What is the working meaning of the concrete mixture, and what are the influencing factors

Workability refers to the fact that the concrete mixture is easy to operate (mixing, transporting, pouring, tamping) and can obtain uniform quality and dense forming, also known as workability. Workability is a comprehensive technical property that includes three meanings: fluidity, cohesion and water retention. Fluidity refers to the performance of the concrete mixture under the action of self-weight or mechanical vibration, which can produce flow and evenly and densely fill the formwork; Cohesiveness refers to the performance that there is a certain degree of cohesion between the constituent materials of the concrete mixture, and no delamination and segregation will occur during the construction process; Water retention refers to the performance of concrete mixture that has a certain water retention capacity and will not cause serious water leakage during construction.

Slump tests are often used on construction sites to determine the slump or slump expansion of concrete mixtures as a flow index. The greater the slump or slump expansion, the greater the liquidity. For the dry and hard concrete mixture with a slump value of less than 10mm, the consistency of the mixture was determined by the Viber consistency test as the fluidity index.

The higher the consistency value, the less flowable. The cohesion and water retention of concrete mixtures are mainly evaluated by visual inspection and experience.

The main factors affecting the workability of concrete mixtures include water consumption per unit volume, sand rate, properties of constituent materials, time and temperature, etc. The water consumption per unit volume determines the quantity and consistency of cement slurry, which is the most important factor affecting the workability of concrete. The sand rate refers to the percentage of the mass of sand in concrete to the total mass of sand and stone.

The properties of the constituent materials include the water demand and water secretion of cement, the characteristics of aggregates, the characteristics of admixtures and admixtures, etc. In 2011, he was awarded the examination center of "Construction Engineering Management and Practice" for first-class constructors.

The workability of concrete is the ability to facilitate construction and form a uniform and dense structure.

Because the mixture after concrete water is added to the process of transportation, mixing, pouring, vibration and other processes, if the workability is not good, the mold can not be injected, the segregation is stratified, and the water leakage will directly lead to unqualified strength and durability. Therefore, it is necessary to stipulate the nature of work.

Workability, also known as workability, includes fluidity (the ability to fill the mold), cohesion (no segregation and delamination) and water retention (no water leakage).

Influencing factors: 1. Cement: The type and fineness of cement are affected. Fly ash cement is better, silica water is second, pozzolane cement is viscous, and slag cement is easy to leak water. The finer the fineness, the poor fluidity, the better the cohesion and water retention.

2 units of water consumption. There is a lot of water and good fluidity, but it is easy to stratify, and the water retention of cohesion becomes poor. The principle of fixed water quantity, in the case of fixing the type of coarse aggregate and the maximum particle size, the water consumption is fixed, the sand changes slightly, the cement plus or minus 50 kg, and the workability is generally unchanged.

3. Sand rate. That is, the mass ratio of sand to aggregate. The cement slurry is certain, there is the best sand rate, and the workability is the best at this time.

The sand rate is too large, the sand is too much, and the cement slurry is used to wrap the surface of the sand in large quantities, and the fluidity is small; The sand rate is too small, and the cement slurry needs to fill a large number of stone voids, and the workability is not good.

4. Construction conditions. Whether the stirring vibrate is sufficient.

5. Admixtures. Water reducers, air-entraining agents can improve workability.

Answer] :d Qingsanhong workability of fresh mixed bridge concrete, also known as workability, refers to the comprehensive properties of concrete in terms of fluidity, plasticity, stability and easy density.

The factors affecting the workability of concrete mixtures are: mixture ratio, water-cement ratio, use of mineral admixture, mixing time and speed, etc.

1. Mixture ratio: Mixture ratio refers to the proportion and mixing method of cement, fly ash, sand, gravel and other raw materials. The mix ratio has a great impact on the performance and workability of concrete, and different mix ratios will affect the strength, compactness, crack resistance, etc. of concrete.

2. Water-cement ratio: The water-cement ratio refers to the ratio of water and cement in the mixture. The larger the water-cement ratio, the better the fluidity of the concrete, but it will affect the strength and durability of the concrete.

Therefore, the water-cement ratio needs to be controlled so that it does not affect the strength and durability of the concrete without compromising workability.

3. The use of mineral admixtures: Mineral admixtures refer to materials that are mixed with mineral powder or slag to replace part of cement. The use of appropriate mineral admixtures can improve the crack resistance, durability and durability of concrete, and at the same time, it can also reduce the heat generation and shrinkage of concrete soil.

4. Mixing time and speed: The mixing time and speed of concrete will affect the workability, quality and strength of the concrete head soil, so it is necessary to choose the appropriate mixing time and speed to ensure the quality and workability of the concrete.

5. Construction time and temperature: The hydration reaction of concrete at different temperatures will produce different rates, so it is necessary to control the mixing, formwork and curing of concrete according to the local temperature and construction time to ensure the quality and workability of concrete.

Concrete mixture use

1. Roads and bridges: Concrete can be used in roads, bridges, tunnels, underground garages and other public works, and can be used to make concrete pavement, cement standard bricks, cement pipes, cement manhole covers, etc., with good load-bearing, durability and wear resistance.

2. Water conservancy engineering: concrete can be used in water conservancy projects, such as the construction of dams, rivers, channels, reservoirs, sluices, etc., with good water resistance and impermeability.

3. Pipes and pipelines: Concrete can be used to make pipes and pipelines, such as drainage pipes, oil pipelines, ventilation pipes, cable pipes, ordinary gas pipes, water pipes, sewage treatment pipes, etc., with strong bearing capacity and durability.

4. Decoration: Concrete can also be used for indoor and outdoor decoration, such as concrete floors, walls, decorative columns, railings, flower pots, sculptures, etc., with unique texture and aesthetics.

Concrete mixtures are very versatile and can be applied in construction, roads, water conservancy, pipelines, decoration, and other fields, so the quality and performance of concrete are crucial for various fields.

Answers]: a, c, e

If the sand rate is too small and the mortar is insufficient, the fluidity of the mixture will be increased", the sand rate is too small, the amount of mortar is insufficient, and sufficient mortar lubrication layer cannot be formed around the stone, which will reduce the fluidity of the mixture; "When the water glue is smaller, the cement slurry is thicker, the mixture has better cohesion, less water secretion, and greater fluidity", when the water glue is smaller, the cement slurry is thicker, the cohesive potato pie of the mixture is better, the water secretion is less, but the fluidity is smaller.

Answers]: a, b, c, d

The main factors affecting the workability of concrete falls include water consumption per unit of cryptophonic volume, potato cracking, sand rate, properties of constituent materials, time and temperature, etc. The properties of the constituent materials include the water demand and water permeability of cement, the characteristics of aggregates, admixtures and the characteristics of mixed stove materials.

1. The quantity of cement slurry: to meet the fluidity, it should not be excessive. In the case of the same water-cement ratio, if there is more cement slurry, the greater the fluidity of the mixture. However, if there is too much cement slurry, the cohesion of the mixture will be poor.

2. Cement slurry consistency (water-cement ratio): The mass ratio of water to cement is called water-cement ratio (W C). The water-cement ratio should not be too large or too small. If the water-cement ratio is too small, the fluidity of the concrete mixture is too small, which will make the construction difficult and cannot ensure the compactness of the concrete; Losers.

When the water-cement ratio is too large, it will cause poor cohesion and water retention of the concrete mixture. Whether it is the amount of water or slurry, or the consistency of the cement slurry, it is actually the amount of water used that determines the fluidity of the concrete mixture.

3. Sand rate: Sand rate refers to the mass percentage of sand dosage and the total amount of sand and stone. The sand rate should not be too large or too small, and there is a reasonable sand rate.

When the sand rate is too large, the total surface area of the aggregate increases, the cement slurry layer that wraps the aggregate becomes thinner, and the fluidity of the mixture decreases. If the sand rate is too small, the cohesiveness and water retention of the mixture will deteriorate, resulting in segregation and slurry.

Factors affecting the reasonable sand rate: the maximum particle size and gradation of stones, the fineness modulus of sand, the water-cement ratio, the fluidity requirements, admixtures, etc. During construction, a small sand rate should be selected as much as possible to save cement.

4. Cement varieties and aggregate properties:

Cement: The influence of cement on workability is mainly manifested in the water demand of cement. Concrete mixed with different cements, its workability is in descending order:

Fly ash cement - ordinary cement, Portland cement - slag cement (high fluidity, but poor cohesion) - pozzolane cement (poor fluidity, but good cohesion and water retention).

In terms of aggregates: the larger the maximum particle size of the aggregate, the smaller the total specific surface area, and the greater the fluidity of the mixture; Pebbles are more fluid than crushed stone.

5. Admixture: The admixture can make the concrete mixture obtain good workability without increasing the amount of cement. Not only does the fluidity increase significantly, but it also effectively improves the cohesion and water retention of the mixture.

6. Time and temperature: When the ambient temperature increases, the water evaporation and hydration reaction accelerates, and the corresponding slump decreases. The longer it is left for stirring, the more the water will steam, and the slump will decrease.