grade cement. Generally speaking, the water-cement ratio is inversely proportional to the strength of the concrete. When the water-cement ratio is constant, it is wrong to increase the strength of the concrete to increase the strength of the concrete. At this time, it can only increase the workability of the concrete and increase the shrinkage and deformation of the concrete. .
Therefore, the main factors affecting the compressive strength of concrete are cement strength and water-cement ratio. To control the quality of concrete, the most important thing is to control the two main links of cement quality and water-cement ratio of concrete. In addition, there are other factors that cannot be ignored that affect the strength of concrete.
Coarse aggregate also has a certain impact on the strength of concrete. Therefore, when the project is started, the technical person in charge first determines the coarse aggregate on the spot. When the stone strength is equal, the surface of the crushed stone is rougher than the surface of the pebble, and its adhesion to the cement mortar It is stronger than pebble. When the water-cement ratio is equal or the mix ratio is the same, the concrete strength of concrete prepared by two materials is higher than that of pebble.
Therefore, we generally control the coarse aggregate particle size of concrete to different engineering parts; the type of fine aggregate has a smaller effect on the strength of concrete than coarse aggregate, but the quality of sand also has a certain impact on the quality of concrete. During construction, Strictly control the sand mud content within 3%, therefore, the quality of sand and gravel must meet the requirements of the quality standards for sand and gravel for concrete marking.
Due to the relatively large change in the quality of sand and gravel at the construction site, the site construction personnel must ensure the quality requirements of the sand and gravel, and adjust the water-cement ratio in time according to the moisture content of the sand and gravel at the site to ensure the concrete mix ratio. The experimental mix cannot be matched with the construction mix. Confusing.
At the same time, the quality of concrete is closely related to the type, amount and method of admixture, it is also one of the important factors affecting the strength of concrete. The strength of concrete can only ensure normal development under suitable conditions of temperature and humidity, and it should be maintained in accordance with the provisions of the construction code. The temperature has a certain impact on the strength development of concrete. In the summer, it is necessary to prevent insolation and make full use of the early and late air temperature to pour the concrete; minimize the transport and pouring time to prevent exposure and increase the slump of the mixture when it comes out of the tank; it is not appropriate to water the water during maintenance because The surface temperature rises when it is dry and cools when it is watered. This alternating cold and heat will reduce the strength and crack resistance of concrete. In winter, it is necessary to keep heat and prevent frost damage. In winter construction, comprehensive heat storage method and steam culture method are generally adopted.