Specifically, researchers have developed pilot tests in laboratory with bricks of a smaller size than conventional (60 x 30 cm.) and have used separately two types of ash in their composition.
Fundación Descubre has explained that, on one side, they have worked with bottom ashes, ie those that have larger particle size and are not entrained by the gases that are generated during the combustion and are left in the bottom of the combustion chamber. These residues need a pre-grinding treatment to reduce their size. But on the other hand they have also analyzed fly ashes which, due to its small particle size, are entrained by the combustion gases and are retained in gas cleaning systems such as electrostatic filters. The latter due to their smaller particle size are exempt from any kind of processing.
During the experimentation phase, experts have gradually replaced the clay used in the traditional composition by bottom or fly ash, supplied by a renewable energy generation company in the town of Andújar.
"The composition of these residues is similar to the ceramic raw material. Therefore, in some cases we have introduced 10% of ash, in others we have worked with 20% and in others we have come to replace up to 30% of clay to stipulate what percentage is appropriate," exlained the UJA researcher, Dolores Eliche, responsible for this scientific study, to Fundación Descubre
In order to comply with current regulations and can be used in construction, researchers have established that it must contain 20% of bottom ash or 10% of fly ash as a recommended amount.
These organic materials meet the conditions to be used as facing bricks and according to the researchers, the next step is to build them to real size and check if they continue to maintain the same properties on an industrial scale.
"If we want to obtain quality materials with recycled raw material, we must analyze how the microstructure changes after the incorporation of the residue, which in turn modifies its properties. To do this, we pay full attention to studying the apparent density, absorption and suction of water, mechanical resistance to compression or thermal conductivity," says Dolores Eliche.
The study titled "Investigation of using bottom or fly pine-olive pruning ash to produce environmental friendly ceramic materials" and published in the journal Applied Clay Science is the result of the first of the three sections in which the project "Types of ash to obtain new sustainable ceramic materials," financed by the University of Jaén and sponsored by Caja Rural de Jaén.
Removing the cooking process
The other two parts of the study, in which are currently immersed researchers and that will end in June, focus mainly on the removal of the cooking phase of these ceramic elements. In their opinion, this deals with the most costly step of all manufacturing and, in turn, the most polluting from an environmental point of view.
For this reason, different tests are carried out with ashes of different materials (rice husk, wood boards, alpeorujo, olive bone and pine and olive pruning) in order to determine which type is the most appropriate when dispensing of this stage of the productive process.
These tests are being contrasted with the manufacture of silico-calcareous bricks (traditionally composed of a mixture of quicklime and fine sand) which are pressure molded and do not need to be cooked, since they are steam-hardened or immersed in water. Researchers are also trying to achieve new ceramic materials, such as geopolymers, to look for an alternative to portland cement that during its creation releases large amounts of carbon dioxide. "If we can prepare these types of materials by replacing traditional raw materials with ashes, we will be giving a new life to wastes that today end up deposited in landfills, generating a significant environmental pollution," said the head of this scientific project.