Factors that affect concrete, what are the factors that affect the quality of concrete

The main ones are as follows: Workability The most important properties of concrete mixtures. It comprehensively represents the consistency, fluidity, plasticity, resistance to stratification and segregation of water secretion and easy surface plastering of the mixture.

There are many methods and indexes for measuring and expressing the workability of mixtures, and the slump (mm) measured by the truncated cone slump cylinder and the Vibo time (seconds) measured by the Vibo instrument are mainly used as the main indicators of consistency. Strength The most important mechanical property of concrete after hardening refers to the ability of concrete to resist compression, tension, bending, shear and other stresses. The water-cement ratio, cement variety and dosage, aggregate variety and dosage, as well as mixing, forming and curing all directly affect the strength of concrete.

The strength grade of concrete according to the standard compressive strength (the cube with a side length of 150mm is used as the standard specimen, cured for 28 days under standard curing conditions, and the compressive strength of the cube with a 95% guarantee rate measured according to the standard test method) is called the label, which is divided into C10, C15, C20, C25, etc. The tensile strength of concrete is only 1 13 1 8 of its compressive strength. Improving the ratio of tensile and compressive strength of concrete is an important aspect of concrete modification.

Deformation Concrete will be deformed under load or temperature and humidity, mainly including elastic deformation, plastic deformation, shrinkage and temperature deformation. The elastic deformation of concrete under short-term load is mainly expressed by the elastic modulus. Under the action of long-term load, the phenomenon of constant stress and continuous increase of strain is creep, and the phenomenon of constant strain and continuous decrease of stress is relaxation.

The volumetric deformation due to cement hydration, carbonization of cement stone, and water loss is called shrinkage. The deformation of concrete is divided into two categories, one is the force deformation under the load, such as the deformation of monotonous short-term loading, the deformation under the long-term action of load and the deformation of repeated loading; The other type is not related to force and is called volumetric deformation, such as concrete shrinkage and deformation caused by temperature changes. Durability In general, concrete has good durability.

However, in cold areas, especially in engineering sites where water levels change and when subjected to frequent freeze-thaw alternation in a saturated state, concrete is prone to damage. For this reason, there are certain frost resistance requirements for concrete. When used in impervious works, concrete is required to have good impermeability and corrosion resistance.

Impermeability, frost resistance, and erosion resistance are concrete durability.

See if your sand is solid, or if it's salty.

Condition of raw materials, control methods and strength, construction and maintenance.

<> influencing factors: 1. Aggregate, the size and gradation of aggregate particle size.

The strength, activity, and content of harmful impurities of the aggregate itself.

2. Quantity and quality of cement slurry.

3. The type and content of additives, the brand of retarder, aerated agent, antifreeze, etc., have an obvious impact on the performance of concrete.

4. Mixing machinery, process, time, etc.

5. Transportation, using non-mixer trucks, the transportation distance is too long, and segregation will occur.

6. Construction, vibration time, location, vibration time is too short and not compact; Too long, segregated. The vibrating part is too sparse and the part is not compact.

7. Improper curing, temperature control measures, too fast cooling or too large temperature difference between the inside and outside of the concrete, cracks may occur.

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 main factors affecting the strength of concrete are: (1) cement strength grade and water-glue ratio; (2) the quality, gradation, shape and surface characteristics of the aggregate; (3) the age of the concrete; (4) Curing temperature and humidity; (5) Test conditions, including specimen shape, size, surface condition and loading speed, etc.

Concrete, for short"Concrete (tóng).": Warning is a general term for engineering composite materials that are cemented into a whole by cementitious materials. The word "concrete" usually refers to the use of water to dismantle mud as cementitious materials, and sand and stone as aggregates; Cement concrete, also known as ordinary concrete, is widely used in civil engineering engineering when it is mixed with water (which can contain admixtures and admixtures) in a certain proportion and is mixed to obtain cement concrete.

Concrete is one of the most important materials for civil engineering today. It is an artificial stone made of cementitious materials, granular aggregates (also known as aggregates), water, and admixtures and admixtures added if necessary in a certain proportion, evenly stirred, densely molded, cured and hardened.

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.

This traveler has a wide range of characteristics, not only in various civil engineering applications, but also in shipbuilding, machinery industry, marine development, geothermal engineering, etc., concrete is also an important material.

1. Cement strength and water-cement ratio.

One of the main indicators of concrete quality is the compressive strength, and the main factors affecting the compressive strength of concrete are cement strength and water-cement ratio. When the water-cement ratio is equal, the compressive strength of the concrete prepared by the high-grade cement is much higher than that of the low-grade cement. In the case of the same cement strength, the concrete strength decreases regularly with the increase of the water-cement ratio.

2. Feeding sequence and mixing time.

According to different construction requirements and conditions, concrete can be mixed centrally at the construction site or in a mixing plant. Before mixing, the batching should be according to the requirements of the mix ratio, the weighing error should be controlled, and the feeding sequence and mixing time have an impact on the quality of concrete, which should be strictly mastered to make the components of the materials mixed evenly.

3. The influence of temperature.

The temperature has a certain influence on the development of concrete strength. 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 transportation and pouring time, prevent exposure to the sun, and increase the slump of the mixture when it comes out of the tank. 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.

The factors affecting the strength of concrete are mainly related to cement grade and water-cement ratio, aggregate, age, curing temperature and humidity.

1. Water-cement ratio.

The compressive strength of concrete is directly proportional to the strength of concrete water cement, according to the formula, when the water-cement ratio is equal, the compressive strength of concrete prepared by high-grade cement is much higher than that of low-grade cement.

Therefore, do not use the wrong cement number when constructing concrete.

In addition, the water-cement ratio is also proportional to the strength of concrete, and the water-cement ratio is large, and the concrete strength is high; The water-cement ratio is small, and the concrete strength is low, therefore, when the water-cement ratio is unchanged, it is wrong to try to increase the cement amount to improve the strength of warm concrete, and only the workability of concrete can be increased at this time, and the shrinkage and deformation of concrete can be increased.

Therefore, the main factor affecting the compressive strength of concrete is the cement strength and water-cement ratio, to control the quality of concrete, the most important thing is to control the water-cement ratio of cement and concrete.

In addition, there are other factors that cannot be ignored that affect the strength of concrete.

2. The influence of coarse aggregates.

Coarse aggregate also has a certain effect on the strength of concrete.

When the stone strength is equal, it is determined by the surface roughness of the aggregate.

For example, the surface of gravel is rougher than that of pebbles, and the adhesion between it and cement mortar is greater than that of pebbles; When the water-cement ratio is equal or the mix ratio is the same, the concrete strength of the concrete prepared by the two materials is stronger than that of pebbles.

Generally, the coarse aggregate of concrete is controlled around the left.

The quality of the sand also has a certain effect on the strength of the concrete.

If the sand has a large mud content and contains a certain amount of harmful impurities, it will also reduce the strength of the concrete.

Therefore, clear sand is usually used in construction.

3. The influence of age.

Under normal curing conditions, the strength of concrete will increase with the increase of age, and the strength will increase rapidly within 7 14 days at first, and slowly after 28 days.

4. The influence of temperature.

Temperature has a great impact on the quality of concrete, and generally concrete should be cured between 18-23 degrees.

The higher the temperature, the faster the strength of the concrete rises, and vice versa.

At -5 degrees, the concrete pouring work must be stopped, and measures must be taken if the concrete pouring continues.

1) Water consumption.

The amount of water consumption is the decisive factor affecting the workability of fresh concrete.

2) Cement. In order for the concrete mixture to flow under its own weight or external vibration force, it must overcome its internal resistance. The internal resistance of the mixture mainly comes from two aspects, one is the friction resistance between the aggregates, and the other is the cohesion of the cement slurry.

3) Aggregates. Aggregate has a great influence on the workability of new belt slow-mix concrete. In the case of a certain amount of concrete aggregate, the fluidity of the concrete mixture mixed with pebbles and river sand is better than that mixed with Kaifu gravel and mountain sand.

This is because the former aggregate has a smooth surface and low frictional resistance, while the latter aggregate has relatively large frictional resistance. The quality of aggregate gradation also affects the workability of the concrete mixture.

The sand rate also has a significant effect on the workability of the concrete mixture.

4) The influence of the storage time and ambient temperature of the mixture.

The concrete mixture will become more and more dry and thick with time, because part of the moisture in the mixture is evaporated, and the other part is consumed by the hydration of cement, so the mixture gradually loses its plasticity and solidifies. Concrete workability is also affected by temperature. As the ambient temperature increases, the workability of the concrete decreases quickly, because the water evaporates and the chemical reaction of the cement proceeds faster.

What are the main factors that affect the strength of concrete? As a non-construction worker, you may not know much about this. But don't worry, let me introduce you to the relevant knowledge of concrete.

What are the main factors that affect the strength of concrete.

1. Curing temperature and humidity: within 20, the lower the curing temperature, the lower the compressive resistance of concrete, but within 20 to 30, the curing temperature has little impact on the compressive resistance of concrete, the curing humidity is high, and the compressive resistance of concrete is also high; 2. Age: Under normal maintenance, the strength will be extended due to the increase of age, and the age will last for a long time, and the strength of concrete will still increase.

The strength grades of concrete are divided into several grades.

There are a total of 14 levels.

According to the relevant requirements, the compressive resistance of the concrete cube is a cube specimen of a standard size with a side length of 150 mm made according to the specification, the same temperature as the ISO test method is 20 degrees Celsius, the humidity is more than 95% of the standard curing room, and the compressive resistance of the concrete cube is measured according to the standard test method.

According to the relevant requirements, the strength grade of building materials should be expressed according to the material name + strength value. For this reason, the concrete strength grade is divided into C10, C20, C30, C40, C50, C55, C60, C70 and C80 according to the mark C and the compressive value.

1. C20 concrete mix ratio.

Conditions: Slump 35 to 50 mm.

Sand: Coarse sand.

Intensity: MPa.

Stones: River stones.

Maximum particle size: mm.

Cement strength grade: , real strength megapascals.

Among them, per m of concrete, there are 326 kg of cement, 598 kg of sand, and 1332 kg of crushed stone.

2. C25 concrete mix ratio.

Conditions: Slump 35 to 50 mm.

Sand: Coarse sand.

Intensity: MPa.

Pebbles: River stones (or pebbles).

Maximum particle size: mm.

Cement strength grade: , real strength megapascals.

Among them, per m of concrete, there are 370 kg of cement, 549 kg of sand, and 1,344 kg of crushed stone.