FG Baustoffe und Bauchemie
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- CO2-reduction (2) (remove)
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The basis of the primary energy supply in the Czech Republic is mainly lignite combustion. Power plants are for example Chvaletice, Melnik, Pocerady, Porici, Prunerov, Ledvice, Tusimice, Tisova and Hodonin [1,2]. Accordingly, there is a large amount of fly ash with its latent hydraulic and puzzolanic properties, depending on the composition. In terms of sustainability, such industrial residues offer huge potential for conversation of resources and often connected with it, a CO2-reduction. Especially lime-rich fly ashes offer a variety of possibilities in the high quality production of self-hardening loam-bricks, having an improved durability. Different clays/loams were mixed with fly ashes (10 to 30 wt-%) and homogenized by addition of water. Out of these mixtures, samples were moulded in different dimensions by using an extruding press. After curing under different humidity conditions at room temperature, the samples were tested for their strength and their durability. The investigations showed, that the choice of the starting materials has significant impact to the workability and the development of the strength. Furthermore, there is an optimal amount for the ash in the recipes to prevent a rapid destruction by capillary water absorption. The modified clay bricks could make a decisive contribution to the improvement of weather resistance e.g. in tropical areas with sudden rain showers.
There is a huge potential for the resource conservation and for reduction of CO2 emissions by using industrial by-products, as well as natural slags or ashes in a precise and high-class manner. Apart from mineral coal fly ash, which is used and certificated as an additive for concrete, especially lime- rich fly ashes with their latent hydraulic and puzzolanic properties offer a variety of possibilities in the high quality production of small-sized components like bricks.
Fine-grain-mixtures from different clays and fly ashes were homogenized and plasticized by the addition of water in an Eirich-mixer. The added amount of ash was varied from 10 to 30 wt%. Out of these mixtures, test items with a sufficient strength for transport were moulded in an extrusion process.
The test samples were stored under various humidity conditions (RH= 33, 65 and 88 %) at 20 °C and, subsequently after different times of self-hardening (28, 70 and 105 days), tested on their strength and durability.
Compressive strength up to 15 MPa was achieved. In order to reach that result, at least 20 wt% of the clay should be substituted by ash to get an increase in strength compared to the pure clay samples.
Further examinations have shown that it is possible to prevent the destruction by capillary water absorption of pure clay/loam specimens by an optimal use of ash in the recipes. Overall, it can be stated that due to the self-hardening potential of these mixtures there is no need for an energy-intensive and highly CO2 emitting combustion process, if the clay is substituted in fine grain mixtures by high lime component fly ashes.