Speaker
Description
High performance (HP) refractory concrete rely mainly on sophisticated, highly densified matrix systems with a high charge of pore-filling alumina and silica micro-powders, deflocculated with efficient polymer admixtures, and bonded with 70% Al2O3 containing calcium aluminate. However, these HP concretes experience a challenge concerning the safe and rapid removal of free pore and hydrate water prior to the utilisation of the refractory concrete as protection linings in industrial furnaces. Their low permeability risks an internal pressure build-up and hydrothermal conditions during the first heat-up. The pressure can potentially exceed the strength of the refractory material if heated too fast. However, time is an important economic factor and creating cracks or even explosive spalling of the refractory lining during the first heat-up could be the consequence if specifically designed dry-out procedures for such highly densified refractory concrete are not entirely followed.
Possibilities to promote a microstructure that allows for more permeability to evacuate the water more easily and at relatively lower temperature without losing the advantage of low porosity and small pore sizes will be discussed in this paper. The hydration and dehydration path of calcium aluminate plays a crucial role in this regard. It will be shown that it is possible to trigger more gel-like calcium aluminate hydrates at the expense of the usually occurring crystalline hydrates, eg. CAH10, C2AH8, C3AH6, AH3, and AH. This calcium aluminate gel releases its water already between 100 and 150°C, at a significantly lower temperature range than the crystalline calcium aluminate hydrates, and even before a high pressure build-up and hydrothermal conditions occur. It creates a more permeable system through which the water can be transported to the surface of the concrete more easily and the risk of pressure build-up is significantly reduced.
Affiliations
Imerys Technology Center
1 rue Le Chatelier
38090 Vaulx Milieu - France
| Keywords | Hydration, CAC, Permeability, Castable, Dry-out |
|---|