Wet Strength

the ability of materials and articles to continuously resist the destructive action of moisture, which results in decreased strength and the development of deformation when alternating moistening and drying processes take place. Wet strength is of great importance in building materials, particularly those used in exterior structures of buildings from which moisture is exuded. The property of wet strength is important in calculating waterproofing and estimating the durability of structures. Uneven moisture in certain layers of building structures and components causes swelling and shrinkage of materials, which leads to the formation of cracks, warping, and gradual loss of strength. Wet strength is most commonly characterized by a certain decrease of both shear and extension strength in meganewtons per sq m (kilograms-force per sq cm) after specimens of a material have undergone a definite number of moisture-change cycles.

The main reason for insufficient wet strength is the open porosity and hydrophilic properties of materials (susceptibility to dampening by water), which is usually associated with the great water-absorbing capacity of the materials. Among the hydrophilic building materials that are most resistant to moisture are dense, well-fired ceramics made of soft homogeneous clays that contain no soluble salts; heavy concretes; and natural stones with a dense, uniform structure. Hydrophobic materials (which do not become waterlogged), such as asphalts, asphalt concretes, and plastic concretes, are distinguished by high wet strength and moisture impermeability, which is why they are used as waterproofing materials. Materials of lowest wet strength include adobe blocks, unimpregnated cardboards, and plaster articles. General means of combating insufficient wet strength of materials include raising their density, increasing the number of closed pores, and reducing their hydrophilic qualities. These measures, in addition to increasing wet strength, result in a reduction of the water-absorbing capacity of the materials.