Air-entraining effect and influence of Cellulose ether admixture on dry-mixed mortar

Air-entraining effect and influence of Cellulose ether admixture on dry-mixed mortar

The air-entraining effect and influence of cellulose ether admixture on dry-mixed mortar were systematically analyzed. 

Incorporating the formulated cellulose ether compound admixture into In the case of water retention and thickening, the air content of dry-mixed mortar is changed by changing the amount of admixture and the amount of water-reducing agent.

The basic performance of the item changes with the air volume of the mortar. Through the comprehensive comparison of various properties, the optimum value of air content of dry-mixed mortar is obtained.

Key words: air content; dry-mixed mortar; cellulose ether; admixture; mortar strength

Construction mortar is a large amount and wide application in construction engineering.

Pan building materials, commercial mortar is the development of the construction industry to a certain stage

It is an inevitable product of protecting the environment, effectively utilizing and saving resources

important national policy. Dry-mixed mortar is an important product in commercial mortar.

However, in the process of promotion and use of dry-mixed mortar, many technical

technical problems, among which the air content in ordinary (masonry, plastering) dry-mixed mortar

The index not only affects the workability of the mortar, but also affects the impermeability,

Strength, adhesion and other properties, especially for waterproof mortar.

Since dry-mixed mortar has high requirements on workability, it must be

Additives are added to improve its performance. At present, water retention at home and abroad

Thickening admixtures are mainly cellulose ethers, cellulose ether admixtures

Can increase workability, adhesion, improve water retention, reduce delamination, improve

High impermeability and frost resistance as well as crack resistance, make the mortar after construction

In the process of saving materials, it has been widely used in many cities in my country.

However, because cellulose ether admixtures have a certain air-entraining effect, usually

Will increase the air content of the mortar. Appropriately increasing the air content of the mortar can increase the

Workability and constructability of adding mortar, improve the impermeability and frost resistance of mortar

performance, heat preservation and some other properties, but if the added amount is not suitable, the

If the air content is too large, there will be more large-diameter air bubbles in the mortar, which will cause

Reduce compressive strength, impermeability pressure, bond strength of mortar and increase sand

shrinkage of pulp. Therefore, how to determine the appropriate amount of dry mix mortar

Admixtures and controlling the appropriate gas content are a technology that needs to be solved urgently.

technical problem. In this paper, through a large number of comparisons and analysis of mortars with different gas content

A comprehensive comparison of performance in all aspects, taking plastering mortar as an example, puts forward

The suitable range of air content and admixture content of dry-mixed mortar. 1 Test method

Mortar Consistency Test

Mortar stratification test

Determining method for determining the degree of mortar stratification. water retention test

Refer to Sichuan Province's "Premixed Mortar

Test method for water retention of mortar in Technical Regulations for Production and Application. according to

The regulations require that the water retention rate of dry-mixed mortar should be greater than or equal to 88%. Mortar density test

Mortar gas content test

Refer to Guangdong Province's "Dry Mixed Mortar Application

Use the test method for gas content of mortar specified in the Technical Regulations. Cube compressive strength test specified in

The test is carried out. Mortar Impermeability Pressure Test

According to the sand specified in Guangdong DBJ/T15-36-2004

The mortar impermeability pressure test method is used to determine the impermeability pressure of mortar for 14 days. Mortar Shrinkage Test

Tensile bond strength

. 2 Variation of properties of dry-mixed mortar with gas content

Analysis 2. 1 Analysis of dry-mixed mortar stratification with the change of air content of mortar

The admixture used in dry-mix mortar is a compound with other components

Admixture, its main air-entraining component is cellulose ether, while water reducing agent and

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The compound also has a certain air-entraining effect. Therefore, this paper analyzes the

Do not change the amount of cellulose ether and water reducer in the mortar admixture to adjust

Air content (B1) of the whole dry-mixed mortar, compared with the standard mortar without admixtures

( B0 ) Do a comparative analysis of various performances including gas content.

Through the air content, stratification, water retention rate, coagulation of dry-mixed mortar

time, density, compressive strength, shrinkage, impermeability pressure and bond strength

Comparative analysis of performance in terms of

The effect of air volume on its performance in various aspects.

The degree of stratification is suitable for determining the mortar mixture during transportation and parking

The stability of the internal components, it is the current domestic standard to characterize the mortar

One of the key indicators of water retention, workability and workability,

Add cellulose ethers to dry mixed mortar to increase water retention

After the thickening agent, as the air content of the mortar increases, its stratification degree decreases obviously

low, the work stability and water retention performance are significantly improved, making the mortar

It is not easy to delaminate and bleed during transportation, which improves the dry mix mortar

construction performance. When the air content of dry-mixed mortar is greater than 9%, its

Delamination is less than 20 mm. Therefore, considering the stratification index, the dry

The air content of the mixed mortar should be greater than 9%. Variation trend of dry-mixed mortar stratification with gas content of mortar

2. 2 Analysis of the change of water retention rate of dry-mixed mortar with the gas content of mortar

Mortar water retention rate is suitable for determining the amount of water in freshly mixed mortar mixtures.

The ability of combined water to absorb or evaporate into the air on the base surface. Mortar water retention

Performance is an important indicator of dry-mix mortar, especially for dry-mix plastering

For mortar, better water retention can make the mortar easy to construct.

During the process, it is easy to scrape down, obtain a flat surface, and ensure that the cement hydration

Moisture is required to effectively prevent the mortar from being caused by water loss after the construction is completed.

Empty drum, cracking, falling off and low strength. On the one hand it can make the mortar

good bond between concrete slabs, on the other hand

Fully hydrate the cement. Regarding the method for determining the water retention of mortar, the water retention performance is characterized by the stratification index.

The method is not easy to operate due to the large error in the actual test.

Accurately reflect the water retention of the mortar. use

Water retention rate to characterize the water retention of mortar. In this way, the stratification and water retention rate are used

Two indicators to comprehensively measure the water retention performance of dry-mixed mortar, we can get

to a more precise conclusion. After incorporating a water-retaining thickener, the building

Whether the mortar is viewed from the stratification index or the water retention index

It can be seen that the water retention performance has been greatly improved.

The layer should be less than 2.0 cm, plastered

The water retention rate of the mortar should not be less than 88%.

After adding the admixture, the water retention rate of the dry-mixed mortar increases with the air content of the mortar.

The increase is obviously improved. In order to meet the requirement of water retention of mortar ≥ 88%, dry

The air content of the powder mortar is not less than 3%. Variation trend of water retention rate of dry-mixed mortar with gas content of mortar

The two water retention indicators were compared,

Changes in water retention properties of mortar reflected by two indicators

Basically the same. For the water-retaining thickeners used, the results show

The index requirements of stratification are more stringent than the water retention rate, and the

More restrictions come. 2. 3 Analysis of the change of the setting time of dry-mixed mortar with the gas content of the mortar

Because the main component of the water-retaining thickener admixture used is fiber

The plain ether is a non-ionic hydroxy cellulose ether, which has a certain retarding effect.

answer. Therefore, with the increase of cellulose ether content in the admixture, the dry-mixed sand

The pulp setting time increases accordingly. therefore,                                                                    

       mortar

Condensation time varies with gas content actually has no direct

The relationship is caused by the retarding effect of cellulose ether, and the setting time of dry mortar should be

The demand is determined by the negotiation between the supply and demand sides, generally more than 8 hours. 2. 4 Analysis of the change of dry-mixed mortar density with the gas content of the mortar

Density test for dry-mix mortars for determination of tamping of mortar mixtures

After the mass density to determine each group of mortar mixtures per cubic meter

the actual amount of the material. When the mortar is mixed with air-entraining admixtures,

A large number of tiny air bubbles will be introduced into the mortar, making the interior of the mortar void

The rate is greatly increased, thereby reducing the compactness of the mortar and reducing the density of the mortar.

249 2012 No. 3 Li Han, et al: Air-entraining effect and influence of composite admixtures on dry-mixed mortar

Variation trend of dry-mixed mortar setting time with gas content of mortar

Therefore, the density of dry-mixed mortar increases with the air content of dry-mixed mortar.

increase and decrease. This lowering relationship

almost become linear, which is a function of the mortar density in many experiments

Qualitatively compare the reasons for the air content of the mortar. JGJ70-90 stipulates that sand

The density of the slurry shall not be lower than 1800 kg/m3. From this point of view, the dry-mixed sand

The air content of pulp shall not be higher than 20%.

2. 5 The 7-day compressive strength of dry-mixed mortar varies with the air content of the mortar

analyze

The increase in the air content of the mortar will introduce a large number of large pores inside the mortar

Diameter harmful air bubbles, reducing the compactness of the mortar and thus reducing the resistance of the mortar

compressive strength. When the air content of the mortar is small,

As the air content of dry-mix mortar increases, its 7-day compressive strength slightly

improve. This aspect is due to the air content of the dry-mixed mortar in the mix ratio.

The small increase is caused by the small air entrainment effect of the superplasticizer, and at the same time

The 7-day compressive strength of the mortar due to the water reducing effect of the water reducing agent

Slightly increased; on the other hand, when the air content of the mortar is controlled in a lower range

When inside, the admixture introduces some small bubbles, these microscopic

Small air bubbles are not harmful air bubbles, their introduction is beneficial to increase the sand

The elastic modulus of the mortar is slightly improved, and the compressive strength of the mortar is slightly improved.

It can also play a role in thermal insulation. In order to make the air-containing dry mix mortar

The amount will not cause a significant decrease in its compressive strength, dry-mixed mortar

The gas content should not be higher than 10%. Variation trend of 7-day compressive strength of dry-mixed mortar with air content of mortar

2. 6 The 28-day compressive strength of dry-mixed mortar varies with the air content of the mortar

analysis

Since the admixture of dry-mixed mortar contains a large amount of mineral powder (about

4% of the total mass of mortar solids), its pozzolanic effect on dry-mix mortar

The late strength has a significant improvement effect. Therefore, the mortar containing

28-day compressive strength of dry-mix mortar with admixture at low air volume

The degree is significantly higher than the benchmark mortar. As the air content of dry-mixed mortar increases

Plus, a large number of large-diameter harmful pores are continuously introduced into the mortar, and the sand

The density of the grout is greatly reduced, resulting in a significant 28-day compressive strength of the mortar

reduce. Variation trend of 28-day compressive strength of dry-mixed mortar with air content of mortar

2. 7 The 56-day shrinkage rate of dry-mixed mortar varies with the air content of the mortar

analyze

An important factor affecting the durability of dry-mixed mortar is the cracks in it.

sew. There are many reasons for cracks, drying shrinkage is one of the important reasons

one. As the air content of dry-mixed mortar increases

Plus, the shrinkage rate of the mortar is significantly increased, which is due to the increase in the air content.

The various voids inside the mortar are greatly increased, so that the mortar is

Greater volume shrinkage occurs during drying. Shanghai, Beijing, Sichuan

The local dry-mixed mortar technical regulations stipulate that the dry-mixed mortar shrinkage rate

It should not be greater than 5‰, the smaller the mortar shrinkage, the better, so the dry-mixed mortar

The gas content should not be too large. The 56-day shrinkage rate of dry-mixed mortar varies with the air content of the mortar

2. 8 Analysis of the change of the impermeability pressure of dry-mixed mortar with the gas content of the mortar

Many studies have shown that a modest increase in

The air content of the mortar can introduce an appropriate amount of fine particles into the mortar.

Uniform and independent but not interconnected air bubbles, effectively cut off the hair in the mortar

Fine pore channels prevent the penetration of moisture, thereby enhancing the impermeability of the mortar

can. However, if too much air content is introduced, it will cause the mortar

The drop in impermeability, as evidenced by the results reflected in Figure 8,

When the air content of dry-mixed mortar is about 3%, the impermeability of mortar

the highest point possible. But when the air content of dry-mixed mortar is higher than

At 10%, the impermeability of the mortar drops sharply, mainly because

Introduce too many harmful pores with large pore size, it is difficult to completely close, it

They form interconnected voids with each other. The impermeability pressure of dry-mixed mortar shall not be lower than

0.4 MPa, the author concluded that the air content of the dry-mixed mortar should not be higher than 10%. Variation trend of anti-seepage pressure of dry-mixed mortar with gas content of mortar

2. 9 Analysis of the change of the bond strength of dry-mixed mortar with the gas content of the mortar

It is a dry-mixed mortar that is mixed with cellulose ether compound admixtures.

28-day bond tensile strength as a function of mortar air content.

After adding cellulose ether compound admixture to the mortar,

Conducive to the improvement of bond tensile strength up to 30%

above. However, the bond strength of dry-mixed mortar varies with the air content of the mortar.

But there are no rules. Generally speaking, the compressive strength of cement mortar

The higher it is, the higher its bond strength with other materials, and the study shows

The compressive strength of dry-mixed mortar basically decreases with the increase of air content.

low, especially when the gas content is higher.

The conclusion should be that with the increase of air content, the dry mix mortar

The bond strength is reduced, when in fact the result obtained is not the same.

After adding cellulose ether admixtures into the mortar, the cement at the interface

The hydration of

And improve the bond strength of dry-mixed mortar and base surface. Cement water at the interface

The effect of the increase of the chemical on the improvement of the bond strength and the improvement of the air content of the mortar

The combined effect of high on the reduction of bond strength, as well as the combination of water reducing agent and mineral

The effect of powder, etc., the combined effect of these factors makes the dry-mixed mortar strong

The degree is higher than the benchmark mortar. Variation trend of bond strength of dry-mixed mortar with air content of mortar

3 Conclusion

Using composite cellulose ether admixture, the following conclusions can be drawn: 1) Considering the performance of layering degree and water retention rate, dry-mixed mortar

The gas content should not be less than 9%. 2) From compressive strength,