Clay soil can be strengthened by adding lime, which improves its properties for construction projects like highways and airports. The amount of lime needed varies, but generally, 1% to 3% is enough. Lime combines with clay minerals, increasing the soil's plastic limit and decreasing its liquid limit. Excess lime boosts soil strength by forming cement-like products around clay minerals. Over time, these products crystallize into stronger minerals. Lime also raises the soil's moisture content and lowers its density, while improving its permeability and resistance to frost.