Technical method to reduce shrinkage and cracking of foam concrete

Overview of lightweight concrete

Lightweight concrete, also known as foamed concrete, is to fully foam the foaming agent mechanically through the foaming system of the foaming machine, mix the foam and cement slurry evenly, and then pass the pumping system of the foaming machine for in-situ construction Or mold forming, a new type of lightweight thermal insulation material with a large number of closed pores formed by natural curing. It is a bubble-shaped heat-insulating material, and its outstanding feature is the formation of closed foam cells inside the concrete, which makes the concrete lightweight and heat-insulating; it is also a special variety in aerated concrete, and its pore structure and material properties are close For aerated concrete, the difference between the two is only the difference between the shape of the pores and the means of aerated concrete.

Lightweight concrete is commonly used in many engineering constructions, and lightweight concrete refers to concrete made of lightweight coarse and fine aggregates and cement. Lightweight concrete is a general term for concrete with a bulk density not greater than 1950kg/m3. So what type of lightweight concrete is included?

There are three main categories of lightweight concrete

1. The apparent density of lightweight aggregate concrete is 800~1950 kg/m3. Lightweight aggregates include pumice, volcanic slag, ceramsite, expanded perlite, expanded slag, slag, etc.

2. Hollow concrete (foamed concrete, aerated concrete), its apparent density is 300-1000 kg/m3. Foamed concrete is made of cement paste or cement mortar and stabilized foam. Aerated concrete is made of cement, water and gas generating agent.

3. Macroporous concrete (ordinary macroporous concrete, light aggregate macroporous concrete) has no fine aggregate in its composition. The apparent density of ordinary macroporous concrete ranges from 1500 to 1900 kg/m3 and is prepared from crushed stone, soft stone and heavy slag as aggregates. The apparent density of light aggregate macroporous concrete is 500-1500 kg/m3, and it is made of ceramsite, pumice, broken brick, slag, etc.

Application of lightweight concrete

Lightweight concrete is widely used in energy-saving wall materials due to its good characteristics, and has also been used in other areas. At present, the application of lightweight concrete in China is mainly cast-in-place roof insulation, lightweight wall panels, and compensation foundations. However, making full use of the good characteristics can continuously expand its application fields in construction engineering, speed up the progress of the project, and improve the quality of the project. The details are as follows:

⑴Used as a retaining wall. Mainly used as a rock wall for the port. Used as a lightweight backfill material behind the quay wall can reduce the vertical interception load and also reduce the lateral load on the quay wall. This is because it is a rigid body with good bonding performance. It does not exert lateral pressure on the quay wall along the periphery, and the settlement is reduced, and the maintenance cost is reduced, thereby saving a lot of expenses. Foamed concrete can also be used to improve the stability of the embankment slope. It can replace part of the soil on the slope. As it reduces the quality, it reduces the force that affects the stability of the slope.

(2) Construct sports fields and track and field tracks. Use permeable foamed concrete with strong drainage capacity as a lightweight foundation, covered with gravel or artificial turf, as a sports field. The density of foam concrete is 800-900kg/m³ such sports fields can be used for hockey, football and tennis activities. Or it can be used as a track and field track if it is covered with a 0.05m thick porous asphalt layer and a plastic layer on the foam concrete.

⑶As a sandwich component. Lightweight concrete can be used as the inner core in the prefabricated reinforced concrete components, so that it has good performance of light weight, high strength and heat insulation. Foamed concrete with a density of 400-600kg/m&sup3 is usually used.

⑷ Pipeline backfilling. Underground abandoned oil tanks, pipelines (with crude oil, chemicals), sewage pipes and other cavities are likely to cause fires or collapses. Using foam concrete backfilling can solve these problems, and the cost is low. The density of foam concrete depends on the diameter of the pipe and the groundwater level, generally 600-1100kg/m³.

⑸ Lean concrete filling layer. Due to the use of flexible hoses, foam concrete has great workability and adaptability, so it is often used for lean concrete fills. If the requirement for thermal insulation is not very high, use a density of 1200kg/m³ the lean concrete fill layer with an average thickness of 0.05m; if the requirement for thermal insulation is high, use lean concrete with a density of 500kg/m³ The filling layer has an average thickness of 0.1-0.2m.

⑹ Roof slope. Foamed concrete is used for roof slopes and has the advantages of light weight, fast construction speed, and low price. The slope is generally 10mm/m. The thickness is 0.03-0.2m, and the foam concrete with a density of 800-1200kg/m³ is used.

⑺ Support for the bottom of the storage tank. Pour the foam concrete steps on the bottom of the steel storage tank (containing crude oil and chemicals). If necessary, it can also form a convex foundation. This can ensure that the support of the entire tank bottom is in the best stress state during welding. A continuous support allows the storage tank to adopt a thin plate bottom. At the same time, the convex foundation is easy to clean. The use density of foam concrete is 800-1000kg\m³.

⑻Used for landscaping. The foam concrete is made into a bulk density of 600-1000kg/m³ it can be used for garden rockery, garbage bins, tables and stools, etc.

⑼ National defense (modern warfare uses information and advanced mobile equipment as attack tools). The foamed cement can be used in military projects destroyed by enemy bombing, such as airports and important traffic roads. The project destroyed by the enemy was quickly repaired, and the result of the experiment was that it could be used for aircraft taking off and landing within 10 minutes after repairing, and the tanks passed.

⑽Others. Foamed concrete can also be used for insulation filling of firewalls, sound insulation floor filling, tunnel lining backfilling, and power supply and water pipeline isolation.

The shrinkage, cracking and water absorption of foamed concrete are three closely related problems. Generally speaking, due to poor early maintenance, insufficient water-saving measures or strict conditions during use, foamed concrete will cause the internal water to evaporate, resulting in volume shrinkage, cracking or a large amount of water absorption. The excessive water absorption of foamed concrete will again reduce the thermal insulation effect. From the preparation process of the foamed concrete and the observation and study of the cross section of the hardened body, it is found that most of the pores in the foamed concrete are relatively independent closed pores. Therefore, the well-preserved foam concrete is soaked in water, and its water absorption is mainly concentrated on the surface, but the water absorption is not high. The main factors affecting the shrinkage, cracking and water absorption of foam concrete are as follows:

1. The influence of cement dosage

During the hydration and hardening process, the solid content of ordinary Portland cement increases, while the cement + water system shrinks. Secondly, the hydration process of cement is accompanied by thermal effects, which cause initial volume expansion and cooling and shrinkage, leading to an increase in apparent shrinkage. In addition, in the process of cement hydration, the phenomenon of autogenous shrinkage is caused by water absorption. Therefore, generally, if other conditions are basically the same, the amount of cement increases, and the shrinkage rate of foamed concrete will increase accordingly. Cement is also one of the important factors to ensure strength, so the range of cement dosage is appropriate.

2. Influence of cement type

Not all cement before and after volume hardening is shrinkage, cement before and after volume hardening does not shrink but expand. Therefore, if appropriate expansive cement is used, the overall shrinkage rate of foam concrete can be compensated or reduced to a certain extent. However, expansive cement not only affects the volume change, but also affects a series of other properties. Excessive introduction will cause damage to the structure of hardened foamed concrete. Therefore, the type and amount of expansive cement must be determined through experiments.

3. The influence of aggregate

Foamed concrete can only be mixed with a part of the fine aggregate. Due to the chemical inertia of the aggregate, excessive mixing will result in a significant decrease in the strength of the foamed concrete, so its content is limited to a certain extent. After the density, water-cement ratio and other process parameters of the foamed concrete are basically determined, as the fine aggregate increases, the amount of cement will decrease. Therefore, there are many more suitable options for hybrid polymerization.

4. The influence of water-cement ratio and protection system

The molded water-cement ratio of foamed concrete is usually as high as 0.7 or even 0.8, and excess water will remain in the pores of the hardened foamed concrete, which accounts for about 50% of the molded water. When the relative humidity of the environment is low or the temperature of the environment is high, the water will evaporate and escape. Especially in the early stage of hardening, the structure of foam concrete is still relatively weak. If it is not well maintained, it is easy to lose water, leading to greater shrinkage and surface cracking, weakening the internal structure of the hardened body, resulting in high water absorption rate of hardened foam concrete. Therefore, the initial water-cement ratio of foamed concrete becomes a prerequisite for the shrinkage of hardened foamed concrete. One of the key technologies for preparing low-shrinkage foam concrete is to control the low water-cement ratio.

5. Technical methods to reduce shrinkage and cracking of foam concrete

According to the above analysis, the technical measures to reduce the shrinkage of foam concrete and prevent cracking and water absorption mainly include the following aspects:

(1) Appropriate amount of cement;

(2) Add appropriate expansive cement;

(3) Low forming water-cement ratio;

(4) Optimize the maintenance system and strengthen early water saving;

(5) Use water repellent (mixed or surface coating).

The price of lightweight concrete

The price of lightweight concrete varies randomly with production costs, transportation costs, international conditions, exchange rates, and the market supply and demand of lightweight concrete. Tanki New Materials Co. Ltd aims to help all industries and chemical wholesalers find high-quality products by providing a full range of products. If you are looking for lightweight concrete, please contact us for the latest price.

Suppliers of lightweight concrete

As a global supplier of lightweight concrete, Tanki New Materials Co., Ltd. Has extensive experience in the performance, application and cost-effective manufacturing of advanced and engineering materials. The company has successfully developed a series of foam concrete additives (including lightweight concrete, CLC blocks provide concrete foaming agents, superplasticizers, foam concrete strength enhancers, etc.), high-purity targets, and functional materials. Ceramics and structural equipment, and provide OEM services