Many modern houses with "warm" facades eventually begin to be covered with thin cracks. At first, they are almost imperceptible, but then water gets into them, it freezes in winter - and the concrete gradually begins to collapse from the inside. Scientists from Perm have found a way to slow down this process. The development was presented by specialists from Perm Polytechnic.
The problem is related to lightweight porous concrete, which is often used in the construction of energy-efficient homes. To make the material better retain heat, foam glass granules made from recycled broken glass - bottles and window panes - are added to it. The glass is crushed, heated, bubbles appear inside, and the material becomes light and porous, almost like pumice. Such concrete retains heat well, does not burn, and does not rot.
However, over time, moisture penetrates the walls, alkalis from the cement begin to react with silicon in the foam glass. A gel forms inside, which absorbs water, swells, and begins to press on the concrete from the inside. Because of this, thin, cobweb-like cracks can form on the facades. The process is especially fast in cold and humid climates. According to researchers, without additional protection, such blocks can begin to collapse within 10–15 years after construction.
Existing methods for protecting such concrete are either expensive or do not provide a full guarantee. Scientists from Perm Polytechnic proposed a new approach - to use metakaolin, a special fine powder based on aluminosilicate clay. Unlike conventional additives such as talc or graphite, it not only prevents granules from sticking together during production but also helps block the destructive chemical reaction inside the concrete.
To test the effectiveness, researchers made three types of granules: ordinary, with silicon dioxide, and with metakaolin. Then they made concrete from them and compared the results. According to Vitaly Shamanov, Dean of the Construction Faculty of PNIPU, concrete with silicon dioxide was almost no different from standard, but the material with metakaolin turned out to be significantly stronger - 3.3 MPa versus 2.6 MPa, which is about 27% higher.
In addition, the concrete began to absorb less water: the indicator decreased from 13.7% to 11.9%. The less moisture gets inside the material, the lower the risk of cracks and destruction. Scientists explain that metakaolin acts as a kind of "trap" for alkalis: it binds sodium and potassium from cement and prevents them from reacting with glass. At the same time, foam glass retained its lightness and thermal insulation properties.
For construction companies, this means the ability to produce higher quality blocks and panels without a significant increase in cost. And for residents - homes that will remain free of cracks and destruction longer.