Low-cement refractory castables are unshaped refractory materials that have been widely used in recent years, mainly including aluminum silicate, magnesia, and silicon. Its strength has been greatly improved, which is caused by many factors, among which the ingenious use of superfine powder and the ingenious use of high-efficiency admixtures play an important role.
The preparation process of low cement refractory castables is stricter, so there are many factors that affect performance, mainly including ultra-fine powder, aluminate cement and admixtures. The amount of refractory aggregate and water are also important factors affecting its performance.
(1) Superfine powder
In low cement refractory castables, ultrafine powder mainly acts as a dispersion accelerator and structure compacting agent. The former makes the cement particles highly dispersed without flocculation, and the latter makes the micropores of the tissue structure fully filled to increase the strength. The types of ultrafine powder include SiO2, α-Al2O3, Ca2O3, ZrO2 and MgO. The specific surface area of SiO2 ultrafine powder is about 20m2/g, and its particle size is about 1/100 of that of cement particles, so it has good dispersibility and filling properties.
(2) Aluminate cement
There are many varieties of aluminate cement, and the types are different, and the properties of low-cement refractory castables are also different. For example, when the mix ratio and process conditions are basically the same, the amount of CA-50 cement and CA-70 cement are both 5%, and the compressive strength after drying, 800°C and 1100°C is 45MPa, 51MPa and 59MPa respectively. , The latter corresponding to 65, 70 and 74MPa.
(3) Refractory aggregate
Refractory aggregates generally do not use crushed aggregates, but use multi-stage particle grading. Different types of refractory aggregates have different properties of low-cement castables formulated. Different types of refractory aggregates have different drying compressive strengths of their castables. That is, the quality of refractory aggregates directly affects its performance. Because good bone fragments have low porosity and low water absorption, the castable requires less water and its performance can be improved.
(4) Water consumption
The water consumption of low cement series refractory castables, like other refractory castables, is also under the premise of ensuring the workability of the mixture, the less water the better. In this way, after the castable molded body is hardened, the pores are small, the total pore volume is reduced, the structure is dense, the linear change after firing is small, and the strength is improved.
The latest research results prove that low water content can not only reduce the total porosity of low-cement refractory castables, but also accelerate the early hydration of aluminate cement, so that the hydrate contains less bound water, and at the same time, the unit cementing capacity is somewhat different. Reinforced, so it helps to improve its normal temperature, drying and medium temperature strength.
