Kalkbindemidler

Kalkbindemidler, often translated as lime binders, are hydraulic or semi-hydraulic binders derived primarily from calcium oxide, also known as quicklime. These binders are produced by heating limestone (calcium carbonate) to high temperatures in a kiln, a process called calcination. This process drives off carbon dioxide, leaving behind calcium oxide. When water is added to quicklime, a chemical reaction called slaking occurs, producing calcium hydroxide. This calcium hydroxide, when mixed with water and aggregate, forms a paste that hardens over time.

The hardening of lime binders occurs through two main mechanisms. Firstly, carbonation: calcium hydroxide reacts with atmospheric carbon dioxide to form calcium carbonate, the original mineral. This process is slow and can continue for extended periods, contributing to the long-term strength and durability of lime-based mortars and plasters. Secondly, hydraulic lime binders also undergo hydration reactions, similar to Portland cement, when exposed to water. This hydraulic set allows them to harden even in submerged conditions and contributes to a faster initial strength development compared to pure non-hydraulic lime.

Kalkbindemidler have been used as construction materials for millennia, playing a significant role in ancient Roman and medieval architecture. They are known for their breathability, flexibility, and self-healing properties, making them suitable for historic building restoration. Modern applications include mortars, plasters, soil stabilization, and certain types of renders. The environmental profile of lime binders is also noteworthy, as the carbonation process reabsorbs carbon dioxide, potentially making them carbon-neutral or even carbon-negative over their lifecycle, depending on production methods.