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Binder is a type of refractory material, which bonds refractory aggregates and powders and provides strength to the refractory materials. Aluminate cement is a type of inorganic binder that mainly provides strength to refractory materials through the hydration of cement. Aluminate cement can be categorized into calcium aluminate cement, barium aluminate cement, and barium aluminate zirconia cement, with calcium aluminate cement being the most widely used.
Calcium aluminate is a hydraulic setting material made by finely grinding calcium aluminate clinker produced by sintering or melting methods. It features quick setting, high strength, refractoriness, and resistance to sulfate erosion. According to Al₂O₃ content percentage, it can be divided into: CA-50 cement (50%≤Al₂O₃<60%), CA-60 cement (60%≤Al₂O₃<68%), CA-70 cement (68%≤Al₂O₃<77%), and CA-80 cement (77%≤Al₂O₃).
Aluminate cement binding properties are mainly achieved through the hydration of calcium aluminate. Different chemical compositions of cement result in different mineral compositions. In aluminate cement, its chemical composition and refractoriness are shown in the table below:
Aluminate cement chemical composition and refractoriness
|
Cement Type |
Chemical Composition/% |
Refractoriness ℃ |
||||
|
Al₂O₃ |
SiO₂ |
CaO |
Fe₂O₃ |
R₂O |
||
|
CA-50 |
50-60 |
≤8 |
30-39 |
≤2.5 |
≤0.4 |
≥1460 |
|
CA-60 |
60-68 |
≤5 |
27-32 |
≤2.0 |
≤0.4 |
1500 |
|
CA-70 |
68-77 |
≤1 |
21-28 |
≤0.7 |
≤0.4 |
1660 |
|
CA-80 |
≥77 |
≤0.5 |
18-22 |
≤0.5 |
≤0.4 |
＞1750 |
Aluminate cement mortar strength is shown in the table below:
Aluminate cement compressive strength and flexural strength
|
Cement Type |
Compressive Strength/MPa |
Flexural Strength/MPa |
||||
|
6h |
1d |
3d |
6h |
1d |
3d |
|
|
CA-50 |
20 85(28d) |
40 |
50 |
3 10(28d) |
5.5 |
6.5 |
|
CA-60 |
20 |
45 |
2.5 |
5.0 |
||
|
CA-70 |
30 |
40 |
5.0 |
6.0 |
||
|
CA-80 |
25 |
30 |
4.0 |
5.0 |
||
Aluminate cement sets and hardens quickly
The 1d strength can reach more than 80% of the maximum strength, and is mainly used for projects with urgent construction periods, such as national defense, roads, and special emergency repair projects. Aluminate cement has a large hydration heat and concentrated heat release. The hydration heat released within 1d is 70% to 80% of the total, which makes the internal temperature of the concrete rise higher. Even if it is constructed at -10℃, aluminate cement can set and harden quickly, and can be used for winter construction projects.
Aluminate cement has strong sulfate corrosion resistance
Under ordinary hardening conditions, aluminate cement has a strong resistance to sulfate corrosion because the cement stone does not contain tricalcium aluminate and calcium hydroxide, and has a large density.
Aluminate cement has high heat resistance
If refractory coarse and fine aggregates (such as chromite, etc.) are used, heat-resistant concrete with a service temperature of 1300 to 1400℃ can be made.
However, the long-term strength and other properties of aluminate cement tend to decrease, and the long-term strength decreases by about 40% to 50%. Therefore, aluminate cement is not suitable for long-term load-bearing structures and projects in high temperature and high humidity environments. It is only suitable for emergency military projects (road and bridge construction), emergency repair projects (leakage plugging, etc.), temporary projects, and the preparation of heat-resistant concrete.
In addition, aluminate cement mixed with silicate cement or lime not only produces flash setting, but also cracks and even destroys the concrete due to the formation of highly alkaline hydrated calcium aluminate. Therefore, during construction, in addition to not mixing with lime or silicate cement, it must not be used in contact with unhardened silicate cement.
