The researchers studied how using recycled concrete instead of natural aggregates affects the strength and permeability of concrete. They replaced different percentages of natural aggregates with recycled ones and found that concrete with 30% recycled aggregates can be used in structures without losing too much strength. However, using recycled aggregates makes the concrete more permeable, meaning it absorbs more water. Overall, concrete with some recycled aggregates is strong enough for structures, but it may not be as watertight as concrete made with only natural aggregates.