How to control the moisture content of concrete aggregate

Controlling the moisture content of concrete aggregate in the production process of mixer is a very important link, and too high or too low moisture content will seriously affect the quality of aggregate. The premise of controlling the moisture content of aggregate is to detect the moisture content of aggregate first. MS-590 microwave moisture meter, can achieve high precision and high accuracy of the need to measure sand moisture, by installing into the actual production environment for the first test, can achieve accurate monitoring of the precision and accuracy of each batch of sand moisture, and can achieve real-time transmission of data and digital communication.

At the same time, it can also be used to measure concrete and directly measure the water content. Can be installed in a concrete mixer.

1. At present, the national standard "Design Code for Ordinary Concrete Mix (JGJ55-2011)" stipulates the water content of aggregate in the design of concrete mix as follows

The national requirement theoretically requires the aggregate to be in a dry state, and it has been used.

2. The design basis of concrete mix ratio: "Design Regulations for Ordinary Concrete Mixture" (JGJ 55 2011), "Code for Construction and Acceptance of Concrete Structure Engineering" (GB 50204 2002), "Concrete Quality Control Standards" (GB 50164 92), "Test Methods for Ordinary Concrete Mixture Properties" (GB T 50080 2002), "Test Methods for Mechanical Properties of Ordinary Concrete" (GB T 50081 2002), " Concrete strength inspection and evaluation standards (GB T 50107 2010) and sand, stone, admixtures, admixtures related standards.

3. The concrete mix design process is generally divided into four stages: preliminary mix calculation, benchmark mix ratio determination, experimental mix ratio determination and construction mix ratio determination. Through this series of work, the optimal mix ratio of each component of the concrete is selected.

1. Design requirements and materials.

1. Design requirements: C30 cushion cap concrete, using pumping construction, slump 120mm 160mm.

2. Materials: Huaxin cement, FCE=; Coarse aggregate: using Hubei Yangxin 5 25mm and 25 two kinds of gravel to match, composing 5 continuous graded gravel, according to 5 25mm:

25:2 (weight ratio) ratio; Fine aggregate: medium sand in Xishuiba River area, mx=; External admixture:

Wuhan Qingyuan grade fly ash; Admixture: Shanxi Wupeng WP retarding high-efficiency superplasticizer.

2. Calculation. 1、fcu,0=fcu+。

2、w/c=aa×fce/(fcu,o+aa×ab×fce)=

3. According to the construction requirements, the design slump of concrete is 120mm 160mm, the unit water consumption is 215kg, and the water reduction rate is δ=22% with the addition of retarding high-efficiency superplasticizer, then the concrete unit water consumption: MW0 = MW (1-δ) = 215 (1-22%) = 168kg.

4. Unit cement consumption: mc=mwo w c=168

5. For cement replaced with fly ash, the substitution coefficient is =, then there is.

Cement dosage: mc0 = mc ( kg.

Fly ash dosage: MF0 = MC.

Dosage of superplasticizer: MFDN0=(MC0+ MF0) kg.

6. Assuming that the unit bulk density of concrete MCP=2400kg m and the sand rate s=40%, there are:

mc0+ mf0+ ms0+ mg0+ mw0= mcp

mso/(mso+mgo) ×100%=βs

obtained: fine aggregate MS0 = 757kg, coarse aggregate MG0 = 1136kg.

Then the concrete mix ratio: mc0: ms0: mg0: mf0: mfdn0: mw0=:168

3. According to the regulations, if the water-cement ratio is reduced compared with the benchmark water-cement ratio, the water-cement ratio w c =

1. Unit cement consumption.

mc=mwo/w/c=168/

2. For cement replaced with fly ash, the substitution coefficient is =, then there is.

Cement dosage: mc1 = mc ( kg.

Fly ash dosage: MF1 = MC.

Dosage of superplasticizer: MFDn1=(MC1+ MF1) kg.

3. Assuming that the unit bulk density of concrete MCP=2400kg m, and the sand rate s=39%, there are:

Fine aggregate MS1 = 730kg, coarse aggregate MG1 = 1142kg.

Then the concrete mix ratio: mc1: ms1: mg1: mf1: mfdn1: mw0=:168

1. JGJ55-2011 "Ordinary Concrete Mix Ratio Design", the above table on page 13, because it is now all large-fluidity concrete, so the water consumption of plastic concrete in the old castle is selected for the table field.

2. The water consumption should be determined according to: coarse aggregate type and particle size, slump or vib consistency, and sand type.

Refer to GJ55-2011 "Design of Ordinary Concrete Mix Ratio", the above table on page 13, determined by experience.

3. The unit water consumption in the concrete mix ratio is mainly selected based on experience.

Refer to JGJ55-2011 "Design of Ordinary Concrete Mix Ratio".

4. The mix ratio design should be based on the aggregate in the dry state, the moisture content of the fine aggregate should be less than that of the coarse aggregate.

For reference, see the "Code for the Design of Ordinary Concrete Mixture" JGJ 55-2011, which stipulates.

Theoretically, this is feasible, and a part of the water in the pores of the aggregate will not participate in the hydration reaction, that is, the upper limit of the moisture content set by the above clause.

yes, hee-hee-hee-hee.

For example, the theoretical water content of each square concrete is 185kg, the sand moisture content of the stone is 1% (the theoretical design is 1000kg per side) and the construction mix ratio is converted into the construction mix ratio, that is, the sand is 700+700*5%%=700+35=735kg

Stone 1000 + 1000 * 1% = 1010kg water = 185-35-10 = 145kg After calculation, the bulk density of the theoretical mix ratio = the construction mix ratio.

So if the moisture content is not accurate, either more sand and gravel or less water. Or the opposite. Trigger concrete performance.

The water content of the aggregate has saturated surface dry and natural water content, and the measured water content refers to the natural water content. Saturated water content = natural water content - water absorption of the material.

Saturated water content, natural water content, the moisture content of the aggregate also has a great impact on the concrete pouring, how the aggregate has a large water content, the water content of the aggregate should be subtracted from the water consumption in the mix ratio, in order to ensure the workability of the concrete.

Hello, the current national standard "Ordinary Concrete Mix Design Regulations (JGJ55-2011)" in the concrete mix design of aggregate water content to make provisions: 1. The concrete mix design should meet the design requirements of concrete preparation strength, mixture properties, mechanical properties and durability. The test methods for the properties, mechanical properties and durability of concrete mixtures shall conform to the provisions of the current national standards "Standard for Test Methods for the Performance of Ordinary Concrete Mixtures" GB T50080, "Test Methods for Mechanical Properties of Ordinary Concrete" GB T50081 and "Standard for Test Methods for Long-term Performance and Durability of Ordinary Concrete" GB T50082.

2. The concrete mix design should use the raw materials actually used in the project, and should meet the relevant requirements of the current national standards; The mix ratio design should be based on the dry aggregate, the moisture content of fine aggregate should be less than that of coarse aggregate. Hope it helps.

Summary. When the concrete slump is large, is it to increase the moisture content of the aggregate or reduce the moisture content of the aggregate: the greater the collapse of the concrete, the larger the moisture content of the concrete, the smaller the aggregate, so the greater the shrinkage!

Concrete will always be slightly expanded and deformed in water, and will always shrink and deform in air, so the larger the water-cement ratio in the condensation process of concrete, the greater the shrinkage; Large water secretion, high surface water content, and large early surface shrinkage; The higher the moisture content of concrete, the greater the amount of cement slurry, the greater the slump, and the greater the shrinkage. The smaller the aggregate particle size, the higher the sand rate, and the smaller the particle diameter of the concrete concrete condensed aggregate in the later stage, the greater the shrinkage!

When the concrete slump is large, is it to increase the moisture content of aggregate or reduce the moisture content of aggregate?

When the concrete slump is large, is it to improve the water content of aggregate or reduce the moisture content of aggregate: the greater the concrete slump, the larger the moisture content of the concrete, the smaller the aggregate, so the greater the shrinkage! Concrete will always be slightly expanded and deformed in water, and will always shrink and deform in air, so in the process of condensation, the larger the water-type laugh-ash ratio, the greater the shrinkage; Large water secretion, high surface water content, and large early surface shrinkage; The higher the moisture content of concrete, the greater the amount of cement slurry, the greater the slump, and the greater the shrinkage. The smaller the aggregate particle size, the higher the sand rate, and the smaller the diameter of the concrete concrete condensed aggregate in the later stage, the greater the shrinkage!

1. After the concrete collapse is too large, the ability of the slurry to wrap the aggregate will definitely decrease, and the aggregate will sink and the slurry will float to form a segregation phenomenon. The main reason for this phenomenon is that the amount of water (admixture) is too large, which can be solved by reducing the amount of water or admixture. 2. The sand rate is not suitable.

The total amount of sand and gravel is unreasonable, more or less will lead to the phenomenon of segregation concrete: cement, sand, stone, water have a fixed proportion, if it is mixed in accordance with the specified proportion, it may be caused by the large water content of sand and stone. Because in a given ratio of cement, sand, stone, and water, sand and stone both refer to those that do not contain water.

Concrete, also known as concrete, its proportion is: a, with 325 cement, particle size 5 40mm stone, medium sand preparation site mixing boy to do the year pouring C15 concrete: water 202kg, cement 331kg, sand 639kg, stone with 325 cement, particle size 5 40mm stone, sand preparation of on-site mixing and pouring C20 concrete:

203kg of water, 390kg of cement, 585kg of sand, Shizi Huqing used No. 425 cement, 5 40mm stone with particle size, and medium sand to prepare C30 concrete mixed and poured on site: 204kg of water, 434kg of cement, 583kg of sand, and 1254kg of stone.

Concrete aggregate is generally produced by wet process, that is, a large amount of water is used to wash the aggregate with manufactured sand during the production process. The moisture content of the newly produced finished sand is about 12% to 15%%, and too much free water needs to be removed. The new specification has greatly increased the content of stone powder and fine particles, resulting in a huge change in the difficulty of dewatering fine aggregates.

In order to reduce the moisture content to the specified range and be stable, a combination of mechanical dewatering and natural dehydration is adopted.

Natural dehydration: At present, the method and process of natural dehydration of domestic hydropower projects are artificial sand cutting, stacking dehydration and artificial sand extraction are carried out separately, and the water content can be reduced to less than 6 and stable after 3 5 days of storage dehydration. By the artificial sand and gravel powder content and the initial moisture content is different, the general stone powder content is in the range of 10 17, the initial moisture content of the sand is 15 17, the initial dehydration rate is fast within about 48 hours, the moisture content can generally be reduced to 8 10, when the moisture content is reduced to 8 10, and then reduced to about 6 The dehydration rate is significantly slowed down, and it generally takes 3 5d time.

According to the daily production of 1 50,000 tons of finished sand and the daily consumption of 1 50,000 tons of sand, the finished sand silo is stored for 50,000 m, and the natural dehydration time is about 5 days.

Mechanical dehydration: At present, the methods and processes used for artificial sand dehydration in domestic hydropower projects mainly include screening dehydration, vacuum dehydration, centrifugal dehydration, etc., among which vacuum dehydration and centrifugal dehydration have good effects, but the treatment capacity is low and the investment is high; The screening and dehydration are all dehydrated by vibrating screen, which has high dehydration treatment capacity, but the dehydration effect is poor. Due to the high production capacity of artificial sand, and the installation of dewatering screen is the production and processing system has been put into operation after the increase, by the site layout and other reasons, finally, choose to use linear vibrating screen dewatering, installation linear vibrating screen, after the test can make the moisture content of the sand from about 25 to about 15 in the initial stage.

The water content of the aggregate is difficult to control, and the water content of the upper, middle and lower parts of the pile is different, and the shady and sunny sides are also different. Moisture content tests cannot be representative, and they are deceptive.