What are the factors that affect the strength of concrete

First, the strength of cement and water-cement ratio.

The strength of cement and the water-cement ratio are the ones that determine the strength of concrete.

The most important factor. Cement is a cementing component in concrete, and its strength directly affects the strength of concrete. Under the condition of the same mix ratio, the higher the strength of the cement, the higher the strength of the concrete.

When the same cement (same variety and strength) is used, the strength of the concrete is mainly determined by the water-cement ratio; In the case that the concrete can be fully compacted, the larger the water-cement ratio, the more pores in the cement stone, the lower the strength, and the smaller the adhesion with the aggregate, the lower the strength of the concrete. Conversely, the smaller the water-cement ratio, the higher the strength of the concrete. Second, the influence of aggregate The surface condition of the aggregate affects the bonding of cement stone and aggregate, thereby affecting the strength of concrete.

The surface of the gravel is rough and the cohesion is large; The pebble surface is smooth and has little cohesion. Therefore, under the same condition of mix ratio, the strength of crushed stone concrete is higher than that of pebble concrete. The maximum particle size of the aggregate also has an effect on the strength of the concrete, the larger the maximum particle size of the aggregate, the smaller the strength of the concrete.

The smaller the sand rate, the compressive strength of the concrete.

The higher it is, the lower the compressive strength of the concrete. 3. Admixtures and admixtures Mixing admixtures into concrete can make concrete obtain early strength and high strength.

Performance, the addition of early strength agent in concrete can significantly improve the early strength; Add superplasticizer.

The water consumption of mixing can be greatly reduced, and the concrete can still be well formed and compacted under a low water-cement ratio, and a high strength of 28d can be obtained. Adding admixture to concrete can improve the compactness of cement stone, improve the interface bond strength of cement stone and aggregate, and improve the long-term strength of concrete. Therefore, the incorporation of high-efficiency superplasticizer and admixture into concrete is a necessary technical measure for the preparation of high-strength and high-performance concrete.

Fourth, the temperature and humidity of curing The hardening of concrete is the result of cement hydration and condensation hardening. The curing temperature has a significant effect on the hydration rate of cement, the curing temperature is high, the initial hydration rate of cement is fast, and the early strength of concrete is high. Humidity is powerful.

Ensuring the moisture required for the normal hydration of cement is conducive to the growth of strength. Below 20, the lower the curing temperature, the lower the compressive strength of the concrete, but in the range of 20 30, the curing temperature has little effect on the compressive strength of the concrete. The higher the curing humidity, the higher the compressive strength of the concrete, and conversely, the lower the compressive strength of the concrete.

Fifth, the age of concrete under normal curing conditions, its strength will increase with the increase of age. In the first 7 14 days, the strength increased rapidly, and after 28 days, the growth was slow, and the age continued for a long time, and the strength of concrete still increased.

The main factors affecting the strength of concrete are: cement strength and water-cement ratio, age, curing temperature and humidity, and construction quality.

The factors that affect the strength of concrete are cement strength, water-cement ratio, aggregate

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.

Water-cement ratio: The water-cement ratio, also known as the water-cement ratio, refers to the weight ratio of the amount of water in the concrete to the amount of cement. 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.

Aggregate: 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 surface of the pebble, 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 strength of the two materials is higher than that of the gravel.

Concrete:

Concrete refers to a mixture made of cementing materials (organic, inorganic or organic-inorganic composites), granular aggregates, water and chemical admixtures and mineral admixtures that need to be added in appropriate proportions, or formed into composite materials with a stacking structure after hardening.

Fit in the right proportions. Concrete has the characteristics of abundant raw materials, low cost and simple production process, so that the amount of concrete is getting larger and larger. At the same time, concrete also has the characteristics of high compressive strength, good durability and wide range of strength grades.

These features make it very versatile.

Concrete is a building material full of life. With the continuous development of concrete composition materials, people's understanding of material composite technology is constantly improving. The performance requirements for concrete are not only limited to compressive strength, but on the basis of strength, more attention is paid to the balance and coordination of comprehensive indicators such as durability and deformation performance of concrete.

1. The main influencing factors are:

1) Cement strength:

The strength of concrete mainly comes from the cement stone and the bond strength with the aggregate.

The higher the strength of the cement, the higher the strength of the cement stone itself and the bond strength with the aggregate, and the higher the strength of the concrete.

2) Water-cement ratio:

The theoretical water requirement for complete hydration of cement is about 23% of the weight of cement, but when the concrete is actually mixed, in order to obtain good workability, the water-cement ratio is about between, and after the excess water evaporates, the pores are left inside the concrete, and the larger the water-cement ratio, the larger the pores left by Li Pei, so that the effective bearing area is reduced, and the concrete strength is smaller.

3) The quality of aggregates

If the content of harmful substances in the aggregate is high, the strength of the concrete is low, and the strength of the aggregate itself is insufficient, which may also reduce the strength of the concrete.

4) Construction conditions:

The construction conditions mainly refer to stirring and vibrating molding.

Generally speaking, mechanical stirring is more uniform than manual stirring, so the strength is relatively high; The longer the mixing time, the stronger the concrete.

5) Maintenance conditions:

The curing temperature and humidity after concrete pouring are the main external factors that determine the development of strength.

The curing environment temperature is high, the cement hydration speed is accelerated, the concrete strength development is also fast, and the early strength is high.

2. Measures to improve the strength of concrete:

1) Use high-grade cement.

2) Reduce the water-cement ratio as much as possible, or use dry hard concrete.

3) Use high-quality sand and gravel aggregates to choose a reasonable sand rate.

4) Mechanical stirring and mechanical vibration are used to ensure the uniformity of stirring and compactness of vibration, and strengthen construction management.

5) Improve the maintenance conditions, ensure a certain temperature and humidity conditions, and if necessary, spring can be used to moist heat treatment to improve the early strength.

Especially for the concrete mixed with mixed materials or the concrete prepared with fly ash cement, slag cement and pozzolanic cement, the enhancement effect of moist heat treatment is more significant, and the disturbance can not only improve the early strength, but also the later strength.

6) Add water reducing agent or early strength agent to improve the strength or early strength of concrete.

7) Silica fume or ultra-fine slag powder is also an effective measure to improve the strength of concrete