Improvement of the sustainability of refractory monolithic linings by optimisation of particle shape

The first innovation target was to generate and provide knowledge on material design, and especially the development of a smart particle distribution, with the aim of improving the mechanical properties of monolithics during the initial heat treatment. Latest technological developments have not only allowed the systematic and quantitative characterisation of the shape of the grains typically used in the coarse fraction of monolithics, but also enable suppliers of these grains (raw materials) to produce tailored, or at least controlled, grain shapes. The combination of these two advancements opens new opportunities for refractory engineers to design products with tailored particle distribution and improved properties.

The second innovation target was to develop reliable mechanical and structural characterisation methods applicable up to high temperature. In order to heat up, as fast as possible, the refractory lining, the behaviour of the monolithics has to be known from room temperature up to service temperature. During the first heating, the monolithic refractory product is unstable. Reactions such as dehydration of hydraulic bonding phases and other phase transformations occur, which lead to steam pressure increasing in the pores of the materials, to shrinkage or to expansion and to structural rearrangements. Extensive stresses may arise and then cause the failure of the monolithic linings if the first heating is not well mastered. For the assessment of the mechanical resistance, a key issue is to assess the strength of the refractory monolithic under different stresses (tensile, compression and flexural) and, as previously stated, up to service temperature. Besides that, measurement of the evolution of permeability/porosity with increasing temperature provides decisive clues on the structural changes within the refractory monolithic during heat-up.

The third innovation target was the determination of the Drucker-Prager criterion to predict, with models, the possible failure of refractory linings from room up to high temperature. Stresses arising within refractory linings in service are extremely complex, typically multiaxial and unsteady, and thus technically almost impossible to reproduce in laboratory tests. However, the finite element method (FEM) nowadays is able to simulate the occurrence and distribution of stresses in complex structures like refractory linings being heated up. Nonetheless, FEM models still need criterions to predict where and when a refractory lining will fail. One of these criteria is the Drucker-Prager failure criterion, which shows the decisive advantages of being easy to implement and being based on the results from only two mechanical tests.