Technical Paper


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Figure 1: Initial vibration flow and after 30 mins


phases and organic additives. Since RP500 contains a deflocculation system combined with hydratable calcium aluminate phases it can replace the AL200 of the reference formulation and one percent of the CMA without significantly affecting the overall chemical composition of the castable.


The rheology of the castables with AL200 and RP500 is quite similar. Both achieve already with 3.5% water addition an excellent vibration flow profile at the three tested ambient temperatures, 5, 20 and 35ºC. The structuration as function of temperature is shown in Figure 3 and Figure 4. The reference formulation with AL200 shows the typical temperature dependence with a quite long structuration process at 5°C, starting after more than 20h with a small increase of velocity due to the slowly progressing hardening process. With RP500, the temperature dependence is significantly reduced through an accelerating effect at 5°C. The beginning of the structuration process is accelerated to less than 6h while the structuration processes at 20 and 35°C remain quite similar to the reference mix with AL200.


Using the time to reach the ultrasonic velocity of 2750 m/s as working time indicator (Figure 5) and 4000 m/s as setting time (Figure 6) it becomes obvious that RP500 has a stabilizing effect. Especially the structuration at


Raw Material Tabular alumina


Sintered Spinel Reactive Alumina


Calcium Magnesium Aluminate Binder Deflocculant


Deflocculating active compound Water


Table 4: Model alumina-spinel castable


Figure 2: Ultrasound profile and heat flow


5°C is significantly changed compared to the mix with AL200. While the reference castable shows almost an inversely proportional linear function of the temperature, the castable with RP500 has a relatively flat profile with an apparent temperature independence. Further tests have shown that retarders can be used in combination with RP500 to achieve for example a longer working time at 35°C. If the retarder is kept in the formulation also for use at 20 and 5°C then the effect of low temperature dependence is still kept when RP500 is used in the formulation. The use of RP500 results in a quicker strength development, visible already after 8h at 5°C. It is interesting to note that RP500 creates strength at 5ºC even slightly earlier than at 20ºC. Strength after firing at high temperature remains unaffected.


Improvement of the dry-out process of dense deflocculated castables


Three different model recipes (LCC, MCC, RCC) as shown in Tables 5-7 have been chosen to study the effect of the permeability enhancing active compound (PEAC) on dry-out and other properties. In previous studies [2, 3] it was found that a dosage of 2.5% of PEAC (MP20) gives the best compromise between sufficient flow and green strength, and a


Specification 0-5mm


0-1mm P152SB


CMA 72 (CMA) Peramin® REFPAC®


Al200 (AL200) 500 (RP500)


%


66 14 11 9


+0.1 -


+3.5 %


66 14 11 8 - 1


+3.5


Figure 3: Ultrasound velocity with AL200 16 ENGINEER THE REFRACTORIES


Figure 4: Ultrasound velocity with RP500 September 2017 Issue


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