Reheating Furnace Refractories High Alumina Cement
Description
Technical Parameters
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There are various types of high alumina cement, which can be classified into CA-50, CA-70, and CA-80 types based on the differences in aluminum and calcium content. Among them, CA-50 is known for its yellow tone, and its raw materials mainly come from alumina and limestone. CA-70 is favored for its low impurities, superior setting characteristics, and fire resistance compared to CA-50 refractory cement, and is often used as a binder for low cement refractory castables. As for CA-80, its aluminum content is as high as 80% and it contains α - AL2O3 micro powder, so it often serves as a binder in high-end refractory castables. Thanks to their high aluminum content and low calcium content, these two types of cement can significantly improve the setting speed and medium temperature strength of refractory castables, while extending their service life for later strength.
01
Heat Resistance
The solid-state reaction that occurs at high temperatures replaces hydration bonding with sintering bonding, allowing it to maintain high strength at high temperatures.
02
Hydration Heat Characteristics
The hydration heat of it is relatively high and mainly concentrated in early release. This characteristic makes it particularly suitable for winter construction.
03
Resistance to sulfate corrosion
Due to its main component being low calcium aluminate and extremely low content of free calcium oxide, its cement stone structure is dense, which makes it have good resistance to sulfate corrosion.
04
Alkali Resistance
When it comes into contact with alkaline solutions or when concrete aggregates contain small amounts of alkaline compounds, erosion reactions will occur.
Chemical Composition & Physical Property
| Brand | CA-70 | CA-75 | CA-80 |
| Chemical composition (%) | |||
|
Al2O3 (%) min |
68.5-70.5 |
73.5-75.5 |
78.5-80.5 |
|
CaO (%) max |
29.5-30.5 |
23.5-24.5 |
17.5-19.5 |
|
SiO2 (%) max |
0.5 |
0.45 |
0.35 |
|
Fe2O3 (%) max |
0.3 |
0.25 |
0.26 |
|
Specific surface area (m2/kg) min |
420 |
420 |
420 |
|
Initial setting time: (h: min) |
≥0:30 |
≥0:30 |
≥0:30 |
|
Final setting time: (h: min) |
<6:00 |
<6:00 |
<6:00 |
|
Bending Strength (Mpa) |
|||
|
24 hr |
≥7.0 |
≥6.0 |
≥4.0 |
|
72 hr |
≥12.0 |
≥10.0 |
≥5.0 |
|
Compressive strength (Mpa) |
|||
|
24 hr |
≥45.0 |
≥40.0 |
≥25.0 |
|
72 hr |
≥65.0 |
≥62.0 |
≥30.0 |
|
Refractoriness (℃) |
1690 |
1730 |
1790 |
Precautions for using
1) The most suitable hardening temperature for high aluminous cement is about 15 ℃, and the ambient temperature during construction should generally not exceed 25 ℃ to avoid strength reduction caused by crystal transformation. In addition, concrete mixed with high alumina cement is not suitable for steam curing.
(2) It is strictly prohibited to mix it with Portland cement or lime, and direct contact with uncured Portland cement concrete should be avoided to prevent instant setting, which may affect construction progress and strength.
(3) Due to the influence of crystal transformation and aging of aluminate gel, the long-term strength of high alumina cement shows a downward trend. Therefore, when used in engineering, the design should be based on the minimum stable strength and determined through testing according to relevant standards.
* Imported new kraft paper with moisture-proof
* Leaking proof package, 25kg / bag, can be packaged as per the user's requirements.
* Stored in dry place away from moisture. One year shelf life.
Guidelines for the addition and application of high alumina cement in refractory castables
The higher the alumina content, the higher the fire resistance; The content of calcium oxide increases with the decrease of aluminum oxide content. Adding aluminous cement as a binder in refractory castables can significantly shorten the demolding time within 24 hours. However, the addition of the aluminous cement can also affect the flowability of refractory castables and the process of construction and demolding, so improper use may have adverse effects on construction.
The process of it can be divided into three stages: dissolution, nucleation, and precipitation. For example, the CA-50 is commonly used in the production of medium and low-grade refractory castables. However, it should be noted that CA-50 cement has the lowest strength at 800 ℃. Therefore, when the furnace lining is used at a temperature of exactly 800 ℃, selecting refractory castables becomes particularly difficult because the low temperature actually limits the use of ordinary refractory castables. At this point, low cement castables become a suitable choice, with low calcium content, excellent strength performance at medium temperatures, and good strength for later use.
In contrast, the high aluminous cement of CA-70 and CA-80 has a higher aluminum content and a relatively smaller addition ratio. They are suitable for low cement refractory castables, which not only enhance the strength of refractory castables, but also further reduce the calcium content and improve the performance of medium temperature strength.
In summary, when adding the high aluminous cement to refractory castables, it is necessary to comprehensively consider the bonding situation and operating temperature. According to specific requirements, choose to add CA-50 or CA-70 and CA-80 to ensure the optimal performance of refractory castables.
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