Give examples to illustrate the difference between internal mixing and external mixing of concrete admixtures

The so-called internal mixing of concrete admixtures can replace part of the cement. Silica fume is used to replace the cement. There are two types: equal replacement and partial replacement. The equal replacement is the silica fume content to replace the equal amount of cement, and the partial replacement is 1kg. Silica fume replaces 1 to 3 kg of cement. For research, the general dosage is 5 to 30%, and the water-cement ratio generally remains unchanged.

External mixing does not replace cement, but only improves workability. Silica fume is mixed into concrete like an admixture, that is, silica fume is added without reducing the amount of cement. The dosage is generally 5 to 10%. Due to the different usage of silica powder, the properties of the concrete obtained are not the same. The mechanical properties of the concrete obtained by the external mixing method are much higher, but the amount of cementitious materials in the concrete is increased.

There are the following differences between internal mixing and external mixing of concrete admixtures

1. The dosage formula is different

Internal mixing means that the admixture is included in the cementitious material , the dosage formula is: A/(A+B)*100%;

A——the amount of admixture; B——the amount of cementitious material.

External admixture means that the admixture is not included in the cementitious material. The dosage formula is: A/B*100%.

A——Amount of admixture; B——Amount of cementitious material.

Example: If there are 100g of water, and the salt water is mixed into 5% by internal and external mixing methods, then the amounts of salt are:

Internal mixing method: The material is part of the whole, and the whole is considered to be 100%, which includes salt and water, then the overall mass = mass of water/proportion of water = 100/(1-5%) = 105.26g, then the amount of salt It is 105.26-100=5.26g

External doping method. It takes 100g of water as 100% of the whole, and the admixture as part of the whole, so 100gx5%=5g of salt should be added

2. The conditions for the dosage are different

Concrete admixtures Internal mixing method – using silica fume to replace cement, which can be divided into two types: equal amount replacement and partial replacement. The equal amount replacement is the silica fume content to replace the equal amount of cement, and the partial replacement is 1kg silica fume instead of 1~3kg cement. As a research The general dosage is 5 to 30%, and the water-cement ratio generally remains unchanged.

External admixture method – silica fume is mixed into concrete like an admixture, that is, silica fume is added without reducing the amount of cement. The dosage is generally 5 to 10%.

　3. The properties of the concrete obtained are different

Due to the different usage of silica powder, the properties of the concrete obtained are not the same. The mechanical properties of the concrete obtained by the external mixing method are much higher, but the increase The amount of cementitious materials in concrete.

1. Use cement to stabilize coarse-grained soil (the maximum particle size of the particles is less than 50mm and the content of particles less than 40mm is not less than 85%) and medium-grained soil (the maximum particle size of the particles is less than 30mm and among them The mixture obtained (the content of particles smaller than 20 mm is not less than 85%) is regarded as the raw material used as crushed stone or gravel, and is simply called cement gravel or cement gravel.

2. Its characteristics are high strength, good water stability, good frost resistance, erosion resistance, and low temperature shrinkage and dry shrinkage. It is an excellent base material; used for cement concrete pavement base and asphalt pavement base at all levels.

Use the internal mixing method to calculate the cement dosage. How to use the internal mixing method to calibrate the curve?

Concrete admixtures are first calculated using the internal mixing method, and then 1000KG of materials are added. Then use EDTA to calibrate, and the curve is calibrated.

The internal mixing method is “Cement: Mixture=X: (X+Y)”. (where