How To Make Refractory Cement?
Refractory cement, also known as furnace cement, fire cement, high-temperature cement, etc. the refractory cement is a hydraulic binder produced by burning and grinding clinker of bauxite and lime.
The refractory cement require refractoriness of 1580℃ and above. There are various types of refractory cement, such as high alumina cement, calcium aluminate cement, phosphate refractory cement, calcium magnesium aluminate cement, etc.
Making refractory cement in an easy way
High alumina cement is common among all types of refractory cement, so we study refractory cement based on the data of high alumina cement.
Table1: composition of high alumina cement
|Constituents||Silica||Alumina||Lime||Iron Oxide||Titanium||Magnesium||Insoluble Resides|
High alumina cement manufacturing process can begenerally divided into five steps as follows:
Cement clinker and gypsum are fed into cement grinding plant, which usually consist of cement roller press, cement ball mill or vertical cement mill. After cement grinding, the finished cement with desired chemical composition and physical properties will be produced;
Highlights of refractory cement
Fast setting early strength
1d strength can reach more than 80% of the highest strength, belongs to rapid hardening cement. When using high alumina cement, control its hardening temperature. The most suitable hardening temperature is about 15 ° C, and generally should not exceed 25 ° C. If the temperature is too high, the dicalcium aluminate hydrate will be converted into tricalcium aluminate hydrate, reducing the strength. In humid and hot conditions, the intensity decreases more severely.
Large hydration heat & Good heat resistance
The heat generation is concentrated. Within 1d, 70% to 80% of the total hydration heat can be released, while the Portland cement only emits 25% to 50% of the total hydration heat.
The concrete prepared with high alumina cement also has 70% of the original strength at a temperature of 900 ° C, and it still maintain about 53% of the strength when it reaches 1300 ° C. These remaining strengths are resulted in the solid phase reaction between the various components in the cement stone to form a ceramic body.
Strong sulfate resistance and poor alkali resistance
High alumina cement does not precipitate calcium hydroxide when hydrated, and with a dense structure after hardening, so it has good resistance to sulfate and seawater corrosion. At the same time, it has good stability to aggressive solutions such as carbonated water and dilute hydrochloric acid. However, after the crystal is transformed into stable tricalcium aluminate hydrate, the porosity increases and the corrosion resistance decreases accordingly. High alumina cement has no resistance to alkali corrosion, so try to avoid alkaline corrosion.
The long-term strength tends to decrease
With the passage of time, CAH10 or C2AH8 will gradually be transformed into relatively stable C3AH6. As a result of the crystal transformation, free water will precipitate out of the set cement, increasing the pore volume. At the same time, because C3AH6 itself has low strength, the long-term strength of set cement will decrease.
Applications of refractory cement
- Based on its characteristics, the refractory cement can be applied to urgent projects, such as pressure, road and special emergency repair projects,
- Refractory cement is also used for winter construction projects.
- Besides, refractory cement can be used to cement various refractory aggregates (such as corundum, calcined bauxite, etc.) into refractory mortar or concrete, apply for cement rotary kiln lining and other industrial kiln linings.
High aluminum cement is not suitable for neither mass concrete projects, nor long-term load-bearing structures and projects in high temperature and humidity environments, projects in contact with alkaline solutions. It should also be noted that high aluminum cement products can not be steam curing.
In addition, without test, high alumina cement can’t mix up with cementing material that can precipitate calcium hydroxide , such as Portland cement or lime, even avoiding contact in the process of mixing and placing concrete. High alumina cement shall not contact with Portland cement that has not yet hardened, avoiding intensity drops, and shorten the setting time, even instantaneous condensation phenomenon.
Because the strength of aluminate cement concrete decreases greatly in the later period, the design should be based on the minimum stable strength, whose value is determined by the test according to relevant regulations
Technical requirements for refractory cement
Fineness: the finer the cement particles are, the larger the specific surface area is, the faster and more sufficient the hydration reaction is, and high the earlier and later strength is. In China, according to the national regulations, specific surface area should be more than 300 square meters per kilogram.
Setting time: To ensure enough time to complete the mixing, transportation, and other processes, the cement initial setting time should not be too short, better more than 45 minutes; After construction, cement is required to harden as soon as possible, so final setting time should not be too long, better less than 390 minuts.
Volume stability: the volume stability of cement refers to the uniformity of volume change of cement slurry in the process of setting and hardening. If the volume change is not uniform, the volume stability is poor, prone to warpage and cracking, reduce the quality of engineering and even result in accidents.