Concrete is up to 70% of the quantity for a project. There are many types of concrete included in construction such as lightweight concrete, precast block concrete, self-compacting concrete ... For lightweight concrete and precast concrete perhaps more popular and more popular but what is self-compacting concrete, surely not many people know. So let's learn the concept of self-compacting concrete is what? What are the characteristics and production methods? What is self-compacting concrete concept? What are the characteristics and production methods?
1. What is self-compacting concrete?
Self-compacting concrete is a special liquid concrete that can flow by its own weight to completely fill the mold or formwork, even in dense reinforcement places without any other work such as using vibratory compactor, compacted ... while still ensuring the uniformity of the concrete block when frozen or self-compacting concrete is concrete capable of self-compacting. With this feature, the fresh concrete mortar can compact all corners of the mold or narrow positions - the most difficult to pour without the use of other machines or mechanical impact.
2. Characteristics of self-compacting concrete – DUFAGO
As mentioned above, self-compacting concrete has very good flowability so that it can compact itself and fill molds and formwork. In order to do that, the freshly mixed concrete mortar must be balanced between the flowability and non-stratification of the concrete mixture. This is determined by the amount of additives (we will write more in section 3) and the types of additives mentioned below.
- Superplasticizer additive: It is necessary to use this additive to achieve high ductility of the concrete mixture;
- Fine admixture: Using a large amount to increase the flexibility of cement mortar;
- Large aggregate content such as sand stone gravel must be less than that of conventional concrete.
In addition to the use of the above basic additives to create the characteristics of self-compacting concrete, the construction process must also pay attention to the differences compared to ordinary concrete as follows:
The start and end of setting (hardening) of self-compacting concrete tends to be slower than that of plain concrete.
- Pumping capacity of self-compacting concrete with concrete pumps is higher than that of normal concrete.
- Due to high ductility and yield resulting in quality fluctuations and problems during mixing and construction, when using self-compacting concrete materials, there should be requirements for quality control, production inspection and inspection Construction is stricter than conventional concrete.
- Because there is no external mechanical impact, pay attention to the time to maintain the quality as well as ensure the flow during the transportation is greater than that of normal concrete.
3. Technology and method of producing self-compacting concrete – DUFAGO
3A. Technology for self-compacting concrete production - DUFAGO
This concrete production can use the same technology as in the production of other types of concrete, still using forced, self-propelled concrete mixers ... or mixing plants as usual but with special requirements on the aggregate.
3B. Requirements for self-compacting concrete production materials - DUFAGO
Raw materials for the manufacture of self-compacting concrete including cement, fine admixtures, superplasticizers, small aggregates and large aggregates. The quality of self-compacting concrete depends on the quality of the constituent materials and precise mixed design techniques.
- For cement:
Cement is the decisive factor for adhesion, cohesion between aggregate components of concrete. The quality of the hardened concrete depends not only on the curing of the concrete after pouring but also on the cohesion strength of the concrete. When choosing cement for self-compacting concrete production, it is necessary to choose cement rich in belite, with low heat-exuding with small C3A and C4AF components. Especially, using cement with small C3A and C4AF in self-compacting concrete will give high dispersion effect of the additive. These cement parameters you should refer to carefully before buying.
In addition, the quality of cement is also an important factor determining the quality of finished concrete, so it is necessary to choose a reputable cement brand, such as Bim Son Cement, Hoang Thach Cement, Ha Tien Cement…
– Small aggregate and coarse aggregate.
The proportion of coarse aggregate is usually 0.37-0.47% by quantity and plays an important role in the quality of self-compacting concrete. Here we pay much attention to a small aggregate of sand that needs to be of good quality. Using river sand, clean sand and no impurities will increase the quality of the concrete which will self-compact after pouring. As for the coarse aggregate of gravel, and stone, it is also necessary to pay attention to cleanliness, the ratio of rotten stones and crushed stones is not much. Especially, small gravel will give better quality than big gravel, reducing porosity, and increasing the consistency of concrete after hardening.
However, when producing self-compacting concrete, attention should be paid to the small proportion of aggregate and coarse aggregate that is needed less than conventional concrete to ensure self-compacting, self-flowing and ductility.
– Smooth additives and superplasticizers.
These are two important components that determine the flowability and self-compacting of concrete, in which the fine admixture increases the ductility of the fresh concrete and the superplasticizer helps reduce water at a high level to remove air bubbles to avoid emptying of concrete after hardening.
Fine additives used in the manufacture of self-compacting concrete have many types such as silica fume, thermal ash, blast furnace slag, limestone powder, fly ash ...
In the fabrication of self-compacting concrete, two types of superplasticizer are commonly used: a high-degree water-reducing superplasticizer (30-40% of mixed water) and a high-degree air-entraining superplasticizer. The requirement for superplasticizer additive for self-compacting concrete in addition to increasing the flow rate of the concrete mixture must also be able to maintain workability over time.
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Some types of superplasticizers are detailed below.
3C. Self-compacting concrete mix - DUFAGO
The composition of self-compacting concrete mix is listed in the table below
Table : Composition of self-compacting concrete kg/m3
3D. Technical requirements to be needed - DUFAGO
As with conventional concrete, the minimum requirements required for self-compacting concrete are:
– Ensuring the time to maintain the flexibility over time is sufficient for construction (transporting, pumping into the pouring items ...);
– Grade concrete at the design age (according to the required compressive strength);
– Waterproofing grade and requirements for durability
– Other features: flexural strength, anti-shrink ...
In addition, the technical requirements for self-compacting concrete mortar mixes depend on the construction conditions and are given as follows:
– The flexibility of self-compacting concrete mortar is shown through the melt diameter of the mixture (tested by the method of tapering): Time to reach diameter D50cm after 3 ÷ 6 seconds and Dmax = 65 ÷ 75 cm;
– Self-compacting ability of self-compacting concrete when flowing through the reinforcing bar slot (tested by Lbox): H 2 ≥ 0.8; H1
* Self-compacting feature:
Ability to flow through the reinforcing bar of the same size as reality or according to 3 self-compacting levels as follows:
– Level 1: self-compacting capacity of the concrete mixture in areas with high reinforcement density (clear distance between reinforcing bars is 35 ÷ 60 mm);
– Level 2: self-compacting capacity of the concrete mixture in regions with average reinforcement density (clear distance between reinforcing bars is 60 (200 mm);
– Level 3: self-compacting of the concrete mixture in areas with low reinforcement density (clear distance between reinforcing bars is> 200 mm);
4. Vietnamese Standards (TCVN) for self-compacting concrete.
4A.TCVN for additives
In the experiment using Formusa fly ash additive, the properties of fly ash were tested according to TCVN 6016:1995; TCVN 6017:1995; TCVN 4030:1985; 14BC 105-1999.
4B. TCVN for cement
Self-compacting concrete has many advantages and is widely used in construction. However, the production of self-compacting concrete needs to be done strictly technically to ensure the quality of concrete mortar as well as the quality of the work. Above, Dufago has presented full basic information about self-compacting concrete and production methods and technology. If you have any questions please leave a comment or call us for advice. Dufago fully presented basic information about self-compacting concrete and production methods and technology. If you have any questions please leave a comment or call us for advice.