Concrete's susceptibility to water absorption is due to the capillary action within the pores of its hydrated cement paste. This action draws water in, creating the need for waterproofing admixtures to prevent such penetration. The efficacy of these admixtures is contingent upon the water pressure, with variations arising from different conditions such as rain, capillary rise, or hydrostatic pressure in structures intended to hold water.

Waterproofing admixtures render concrete hydrophobic, repelling water and altering the interaction between the water and the capillary walls. Common substances used in these admixtures include stearic acid and certain fats derived from plants and animals.

A clear distinction is made between waterproofing admixtures, which integrate with the concrete mix, and water repellents, which are silicone resins applied to the surface. In addition, there are waterproofing membranes, which are bitumen coatings that form an elastic film on concrete.

The presence of bacteria, fungi, or insects can be detrimental to concrete, leading to steel corrosion and surface staining. Given the concrete's rough texture, traditional cleaning methods are ineffective, requiring an admixture within the concrete that is lethal to these organisms. These admixtures, such as polyhalogenated phenols, dieldrin emulsions, and copper compounds, can be antibacterial, fungicidal, or insecticidal and are mixed into the concrete to protect against biological threats.